Next Article in Journal
Terminal Fan Deposition and Diagenetic Control in the Lower Paleogene of the Shahejie Formation, Bonan Sag, Bohai Basin, China: Insights into Reservoir Quality
Previous Article in Journal
Trends and Applications of Green Binder Materials for Cemented Paste Backfill Mining in China
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Minerals
Volume 15
Issue 2
10.3390/min15020098
minerals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Key Characteristics and Controlling Factors of the Gas Reservoir in the Fourth Member of the Ediacaran Dengying Formation in the Penglai Gas Field, Sichuan Basin

by
Hongwei Chen
1,
Shilin Wang
1,*,
Ahmed Mansour
1,2,
Qirong Qin
1,
Mohamed S. Ahmed
3,
Yongjing Cen
4,
Feng Liang
4,
Yuan He
5,
Yi Fan
5 and
Thomas Gentzis
6,*
1
School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China
2
Geology Department, Faculty of Science, Minia University, Minia 61519, Egypt
3
Department of Geology and Geophysics, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
4
PetroChina Southwest Oil & Gas Field Company, Central and Northern Sichuan Gas Production Management Office, Suining 629000, China
5
Research Institute of Petroleum Exploration and Development, PetroChina Southwest Oilfield Company, Chengdu 610041, China
6
Core Laboratories LP, 6316 Windfern Road, Houston, TX 77040, USA
*
Authors to whom correspondence should be addressed.
Minerals 2025, 15(2), 98; https://doi.org/10.3390/min15020098
Submission received: 13 December 2024 / Revised: 15 January 2025 / Accepted: 18 January 2025 / Published: 21 January 2025
(This article belongs to the Section Mineral Exploration Methods and Applications)
Browse Figures
Versions Notes

Abstract

:
This study focuses on the PS8 well in the Penglai Gas Field (Sichuan Basin), a newly identified key exploration area, where high-yield gas testing has been achieved from the Ediacaran Fourth Member of the Dengying Formation. Comprehensive analyses of drilling cores, cuttings, thin sections, analytical data, well logging, and production testing data were conducted to investigate the main characteristics of the gas reservoir and the factors controlling the formation model of the reservoir. The results reveal that the reservoir rocks in the Fourth Member of the Dengying Formation are primarily algal-clotted dolomite, algal-laminated dolomite, and arenaceous dolomite. The reservoir porosity is dominated by secondary pores, such as algal-bonded framework pores, intergranular dissolved pores, and intercrystalline dissolved pores, which contribute to the overall low porosity and extremely low permeability. The gas reservoir is classified as a unified structural–lithological reservoir, with the upper sub-member of the Fourth Member serving as a completely gas-bearing unit. This unit is characterized as an ultra-deep, dry gas reservoir with medium sulfur and medium CO2 contents. The development of this gas reservoir follows a “laterally generated and laterally stored, upper generation and lower storage” reservoir formation model. Regional unconformities and fracture systems developed during the Tongwan II Episode tectonic movement provide efficient pathways for hydrocarbon migration and accumulation. The high-quality source rocks in the lower Cambrian Qiongzhusi Formation serve as both the direct cap rock and lateral seal of the gas reservoir, creating an optimal source–reservoir spatial configuration. This study provides valuable insights into the giant gas reservoir of the Dengying Formation, which can aid in optimizing exploration activities in the Sichuan Basin.

Graphical Abstract

1. Introduction

With the continuous growth of China’s energy demand driven by economic and social development, mid-shallow oil and gas resources are increasingly depleted in both quantity and quality, making exploration more challenging [1]. Meanwhile, deep and ultra-deep oil and gas resources, which hold significant untapped potential, have gradually become the primary focus of exploration endeavors [2,3]. The Sichuan Basin, a key region for marine deep and ultra-deep oil and gas exploration in China, has yielded several major carbonate gas fields, such as Puguang and Yuanba. Among these, the Ediacaran Dengying Formation, representing the oldest marine carbonate strata in the Sichuan Basin, marks a pivotal transition from terrestrial to marine sedimentary environments and is rich in oil and gas resources [4,5,6,7,8]. The first discovery of a large Ediacaran gas field in China occurred in 1964 when gas was tested from the WJ well. This discovery spurred further exploration of gas reservoirs within the Dengying Formation [9]. Previous studies have revealed the crucial role of paleo-uplifts in controlling regional deposition patterns, reservoir quality, and hydrocarbon accumulation, thereby marking them as favorable areas for hydrocarbon enrichment [10,11]. Additionally, algal mound models, karst reservoir formation, and sedimentary environmental conditions that were prevalent during deposition of the Ediacaran Dengying Formation in the Sichuan Basin were further interpreted [12,13,14,15,16,17]. However, the findings of these previous studies addressed single influencing factors such as sedimentary facies or reservoirs, but lacking gas-reservoir-forming models that comprehensively consider multiple influencing factors. Additionally, the limited geological understanding of paleo-uplifts and associated processes has impeded significant exploration breakthroughs in the Ediacaran Dengying Formation for decades. It was not until 2011, when the GS1 well achieved a high-yield gas flow exceeding one million cubic meters per day from the Dengying Formation, that the exploration prospects in the Ediacaran–lower Paleozoic strata of the central Sichuan paleo-uplift area became clear [8,18,19]. Therefore, this paper is implemented to comprehensively analyze the impacts of source rock conditions for gas generation, migration pathways, sedimentary facies, and karstification alongside the results of previous studies on the development of gas reservoirs in the Fourth Member of the Dengying Formation in the Penglai Gas Field.
Recently, efficient development of the Anyue giant gas field has recently accelerated exploration activities in the northern slope of the central Sichuan paleo-uplift. Multiple exploration wells in the platform margin zone of the northern slope have reported significant gas reserves in the Dengying Formation. Notably, the gas testing results from the PT1 and PS8 wells in the Penglai Gas Field have demonstrated the vast potential of the Ediacaran Dengying Formation. The PT1 well achieved a commercial gas flow exceeding 1,000,000 m3/day in the Second Member, while the PS8 well reached a commercial gas flow exceeding 400,000 m3/day in the Fourth Member [20,21,22]. However, there were significant differences between the post-testing results of the gas reservoir in the Fourth Member of the Dengying Formation in the PS8 well area and the pre-drilling predicted gas accumulation model, which rendered the model ineffective in guiding further exploration. Therefore, this study is conducted based on well logging and testing results, combined with a comprehensive analysis of geological data from the PS8 well area. The aims of this study are (1) to interpret the major characteristics and controlling factors of the gas reservoir in the Fourth Member of the Dengying Formation, and (2) to establish an accurate accumulation model for the gas reservoir to provide valuable guidance for future exploration activities in the PS8 well area.

2. Geologic Setting

The studied area is structurally located in the northern part of the gentle tectonic zone of the central Sichuan paleo-uplift, situated in the center of the Sichuan Basin [23] (Figure 1A). It is bounded by the platform margin zone to the east, west, and north, and by the intraplatform zone to the south. The Dengying Formation in the Penglai Gas Field can be divided into four distinct members, from bottom to top (Figure 1B), with the Fourth and Second members being rich in algae, while the Third and First members being algae-poor [24]. The four members are deposited continuously. The Second and Third Members exhibit unconformable contacts, influenced by the Tongwan I tectonic movement, while the Tongwan II tectonic movement causes unconformable contacts between the Fourth Member of the Dengying Formation and the overlying Qiongzhusi Formation [25,26].
The Fourth Member of the Dengying Formation in the PS8 well is primarily characterized by the development of platform margin subfacies. The main sedimentary microfacie types including algal mound microfacies, grain beach microfacies, and interbeach marine microfacies. Algal mound microfacies are predominantly composed of algal-clotted dolomite, algal stromatolitic dolomite, and algal-laminated dolomite. Grain beach microfacies consist of sandy dolomite, while interbeach marine microfacies are represented by powdery crystalline dolomite, micritic dolomite, and siliceous dolomite [27].
The northern slope of the central Sichuan paleo-uplift (Figure 1A) has undergone several stages of crustal movements during deposition, attributed to the Tongwan II tectonic event. This area also includes the Deyang–Anyue rift trough, which initially experienced slow uplifting, with the northern slope being lower than the Gaoshiti–Moxi area [28]. During the early Caledonian, regional tension intensified, leading to extensional rifting within and along the edges of the basin. By the late Caledonian, the central Sichuan paleo-uplift had essentially developed [29]. During the Hercynian orogeny, following multiple uplifts and erosions, the structural pattern of the northern slope and the Gaoshiti–Moxi area stabilized into a saddle–dome shape. In the early Indosinian orogenic cycle, structural inversion transformed the central Sichuan paleo-uplift into a southeastward uplift with a northwestward subsidence. This resulted in an increased dip angle of the strata on the northern slope, followed by a southeastward uplift and a slight uplift in the northwest Sichuan area [30].
Furthermore, during the Jurassic–Cretaceous Yanshanian orogenic event, the surrounding mountains of central Sichuan experienced rapid uplift, leading to compression and strike–slip deformation in the northwest of Sichuan, which resulted in the development of a foreland basin [31]. The subsequent Himalayan movement caused intense compression in the southern segment of the Longmen Mountains, further uplifting and shaping the central Sichuan paleo-uplift. As a result, the northern slope transformed into a slope belt, with compression in the southern segment of the Longmen Mountains narrowing the western segment and stabilizing the eastern segment [32]. The Gaoshiti–Moxi area underwent relative uplift, and the structural axis shifted southeastward [33]. Although the PS8 well is located within an uplift area, its proximity to the compression zone led to relative subsidence, resulting in the formation of a monoclinic structure.

3. Materials and Methods

In this study, all samples were collected through core sampling and from natural gas and formation water during the single-well gas testing process. The sampling depths were corrected after relocation. The experimental tests were completed at the Analysis and Experiment Center of the Exploration and Development Research Institute of PetroChina Southwest Oil and Gas field Company.
The gas samples were purified to remove impurities such as O2 and H2O. After standardization, the gas was allowed to stabilize. Once stabilized, it was tested using a natural gas analyzer (model K50414) under ambient conditions of 19 °C and 50% relative humidity (RH). The national standards, such as “Analysis of Natural Gas Composition–Gas Chromatography Method: GB/T 13610-2020” and “Calculation Methods for Calorific Value, Density, Relative Density, and Wobbe Index of Natural Gas: GB/T 11062-2020” were used [34,35].
Carbon isotope analysis of natural gas composition was conducted using after pre-treatment using a gas chromatograph and flow meter, with the flow rate adjusted to ensure a sample purity of 99.99%. Subsequently, the stable isotope ratio mass spectrometer (model K50150) was used to conduct the analysis under ambient conditions of 23–25 °C and 60%–62% RH [36]. The petroleum and natural gas industry standard “Analysis Methods for Carbon and Oxygen Isotopes in Organic Matter and Carbonate Rocks: SY/T 5238-2019” was used [36].
To conduct the Oilfield Water Analysis, the collected samples were first filtered through a 0.45 μm cellulose acetate filter membrane to remove suspended solids, algae, and precipitates. Subsequently, hydrochloric acid was added to the samples to adjust the pH to less than 2. The water samples were then transferred into hard glass bottles whose inner walls have been wetted with 5 mL of nitric acid solution. After shaking uniformly, the samples were sealed. Finally, the analysis of samples was performed using an ion chromatograph (model K34233), in accordance with the industry standard “Analysis Methods for Oilfield Water—SY/T 5523-2016” [37,38].
Analysis of full-diameter porosity and permeability of rocks was carried out, whereby a 25 mm diameter cylinder was drilled from the obtained core samples using a water drill. Surface contaminants were cleaned off, and the cylinder was dried in a constant temperature oven at 50 °C. Both ends of the cylinder were flattened using a core grinding machine to achieve a height of 25 mm. After being immersed in a saturation liquid for 24 h, the samples were removed and tested using a whole-diameter core permeability device (model K34277) and a whole-diameter helium porosimeter (model K36517), following the national standard “Core Analysis Methods: GB/T 29172-2012” [39].
Temperature and pressure data were obtained using a PPS28 type 30K memory electronic pressure gauge (Pioneer Petrotech Services Inc., Calgary, AB, Canada) [40]. This section preparation was conducted using a rock sample slicing machine to cut the core samples into small pieces of 25 × 46 mm. Then, a grinding wheel, sandpapers, and a polishing machine were employed to enhance the flatness and smoothness of the sample surface. Afterwards, the samples are adhered to microscope slides using epoxy resin. An automatic rock grinding machine is used to grind and polish the samples down to a thickness of 40 μm. Finally, a diamond suspension liquid is applied for polishing. In the preparation of regular thin sections, blue and red casting resins are formulated using oil-soluble blue dye and red ink, respectively. The microscopic pore structures of 369 ordinary thin sections and 54 cast thin sections of various dolomites were observed under an XL 30 scanning electron microscopy (SEM). The samples used for thin sections spanning a depth range of 6893–7250.9 m.
Seismic data in the form of 3D seismic lines were collected from the PetroChina Southwest Oil and Gas field Company, Chengdu, China. The seismic lines as well as the seismic cross-section were interpreted using GeoEast software [39]. The well logging of the PS8 well was conducted using series instruments model 5700 and MAX500, for measuring the natural gamma ray, neutron, density, dual-lateral resistivity, flushed zone resistivity, and caliper logs. The collected well logging curves were standardized using the histogram method. A unified well logging interpretation model was then applied to calculate porosity and permeability using acoustic compressional, density, and compensated neutron log [41,42]. Subsequently, the Archie equation was used to calculate water saturation. A comprehensive interpretation of the gas-bearing intervals was performed using several methods, such as the porosity overlap, P1/2 normal probability analysis, porosity-saturation cross-plot, and compressional-shear wave velocity ratio method.

4. Results

4.1. Core Description and Thin Section Analysis

Through the identification and description of core intervals, combined with blue and red cast microscopic thin section analyses, several pore types have been observed in sediments from the Fourth Member of the Dengying Formation in the PS8 well. These include intercrystalline and intergranular dissolved pores, and algae-bonded framework pores (Figure 2). Dissolved cavities and fractures are evident in several cores (Figure 2, Figure 3 and Figure 4). Algal-laminated dolomites with abundant intercrystalline dissolved pores are observed in a blue cast thin section of samples from the Fourth Member (Figure 2a and Figure 4). Additionally, algae-clotted dolomite from a core at a depth of 6987.67–6987.79 m is characterized by both horizontal and high-angle fractures (Figure 2b). These fractures are partially filled with bitumen (Figure 2b). Algae-laminated dolomite with abundant bedding-parallel dissolved pores and layered dissolution fractures is also observed, both filled with bitumen (Figure 2c). Under a red cast thin section, algae-clotted dolomite with intergranular dissolved pores, some of which are partially filled with bitumen, is observed (Figure 2d). Furthermore, sand-clast dolomites in core samples exhibit numerous bedding-parallel dissolved pores and irregular vugs, some of which are filled with quartz (Figure 2e). For example, core samples occurring at a depth of 6986.50–6986.64 m show these features. Algal-clotted dolomite with algal-bonded pores, partially filled with dolomite and bitumen, is observed under blue cast thin sections, such as the sample at a depth of 6983.53 m (Figure 2f). These results are consistent with the mineralogical composition observed in the core samples under SEM, which shows abundant algal-clotted dolomites and calcite crystals in core samples at depths of 7050.15 m, 7058.06 m, and 7058.22 m (Figure 4A–C). Additionally, clay minerals are also present in the core sample 7058.31 m (Figure 4D).

4.2. Porosity and Permeability

A detailed statistical analysis of the physical properties from core samples collected from the Fourth Member of the Dengying Formation is shown in Figure 3. The porosity values for 64 core samples are in the range of 2.02%–10.82%. Most of these samples (accounting for 64.1%) have porosity values ranging between 2% and 4%. The permeability measurements from 49 core samples range from 0.0005 to 15.8 mD. Permeability values are predominantly distributed within the ranges of 0.1–1 mD and 1–10 mD, accounting for 36.7% and 42.9% of the total samples, respectively.
Minerals 15 00098 g003
Figure 3. Histogram illustrating the statistical analysis of physical properties of core samples from the Fourth Member of Dengying Formation in PS8 well. Panel (a) displays the distribution of the measured porosity values, while panel (b) shows the distribution of permeability values.
Figure 3. Histogram illustrating the statistical analysis of physical properties of core samples from the Fourth Member of Dengying Formation in PS8 well. Panel (a) displays the distribution of the measured porosity values, while panel (b) shows the distribution of permeability values.
Minerals 15 00098 g003
Minerals 15 00098 g004
Figure 4. Photomicrographs taken under scanning electron microscopy (SEM) showing various types of mineral compositions from core samples of the Fourth Member of the Dengying Formation in the PS8 well. The corresponding core depth for each photomicrograph is provided. (A) Dolomite crystals, core sample at 7058.06 m. (B) Mineralogical composition showing calcite crystals surrounded by calcified extracellular polymeric substances, core sample at 7058.22 m. (C) Mineralogical composition illustrating calcite with its surface encapsulated by calcified bacteria, core sample at 7050.15 m. (D) Clay minerals recovered from core sample at 7058.31 m. The yellow arrow indicates dolomite crystals, the red arrows highlight calcite, and the orange arrow points to clay minerals.
Figure 4. Photomicrographs taken under scanning electron microscopy (SEM) showing various types of mineral compositions from core samples of the Fourth Member of the Dengying Formation in the PS8 well. The corresponding core depth for each photomicrograph is provided. (A) Dolomite crystals, core sample at 7058.06 m. (B) Mineralogical composition showing calcite crystals surrounded by calcified extracellular polymeric substances, core sample at 7058.22 m. (C) Mineralogical composition illustrating calcite with its surface encapsulated by calcified bacteria, core sample at 7050.15 m. (D) Clay minerals recovered from core sample at 7058.31 m. The yellow arrow indicates dolomite crystals, the red arrows highlight calcite, and the orange arrow points to clay minerals.
Minerals 15 00098 g004

4.3. Fluids in Gas Reservoir

The fluid analysis results for the gas reservoir in the Fourth Member of the Dengying Formation are summarized in Table 1 and Table 2. The relative density of natural gas is in the range of 0.65–0.73 g/L, with an average of 0.69 g/L. Methane is the predominant gas component, accounting for 81.57%–90.14% (85.51% on average). Ethane is present in small amounts, ranging from 0.02% to 0.07% (0.05% on average). Nitrogen content is in the range of 0.19%–0.53% (average 0.43%). The carbon dioxide (CO2) content ranges from 9.09% to 17.27% (average 13.23%). The helium content ranges from 0.01% to 0.07%, with an average of 0.03%. Hydrogen sulfide concentrations are in the range of 0.40%–1.15% (average 0.64%). The methane carbon isotope values range from −30.02‰ to −32.33‰ (average −31.33‰). Ethane carbon isotope values range from −24.92‰ to −31.98‰, averaging −27.28‰.
Formation water analysis reveals that the water density ranges from 1.11 to 1.18 g/m3, with a pH value that varies between 4.10 and 6.86. Potassium ion (K+) content is in the range of 822–3770 mg/L, while sodium ion (Na+) content falls in the range of 6250–28,800 mg/L. Calcium ion (Ca2+) levels range from 23,500 to 68,700 mg/L, and magnesium ion (Mg2+) content varies from 10,900 to 34,600 mg/L. Barium ion (Ba2+) content falls in the range of 684–6500 mg/L, and chloride ion (Cl−) content is in the range of 92,200–178,000 mg/L. Sulfate ion (SO42−) concentrations range from 14.6 to 29.7 mg/L. The total mineralization of the water chemistry spans from 148,000 to 290,000 mg/L.

5. Discussion

5.1. Gas Reservoir Characteristics

5.1.1. Reservoir Characteristics

Through the analysis of core intervals, thin section data, and well logging results, the reservoir characteristics of the Dengying Formation in the Sichuan Basin are evaluated for optimal hydrocarbon exploration. Additionally, previous studies on the reservoir properties of the Dengying Formation in the Sichuan Basin are further considered for comparative analysis [43,44,45,46]. The reservoir development characteristics in the PS8 well are similar to those in other regions of the Sichuan Basin, both being weathered karst reservoirs that possess conditions conducive to the formation of large-scale gas accumulations. It is determined that the reservoirs in the Fourth Member of the Dengying Formation in the PS8 well are predominantly developed within mound–beach bodies. The reservoir rocks consist of algal-clotted dolomite, algal stromatolitic dolomite, and sandy dolomite (Figure 4). These reservoirs are characterized by a variety of pore types, including pores, caves, and fractures. Secondary porosity, particularly in the form of algal-bonded framework pores, interparticle dissolved pores, and intercrystal dissolved pores, is predominant (Figure 2). Algal-bonded framework pores are mainly developed in algal-clotted dolomite and algal stromatolitic dolomite (Figure 2f). These pores typically have diameters greater than 1 mm and are distributed in strip-like, grid-like, or spot-like patterns. Interparticle and intercrystal dissolved pores are found in algal-clotted dolomite, algal stromatolitic dolomite, and sandy dolomite, with pore diameters typically ranging from 0.01 to 0.1 mm, exhibiting irregular pore morphology. Core samples reveal numerous dissolved cavities and fractures. Most of these cavities are filled with bitumen, although some contain quartz (Figure 2c,e). The cavities are mostly small, with diameters ranging from 2 to 6 mm. Larger cavities, exceeding 20 mm in diameter, are less common and tend to be elliptical or irregular in shape. Fractures are primarily high-angle, with some low-angle, horizontal, and network fractures (Figure 2b). The SEM analysis of the dolomite samples reveals that the mineral composition is predominantly dolomite and calcite (Figure 4A–C), with a relatively small amount of clay minerals (Figure 4D). Some particle surfaces are smooth and exhibit a self-formed rhombic shape, which is consistent with the morphological characteristics of dolomite.
The reservoir thickness of the Fourth Member in the Penglai Gas Field ranges from 63.7 to 149 m, with an average thickness of 116.5 m and an average reservoir-to-ground ratio of 32.6%. The reservoir thickness of individual reservoir layers of the Dengying Formation varies significantly among wells, ranging from a few meters to 20 m (Figure 5). Overall, the observed reservoir thickness is dominated by thin layers, with fewer instances of thick layers, but the cumulative reservoir thickness of a single well is relatively large. The average core porosity is 3.84%, with a median value of 2.86% (Figure 3a), whereas core permeability measurements range from 0.0005 to 15.8 mD, with an average of 2.363 mD and a median of 1.13 mD (Figure 3b). Overall, the reservoir exhibits low porosity and low permeability characteristics. However, in localized areas, the interconnection between fractures and pores enhances pore connectivity, resulting in regions of low porosity and high permeability.

5.1.2. Gas Reservoir Fluid Characteristics

The original formation pressure and temperature measurements of the gas reservoir in the Fourth Member of the Dengying Formation are presented in Table 1. The formation pressures are in the range of 69.32–70.66 MPa, with pressure coefficients of 1.00–1.03 (Table 3). Temperature values are in the range of 158.2–163.8 °C, and the geothermal gradient is in the range of 2.09–2.16 °C/100 m (Table 3). These values indicate that the gas reservoir operates under normal temperature and pressure conditions [47]. The formation pressures and mid-reservoir temperatures of the PS8 well are similar to values recorded in the PS7, PS9, and PS10 wells, suggesting relatively similar temperature and pressure regimes. This uniformity reflects comparable reservoir-forming conditions across the wells, indicating that they are the same gas reservoir system.
The natural gas in the Fourth Member in the Penglai Gas Field has a dryness coefficient exceeding 0.99, indicating that it is predominantly dry gas. The analysis of the natural gas composition in the Penglai Gas Field reveals that wells PS7 and PS10 exhibit higher CO2 content and lower methane content compared to the PS8 and PS9 wells (Table 1) [48]. This variation may be attributed to the extensive reaction between acid fluids, plugging agents, and the reservoir rocks during the acid fracturing test, which generated additional CO2 and reduced methane content [49]. Therefore, it can be concluded that the gas reservoir is classified as a medium-sulfur and medium-CO2 dry gas reservoir. The formation water associated with this reservoir is of the CaCl2 type, characterized by high salinity, acidic pH, and the presence of various trace elements, suggesting that the gas reservoir is located in an ultra-deep enclosed environment [50].

5.1.3. Gas Reservoir Type

Based on well logging results, regional sedimentary background, and actual test data from individual wells of the Penglai Gas Field, the gas reservoir within the Fourth Member of the Dengying Formation has been examined (Figure 5). This reservoir is classified as a structural–stratigraphic gas reservoir, situated within a large monoclinic structural setting (Figure 5). In the horizontal plane, the distribution of the gas reservoir is controlled by both the slope structural background and lithological traps. To the south and east of the basin, the updip direction of the gas reservoir is characterized by impermeable, thick lithological zones within intraplatform depressions. In contrast, the northern and western sides are sealed by dense lithological zones formed in interbeach depressions. Vertically, the Fourth Member of the Dengying Formation constitutes a single gas reservoir. The upper sub-member of the Fourth Member is characterized by thick mound–beach karst reservoirs that are continuously developed across large areas and are gas-bearing. This upper sub-member is characterized by the presence of edge water in its lower parts, with a unified gas–water interface and a consistent pressure and temperature system. In contrast, the lower sub-member of the Fourth Member was deposited under deep-water environmental conditions, resulting in limited deposition and/or absence of mound–beach bodies [51,52]. Thus, it has less well-developed reservoirs, with limited lateral connectivity and fewer gas-bearing strata due to the separation between the gas reservoirs via compact lithologies, such as micritic dolomite, in both the updip and downdip directions, primarily consisting of water-bearing reservoirs. This results in variable internal trapped water interfaces during hydrocarbon migration. Additionally, this indicates that the upper sub-member of the Fourth Member shows a complex nature of being a structural–stratigraphic reservoir type [49,50,53].

5.2. Gas Reservoir Controlling Factors

5.2.1. Source Rock and Cap Rock Conditions

The geological exploration of the Ediacaran Dengying Formation on the northern slope of the central Sichuan paleo-uplift has revealed significant potential, which is closely linked to its excellent source rock characteristics. Previous studies have shown that the gas reservoir in the Fourth Member of the Dengying Formation in the Sichuan Basin benefits from three major source rocks [53]. This includes source rock mudstone and shale strata from the Doushantuo Formation, the mudstone strata from the Third Member of the Dengying Formation, and the mudstone and shale strata from the Cambrian Qiongzhusi Formation [54,55,56]. All three sets of source rocks are characterized by good to excellent organic matter richness, with average TOC values of 2.06 wt.%, 1.19 wt.%, and 1.88 wt.%, respectively. The vitrinite reflectance values (VRo) values are in the range of 2.08%–3.82%, 3.16%–3.21%, and 1.83%–3.90%, indicating the organic matter is in the overmature stage [57]. During the early Caledonian, a large-scale transgression occurred, leading to the deposition of organic carbon-rich black shale and mudstone of the Qiongzhusi Formation in the central Sichuan area [58]. Due to the higher elevation of the ancient landform on the northern slope, the accommodation space was higher, resulting in thicker source rocks in the Qiongzhusi Formation with better organic matter preservation conditions compared to the rest of central Sichuan area. This has resulted in the formation of high-quality source rocks in the northern slope region.
Multiple exploratory wells on the northern slope have confirmed that the thickness of source rocks in the Qiongzhusi Formation, which overlies the Fourth Member of the Dengying Formation, ranges from 307 m to 460 m. Specifically, the source rock thickness of the Qiongzhusi Formation in well JT1 is 385 m, with a measured organic carbon content of 0.78 wt.% to 2.49 wt.%, indicating a fair to very good organic matter richness. The VRo values range from 2.01% to 2.43%, indicating that the source rocks are in the overmature stage [59]. In Penglai Gas Field, the natural gas in the reservoirs of the Fourth Member is predominantly hydrocarbon gas, with methane volume fractions ranging from 81.57% to 90.14%, and low volumes of heavy hydrocarbons (C2+), indicating a high degree of maturity. The carbon isotope composition of the hydrocarbon components of the natural gas shows a wide distribution, with δ13C1 values ranging from −32.33‰ to −30.02‰ and δ13C2 values ranging from −31.98‰ to −24.92‰. The small difference between δ13C2 and δ13C1 reflects the characteristics of marine sapropelic-type parent material gas generation [60]. The δ13C2 values of natural gas in the PS8 well are heavier than those of the kerogen in the mudstones and shales of the Qiongzhusi Formation. The carbon isotopes of methane and ethane are similar to those of the Ediacaran natural gas reservoirs in the Gaomo area (Figure 6), indicating a similar source of natural gas [61]. However, the distribution range of ethane carbon isotopes is broader, with some values approaching those of the kerogen in the Qiongzhusi Formation and others closer to the δ13C2 values of the carbonates in the Dengying Formation. This suggests that the natural gas reservoir in the Fourth Member of the Dengying Formation has mixed-source characteristics of released gases, with gas generated and expelled from the Ediacaran and Cambrian source rock layers.
Drilling data from the PS8 well reveal that the gas reservoirs in the Fourth Member are buried at depths greater than 6900 m. The overlying strata of the gas reservoirs consist of well-developed mudstone and shale, dense carbonate rocks, and gypsum salt rocks. These layers exhibit significant sedimentary thicknesses (>2000 m) and widespread distribution. Above the Fourth Member, the black mudstone and shale of the lower Cambrian Qiongzhusi Formation, which has a thickness in the range of 313–350 m, acts as a direct cap rock. These black mudstones and shales provide excellent sealing conditions for the gas reservoirs in the Fourth Member.

5.2.2. Reservoir Conditions

The formation of high-quality reservoirs in the platform margin zone of the Fourth Member is controlled by both sedimentary facies and karstification. The gas reservoir mainly develops within the mound–beach body facies. During the early depositional stage of the Fourth Member, the paleomorphology was relatively low, with a stable sea level, and the environment was relatively calm, with low energy [62,63]. Lithology mainly consisted of low-energy, fine-grained micritic dolomite and powdery crystalline dolomite, typical of intertidal marine sedimentary microfacies [4]. In locally uplifted areas, sunlight exposure, stronger hydrodynamic conditions, and abundant nutrients allowed for microorganisms to proliferate, forming algal-clotted dolomite and constituting morphologically uplifted mound–beach bodies. However, these bodies had small scales, poor reservoir development, and were isolated by dense micritic dolomite, resulting in a planar distribution vertical superimposition characteristics.
By the late depositional stage (upper sub-member) of the Fourth Member, a phase of relative sea level regression took place, causing shallower water column and hydrodynamic conditions to intensify [8,51,52]. Due to widespread sunlight exposure, microorganisms proliferated, with deposition primarily consisting of algal-clotted dolomite and psammitic dolomite (Figure 2) [48,53]. Mound–beach bodies developed abundantly, while low-energy, fine-grained micritic dolomite deposition became less common, limiting the separation between individual mound–beach bodies. The mound–beach bodies interconnected to create large-scale mound–beach groups with significant vertical superimposition. Algal-bonded framework pores were highly developed within these mound–beach bodies. Although these pores were later filled with dolomite or bitumen due to diagenesis, they still represented areas with relatively high porosity and permeability zones within the reservoir. These sedimentary facies provided good channels for fluid passage during later diagenesis and contributed to the formation of secondary dissolution pores. The extensive development of the mound–beach facies significantly promoted constructive diagenesis, providing the material foundation for the large-scale development of high-quality reservoirs in the upper sub-member of the Fourth Member.
During the late depositional stage of the Fourth Member, frequent sea level fluctuations resulted in repeated exposure of mound–beach bodies above sea level, leading to penecontemporaneous karstification (Figure 7a–c). This process, which corresponds to high-frequency sedimentary cycles of the mound–beach bodies, is characterized by stratification. Meteoric water leaching influenced the formation of selective dissolution pores in the Fourth Member, which increased pore space and laying the foundation for subsequent enlargement, leading to the development of epikarstification. However, penecontemporaneous karstification is relatively small in scale, with thin, single-stage features that were partially compromised by compaction and cementation, limiting its reservoir properties [64].
The Tongwan II tectonic movement at the end of the Ediacaran led to a large-scale uplift of the Dengying Formation, resulting in a phase of sea level regression in the slope zone of the central Sichuan paleo-uplift [65]. This region underwent extensive epikarstification due to prolonged exposure time and intense karst processes. Under active weathering conditions and leaching from meteoric freshwater [66], enhanced dissolution and expansion of the early-formed penecontemporaneous cavities took place, creating non-fabric dissolution pores and caves. These developed cavities interconnected with fractures, significantly improving the physical properties of the gas reservoir and constituting the main pathways for gas migration (Figure 7d–f).
The formation of high-quality gas reservoirs in the platform margin zone of the Fourth Member of the Dengying Formation results from multi-stage karstification. Syngenetic karstification initially establishes the foundation for reservoir development, while epigenetic karstification further enhances and expands the reservoir capacity through various processes, leading to the creation of numerous high-quality reservoirs. These reservoirs provide favorable storage conditions for subsequent hydrocarbon migration and accumulation. Furthermore, the Tongwan tectonics in the central Sichuan paleo-uplift resulted in the formation of regional unconformities [67]. Combined with an extensively developed fracture system, these unconformities effectively connect the source rocks to the reservoirs, thereby creating optimal conditions for gas migration and accumulation.

5.2.3. Central Sichuan Uplift and Gas Preservation Potential

The central Sichuan paleo-uplift plays a crucial role in the formation and distribution of gas reservoirs in the Dengying Formation [68]. The tectonic evolution and burial history of the hydrocarbon source rocks in central Sichuan indicate that since its formation in the lower Cambrian, the uplift has experienced various evolutionary stages but generally exhibits characteristics of inherited development (Figure 8 and Figure 9) [69]. From the early Cambrian to the Permian (Figure 8a), the Deyang–Anyue rift trough and the central Sichuan uplift gradually formed and entered the development stage [70]. The entire basin exhibited a tectonic pattern of uplift in the west, a high region in the middle, and a depression in the southeast. During the Silurian, the northern slope underwent a subsidence phase, followed directly by significant uplift. During the subsidence phase, the source rocks of the lower Cambrian Qiongzhusi Formation, located on the northern slope of the Sichuan Basin, gradually entered the early mature stage of the oil window, with an average VRo exceeding 0.5% [71]. This led to the expulsion of a small amount of liquid hydrocarbons. Additionally, the temperature of the Qiongzhusi Formation ranged from 80 to 110 °C [72]. During this period, the PS8 well area consistently remained at a relatively high position within the central Sichuan paleo-uplift, making it an important area for gas migration and accumulation, thus fostering the formation and enrichment of ancient hydrocarbon reservoirs.
From the end of the Permian to the Triassic (Figure 8b), the morphology of the ancient uplift underwent significant changes, evolving from a wide and gentle uplift into a large-scale anticline with an east-west axial orientation, centered along the Moxi–Gaoshiti–Ziyang–Leshan axis [73]. During this period, as the burial depth of the Qiongzhusi Formation source rocks increased, they gradually re-entered the hydrocarbon generation stage (VRo > 0.5%). The uplift of the ancient structures caused the liquid hydrocarbons generated by the Qiongzhusi Formation source rocks to migrate along unconformity surfaces and other pathways into the lithologic traps within the mound–beach facies of the PS8 well. Subsequently, during the Triassic, substantial amounts of liquid hydrocarbons were generated and expelled due to high maturity levels (1.3% < VRo < 2.0%) and a formation temperature ranging from 160 to 190 °C. Simultaneously, the Qiongzhusi Formation source rocks acted as a direct cap rock, sealing the liquid hydrocarbons and allowing them to accumulate and form reservoirs within the reservoir rocks.
From the late Triassic to the Cretaceous (Figure 8c), tectonic activity driven by the thrust nappe of the Longmen and Jiulong Mountains caused a further southeastward migration of the tectonic axis in central and northwestern Sichuan. As a result, the Gaoshiti–Moxi area experienced additional compression and uplift, while the PS8 well area, located near the front of the Longmen Mountains, subsided due to intense compression. This increased the burial depth of the strata and raised in formation temperature, causing early-formed liquid hydrocarbons to undergo thermal cracking to generate gaseous hydrocarbons [74]. Concurrently, the source rocks of the Qiongzhusi Formation reached their peak stage of gas generation, with VRo values reaching up to 2.0% in the Middle Jurassic [75]. The thermal cracking of oil into gas also resulted in significant overpressure, which drove the gaseous hydrocarbons to migrate along unconformity surfaces, fractures, and other available pathways. At the same time, the development of dense lithologies, such as micritic dolomite in the intertidal flat microfacies, acted as lateral seals, preventing the migration of the generated gas. From the Himalayan orogeny to the present, intense compressive stress has caused significant tectonic deformations in the Sichuan Basin [75]. However, structural deformation in the central Sichuan paleo-uplift has been minimal, preserving the original trap morphology and hydrocarbon reservoir structure, preventing the loss of migrated gas. These favorable preservation conditions contributed to the development of exceptionally large gas reservoirs in the Dengying Formation.

5.3. Gas Reservoir Formation Model

Based on the findings outlined above and a comprehensive analysis of previous studies on the Penglai Gas Field and adjacent hydrocarbon reservoirs [76,77,78,79,80,81,82,83], a gas reservoir formation model for the PS8 well is developed (Figure 10). In the Fourth Member of the Dengying Formation, the gas reservoirs are part of the second gas-bearing system, which lies above older sedimentary successions of the Sichuan Basin, including the Ediacaran–lower Paleozoic gas-bearing system [84]. This karst reservoir, associated with the mound–beach facies in the Fourth Member, is capped by thick black mudstones and shales of the lower Cambrian Qiongzhusi Formation (Figure 10). The gas reservoirs in the Fourth Member exhibit two distinct modes: “lateral generation and lateral storage” and “upper generation and lower storage” (Figure 10a). To the west of the PS8 well, the Deyang–Anyue rift is located, where the Dengying Formation has been significantly uplifted and eroded due to the activation of the Tongwan II tectonic movement [67]. This uplift and erosion resulted in the complete removal of the Third and Fourth members of the Dengying Formation, leaving only the First and part of the Second members.
In the Penglai Gas Field, the thick black mudstones and shales of the Ediacaran Doushantuo Formation, Third Member of the Dengying Formation, and Qiongzhusi Formation, suggest the mixed-source characteristics of released gases [69]. However, the hydrocarbon generation and expulsion of the Doushantuo Formation and the Third Member of the Dengying Formation in central Sichuan is relatively weak, providing only a small amount of gas sources [70,71]. This indicates that the Qiongzhusi Formation is the primary source rock of gas generation potential for gas reservoirs in the Fourth Member of the central Sichuan paleo-uplift. In the study area, the Qiongzhusi Formation directly overlies the Second Member of the Dengying Formation and laterally connects with the karst reservoir of the Fourth Member due to the presence of a fault (Figure 10). The natural gas generated in the laterally connected source rocks migrates to the karst reservoir in the Fourth Member through unconformities and developed fracture systems, forming a laterally extended reservoir. At the same time, the Fourth Member is in direct contact with the overlying source rocks of the Qiongzhusi Formation (Figure 10). The natural gas generated in these overlying source rocks is forced by overpressure to migrate downwards along unconformities and developed fracture systems into the karst reservoir of the Fourth Member, forming an “upper generation and lower storage” pattern. The mudstones and shales of the Qiongzhusi Formation prevent the migration of the generated natural gas, allowing for the formation of large natural gas reservoirs in the Fourth Member of the Dengying Formation (Figure 10b).

6. Conclusions

An integrated approach involving ordinary and cast thin sections, carbon isotope analysis of natural gas composition, well logging, measurements of porosity and permeability of rocks, along with temperature and pressure data from core and cutting samples of the Fourth Member of the Ediacaran Dengying Formation in the PS8 well (Sichuan Basin) was conducted. The results indicated that high-quality gas reservoirs occur in the upper sub-member of the Fourth Member of the Dengying Formation. These reservoir rocks consist of algal-clotted dolomite, algal stromatolitic dolomite, and sandy dolomite. The gas reservoirs in the Fourth Member are classified as a complex structural–stratigraphic reservoir, situated within a large monoclinic structure. It is primarily influenced by paleo-uplifts and compacted lithologies, which control the migration pathways, distribution, and entrapment of natural gas. Additionally, the released gas from possible source rock layers accumulated in structural highs, resulting in a dry gas reservoir with moderate levels of sulfur and CO2 content. The high-quality karst reservoirs developed in the mound–beach bodies in the Fourth Member provide favorable storage conditions. The tectonic evolution of the central Sichuan paleo-uplift enabled significant migration and storage into the gas reservoirs. The natural gas in the reservoirs of the Fourth Member primarily originates from the thermally mature, organic carbon-rich black shale and mudstone source rocks of the lower Cambrian Qiongzhusi Formation. The Qiongzhusi Formation not only provides abundant gas generation and production for the reservoirs in the Fourth Member of the Dengying formation but also act as a direct cap rock, offering excellent sealing conditions. It occurs directly above the Second Member of the Dengying Formation and laterally connects with the karst reservoir of the Fourth Member, forming a laterally extended reservoir. These gas reservoirs benefit from excellent source rock quality and storage conditions, forming a source–reservoir model of “laterally generated and laterally stored, upper generation and lower storage” pattern.

Author Contributions

Conceptualization, S.W., A.M., Q.Q. and T.G.; methodology, H.C.; software, Y.F., Y.H. and Y.C.; validation, S.W., F.L. and A.M.; formal analysis, H.C.; investigation, Y.H.; resources, F.L., Y.H. and Y.F.; data curation, S.W., Y.F., Y.H. and T.G.; writing—original draft preparation, H.C. and S.W.; writing—review and editing, S.W., A.M., H.C., T.G. and M.S.A.; visualization, A.M.; supervision, S.W.; project administration, S.W. and Q.Q.; funding acquisition, A.M. and M.S.A. All authors have read and agreed to the published version of the manuscript.

Funding

The authors declare funding from the National Natural Science Foundation of China (grant no. W2433105) and Researchers Supporting project number (RSP2025R455), King Saud University, Riyadh, Saudi Arabia.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We thank PetroChina Southwest Oil & Gas Field Company, Sichuan, China for their core samples and data used to conduct this study. Additionally, this work was funded by the National Natural Science Foundation of China (grant no. W2433105) and Researchers Supporting project number (RSP2025R455), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

Thomas Gentzis is employed by Core Laboratories, and Yongjing Cen, Feng Liang, Yuan He, and Yi Fan are employed by PetroChina Southwest Oil & Gas Field Company. The other authors declare no commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Wang, S.L.; Mansour, A.; Li, C.; Su, P.D.; Meng, L.J.; Ahmed, M.S. Source rock assessment and organic matter characterization of the Oligocene upper Shahejie and Dongying formations in the Nanpu depression of the saline lacustrine Bohai Bay basin, China: Geochemical, palynological, and mineralogical perspectives. Mar. Pet. Geol. 2024, 165, 106902. [Google Scholar] [CrossRef]
  2. Ma, Y.S.; Li, M.W.; Cai, X.Y.; Xu, X.H.; Hu, D.F.; Qu, S.L.; Li, G.S.; He, D.F.; Xiao, X.M.; Zeng, Y.J.; et al. Mechanisms and exploitation of deep marine petroleum accumulations in China: Advances, technological bottlenecks and basic scientific problems. Oil Gas Geol. 2020, 41, 655–672, 683. [Google Scholar]
  3. Yang, Y.; Wen, L.; Xie, J.R.; Luo, B.; Huang, P.H.; Ran, Q.; Zhou, G.; Zhang, X.H.; Wang, H.; Tian, X.W.; et al. Progress and direction of marine carbonate gas exploration in Sichuan basin. China Pet. Explor. 2020, 25, 44–55. [Google Scholar]
  4. Zhou, Z.; Wang, X.Z.; Xie, L.; Mo, J.; Zhang, J. Reservoir features and physical influences of the Sinian Dengying Formation in central Sichuan, China. Nat. Gas Geosci. 2014, 25, 701–708. [Google Scholar]
  5. Zhou, J.G.; Yao, G.S.; Yang, G.; Zhang, J.Y.; Hao, Y.; Wang, F.; Gu, M.F.; Li, W.Z. Genesis mechanism of the Sinian-Cambrian Reservoirs in the Anyue Gas Field, Sichuan Basin. Nat. Gas Ind. 2015, 35, 36–44. [Google Scholar]
  6. Ma, X.H.; Yang, Y.; Wen, L.; Luo, B. Distribution and exploration direction of medium- and large-sized marine carbonate gas fields in Sichuan Basin, SW China. Pet. Explor. Dev. 2019, 46, 1–13. [Google Scholar] [CrossRef]
  7. Huang, S.P.; Jiang, H.; Wang, T.S.; Wen, L.; Guan, S.W.; Zeng, F.Y.; Zhu, G.Y.; Tian, X.W.; Zhang, T.Y. Accumulation conditions and favorable exploration zones for natural gas in 8000 meters marine ultra-deep strata in the Sichuan basin. Acta Geol. Sin. 2023, 97, 1544–1560. [Google Scholar]
  8. Li, X.; Zhu, G.Y.; Zhang, Z.Y. Genesis of ultra-deep dolostone and controlling factors of large-scale reservoir: A case study of the Sinian Dengying Formation and the Cambrian Longwangmiao Formation in the Sichuan Basin. Sci. China. Earth. Sci. 2024, 67, 2352–2382. [Google Scholar] [CrossRef]
  9. Zhou, H.F.; Dai, X.; Jia, M.; Zhang, R.; Li, G.H.; Li, N.; Yang, Q.; Bai, R. Hydrocarbon accumulation characteristics of the second member of Sinian Dengying Formation in the north slope of central Sichuan paleo-uplift. Lith. Res. 2022, 34, 130–138. [Google Scholar]
  10. Kang, Y.C. Formation, development, and hydrocarbon prospects of the central Sichuan Uplift. Pet. Geol. Explor. 1988, 10, 12–23. [Google Scholar]
  11. Luo, B.; Zhou, G.; Luo, W.J.; Xia, M.L. Discovery from Exploration of Lower Paleozoic-Sinian System in Central Sichuan Palaeo-uplift and its Natural Gas Abundance Law. China. Pet. Explor. 2015, 20, 18–29. [Google Scholar]
  12. Li, A.P.; Gao, D.; Hu, M.Y.; Zhao, Y.R.; Zhu, C.Y.; Dai, Y.C. Deposition model and main factors controlling depositional processes for microbialites in the Fourth Member, Dengying Formation, central Sichuan Basin. Acta Sedimentol. Sin. 2023, 41, 1080–1096. [Google Scholar]
  13. Guo, H.W.; Fu, M.Y.; Song, R.C.; Liu, W.; Zhao, L.; Shen, Q.Y. Algal Type and Sedimentary Model of the 4th Member, Dengying Formation in the Gaoshiti Area of Chuanzhong. Acta Sedimentol. Sin. 2022, 40, 217–228. [Google Scholar]
  14. Liu, W.; Shen, Q.Y.; Dong, S.Y.; Li, T.; Geng, C.; Jiang, L.; Cai, X.H.; Song, R.C. Study of karst period of time of the Dengying Formation Member 4 reservoir in Gaoshiti area, Sichuan, China. J. Chengdu Univ. Tech. (Sci. Tech. Ed.) 2019, 46, 575–585. [Google Scholar]
  15. Zhang, X.H.; Peng, H.L.; Tian, X.W.; Zhao, L.Z.; Huang, P.H.; Wang, H.; Ma, K.; Yang, D.L.; Wang, Y.L.; Zhang, X.; et al. Influence of difference among bioherm beach facies reservoirs on exploration model: An example from Sinian Dengying Formation, central Sichuan Basin. Nat. Gas Explor. Dev. 2019, 42, 13–21. [Google Scholar]
  16. Zhang, M.; Dai, X.F.; Pang, C.X.; Jiang, L.; Geng, C.; Xu, Y.P. Identification and application of the gas reservoirs in the intra-platform of the Sinian Dengying Formation in central Sichuan Basin. Nat. Gas Geos. 2021, 32, 764–771. [Google Scholar]
  17. Zhu, X.; Gu, Y.F.; Jiang, Y.Q.; Tang, T.K.; Xu, W.; Li, K.H.; Deng, H. Characteristics and reservoir body classification & evaluation of Sinian Dengying karst reservoirs in the Gaoshiti Block of central Sichuan Basin. Nat. Gas Ind. 2019, 39, 38–46. [Google Scholar]
  18. Ma, X.H. A golden era for natural gas development in the Sichuan Basin. Nat. Gas Ind. 2017, 37, 1–10. [Google Scholar] [CrossRef]
  19. Li, J.; Yang, C.L.; Xie, W.R.; Rui, Y.R.; Wang, X.B.; Zhang, L.; Xie, Z.Y.; Guo, Z.Q. Differences of natural gas accumulation and play fairways in the marginal zone and interior of Sinian platform in Anyue gas field, Sichuan Basin. Oil Gas Geol. 2023, 44, 34–45. [Google Scholar]
  20. Yang, W.; Wei, G.Q.; Xie, W.R.; Jin, H.; Zeng, F.Y.; Su, N.; Sun, A.; Ma, S.Y.; Shen, J.H.; Wu, S.J. Hydrocarbon accumulation and exploration prospect of mound-shoal complexes on the platform margin of the Fourth Member of Sinian Dengying Formation in the east of Mianzhu-Changning rift, Sichuan Basin, SW China. Pet. Explor. Dev. 2020, 47, 1174–1184. [Google Scholar] [CrossRef]
  21. Yang, Y.; Wen, L.; Song, Z.Z.; Zhang, B.J.; Yan, W.; Zhou, G.; Tian, X.W.; Zhong, Y.; He, Y.; Ma, K.; et al. Breakthrough and potential of natural gas exploration in muli-layer system of Penglai gas area in the north of central Sichuan paleo-uplift. Acta Pet. Sin. 2022, 43, 1351–1368, 1394. [Google Scholar]
  22. Li, Z.Z.; Shi, J.H.C.; Wang, J.H.; Liang, F. Characteristics of residual hill-type reservoir of Sinian Dengying Formation in Deyang-Anyue ancient rift trough, central Sichuan and its significance for oil and gas exploration. Nat. Gas Geos. 2022, 33, 1263–1275. [Google Scholar]
  23. Cen, Y.J.; Liang, F.; Wang, L.E.; Liu, Q.Y.; Chen, H.W.; Wang, S.L.; Dang, Y.J.; Lei, B.Z. Reservoirs characteristics and genesis mechanism in the fourth member of the Sinian Dengying Formation of PS8 well area in Sichuan Basin. China. Offs. Oil Gas 2024, 36, 70–80. [Google Scholar]
  24. Zhang, B.J.; Zhong, Y.; Zhou, G.; Yan, W.; Li, K.Y.; He, Y.; Zhao, L.K.; Long, H.Y.; Lv, W.Z.; Qiao, Y.P. Sedimentary microfacies evolution and comprehensive evaluation of gas reservoir of the Dengying Member 2 in Penglai area, central Sichuan Basin. Mar. Pet. Geol. 2023, 28, 1–10. [Google Scholar]
  25. Geng, X.T.; Xing, F.C.; Yan, H.J.; Fu, H.; Cai, H.B.; Liu, Z.B.; Chen, X.Q.; Gu, Q. Reservoir characteristics of the fourth member of Sinian Dengying Formation and its implications for oil and gas exploration in Moxi area, Sichuan Basin. Lith. Res. 2022, 34, 126–140. [Google Scholar]
  26. Zhao, L.Z.; Wang, Z.C.; Yang, Y.; Duan, S.F.; Wei, G.Q.; Luo, B.; Wen, L.; Ma, S.Y.; Feng, Q.F.; Liu, J.J.; et al. Important discovery in the second member of Dengying Formation in Well Pengtan 1 and its significance, Sichuan Basin. China. Pet. Expl. 2020, 25, 1–12. [Google Scholar]
  27. Wang, W.Z.; Yang, Y.M.; Wen, L.; Luo, B.; Luo, W.J.; Xia, M.L.; Sun, S.N. A study of sedimentary characteristics of microbial carbonate: A case study of the Simian Dengying Formation in Gaomo area, Sichuan basin. Geol. China 2016, 43, 306–318. [Google Scholar]
  28. Wang, Z.C.; Xie, W.R.; Jiang, H.; Su, W.; Huang, S.P.; Gu, M.F.; Ma, S.Y.; Shi, Y.Z.; Jiang, Q.C. Episodes of Caledonian movement and their significance for hydrocarbon accumulation in Sichuan Basin. Mar. Orig. Pet. Geol. 2023, 28, 349–359. [Google Scholar]
  29. Jiang, H.; Wang, Z.C.; Du, H.Y.; Zhang, C.M.; Wang, R.J.; Zou, N.N.; Wang, T.S.; Gu, Z.D.; Li, Y.X. Tectonic evolution of the Leshan-Longnvsi paleo-uplift and reservoir formation of Neoproterozoic Sinian gas. Nat. Gas Geos. 2014, 25, 192–200. [Google Scholar]
  30. Li, Q.; Liu, G.D.; Song, Z.Z.; Sun, M.L.; Zhu, L.Q.; Tian, X.W.; Ma, K.; Yang, D.L.; Wang, Y.L.; Cao, Y.S.; et al. Influence of tectonic evolution of the northern slope in the central Sichuan paleo-uplift on the Sinian-Cambrian hydrocarbon accumulations. Pet. Geol. Explor. 2022, 44, 997–1007. [Google Scholar]
  31. Yuan, H.F.; Liu, Y.; Xu, F.H.; Wang, G.Z.; Xu, G.S. The fluid charge and hydrocarbon accumulation, Sinian reservoir, Anpingdian-Gaoshiti Structure, Central Sichuan Basin. Acta Pet. Sin. 2014, 30, 727–736. [Google Scholar]
  32. Zhang, X.; Chen, K.; Ma, B.; Ran, Q.; Chen, X.; Zou, D.Y.; Lv, W.Z.; Zhao, C.N. The structural evolution characteristics of the Sinian Dengying Formation gas reservoir and its controlling mechanism in the Anyue Gas Field, Sichuan Basin, China. J. Chengdu Univ. Tech. (Sci.Tech. Ed.) 2018, 45, 698–708. [Google Scholar]
  33. Yang, P.; Yuan, H.F.; Ma, K.; Xiao, Q.R.; Ye, Z.X.; Li, Y.J.; Shen, C.; Tan, Q.; Kuang, M.Z.; Xu, T. Diagenetic fluid evolution and hydrocarbon accumulation history of second Member of the Sinian Dengying Formation in the Taihe gas area, central Sichuan basin: Evidence from petrology, in situ geochemistry, fluid inclusions and chronology. Acta Geol. Sin. 2023, 97, 2332–2353. [Google Scholar]
  34. Zhang, P.Y.; Luo, Q.; Zhou, L.; Wang, H.L. Applicability analysis of China’s natural gas analysis and testing standards under hydrogen-blended conditions. Chem. Eng. Oil Gas 2023, 52, 103–106, 117. [Google Scholar]
  35. Luo, Q.; Liu, H.F.; Cheng, Y.; Li, X.H.; Ding, S.J.; Zhou, L. A sound light spectrum correlation method for determining the calorific value of natural gas. Chem. Eng. Oil Gas 2022, 51, 95–100. [Google Scholar]
  36. Qi, Y.L. On-line analysis method of carbon and oxygen isotopes in trace carbonate rocks and its application: A case study of Bonan Sag in Bohai Bay Basin. Petro. Geol. And. Reco. Effi. 2022, 29, 45–52. [Google Scholar]
  37. Wang, H.; Zhou, W.; Xie, R.C. Oil-water recognition and distribution in the Yan-9 oil reservoirs, Yuan 72 block, Hujianshan Oil Field, northern Shaanxi. Sediment. Geol. Tethyan Geol. 2013, 33, 76–81. [Google Scholar]
  38. Luo, N.; Liu, Z.P.; Yin, Z.H.; Hou, J.Q. Identifying reservoir fluid nature with the ratio of compressional wave velocity to shear wave velocity. Well Logging Tech. 2008, 32, 331–333. [Google Scholar]
  39. Hong, X.; Kang, N.; Li, Y.H.; Duan, F.; Tang, L.; He, W.; Wang, X. Physical property analysis and evaluation of shale oil reservoirs in the Third Member of Shahejie Formation in F Oilfield. Tech. Inno. And. Appl. 2023, 13, 81–85. [Google Scholar]
  40. Tang, Y.L.; Liu, W.L.; Yan, X.; Chen, X.; Sun, Q. Uncertainty evaluation and method improvement for determination of Cl−, SO42− in oilfield water by ion chromatography. Guangdong. Chem. Indu. 2024, 51, 173–175. [Google Scholar]
  41. Zhao, Y.G. A new method for logging identification and evaluation of low-resistivity gas layers: A case study of the Dongsheng Gasfield in the Ordos Basin. Nat. Gas Ind. 2020, 40, 47–54. [Google Scholar]
  42. Qi, B.Q.; He, H.J.; He, L.; Miao, Q.; Zhao, N.; Huang, H.; Lu, S.H. Rock electric analysis and gas zone identification of karst reservoirs, north slope of central Sichuan paleouplift. Nat. Gas Expl. Dev. 2024, 47, 24–32. [Google Scholar]
  43. Luo, B.; Yang, Y.M.; Luo, W.J.; Wen, L.; Wang, W.Z.; Chen, K. Controlling factors and distribution of reservoir development in Dengying Formation of paleo-uplift in central Sichuan Basin. Acta Pet. Sin. 2015, 36, 416–426. [Google Scholar]
  44. Song, J.M.; Luo, P.; Liu, S.G.; Li, Z.W.; Sun, W.; Tang, X.; Yang, D.; Yu, J.J. The deposition and reservoir characteristics of Dengying Formation in western Sichuan Basin, China. J. Chengdu. Univ. Tech. (Sci. Tech. Ed.) 2018, 45, 27–44. [Google Scholar]
  45. Li, Y.; Wang, X.Z.; Feng, M.Y.; Zeng, D.M.; Xie, S.Y.; Fan, R.; Wang, L.J.; Zeng, T.; Yang, X.F. Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas. Pet. Expl. Dev. 2019, 46, 52–64. [Google Scholar] [CrossRef]
  46. Sun, Z.M.; Bian, C.R.; Zhang, R.Q.; Sun, W.; Wu, C.Y.; Lin, J.H. Natural gas exploration prospect of the platform marginal zone of the fourth member of Sinian Dengying Formation in southeastern Sichuan basin. Geoscience 2022, 36, 979–987. [Google Scholar]
  47. Chen, Y.B.; Wang, Y.Q.; Hu, Y. Characteristics and main factors controlling the Jurassic gas reservoirs in the middle section of the Western Sichuan Depression. Pet. Geol. Explor. 2015, 37, 561–565, 574. [Google Scholar]
  48. Feng, J.; Zhang, Y.J.; Zhang, Z.W.; Fu, X.F.; Wang, H.X.; Wang, Y.C.; Liu, Y.; Zhang, J.L.; Li, Q.; Feng, Z.H. Characteristics and main control factors of Ordovician shoal dolomite gas reservoir in Gucheng area, Tarim Basin, NW China. Pet. Explor. Dev. 2022, 49, 45–55. [Google Scholar] [CrossRef]
  49. He, J.Y.; Cheng, H.; Xiang, H.; Zhai, X.P.; Geng, Y.D.; Wang, H.B. Optimizing the displacement of temporary plugging and diversion fracturing of the carbonate reservoirs in Tahe Oilfield. Oil Drill. Prod. Tech. 2021, 43, 233–238. [Google Scholar]
  50. Yang, G.; Shi, X.W.; Huang, D.; Wang, H.; Ding, W. Characteristics and major controls of weathering crust gas reservoirs in T2l43 in the Longgang Gas Field, Sichuan Basin. Nat. Gas Ind. 2014, 34, 17–24. [Google Scholar]
  51. Han, H.F. Technological measures for improving single-well productivity of gas reservoirs of Upper Sinian Deng- 4 Member in the Sichuan Basin. Nat. Gas Ind. 2017, 37, 40–47. [Google Scholar]
  52. Wang, L.; Yang, S.L.; Peng, X.; Liu, Y.C.; Xu, W.; Deng, H. Pore Structure Characteristics and Storage-Seepage Capability of Multi-Type Reservoirs in Fracture-Cavity Carbonate Gas Reservoirs: A Case Study of Deng- 4 Member in Gaoshiti—Moxi Area, Sichuan Basin. J. Jilin Univ. (Earth Sci. Ed.) 2019, 49, 947–958. [Google Scholar]
  53. Xie, W.R.; Yang, W.; Wang, Z.C.; Wei, G.Q.; Ma, S.Y.; Hao, T.; Su, N.; Li, W.Z.; Wu, S.J.; Wang, X.D. Characteristics and main controlling factors on the development of a platform margin belt and its effect on hydrocarbon accumulation: A case study of Dengying Formation in Sichuan Basin. Chin. J. Geol. 2021, 56, 867–883. [Google Scholar]
  54. Wei, G.Q.; Wang, Z.H.; Li, J.; Yang, W.; Xie, Z.Y. Characteristics of source rocks, resource potential and exploration direction of Sinian and Cambrian in Sichuan Basin. Nat. Gas Geos. 2017, 28, 1–13. [Google Scholar] [CrossRef]
  55. Wu, X.Q.; Zhou, L.F.; Zhao, S.S.; Qian, Y.X.; Wang, Y.Q.; Yang, J.; Wang, D. Geochemical characteristics of reservoir bitumen from Dengying Formation in Langzhong area of Sichuan Basin and its implication. Acta Pet. Sin. 2022, 43, 483–493. [Google Scholar]
  56. Yuan, B.G.; Dai, X.; Chen, J.P.; Zhu, H.; Ni, Y.Y. Hydrocarbon generation potential of source rocks of Sinian Doushantuo Formation, Sichuan Basin and its periphery. Nat. Gas Explor. Dev. 2024, 47, 1–10. [Google Scholar]
  57. Xu, C.C.; Shen, P.; Yang, Y.M.; Luo, B.; Huang, J.Z.; Jiang, X.F.; Xie, J.R.; Cen, Y.J. Accumulation conditions and enrichment patterns of natural gas in the Lower Cambrian Longwangmiao Fm reservoirs of the Leshan-Longnüsi Paleohigh, Sichuan Basin. Nat. Gas Ind. 2014, 34, 1–7. [Google Scholar]
  58. Xie, W.R.; Jiang, H.; Ma, S.Y.; Wang, Z.C.; Hao, T.; Fu, X.D.; Su, N.; Li, W.Z.; Wu, S.J.; Wang, X.D.; et al. Sedimentary evolution characteristics and favorable exploration directions of Deyang-Anyue Rift within the Sichuan Basin in Late Sinian-Early Cambrian. Nat. Gas Geos. 2022, 33, 1240–1250. [Google Scholar]
  59. Lu, K.L.; Wu, K.J.; Li, Z.J.; Sun, Y.H.; Xu, S.H.; Liang, F.; Liu, L.; Li, S. Characteristics and evolution model of hydrocarbon accumulation of Cambrian Longwangmiao Formation in the north slope of central Sichuan paleo-uplift. Lith. Res. 2024, 36, 159–168. [Google Scholar]
  60. Li, J.; Li, Z.S.; Wang, X.B.; Wang, D.L.; Xie, Z.Y.; Li, J.; Wang, Y.F.; Han, Z.X.; Ma, C.H.; Wang, Z.H.; et al. New indexes and charts for genesis identification of multiple natural gases. Pet. Explor. Dev. 2017, 44, 503–512. [Google Scholar] [CrossRef]
  61. Wu, W.; Luo, B.; Luo, W.J.; Wang, W.Z. Further discussion about the origin of natural gas in the Sinian of central Sichuan paleo-uplift, Sichuan Basin, China. Nat. Gas Geos. 2016, 27, 1447–1453. [Google Scholar] [CrossRef]
  62. Zhou, H.; Li, W.; Zhang, B.M.; Liu, J.J.; Deng, S.H.; Zhang, S.B.; Shan, X.Q.; Zhang, J.; Wang, X.B.; Jiang, H. Formation and evolution of Upper Sinian to Lower Cambrian intraplatformal basin in Sichuan Basin. Acta Pet. Sin. 2015, 36, 310–323. [Google Scholar]
  63. Peng, H.L.; Ma, K.; Zhang, X.H.; Wen, L.; Wang, Y.L.; Tian, X.W.; Li, Y.; Yang, D.L.; Zhong, J.Y.; Sun, Y.T.; et al. Sequence Stratigraphic Characteristics and Sedimentary Evolution Model of the Late Ediacaran in the Sichuan Basin. Acta Sedimentol. Sin. 2021, 39, 1440–1450. [Google Scholar]
  64. Wang, J.Q.; Deng, J.X.; Liu, Z.H.; Yan, L.L.; Xia, H. Petrophysical properties and their influencing factors of carbonates in the fourth member of Sinian Dengying Formation, Sichuan Basin, SW China. Pet. Explor. Dev. 2023, 50, 1–14. [Google Scholar] [CrossRef]
  65. Xia, Q.Y.; Yan, H.J.; Xu, W.; Zhang, L.; Luo, W.J.; Deng, H.; Yu, J.C. Paleokarst microtopography of the Sinian top and its development characteristics in Moxi area, central Sichuan Basin. Acta Pet. Sin. 2021, 42, 1299–1309, 1336. [Google Scholar]
  66. Li, X.T.; Pan, R.F.; Yan, J.; Li, Y.; Zhang, F.R. Karst Paleogeomorphology Features of the Fourth Member of Dengying Formation in Sichuan Basin and the Significance of Oil and Gas Exploration. Geol. Sci. Tech. Info. 2018, 37, 191–195. [Google Scholar]
  67. Xie, W.R.; Yang, W.; Wei, G.Q.; Zeng, F.Y.; Jin, H.; Shi, Z.S.; Wu, S.J. Controlling of Tongwan Movement on the formation of Dengying karst reservoir in Sichuan Basin. Chin. J. Geol. 2017, 52, 254–269. [Google Scholar]
  68. Liang, F.; Tan, B.; Wang, L.E.; Xiong, Y.X.; Liu, Q.Y.; Zhang, H.; Lou, T.; Lu, M.Y.; Wang, M. Characteristics and main controlling factors of dolomite reservoir in the second member of Upper Sinian Dengying Formation, Penglai gas area, Central Sichuan Paleo-uplift. Nat. Gas Geos. 2024, 35, 1816–1832. [Google Scholar]
  69. Zhong, Y.; Li, Y.L.; Zhang, X.B.; Liu, S.G.; Wu, F.R.; Liu, D.J.; Deng, X.J.; Chen, S.; Yang, F.; Li, X.J.; et al. Evolution characteristics of Central Sichuan palaeouplift and its relationship with Early Cambrian Mianyang Changning intracratonic sag. J. Chengdu Univ. Tech (Sci. Tech. Ed.) 2014, 41, 703–712. [Google Scholar]
  70. Ma, K.; Wen, L.; Zhang, B.J.; Li, Y.; Zhong, J.Q.; Wang, Y.L.; Peng, H.L.; Zhang, X.H.; Yan, W.; Ding, Y.; et al. Segmented evolution of Deyang-Anyue erosion rift trough in Sichuan Basin and its significance for oil and gas exploration, SW China. Pet. Explor. Dev. 2022, 49, 274–284. [Google Scholar] [CrossRef]
  71. Shi, Y.Z.; Wang, Z.C.; Xu, Q.C.; Hu, S.B.; Huang, S.P.; Jiang, H.; Jiang, Q.C.; Fu, X.D.; Li, W.Z.; Liu, R.H.; et al. Reconstruction and application of thermal history of old strata in superimposed basin: A case study on the Sinian-Cambrian in the central Sichuan paleo-uplift of the Sichuan Basin. Nat. Gas Ind. 2024, 44, 29–43. [Google Scholar]
  72. Ma, K.; Shen, P.; Wang, Z.C.; Tian, X.W.; Peng, H.L.; Wang, H.; Zhang, X.H.; Sun, Y.T.; Luo, B.; Wang, Y.L.; et al. Natural gas exploration potential of Longwangmiao Formation on the north slope of Chuanzhong paleo-uplift from the characteristics of “Four Paleo”. Nat. Gas Geos. 2019, 30, 1451–1464. [Google Scholar]
  73. Ma, K.; Zhang, X.H.; Peng, H.L.; Sun, Y.T.; Yang, D.L.; Tian, X.W.; Zhong, J.W.; Wang, Y.L. Tectonie evolution of Moxi north slope in Sichuan Basin and its effect on forming Sinian oil and gas reservoirs. Nat. Gas Explor. Dev. 2020, 43, 8–15. [Google Scholar]
  74. Allen, P.A.; Allen, J.R. Basin Analysis: Principals and Applications; Blackwell Scientific Publications: Oxford, UK, 1990; pp. 282–283. [Google Scholar]
  75. Ma, K.; Zhang, B.J.; Xu, S.L.; Yan, W.; Zhou, G.; Zhang, X.; Wu, L.Y.; Jiang, H.; Wang, W.Z.; Xu, X. Characteristics of natural gas accumulation in the norther slope of the middle Sichuan paleo-uplift. Nat. Gas. Geos. 2024, 35, 635–644. [Google Scholar]
  76. Li, Z.Y.; Jiang, H.; Wang, Z.C.; Wang, T.S.; Lu, W.H.; Lv, Z.G. Control of tectonic movement on hydrocarbon accumulation in the Sinian strata, Sichuan Basin. Nat. Gas Ind. 2014, 34, 23–30. [Google Scholar]
  77. Yang, Y.M.; Wang, W.Z.; Wen, L.; Luo, B.; Zhang, X.; Chen, X.; Jia, M.; Long, H.Y. Sedimentary evolution characteristics and large-scale natural gas accumulation pattern of microbial carbonate in the slope area of major paleo uplift, the Sichuan Basin. Nat. Gas Ind. 2021, 41, 38–47. [Google Scholar]
  78. He, D.B.; Yan, H.J.; Yang, C.C.; Wei, Y.S.; Zhang, L.J.; Guo, J.L.; Luo, W.J.; Liu, X.X.; Hu, D.; Xia, Q.Y.; et al. Gas reservoir characteristics and technical countermeasures for development in the fourth Member of Dengying Formation in Anyue gas field. Acta Pet. Sin. 2022, 43, 977–988. [Google Scholar]
  79. Tian, X.W.; Zhang, X.H.; Peng, H.L.; Ma, K.; Yang, D.L.; Sun, Y.T. Productivity differences of gas reservoirs in the Fourth Member of Sinian Dengying Formation in Gaoshiti-Moxi area, central Sichuan Basin. Xinjiang Pet. Geol. 2019, 40, 673–679. [Google Scholar]
  80. Yang, W.; Wei, G.Q.; Xie, W.R.; Su, N.; Zeng, F.Y.; Hao, C.G.; Bai, Z.Z.; Li, R.; Wu, X.Q.; Su, Y.Q. Main controlling factors and genetic mechanism for the development of high-quality reservoirs in the mound-shoal complexes on the platform margin mound-beach body at platform margin of the inner cratonic rift: Case study of the fourth member of Dengying Formation in the east side of the Deyang-Anyue cratonic rifts, Sichuan Basin. Nat. Gas Geos. 2022, 33, 1541–1553. [Google Scholar]
  81. Shuai, Y.H.; Liu, K.Y.; Hu, G.Y.; Wang, T.S.; Tian, X.W.; Zhang, B.; Chen, Z.X. Gas accumulation mechanisms of the Sinian reservoir in the Sichuan basin and their significance for deep gas exploration. Acta Geol. Sin. 2021, 95, 3400–3412. [Google Scholar]
  82. Xie, Z.Y.; Wei, G.Q.; Li, J.; Xu, L.; Zhang, L.; Li, Q.; Li, Z.j.; Wu, S.J.; Guo, Z.Q.; Hao, A.S. Geochemical characteristics and accumulation pattern of gas reservoirs of the Sinian-Permian in central Sichuan uplift zone, Sichuan Basin. China Pet. Explor. 2021, 26, 50–67. [Google Scholar]
  83. Wei, G.Q.; Yang, W.; Zhang, J.; Xie, W.R.; Zeng, F.Y.; Su, N.; Jin, H. The pre-Sinian rift in central Sichuan Basin and its control on hydrocarbon accumulation in the overlying strata. Pet. Explor. Dev. 2018, 45, 179–189. [Google Scholar] [CrossRef]
  84. Wei, G.Q.; Yang, W.; Xie, W.R.; Jin, H.; Su, N.; Sun, A.; Shen, J.H.; Hao, C.G. Accumulation modes and exploration domains of Sinian-Cambrian natural gas in Sichuan Basin. Acta Pet. Sin. 2018, 39, 1317–1327. [Google Scholar]
Minerals 15 00098 g001
Figure 1. (A) Location map illustrating the key structural features of the PS8 well area (modified after [23]). The solid black line from “a” to “b” represents the location of the cross-section passing through four wells in the Penglai Gas Field, whereas the solid green line indicates the seismic cross-section. The insert map shows the central Sichuan paleo-uplift with a focus on the Penglai Gas Field, which includes the studied PS8 well. The red solid star marks the position of the PS8 well. The blue background represents the platform margin belt of the Dengying Formation, while the red background denotes the intrastage belt of the Dengying Formation. (B) Generalized lithostratigraphic chart of the Dengying Formation in the PS8 well, showing the various lithofacies changes, their corresponding thicknesses, and the tectonic movements during deposition.
Figure 1. (A) Location map illustrating the key structural features of the PS8 well area (modified after [23]). The solid black line from “a” to “b” represents the location of the cross-section passing through four wells in the Penglai Gas Field, whereas the solid green line indicates the seismic cross-section. The insert map shows the central Sichuan paleo-uplift with a focus on the Penglai Gas Field, which includes the studied PS8 well. The red solid star marks the position of the PS8 well. The blue background represents the platform margin belt of the Dengying Formation, while the red background denotes the intrastage belt of the Dengying Formation. (B) Generalized lithostratigraphic chart of the Dengying Formation in the PS8 well, showing the various lithofacies changes, their corresponding thicknesses, and the tectonic movements during deposition.
Minerals 15 00098 g001
Minerals 15 00098 g002
Figure 2. Core samples and cast thin section photomicrographs under polarized light microscopy from the Fourth Member of the Dengying Formation in the PS8 well. (a) A blue cast thin section photomicrograph shows intercrystalline dissolved pores within algal-laminated dolomite, sample depth 7058.04 m. (b) Algal-clotted dolomite exhibits horizontal and high-angle fractures, which are partially filled with bitumen, sample depth 6987.67–6987.79 m. (c) Algal-laminated dolomite features bedding-parallel dissolved pores filled with bitumen, sample depth 7240.89–7241.04 m. (d) A red cast thin section reveals algal-clotted dolomite with intergranular dissolved pores, some of which are partially filled with bitumen, sample depth 7092.42 m. (e) Sand-clast dolomite core shows numerous bedding-parallel dissolved pores and irregular vugs, with some vugs filled with quartz, sample depth 6986.50–6986.64 m. (f) A blue cast thin section reveals algal-clotted dolomite with algal-bonded pores, partially filled with dolomite and bitumen, sample depth 6983.53 m.
Figure 2. Core samples and cast thin section photomicrographs under polarized light microscopy from the Fourth Member of the Dengying Formation in the PS8 well. (a) A blue cast thin section photomicrograph shows intercrystalline dissolved pores within algal-laminated dolomite, sample depth 7058.04 m. (b) Algal-clotted dolomite exhibits horizontal and high-angle fractures, which are partially filled with bitumen, sample depth 6987.67–6987.79 m. (c) Algal-laminated dolomite features bedding-parallel dissolved pores filled with bitumen, sample depth 7240.89–7241.04 m. (d) A red cast thin section reveals algal-clotted dolomite with intergranular dissolved pores, some of which are partially filled with bitumen, sample depth 7092.42 m. (e) Sand-clast dolomite core shows numerous bedding-parallel dissolved pores and irregular vugs, with some vugs filled with quartz, sample depth 6986.50–6986.64 m. (f) A blue cast thin section reveals algal-clotted dolomite with algal-bonded pores, partially filled with dolomite and bitumen, sample depth 6983.53 m.
Minerals 15 00098 g002
Minerals 15 00098 g005
Figure 5. Stratigraphic chart showing a correlation between gas reservoir intervals in the PS8 well and adjacent wells in the Penglai Gas Field (see Figure 1 for the (a,b) cross-section location).
Figure 5. Stratigraphic chart showing a correlation between gas reservoir intervals in the PS8 well and adjacent wells in the Penglai Gas Field (see Figure 1 for the (a,b) cross-section location).
Minerals 15 00098 g005
Minerals 15 00098 g006
Figure 6. Distribution of carbon isotopes in kerogen of source rocks and natural gas in the Ediacaran–lower Paleozoic strata in the central Sichuan uplift (modified after [9]).
Figure 6. Distribution of carbon isotopes in kerogen of source rocks and natural gas in the Ediacaran–lower Paleozoic strata in the central Sichuan uplift (modified after [9]).
Minerals 15 00098 g006
Minerals 15 00098 g007
Figure 7. Microscopic photographs and hand specimen cores showing syngenetic and epigenetic karst developed in the Fourth Member of the Dengying Formation. (a) Microscopic photograph illustrating the psammitic dolomite and moldic pore, sample depth 7243.6 m, well PS7. (b) Algal-clotted dolomite and moldic pore, sample depth 7063.56 m, well PS8. (c) Algal-clotted dolomite and irregular vug, partially filled with bitumen, sample depth 7060.5–7060.6 m, well PS8. (d) Micritic dolomite with a horizontal underflow, sample depth 6987.5–6987.6 m, well PS9. (e) Psammitic dolomite with vertical seepage and solution channel filled with bitumen, sample depth 7245.8–7245.9 m, well PS7. (f) Algal-clotted dolomite with interconnected pores by fractures, sample depth 7048.8 m, well PS8.
Figure 7. Microscopic photographs and hand specimen cores showing syngenetic and epigenetic karst developed in the Fourth Member of the Dengying Formation. (a) Microscopic photograph illustrating the psammitic dolomite and moldic pore, sample depth 7243.6 m, well PS7. (b) Algal-clotted dolomite and moldic pore, sample depth 7063.56 m, well PS8. (c) Algal-clotted dolomite and irregular vug, partially filled with bitumen, sample depth 7060.5–7060.6 m, well PS8. (d) Micritic dolomite with a horizontal underflow, sample depth 6987.5–6987.6 m, well PS9. (e) Psammitic dolomite with vertical seepage and solution channel filled with bitumen, sample depth 7245.8–7245.9 m, well PS7. (f) Algal-clotted dolomite with interconnected pores by fractures, sample depth 7048.8 m, well PS8.
Minerals 15 00098 g007
Minerals 15 00098 g008
Figure 8. Regional maps showing the location of the PS8 well area in relation to the tectonic evolution of the Sichuan Basin from the Pre-Cambrian to recent. (a) Pre-Cambrian tectonic evolution. (b) Tectonic activity prior to Permian in the study area. (c) Tectonic evolution before the late Triassic. (d) Recent tectonic stability of the present-day study area.
Figure 8. Regional maps showing the location of the PS8 well area in relation to the tectonic evolution of the Sichuan Basin from the Pre-Cambrian to recent. (a) Pre-Cambrian tectonic evolution. (b) Tectonic activity prior to Permian in the study area. (c) Tectonic evolution before the late Triassic. (d) Recent tectonic stability of the present-day study area.
Minerals 15 00098 g008
Minerals 15 00098 g009
Figure 9. Thermal evolution and hydrocarbon charging history of source rocks in the Qiongzhusi Formation on the northern slope of the central Sichuan paleo-uplift (modified after [72]).
Figure 9. Thermal evolution and hydrocarbon charging history of source rocks in the Qiongzhusi Formation on the northern slope of the central Sichuan paleo-uplift (modified after [72]).
Minerals 15 00098 g009
Minerals 15 00098 g010
Figure 10. (a) Cross-sectional seismic profile passing through Well JT1 and PS8. (b) Reservoir formation model of the Fourth Member of the Dengying Formation in PS8 well.
Figure 10. (a) Cross-sectional seismic profile passing through Well JT1 and PS8. (b) Reservoir formation model of the Fourth Member of the Dengying Formation in PS8 well.
Minerals 15 00098 g010
Table 1. Distribution of natural gas composition and carbon isotope data for the Fourth Member of the Dengying Formation in the PS8 well, Penglai Gas Field.
Table 1. Distribution of natural gas composition and carbon isotope data for the Fourth Member of the Dengying Formation in the PS8 well, Penglai Gas Field.
PS8
Well		Natural Gas Composition Content (%)Relative Density of Natural GasCarbon Isotope (‰)
CH4C2H6C3H8N2CO2H2HeH2SCH4C2H6
Min90.140.0200.190.2400.0100.52−32.33−31.98
Max94.260.260.010.389.097.360.010.660.65−32.18−25.82
Average92.050.100.274.712.460.010.400.59−32.26−28.90
Table 2. Distribution of water chemical analysis data for the Fourth Member of the Dengying Formation in the PS8 well, Penglai Gas Field.
Table 2. Distribution of water chemical analysis data for the Fourth Member of the Dengying Formation in the PS8 well, Penglai Gas Field.
PS8
Well		Analysis Items (mg/L)Total Salinity (mg/L)Density
(g/m3)		pH
K+Na+Ca2+Mg2+Ba2+Cl−SO42−
Min691336064,40031,800246165,00019.1270,0001.1823.61
Max822625074,10034,600819182,00056.9294,0001.1916.18
Average754.4515667,68033,020572.8172,80031.9281,4001.1855.19
Table 3. Measured values of formation pressure and temperature for the Fourth Member Gas Reservoir of the Dengying Formation in the PS8 well area.
Table 3. Measured values of formation pressure and temperature for the Fourth Member Gas Reservoir of the Dengying Formation in the PS8 well area.
WellVertical Depth at the Middle of the Production Layer (m)Formation Pressure (MPa)Pressure CoefficientTemperature at the Middle of the Production Layer (°C)
PS77217.7270.661.00158.2
PS87078.7070.071.01162.9
PS96941.4769.321.02163.8
PS106913.7669.651.03163.5
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Chen, H.; Wang, S.; Mansour, A.; Qin, Q.; Ahmed, M.S.; Cen, Y.; Liang, F.; He, Y.; Fan, Y.; Gentzis, T. Key Characteristics and Controlling Factors of the Gas Reservoir in the Fourth Member of the Ediacaran Dengying Formation in the Penglai Gas Field, Sichuan Basin. Minerals 2025, 15, 98. https://doi.org/10.3390/min15020098

AMA Style

Chen H, Wang S, Mansour A, Qin Q, Ahmed MS, Cen Y, Liang F, He Y, Fan Y, Gentzis T. Key Characteristics and Controlling Factors of the Gas Reservoir in the Fourth Member of the Ediacaran Dengying Formation in the Penglai Gas Field, Sichuan Basin. Minerals. 2025; 15(2):98. https://doi.org/10.3390/min15020098

Chicago/Turabian Style

Chen, Hongwei, Shilin Wang, Ahmed Mansour, Qirong Qin, Mohamed S. Ahmed, Yongjing Cen, Feng Liang, Yuan He, Yi Fan, and Thomas Gentzis. 2025. "Key Characteristics and Controlling Factors of the Gas Reservoir in the Fourth Member of the Ediacaran Dengying Formation in the Penglai Gas Field, Sichuan Basin" Minerals 15, no. 2: 98. https://doi.org/10.3390/min15020098

APA Style

Chen, H., Wang, S., Mansour, A., Qin, Q., Ahmed, M. S., Cen, Y., Liang, F., He, Y., Fan, Y., & Gentzis, T. (2025). Key Characteristics and Controlling Factors of the Gas Reservoir in the Fourth Member of the Ediacaran Dengying Formation in the Penglai Gas Field, Sichuan Basin. Minerals, 15(2), 98. https://doi.org/10.3390/min15020098

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop pFad - Phonifier reborn

Pfad - The Proxy pFad of © 2024 Garber Painting. All rights reserved.

Note: This service is not intended for secure transactions such as banking, social media, email, or purchasing. Use at your own risk. We assume no liability whatsoever for broken pages.


Alternative Proxies:

Alternative Proxy

pFad Proxy

pFad v3 Proxy

pFad v4 Proxy