Next Article in Journal
Structural Analysis of Aggregates in Clayey Tailings Treated with Coagulant and Flocculant
Previous Article in Journal
Optimized Hydrothermal Alteration Mapping in Porphyry Copper Systems Using a Hybrid DWT-2D/MAD Algorithm on ASTER Satellite Remote Sensing Imagery
 
 
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 6
10.3390/min15060625
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
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Study on Reservoir Characteristics, the Tightening Process and Reservoir Quality in Source-to-Sink Systems in the Xu-2 Member of the Xujiahe Formation in the Western Sichuan Basin, Western China

by
Dong Wu
1,2,3,
Yu Yu
4,*,
Liangbiao Lin
4,
Sibing Liu
3,
Binjiang Li
3 and
Xiaolong Ye
3
1
State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 102206, China
2
SINOPEC Key Laboratory of Geology and Resources in Deep Stratum, Beijing 102206, China
3
College of Energy (College of Modern Shale Gas Industry), Chengdu University of Technology, Chengdu 610059, China
4
Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(6), 625; https://doi.org/10.3390/min15060625
Submission received: 30 April 2025 / Revised: 5 June 2025 / Accepted: 7 June 2025 / Published: 9 June 2025
(This article belongs to the Special Issue Natural and Induced Diagenesis in Clastic Rock)
Browse Figures
Versions Notes

Abstract

The Upper Triassic Xujiahe Formation in the western Sichuan Basin is rich in natural gas resources and is one of the main tight sandstone gas-producing layers in the Sichuan Basin. Taking the tight sandstone of the second member of the Xujiahe Formation (Xu-2 Member) in the western Sichuan Basin as the study target, based on the analysis of the rock sample, a thin section, scanning electron microscopy, inclusion, the carbon and oxygen isotope, the petrological characteristics, the reservoir properties, the diagenetic sequences, and the pore evolution processes were revealed. The tight sandstones are composed of litharenite, sublitharenite, and feldspathic litharenite with an average porosity of 3.81% and a permeability mainly ranging from 0.01 to 0.5 mD. The early to late diagenetic stages were revealed, and the diagenetic evolution sequence with five stages was constructed. The Xu-2 sandstones were subdivided into three different types, and each type has its own tightening factors and processes. In the quartz-rich sandstone, the compaction and pressure solution were the primary causes of reservoir tightening, while late fracturing and dissolution along fractures were the main factors improving reservoir properties. In the feldspar-rich sandstone, early dissolution was a primary factor in improving porosity, while carbonate and quartz cements generated by dissolution contributed to a decrease in porosity. In the rock-fragment-rich sandstone, chlorites formed in the early stage and dissolution were the main factors of reservoir quality improvement, while the authigenic quartz formed in the middle diagenetic stage was the primary cause of reservoir tightening. Four major source-to-sink systems were identified in the western Sichuan Basin and they have different reservoir characteristics and reservoir quality controlling factors. This study will contribute to a deeper understanding of the characteristics, diagenetic evolution, and tightening process of tight sandstone reservoirs, effectively promoting scientific research and the industrial development of tight sandstone gas in the Xu-2 Member of the Sichuan Basin.

1. Introduction

Natural gas, as a kind of clean energy, is increasingly valued and widely used in the context of global carbon neutrality and will undoubtedly become an important component of the future world energy system [1,2,3]. Tight sandstone gas, as one of the main types of unconventional natural gas resources, has made breakthrough progress in exploration and development in recent years, becoming a key factor in increasing natural gas storage and production [1,4,5,6]. The tight sandstone is generally identified with a porosity of less than 10% and an air permeability of less than 1 mD [7,8,9,10]. Exploring natural gas enrichment zones with commercial exploration and extraction value in large-scale tight sandstone is crucial in tight sandstone reservoir studies. The study of the reservoir tightening process and natural gas accumulation process is particularly important for increasing the storage and production of natural gas resources [11]. Determining the coupling relationship between reservoir tightening and natural gas accumulation is the basis for achieving the efficient exploration and development of tight sandstone gas reservoirs. For deep reservoirs, if the tightening process is slow, natural gas can easily accumulate. On the contrary, if the tightening process is rapid, it is hard for natural gas to accumulate.
Previous studies have revealed that the distribution of high-quality tight sandstone reservoirs is influenced by factors such as sedimentary facies, diagenesis, tectonic activity, hydrocarbon activity, reservoir characteristics, and tightening processes of sandstones [5,9,11,12,13,14,15,16,17,18]. The sedimentary facies, as well as sandstone types and petrological components, are commonly determined by source-to-sink systems [19]. The geomorphic units on the Earth’s surface include denudational landforms and sedimentary landforms. The denudation products formed in denudational landforms are transported to sedimentary landforms. This whole system is known as the source-to-sink system [20,21]. The source-to-sink system also controls diagenetic events and physical and chemical processes during diagenesis, resulting in different pore structures and the heterogeneity of the reservoir [19,22,23]. Detrital grains from different sources stack with each other, resulting in the diversity of tight sandstone types. The tightening processes of different types of sandstones are inevitably different.
The Sichuan Basin is one of the major gas basins in China [24,25,26,27]. Since the 1970s, gas fields, including Xinchang, Zhongba, and Pingluoba, have been discovered, and the Xujiahe Formation in the western Sichuan Basin has been revealed as a key layer for tight sandstone gas exploration [11]. The second member of the Xujiahe Formation (Xu-2 Member) is one of the main gas layers, having a complex composition [27]. Based on comprehensive testing and analysis techniques, this paper identifies three main types of sandstones in the Xu-2 Member in the western Sichuan Basin to study the tightening processes and reservoir quality in four major source-to-sink systems. This study will contribute to a deeper understanding of the characteristics, diagenetic evolution, and tightening process of tight sandstone reservoirs, effectively promoting scientific research and the industrial development of tight sandstone gas in the Xu-2 Member of the Sichuan Basin.

2. Geologic Background

2.1. Structural Setting

The Sichuan Basin is in southwestern China (Figure 1a), with an area of over 18 × 104 km2 [11]. The Sichuan Basin belongs to the Yangtze Platform structurally and has a Precambrian crystalline basement [11,27]. The western Sichuan Basin covers an area of approximately 5 × 104 km2 [28] and is bounded by the Longmenshan Fold Belt to the west (Figure 1b), the Micangshan Uplift to the north, the Daxiangling Fold Belt to the south, and the gentle fold belt in central Sichuan Basin to the east [27,28]. Based on structural characteristics, the western Sichuan Basin was further subdivided into six secondary tectonic units, namely the Longmenshan Fold Belt, the Zitong Depression, the Anxian-Yazihe–Dayi Fault-fold Belt, the Chengdu Depression, the Zhixin Structural Belt, and the Xiaoquan–Xinchang Structural Belt [11].
The western Sichuan Basin was a part of the passive continental margin from the Sinian to the Middle Triassic, mainly developing marine carbonate formations [28]. In the early period of the Late Triassic, influenced by the compression caused by the Longmenshan Fold Belt, the western Sichuan Basin transformed into a foreland basin and developed terrigenous clastic formations [11,28]. The western Sichuan Basin has undergone tectonic movements such as the Indosinian, Yanshanian, and Himalayan periods during its long geological history, with significant changes in stratigraphic thickness and rock density [11,27,29].

2.2. Stratigraphy and Sedimentary Facies

The thickness of the Xujiahe Formation in the western Sichuan Basin gradually decreases from west to east [27]. In a relatively complete stratigraphic sequence of the Xujiahe Formation, five members were subdivided from bottom to top, namely the Xu-1, Xu-2, Xu-3, Xu-4, and Xu-5 members. The deposits of the Xu-1, Xu-3, and Xu-5 members mainly consist of dark gray shale interbedded with sandstone and coal, which are the main source rocks in the western Sichuan Basin [11,26,28]. The deposits of the Xu-2 and Xu-4 members mainly consist of light gray sandstone interbedded with mudstone, shale, and coal (Figure 2), which are the main reservoir rocks in the western Sichuan Basin [11,26,27].
The Xujiahe Formation in the western Sichuan Basin has plenty of animal and plant fossils. The fossils, as well as previous studies, suggested that this formation was accumulated in sedimentary environments such as alluvial fans, lakes, lacustrine deltas, marine deltas, shorelines, and bays. From early to late, it changed from marine to transitional to terrestrial environments [26,27,28]. During the early stage of sedimentation of the Xu-2 Member, the clastic supply of the Micangshan and Dabashan Mountains was sufficient. The locally uplifted Longmenshan Mountain only formed a small-scale delta [30]. During the middle stage of sedimentation, the clastic supply of the Dabashan and Longmenshan Mountains increased, and the sand bodies from different mountains were connected with each other [30,31]. During the late stage of sedimentation, the scale of the deposits in the northern part expanded, while the range of the delta formed by the Kangdian ancient land in the southern part relatively shrank. The delta from the Longmenshan Mountain migrated southward [30]. The Xu-2 Member in the western Sichuan Basin was mainly deposited in the marine delta front, and the sandstones were mainly accumulated in underwater distributary channels and mouth bars [28].

3. Data and Methods

Cores are the main kind of data for the analysis of petrology, diagenesis, and the diagenetic process. Thin sections (standard 0.03 mm in thickness) were prepared after impregnation with blue epoxy under vacuum and stained with Alizarin Red S to identify the carbonate minerals. Microscopic observation and point-counting (300 points per thin section) were used to analyze the composition and texture of 6335 rock samples with a Leica polarizing microscope. A total of 1537 samples obtained from cores were used to analyze the porosity and permeability of reservoirs. Based on the microscopic observation and reservoir quality analysis, the grain size, pore volume, diagenetic minerals, and relative timing of diagenetic events were revealed. The scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) by the Quanta250 FEG (FEI Company, Hillsboro, USA) and INCA X-Max20 instruments (Oxford Instruments, Abingdon, UK), respectively, were used to examine 65 samples obtained from cores of the Xu-2 Member, and 500 pictures of these samples were taken for the identification of authigenic clay minerals, quartz, and carbonate cements.
By comprehensively utilizing the temperature measurement data of inclusion samples, carbon, and oxygen isotope data, the characteristics of diagenetic fluids in the Xu-2 Member in the western Sichuan Basin can be revealed [11,17,32,33]. Based on the characteristics of diagenetic minerals and diagenetic fluids discovered in this study, as well as the burial history of the western Sichuan Basin obtained from previous studies [34,35,36], the diagenetic evolution sequence was determined. The occurrence time and depth of the main diagenetic events were clarified. Using the method proposed by previous studies [11,37], the initial porosity of sedimentary sands and the quantitative evolution of the primary pores during the burial process can be calculated. Based on the analysis of the thin section, inclusion temperature, and isotope data, the impact of the main diagenetic events on the reservoir properties and the quantitative evolution of pores were revealed. The differential tightening processes in the Xu-2 sandstone were determined by describing and comparing the diagenetic sequence and pore evolution in different types of reservoirs. The influencing factors of high-quality reservoirs were clarified then.

4. Results

4.1. Lithology Characteristics of the Xu-2 Member in the Western Sichuan Basin

The lithologic composition is not only the basis for the classification of clastic rocks but also directly affects the diagenesis of clastic reservoirs, thereby affecting the tightening processes of reservoirs [6,11]. The clastic components of the Xu-2 sandstone in the western Sichuan Basin include quartz, rock fragment, and feldspar (Figure 3). Rock fragments and quartz constitute the main detrital minerals of tight sandstones (Figure 4a). The content of feldspar is relatively low. The tight sandstone also contains a small amount of mica, chlorite, and heavy minerals, less than 3%. The rock fragments are mainly composed of sedimentary rock debris and metamorphic rock debris with a small amount of volcanic rock debris (Figure 4b).
Various types of rocks were discovered in the Xu-2 Member in the western Sichuan Basin, mainly composed of litharenite, sublitharenite and feldspathic litharenite (Figure 4a). Litharenites were commonly observed, accounting for 52.4% of the total samples, followed by sublitharenite and feldspathic litharenite, accounting for 16.7% and 21.8% of the total samples, respectively.

4.2. Reservoir Properties of the Xu-2 Member in the Western Sichuan Basin

The porosity of the Xu-2 sandstone in the western Sichuan Basin mainly ranges from 1.0% to 5.0% (accounting for about 80% of total samples), with an average of 3.81%. The permeability mainly varies from 0.01 to 0.5 mD (accounting for about 80% of the total samples). The permeability of the Xu-2 sandstone is low, and it only increases when fractures occur in reservoirs (Figure 5).
The primary pores were mainly discovered in reservoirs with a relatively high quartz content (Figure 6). The burial depth of the Xu-2 Member in the western Sichuan Basin commonly ranges from 4000 to 5500 m. Affected by the overlying load pressure, only some primary pores were well preserved. Most of the primary pores shrunk, filled with carbonate cements, chlorite, and siliceous cements. The long-axis diameter of these pores is approximately 30 to 350 μm.
Secondary dissolution pores widely developed in the Xu-2 Member. The intragranular dissolution pores were mainly formed by the dissolution of feldspar along the cleavage (Figure 6). In some samples, the dissolution was relatively intense, and the grains were completely dissolved. In rock fragments, easily soluble components were dissolved, leaving a few insoluble residues. Intergranular dissolution pores were generally formed by the re-dissolution of carbonate cements filling in the primary pores. The size of secondary dissolution pores is relatively small, with long-axis diameters ranging from 5 to 20 μm. In some feldspar samples, the dissolution was strong and the long-axis diameters of the dissolution pores reached approximately 150 μm. Secondary dissolution pores are mostly distributed in isolation.
Intercrystalline pores were also discovered. They were formed between authigenic mineral crystals. Due to the widespread cementation in the sandstone reservoir of the Xu-2 Member, various types of intercrystalline pores, including intercrystalline pores of siliceous cements, intercrystalline pores of carbonate cements, intercrystalline pores of illite, and intercrystalline pores of chlorite, developed. The size of intercrystalline pores is generally small, less than 10 μm. The connectivity between these pores is extremely poor.

4.3. Diagenetic Minerals of the Xu-2 Member in the Western Sichuan Basin

4.3.1. Carbonates

Carbonates are common cementing materials in the Xu-2 Member in the western Sichuan Basin, with two main occurrence states. A type of carbonate cement appears as basal calcites. The floating detrital grains have point-long contacts. These carbonate cements extensively fill the primary intergranular pores, as well as early dissolution pores, indicating an early precipitation time of calcites [27]. The content of this type of carbonate cement can reach 30%. Another type of carbonate cement mainly fills the secondary dissolution pores of feldspar (Figure 6a). These cements include calcite, a small amount of dolomite, and Fe-dolomite (Figure 6b), revealing that this type of cement mainly precipitates after feldspar dissolution events.

4.3.2. Quartz

There are two main occurrence states of quartz cements in the Xu-2 Member in the western Sichuan Basin. They are quartz overgrowths and small authigenic quartz crystals filling in pores. The quartz overgrowths are common and formed in multiple stages (Figure 6c). The development degree of quartz overgrowths varies among different types of sandstones and is positively correlated with the content of the detrital quartz. Obviously, the quartz overgrowths are more common in sandstones with more detrital quartz and less carbonate cement. Autogenic quartz generally fills intergranular or intragranular dissolution pores with smaller completely formed crystals (Figure 6d).

4.3.3. Clay Minerals

The clay minerals in sandstones are important factors that affect the reservoir quality [20,38,39,40,41,42]. The content, composition, occurrence, and other factors of clay minerals affect the reservoir quality of sandstones to varying degrees. The authigenic clay minerals that have a significant impact on reservoir properties in the Xu-2 Member in the western Sichuan Basin are chlorites (Figure 6e,f). The authigenic illite is less common, and the kaolinite is rarely observed (Figure 3f).
The authigenic chlorites in the Xu-2 sandstone in the western Sichuan Basin are mainly distributed in fine-grained or medium-grained sandstones with a relatively high content of rock fragments. The authigenic chlorites, generally characterized by flake-like crystals, mainly grow vertically on the grain edge in the form of a grain coating and pore lining. A small amount of authigenic chlorite filling in pores can be observed with two growth stages. The precipitation of most authigenic chlorite occurs during the early diagenetic stage. It is revealed by the low contact degree between grains with grain-coating chlorite. The pore-lining chlorite is commonly thick, up to 15 μm, which effectively preserves primary intergranular pores (Figure 6e).

4.4. Compaction of the Xu-2 Member in the Western Sichuan Basin

The Xu-2 sandstone in the western Sichuan Basin is deeply buried with a long burial history. The reservoir is thus strongly compacted (Figure 7a). Based on microscopic observation of thin sections, it is discovered that the long axes of mica and rock debris are roughly parallel, especially in siltstone and fine-grained sandstone. Phyllite, mudstone, schist, and other soft rock debris are elongated and deformed, while rigid rock debris is observed with fractures. Long and concave–convex contacts of grains are common (Figure 7b).

4.5. Dissolution of Framework Grains of the Xu-2 Member in the Western Sichuan Basin

The dissolution is commonly observed in the Xu-2 sandstone in the western Sichuan Basin (Figure 7c). The soluble grains include feldspar, quartz, and rock fragments. Among them, the feldspar dissolution is the most obvious. The dissolution mainly occurs at the grain edges and cleavage of feldspar. In some samples, the feldspar is dissolved into a honeycomb-like structure and even mold pores (Figure 7d,e). The dissolution in rock fragments mainly occurs in soluble minerals, forming intragranular dissolution pores. Calcite and Fe-dolomite cements also undergo dissolution locally. The dissolution effectively increases the pore space of sandstone and plays an important role in improving reservoir quality. The primary intergranular pores are enlarged by dissolution while the selective dissolution of rock debris forms intragranular pores.

4.6. Fractures of the Xu-2 Member in the Western Sichuan Basin

Macro-fractures were observed with the naked eye. The width of these fractures is generally greater than 100 μm. Macro-fractures can be categorized as network fractures, vertical fractures, high dip angle fractures, horizontal fractures, oblique fractures, and low dip angle fractures [43,44]. In the Xinchang Structural Belt, there are mainly horizontal fractures in the Xu-2 Member, followed by oblique fractures and low dip angle fractures. The vertical fractures and high dip angle fractures locally developed, while most of them were not filled [43]. Network fractures were formed through mutual cutting.
Micro-fractures increase permeability and then improve the reservoir properties [45,46]. In the Xu-2 sandstone in the western Sichuan Basin, micro-fractures are observed locally, and some of them cut through particles (Figure 7f). The width of these micro-fractures varies greatly. Narrow micro-fractures are approximately several microns in width, and wide ones can reach 60 μm in width.
Fractures are of great significance for the enrichment of natural gas in the Xu-2 tight sandstone in the western Sichuan Basin. Taking the Xinchang Structural Belt as an example, the sweet spots of the Xu-2 Member can be classified into three categories, namely the fault-, bedding fissure-, and pore-dominated categories [45,46]. The fault-dominated sweet spots are characterized by vertical fractures and high-dip-angle fractures, mainly developed in the fault-fracture areas. The bedding fissure-dominated and pore-dominated sweet spots are characterized by less developed high dip angle fractures, mainly distributed in high-quality tight sandstone reservoirs outside of the fault-fracture areas.
Reservoirs characterized by network fractures have an average permeability higher than 100 mD, and their average open-flow potential can reach 128 × 104 m3/d. Reservoirs with oblique to high-dip-angle fractures generally have an average permeability higher than 10 mD. The average open-flow potential of this type of reservoir can be 22 × 104 m3/d. The permeability of reservoirs without fractures is relatively low, while the porosity and gas saturation can be still relatively high [46]. Fault-dominated reservoirs can be effectively developed based on the existing technology, while bedding fissure-dominated and pore-dominated reservoirs can only be developed after technological breakthroughs.

5. Discussion

5.1. Diagenetic Evolution Sequence

The reservoirs of the Xu-2 Member in the western Sichuan Basin have undergone various diagenetic changes from the early diagenetic stage to the late diagenetic stage. The precipitation of authigenic quartz commonly began at around 60 °C, and the maximum precipitation temperature reached above 190 °C [17], corresponding to an approximate burial depth of 1000–5200 m [11,17]. Based on the lithology characteristics, it was concluded that authigenic chlorites precipitated during the early diagenetic stage. The precipitation temperature of the dissolution product such as authigenic quartz in the Xu-2 Member was used to determine the probable time of dissolution [32,36,47]. The dissolution occurred slightly earlier than the formation of authigenic quartz. A diagenetic evolution sequence can be constructed based on petrographic textural relationships, fluid inclusion and burial history [10,11,17,40]. The relative timing of the diagenetic events was shown to include at least 5 stages, namely the initial mechanical compaction stage, the feldspar leaching and early quartz cementing stage, the quartz overgrowths dissolution and early carbonate cementing stage, the carbonate cement dissolution stage, and the late carbonate cementing stage.

5.2. Quantitative Characterization of Pore Evolution

5.2.1. Initial Porosity

The initial porosity (Φ1) of unconsolidated sandstone can be calculated based on the relationship between the sorting coefficient and porosity of wet sand under surface conditions [11,37,48]. The initial porosity of the Xu-2 sandstone in the western Sichuan Basin was calculated as
Φ1 = 20.91 + 22.90/S0
where Φ1 = initial porosity and S0 = Trask sorting coefficient (= square root of ratio of larger quartile, Q1, of particle to smaller quartile, Q3).
In the western Sichuan Basin, the Xu-2 sandstones are well sorted, with a sorting coefficient ranging from 1.1 to 1.4. Thus, the calculated initial porosity ranges from 37.3% to 41.7%.

5.2.2. Porosity After Compaction

Previous studies indicate that the change caused by compaction without other influencing factors such as cementation in primary porosity is a function dominated by burial depth [11,49]. The porosity after compaction (Φ2) can be calculated as
Φ2 = Φ1 × e−CZ
where Φ2 = porosity after compaction, Φ1 = initial porosity, C = compaction factor, and Z = depth.
The compaction degrees of different types of sandstones in the Xu-2 Member of the western Sichuan Basin vary, resulting in changes in the compaction factor. For the rock sample, the porosity after compaction (Φ2) of different types of reservoirs can be calculated as
Φ2 = Φp × (Φti + Φtd)/Φtp + Φc
where Φp = porosity of rock sample, Φti = intergranular porosity of thin section, Φtd = dissolution porosity of cements of thin section, Φtp = porosity of thin section, and Φc = cement content.
In the layer with rock sample, based on the depth (Z), initial porosity (Φ1), and porosity after compaction (Φ2), the compaction factor (C) can be determined. Subsequently, the porosity after compaction (Φ2) of the unsampled layer can be calculated [11].

5.2.3. Reduced Porosity Due to Cementation

The reduction in porosity due to cementation corresponds to the content of cementing materials.

5.2.4. Increased Porosity Due to Dissolution

As mentioned above, in the deep burial Xu-2 sandstone in the western Sichuan Basin, the secondary pores were primarily formed by the dissolution of feldspar. The increased porosity due to dissolution corresponds to the secondary porosity.

5.3. Mechanism of Reservoir Tightening

Based on compositional differences, the Xu-2 sandstones were further subdivided into quartz-rich, rock-fragment-rich, and feldspar-rich sandstones. The quartz-rich sandstone mainly consists of sublitharenite, with rare litharenite and feldspathic litharenite. The grains are well sorted and subrounded. The main pores in quartz-rich sandstones are intragranular dissolution pores, formed by the dissolution of feldspar and rock fragments. In the rock-fragment-rich sandstone, chlorites are widely distributed. The main pore type in the rock-fragment-rich sandstone is the residual primary pore, with some enlarged pores and intragranular pores formed by the dissolution. The feldspar-rich sandstone is primarily composed of the lithic arkose. The grains are medium-sorted. The main pores in the feldspar-rich sandstone are intragranular dissolution pores of feldspar, with some enlarged pores. Based on the analysis of diagenesis, diagenetic environment, diagenetic stage, pore evolution, and burial history of different types of sandstones, three types of models for reservoir tightening processes were established.

5.3.1. Quartz-Rich Sandstone

In the late Triassic, the Xu-2 sandstone was buried to a depth of approximately 2000 m [11], entering the early diagenetic stage B. In that rapid burial environment, mechanical compaction was the primary factor leading to a decrease in porosity. By the end of the middle Jurassic, the sandstone was buried to a depth of approximately 3000 m, entering the middle diagenetic stage A. The dissolution caused by organic acid locally enhanced the porosity of reservoirs. A pressure solution occurred, resulting in widely distributed quartz overgrowths. Calcite cements occurred locally. As a result of these diagenetic events, the average porosity of the reservoir was approximately 13%. In the late Cretaceous, the reservoir of the Xu-2 Member was buried to a depth of approximately 5500 m, entering the middle diagenetic stage B. Accompanied by the uplift of formation and fracturing of rocks, the dissolution continued to improve reservoir properties. As a result, the average porosity was approximately 6%. In conclusion, compaction and the pressure solution were the primary causes of reservoir tightening in the quartz-rich sandstones, while late fracturing and the dissolution along fractures were the main factors improving reservoir properties (Figure 8).

5.3.2. Feldspar-Rich Sandstone

In the late Triassic, the burial depth of the Xu-2 sandstone was approximately 2000 m [11]. The sandstone entered the early diagenetic stage B. The rapid burial process in the early stage was a primary factor in the decrease in porosity. By the end of the middle Jurassic, the burial depth of the sandstone reached approximately 3000 m, entering middle diagenetic stage A. During this period, the dissolution caused by organic acid widely and obviously enhanced porosity but also generated a significant amount of carbonate and quartz cements that filled the pores. The average porosity of the reservoir was approximately 11%. In the late Jurassic, the burial depth of the sandstone reached approximately 4200 m. The Xu-2 sandstone entered middle diagenetic stage B. The feldspar dissolution generated some pores, while illite and dolomite developed, blocking pores and throats. As a result, the average porosity of the reservoir was approximately 6%. In conclusion, the early dissolution was a primary factor in improving the porosity in this type of reservoir, while the carbonate and quartz cements generated by dissolution contributed to a decrease in porosity (Figure 9).

5.3.3. Rock-Fragment-Rich Sandstone

At the end of the Triassic, the Xu-2 reservoir was buried to a depth of approximately 2000 m [11], entering early diagenetic stage B. The rapid burial process in the early stage was the primary factor in reducing porosity, while the presence of pore-lining chlorites and the impact of overpressure maintained some primary pores. By the end of the middle Jurassic, the Xu-2 reservoir was buried to a depth of approximately 3000 m, entering middle diagenetic stage A. The dissolution caused by organic acid enhanced porosity. Some pores were filled with calcite and quartz cements. At this time, the average porosity was approximately 20%. By the end of the late Jurassic, the sandstone reservoir was buried to a depth of approximately 4200 m, entering middle diagenetic stage B. The feldspar dissolution created some pores and subsequently formed illite and dolomite. The primary pores were widely filled with authigenic quartz. The average porosity was approximately 11%. In the rock-fragment-rich reservoirs, the chlorites formed in the early stage and the dissolution were the main factors in the reservoir quality improvement. The authigenic quartz formed in the middle diagenetic stage was the primary cause of reservoir tightening (Figure 10).

5.4. Source-to-Sink System and Reservoir Quality

The geomorphic units on the Earth’s surface are macroscopically subdivided into denudational landforms and sedimentary landforms. The denudation products formed in denudational landforms are transported to sedimentary landforms. This whole system is known as the source-to-sink system [20,21]. Based on the analysis of provenance, tectonic zones, and depositional zones, four major source-to-sink systems were identified in the western Sichuan Basin during the depositional period of the Xu-2 Member, namely the Zitong source-to-sink system, the Xinchang source-to-sink system, the Yazihe–Chengdu source-to-sink system, and the Dayi source-to-sink system (Figure 1b).
The detrital materials in the Zitong source-to-sink system are primarily from the Micangshan Uplift to the north and partly from the Longmenshan Fold Belt to the west. They were transported through the northern section of the Longmenshan Fold Belt and deposited in the Zitong Depression. The Xinchang source-to-sink system exhibits characteristics of mixed detrital material supply. Some parts of the detrital materials are sourced from the northern Zitong source-to-sink system, and other parts are from the Qinling and Dabashan Mountains in the east. The northern detrital material supply is dominant in the Xinchang source-to-sink system. Compared to the Zitong source-to-sink system, the Xinchang source-to-sink system is situated further from the provenance. The detrital materials in the Yazihe–Chengdu source-to-sink system are mainly from the Longmenshan Fold Belt, transported through the middle section of this fold belt, and deposited in the Anxian–Yazihe–Dayi Fault-fold Belt. The detrital materials in the Dayi source-to-sink system primarily originate from the Longmenshan Mountain and the Kangdian ancient land to the southwest, transported through the middle and southern sections of the Longmenshan Fold Belt and deposited in the Anxian-Yazihe-Dayi Fault-fold Belt.

5.4.1. Lithology Characteristics in Different Source-to-Sink Systems

The Xu-2 Member in the Zitong source-to-sink system is dominated by rock-fragment-rich sandstone. The average content of quartz is 61.17%. The average feldspar content is high among all source-to-sink systems at 12.13%. The rock fragment content is relatively high, at 26.70% (Figure 11a). The metamorphic rock fragments and sedimentary rock fragments are predominant, with average values of 12.52% and 9.70%, respectively, while volcanic rock fragments account for only 4.52%.
The petrological characteristics of the eastern and western areas of the Xinchang source-to-sink system are a little different. In the western Xinchang source-to-sink system, the content of quartz is high, averaging 69.47%. The average feldspar content is 8.84%, and the rock fragment content is 21.69% (Figure 11b). Metamorphic rock fragments and sedimentary rock fragments are predominant, with average values of 9.06% and 9.81%, while volcanic rock fragments account for only 2.26%. In the eastern part of the Xinchang source-to-sink system, the quartz content is high, averaging 68.67%; the average feldspar content is relatively low, at 5.39%; and the rock fragment content is relatively high, at 25.94% (Figure 11c). Metamorphic rock fragments and sedimentary rock fragments are predominant, with average values of 15.08% and 9.94%, while volcanic rock fragments are rare, with an average value of only 1.44%.
In the Yazihe area, the quartz content is high, averaging 72.54%; the average feldspar content is 8.84%; and the rock fragment content is relatively low, at 18.63% (Figure 11d). Metamorphic rock fragments and sedimentary rock fragments are predominant, with average values of 9.06% and 8.53%, while volcanic rock fragments account for only 1.96%. In the Chengdu area, the average quartz content is 67.44%, the average feldspar content is 7.36%, and the rock fragment content is 25.20% (Figure 11e). Metamorphic rock fragments and sedimentary rock fragments are predominant, with average values of 11.56% and 11.50%, while volcanic rock fragments are rare, with an average value of only 3.19%.
The Dayi source-to-sink system is dominated by rock-fragment-rich sandstone, with an average quartz content of 68.41%. The average content of feldspar is the lowest among all source-to-sink systems, at 4.80%. The rock fragment content is relatively high, at 26.81% (Figure 11f), with metamorphic and sedimentary rock fragments being predominant, averaging 7.99% and 8.56%. Volcanic rock fragments account for only 3.67%.

5.4.2. Reservoir Properties in Different Source-to-Sink Systems

The reservoirs in the Zitong source-to-sink system have high porosity and permeability. The average porosity is 6.58% and the average permeability is 0.41 mD. The western area of the Xinchang source-to-sink system is characterized by high porosity and medium-high permeability. The porosity of reservoirs is about 3.58%, and average permeability is 0.21 mD. The eastern area of the Xinchang source-to-sink system has reservoirs with medium-high porosity and medium-high permeability. The average porosity is 3.19% and the average permeability is 0.22 mD. In the western Yazihe–Chengdu source-to-sink system, the reservoirs have medium porosity and low permeability. The average porosity is 3.66% and the average permeability is 0.17 mD. The eastern Yazihe–Chengdu source-to-sink system exhibits medium-high porosity and medium-high permeability. The average porosity is 4.87% and the average permeability is 0.189 mD. The Dayi source-to-sink system has reservoirs with low porosity and medium-high permeability. The reservoirs have an average porosity of 2.87% and an average permeability of 0.29 mD, as well as a good relationship between porosity and permeability.

5.4.3. Reservoir Quality and Its Controlling Factor in Different Source-to-Sink Systems

In the Xinchang source-to-sink system, the content of quartz increases, leading to higher porosity and permeability. While the quartz content becomes excessively high, the porosity decreases (Figure 12a). The content of feldspar exhibits a weak negative correlation with the porosity. An increase in the content of feldspar results in reduced permeability in some samples (Figure 12b). This indicates that the preservation of primary pores related to quartz has a relatively stronger impact on reservoir properties, while the dissolution of framework grains and reconstruction of secondary pores related to feldspar has a relatively weaker impact on reservoir properties in the Xinchang source-to-sink system.
In the Yazihe–Chengdu source-to-sink system, the relationship between quartz content and reservoir property is not obvious (Figure 12c). The content of feldspar shows a positive correlation with porosity and a negative correlation with permeability (Figure 12d). It demonstrates that in the Yazihe–Chengdu source-to-sink system, the preservation of primary pores related to quartz has an insignificant impact on reservoir properties, while the reconstruction of secondary pores related to feldspar dissolution has a relatively stronger impact on reservoir properties.
In the Zitong source-to-sink system, the relationship between quartz content and porosity is not obvious, while the feldspar content shows a weak positive correlation with porosity (Figure 13a,b). The reservoir properties in the Zitong source-to-sink system are somewhat influenced by the reconstruction of secondary pores related to dissolution.
In the Dayi source-to-sink system, the quartz content is positively correlated with porosity and permeability (Figure 13c,d), while the feldspar content is negatively correlated with porosity and permeability (Figure 13e,f). This indicates that both the preservation of primary pores related to quartz and the reconstruction of secondary pores related to feldspar have impacts on reservoir properties in the Dayi source-to-sink system.
The Zitong source-to-sink system is relatively close to the provenance, with more feldspar-rich sandstones and rock-fragment-rich sandstones. Dissolution occurs locally in the early and middle diagenetic stages, forming reservoirs with primary pores supplemented by secondary pores. The primary pore structures of the Xinchang source-to-sink system are well preserved, with overall good reservoir properties. The chlorite, quartz, and coarse grains have a strong impact on reservoir quality by preserving primary intergranular pores. The dissolution in the Yazihe–Chengdu source-to-sink system is common, and the reservoir is strongly influenced by secondary pores related to feldspar. The Dayi source-to-sink system is located in the fault-fold belt, where the reservoir is strongly compacted. However, factors such as quartz and coarse grains, which resist compaction, have an impact on reservoir quality, and the presence of fractures improves the permeability.

6. Conclusions

Five major conclusions were derived from this study:
  • The clastic components of the tight sandstones of the Xu-2 Member in the western Sichuan Basin include quartz, rock fragment, and feldspar. Rock fragments constitute the main detrital minerals. The tight sandstones are composed of litharenite, sublitharenite, and feldspathic litharenite. Litharenites are commonly observed. The porosity of the Xu-2 sandstone mainly ranges from 1.0% to 5.0% and the permeability mainly ranges from 0.01 to 0.5 mD.
  • The diagenetic minerals of the Xu-2 sandstone are mainly carbonates, quartz, and clay minerals. The basal calcites formed in the early precipitation time extensively fill the primary intergranular pores and early dissolution pores. Another type of calcite, a small amount of dolomite, and Fe-dolomite mainly precipitate after feldspar dissolution events and fill the secondary dissolution pores of feldspar. The quartz overgrowths are more common with more detrital quartz and less carbonate cement. Autogenic quartz generally fills intergranular or intragranular dissolution pores. The chlorite is the main clay mineral and is distributed with a relatively high content of rock fragments. The precipitation of most chlorite occurs during the early diagenetic stage. As a result, the chlorite effectively preserves primary intergranular pores.
  • The compaction is strong in the deeply buried tight sandstones of the Xu-2 Member, resulting in a decrease in porosity. The dissolution of framework grains enhances the porosity. The relative timing of the diagenetic events was concluded in at least five stages, namely the initial mechanical compaction stage, the feldspar leaching and early quartz cementing stage, the quartz overgrowths dissolution and early carbonate cementing stage, the carbonate cement dissolution stage, and the late carbonate cementing stage. The initial porosity, porosity after compaction, reduced porosity due to cementation and increased porosity due to dissolution in the diagenetic evolution sequence were calculated.
  • The Xu-2 sandstones were further subdivided into the quartz-rich, rock-fragment-rich and feldspar-rich sandstones. In the quartz-rich sandstone, the compaction and pressure solution were the primary causes of reservoir tightening, while late fracturing and dissolution along fractures were the main factors improving reservoir properties. In the feldspar-rich sandstone, early dissolution was a primary factor in improving porosity, while carbonate and quartz cements generated by dissolution contributed to a decrease in porosity. In the rock-fragment-rich sandstone, chlorites formed in the early stage and dissolution were the main factors in reservoir quality improvement, while the authigenic quartz formed in the middle diagenetic stage was the primary cause of reservoir tightening.
  • Four major source-to-sink systems were identified. The Zitong source-to-sink system is relatively close to the provenance, and dissolution in the early and middle diagenetic stages of feldspar-rich sandstones and rock-fragment-rich sandstones improved reservoir quality. In the Xinchang source-to-sink system, the chlorite, quartz, and coarse grains have a strong impact on reservoir quality by preserving primary intergranular pores. In the Yazihe–Chengdu source-to-sink system, the dissolution is common and the reservoir is strongly influenced by secondary pores related to feldspar. In the Dayi source-to-sink system, factors resisting compaction such as quartz and coarse grains have an impact on reservoir quality, and the fractures caused by compaction improve the permeability.

Author Contributions

Conceptualization, D.W.; methodology, Y.Y.; software, L.L. and B.L.; validation, Y.Y.; formal analysis, D.W. and X.Y.; investigation, Y.Y.; resources, S.L.; data curation, S.L.; writing—original draft preparation, Y.Y.; writing—review and editing, D.W.; visualization, L.L.; supervision, L.L.; project administration, L.L.; funding acquisition, D.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Open Fund (Different diagenetic evolution of tight sandstone reservoirs in Xujiahe Formation, western Sichuan Basin and its significance for hydrocarbon accumulation) of the SINOPEC Key Laboratory of Geology and Resources in Deep Stratum.

Data Availability Statement

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

Acknowledgments

We sincerely thank Hongde Chen and Zhengxiang Lü for their valuable work. We also thank Bo Pan, Xinglong Wang and Zhikang Wang. We gratefully acknowledge the insightful reviews and constructive suggestions from the editors and anonymous reviewers.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
SEMScanning electron microscopy
EDSEnergy dispersive spectrometer
Φ1Initial porosity
Φ2Porosity after compaction
ΦpPorosity of rock sample
ΦtpPorosity of thin section
ΦtiIntergranular porosity of thin section
ΦtdDissolution porosity of cements of thin section
ΦcCement content
S0Trask sorting coefficient
Q1Larger quartile of particle
Q3Smaller quartile of particle
CCompaction factor
ZDepth
QQuartz
RFRock fragments
FFeldspar
PPores
SRFSedimentary rock debris
MRFMetamorphic rock debris
VRFVolcanic rock debris
CalCalcites
AQAutogenic quartz
QOQuartz overgrowths
ILIllite
Fe-DolFe-dolomites
ChChlorites
MiMica
FrFractures
T3Late Triassic
J1Early Jurassic
J2 Middle Jurassic
J3 Late Jurassic
K Cretaceous
EPaleogene

References

  1. Zou, C.N.; Zhu, R.K.; Wu, S.T.; Yang, Z.; Tao, S.Z.; Yuan, X.J.; Hou, L.H.; Yang, H.; Xu, C.C.; Li, D.H.; et al. Types, characteristics, genesis and prospects of conventional and unconventional hydrocarbon accumulations: Taking tight oil and tight gas in China as an instance. Acta Pet. Sin. 2012, 33, 173–187, (In Chinese with English Abstract). [Google Scholar]
  2. Churchill, S.A.; Inekwe, J.; Smyth, R.; Zhang, X. R&D intensity and carbon emissions in the G7: 1870–2014. Energy Econ. 2019, 80, 30–37. [Google Scholar]
  3. Zhong, Z.Q.; Chen, Y.Q.; Fu, M.Y.; Li, M.Z.; Yang, K.S.; Zeng, L.P.; Liang, J.; Ma, R.P.; Xie, Q. Role of CO2 geological storage in China’s pledge to carbon peak by 2030 and carbon neutrality by 2060. Energy 2023, 272, 127165. [Google Scholar] [CrossRef]
  4. Fic, J.; Pedersen, P.K. Reservoir characterization of a “tight” oil reservoir, the middle Jurassic Upper Shaunavon Member in the Whitemud and Eastbrook pools, SW Saskatchewan. Mar. Pet. Geol. 2013, 44, 41–59. [Google Scholar] [CrossRef]
  5. Stroker, T.M.; Harris, N.B.; Elliott, W.C.; Wampler, J.M. Diagenesis of a tight gas sand reservoir: Upper Cretaceous Mesaverde Group, Piceance Basin, Colorado. Mar. Pet. Geol. 2013, 40, 48–68. [Google Scholar] [CrossRef]
  6. Wu, D.; Li, H.; Jiang, L.; Hu, S.; Wang, Y.; Zhang, Y.; Liu, Y. Diagenesis and reservoir quality in tight gas bearing sandstones of a tidally influenced fan delta deposit: The Oligocene Zhuhai Formation, western Pearl River Mouth Basin, South China Sea. Mar. Pet. Geol. 2019, 107, 278–300. [Google Scholar] [CrossRef]
  7. Jia, C.Z.; Zou, C.N.; Li, J.Z.; Li, D.H.; Zheng, M. Assessment criteria, main types, basic features and resource prospects of the tight oil in China. Acta Pet. Sin. 2012, 33, 343–350, (In Chinese with English Abstract). [Google Scholar]
  8. Meng, Y.; Wang, Z.; Zhang, F.; Meng, F.; Jiao, J.; Shi, L. Characteristics and forming mechanism of tight sandstones in the Paleogene Shahejie Formation of southern West Sag, Liaohe Depression. J. Palaeogeogr. 2016, 18, 569–580, (In Chinese with English Abstract). [Google Scholar]
  9. Lai, J.; Wang, G.W.; Wang, S.; Cao, J.T.; Li, M.; Pang, X.J.; Zhou, Z.L.; Fan, X.Q.; Dai, Q.Q.; Yang, L.; et al. Review of diagenetic facies in tight sandstones: Diagenesis, diagenetic minerals, and prediction via well logs. Earth-Sci. Rev. 2018, 185, 234–258. [Google Scholar] [CrossRef]
  10. Wu, D.; Liu, X.; Du, Y.; Jiang, L.; Cheng, Z. Predictive distribution of high-quality tight reservoirs of coarse clastic rocks by linking diagenesis to sedimentary facies: Evidence from the upper Sha 4 Member in the northern Bonan Sag, Bohai Bay Basin, eastern China. Interpretation 2018, 6, T413–T429. [Google Scholar] [CrossRef]
  11. Lin, L.B.; Yu, Y.; Nan, H.L.; Chen, H.D.; Liu, L.; Wu, D.; Wang, Z.K. Reservoir tightening process and its coupling relationship with hydrocarbon accumulation in the fourth member of Upper Triassic Xujiahe Formation in the Western Sichuan Depression, Sichuan Basin. Oil Gas Geol. 2021, 42, 816–828, (In Chinese with English Abstract). [Google Scholar]
  12. Nygard, R.; Gutierrez, M.; Gautam, R.; Høeg, K. Compaction behavior of argillaceous sediments as function of diagenesis. Mar. Pet. Geol. 2004, 21, 349–362. [Google Scholar] [CrossRef]
  13. McKinley, J.M.; Atkinson, P.M.; Lloyd, C.D.; Ruffell, A.H.; Worden, R.H. How porosity and permeability vary spatially with grain size, sorting, cement volume, and mineral dissolution in fluvial Triassic sandstones: The value of geostatistics and local regression. J. Sediment. Res. 2011, 81, 844–858. [Google Scholar] [CrossRef]
  14. Kordi, M.; Turner, B.; Salem, A.M. Linking diagenesis to sequence stratigraphy in fluvial and shallow marine sandstones: Evidence from the Cambrian–Ordovician lower sandstone unit in southwestern Sinai, Egypt. Mar. Pet. Geol. 2011, 28, 1554–1571. [Google Scholar] [CrossRef]
  15. Ozkan, A.; Cumella, S.P.; Milliken, K.L.; Laubach, S.E. Prediction of lithofacies and reservoir quality using well logs, late cretaceous Williams Fork Formation, Mamm Creek field, Piceance basin, Colorado. AAPG Bull. 2011, 95, 1699–1723. [Google Scholar] [CrossRef]
  16. Li, Y.; Chang, X.; Yin, W.; Sun, T.; Song, T. Quantitative impact of diagenesis on reservoir quality of the Triassic Chang 6 tight oil sandstones, Zhenjing area, Ordos Basin, China. Mar. Pet. Geol. 2017, 86, 1014–1028. [Google Scholar] [CrossRef]
  17. Pan, B.; Chen, H.D.; Lin, L.B.; Yu, Y.; Wu, D.; Dong, Y.X. Diagenesis and reservoir quality of the second member of the Upper Triassic Xujiahe Formation tight gas sandstones in the Western Sichuan Depression, southwest China. Geol. J. 2021, 56, 3187–3206. [Google Scholar] [CrossRef]
  18. Zheng, H.R.; Liu, Z.Q.; Xu, S.L.; Liu, Z.F.; Liu, J.L.; Huang, Z.W.; Huang, Y.Q.; Shi, Z.L.; Wu, Q.Z.; Fan, L.X.; et al. Progress and key research directions of tight gas exploration and development in Xujiahe Formation, Sinopec exploration areas, Sichuan Basin. Oil Gas Geol. 2021, 42, 765–783, (In Chinese with English Abstract). [Google Scholar]
  19. Luo, J.L.; Li, C.; Lei, C.; Cao, J.J.; Song, K.P. Discussion on research advances and hot issues in diagenesis of clastic-rock reservoirs. J. Palaeogeogr. (Chin. Ed.) 2020, 22, 1021–1040, (In Chinese with English Abstract). [Google Scholar]
  20. Allen, P.A. From landscapes into geological history. Nature 2008, 451, 274–276. [Google Scholar] [CrossRef]
  21. Walsh, J.P.; Wiberg, P.L.; Aalto, R.; Nittrouer, C.A.; Kuehl, S.A. Source-to-sink research: Economy of the Earth’s surface and its strata. Earth-Sci. Rev. 2016, 153, 1–6. [Google Scholar] [CrossRef]
  22. Dutton, S.P.; Loucks, R.G.; Day-Stirrat, R.J. Impact of regional variation in detrital mineral composition on reservoir quality in deep to ultradeep lower Miocene sandstones, western Gulf of Mexico. Mar. Pet. Geol. 2012, 35, 139–153. [Google Scholar] [CrossRef]
  23. Joe, H.S.; Macquaker, K.G.; Taylor, M.K.; David, P. Compositional controls on early diagenetic pathways in fine-grained sedimentary rocks: Implications for predicting unconventional reservoir attributes of mudstones. AAPG Bull. 2014, 98, 587–603. [Google Scholar]
  24. Lai, J.; Wang, G.; Ran, Y.; Zhou, Z. Predictive distribution of high-quality reservoirs of tight gas sandstones by linking diagenesis to depositional facies: Evidence from Xu-2 sandstones in the Penglai area of the central Sichuan basin, China. J. Nat. Gas Sci. Eng. 2015, 23, 97–111. [Google Scholar] [CrossRef]
  25. Wang, Y.; Zhang, K.; Gan, Q.; Zhou, W. Fracture development characteristics in the upper Triassic Xujiahe Formation, western Sichuan depression (China). J. Pet. Sci. Eng. 2015, 135, 542–551. [Google Scholar] [CrossRef]
  26. Luo, L.; Meng, W.; Gluyas, J.; Tan, X.; Gao, X.; Feng, M.; Kong, X.; Shao, H. Diagenetic characteristics, evolution, controlling factors of diagenetic system and their impacts on reservoir quality in tight deltaic sandstones: Typical example from the Xujiahe Formation in Western Sichuan Foreland Basin, SW China. Mar. Pet. Geol. 2019, 103, 231–254. [Google Scholar] [CrossRef]
  27. Wu, D.; Liu, S.; Chen, H.; Lin, L.; Yu, Y.; Xu, C.; Pan, B. Investigation and prediction of diagenetic facies using well logs in tight gas reservoirs: Evidences from the Xu-2 member in the Xinchang structural belt of the western Sichuan Basin, western China. J. Pet. Sci. Eng. 2020, 192, 107326. [Google Scholar] [CrossRef]
  28. Xu, H.; Liu, M.J.; Zhang, Z.; Ye, S.J.; Yang, Y.T.; Wu, L.; Zhang, L.; Nan, H.L.; Tan, X.C.; Zeng, W.; et al. Diagenesis and porosity evolution of the 3rd member of Xujiahe Formation tight sandstone reservoir in the Western Sichuan Depression, Sichuan Basin. Nat. Gas Geosci. 2022, 33, 344–357, (In Chinese with English Abstract). [Google Scholar]
  29. Gao, J.; Li, H.L.; He, Z.L.; Li, S.; Liu, G.X.; Yuan, Y.S.; Li, Y.Q.; Li, T.Y.; He, S. Pressure evolution, enrichment and preservation of normal-pressure shale gas in the Pengshui area of eastern Chongqing. Nat. Gas Ind. 2022, 42, 124–135, (In Chinese with English Abstract). [Google Scholar]
  30. Chen, H.D.; Liu, L.; Lin, L.B.; Wang, X.L.; Wang, Z.W.; Yu, Y.; Zeng, J.; Li, P.W. Depositional responses of Xujiahe Formation to the uplifting of Longmenshan during the Late Triassic, Western Sichuan Depression. Oil Gas Geol. 2021, 42, 801–815, (In Chinese with English Abstract). [Google Scholar]
  31. Wang, X.L.; Liu, L.; Lin, L.B.; Chen, H.D.; Liu, J.L.; Pan, B.; Wang, Z.K.; Liu, K.L. Sedimentary micro-facies and distribution of sand bodies in the 2nd member of Xujiahe Formation, Xinchang area, western Sichuan Depression, China. J. Chengdu Univ. Technol. (Sci. Technol. Ed.) 2021, 48, 23–34, (In Chinese with English Abstract). [Google Scholar]
  32. Liu, S.B.; Shen, Z.M.; Liu, H.N.; Lyu, Z.X.; Wang, P. Mechanism of water-rock interaction of the Upper Triassic Xujiahe Formation in the middle part of western Sichuan depression. Acta Pet. Sin. 2013, 34, 47–58, (In Chinese with English Abstract). [Google Scholar]
  33. Gao, J.; Li, H.L.; He, Z.L.; Cai, X.Y.; Li, S.J.; Liu, G.X.; Yuan, Y.S.; Lin, J.H.; Li, Z. Multi-stage hydrocarbon accumulation in Cambrian Xixiangchi Group, Pingqiao area, southeastern Sichuan and its implications for hydrocarbon exploration. Earth Sci. Front. 2023, 30, 263–276, (In Chinese with English Abstract). [Google Scholar]
  34. Chen, Z.Y.; Meng, X.W.; Shen, K.Y.; Zhang, X.W.; Song, X.B. Analysis of gas accumulation process of the fourth member of Leikoupo Formation., Western Sichuan Basin. J. Northeast Pet. Univ. 2021, 45, 1–9, (In Chinese with English Abstract). [Google Scholar]
  35. Wang, W.; Zhao, L.Z.; Luo, B.; Liu, R.; Li, Y.; Zhao, L.K.; Pei, S.Q.; Hu, T. Relationship between abnormal high pressure evolution of Permian volcanic rocks and natural gas accumulation in the western Sichuan Basin. Acta Pet. Sin. 2021, 42, 1437–1445, (In Chinese with English Abstract). [Google Scholar]
  36. Zhang, S.; Yang, Y.; Zhang, L.; Cao, Y. Formation Mechanism of Secondary Quartz and Its Influence on Physical Properties of Xu 2 Member Reservoir in Western Sichuan Depression. Xinjiang Pet. Geol. 2023, 44, 25–32, (In Chinese with English Abstract). [Google Scholar]
  37. Beard, D.C.; Weyl, P.K. Influence of texture on porosity and permeability of unconsolidated sand. AAPG Bull. 1973, 57, 349–369. [Google Scholar]
  38. Ehrenberg, S.N. Preservation of anomalously high porosity in deeply buried sandstones by grain-coating chlorite: Examples from the Norwegian continental shelf. AAPG Bull. 1993, 77, 1260–1286. [Google Scholar]
  39. Lander, R.H.; Larese, R.E.; Bonnell, L.M. Toward more accurate quartz cement models: The importance of euhedral versus noneuhedral growth rates. AAPG Bull. 2008, 92, 1537–1563. [Google Scholar] [CrossRef]
  40. Mansurbeg, H.; Morad, S.; Salem, A.; Marfil, R.; El-Ghali, M.A.K.; Nystuen, J.P.; Caja, M.A.; Amorosi, A.; Iglesia, A.L. Diagenesis and reservoir quality evolution of palaeocene deep-water, marine sandstones, the Shetland-Faroes Basin, British continental shelf. Mar. Pet. Geol. 2008, 25, 514–543. [Google Scholar] [CrossRef]
  41. Schmitt, M.; Fernandes, C.P.; da Cunha Neto, J.A.; Wolf, F.G.; dos Santos, V.S. Characterization of pore systems in seal rocks using nitrogen gas adsorption combined with mercury injection capillary pressure techniques. Mar. Pet. Geol. 2013, 39, 138–149. [Google Scholar] [CrossRef]
  42. Wilson, M.J.; Shaldybin, M.V.; Wilson, L. Clay mineralogy and unconventional hydrocarbon shale reservoirs in the USA. I. Occurrence and interpretation of mixed-layer R3 ordered illite/smectite. Earth-Sci. Rev. 2016, 158, 31–50. [Google Scholar] [CrossRef]
  43. Li, W.P.; Liu, Z.Q.; Hu, Z.Q.; Jin, W.J.; Li, P.W.; Liu, J.L.; Xu, S.L.; Ma, A.L. Characteristics of and main factors controlling the tight sandstone reservoir fractures in the 2nd member of Xujiahe Formation in Xinchang area, Western Sichuan Depression, Sichuan Basin. Oil Gas Geol. 2021, 42, 884–1010, (In Chinese with English Abstract). [Google Scholar]
  44. Li, P.W.; Hu, Z.Q.; Liu, Z.Q.; Xu, S.L.; Liu, Z.F.; Wang, A.; Liu, J.L.; Jin, W.J. Types of the deep tight sandstone reservoirs and their different controlling in the second member of Xujiahe Formation in Xinchang area, western Sichuan Basin. Nat. Gas Geosci. 2024, 35, 1136–1149, (In Chinese with English Abstract). [Google Scholar]
  45. Liu, J.L.; Hu, Z.Q.; Liu, Z.Q.; Jin, Q.; Xiao, K.; Bi, Y.; Li, J. Gas pool sweet spot models and their forming mechanism in the Xu 2 Member in Xinchang area, Western Sichuan Depression, Sichuan Basin. Oil Gas Geol. 2021, 42, 852–862, (In Chinese with English Abstract). [Google Scholar]
  46. Liu, J.L.; Liu, Z.Q.; Liu, Z.F.; Liu, Y.L.; Shen, B.J.; Xiao, K.H.; Bi, Y.X.; Wang, X.W.; Wang, A.; Fan, L.X.; et al. Geological characteristics and models of fault-fold-fracture body in deep tight sandstone of the second member of Upper Triassic Xujiahe Formation in Xinchang structural belt of Sichuan Basin, SW China. Pet. Explor. Dev. 2023, 50, 603–614. [Google Scholar] [CrossRef]
  47. Berger, G.; Lacharpagne, J.; Velde, B.; Beaufort, D.; Lanson, B. Kinetic constraints on illitization reactions and the effects of organic diagenesis in sandstone/shale sequences. Appl. Geochem. 1997, 12, 23–35. [Google Scholar] [CrossRef]
  48. Scherer, M. Parameters influencing porosity in sandstones: A model for sandstone porosity prediction. AAPG Bull. 1987, 71, 485–491. [Google Scholar] [CrossRef]
  49. Hubbert, M.K.; Rubey, W.W. Role of fluid pressure in mechanics of overthrust faulting: I. Mechanics of fluid-filled porous solids and its application to overthrust faulting. Geol. Soc. Am. Bull. 1959, 70, 115–166. [Google Scholar] [CrossRef]
Minerals 15 00625 g001
Figure 1. (a) Location and tectonic divisions of the Sichuan Basin. I, eastern Sichuan Basin; II, southern Sichuan Basin; III, western Sichuan Basin; IV, central Sichuan Basin. The orange box represents the location of (b). (b) Location of the wells and tectonic divisions of the western Sichuan Basin.
Figure 1. (a) Location and tectonic divisions of the Sichuan Basin. I, eastern Sichuan Basin; II, southern Sichuan Basin; III, western Sichuan Basin; IV, central Sichuan Basin. The orange box represents the location of (b). (b) Location of the wells and tectonic divisions of the western Sichuan Basin.
Minerals 15 00625 g001
Minerals 15 00625 g002
Figure 2. Stratigraphic column of the Xu-2 Member in the western Sichuan Basin.
Figure 2. Stratigraphic column of the Xu-2 Member in the western Sichuan Basin.
Minerals 15 00625 g002
Minerals 15 00625 g003
Figure 3. Lithology characteristics of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. (a) Quartz and rock fragments with carbonate cements and quartz overgrowths, well Hl1, 4227.7 m, plane-polarized light. (b) Long and concave–convex contacts of grains including quartz, feldspar, and rock fragments, well Xc11, 4936.8 m, crossed-polarized light. (c) Residual primary pore, quartz grain, and quartz overgrowth, well Xc11, 4931.7 m, plane-polarized light. (d) Metamorphic rock debris (phyllite debris), well Xc11, 4936.8 m, crossed-polarized light. (e) K-feldspar and pores, well Cx560, 4814.6 m, SEM. (f) Illite filling in the pore, well Xc3, 4735.5 m, SEM. Cal, calcites; Q, quartz; RF, rock fragments; F, feldspar; P, pores; QO, quartz overgrowths; IL, illite.
Figure 3. Lithology characteristics of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. (a) Quartz and rock fragments with carbonate cements and quartz overgrowths, well Hl1, 4227.7 m, plane-polarized light. (b) Long and concave–convex contacts of grains including quartz, feldspar, and rock fragments, well Xc11, 4936.8 m, crossed-polarized light. (c) Residual primary pore, quartz grain, and quartz overgrowth, well Xc11, 4931.7 m, plane-polarized light. (d) Metamorphic rock debris (phyllite debris), well Xc11, 4936.8 m, crossed-polarized light. (e) K-feldspar and pores, well Cx560, 4814.6 m, SEM. (f) Illite filling in the pore, well Xc3, 4735.5 m, SEM. Cal, calcites; Q, quartz; RF, rock fragments; F, feldspar; P, pores; QO, quartz overgrowths; IL, illite.
Minerals 15 00625 g003
Minerals 15 00625 g004
Figure 4. (a) Ternary diagram showing the compositions of framework grains of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. (b) Ternary diagram showing the compositions of rock fragments of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. Q, quartz; F, feldspar; RF, rock fragments; SRF, sedimentary rock debris; MRF, metamorphic rock debris; VRF, volcanic rock debris.
Figure 4. (a) Ternary diagram showing the compositions of framework grains of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. (b) Ternary diagram showing the compositions of rock fragments of the tight sandstones of the Xu-2 Member in the western Sichuan Basin. Q, quartz; F, feldspar; RF, rock fragments; SRF, sedimentary rock debris; MRF, metamorphic rock debris; VRF, volcanic rock debris.
Minerals 15 00625 g004
Minerals 15 00625 g005
Figure 5. Interval distribution of (a) porosity and (b) permeability of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Figure 5. Interval distribution of (a) porosity and (b) permeability of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Minerals 15 00625 g005
Minerals 15 00625 g006
Figure 6. (a) Calcites filling in the secondary dissolution pores, well Dya1, 5529.8 m, plane-polarized light. (b) Fe-dolomite and dissolution pores with EDS, well Xc101, 5039.8 m, SEM. (c) Quartz overgrowths, well Xc5, 4740.4 m, cross-polarized light. (d) Autogenic quartz filling in the pores, well Xc10, 4883.4 m, SEM. (e) Grain-coating chlorites and secondary dissolution pores associated with the feldspar dissolution, well Dya1, 5592.8 m, plane-polarized light. (f) Chlorites and pores, well Xc10, 4932.0 m, SEM. Cal, calcites; P, pores; Fe-Dol, Fe-dolomites; Q, quartz; QO, quartz overgrowths; AQ, autogenic quartz; RF, rock fragments; Ch, chlorites.
Figure 6. (a) Calcites filling in the secondary dissolution pores, well Dya1, 5529.8 m, plane-polarized light. (b) Fe-dolomite and dissolution pores with EDS, well Xc101, 5039.8 m, SEM. (c) Quartz overgrowths, well Xc5, 4740.4 m, cross-polarized light. (d) Autogenic quartz filling in the pores, well Xc10, 4883.4 m, SEM. (e) Grain-coating chlorites and secondary dissolution pores associated with the feldspar dissolution, well Dya1, 5592.8 m, plane-polarized light. (f) Chlorites and pores, well Xc10, 4932.0 m, SEM. Cal, calcites; P, pores; Fe-Dol, Fe-dolomites; Q, quartz; QO, quartz overgrowths; AQ, autogenic quartz; RF, rock fragments; Ch, chlorites.
Minerals 15 00625 g006
Minerals 15 00625 g007
Figure 7. (a) Deformation of the flexible mica and concave–convex grain contacts, well Dyi 4, 5472.0 m, crossed-polarized light. (b) Deformation of the flexible mica, well Gm 4, 5116.5 m, crossed-polarized light. (c) Secondary dissolution pores associated with the feldspar and sericite, well Dyi 4, 5464.9 m, plane-polarized light. (d) Mold pores associated with the feldspar dissolution, well Hl 1, 4341.3 m, plane-polarized light. (e) Secondary dissolution pores associated with the K-feldspar (EDS), well Xc8, 5005.3 m, SEM. (f) Micro-fractures cutting through particles, well Cf563, 4439.7 m, plane-polarized light. Q, quartz; F, feldspars; RF, rock fragments; Mi, mica; P, pores; Fr, fractures.
Figure 7. (a) Deformation of the flexible mica and concave–convex grain contacts, well Dyi 4, 5472.0 m, crossed-polarized light. (b) Deformation of the flexible mica, well Gm 4, 5116.5 m, crossed-polarized light. (c) Secondary dissolution pores associated with the feldspar and sericite, well Dyi 4, 5464.9 m, plane-polarized light. (d) Mold pores associated with the feldspar dissolution, well Hl 1, 4341.3 m, plane-polarized light. (e) Secondary dissolution pores associated with the K-feldspar (EDS), well Xc8, 5005.3 m, SEM. (f) Micro-fractures cutting through particles, well Cf563, 4439.7 m, plane-polarized light. Q, quartz; F, feldspars; RF, rock fragments; Mi, mica; P, pores; Fr, fractures.
Minerals 15 00625 g007
Minerals 15 00625 g008
Figure 8. Process and mechanism of the reservoir tightening of the quartz-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Figure 8. Process and mechanism of the reservoir tightening of the quartz-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Minerals 15 00625 g008
Minerals 15 00625 g009
Figure 9. Process and mechanism of reservoir tightening of the feldspar-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Figure 9. Process and mechanism of reservoir tightening of the feldspar-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Minerals 15 00625 g009
Minerals 15 00625 g010
Figure 10. Process and mechanism of reservoir tightening of the rock-fragment-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Figure 10. Process and mechanism of reservoir tightening of the rock-fragment-rich sandstone of the tight sandstones of the Xu-2 Member in the western Sichuan Basin.
Minerals 15 00625 g010
Minerals 15 00625 g011
Figure 11. Content of quartz, feldspar, and rock fragments of the Xu-2 Member in the (a) Zitong source-to-sink system, (b) western Xinchang source-to-sink system, (c) eastern Xinchang source-to-sink system, (d) Yazihe area, (e) Chengdu area, (f) and Dayi source-to-sink system of the western Sichuan Basin.
Figure 11. Content of quartz, feldspar, and rock fragments of the Xu-2 Member in the (a) Zitong source-to-sink system, (b) western Xinchang source-to-sink system, (c) eastern Xinchang source-to-sink system, (d) Yazihe area, (e) Chengdu area, (f) and Dayi source-to-sink system of the western Sichuan Basin.
Minerals 15 00625 g011
Minerals 15 00625 g012
Figure 12. (a) Relationship between quartz content and porosity in the Xinchang source-to-sink system. (b) Relationship between quartz content and permeability in the Xinchang source-to-sink system. (c) Relationship between feldspar content and porosity in the Xinchang source-to-sink system. (d) Relationship between feldspar content and permeability in the Xinchang source-to-sink system. (e) Relationship between quartz content and porosity in the Yazihe–Chengdu source-to-sink system. (f) Relationship between quartz content and permeability in the Yazihe–Chengdu source-to-sink system. (g) Relationship between feldspar content and porosity in the Yazihe–Chengdu source-to-sink system. (h) Relationship between feldspar content and permeability in the Yazihe–Chengdu source-to-sink system. The arrow shows the trend of the value change.
Figure 12. (a) Relationship between quartz content and porosity in the Xinchang source-to-sink system. (b) Relationship between quartz content and permeability in the Xinchang source-to-sink system. (c) Relationship between feldspar content and porosity in the Xinchang source-to-sink system. (d) Relationship between feldspar content and permeability in the Xinchang source-to-sink system. (e) Relationship between quartz content and porosity in the Yazihe–Chengdu source-to-sink system. (f) Relationship between quartz content and permeability in the Yazihe–Chengdu source-to-sink system. (g) Relationship between feldspar content and porosity in the Yazihe–Chengdu source-to-sink system. (h) Relationship between feldspar content and permeability in the Yazihe–Chengdu source-to-sink system. The arrow shows the trend of the value change.
Minerals 15 00625 g012
Minerals 15 00625 g013
Figure 13. (a) Relationship between quartz content and porosity in the Zitong source-to-sink system. (b) Relationship between feldspar content and porosity in the Zitong source-to-sink system. (c) Relationship between quartz content and porosity in the Dayi source-to-sink system. (d) Relationship between quartz content and permeability in the Dayi source-to-sink system. (e) Relationship between feldspar content and porosity in the Dayi source-to-sink system. (f) Relationship between feldspar content and permeability in the Dayi source-to-sink system.
Figure 13. (a) Relationship between quartz content and porosity in the Zitong source-to-sink system. (b) Relationship between feldspar content and porosity in the Zitong source-to-sink system. (c) Relationship between quartz content and porosity in the Dayi source-to-sink system. (d) Relationship between quartz content and permeability in the Dayi source-to-sink system. (e) Relationship between feldspar content and porosity in the Dayi source-to-sink system. (f) Relationship between feldspar content and permeability in the Dayi source-to-sink system.
Minerals 15 00625 g013
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

Wu, D.; Yu, Y.; Lin, L.; Liu, S.; Li, B.; Ye, X. Study on Reservoir Characteristics, the Tightening Process and Reservoir Quality in Source-to-Sink Systems in the Xu-2 Member of the Xujiahe Formation in the Western Sichuan Basin, Western China. Minerals 2025, 15, 625. https://doi.org/10.3390/min15060625

AMA Style

Wu D, Yu Y, Lin L, Liu S, Li B, Ye X. Study on Reservoir Characteristics, the Tightening Process and Reservoir Quality in Source-to-Sink Systems in the Xu-2 Member of the Xujiahe Formation in the Western Sichuan Basin, Western China. Minerals. 2025; 15(6):625. https://doi.org/10.3390/min15060625

Chicago/Turabian Style

Wu, Dong, Yu Yu, Liangbiao Lin, Sibing Liu, Binjiang Li, and Xiaolong Ye. 2025. "Study on Reservoir Characteristics, the Tightening Process and Reservoir Quality in Source-to-Sink Systems in the Xu-2 Member of the Xujiahe Formation in the Western Sichuan Basin, Western China" Minerals 15, no. 6: 625. https://doi.org/10.3390/min15060625

APA Style

Wu, D., Yu, Y., Lin, L., Liu, S., Li, B., & Ye, X. (2025). Study on Reservoir Characteristics, the Tightening Process and Reservoir Quality in Source-to-Sink Systems in the Xu-2 Member of the Xujiahe Formation in the Western Sichuan Basin, Western China. Minerals, 15(6), 625. https://doi.org/10.3390/min15060625

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