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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Earth Sciences".

Deadline for manuscript submissions: closed (20 March 2025) | Viewed by 10063

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Dr. Guoheng Liu

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1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
2. Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Interests: unconventional resources; silicon enrichment; oil-gas accumulation; palaeoenvironmental reconstruction
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Dr. Jianhua Zhao

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1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
2. Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Interests: unconventional resources; basin research
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Dr. Xiaolong Sun

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1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
2. Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Interests: CO₂ geological storage; reservoir geology; fluid–rock interaction
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Dr. Yuqi Wu

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1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
2. Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
Interests: modeling and characterization of subsurface reservoirs; diagenesis analysis and simulation; digital rock physics; shale gas and oil
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Special Issue Information

Dear Colleagues,

This is the second volume of the previously successful Special Issue "The Exploration and Development of Unconventional (Mainly Shale) Hydrocarbon Resources" (Link: https://www.mdpi.com/journal/processes/special_issues/760MCZ74Y9).

The exploration and development of hydrocarbons (gas and oil) in unconventional reservoirs have attracted a great deal of attention due to the vast potential in these areas. Over the past two decades, the production of hydrocarbons from reservoirs with disparate depositional environments has rapidly increased in many countries (e.g., North America and China) due to the application of horizontal drilling and hydraulic fracturing. However, there are still many scientific issues that are implicated in the sustainable development of hydrocarbon resources, including the hydrocarbon accumulation mechanisms and models, hydrocarbon occurrence state, and hydrocarbon loss mechanism.

Therefore, we announce a Special Issue on “The Exploration and Development of Unconventional Hydrocarbon Resources” in order to present up-to-date advances in the theories and methodologies that are related to accumulation mechanisms for unconventional reservoirs. This Special Issue will mainly focus on the underlying scientific issues that are related to the accumulation and depletion of hydrocarbon mechanisms in shale reservoirs, in an attempt to improve our fundamental understanding of these processes for the high single-well productivity and low-cost sustainable development of hydrocarbon.

You may choose our Joint Special Issue in Processes.

Dr. Guoheng Liu
Dr. Jianhua Zhao
Dr. Xiaolong Sun
Dr. Yuqi Wu
Guest Editors

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Keywords

genesis and evolution of gas/oil and multiscale pores
genetic and distribution patterns of fractures
geological controls on reservoirs quality
hydrocarbon accumulation/depletion mechanisms
petrophysical characterization of formations
fluid flow and fluid&ndash
shale interactions

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Published Papers (8 papers)

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Research

16 pages, 7244 KiB

Open AccessArticle

Experimental Investigation on the Tensile Mechanical Behavior of Layered Shale Using Direct and Indirect Test Methods

by Ali. M. Fadhel, Tianshou Ma and Haonan Wang

Appl. Sci. 2025, 15(5), 2669; https://doi.org/10.3390/app15052669 - 1 Mar 2025

Viewed by 770

Abstract

An accurate understanding of the tensile mechanical behavior of shale rock is essential for optimizing shale gas drilling and hydraulic fracturing operations. However, the mechanical behavior of shale is significantly influenced by its anisotropy. Therefore, this study investigated the tensile mechanical behavior of layered shale by combining acoustic emission (AE) monitoring with two testing methods: the Brazilian splitting test (BST) and a novel direct tensile test (DTT). The impact of anisotropy on the tensile mechanical behavior and failure modes of layered shale under different test methods was evaluated. Additionally, seven anisotropic tensile strength criteria were compared and validated using the experimental results. The results show that: (1) As the loading angle (β) increased, the tensile strength measured by both BST and DTT increased. Both methods exhibited maximum tensile strength at β = 90° and minimum tensile strength at β = 0°. The anisotropy ratios for BST and DTT were 1.52 and 2.36, respectively, indicating the significant influence of the loading angle on tensile strength. (2) The AE results indicated that both DTT and BST specimens exhibited brittle failure characteristics. However, the DTT specimens demonstrated more pronounced progressive failure behavior, with failure modes categorized into four types: tensile failure across the bedding plane, shear failure along the bedding plane, and two types of tensile–shear mixed failure. In contrast, the BST specimens primarily exhibited tensile–shear mixed failure, except for tensile failure along the bedding plane at β = 0° and tensile failure across the bedding plane at β = 90°. (3) Neither of the two test methods could fully eliminate the influence of anisotropy, but three anisotropic tensile criteria, the Lee–Pietruszczak criterion, the critical plane approach criterion, and the anisotropic mode I fracture toughness criterion based on the stress–strain transformation rule demonstrated high accuracy in predicting tensile strength. Furthermore, in alignment with previous studies, the indirect tensile strength of various rock types was found to range between one and three times the direct tensile strength, and a linear correlation between the two variables was established, with a coefficient of approximately 1.11. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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21 pages, 32807 KiB

Open AccessArticle

Analysis of Hydrocarbon Enrichment in Tight Sandstone Reservoirs in the Eastern Baiyun Depression

by Xudong Wang, Nansheng Qiu, Xiangtao Zhang, Zhuochao Wang and Zhiye Li

Appl. Sci. 2024, 14(22), 10703; https://doi.org/10.3390/app142210703 - 19 Nov 2024

Viewed by 724

Abstract

Based on the special geological background of the east and north slopes of the Baiyun Depression, the development conditions of Paleogene structure–lithology traps, the development conditions of high-quality reservoirs and the difficulty in characterizing the distribution characteristics are studied in this paper. It is concluded that the eastern Baiyun is located on the Baiyun–Liwan continental–oceanic large-scale intershell separation system, with a complex tectonic background and a tectono-sedimentary pattern of “fault and uplift interlocking and uplift and depression interphase”. The palaeo source sink system of the low bulge in the east of Yundong is restored, the favorable position of reservoir collective development and the favorable characteristics of reservoir–cap assemblage are clarified, and the paleo-geomorphology and sedimentary filling evolution law are clarified. Guided by the drive of oil and gas accumulation, three types of large and medium-sized structure–stratigraphic traps have been implemented in the eastern Baiyun system, including the convex inclined end, the restricted fault gully and the magmatic floor intrusion, and the corresponding oil and gas accumulation models have been perfected. By studying the structure, source and sink system and trap characterization of the eastern Baiyun basin, the development conditions and exploration direction of the large and medium-sized Palaeogene traps are systematically summarized. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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16 pages, 12033 KiB

Open AccessArticle

Natural Gas Enrichment Processes and Differential Accumulation Models in the Central Anticline Belt of the Xihu Sag, East China Sea Shelf Basin

by Yinshan Chang, Yiming Jiang, Jun Qin, Wenqi Chang, Zhiwu Xiong, Fujia Ji, Ruoyu Zhang and Zhiwei Zeng

Appl. Sci. 2024, 14(22), 10242; https://doi.org/10.3390/app142210242 - 7 Nov 2024

Viewed by 991

Abstract

The Central Anticline Belt of the Xihu Sag is one of the structural units with the most abundant natural gas in the East China Sea Shelf Basin. However, there are significant differences among the anticline units in terms of the scale of natural gas enrichment, occurrence horizons, types of gas reservoirs, accumulation processes, and gas-bearing properties of different strata, which influence the optimization of exploration zones and the orientation of exploration in deep-buried areas. This study conducted a comprehensive analysis in terms of the structural evolution, fault activity, hydrocarbon charging stages, and process of hydrocarbon accumulation. It clarifies that (1) the preservation condition is one of the core factors for the differential enrichment of natural gas in the Central Anticline Belt. Under the background of differential compression of the Longjing Movement, late-stage and E-W-trending faults are commonly developed in the anticline cores of the strong compression area in the south, which damage the effectiveness of traps, resulting in a large amount of natural gas escaping and being locally adjusted and accumulated in shallow effective traps. The gas reservoirs show the characteristics of multiple accumulation horizons and a small scale. In the moderately strong compression area in the north, the E-W-trending faults have weak activities and shallow incision horizons. The original gas reservoirs are not damaged, and the structures are fully filled. (2) The coupling between faults and sand bodies determines the degree of oil and gas enrichment. In the weakly compressed area in the west, late-stage E-W-trending faults are not developed, and the preservation conditions are good. The main controlled faults on the flanks of the anticline are highly active, and the coupling degree between faults and sand bodies is good, resulting in a high gas saturation. However, the transport capacity in the anticline cores is relatively poor, with a low gas saturation. (3) The differences in the paleo-structural characteristics affect the degree of oil and gas enrichment. The paleo-structures formed before the Longjing Movement provided favorable conditions for the early convergence of oil and gas. Natural gas has the characteristics of multi-stage charging, and the deep gas reservoirs have higher gas saturation than the shallow ones. On this basis, this study proposed two natural gas accumulation processes developed in the Central Anticline Belt of the Xihu Sag under the background of differential compression. One is where the hydrocarbon convergence occurs first and then oil and gas transport and accumulate into the reservoirs; the other one is where the hydrocarbon convergence and accumulation occur simultaneously, followed by gas adjustment. This paper also concludes three differential accumulation models: the local enrichment and accumulation model of gas in the strongly compressed zone, the integrated enrichment and accumulation model in the medium-strongly compressed zone, and the fault–sand coupling accumulation model in the weakly compressed zone. The results of this research have great significance for the subsequent exploration, hydrocarbon enrichment style analysis, and further strategy in the deep-buried, tight to low-permeable reservoirs in ocean exploration areas. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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19 pages, 12318 KiB

Open AccessArticle

Sedimentary Environment Reconstruction and Organic Matter Enrichment Mechanisms in Various Lithofacies of the Lacustrine Shale: A Case Study of the Da’anzhai Member, Central Sichuan Basin, China

by Yuting Peng, Yingxiao Fu, Senran Chen and Enze Wang

Appl. Sci. 2024, 14(22), 10192; https://doi.org/10.3390/app142210192 - 6 Nov 2024

Cited by 1 | Viewed by 951

Abstract

Jurassic lacustrine shale in the Sichuan Basin is a focal exploration area in China, while the pronounced heterogeneity presents challenges, necessitating detailed research as a prerequisite. This study aims at the Jurassic Ziliujing Formation Da’anzhai shale in the central Sichuan Basin, systematically characterizing its geological features. Employing geochemical methods, we reconstructed the paleo-sedimentary environments and explored the mechanisms behind the organic matter enrichment. The findings reveal that the Da’anzhai shale exhibits three lithofacies: organic-rich argillaceous shale (ORA), organic-poor argillaceous shale (OPA), and organic-rich mixed shale (ORM). The sedimentary period was marked by a warm and humid climate, predominantly depositing in anoxic environments with freshwater to brackish conditions. The watershed areas that are provenance sources for the shale clastics are experiencing strong weathering. Significant differences in the sedimentary environments of various lithofacies’ shale were observed. Redox conditions and paleoclimate were identified as the primary factors controlling organic matter enrichment in the Da’anzhai shale of the study area. Salinity also played a role in organic matter enrichment, while terrigenous debris influx and paleo-productivity did not exert a significant controlling effect on organic matter enrichment. Utilizing the reconstructed ancient sedimentary environments, we developed sedimentary models for different lithofacies’ shale, contributing to a deeper understanding of lithofacies’ diversity and the mechanisms governing organic matter enrichment in lacustrine environments. This study provides new information for further understanding the response mechanism of lacustrine shales to the Toarcian Oceanic Anoxic Event in the Early Jurassic from the perspective of elemental geochemistry. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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14 pages, 8798 KiB

Open AccessArticle

Characteristics and Origin of Natural Gas in Yongfeng Sub-Sag of Bogda Mountain Front Belt

by Xiangcan Sun, Yi Chen, Xingui Zhou, Zhongkai Bai, Yukun Du, Lei Wen and Kun Yuan

Appl. Sci. 2024, 14(19), 9085; https://doi.org/10.3390/app14199085 - 8 Oct 2024

Cited by 1 | Viewed by 770

Abstract

By systematically analyzing the natural gas composition, carbon isotopes, and source rock characteristics in the Yongfeng sub-sag of the Bogda Mountain front belt, natural gas characteristics were determined, and the genetic types and sources of natural gas were investigated. The research results indicate that methane is the main component of natural gas in the Yongfeng sub-sag, with low levels of heavy hydrocarbons and a high drying coefficient. These characteristics make it dry gas, which refers to natural gas with a methane content of over 95%. The ethane carbon isotope δ¹³C₂ of natural gas is −28.5‰ and belongs to oil type gas. The methane carbon isotope δ¹³C₁ of natural gas is −58.6‰~−59.4‰, has a relatively depleted methane carbon isotope value, shows significant differences from the surrounding natural gas methane carbon isotope, and belongs to the category of biogenic gas. The Permian Lucaogou Formation is the main source rock in the study area, with good organic matter abundance. The microscopic components of kerogen are mainly composed of sapropelic formations and the organic matter type is I–II₁. The source rock has a high maturity and has reached the mature stage, mainly consisting of oil and wet gas. The ethane carbon isotope of natural gas in the Yongfeng sub-sag shows as oil type gas, which is consistent with the kerogen type of the Lucaogou Formation source rocks, indicating that the natural gas mainly comes from the Lucaogou Formation source rocks. Based on comprehensive data and information on natural gas composition, carbon isotopes, and burial history of the source rocks, it is believed that some of the crude oil generated from the Lucaogou Formation in the early stage underwent biodegradation due to tectonic uplift, resulting in biogenic methane and the formation of crude oil biodegraded gas. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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19 pages, 6037 KiB

Open AccessArticle

Characteristics and Genesis of Pore–Fracture System in Alkaline Lake Shale, Junggar Basin, China

by Yifan Jiao, Xianglu Tang, Wenjun He, Liliang Huang, Zhenxue Jiang, Leilei Yang and Caihua Lin

Appl. Sci. 2024, 14(12), 5239; https://doi.org/10.3390/app14125239 - 17 Jun 2024

Viewed by 1086

Abstract

Unconventional oil and gas resources are indispensable, and shale oil is one of them. The Junggar Basin is a typical superposition oil and gas basin in China, with reserves of 100 million tons in many areas and various types of oil and gas reservoirs. The Permian Fengcheng Formation in Mahu Sag has great potential for oil generation, making the study of the Fengcheng Formation reservoir in Mahu Sag particularly important. Based on previous studies, the core sample from well Maye-1 is divided into four lithologies according to mineral composition: felsic shale, dolomitic felsic shale, clay-bearing felsic shale, and siltstone interlayers. Through core observation and description, it is found that the macroscopic porosity of each lithology is well-developed, with felsic shale exhibiting the highest macroscopic fracture density, followed by siltstone interlayers, and clay-bearing felsic shale showing the least development. Argon ion polishing scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) techniques show that the siltstone interlayer pore development is the best, with pore sizes ranging from 100 to 4000 nm. The fracture development of dolomitic felsic shale is the most significant, with fractures contributing up to 80.14%. The porosity of clay-bearing felsic shale is only 1.12%. The development of pores and fractures in the study area is related to sedimentary tectonic factors and diagenesis. It mainly exhibits three types of subfacies deposits, namely semi-deep lake subfacies, shallow lake subfacies, and lakeshore lake subfacies, predominantly composed of felsic shale. Strong tectonic movements contribute to the formation of macroscopic fractures. Diagenesis plays a crucial role in the formation of microscopic pores. The Fengcheng Formation is primarily influenced by compaction, pressure dissolution, dissolution, and metasomatism. These various diagenetic processes collectively promote the formation of pores, ultimately leading to the development of a multi-scale porosity system in the Fengcheng Formation. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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23 pages, 17533 KiB

Open AccessArticle

An Analysis of Silurian Paleo–Tethys Hydrocarbon Source Rock Characteristics in North Africa, the Middle East, and South China

by Enze Xu, Yaning Wang, Shangfeng Zhang, Rui Zhu, Jianhao Liang, Rui Han, Gaoyang Gong, Min Xu and Xin Cheng

Appl. Sci. 2024, 14(2), 663; https://doi.org/10.3390/app14020663 - 12 Jan 2024

Viewed by 2314

Abstract

In this study, we elucidate the genesis and distribution patterns of Silurian hot shale hydrocarbon source rocks by utilizing a comparative analysis of the evolutionary characteristics of plate tectonic activity in the Paleo–Tethys Ocean and the sedimentary filling characteristics of key basins in North Africa, the Middle East, and South China. We propose an explanation for the sedimentary genesis of world-class Silurian hydrocarbon source rocks in the Paleozoic craton basin of the ancient Tethys tectonic domain. This is achieved by scrutinizing the plate tectonic activity and evolution of the ancient Tethys Ocean and combining these findings with the paleotectonic sedimentation background of North Africa, the Middle East, and South China. Additionally, we compare Silurian hydrocarbon source rocks from these regions. The deep-water stagnant environment of the land shelf favors the preservation of organic matter, thereby forming high-quality hydrocarbon source rocks. Conversely, the shallow-water body of the land shelf is more turbulent, thus resulting in the poorer preservation of organic matter and, consequently, lower-quality hydrocarbon source rocks. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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20 pages, 17822 KiB

Open AccessArticle

Diagenesis of the Permian Fengcheng Formation in the Mahu Sag, Junggar Basin, China

by Bin Bai, Jiwei Liang, Chaocheng Dai, Wenjun He, Ying Bai, Xiaobin Chang, Meng Zheng, Hanlin Li and Hao Zong

Appl. Sci. 2023, 13(24), 13186; https://doi.org/10.3390/app132413186 - 12 Dec 2023

Cited by 5 | Viewed by 1484

Abstract

The Fengcheng Formation in the Mahu sag of the Junggar Basin was primarily composed of detritus, pyroclastic material, carbonates, and evaporites. In order to establish the diagenesis pathways of the Fengcheng Formation, some methods of polarized light microscope, SEM, CL, EPMA, LR, and fluid inclusion analysis were applied to discuss the diagenesis process. The results showed the following: (a) The formation of an alkaline lake was the result of the influence of a high concentration of sodium-rich sources, and it led to the preservation of alkaline minerals in the stratum. (b) After the sediments were buried, three mineral assemblages were formed in the Fengcheng Formation, which are carbonate mineral assemblages (i.e., calcite + ferreous dolomite), reedmergnerite and carbonate mineral assemblages (i.e., reedmergnerite + calcite + ferreous dolomite), and reedmergnerite and alkaline mineral assemblages (i.e., reedmergnerite + shortite + trona), respectively. (c) According to the homogenization temperature of reedmergnerite primary fluid inclusions, the alkaline diagenesis of Fengcheng Formation was divided into an early stage (≤100 °C) and a middle stage (>100 °C), respectively. The earlier stage is marked by the formation of ferrous saddle dolomite, quartz dissolution, and the agglutination of laumontite. These processes occurred under normal burial conditions. The latter is marked by the reedmergnerite’s appearance, which is correlated with the deep hydrothermal activity controlled by faults. (d) Based on sedimentary and diagenetic factors, including climate, provenance, diagenetic surroundings, and the action of subsurface fluid, the alkaline deposition-diagenesis model for shale series in four stages of the Fengcheng Formation was established. Full article

(This article belongs to the Special Issue The Exploration and Development of Unconventional Hydrocarbon Resources, 2nd Edition)

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