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Advances in Petroleum Geology and Unconventional Oil and Gas

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H1: Petroleum Engineering".

Deadline for manuscript submissions: closed (10 March 2023) | Viewed by 18382

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Prof. Dr. Weibo Sui

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College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
Interests: reservoir monitoring; intelligent well completion; distributed fiber-optic sensors; digital rock physics

Special Issue Information

Dear Colleagues,

The exploration and development of unconventional oil and gas has made significant progress due to the shift in geological thinking and the use of horizontal well and multi-stage fracturing technology. However, there are still a number of challenges, including the diversity and complexity of geological environments in different sedimentary basins, the transport mechanism of oil and gas in shale or tight sandstone reservoirs and the fast-changing stimulation, testing and monitoring methods. This Special Issue aims to publish high-quality, peer-reviewed original research and articles on the latest theories and techniques in the field of petroleum geology and unconventional oil and gas. The key themes of this Special Issue include: petroleum geology; unconventional oil and gas accumulation mechanism; source rock microscopic and macroscopic characterization; digital rock physics for shale and tight sandstone; fluid and heat flow; fluid transport mechanism in shale and tight sandstone reservoirs; hydraulic fracturing and related stimulation techniques; fracture propagation models; unconventional reservoir testing and monitoring methods; distributed fiber-optic sensing; unconventional reservoir simulation and production forecasting models; CCUS with unconventional reservoir development; unconventional EOR technology; artificial-lift production techniques; and deep learning and big data analytic methods used for unconventional oil and gas development.

Prof. Dr. Weibo Sui
Guest Editor

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Keywords

unconventional oil and gas
hydraulic fracturing
petroleum geology
source rock characterization
digital rock physics
fracture propagation
temporary plugging agent
reservoir simulation
productivity model
deep learning
big data analytics
Artificial-lift method
fluid seepage theory
reservoir monitoring
CCUS
EOR
sedimentary basin
fluid and heat flow
distributed fiber-optic sensing

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Published Papers (10 papers)

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Research

16 pages, 4105 KiB

Open AccessArticle

Optimization of Mathematical Function-Shaped Fracture Distribution Patterns for Multi-Stage Fractured Horizontal Wells

by Yi Zou, Desheng Zhou, Xianlin Ma, Yenan Jie, Xiaoxiang Wang and Hongxia Liu

Energies 2023, 16(13), 4987; https://doi.org/10.3390/en16134987 - 27 Jun 2023

Viewed by 1076

Abstract

A conventional oil and gas well does not have a natural production capacity, which necessitates a hydraulic fracturing operation. The effectiveness of the fracturing directly impacts the economic benefit of a single well. Among the various parameters, including fracture spacing, fracture width, and conductivity, fracture half-length is one of the main influencing factors on the productivity of horizontal wells. For conventional homogeneous reservoirs, research mainly focuses on fracture patterns with equal fracture lengths. However, in actual production processes, due to mutual interference and the superimposition of drainage areas between fractures, the production distribution of each fracture is non-uniform. Typical fracture distribution patterns mainly include uniform, staggered, dumbbell, and spindle. While many believe that the dumbbell-shaped fracture distribution pattern has the best effect, there has been no quantitative study on the length of each fracture under the dumbbell-shaped pattern. Based on this, this paper proposes a modeling approach for function-shaped fracture distribution that takes advantage of the high production of edge fractures and the low output of middle fractures in horizontal wells. The influence of this approach on production capacity is studied. Constant, linear, and parabolic functions are used to establish the relationship between fracture position and fracture half-length, optimizing the fracture distribution function to achieve the best production effect. This method can guide the horizontal well fracture distribution in the block to maximize productivity. The results show that the parabolic function-shaped model is better than the linear function-shaped model and the constant function-shaped model is the least effective. The research presented in this paper offers a new idea for optimizing on-site fracturing plans. It utilizes mathematical expressions to describe the parameters that affect productivity, which provides valuable guidance for designing multi-stage fractured horizontal wells in the field. In the future, this research will be extended by exploring the optimal fracture distribution function under different formation conditions. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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14 pages, 4892 KiB

Open AccessArticle

The Strike-Slip Fault Effects on Tight Ordovician Reef-Shoal Reservoirs in the Central Tarim Basin (NW China)

by Yawen Zhao, Guanghui Wu, Yintao Zhang, Nicola Scarselli, Wei Yan, Chong Sun and Jianfa Han

Energies 2023, 16(6), 2575; https://doi.org/10.3390/en16062575 - 9 Mar 2023

Cited by 5 | Viewed by 1548

Abstract

The largest carbonate condensate field in China has been found in the central Tarim Basin. Ordovician carbonate reservoirs are generally attributed to reef-shoal microfacies along a platform margin. However, recent production success has been achieved along the NE-trending strike-slip fault zones that intersect at the platform margin. For this contribution, we analyzed the strike-slip fault effects on the reef-shoal reservoirs by using new geological, geophysical, and production data. Seismic data shows that some NE-trending strike-slip faults intersected the NW-trending platform margin in multiple segments. The research indicated that the development of strike-slip faults has affected prepositional landforms and the subsequent segmentation of varied microfacies along the platform margin. In addition, the strike-slip fault compartmentalized the reef-shoal reservoirs into multiple segments along the extent of the platform margin. We show that fractured reef-shoal complexes are favorable for the development of dissolution porosity along strike-slip fault damage zones. In the tight matrix reservoirs (porosity < 6%, permeability < 0.5 mD), the porosity and permeability could be increased by more than 2–5 times and to 1–2 orders of magnitude in the fault damage zone, respectively. This suggests that high production wells are correlated with “sweet spots” of fractured reservoirs along the strike-slip fault damage zones, and that the fractured reservoirs in the proximity of strike-slip fault activity might be a major target for commercial exploitation of the deep Ordovician tight carbonates. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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15 pages, 6381 KiB

Open AccessArticle

Microscopic Study of Shale Anisotropy with SEM In Situ Compression and Three-Point Bending Experiments

by Weibo Sui, Yulong Wang and Junwei Li

Energies 2023, 16(5), 2440; https://doi.org/10.3390/en16052440 - 3 Mar 2023

Cited by 3 | Viewed by 1649

Abstract

The microscopic anisotropy of shale has an important impact on its mechanical properties and crack behavior, so it is essential to understand the microscopic origin of anisotropic growth with a more effective laboratory work scheme. Uniaxial compression test and three-point bending test are considered to be efficient means to study the elastic properties and crack behavior of rocks. In this paper, uniaxial compression experiments and three-point bending experiments were conducted on shale outcrops in the Changqing area using field emission scanning electron microscopy (SEM) and in situ tensile testing, and the microscopic deformation and crack processes were quantitatively characterized by the digital image correlation (DIC) method. For the compression experiments, the observation of the first principal strain fields indicated that the microscopic anisotropy of shale was related to the bedding planes, and the microscopic deformations were mainly concentrated in the clay mineral accumulation area and at the microcracks. Elastic moduli and compressive strengths of specimens with different bedding angles were affected by the strong shear stress effects. The specimens with a bedding angle of 30° showed lower peak loads and compressive strengths, and the specimens with a bedding angle of 60° had lower elastic moduli. Three-point bending experiments were conducted for studying the effects of crack-bedding orientation relationships on cracking processes, and four critical fracturing mechanical properties were calculated. The short transverse-type cases were prone to break and had a lower peak load, tensile strength, fracture toughness and elastic-bending modulus. The divider-type cases were more difficult to break, formed a more tortuous crack and had a higher tensile strength, fracture toughness and elastic-bending modulus. The arrester-type cases had a middle range of mechanical parameters but developed the longest cracks. This study provides a feasible experimental and analysis method for understanding the microscopic anisotropy of shale samples. The small specimen size also makes the requirements of core samples easier to be satisfied considering the field application. Furthermore, the anisotropy of cracking processes can be understood better by building the connections between microstructural characteristics and mechanical performances. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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13 pages, 5252 KiB

Open AccessArticle

A Study of the Non-Linear Seepage Problem in Porous Media via the Homotopy Analysis Method

by Xiangcheng You, Shiyuan Li, Lei Kang and Li Cheng

Energies 2023, 16(5), 2175; https://doi.org/10.3390/en16052175 - 23 Feb 2023

Cited by 8 | Viewed by 1738

Abstract

A non-Darcy flow with moving boundary conditions in a low-permeability reservoir was solved using the homotopy analysis method (HAM), which was converted into a fixed-boundary mathematical model via similarity transformation. Approximate analytical solutions based on the HAM are guaranteed to be more accurate than exact analytical solutions, with relative errors between 0.0089% and 2.64%. When λ = 0, the pressure drop of the Darcy seepage model could be instantaneously transmitted to infinity. When λ > 0, the pressure drop curve of the non-Darcy seepage model exhibited the characteristics of tight support, which was clearly different from the Darcy seepage model’s formation pressure distribution curve. According to the results of the HAM, a moving boundary is more influenced by threshold pressure gradients with a longer time. When the threshold pressure gradients were smaller, the moving boundaries move more quickly and are more sensitive to external influences. One-dimensional, low-permeability porous media with a non-Darcy flow with moving boundary conditions can be reduced to a Darcy seepage model if the threshold pressure gradient values tend to zero. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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20 pages, 7051 KiB

Open AccessArticle

Impact of Terrigenous Organic Matter Input on Organic Matter Enrichment of Paleocene Source Rocks, Lishui Sag, East China Sea

by Xu Han, Dujie Hou, Xiong Cheng and Yan Li

Energies 2023, 16(4), 2046; https://doi.org/10.3390/en16042046 - 19 Feb 2023

Cited by 2 | Viewed by 1801

Abstract

To clarify the organic matter (OM) enrichment of the Lishui Sag, the factors influencing the variable abundance of OM in the Lingfeng Formation are studied using organic geochemical data. The source rocks of the Lingfeng Formation have medium–high total organic carbon (TOC) values (0.53–3.56%). The main type of kerogen is II2-III. Compared to the shallow marine subfacies source rocks, the TOC of the delta front subfacies source rocks is higher. The distribution of biomarkers shows that the redox environment of the delta front subfacies source rock is the sub-oxidizing and oxic environment, and the source rock is mainly supplied by terrigenous higher plants; the redox environment of shallow marine subfacies source rocks is a sub-reducing and suboxic environment, and the OM mainly comes from algae. The link between OM input and OM abundance demonstrates that terrigenous OM (TOM) input has a considerable influence on OM abundance. However, there is no obvious relationship between preservation and OM abundance, which suggests that preservation is not the determining element in OM enrichment. The strong sediment flux decreases the amount of time that OM is exposed to oxygen. As a result, delta front subfacies with large TOM input have a huge number of excellent source rocks. This paper proposes a “delta front-OM input model” for excellent source rocks. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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12 pages, 3471 KiB

Open AccessArticle

Development and Analysis of Mathematical Plunger Lift Models of the Low-Permeability Sulige Gas Field

by Wenbin Cai, Huiren Zhang, Zhimin Huang, Xiangyang Mo, Kang Zhang and Shun Liu

Energies 2023, 16(3), 1359; https://doi.org/10.3390/en16031359 - 28 Jan 2023

Cited by 1 | Viewed by 1898

Abstract

The Sulige is a low-permeability tight gas sandstone field whose natural gas production has gradually declined with continuous development. The primary reason was that most of the wells in the field flew below their critical rates and liquids started to accumulate in the wellbore at different levels, which resulted in the production reduction due to the wellbore pressure decrease and back pressure increase on the produced gas. An artificial lift was required to remove the liquids from those wells. With the advantages such as simple installation and operation, low cost and high liquid-carrying capacity, the plunger lift has been proven effective in the Sulige Gas Field. In this paper, firstly, a series of mathematical models were developed to investigate plunger displacement and velocity in the uplink and downside phases, fluid leakage in the uplink phase, and the characteristics of tubing pressure and casing pressure in the uplink and pressure build-up phases. Then, taking well X1 and well X2 at Su 59 area of the gas field as an example, the established mathematical models were applied to estimate its tubing and casing pressure, plunger moving displacement and speed, fluid leakage during the uplink phase, and gas production during the plunger lift. Hence, the well production cycle operated by the maximum gas rate was optimized. This study provides a theoretical basis for the optimal design of plunger lift parameters and the improvement of gas production. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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17 pages, 3560 KiB

Open AccessArticle

Extraordinarily High Organic Matter Enrichment in Upper Permian Wujiaping Formation in the Kaijiang-Liangping Trough, Sichuan Basin

by Yao Du, Xingzhi Wang, Ruifeng Tang, Yiqing Zhu, Cong Yang, Hongfei Zhou and Qian Pang

Energies 2023, 16(1), 349; https://doi.org/10.3390/en16010349 - 28 Dec 2022

Cited by 2 | Viewed by 1544

Abstract

The study of extraordinarily high organic matter content (EHOMC) is beneficial to promote the fine evaluation of shale oil and gas, but so far, there have been few studies on its mechanism. This paper carried out a comprehensive lithological and geochemical analysis of the black shales of the Wujiaping Formation in the Kaijiang-Liangping Trough. The results showed that the black shales of the Wujiaping Formation can be divided into two units (the upper and lower parts), and EHOMC occurs in its upper part. The redox-sensitive trace elements (RSTEs), Mo_EF-U_EF covariation, and Ni/Co correlation showed that the lower part of Wujiaping Formation was a weakly restricted oxidation environment, while the upper part evolved into a sulfidation reducing environment. The productivity indicator elements (Ba_XS, Ni_XS, Cu_XS, P, and Mo) indicated that the upper Wujiaping Formation had higher primary productivity than the lower part. However, rare earth elements ((La/Yb)_N) indicated that the deposition rate in the lower part of the Wujiaping Formation was higher than that in the upper part. In general, although the oxygenated water in the lower part of the Wujiaping Formation is not conducive to the preservation of organic matter, the high input of nutrients from land sources and the high deposition rate inhibit the decomposition of organic matter, so the lower part has a certain degree of organic matter accumulation. The sulfidation reducing environment and high paleoproductivity are the main reasons for the enrichment of organic matter in the upper part of the Wujiaping Formation. In addition, the sulfidation reducing environment and high paleoproductivity occurred during the violent upwelling at the end of Guadeloupe, a period of high sea level, these factors have jointly contributed to the enrichment of OM in the upper the Wujiaping Formation. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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21 pages, 5597 KiB

Open AccessArticle

Chemometric Classification and Geochemistry of Crude Oils in the Eastern Fukang Sag, Junggar Basin, NW China

by Erting Li, Yan Li, Baoli Xiang, Dujie Hou, Julei Mi, Xu Han, Yu Zhang and Xiuwei Gao

Energies 2022, 15(23), 8921; https://doi.org/10.3390/en15238921 - 25 Nov 2022

Cited by 3 | Viewed by 1589

Abstract

Thirty oil samples collected from the eastern Fukang Sag were analyzed geochemically for their biomarkers and carbon isotopic compositions. The chemometric methods of principal component analysis and hierarchical cluster analysis, employed to thirteen parameters indicating source and depositional environment, classified the oil samples into three genetically distinct oil families: Family A oils were mainly derived from lower aquatic organisms deposited in a weakly reducing condition of fresh–brackish water, Family B oils came from a source containing predominantly terrigenous higher-plant organic matter laid down in an oxidizing environment of fresh water, and Family C oils received sources from both terrigenous and marine organic matter deposited in a weakly oxidizing to oxidizing environment of brackish water. Indirect oil–source correlations implied that Family A oils were probably derived from Permian source rocks, Family B oils originated mainly from Jurassic source rocks, and Family C oils had a mixed source of Carboniferous and Permian. Biomarker maturity parameters revealed that all three families of oils were in the mature stage. However, Family A oils were relatively less mature than Family B and Family C oils. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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28 pages, 3928 KiB

Open AccessArticle

Petroleum Systems Analysis of Turbidite Reservoirs in Rift and Passive Margin Atlantic Basins (Brazil and Portugal)

by Gustavo Santana Barbosa, Rui Pena dos Reis, Antônio Jorge Vasconcellos Garcia, Gabriel de Alemar Barberes and Gustavo Gonçalves Garcia

Energies 2022, 15(21), 8224; https://doi.org/10.3390/en15218224 - 3 Nov 2022

Cited by 2 | Viewed by 2648

Abstract

Due to the success of oil and gas production, turbidites have become exploratory targets over the past 40 years in the rift and passive margin basins in the North and South Atlantic. The turbiditic reservoirs in rift and passive margin settings of Atlantic sedimentary basins located in Brazil (Campos Basin) and Portugal (Lusitanian Basin) represent potential economic units for the hydrocarbon exploration. However, despite being considered analogous reservoirs, these units present distinct potentials for the accumulation of hydrocarbons. In this context, the work presented discusses the results obtained from the analysis of static (source rock, reservoir rock, seal and trap) and dynamic elements (migration, tectonic, diagenetic and thermal processes) of both studied petroleum systems, using geological, seismic, well, geochemical and petrographic data. The developed methodology of multiscalar characterization of the two petroleum systems was successful, leading to a specific classification of the efficiency of the static and dynamic elements. These served as the basis for a petroleum systems analysis of the potential of turbiditic reservoirs in both analyzed basins. In the Campos Basin, the salt diapirs and the associated faults provided the origin of excellent migration routes for the hydrocarbons generated in lower intervals, allowing them to reach Cretaceous turbidite reservoirs. At Lusitanian Basin, the diagenetic processes reduced significantly the porosities of the potential turbiditic reservoirs, besides the intense influence of the salt tectonics that may have been responsible for the migration of hydrocarbons along faults or by their walls, towards upper formations and to the surface. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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18 pages, 11926 KiB

Open AccessArticle

Numerical Investigation of Liquid Flow Behaviors through Closed Rough Fractures in the Self-Propped Shale Formation

by Qiqi Wang, Mian Chen and Jiaxin Lv

Energies 2022, 15(19), 7052; https://doi.org/10.3390/en15197052 - 26 Sep 2022

Cited by 1 | Viewed by 1407

Abstract

The surface morphology of fractures formed by hydraulic fracturing is usually rough. The roughness of the fracture surface is the main reason the actual fracture conductivity deviates from the ideal flat plate model result. In this paper, based on the three-dimensional reconfiguration of actual rough hydraulic fractures, a randomly generated geometric model of a micro-convex body with a rough fracture surface is used as an example of a hydraulic fracture in a shale reservoir. Assuming that the flow in the fracture conforms to the laminar flow pattern, the velocity and pressure fields of the fluid flow on the fracture surface are solved by the finite element method. The effects of micro-convex body size, uniformity, density, and shape on the non-uniform flow of the rough fracture surface are analyzed. The three-dimensional model shows that the average velocity is minimum in the near fully closed fracture. The fluid bypasses the micro-convex body during the flow, forming multiple nonlinear flow regions. The streamlined tortuosity increases with the density and size of the micro-convex bodies and depends on the distribution of the micro-convex areas. The bypassing accelerates the pressure drop and slows down the flow rate. The greater the degree of micro-convex body aggregation, the more significant the decrease in flow velocity. The more locations where the curvature of the micro-convex edge is not zero, the more nonlinear flow zones can significantly reduce the flow rate and thus affect oil and gas production. Targeted optimization of the proppant placement pattern to make the trailing part of the micro-convex body as close to streamlined as possible can reduce the nonlinear flow area and slow down the flow rate reduction. Full article

(This article belongs to the Special Issue Advances in Petroleum Geology and Unconventional Oil and Gas)

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