Mechanism for the formation of natural fractures and their effects on shale oil accumulation in Junggar Basin, NW China

Zhang, Chen; Liu, Dongdong; Jiang, Zhenxue; Yan, Song; Luo, Qun; Wang, Xin

doi:10.1016/j.coal.2022.103973

Cited by 18 publications

(6 citation statements)

References 53 publications

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“…In the lower section, the tight/shale oil sweet spot spans an area of 1096 km 2 with a larger thickness in the south of the depression . P 2 l 1 is characterized by deltaic and lacustrine facies, with more terrigenous clastic sediments, whereas P 2 l 2 is featured by shallow lacustrine facies, with more carbonate deposits. , …”

Section: Geological Settingmentioning

confidence: 99%

“…The Jimusar Sag, located in the Junggar Basin in northern China, is a depression high in the east and low in the west, with an area of approximately 1278 km 2 . , It is bounded by the Shaqi Uplift in the north, the Santai Uplift in the west, the Fukang Fault in the south, and the Guxi Uplift in the east (Figure a–c). The Jimusar Sag has experienced multistage tectonic movements since the Late Paleozoic, including the Hercynian, Indosinian, Yanshanian, and Himalayan movements. − …”

Section: Geological Settingmentioning

confidence: 99%

“…40 P 2 l 1 is characterized by deltaic and lacustrine facies, with more terrigenous clastic sediments, whereas P 2 l 2 is featured by shallow lacustrine facies, with more carbonate deposits. 37,41…”

Section: Geological Settingmentioning

confidence: 99%

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Oil Mobility Evaluation of Fine-Grained Sedimentary Rocks with High Heterogeneity: A Case Study of the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China

et al. 2023

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The oil mobility in unconventional tight/shale oil reservoirs is complex because of the high heterogeneity in the matrix pore structure and connectivity. Thus, it is difficult to evaluate hydrocarbon exploration potential precisely. In this study, multistep temperature pyrolysis (MTP) Rock-Eval and 1D (dimensional) as well as 2D nuclear magnetic resonance (NMR) techniques were employed to systematically characterize the oil mobility in lacustrine fine-grained sedimentary rocks from the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China. The results show that the Lucaogou Formation fine-grained sedimentary rocks can be subdivided into six types of lithofacies. With the increase of organic matter richness, the content of adsorbed oil increases, whereas the content of movable oil increases first and tends to stabilize (when total organic carbon (TOC) > 4%). This is because when TOC is low, the fine-grained sedimentary rocks need to self-adsorb before oil production; when TOC increases further, the generated oil will break through the absorption limit and charge into the adjacent reservoirs; therefore, the movable oil ceases to increase. Permeability is found to have a greater impact on movable fluid saturation than porosity. Meanwhile, good throat radius and pore connectivity are conducive to oil flow as movable oil is more sensitive to throats rather than pores. Furthermore, a higher content of brittle minerals is not necessarily favorable for oil flow; alternatively, more clay minerals are easy to from cements causing pore blockage, which will essentially hinder oil mobility. Overall, the organic matter content, reservoir pore structure, and rock mineral composition are the main factors affecting tight/shale oil mobility. On the basis of the above research, a conceptual model of oil mobility in different lithofacies’ reservoirs is established. These results have a reference significance for evaluating oil recoverability in fine-grained sedimentary rocks.

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Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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Oil Mobility Evaluation of Fine-Grained Sedimentary Rocks with High Heterogeneity: A Case Study of the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China

et al. 2023

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“…The Middle Permian strata in this area can be divided from bottom to top into the Wulabo, Jingjingzi, Lucaogou, and Hongyanchi Formations, of which the Lucaogou Formation is the target for oil production in the Sag . The Lucaogou Formation was deposited across the entire sag and is about 200–300 m thick on average, with a maximum thickness of 350 m and a tendency to thicken in the west and south, and thin to the East and North. − Based on the lithologies and well-logging properties, the Lucaogou Formation can be categorized into two sub-sections from the bottom to top: the lower member (P 2 l 1 ) and the upper member (P 2 l 2 ). Since 2010, oil flow has been achieved in several wells (such as J30, J174, and J251 in Figure ) from the Lucaogou Formation. , …”

Section: Regional Geologymentioning

confidence: 99%

Distribution of Retained Oil in Shales from the Lucaogou Formation, Jimusar Sag, Northwest China: Insights from Mineralogy and Pore Structure

Wang

Cai

et al. 2023

Energy Fuels

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Shale oil resource is abundant in the world, which has been the dominant incremental oil production in recent years for several countries. A determination of pore structure, as well as the state and distribution of retained oil, not only is critical in identifying the controlling factors for the differential accumulation of shale oil but also affects the exploration and development of potentially favorable intervals in shale-oil systems. Twelve lacustrine shale samples from Lucaogou Formation (P2l) of Junggar Basin were selected to analyze the influence of mineral compositions and organic matter abundance on the pore system development and the retained oil distribution in pore-scale. A series of analyses, including thin section petrography, field emission-scanning electron microscopy (FE-SEM), quantitative evaluation of minerals by SEM, solvent extraction, mercury intrusion porosimetry, and nitrogen physisorption, were carried out to investigate the linkage between pore structure and occurrence of retained oil. The results indicate that the samples from Lucaogou Formation are dominated by slit-shaped, mineral-related pores with a small amount of organic matter-hosted pores. Feldspar has undergone an extensive dissolution, as shown by the development of abundant dissolved inter-particle and intra-particle pores, which significantly improve the reservoir property. The development of quartz overgrowth had a negative impact on the pore structure, and carbonates underwent processes of both dissolution and cementation. The mineral sizes show a positive relationship with pore diameter, and sedimentary microfacies close to the source contained more coarse components such as shore bar and distal bar are more favorable for oil exploration. Retained oil in pores with diameters of 100–1500 nm primarily occur in the free state as a thin oil film, whereas oil in pores with diameters smaller than 100 nm is adsorbed. Moreover, the retained oil volume is affected by organic matter abundance, the storage type, as well as the material source-reservoir configurations.

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“…In addition, natural fractures in reservoirs are crucial for creating a low-carbon environment, as they serve as significant storage spaces for carbon storage [27][28][29][30][31][32]. Consequently, many scholars have conducted research on shale natural fractures [21,[33][34][35][36] and the multi-scale dimensional evaluation of natural fractures in shale has been a hot topic [22,37,38]. Information about natural fractures, such as fracture density, filler, orientation, width, and length, can be obtained from shale outcrops [39] and the natural fracture orientation can serve as a vital indicator of the present-day stress field [40].…”

Section: Introductionmentioning

confidence: 99%

Microscopic Analysis of Natural Fracture Properties in Organic-Rich Continental Shale Oil Reservoirs: A Case Study from the Lower Jurassic in the Sichuan Basin, China

Bai

Huang

Wang

et al. 2023

JMSE

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Natural fractures are of paramount importance in storing carbon in shale oil reservoirs, where ultra-low porosity and permeability necessitate their essentiality for enhanced oil recovery. Therefore, comprehensively clarifying the characteristics of natural fractures in shale oil reservoirs is imperative. This paper focuses on investigating the microscopic features of natural fractures in organic-rich continental shale oil reservoirs that are commonly found in the Lower Jurassic strata of the Sichuan Basin, employing them as a representative example. Multiple methods were utilized, including mechanical testing, Kaiser testing, multi-scale CT scanning (at 2 mm, 25 mm, and 100 mm scales), and a numerical simulation of fluid seepage in fracture models. The results revealed that the in situ stress of the target seam displays the characteristic of σH > σv > σh, with σv and σh being particularly similar. The relatively high lateral stress coefficient (ranging from 1.020 to 1.037) indicates that the horizontal stresses are higher than the average level. Although the 2 mm CT scan provides a more detailed view of fractures and connected pores, it primarily exhibited more pore information due to the high resolution, which may not fully unveil additional information about the fractures. Thus, the 25 mm shale core is a better option for studying natural fractures. The tortuosity of the different fractures indicated that the morphology of larger fractures is more likely to remain stable, while small-scale fractures tend to exhibit diverse shapes. The simulations demonstrated that the stress sensitivity of fracture permeability is approximately comparable across different fracture scales. Therefore, our research can enhance the understanding of the properties of natural fractures, facilitate predicting favorable areas for shale oil exploration, and aid in evaluating the carbon storage potential of shale oil reservoirs.

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Mechanism for the formation of natural fractures and their effects on shale oil accumulation in Junggar Basin, NW China

Cited by 18 publications

References 53 publications

Oil Mobility Evaluation of Fine-Grained Sedimentary Rocks with High Heterogeneity: A Case Study of the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China

Oil Mobility Evaluation of Fine-Grained Sedimentary Rocks with High Heterogeneity: A Case Study of the Lucaogou Formation in the Jimusar Sag, Junggar Basin, NW China

Distribution of Retained Oil in Shales from the Lucaogou Formation, Jimusar Sag, Northwest China: Insights from Mineralogy and Pore Structure

Microscopic Analysis of Natural Fracture Properties in Organic-Rich Continental Shale Oil Reservoirs: A Case Study from the Lower Jurassic in the Sichuan Basin, China

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