Controlling factors of Jurassic Da'anzhai Member tight oil accumulation and high production in central Sichuan Basin, SW China

Chen, Shijia; Zhang, Huanxu; Lu, Jungang; Yang, Yueming; Liu, Chaowei; Wang, Li; Zou, Xianli; Yang, Jiajing; Tang, Hongqu; Yao, Yitong; Huang, Youlin; Ni, Shuai; Chen, Yingying

doi:10.1016/s1876-3804(15)30007-0

Cited by 59 publications

(16 citation statements)

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“…Reservoir rocks in the Da'anzhai Member are primarily composed of shelly limestones, 10-30 m thick, which occur widely in the centre of the Sichuan Basin. Based on data provided by the Southwest Oil & Gas Field Company, PetroChina, the porosity of the limestones in the Da'anzhai Member ranges up to 6.8% with an average of 1.7% (see Chen et al, 2015).…”

Section: Geologic Settingmentioning

confidence: 99%

“…The tight oil in the Lower Jurassic Da'anzhai Member appears to be self-sourced and to have been generated by organic-rich lacustrine shale source rocks present within the member itself. The tight Lianggaoshan Formation reservoir is likewise self-sourced by similar OM-rich dark mudstones (Chen et al, 2014;Chen et al, 2015;. In addition, the shale source rocks in these two units have generated the light oils which are reservoired in the Middle Jurassic First Member of the Shaximiao Formation (Li et al, 2017;Lu et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

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Composition of Light Hydrocarbons in Jurassic Tight Oils in the Central Sichuan Basin, China: Origin and Source Rock Correlation

Wei³

et al. 2022

Journal of Petroleum Geology

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Crude oil reserves in tight Middle and Lower Jurassic reservoirs are of increasing exploration interest in the central Sichuan Basin, SW China. However, the origin of these “tight oils” is poorly understood. In this study, sixteen samples of light oils/condensates from tight Middle and Lower Jurassic reservoir rocks were analysed using gas chromatography (GC) and isotope ratio mass spectrometry to investigate the oils’ origin and to classify them into genetic families. The tight oils can be divided into two families. Family I oils occur in the Gongshanmiao oilfield where reservoir units comprise the Da'anzhai Member of the Lower Jurassic Ziliujing Formation, the Lower Jurassic Lianggaoshan Formation, and the First Member of the Middle Jurassic Shaximiao Formation. Family I oils are characterized by relatively low values of the methylcyclohexane (MCH) and cyclohexane (CH) indexes, low values of Mango's parameter K2 for light hydrocarbon composition, and relatively negative δ13C values ranging from ‐30.8‰ to ‐28.9‰. Family I oils are inferred to be self‐sourced by lacustrine shales in the Da'anzhai Member and the Lianggaoshan Formation in the study area, both of which are rich in sapropelic organic matter. These source rocks also charged reservoirs in the First Member of the Shaximiao Formation. By contrast, the newly discovered Family II oils, which occur at the Jinhua oilfield and the as‐yet undeveloped Qiulin and Bajiaochang structures, are reservoired in the Second Member of Shaximiao Formation. Family II oils have higher values of the MCH index, CH index and Mango's K2 parameter, and δ13C values varying from ‐27.5‰ to ‐25.4‰. These oils have similar light hydrocarbon compositions and δ13C values to oils derived from source rocks in the Upper Triassic Xujiahe Formation which contain dominantly humic organic matter. Family II oils are therefore inferred to be derived from the coaly mudstones in the Xujiahe Formation.The different compositions of the tight oils in the First and Second Members of the Shaximiao Formation appear to be controlled by the distribution and thickness of source rocks in the study area. Thus, the Gongshanmiao oilfield where Family I oils occur in the First Member is close to the depocentre of source rocks in the Da'anzhai Member and Lianggaoshan Formation. These source rocks are inferred to have charged the First Member reservoirs which may also be present in nearby oil‐ and gas‐bearing structures such as Nanchong and Yingshan. By contrast, Family II oils occur in tight reservoirs in the Second Member in areas with thick successions of Upper Triassic Xujiahe Formation mudstone source rocks, such as the Jinhua oilfield. In areas where both source rocks are present such as the Zhongtaishan and Lianchi oilfields, Shaximiao Formation reservoirs appear to contain both Family I and Family II oils.

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Section: Geologic Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Composition of Light Hydrocarbons in Jurassic Tight Oils in the Central Sichuan Basin, China: Origin and Source Rock Correlation

Wei³

et al. 2022

Journal of Petroleum Geology

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“…The source rocks of the Da’anzhai Member in the Ziliujing Formation are primarily located in the Da 1 3 submember. They have good hydrocarbon generation capacity, with primarily Type II kerogen and average TOC (total organic carbon content) of more than 1.0% . The vitrinite reflectance of Da’anzhai Member source rocks ranges from 0.9 to 1.5%, implying good oil generation properties.…”

Section: Geological Settingmentioning

confidence: 99%

Distribution and Geochemical Significance of Rearranged Hopanes in Jurassic Source Rocks and Related Oils in the Center of the Sichuan Basin, China

Wang³

et al. 2021

ACS Omega

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Gas chromatography-mass spectrometry (GC-MS) analysis has revealed extremely high abundances of rearranged hopanes in Jurassic source rocks and related crude oils in the center of the Sichuan Basin. The detected rearranged hopanes include 17α(H)-diahopanes (C 27 D and C 29−35 D), early-eluting rearranged hopanes (C 27 E and C 29−33 E), and 18α(H)-neohopanes (C 29 Ts and Ts). Both the 17α(H)-diahopanes and the early-eluting rearranged hopanes exhibit a distribution pattern similar to that of the 17α(H)-hopane series, with a predominance of the C 30 member and the presence of 22S and 22R epimers of hopanes in the extended series (>C 30 ). The results of this study show that the relatively high abundance of rearranged hopanes in Jurassic source rocks in the study area is associated with their depositional environments and with clay-mediated acidic catalysis rather than, as was previously thought, thermal maturity. Shallow lacustrine facies with brackish water and a suboxic to weak reducing sedimentary environment have contributed to the enrichment of rearranged hopanes, and clay-mediated acidic catalysis may also have had a positive influence on their abundance. The distribution patterns of the diahopane series indicate that the oils from Jurassic reservoirs in the Gongshanmiao Oilfield are sourced from Jurassic source rocks. Rearranged hopanes are therefore considered to be effective biomarkers for oil-source correlation in the center of the Sichuan Basin.

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“…The study area is located on the northern margin of the Yangtze Plate and is adjacent to the Qinling fold belt. The Lower Jurassic Da'anzhai Member of the North Sichuan Basin is mainly distributed across the Micangshan and Dabashan arc structures [48][49][50]. The belt overlaps with the arcshaped skirt belt in eastern Sichuan.…”

Section: Geological Settingmentioning

confidence: 99%

Types and Quantitative Characterization of Microfractures in the Continental Shale of the Da’anzhai Member of the Ziliujing Formation in Northeast Sichuan, China

et al. 2021

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A number of wells in the Sichuan Basin of China have tested industrial gas flow pressure arising from the shale of the Da’anzhai section of the Ziliujing Formation, revealing good exploration potential. Microfractures in shales affect the enrichment and preservation of shale gas and are important storage spaces and seepage channels for gas. In order to increase productivity and to reduce the risks associated with shale gas exploration, the types, connectivity, and proportion of microfractures in the Da’anzhai Member have been studied in this work by core and thin section observations, micro-CT, scanning electron microscopy, nitrogen adsorption, and high-pressure mercury intrusion. The results show that four types of fractures have developed in the shale of the Da’anzhai section: microfractures caused by tectonic stress, diagenetic shrinkage fractures of clay minerals, marginal shrinkage fractures of organic matter, and microfractures inside mineral particles. Among these, structural fractures and organic matter contraction fractures are the main types and are significant for shale reservoirs and seepage. The structural microfractures are mainly opened and are well-developed in the shale, with a straight shape, mainly between bedding, with the fracture surface being curved, fully opened, and mainly tensile. Organic matter fractures often develop on the edge of the contact between organic matter and minerals, presenting a slit-like appearance. The fractures related to bedding in the shale are particularly developed, with larger openings, wider extensions, intersecting and expanding, and forming a three-dimensional interconnected pore-fracture system. Based on image recognition, generally speaking, microfractures account for about 20% of the total pore volume. However, the degree of the microfractures’ development varies greatly, depending upon the structural environment, with the proportion of microfractures in fault-wrinkle belts and high-steep zones reaching 40% to 90% of the total pore space. On the other hand, micro-fractures in areas with underdeveloped structures account for about 10% of the total pore space.

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Controlling factors of Jurassic Da'anzhai Member tight oil accumulation and high production in central Sichuan Basin, SW China

Cited by 59 publications

References 1 publication

Composition of Light Hydrocarbons in Jurassic Tight Oils in the Central Sichuan Basin, China: Origin and Source Rock Correlation

Composition of Light Hydrocarbons in Jurassic Tight Oils in the Central Sichuan Basin, China: Origin and Source Rock Correlation

Distribution and Geochemical Significance of Rearranged Hopanes in Jurassic Source Rocks and Related Oils in the Center of the Sichuan Basin, China

Types and Quantitative Characterization of Microfractures in the Continental Shale of the Da’anzhai Member of the Ziliujing Formation in Northeast Sichuan, China

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