Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (6): 69-79.DOI: 10.13745/j.esf.sf.2023.2.29

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Scope and mechanism of deep fluid circulation in karst systems, northern Awati-Manjiaer transition zone, Tarim Basin

YOU Donghua1,2(), PENG Shoutao3, HE Zhiliang4,*(), LIU Yongli5, HAN Jun5, XIAO Chongyang5, LI Yingtao3   

  1. 1. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China
    2. Wuxi Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute, SINOPEC, Wuxi 214126, China
    3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    4. China Petroleum and Chemical Corporation, Beijing 100728, China
    5. Petroleum Exploration and Production Research Institute, Northwest Oilfield Company, SINOPEC, ürümqi 830011, China
  • Received:2023-01-13 Revised:2023-02-15 Online:2023-11-25 Published:2023-11-25

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Abstract:

The transition zone between the Awati and Manjiaer depressions, Tarim Basin is an important area with the development of large-scale fault-associated petroleum reservoirs. Focusing on the fluid events within the fault zone, this study aims to gain deeper insights into the scope and mechanism of deep fluid circulation in karst systems, through comprehensive geological and geochemical analyses of wells TS6, YJ1-1x, SHB1-3x, and SHBP1. The secondary and dolomitic limestones, formed from fine-crystalline dolomite via dedolomitization, and macrocrystalline calcite cements in the Penglaiba Formation of well TS6 are typically 13C, 18O depleted, indicating the depth of karstification in the Shaya uplift can reach ~1200 m (away from the $\mathrm{T}_{7}^{4}$ unconformity). Caves in well YJ1-1x contain four rock layers and are filled with argillaceous siltstone and silty mudstone, with characteristic minerals such as limonite, indicating the presence of lateral fluid flow and weak hydrodynamic conditions. In well SHB1-3x, caves with three rock layers contain argillaceous fillings and volcanic rock debris, and the structural characteristics of calcite and limonite as secondary fillings reveal sediment transport in the underground rivers. The distance between wells YJ1-1x and TS3 (near the erosion line of the Sangtamu Formation) is about 76 km, and the linear distance between wells SHB1-3x and TS3 is about 90 km, indicating long distance lateral fluid flow. The dolomite reservoir of the Yingshan Formation in well SHBP1 is characterized by fault-fluid transformation and continuous deterioration of reservoir performance from bottom to top. The secondary macrocrystalline calcite cements in dolomite are obviously 13C, 18O depleted and 87Sr enriched, which are strongly comparable to the calcite of karst origin in the Tahe area, suggesting the calcite cements may originate from the bottom-up intrusion of deep circulating fluids. The geological model of deep fluid circulation and the existence of subvolcanic rocks in the Yingshan Formation of well SHBY1 indicate the driving force behind fluid migration may come from stratum warming and/or geothermal events. The water-rock interaction during deep fluid circulation is conducive to the development of deep and ultra-deep carbonate reservoirs in the Awati-Manjiaer transition zone under certain conditions.

Key words: deep fluid circulation, karst fluid, carbonate reservoir, Awati-Manjiaer transition zone, Tarim Basin

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