Timing of porosity loss and hydrocarbon charging of the Ordovician carbonate reservoirs in the Shunbei oil field, Tarim Basin, northwestern China

Wang, Bin, Guo, Xiaowen, Cao, Zicheng, Alves, Tiago M. ORCID: https://orcid.org/0000-0002-2765-3760, Zhao, Yongqiang, Tao, Ze, Chen, Jiaxu and Yang, Yi 2025. Timing of porosity loss and hydrocarbon charging of the Ordovician carbonate reservoirs in the Shunbei oil field, Tarim Basin, northwestern China. AAPG Bulletin 109 (8) , pp. 1081-1105. 10.1306/06302521121 Item availability restricted.

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Abstract

The Shunbei oil field of the Tarim Basin comprises important Ordovician carbonate reservoirs associated with strike-slip faults. Here, strike-slip fault zones contain sufficient space to accumulate significant hydrocarbon volumes. However, porosity in the carbonate reservoirs near the strike-slip faults zone can be <2.5% due to calcite cementation of pores, karst features, and fractures. In the present study, the timing of porosity loss and hydrocarbon charging are investigated to reveal four stages of calcite veining. The origin of vein-forming fluid was investigated by rare earth element analyses complemented by C, O, and Sr isotope analyses. The results indicate that fluids forming stage II and III calcite veins were derived from middle–lower Ordovician formation water, which interacted with the host rock. Fluid-forming stage I and IV veins originated from Cambrian formation water and deep hydrothermal fluids. The U-Pb dates indicate that stages I, II, and III veins were generated at 460 ± 12 to 464.8 ± 9.5, 440 ± 16 to 449 ± 15, and 420 ± 20 Ma, respectively, which is consistent with results from the minimum homogenization temperatures of the primary aqueous inclusions combined with burial and thermal histories. This research suggests that the porosity of the carbonate reservoir in the Shunbei oil field was lost during the middle–late Caledonian tectonic movements. Two hydrocarbon charging episodes occurred in these carbonate reservoirs after formation of the stage I, II, and III calcite veins. The timings of the two episodes of oil charge were determined as 400–390 and 250–235 Ma, respectively, corresponding to the early Hercynian and late Hercynian to Indosinian tectonic phases. This study concludes that petroleum accumulation in the carbonate reservoirs is mostly associated with the strike-slip faults, resulting from new reservoir pore spaces created during the early Hercynian and late Hercynian to Indosinian tectonic movements.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	American Association of Petroleum Geologists
ISSN:	0149-1423
Date of First Compliant Deposit:	22 September 2025
Date of Acceptance:	27 June 2025
Last Modified:	22 Sep 2025 10:45
URI:	https://orca.cardiff.ac.uk/id/eprint/181226

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