Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (6): 1515-1529.doi: 10.11743/ogg20230614

• Petroleum Geology • Previous Articles     Next Articles

Types, characteristics, and exploration targets of deep shale gas reservoirs in the Wufeng-Longmaxi formations, southeastern Sichuan Basin

Ruikang BIAN1,2,3(), Chuanxiang SUN1,2,3, Haikuan NIE1,2,3(), Zhujiang LIU4, Wei DU1,2,3, Pei LI1,2,3, Ruyue WANG1,2,3   

  1. 1.State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development,Beijing 102206,China
    2.Key Laboratory of Shale Oil/Gas Exploration and Production Technology,SINOPEC,Beijing 102206,China
    3.Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 102206,China
    4.Exploration Company,SINOPEC,Chengdu,Sichuan 610041,China
  • Received:2023-04-06 Revised:2023-09-05 Online:2023-12-01 Published:2023-12-20
  • Contact: Haikuan NIE E-mail:bianruikang@foxmail.com;niehk.syky@sinopec.com

Abstract:

The southeastern Sichuan Basin serves as a major region for the exploration of deep shale gas reservoirs in the Wufeng-Longmaxi formations to the Sinopec. Due to the constraints of engineering technology, the current drilling depth has focused on the layers at depth less than 4 500 m, while no substantial exploration breakthroughs have been made in the ultra-deep layers with depth exceeding 4 500 m. The structural type acts as a dominant factor governing the local depth differences of shales in this region. Furthermore, it significantly influences shale gas preservation conditions and the applicability of available engineering technologies. Therefore, determining the structural types of deep shale gas reservoirs therein, as well as the characteristics and the overall depth distribution of various types, can provide critical references for subsequent exploration elevation and exploration well emplacement. In this study, the deep shale gas reservoirs in the study area are classified into four major types in terms of structure: the basin-margin-anticline type, the basin-margin-slope type, the highly-steep-structure type, and the basin-interior-syncline type. We determine the characteristics and target areas of these various types of deep shale gas reservoirs. The most favorable exploration targets concluded include the Yangchungou, western Xinchang, Dingshan, Lintanchang, and Guihua structure of the basin-margin-anticline type, as well as the eastern Xinchang, eastern Dongxi, northern Liangcun, and Yongle-Gulin structure of the basin-margin-slope type. The structural type has a certain control effect on the gas-bearing capacity and production of reservoirs. Structure of the basin-margin-anticline type is the best in terms of both gas-bearing capacity and production, followed by the basin-margin-slope type and the highly-steep-structure type. Moreover, the structural type governs the depth distribution of deep shale, thus indirectly controlling the fracturing performance and resource potential. Deep shale gas layers at depth interval 3 500~4 500 m with a great fracturing performance primarily include those of the basin-margin-anticline and basin-margin-slope types, the resources of which accounts for a relatively small proportion. The ultra-deep reservoirs at depth exceeding 4 500 m are seen in these four types of structures, accounting for a large portion in resources. By combining the structural types, depth segmentation, estimated in-place gas, and engineering technology conditions, it is recommended that the deep shale gas reservoirs in the study area should be explored progressively in three stages: (1) targeting shale gas reservoirs of the basin-margin-anticline and basin-margin-slope types at depth interval 3 500~4 500 m for exploration benefit; (2) targeting shale gas reservoirs of the basin-margin-anticline, basin-margin-slope, and highly-steep-structure types at depth interval 4 500~5 000 m for exploration breakthrough; and (3) targeting shale gas reservoirs of the basin-interior-syncline type at depth interval over 5 000 m for exploration appraisal.

Key words: depth distribution, exploration target, structural type, deep shale gas, Wufeng-Longmaxi formations, southeastern Sichuan Basin

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