Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (3): 474-483.doi: 10.11743/ogg20200304

• Petroleum Geology • Previous Articles     Next Articles

Characteristics of natural fractures in marine shale in Fuling area,Sichuan Basin, and their influence on shale gas

Tian He1,2, Zeng Lianbo1,2, Xu Xiang1,2, Shu Zhiguo4, Peng Yongmin3, Mao Zhe1,2, Luo Bing4   

  1. 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China;
    2. College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China;
    3. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;
    4. Research Institute of Exploration and Development of Jianghan Oilfield Branch Company Ltd., SINOPEC, Wuhan, Hubei 430223, China
  • Received:2019-05-15 Revised:2020-04-06 Published:2020-06-16

Abstract: Fractures of various types show different impacts on shale gas enrichment and preservation.Therefore,categorized evaluation and prediction are quite necessary in studying the natural fractures in shale gas reservoirs.A wealth of outcrop,coring and thin section observation,as well as FMI logging interpretation is applied to the discussion of the genetic types,development characteristics,and main controlling factors of natural fractures in marine shale,and the impact of various types of natural fractures on shale gas enrichment and preservation in the Wufeng-Longmaxi Formations,Fuling area,Sichuan Basin.The natural fractures in the study area can be divided into tectonic,diagenetic and abnormally high-pressure fractures in terms of geological origin.In turn,the tectonic fractures can be subdivided into intra-layer aperture fractures,cross-layer shear fractures,layer-parallel shear fractures,whereas diagenetic fractures mainly include lamellar fractures and constricted fractures.The shale formation of the study area is dominated by tectonic and lamellar fractures.The development of tectonic fractures is mainly controlled by structural position,rock mechanical stratigraphy thickness and brittle mineral content.While the development of the lamellar fractures is determined by laminae development,brittle mineral content,abnormal high pressure in fluids,and content and thermal evolution stage of organic matter.Natural fractures of various origins have different influence on shale gas.The aperture fractures and lamellar fractures developed within the shale formation are small in scale,providing better reservoir space for shale gas accumulation.The larger-scale cross-layer shear fractures and layer-parallel shear fractures mainly impact the preservation conditions of shale gas.The underdevelopment of constricted and abnormally high-pressure fractures provides poor effective porosity and thus has little influence on shale gas enrichment and preservation.

Key words: rock mechanics, preservation condition, shale gas, tectonic fracture, diagenetic fracture, Wufeng Formation, Longmaxi Formation, Fuling area, Sichuan Basin

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