Control of medium- to small-scale tectonic deformations on fracture development in Longmaxi Formation shale
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ORIGINAL PAPER
Control of medium- to small-scale tectonic deformations on fracture development in Longmaxi Formation shale Jilin Wang 1,2 & Huihuang Fang 2 & Yunpeng Gong 3 & Yan Zou 2 & Jiegang Liu 1,2
Received: 31 December 2015 / Accepted: 20 December 2016 # Saudi Society for Geosciences 2017
Abstract This study conducted a detailed geological survey and experimental analysis on the area of Golden Buddha Mountain syncline of Nanchuan, Chongqing, to examine the development characteristics and mechanism of fractures in Longmaxi Formation shale. Results showed the following: The width of the microfracture of the Longmaxi Formation shale in the research area ranges from hundreds of nanometers to hundreds of micrometers. The percentage of the shale fracture is high if width is small. The dominant strikes of joints and microfractures are consistent overall, which are the WNW, NW–NWN, NE, and NE–ENE directions. The shale shows that the density and width of the fracture and the permeability in the core of the syncline are larger than those in the wing are. The following conclusions were drawn. (1) Regardless of size, the mechanical origin of fracture is controlled by tectonic deformation. (2) During the Early Yanshanian (J3–K1) Period in the research area, a series of WNW shear fractures, NWN shear fractures, and NW tensile fractures were formed by strong squeezing effect with the NW–SE trending. During the Late Yanshanian–Himalayan Period, the tectonic stress was mainly presented as extrusion with the NE–SW trending and the NW–SE trending stretch, and a series of NE–ENE shear fractures and NE tensile fractures were formed. (3) Medium- to small-scale tectonic
* Jilin Wang [email protected]
1
Key Laboratory of CBM Resources and Reservoir Formation Process, Ministry of Education China University of Mining & Technology, Xuzhou 221008, China
2
School of Resources and Earth Science, China University of Mining and Technology, Xuzhou 221116, China
3
Chinasalt Jintan Co., Ltd, Jintan 213200, China
deformations exert dominant control effects on the fracture development of Longmaxi Formation shale in the research area. (4) A fracture network consists of joints and microfractures in shale in different scales. The finer the microfractures, the denser they grow. Keywords Shale . Fracture . Tectonic deformation . Longmaxi Formation
Introduction Fractures in a shale reservoir mainly exist in the form of microfractures and gradually form a complicated large-scale fracture network system (Yang et al. 2013). Shale gas not only can be stored in natural fractures and intergranular pores in a free state but also can be absorbed on the surface of kerogen and clay particles or dissolved in kerogen and pitch. The development of natural fractures is one of the main factors that control the formation of shale gas (Nie et al. 2009; Wang et al. 2010). The fractures in shale constitute the reservoir of shale gas in the free state and the main channel of gas flow in a shale gas reservoir. The development of fracture determines the producti
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