西南石油大学学报(自然科学版) ›› 2017, Vol. 39 ›› Issue (4): 81-89.DOI: 10.11885/j.issn.16745086.2015.06.02.02

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The In-situ Stress Field Distribution Numerical Simulation of No.3 Coal Seam in the North of Fanzhuang CBM Well Blocks

YIN Shuai1, DING Wenlong2, GAO Mindong3, ZHOU Guangzhao4   

  1. 1. School of Earth Science and Engineering, Xi'an Shiyou University, Xi'an, Shannxi 710065, China;
    2. School of Energy Resources, China University of Geosciences(Beijing), Haidian, Beijing 100083, China;
    3. Shandong Xinwen Mining Group Co. Ltd., Xintai, Shandong 271219, China;
    4. School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China
  • Received:2015-06-02 Online:2017-08-01 Published:2017-08-01

Abstract: To develop effective measures for improving the fracture net of the No. 3 coal seam in the northern Fanzhuang wellblocks, we analyzed Permo-Carboniferous strata tectonic patterns and fault characteristics of the CBM well blocks using 2-D seismic data. Accordingly, the stress field characteristics of the No. 3 coal seam in the Shanxi Formation were analyzed using multiple approaches, including the fracturing method, image logging, and finite element simulation. The results show that values of the three principal stresses follow the order σH > σv > σh; they all increase with depth. σv shows the largest stress gradient of about 0.025 MPa/m, followed by σH, at about 0.018 MPa/m, and σh at about 0.013 MPa/m. The values of σH and σh of the No. 3 coal seam are slightly higher than those in the sand/shale formation of the roof and floor by about 1.0-2.5 MPa, leading to the formation of a fracturing wear layer and making fracture height control difficult. The values of σH-σh are mainly distributed in the range of 2.0-6.0 MPa. This is also the main cause for the high fracturing effect and gas production of the relatively shallow No. 3 coal seam. The imaging logging induced fracture analysis shows that the in-situ stress direction in the study area is located between SN and NNE, which is associated with the Himalayan middle-late tectonic compression movement. The complex local structure characteristics and the existence of faults can result in a change in this direction. Results from finite element simulation of the study area show that the stress plane distribution characteristics are dominated by multiple factors such as buried depth, lithology, folds, and faults. The values of σH and σh of the No. 3 coal seam from simulation are distributed between 15.6-21.0 MPa and 12.5-16.0 MPa, respectively, and are consistent with the measured results.

Key words: Fanzhuang wellblock, CBM, Shanxi Formation, No.3 coal seam, stress, finite element, numerical simulation

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