Oil & Gas Geology ›› 2024, Vol. 45 ›› Issue (6): 1640-1652.doi: 10.11743/ogg20240611

• Petroleum Geology • Previous Articles     Next Articles

In-situ stress in deep coal seams and its control on reservoir physical properties in the Jiaxian area, Ordos Basin

Pengwei MOU1,2(), Peijie LI3, Yanbin YAO1,2,4,5(), Dameng LIU1,2,4, Limin MA3, Xiaoxiao SUN1,2, Yongkai QIU1,2   

  1. 1.School of Energy Resources,China University of Geosciences (Beijing),Beijing 100083,China
    2.Coal Reservoir Laboratory of National Engineering Research Center of CBM Development and Utilization,Beijing 100083,China
    3.Jidong Oilfield Company,PetroChina,Tangshan,Hebei 063000,China
    4.Deep Time Digital Earth Frontier Science Center,Beijing 100083,China
    5.Shanxi Center of Technology Innovation for Coal Measure Mineral Resources Comprehensive Exploration,Taiyuan,Shanxi 030006,China
  • Received:2024-07-23 Revised:2024-08-31 Online:2024-12-30 Published:2024-12-31
  • Contact: Yanbin YAO E-mail:moupengwei@163.com;yyb@cugb.edu.cn

Abstract:

JThe Jiaxian area emerges as a new target for the exploration and development of deep coalbed methane (CBM) in the Ordos Basin. However, the lack of studies on its in-situ stress and the undefined relationships between the in-situ stress and the physical properties of coal seams have hindered efficient CMB production in this area. Using data from logging and core analysis, we develop a logging-based in-situ stress calculation model as constructed by the combined spring model, investigate the in-situ stress distribution in the area and explore the controlling effects of in-situ stress on the fissures, porosity, and permeability of coal reservoirs. The results indicate that the planar distribution of the in-situ stress in the No. 8 coal seam within the Jiaxian area features high in the west and low in the east. The three principal stresses decrease in the order of vertical principal stress (averaging 56.72 MPa), maximum horizontal principal stress (averaging 41.08 MPa), and minimum horizontal principal stress (averaging 37.77 MPa), suggesting a normal-faulting stress regime. The No. 8 coal seam has an average coefficient of lateral pressure of 0.70, indicating that this coal seam resides in a tensile setting overall, which creates favorable conditions for the formation of tensile fissures. The relationships between the reservoir physical properties and various in-situ stress parameters indicate that the physical properties of the No. 8 coal seam in the study area result from the combined effects of the three principal stresses, in which the horizontal principal stress play a predominant role. The porosity and permeability of the coal reservoirs trend downward with an increase in the lateral pressure coefficient and a decrease in the horizontal principal stress difference. The test results of deep CBM content in the study area indicate that the lateral pressure coefficient and the horizontal principal stress difference are reliable indicators of the physical properties of coal reservoirs, establishing them as effective tools for identifying the geologic sweet spots of deep CBM.

Key words: porosity, permeability, lateral pressure coefficient, in-situ stress, deep coalbed methane (CBM), Jiaxian area, Ordos Basin

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