| مستخلص: |
Adopted hydraulic fracturing method to measure in-situ stress, obtained in-situ stress of 26 coalbed methane wells in Southeast margin of Ordos Basin. Through statistical analysis, the correlations and their models between in-situ stress of No. 2 coal seam in Shanxi Formation of Permian and the burial depth of coal seam were established, the distribution law of present stress and its controlled mechanism were revealed. The results show that the average value of the fracture pressure gradients, closure pressure gradients and coalbed reservoir pressure gradients of the No. 2 coal seam in Shanxi Formation of Permian in study area are 1.96, 1.69, 0.71 MPa/100 m, respectively. Coalbed reservoir stress (the maximum horizontal principal stress, the minimum horizontal principal stress, the vertical principal stress ) and the coalbed reservoir pressure both increases linearly with the increasing of the burial depth. The coalbed reservoirs with a burial depth lower than 1 000 m, in-situ stress state principally shows σv > σ >hmax > σhmin, the minimum horizontal principal stress is below 16 MPa, the recent in-situ stress state is tension; the coal reservoir effective stress coefficient equals to 0. 48, lower than the parameter of shales in oil gas basin, which is 0. 80 generally. In-situ stress state of coalbed reservoirs with a burial depth deeper than 1 000 m transforms into σhmax ≥ σv ≥ σhmin, the minimum horizontal principal stress is bigger than 16 MPa,the in-situ stress state transforms into compression. The present in-situ stress is controlled by the regional tectonic stress field of North China, the maximum horizontal principal stress direction is mainly in the NEE-SWW direction. The coal reservoir pressure in the study area is lower, coal reservoir pressure under the conditions of the same depth in southeast margin of Erdos basin is lower 0. 73 -0. 93 MPa than southern Qinshui basin. Coal reservoir stress has positive correlation to the recent stress. As stress increases, the coal reservoir stress increases. [ABSTRACT FROM AUTHOR] |