Study On In-situ Stress Condition Of Coal Reservoir And Effects On CBM Well Production In Yanchuannan Block, Ordos Basin

The in-situ stress is a key factor affects permeability of coal reservoir and the production of coalbed methane (CBM) well. Coal bed methane development geology, rock mechanics, percolation mechanics and other multi-disciplinary theories were comprehensively used, according to the reality of Yanchuannan block in the Ordos Basin, through the methods of experimental analysis, theoretical study and numerical simulation, the fracture development features and its coupling relations and the distribution and evolution of tectonic stress field of coal reservoir at Yanchuannan block were analyzed. The structure in-situ stress field include two stages since Mesozoic. The frist is obvious and Maximum extrusion stress direction is NW-SE.The second stage Maximum extrusion stress direction is NE-SW.According to the test data of CBM exploration and development wells, the magnitude, direction and stress state of current in-situ stress and the distribution of coal reservoir pressure and permeability were systematically analyzed. Below1000m depth,the in-situ stress condition of coal reservoir is σv>σhmax>σh min and the minimum principal stress less than16MPa. Above1000m depth,the in-situ stress condition of coal reservoir is σhmax≥σhmax≥σhmin and the minimum principal stress more than16MPa.The correlations and their models between current in-situ stress and coal reservoir permeability were established according to analysis of stress sensitivity test, the dynamic variation of coal reservoir permeability in the process of CBM production was revealed. Coal reservoir permeability depend on the strength and condiction of in-situ stress.Permeability reduce with effective stress in terms of negative exponent.The exploration area is favorable which buried depth below1000m, tension in-situ stress condition.Based on the analysis of in-situ stress, combined with well test dynamic data, the influence degree of coal reservoir stress to CBM wells production was analyzed which provide scientific basis for Sinopec CBM exploration and development. The coal reservoir stress sensitivity have great influence with coalbed methane (CBM) well production. with the increase of drawdown pressure, gas well production increase amplitude is lesser, and gradually tend to be stable.