Numerical simulation of the in situ stress in a high-rank coal reservoir and its effect on coal-bed methane well productivity

In situ stress has an important influence on coal reservoir permeability, fracturing, and production capacity. In this paper, fracturing testing, imaging logging, and 3D finite-element simulation were used to study the current in situ stress field of a coal reservoir with a high coal rank. The results indicated that the horizontal stress field within the coal reservoir is controlled by the burial depth, folding, and faulting. The σH and σh values within the coal reservoir are 1–2.5 MPa higher than those within the clastic rocks of the roof and floor. The σH–σh values of the coal reservoir are generally between 2 and 6 MPa and increase with burial depth. When the σH–σh value is less than 5 MPa, production from a single well is high, but when the σH–σh value is greater than 5 MPa, production from a single well is low. In addition, the accumulated water production is high when the σH–σh value is greater than 5 MPa, demonstrating that a higher σH–σh value allows the hydraulic fractures to more easily penetrate the roof and floor of the coal seam. In coal-bed methane development regions with high σH–σh values, repeated fracturing using the small-scale plug removal method — which is a fracturing method that uses a small volume of liquid, small displacement, and low sand concentration — is suggested.