Numerical simulation of hydraulic fractures propagation in multiple thin coal seams

The coal seams in eastern Yunnan and western Guizhou have the characteristics of vertical multi-layer lami- nation and the structural weak surfaces of the cleavage cracks are relatively developed. In previous research,the simu- lations of fractures propagation in multiple thin layers are mostly aimed at sandstone reservoirs,and the research on the influence of natural fractures on hydraulic fracturing is mostly aimed at shale and fractured sandstone. Therefore,there is a lack of systematic theoretical research on the propagation of hydraulic fractures in thin coal reservoirs with natural fractures,high Poisson’s ratio and low Young modulus. In this paper,a pseudo three dimensional fractures propagation model was established,considering the dynamic distribution of interlayer flow and the characteristics of cleat fracture development. Taking the coal reservoirs in eastern Yunnan and western Guizhou as an example,the propagation of frac- tures in each layer was simulated and analyzed. The research shows that the different distributions of natural fractures leads to the morphology of fractures in each layer having great differences;the width of fractures captured by natural fractures will decrease,and the risk of sand plugging will increase;the differences of liquid injection volume of each layer will be relatively small when the coal seam has a low Young’s modulus;for wells with determined perforated pa- rameters,the increase of the viscosity of fracturing fluid and the increase of the injection rate can reduce the difference of flow between layers,and then promote the full expansion of each seam length;the fractures height will be decreased by reducing the viscosity and injection rate of fracturing fluid.