Digital Coal Reconstruct And Permeability Model Research By Considering The Fracturing Fluid Pollution

Coal samples have poor reservoir physical property and complicated microscopic structure in eastern Yunnan and western Guizhou.It has the characteristics of typical low porosity and low permeability.In general,its reservoir needs to implement fracturing operation to achieve economic output.But when fracturing operation transform the CBM reservoir at the same time it also can bring certain reservoir damage.It will make the seepage mechanism of coalbed methane complicated and thus affect the coalbed methane production.In order to quantitatively study in micro seepage characteristics of coalbed methane,it is very necessary to master the coal rock pore fissure structure of distribution,and rebuild coal digital image before and after the pollution to characterization coal microstructure of eastern Yunnan and western Guizhou area,so as to establish a set of theory system which can accurately describe coal permeability change before and after the pollution of fracturing fluid.In this article,we select coal samples from eastern Yunnan and western Guizhou to carry out coal damage experiment by different fracturing fluid,discuss damage mechanism of different fracturing fluid to different coal microstructure.We adopt different methods to reconstruct pores and fractures of digital coal respectively and analyze the characteristic of coal matrix pore and fracture structure change before and after fracturing fluid pollution.With the introduction of fractal theory,matrix pore and fracture fractal permeability model is established in the region with the use of reconstructed digital coal core,Finally,the permeability fractal model of pore and fissure is superimposed to establish overall permeability model of coal which can be used to predict the permeability of coal in the area.The results show that the error between overall permeability model and experimental value is small,so the overall permeability model can predict coal permeability more precisely.This research can lay a certain foundation for comprehensive evaluation of fracturing fluid to the influence of coal-bed methane.