The Study On Physical Properties And Recovery Law Of Production Of Zhengzhuang Coal Bed Methane Reservoir

As a clean and high quality substitute energy,coal bed methane has gradually been the world’s general attention.The benefit development of high rank coal bed methane has already been realized in China,but low average gas production per well is still the biggest problem that restricts the efficient development of coalbed methane.At present,the low gas production of CBM wells,large total water production,the long desorption time before production,low gas-to-water ratio,so that,the development of coalbed methane has not come up to the expectation in Zhengzhuang block.Experimental study on gas-water two-phase percolation and coalbed methane production,and the establishment of gas-water two-phase fluid-solid coupling mathematical model in coal seam,that can provide technical support for the optimization of high-efficiency production area.In this paper,by core sampling of coal seam,wire cut sample preparation,and formation Water preparation,The tests of porosity and permeability,stress sensitivity,adsorption-desorption and depressurizing coal bed methane production were carried out.Experimental studies have shown,porosity distribution range of coal is in between0.483%-5.58%,and mostly in between 3%-5%;intrinsic permeability distribution range of coal is in between 0.0059×10^-3-1.13×10^-3μm²,and mostly in between 0.03×10^-3-0.8×10^-3μm².the stress-sensitive damage degree of coal bed is about 51.59%,it is moderately strong stress sensitive.Adsorption-desorption experiments show that the coal is in an unsaturated state,the gas saturation of 3#coal and 15#coal are of 86%and 78%.The experiment of depressurizing coal bed methane production shows that there have different production laws of coalbed methane with different depressurization producting methods.The direct depressurization method has high initial gas production and low final yield;the continuous depressurization method has low initial gas production but high final yield.On the basis of experimental research,the paper aims at the characteristics of multi-scale pores and fractures in coal reservoir,a coupled simulation method of bedrock-micro-fracture hydraulic fracture is established:the characterization of bedrock and micro-fractures is based on the dual-medium model,and the embedded discrete fracture model is used to simulate the hydraulic fracture.A complete gas-water two-phase fluid-solid coupling model of coalbed methane reservoir is formed,using the gas-water two-phase percolation model and the reservoir stress model early established respectively.Using the finite-volume method discrete percolation equation and discrete stress equation of stable extended finite element;then the discrete seepage equation and stress equation is solved by Newton-Raphson iterative method;finally,the numerical solution is obtained by iterative coupled algorithm.The deterministic validation of the fluid-solid coupling model is carried out,the history of drainage and gas production is fitted by actual coalbed methane reservoir,and the optimum parameters of coalbed methane drainage and production are determined.