Experimental Study On Improving CBM Production Capacity By High Temperature Heat Treatment

Most of the coalbed methane(CBM)reservoirs in China are characterized by low pressure,low gas saturation,low permeability and high adsorption characteristics,so "three low and one high" characteristics restrict the efficient production of CBM.At present,the classical theory and technical practice guiding the successful development abroad cannot be transplanted and applied to the tight coal bed reservoir in China.Formation heat treatment,which combined with complex functions of well completion,stimulation and enhanced oil recovery,has great potential.However,relevant knowledge is from the coal chemistry and chemical engineering,high temperature heat treatment for a specific temperature range in downhole,the behavior of adsorption,desorption,diffusion and permeability of CBM is not clear yet.Therefore,it is of great significance to explore and reveal the effect and mechanism of high temperature heat treatment on multi-scale mass transfer capability of CBM.Taking guizhou zunyi maple 2#coal well blocks in longtan group as the research object,carried out 50?,100?,200?,400?,600?,800? series of temperature heat treatment in helium,after heat treatment using isothermal adsorption experiment,seepage experiment,industrial analysis,scanning electron microscopy,acoustic time detection and nitrogen gas adsorption method,contrast after heat treatment of different temperature the adsorption quantity,permeability,surface microscopic morphology,acoustic time,composition,pore characteristics and rock mechanics properties.The characteristics of multi scale mass transfer capability of coal were evaluated.The mechanism of the influence of high temperature heat treatment on the mass transfer ability of coal and rock is revealed.The adsorption capacity and diffusion rate of coal rock were evaluated and its action mechanism was revealed.Coal was carried out isothermal adsorption experiment by different temperature heat treatment,and the diffusion rate of coals are based on pressure attenuation method,combining with the results of industry analysis and nitrogen adsorption after different temperature heat treatment,analyzed the heat treatment temperature on the absorption ability and the diffusion rate of coal.Studies show that 400? after heat treatment,the adsorption capacity and diffusion rate of coal has no obvious change;After 600? heat treatment,coal pore size and specific surface increases,adsorption and diffusion ability enhance;After 800?heat treatment,organic matter on block surface pyrolysis,the adsorption and diffusion capacity are weakened.The relationship between heat treatment temperature and fracture development and permeability of coal is revealed.In this paper,the experiment of core flow and the measurement of acoustic time difference are carried out to describe the macroscopic characteristics of the thermal fracture of coal,and the mechanism of the thermal treatment temperature is explained.The results show that the water evaporates after 100? heat treatment;After 200? heat treatment,interlayer water out;After 400 heat treatment,primary fracture initiation;After 600?heat treatment,the crack propagation was developed;After 800? heat treatment,mineral structure change,fracture network formatted.The mechanical properties of coal rocks after heat treatment were evaluated.Based on the rock elastic-plastic mechanics model,using nitrogen adsorption and acoustic measurements,quantitative evaluation after different heat treatment temperature of coal and rock elastic modulus,shear modulus and poisson's ratio of rock mechanics parameters.The experimental results show that with the increase of heat treatment temperature,the elastic modulus and shear modulus of coal rock decrease,and poisson's ratio increases.This thesis research provides an important theoretical support for high temperature heat treat of CBM well.It is clear that high temperature heat treatment can coordinate relationship between CBM desorption-diffusion-seepage of mutil scale mass transfer significantly.Based on this,the great significance of high temperature heat treatment in economy of CBM development,the optimization of well completion,and the effect of stimulation are discussed.