Coalbed Methane Reservoir Volume Transformation Mechanism In Low Temperature

Coal bed gas is a new type of energy,which has great development potential.However,due to the low permeability of coal bed gas reservoir,the characteristics of low porosity and low pressure,it leads to the difficulty of coal bed gas extraction.The efficiency of coal bed gas mining is reduced.The most commonly used hydraulic fracturing technology is not effective in the use of all coalbed methane reservoirs.In view of this situation,this paper introduces the refrigeration technology into the technology of coal bed gas reservoir reconstruction.The technology can effectively improve the production of coalbed methane in the process of coal bed gas production.To study the transformation mechanism of the freezing method to the coal bed gas reservoir and the influence of low temperature on coal and rock properties,which has important academic value and practical significance to enrich the theory of coalbed methane extraction.Inspection and sorting out the domestic and foreign relevant literatures and field test data,through COMSOL software using equivalent method to establish coal storage layer of low tempreture volume reconstruction in multi field coupling mathematical model,achieve the coal reservoir temperature field,stress field,seepage field distribution rule in the numerical simulation.By changing the relevant parameters in the process of the volume transformation of the low temperature,the influence of the main parameters on the temperature field,stress field and seepage field in the horizontal section and vertical section of the reservoir is obtained.Point out that the injection temperature,injection pressure and coalbed methane reservoir permeability change influence for the modification of the coalbed methane reservoir.Secondly,through the simulation of biaxial compression test,obtained the relationship between macro parameters and microscopic parameters of the coalbed gas reservoir under different temperature.Determine the microscopic parameter value of the coalbed gas reservoir mechanical properties at low temperature.With lower temperature,significant increase in the elastic modulus of coal and rock,the compressive strength and tensile strength increase,enhanced bonding force between the coal and rock particles,brittleness increased.Finally,the particle flow model under different temperature model was established by using PFC2 D software.Analysis of crack propagation rule and evaluate the effect of low temperature transformation of coal reservoir.Using this software simulate crack expansion and extension under the condition of different injection temperature,different injection pressure,non uniform horizontal stress and different porosity.The effect of injection temperature,injection pressure,initial horizontal stress porosity and other parameters on the volume modification of coal reservoirs is studied,and through the research of bottom hole pressure change curve,analysis of the relation between the fracture propagation in coal reservoir and the change of bottom hole pressure.Conclusions show that with the temperature is reduced,crack fracture pressure,primary and secondary cracks generated more,extension distance increases,but the temperature is too low,can lead to stress concentration,thus caused the collapse of coalbed methane reservoir,does not favor the crack extension.