Study On Equivalent Heat Conduction Physics And Numerical Simulation Of Exploitation Of CBM By Vapor Injection

In view of the engineering phenomenon of low gas production and low gas production speed caused by the characteristics of "high adsorption and low permeability" of coalbed methane in China,Taiyuan University of technology proposed a new method to strengthen the coalbed methane exploitation,that is,injecting steam into the coal seam to heat the coal seam and promote the desorption of adsorbed methane gas,so as to increase the production efficiency Increase gas production rate and gas production rate.In this method,it is very important to study the migration of steam and the change of temperature field.The change of coal seam temperature field is mainly caused by heat conduction and convective heat transfer,but the analysis considering the two is more complex,especially for the engineering field personnel.Therefore,this paper obtains the variation law of equivalent heat conduction coefficient through experimental calculation,establishes the equivalent heat conduction Coal model,analyzes the gas production rate and gas production rate of coalbed methane,and obtains the following conclusions:(1)The temperature rise law of the measuring point on the non-prefabricated fracture surface of lean coal and anthracite is different.For lean coal,although the temperature of the measuring points at the prefabricated fracture surface and the non-prefabricated fracture surface also has obvious periodicity,and its periodicity is similar to that of the temperature change on the fracture surface,the distribution and connectivity of the original pores and fractures at each point in the lean coal body are uneven,The time of steam entering two measuring points and the temperature of steam arriving at two measuring points are not the same,which leads to the different proportion of heat conduction and convective heat transfer in the heating process of meager coal measuring points.This is the reason why the temperature variation law of meager coal measuring points in the same layer is not similar.However,the temperature rise of anthracite non prefabricated fractured coal mainly depends on heat conduction,so there is no stage.(2)The temperature rise law of the measuring point on the non-prefabricated fracture surface of lean coal and anthracite is different.The temperature rising process at the measuring point on the non-prefabricated fracture surface of lean coal also has obvious stages,and its stages are similar to those on the fracture surface.In addition,the distribution and connectivity of the original pores and fissures at each point in the lean coal body are not uniform,which makes the time that steam enters into the two measuring points and the temperature when it arrives at the measuring points not the same,which leads to the different proportion of heat conduction and convection heat transfer in the process of temperature rise of the lean coal measuring points,which is the reason why the temperature change law of the same layer of lean coal measuring points is not similar.However,the temperature rise of anthracite nonprefabricated fractured coal body depends on heat conduction,and there is no stage.(3)The equivalent heat conduction coefficient is used to describe the strong and weak effect of steam heat conduction to coal body.In the range of room temperature-190 ?,the equivalent heat conduction coefficient of anthracite parallel bedding direction is(0.31-0.00012*T)w/(m*k),and the equivalent heat conduction coefficient in vertical bedding direction is(0.27-0.00043*T)w/(m*k).The development of cracks also affects the size of the equivalent heat conduction coefficient.The more the cracks develop,the greater the equivalent heat conduction coefficient.(4)Before high temperature steam injection,the permeability of anthracite parallel to the bedding direction is slightly greater than that of anthracite vertical to the bedding direction,and the permeability increment of anthracite parallel to the bedding direction is greater than that of anthracite vertical to the bedding direction after high temperature steam injection.The higher the final temperature,the greater the increase of permeability,and the fitting relationship between them can be described by exponential function.(5)In the steady-state heat transfer stage,the permeability of anthracite still changes,and the change rules are different at different temperature positions and different distances from the prefabricated fracture surface.The higher the temperature is,the larger the permeability change proportion is in the unsteady heat transfer stage,while the lower the temperature is,the smaller the permeability change proportion is in the unsteady heat transfer stage To be lower than the proportion of permeability change in steady-state heat transfer stage.(6)Compared with the conventional exploitation,the annual gas production of coal-bed methane produced by hot steam injection increased significantly.At the same time,the pore pressure of coal-bed methane produced by hot steam injection decreased faster than that produced by conventional exploitation.In the whole production period,the total gas production of the former is nearly doubled,which has significant engineering effect.Due to the existence of hydraulic fracture,the equivalent thermal conductivity at the fracture is different from that without fracture.The temperature of the coal above and below the fracture first rises,the heating area of the coal seam increases,and the overall temperature rise of the coal seam is faster.