Multi-reservoir production damage physical simulation system and its application in coal-measure gas production

Coal measures are thin and stacked on top of each other.It is objectively impossible to avoid a combined mining in fracturing operations.The operators subjectively hope that the combined mining can solve the problem of high yield in a single layer.However,the factors that affect the productivity of coal measure reservoirs are very complicated,and some traditional methods cannot quantitatively analyze the damage degree of combined mining.Diagnosis and prevention require a simulation system to provide the original measurement data of fluid flow characteristics.Therefore,aiming at the problem that it is impossible to measure the combined production permeability of coal measures,the physical simulation system of multi-reservoir mining damage based on “equivalent gas well production” is introduced to test the production and pressure of any layer and any mining method in the process of coal measures mining under the environment of reservoir pressure and temperature,and the idea of production damage evaluation is put forward.The application demonstrates that ① the gas flow damage before and after any reservoir damage can be well consistent with the permeability damage.Therefore,the reservoir damage flow method is proposed to replace the permeability method for production damage evaluation in order to solve the problem that the coal measures gas production layer length and flow area cannot be selected and the permeability cannot be obtained.② Taking the flow rate and pressure of commingled production test as the boundary conditions,the flow state of natural gas in different producing layers after mixing in the wellbore is numerically simulated.The calculation model of entropy production in the formation and wellbore during the commingled of coal measures gas is established based on the perspective of energy.It is found that the energy loss of gas flow leads to the decrease of gas production in coal measures,and the “gas mixing damage” is proposed as a new type of reservoir production damage.③ The flow rate method is used to evaluate the flow rate change rate of equal pressure before and after the damage of working fluid,and the suitable drilling and completion fluid for Linxing coal measure is selected.The results show that the physical simulation system of multi-reservoir gas recovery can systematically support the analysis of reservoir sensitivity types and degrees,mechanism research,and working fluid optimization during coal measure natural gas mining,providing a method and basis for the optimization of coal measure gas co-production and the formulation of measures to increase the production.