Mechanism And Effect Evaluation Of Commingled Production Of CBM Reservoir And Tight Gas Reservoir

Coalbed methane(CBM)reservoirs and tight gas have exploitation potential in X block.It is necessary to search the co-production adaptability and effect of CBM reservoirs and tight gas reservoirs,in order to improve the recovery efficiency of unconventional gas reservoirs and exploit unconventional natural gas resources efficiently.Firstly,this paper analyses gas production mechanism of CBM reservoirs and tight gas reservoirs respectively.Interference mechanism of combined prodution is further studied to make foundations of demonstrating the adaptability of CBM and tight gas combined produciton.Secondly,through combining the pressure propagation model,gas and water productivity equations,material balance equations with wellbore pressure drop model,the coupled gas production model of CBM and tight gas reservoirs is established,and the dynamic analysis software of commingled production is programmed.Then,based on the three dimensions of geological,engineering and drainage factors,the sensitivity factors affecting the co-production of CBM reservoirs and tight gas reservoirs are studied by single factor and orthogonal test multi-factor sensitivity analysis method,and the key influencing factors are obtained,which provides a reference basis for the optimization of commingled production parameters.Finally,by employing the software,the production effects of two combined CBM reservoirs and combined CBM /tight gas reservoirs are compared and analyzed,and the optimal development scheme of multi-reservoirs combined prodcution is determined.The results show that CBM reservoirs and tight gas reservoirs are suitable for co-production,because backfilling is difficult to occur when the lowest pressure at the pump suction exists and the influence of start-up pressure gradient and capillary force are included.Permeability ratio,initial water saturation,production layer thickness,fracture half-length and supply radius are the key factors affecting the combined production effect.When the gas reservoir supply radius is 200 m,the fracture conductivity is higher than 200-300 m D·m.The casing pressure threshold is 1.5-1.7 MPa,the production effect is the best.The combined production and separate production of the two CBM reservoirs will not affect the ultimate recovery rate,but the combined production greatly shortens the mining time,which reduce the cost and create huge economic benefits.There is a little differences between the combined production and separate production of upper CBM reservoirs and lower tight gas reservoirs,but the combined production of upper tight gas reservoirs and lower coal reservoirs is better than the single production.This paper provides a theoretical basis for the scheme formulation of commingled production test wells of CBM reservoirs and tight gas reservoirs in block X,and provides decision-making basis for whether and how to combine production of similar gas reservoirs.