Productivity equation and influencing factors of co-producing coalbed methane and tight gas

Coalbed methane,tight gas and shale gas(three gases) occurred in coal bearing strata are rich in resources and achieving a co-production from one well bore will significantly improve the resource recovery rate and economic benefits. However,the flow state of gas and water under the co-production process are still unclear. In this paper,a two layered gas reservoirs model in fractured vertical well was firstly established using the equivalent seepage theory. The production equation was proposed and the factors influencing the production rate during the gas drainage and gas-water co-producing rate was also analyzed. The results show that:the multi-layer linear seepage equation is established by re- ferring to the parallel principle,and the reasonable production pressure difference can also be acquired;during the wa- ter drainage period,the smaller the physical compressibility is,the higher the water production rate,and the higher the pressure difference is;the flow discharge radius and the initial permeability affect the water production rate,but show little influence on reasonable pressure difference;during the gas and water co-production period,the initial permeabili- ty and Langmuir stress constant have some influence on reasonable pressure difference,however,the coal compressibil- ity,fracture diversion ability and elastic modulus have little effect on pressure difference determination. The results are of significance in clearing the flow process of gas and water,conducting production analysis,and establishing reasona- ble drainage system.