The influencing factors of gas well productivity for volcanic gas reservoirs in Xushen gas field

Many development laws of volcanic gas reservoirs in the Xushen gas field,Songliao Basin,need further studies,and the production test wells showed complex characteristics of gas well productivity in volcanic gas reservoirs,hence,a better understanding of the main influencing factors of gas well productivity is the key issue for the successful development of this gas field.Therefore,we have done researches on the influencing factors from the macro and the micro aspects by adopting the data of geology,production testing,well testing and indoor core experiments.From a point of macroscopic view,the distribution range,structural locations and reservoir types of volcanic framc play roles on controlling the gas well productivity;the characteristics of small scale and multiple changes of volcanic facies result in a large variation in productivity and poor contrast between offset wells.From a point of microscopic view,the pattern,scale and petro-physical properties of the flowing area between the bottom hole and the formation have the effect on the gas well productivity,so the narrower flowing area and the lower formation coefficient make many wells' gas productivity decline rapidly;furthermore,the skin coefficient,special seepage characteristics(starting pressure gradient and stress sensitivity),and water breakthrough in gas wells influence the gas well productivity in various degrees.Besides,any possible accidents existing in production tests,such as fracturing fluid backflow,gas well cleanout period and testing time,may also lead to deviations on the recognition of well productivity.