Dynamic Inversion And Application Research Of Water-producing Gas Wells In Tight Gas Reservoir

Nowadays,caused by pore water,increasing number of gas wells in tight gas reservoir is struggling with water producing problem,the determination of formation and fracture parameters of these wells is the key and difficult point in the development of gas reservoir.However,due to the particularity in formation and flow condition,some complex seepage mechanics exist in tight gas reservoir two-phase flow,which would challenge the dynamic inversion method for these wells.Therefore,aiming at solving key points and difficulties in inversion process,this paper comprises the theory and methods in petroleum engineering as well as applied mathematics to carry out research on inversion method for water producing gas wells in tight gas reservoir.Firstly,the seepage mechanics for gas-water flow in tight gas reservoir are concluded based on the producing practice and literature investigation.Then,the stress-sensitivity of relative permeability curve together with absolute permeability stress-sensitivity,slippage flow,is taken into account to construct mathematical model.Compared with traditional model which ignore complex seepage,this model could be used to describe the gas-water flow in tight gas reservoir better.Then,the mathematical model above is solved to obtain numerical model to provide technical guarantee for dynamic inversion.Based on the numerical model,the flowing pressure characteristics of fractured water producing gas wells with complex seepage mechanics are analyzed,the influencing factors are also been investigated.This work shows that the complex seepage mechanics and water producing phenomenon would lead to the difference between the pressure derivative plots of water producing gas wells and conventional wells.For example,under the influence of relative permeability curve stress-sensitivity,the pressure derivative plot would shift upward or downward,and the production indexes would also been changed.Therefore,traditional model could not be used to match the pressure derivative plot and production data,while the numerical model considering complex seepage mechanics built in this paper could be used in the dynamic inversion process.Meanwhile,aiming at the difficulties in flow regime determination caused by the shift in pressure derivative plot,the gas-water two phase flow mathematical model for tight gas reservoir is solved by semi-analytical method.By introducing pseudo-parameters considering complex seepage mechanics,the analysis equations for typical flow regimes,such as formation linear flow,pseudo-radial flow and boundary dominated flow,are derived.And the determination equations for initial absolute permeability,fracture half-length and gas reserve are obtained.The work above could be used to diagnose and analysis the flow regimes,and together with relationship between parameters and analysis curve to determine the formation/fracture parameters.Finally,two dynamic inversion methods are proposed based on numerical model and flow regime analysis equations above,respectively.Especially,for the flow regime analysis method,the calculation procedure for pseudo-parameters considering complex seepage mechanics is modified by the concept of equivalent relative permeability curve.Then,the inversion methods based on the numerical model and the flow regime analysis equations are combined to obtain a comprehensive dynamic inversion technology,which comprises flow regime analysis,history match for log-log plot and history match for production data.Finally,examples are analyzed to validate this technology.In conclusion,this paper takes complex seepage mechanics including relative permeability curve stress-sensitivity into consideration,and comprises seepage model construction,pressure response analysis,dynamic inversion method investigation and example validation to obtain comprehensive dynamic inversion technology,which could be used to determine the formation and fracture parameters.