Research And Application Of Diagnostic Fluid Injection Test Method For Shale Gas Reservoir

Due to the lithologic density,low porosity and ultra-low permeability of shale formations,most shale gas wells need to use volumetric fracturing technology to obtain shale gas production.However,before the volume fracturing construction,it is necessary to obtain reliable shale formation physical parameters and mechanical characteristics parameters.At present,relying only on logging data interpretation and indoor core experimental analysis,it is difficult to obtain real properties of the formation.Therefore,the diagnostic fluid injection test technique(DFIT)provides a new idea for interpretating and evaluating formation parameters and far-well fracture parameters.The pressure drop test data is used to identify gas well flow patterns,and the method of predicting fracture extension and formation parameters are obtained.Based on a large number of literatures and the analysis theory which is before fracture closure,a numerical difference method was used to solve the seepage model for shale gas well diagnostic fluid injection test in this paper.The shale formation pressure was solved and pressure curves were drawn.The descending derivative and the pressure derivative double logarithmic curve are used to analyze flow patterns of the shale gas well after the fracture is closed according to the slope of the curve tangent,which provides a theoretical basis for the fracture and formation parameters.In this paper,the G-function pressure drop interpretation method for shale reservoir fracture closure is studied,the G function characteristic curve fitting method is proposed and the fracture closure parameters are obtained.Further,by introducing the F-function after fracture closure,a method for interpretation of formation parameters including Ffunction characteristic curve fitting method is proposed.Finally,a set of interpretation module for shale reservoir pressure drop data was developed to explain the data of the actual shale gas well from diagnostic fluid injection test,small test fracturing and main fracturing pump.The interpretation results from the module were compared with Meyer commercial software simulation results and microseismic monitoring data to verify the applicability of the module in shale reservoir pressure drop test analysis.