The Estimation of Permeability and Reservoir Pressure From Bottom Hole Pressure Build-Up Characteristics

Abstract

Abstract This paper presents a simple and practical method for the estimation ofeffective permeability and reservoir pressures from the rise in bottom holepressure when a well is shut in. The equations on which the method is basedconsider a stabilized well producing from a uniform formation when flow is shutoff at the sand face followed by the unsteady state flow of a compressibleliquid from regions far from a well to points closer in during the build-upperiod. An approximation for extending the method for two-phase flow in thereservoir is also presented. In order to compare the effects of extremes in the conditions existing atthe external boundary of the reservoir, two general equations defining thebuild-up characteristics of the reservoir are shown: first, for a reservoirwith constant pressure maintained at the radius of drainage, and second, for areservoir with no influx over the radius of drainage. These equations definethe build-up characteristics for the shut-in well as functions of time, thepermeability and porosity of the drainage area, the viscosity andcompressibility of the fluid flowing, the production rate prior to shut-in, andthe radius of drainage of the well. When a well is shut in at the surface, rather than at the sand face, flowwill continue into the well bore after shut-in due to the compressibility ofthe fluids in the bore. The effect upon the build-up characteristics of thisflow into the well after shut-in has been studied by means of the electricalanalyzer. From the basic relationships and consideration of the limitations dueto continued flow after shut.in, methods have been developed for the estimationof the effective permeability of an area from the plot of the build-upcharacteristics of the well producing that area. T.P. 2849