Effect of Interference on Pressure Build-Up - A Method for Calculating Porosity-Thickness Product

Abstract

Abstract The purpose of this paper is to present the results of a theoretical study of the effect of interwell interference on pressure buildup in a shut-in well in multi-well reservoirs. An equation was developed which describes pressure buildup in a homogeneous, infinite reservoir of uniform thickness containing a single, mobile fluid which is slightly compressible. Using this equation, the pressure buildup in a shut-in well in a reservoir containing a number of offset producing wells was calculated on an electronic digital computer. For this study the offset wells had specified,, variable production rates. These computations illustrate the nature of pressure interference during pressure buildup tests. The study shows that offset producing wells can cause appreciable pressure drawdown at a shut-in well. The existence of interference does not obviate the use of the conventional Horner technique for estimating permeability and static well pressure from pressure buildup tests. A method is derived for calculating the average porosity-thickness product for a reservoir from a change in pressure interference which is induced by altering production rates of offset wells. Information required for this calculation includes the change in pressure interference, slope of the buildup curves, average fluid compressibility, well locations, and production histories of all wells. An analysis was made of the error in porosity-thickness product resulting from errors in pressure measurements and other factors required in the calculations. Introduction Pressure buildup tests have been used for a number of years to determine the static bottom-hole well pressure. More recently, these tests have also been used the average reservoir permeability in the drainage area of the shut-in well. Perhaps the most widely used method for interpreting pressure buildup data to obtain the static pressure and average permeability is the one proposed by Horner, based on the theoretical analysis of pressure buildup in a single well in an infinite reservoir.