Pressure Transient Behavior of the Composite Reservoir

ABSTRACT The composite reservoir, representing a variety of important reservoir configurations, has been studied using a semi-analytical method to determine the characteristics of its pressure transient response. This study extends the work of a previous semi-analytical study1 whose primary concentration was on the pressure transient response in the "altered zone", the zone nearest the wellbore. Important conclusions regarding the nature and duration of the transition period between the altered and unaltered zones are given. This study also presents information which corrects conclusions given in a previous study2 done with a numerical simulator. Specifically, this study shows that the slope of the semilog straight line representing the unaltered zone is independent of the storage ratio. The study presents equations for calculating mobility in the altered and unaltered zones, for calculating the radius of the altered zone using traditional graphical analysis of well test data and for calculating the skin factor.