Material Balance Equation in Geopressured Reservoirs

Abstract

A material balance equation (MBE) is developed for geopressured reservoirs which takes into account the water and rock expansion and pore volume reduction as pressure declines in the reservoir. Data from a typical geopressured reservoir was used both in the MBE and in a four component, three dimensional reservoir simulator developed by ARCO Oil and Gas Co. which was modified for use in a geopressured reservoir. Few example problems for different critical gas saturations are presented. The results of the proposed MBE are within 4% of those predicted after 27 years of production by the reservoir simulator. Ignoring the rock and fluid compressibilities reduces the new MBE to the one introduced by schilthuis. Using schilthuis equation in a geopressured reservoir gives misleading result of up to 7 times higher gas and water in place, or much lower recovery factors.