Pressure Maintenance and Model Studies

Abstract

AbstractPressure maintenance programs play an important role in the efficient and economical recovery of oil and gas. For this reason, it is advantageous to consider carefully all of the factors involved in the design of an efficient pressure maintenance program. The purpose of this article is to (1) review the methods of evaluating past reservoir performance and predicting future performance for various proposed plans of pressure maintenance operations, and (2) discuss the use of potentiometric model studies in designing pressure maintenance programs. The following aspects of model studies are discussed at length: (1) purpose of model studies, (2) how model studies are carried out, (3) technique employed in the construction of potentiometric models, (4) sweep patterns and how they are obtained from a potentiometric model, and (5) model data and how it is used in evaluating a pressure maintenance waterflood program. Since the ultimate recovery of hydrocarbons under certain pressure maintenance programs will depend on how the injected water, gas or other types of fluid will sweep the reservoir, it is concluded that model studies can play a very important part in evaluating various proposed plans of operation, in determining the best locations for injection wells, in determining the proper distribution of injection between wells and in picking locations of producing wells which would increase ultimate recovery and profit.How Are the Injection Requirements for Pressure Maintenance Programs Determined?The first signs of reservoir trouble generally are detected from a study of the reservoir behavior after the field has been developed and produced. Rapidly falling reservoir pressures, increasing gas-oil ratios and increasing water production may be the first indicators of trouble. One of the best recognized and most important tools for studying the past performance of a reservoir is the material balance which is discussed abundantly in the literature. Digital computers and electronic reservoir simulation are used for the prediction of future performance of the reservoir under various operating conditions. From these studies, the future needs for the pressure maintenance program can be determined. In other words, how much injection is needed to maintain the pressure at the desired level, or to stop shrinkage or expansion of the gas cap, and how much natural water influx, if any, may be experienced in the future for the different plans of operation?