The Material Balance Approach vs Reservoir Simulation as an Aid to Understanding Reservoir Mechanics

Abstract

American Institute of Mining, Metallurgical and Petroleum Engineers Inc. This paper was prepared for the 45th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Oct 4–7, 1970. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract Recent years have witnessed great strides in reservoir simulation techniques. Numerous reservoir simulators have been developed, and are being employed in comprehensive reservoir production optimization studies. With increased emphasis on total simulation employing mathematical models, one cannot help wondering whether the classical material balance methods are passe. The present article attempts to demonstrate the value of material balance type studies as aids to gaining an understanding of oil reservoir behavior. The generality of the material balance approach is discussed, that is, the employment of a single material balance equation, but in certain prediction calculations, different saturation equations prediction calculations, different saturation equations for different combinations of the basic oil production processes, i.e. gas cap expansion (with production processes, i.e. gas cap expansion (with gravity segregation, with or without counterflow), solution gas drive, and water drive. Limitations of this method, as well as certain complicating features are pointed out. Both integral and differential forms of overall material balances are discussed, and some of the basic characteristics of each, which are often overlooked, are brought out. The value of the material balance approach vs. numerical simulation is discussed, and the chief advantages of each technique are pointed out using specific examples. It is suggested that the material balance approach, presented with the unified concept proposed here, will continue to be of value in gaining a basic understanding of oil reservoir production processes, and their mutual interactions. Introduction The most important development in petroleum engineering during the last decade has been the extensive use of reservoir simulators for simulating complex problems which could not have been solved by conventional material balance methods. The value and the degree of sophistication of such simulators will increase in the years to come. At the same time we believe that the material balance approach will continue to be a valuable tool in gaining an understanding of reservoir mechanics. It is particularly useful as a teaching aid, especially with the unified concept discussed below, which helps to show both its advantages and limitations. The chief objective of the present article is to discuss some of our experiences with teaching advanced reservoir engineering both from the classical and the simulation points of view.