A Method of Estimating Oil and Gas Reserves

Abstract

In the management of oil properties, it is always desirable to know thefuture behavior of oil wells and oil reservoirs. Some estimation of thequantity of oil and gas that will be produced must be made as a basis fordecisions on possible returns on investments in lifting equipment, drilling ofadditional wells, and other operating expenditures. In new or wildcat areas, operating expenditures are considered highly speculative, but in the completionof partly drilled and the operation of producing fields it is good business toremove as much speculation as possible. An accurate knowledge of oil and gasreserves in such cases would solve many management problems.The term" oil reserves" usually signifies the future ultimate recoverywithout specifying the method of production. Thus with changing methods andinnovations in the production industry, reserves of any definite reservoir maybe increased. by increasing the portion of oil recovered. The usual reserveestimates are made by comparisons of well and formation characteristics, byusing a percentage recovery on the oil content of the formation volume usingporosity data, by extending production curves on non-prorated wells, or byextending bottom-hole pressure-production curves. The most reliable methodwould appear to be one that would estimate the initial quantity of oil and gaspresent and then obtain percentage recovery values for various productivemethods and formations from experience.It is the purpose of this paper to describe a method of estimating the initialquantity of oil and gas present in a reservoir. The method is based on fieldoperating data and the properties of crude oil-gas mixtures. The principlesinvolved, the data required, the assumptions necessary, and an example of themethod will be given. The method is entirely independent of sand volumes andformation porosities.