Waterflood Prediction Of Partially Depleted Reservoirs

Publication Rights Reserved This paper is to be presented at the California Regional Meeting of the Society of Petroleum Engineers of AIME in Santa Barbara, Calif., on Oct. 24–25, 1963, and is considered the property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of JOURNAL OF PETROLEUM TECHNOLOGY or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in JOURNAL OF PETROLEUM TECHNOLOGY or SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted on request, providing proper credit is given that publication and the original presentation of the paper. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered for publication in one of the two SPE magazines with the paper. A method is presented to calculate the performance of waterfloods which are started when the oil saturation is high and enough gas still remains in the reservoir oil to affect appreciably the rate of oil recovery. The interest in this type of flooding stems from the rapid recovery compared to waterflooding after depletion by the expansion of the dissolved gas. The quick recovery influences the rate of return on the investment. The predictions for five-spot or other pattern floods are obtained by summing the performances of the individual channels bounded by streamlines obtained from the potentiometric model for the pattern. The times and rates are calculated using the shape factors and volumes determined from the equipotentials and streamlines of the potentiometric model. The recovery calculations at all times include the changing oil, water, and gas saturations throughout the pattern as influenced by the oil, water, and gas permeabilities and the quantity of water that has been injected. The recovery as a function of time is determined by the progress of an oil bank created by the injected water and a second downstream oil bank formed by the displaced gas. The flow of oil and gas in the second oil bank is governed by the permeabilities to oil and gas in this section. Several examples are presented in order that engineers may ascertain the relative order of the effect of time, recovery, and rates as functions of the viscosity of reservoir oil, initial gas saturation, and distance between wells. The data for the linear and five-spot patterns are presented. By the use of the high-speed digital computer, a performance calculation can be made in about 1–1/2 minutes.