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A method to predict the reserves and performance of a waterflood utilizing peripheral injection is developed. It is a modification of the method used by Prats, et al. to predict the reserves and performance of a five-spot waterflood system. Both theoretical and experimental work are involved in the procedures.
Experimental data obtained by Prats, et al. for the five-spot system and by Dyes, Caudle, and Erickson for a direct line drive system were modified for use in the peripheral system. Theoretical procedures are used to predict injectivity prior to fill-up. After water breakthrough, injectivity is predicted from experimental data. The method presented is believed to be more accurate for predicting reserves and performance of a peripheral waterflood than methods utilizing a constant injection rate or methods not considering the buildup of an oil bank ahead of the water front.
Waterflooding by peripheral injection is becoming more common. This is due, in most cases, to allowable restrictions or to the practice of initiating water flooding in the early life of a field to maintain pressure at an optimum point. If a sufficient rate of water injection can be maintained through a peripheral system, it will usually be selected over a pattern type system because of the lower initial investment and operating expense. A review of material available, both analytical and empirical, to assist in the prediction of waterflood performance indicated that a wealth of information 3,4,5,6,7,8,9,10,11,12,13,14 had been published on the five-spot pattern waterflood but very little 15,16 was available on the peripheral system. It was decided to determine if some of the material available on the five-spot could be modified for use in the peripheral system.
Prats et al devised a comprehensive method of predicting the reserves and performance of five-spot waterfloods. Their method takes into consideration more variables than most other accepted methods and was therefore selected for modification to enable prediction of reserves and performance of a waterflood utilizing a peripheral injection system.
Prats et al. based their method on being able to accurately predict injection rates over the life of a waterflood. Both theoretical and experimental work were performed to develop a method for computing injection rate. This method not only assumes that injection rate into a layer is proportional to the permeability capacity, but also takes into account the effect of the water and oil banks and the fluid mobilities within each of the banks. It involves primarily the prediction with time of the rate of injection into and the type of production from each individual layer.