S.M. Farouq Ali

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

Recent years have witnessed great strides il reservoir simulation techniques. Numerous reservoir simulators have been developed, and are bein! 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 for different combinations of the basic oil production processes, i.e. gas cap expansion (with gravity segregation, with or without counterblow) solution gas drive, and water drive. LiiiiitatiOiiS 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.

Tertiary Recovery of the Bradford Crude Oil by Micellar Solutions, from Linear and Two-Dimensional Porous Media

Micellar solutions should be tailored for a given crude oil, so that the 2 are miscible over the widest possible range. Lack of miscibility would lead to inefficient displacement. Mobility control at the rear of the slug is critical in determining oil recovery, which increased with the polymer concentration in the buffer. Buffers, consisting of glycerin/water mixtures, showed that even partial mobility control (mobility ratio > 1) can be adequate. Small amounts of isopropyl alcohol in the buffer tended to increase recovery. Oil recovery increased with an increase in the mobility buffer size, however, a 20% buffer is nearly as effective as larger buffers. Oil recovery increases with solvent slug size, however, the recovery ratio decreases, over the range studied. A micellar solution flood, with adequate mobility control, would sweep approx. 60% of the pattern area. Micellar solution floods are relatively insensitive to flood advance rate.

Simulation of In-Situ Combustion in a Two-Dimensional System

A 2-dimensional mathematical model of the forward combustion process was developed and used for studying the effects of fuel content and air-injection rate on the sweep efficiency attained in in situ combustion. The model incorporates the effects of single-phase gas flow, heat generation by a combustion front, change of permeability in the burned zone, heat transfer by conduction and convection within the reservoir, and heat loss by conduction to the adjacent formations. A numerical scheme was developed to solve the system of partial differential equations constituting the model. The model was used to investigate combustion in a quadrant of a 5-spot pattern. It was found that as the fuel content of the reservoir increases (0.5 to 2.0 lb/cu ft), the sweep efficiency at combustion front breakthrough increases (68 to 84%) and tends to reach a plateau. The advantage of a high sweep may be offset, however, by a corresponding increase in heat loss and total air requirement. Sweep efficiency did not show a consistent trend with variation in the air injection rate for a given fuel content. For a constant air-injection rate, the percent heat loss from the reservoir increases linearly with the fuel content. (14 refs.)

Steamflooding after Steam Soak - Effect of Water Saturation Build-up on Oil Recovery

The presence of water saturation buildup near the well bore may influence the steamflood oil recovery, the magnitude of the effect being dependent on oil viscosity. Thus, the effect is appreciable for low viscosity oils, becoming less pronounced for higher viscosities. It was found that a high water saturation in the vicinity of both the injection and production wells is likely to be unfavorable, and should be avoided in steamflood development. In all cases studied, the water saturation buildup was more injurious to oil recovery in the case of high, rather than low initial oil saturations. In both cases, the oil recovery decreased as the water zone size increased.

A Theoretical And Experimental Study Of Steam Drive

Results of theoretical and experimental investigation of the steam-drive process, or steam flooding, are presented. The displacement of oil and water by steam was represented by a system of 5 partial differential equations. The equations were solved by use of a combination finite difference technique. The mathematical model included vaporizations and condensation effects, as well as changes in viscosity and density due to temperature changes. Two- dimensional flow of heat in the adjacent formation was considered. The model was used to simulate the results of one of the experiments. The experimental work performed provided information on the relative roles of steam distillation and viscosity reduction in oil recovery by a steam flood, for partially distillable oils. (14 refs.)