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Abstract

A numerical simulation study was conducted to determine the optimum injector location for steamflooding steeply dipping reservoirs with five-spot pattern configurations. The model reservoir has either 20 or 45 dip, is bounded by an updip gas cap and a downdip edgewater and is steamflooded with one, two, or three five-spot patterns in the direction of dip. patterns in the direction of dip. The study showed that steamflood performance in dipping reservoirs can be improved by placing the injector downdip from the pattern center. The optimum injector location for most situations was found to be about halfway between the pattern center and the downdip producer row. This off-center, downdip steam injection produces the producer row. This off-center, downdip steam injection produces the highest steamflood oil recovery among all injection locations considered in the simulation study.

Introduction

Five-spot and inverted nine-spot are commonly used in steamflooding reservoirs with line or no dip. These pattern configurations have also been used for dipping reservoirs while ignoring the effect of dip on steamflood performance. 1 Five-spot is more commonly used for steamflooding dipping reservoirs because it becomes a middle-staggered line drive if one side of the pattern is aligned with the direction of dip.

A recent simulation study of steamflooding in a steeply dipping reservoir with an updip gas cap and a downdip edgewater has shown that the injected steam becomes unevenly distributed between the updip and downdip parts of the reservoir as a result of gravity. Steam preferentially flows updip, causing early steam breakthrough to the updip producer while the downdip producer remains cold. This imbalance of steam flow produces poor areal and vertical sweep by steam and results in reduced steamflood efficiency, It was apparent that for dipping reservoirs the injector must be located off-center in a steamflood pattern to distribute steam more evenly.

A numerical simulation study was conducted to investigate how the injector location affects steamflood oil recovery and to determine the optimum injector location in steeply dipping reservoirs having an updip gas cap and a downdip edgewater. This paper describes the simulation study and presents the optimum injector locations for steamflooding steeply dipping reservoirs.

RESERVOIR AND FLUID MODELS
Reservoir Grid

Figures 1 through 3 show the 3D reservoir models used in this study, representing steamflood development with one, two, and three five-spot patterns in the direction of dip, respectively. The base models place the injectors at the pattern centers so that when viewed in the place the injectors at the pattern centers so that when viewed in the direction perpendicular to the bedding plane, the injector and two corner producers represent one-half of a five-spot pattern. Producers are located on one side of the model, and the injectors are located midway between two adjacent producers on the opposite side. The distance between a producer and the injector is 354 ft. The homogeneous 72-ft sand was divided equally into 4 communicating layers.

Both the gas cap and edgewater were represented by a 150-ft long outer block and a 50-ft long inner block. A fictitious injector and producer operating at a constant specified pressure were used to producer operating at a constant specified pressure were used to maintain the gas cap or edgewater pressure as if they were infinite in size. High y-direction permeability was used in the gas cap and edgewater to assimilate uniform pressure in the y-direction during injection or withdrawal of fluids from the model.

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