Pattern Configuration Effect on Steamflood Performance
Authors: Chu Chieh 
Published: December 2007

This two-part simulation study showsthat a well in a five-spot pattern, situated away from its pattern location, could cause a substantial pattern, situated away from its pattern location, could cause a substantial loss in oil production, andthat a five-spot pattern is superior in performance to an inverted 7-, 9-, or 13- spot pattern. performance to an inverted 7-, 9-, or 13- spot pattern.

Introduction

The purpose of this study is to determine the effect of pattern configuration on steamflood performance. pattern configuration on steamflood performance. The study is composed of two parts: the first part deals with irregular five-spot patterns, and the second part compares the relative merits of five-spot vs inverted 7-, 9-, and 13-spot patterns.

Steam injection and oil production wells in a steam displacement project in principle should be drilled according to regular patterns. However, it is often more convenient in actual field operations to drill wells in locations that result in irregular pattern shapes. Irregularly shaped five-spot patterns result in unequal distances between injectors and producers. Injected steam tends to channel through the reservoir preferentially toward some producers rather than preferentially toward some producers rather than others. The areal sweep efficiency is reduced and oil recovery suffers. How much loss in oil recovery results when some wells are placed away from their ideal locations? The first part of this research tries to answer this question. Three cases were studied:a single producer off-pattern,a single injector off-pattern, andseveral wells off-pattern in adjacent patterns.

Note that the off-pattern wells studied here patterns. Note that the off-pattern wells studied here refer to wells that are moved away from their regular pattern locations, not to extra wells existing inside pattern locations, not to extra wells existing inside regular patterns.

Steamfloods in practice have been conducted in five-spot patterns, inverted seven-spot patterns and inverted 13-spot patterns. A well-accepted principle is that in a displacement project, the ratio of the number of producers to the number of injectors should equal the ratio of average injectivity to average productivity. The extremely high steam-to-oil mobility ratio favors high producer/injector ratio. The producer/injector ratios of five-spot and inverted 7-, 9-, and 13-spot patterns are one, two, three, and five, respectively. One must determine which pattern configuration is the best choice for steamflooding. The second part of this study determines the best configuration by comparing steamflood performance of the four different configurations.

This research was conducted using a nine-point steam model where fluids and heat are allowed to flow diagonally as well as in the x and y directions. The formulation of a nine-point, finite-difference scheme for cold displacement processes was discussed by Yanosik and McCracken. The method involves simultaneous calculation of the pressures and saturations for a grid block and its eight neighbors; this determines the flow terms in all directions implicitly. Here, a modified version of the nine-point scheme was incorporated into the steam model reported by Coats.

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