Using horizontal wells in a waterflooding process, a higher sweep efficiency for less cost is expected as opposed to the use of classical patterns by vertical wells. However, the use of horizontal wells is very sensitive to the well pattern designed to operate such a process. The paper presents an analysis of how the overall efficiency of a waterflooding process is influenced by the well pattern using horizontal injectors and producers in different configurations.

Recent investigations used vertical injectors and horizontal producers, with the horizontal well completed at the top of formation and having its toe close to the injection well, which was perforated at the lower part of formation. This process, known as a short-distance Toe-To-Heel Waterflooding "(TTHW) process", was found sound for the light-heavy oils with viscosity up to 2,000 cP, and proved to have maximum efficiency for relatively thick formations.

The general necessity to inject higher water rates, simultaneously with the preservation of a certain control on the injection, prompted the investigation of the use of horizontal wells as injectors both for light-heavy oil and light oil recovery in thin oil reservoirs in a long distance displacement configuration, as well.

A two phase two dimensional numerical simulator for thin formations to investigate the Waterflooding by Horizontal Injectors and Producers, including an "areal" TTHW process, was used. Both the sink/source and the discretized well were considered, in order to estimate the effect of pressure drop along both injectors and producers on the oil recovery performance. The results showed that the pressure loss along the horizontal section has a significant influence on the sweep efficiency.

A numerical simulation study for 10 oils having viscosities between 1 cP and 150 cP was undertaken. The study was performed for both long-distance and short-distance displacement configurations, although for some oil viscosity values it was made just for illustrative purposes. The main parameters, such as time of water break-through, oil recovery at break-through, sweep efficiency, injection-production pressure drop, etc were analyzed in all cases.

For optimization purposes two types of configuration were investigated: a staggered parallel horizontal wells configuration, having their heels in opposite directions and their toes arranged in a direct line, and an L shaped configuration, with perpendicular horizontal wells having their toes relatively close to each other.

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