Over bottom water, a horizontal well will usually perform better than a vertical well because the oil-water contact rises in the shape of a crest instead of a cone. Analytical models have predicted greater critical rates for horizontal wells and greater recovery at water breakthrough when the horizontal well is produced at higher than the critical rate. However, as with vertical wells, horizontal wells may water out before getting an economically sufficient recovery factor. The objective of this paper is to evaluate the strategy of waterflooding over bottom water using the π-mode production strategy.

The objective of π-mode production is to accelerate recovery and achieve 50% recovery efficiency in less than 5 years through waterflooding. This is accomplished by production at a constant oil rate and full voidage replacement through reinjection of produced water. As in previous work, this paper employs the horizontal well couplet with one injector and one producer. Simulations reported in previous studies have demonstrated the feasibility of this waterflood strategy, first for homogeneous and then for heterogeneous reservoirs. This paper determines when the π-mode production strategy is effective over bottom water. In addition, the π-mode production strategy is compared to an array of horizontal well production wells without injection.

Simulations performed for a variety of well spacing, different reservoir thicknesses, different mobility ratios, and different aquifer sizes are compared for recovery and net present value versus time for both the π-mode production strategy and production well strategies. Results quantify optimal well spacing and show that the π-mode production strategy is effective over small aquifers while production wells without injection work better for large aquifers.

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