Horizontal well stream function model for improved waterflood performance and evaluation

Abstract

This paper describes the construction of a new streamtube numerical reservoir simulator and detailed results of recovery performances of mixed five-spot pattern waterfloods. Newly defined stream functions for horizontal wells were combined with conventional (vertical well) stream functions to implement streamtube modeling of horizontal wells in mixed pattern waterfloods. The horizontal wellbore was approximated with a finite, distributed line source in two dimensions. The new streamtube simulator was used to numerically simulate the recovery performance of horizontal wells in mixed five-spot pattern waterfloods. The numerical study encompassed a wide range of horizontal wellbore lengths as well as three magnitudes in mobility ratios.Horizontal well five-spot patterns have higher recovery performance than mixed patterns. Mixed five-spot patterns (horizontal wells used in conjunction with vertical wells in) also show accelerated recovery, but they require more pore volumes of water injected per pore volume hydrocarbon produced. Interestingly, longer horizontal wellbores require more injected pore volumes of water to displace the same amount of pore volume of hydrocarbons than shorter wellbores.Breakthrough areal sweep efficiency of mixed patterns decreased with increase in horizontal wellbore length. Nonetheless, mixed patterns with horizontal injectors and vertical producers consistently gave higher breakthrough sweep efficiencies than other patterns with vertical injectors and horizontal producers. This performance difference was considerably greater for unfavorable (M > 1) mobility ratio waterfloods than for favorable mobility ratio floods (M < 1).