Heterogeneous reservoirs undergoing waterflooding contain low-permeability zones in which oil in the low-permeability zones is bypassed by water. Profitability of producing from heterogeneous reservoirs can be poor because of premature water-breakthrough through high-permeability layers. It seems possible to improve the profitability of producing from heterogeneous reservoirs by diverting the injected water from preferentially flowing through high to low-permeability zones. The profitability improves because of a small increase in ultimate oil recovery and/or a large reduction in cumulative water production. The objective of this study is to investigate the applicability of the technology, referred to as indirect waterflooding, in different types of heterogeneous reservoirs.
We performed numerical simulations of waterfloods on a generic five-spot pattern for three different reservoir cases. The reservoirs had properties typical of a San Andres Formation. The first case, with vertical-heterogeneity, showed that ultimate oil recovery might be improved by up to 13% OOIP with indirect waterflooding. The second case, with areal-heterogeneity and a low kv/kh, showed that water production might be reduced by as much as 27%. The third case, with areal heterogeneity and a zero kv/kh, showed that water production might be reduced by 31%. Actual recoveries are sensitive to reservoir properties, especially in the magnitude of the vertical permeability.