Dong, Pengfei (Rice University) | Puerto, Maura (Rice University) | Jian, Guoqing (Rice University) | Ma, Kun (Total E&P) | Mateen, Khalid (Total E&P) | Ren, Guangwei (Total E&P) | Bourdarot, Gilles (Total E&P) | Morel, Danielle (Total E&P) | Bourrel, Maurice (Total E&P) | Biswal, Sibani Lisa (Rice University) | Hirasaki, George (Rice University)
Pengfei Dong, Maura Puerto, and Guoqing Jian, Rice University; Kun Ma, Khalid Mateen, Guangwei Ren, Gilles Bourdarot, Danielle Morel, and Maurice Bourrel, Total E&P; and Sibani Lisa Biswal and George Hirasaki, Rice University Summary Oil recovery in heterogeneous carbonate reservoirs is typically inefficient because of the presence of high-permeability fracture networks and unfavorable capillary forces within the oil-wet matrix. Foam, as a mobility-control agent, has been proposed to mitigate the effect of reservoir heterogeneity by diverting injected fluids from the high-permeability fractured zones into the low-permeability unswept rock matrix, hence improving the sweep efficiency. This formulation provides both mobility control and oil/water IFT reduction to overcome the unfavorable capillary forces preventing invading fluids from entering an oil-filled matrix. Thus, as expected, the combination of mobility control and low-IFT significantly improves oil recovery compared with either foam or surfactant flooding. A three-component surfactant formulation was tailored using phase-behavior tests with seawater and crude oil from a targeted reservoir. N/m and strong foam in porous media when oil is present. Foam flooding was investigated in a representative fractured core system, in which a well-defined fracture was created by splitting the core lengthwise and precisely controlling the fracture aperture by applying a specific confining pressure. The foam-flooding experiments reveal that, in an oil-wet fractured Edward Brown dolomite, our low-IFT foaming formulation recovers approximately 72% original oil in place (OOIP), whereas waterflooding recovers only less than 2% OOIP; moreover, the residual oil saturation in the matrix was lowered by more than 20% compared with a foaming formulation lacking a low-IFT property. The selective diversion effect of this low-IFT foaming system effectively recovers the trapped oil, which cannot be recovered with single surfactant or high-IFT foaming formulations applied to highly heterogeneous or fractured reservoirs. Introduction Carbonate reservoirs are thought to hold approximately 60% of crude oil and 40% of natural-gas reserves in the world (Akbar et al. 2000). However, oil recovery in carbonate reservoirs poses great challenges to the petroleum industry. These fracture networks provide a bypass, usually called a thief zone, for the fluids injected into the reservoirs. In addition, approximately 80 to 90% of carbonate reservoirs are intermediate-wet or oil-wet (Treiber and Owens 1972; Chilingar and Yen 1983), resulting in an unfavorable condition for spontaneous imbibition by capillary forces (Hirasaki and Zhang 2004). These characteristics of carbonate reservoirs cause low sweep and displacement efficiency and, hence, low oil-recovery rates.