Surfactant oil recovery in fractured carbonates: Experiments and modeling of different matrix dimensions

Oil recovery from fractured carbonate reservoirs by water flooding is often inefficient due to the commonly oil-wet nature of these rocks and the lack of sufficient spontaneous capillary imbibition driving force to push oil out from the matrix to the fracture network. Chemical processes such as surfactant/alkali-induced wettability alteration and interfacial tension (IFT) reduction have shown great potential to reduce the residual oil saturation in matrix blocks, leading to significant incremental oil recovery (IOR). However, the time required to achieve a significant amount of oil recovery is the most crucial deciding factor in field projects. The magnitude of recovery and response time of any chemical process depends on the degree of wettability alteration and LH reduction, the nature and density of fracture network, and the matrix block size. Oil recovery experiments were performed for the same matrix rock and chemical formulation, but for different sized cores to gain a better understanding of the time dependence of the recovery process. The measured oil recoveries were history-matched. The simulation models were then used to predict the recovery response times for larger cores. The controlled and systematic laboratory measurements for several core sizes helped in developing dimensionless scaling groups to aid in understanding the time dependence and the upscaling of laboratory results to field-scale applications. This finding is significant as it illustrates the extent of wettability alteration. and IFT reduction needed in fractured reservoirs. Laboratory measurements and simulation work substantiate the validity and the range of applicability of upscaled procedures and indicate the importance of viscous and buoyancy forces in larger field cases. The results of this work will be useful for the design of future field projects. (C) 2014 Elsevier B.V. All rights reserved.