A Laboratory Investigation of the Effects of Temperature, Hardness, Surfactants, and Alkaline on Oil Recovery from Carbonate Reservoirs Using Spontaneous Imbibition Tests

Abstract

More than 50 % of the known petroleum reserves are stuck in carbonate reservoirs, which can be divided into limestone, chalk, and dolomite. On average, the oil recovery from carbonates is below 30 % due to low water wetness, natural fractures, low permeability, and inhomogeneous rock properties. Therefore, there is increasing interest to improve oil recovery from carbonate reservoirs, as we are challenged to make up depleted reserves. Although there is a great potential to improve oil recovery in carbonate reservoirs, the research in this area is very limited due to technical and economic challenges. Chemical enhanced oil recovery research in carbonate reservoirs has been focused on using such as surfactant and alkaline increase oil recovery or to change oil-wet to more water-wet to enhance water imbibition into matrix blocks. Wettability alteration results in spontaneous imbibition of water into oil containing matrix, thus driving oil out of the matrix. Wettability alteration has been formulated with surfactant adsorption, and relative permeability and capillary curves are modified based on the degree of wettability alteration. Many research has been investigated in a lab scale how a wettability of reservoir rocks affected in oil recovery and how wettability alteration can be controlled to maximize the oil recovery in limestone rocks. The objective of this study is to investigate the effects of temperature, hardness, surfactants, and alkaline on oil recovery from limestone rock. In order to investigate the effect of these parameters, the limestone rocks were placed in the oven in brine to simulate realistic reservoir conditions. Then, they were aged in crude oil in the oven. After that, the solution with various compositions of surfactant, alkaline, and hardness were tested by spontaneous imbibition test. The spontaneous imbibition test in this study was performed at 25 oC and 80 oC with different limestone rocks. The results show that, at high temperature, the oil recovery is higher than at low temperature. The hardness has various impacts on the wetting properties. and are important in changing wettability on limestone surface and were proved by increase in oil recovery. ion was demonstrated by the very small increase in oil recovery. The alkaline has increased oil recovery from limestone rocks.