Modeling and Assessment of Wettability Alteration Processes in Fractured Carbonates using Dual Porosity and Discrete Fracture Approaches

Abstract

Abstract Naturally fractured reservoirs (NFR) with significant oil reserves consist of highly conductive fractures and low permeable matrix media. The matrix rock is usually oil or mixed wet and cause a large amount of the oil remain stagnant after primary and secondary oil recovery processes. Recent laboratory studies have revealed that the injection of chemicals such as surfactant and alkali can change the wettability of the matrix to more water wet and help to mobilize and produce the remaining oil from matrix. Despite numerous publications on successful laboratory experiments, research on simulation and accurate modeling of the process is still very scarce. This paper focuses on the mechanistic modeling of the wettability alteration by chemical injection in NFRs using dual porosity MINC (multiple interacting continua) method. Oil recovery from NFRs is a large target in the oil industry but requires new technologies including more advanced simulation tools to produce it cost effectively. Applications of the new technologies require numerical simulators capable of modeling the interaction between fractures and matrix in transport of the injected and produced materials. Inclusion of the wettability alteration due to surfactant injection in dual porosity model allows for the extension of the laboratory results to the field scale. This work opens up an area to mechanistic simulation of the oil recovery from NFRs in field scale using dual porosity multiple interacting continua, MINC, method. We present the wettability alteration model in NFR carbonates using surfactants with a dual porosity model including matrix subgrid capabilities. The model is tested against both published fractured block experiment and a discrete fracture model. The impact on oil recovery of key process parameters such as surfactant concentration and phase behavior, injection/production rate, fracture-matrix permeability ratios, fracture intensity and initial water saturation are investigated. To the best of our knowledge this is the first time that wettability alteration is coupled with a dual porosity model to estimate the oil recovery from NFRs. Both advantages and limitations of the dual porosity and discrete fracture in the context of wettability modification with chemicals are discussed to provide guidelines and insights for future research.