Low salinity waterflood (LSW) has become an attractive enhanced oil recovery (EOR) method as it shows more advantages than conventional chemical EOR methods in terms of chemical costs, environmental impact, and field process implementation. Extensive laboratory studies in the past two decades have proposed several pore-scale mechanisms of oil displacement during LSW flooding, which are still open for discussion. However, the capability of reservoir simulators to model accurately this process is very limited. This paper provides a critical review of the state of the art in research and field applications of LSW. The focus is on a widely agreed mechanism that is the wettability alteration from preferential oil wetness to water wetness of formation rock surfaces. Ion exchange and geochemical reactions have been experimentally found to be important in oil mobilization due to enhanced water spreading at low salinity. To evaluate the significance of this surface wetting mechanism, a comprehensive ion exchange model with geochemical processes has been developed and coupled to the multi-phase multi-component flow equations in an equation-of-state compositional simulator. This new model captures most of the important physical and chemical phenomena that occur in LSW, including intra-aqueous reactions, mineral dissolution/precipitation, ion exchange and wettability alteration. The proposed LSW model is tested using the low-salinity core-flood experiments reported by Fjelde et al. (2012) for a North Sea reservoir and the low-salinity and high-salinity heterogeneous core-flood experiments by Rivet (2009) for a Texas reservoir. Excellent agreements between the model and the experiments in terms of effluent ion concentrations, effluent pH, and oil recovery were achieved. In addition, the model was also proved to be highly comparable with the ion-exchange model of the geochemistry software PHREEQC for both low salinity and high salinity (Appelo, 1994). Important observations in laboratory and field tests such as local pH increase, decrease in divalent effluent concentration, mineralogy contributions, and the influence of connate water and injected brine compositions can be reproduced with the proposed LSW model. Built in a robust reservoir simulator, it serves as a powerful tool for LSW design and the interpretation of process performance in field tests.
Waterflooding has been practiced for several decades as a means of secondary recovery. This process is successful if there is uniform resistance to the injected water. However, due to its nature of heterogeneity, the injected water flows to the less resistant path, resulting in poor sweep efficiency. As one of many candidates to overcome this problem, polymer systems mixing with several types of chemical agents have been researched and applied for several years. In this article, the authors reviewed and summarized the Relative Permeability Modification/Disproportionate Permeability Reduction and water shutoff treatments.
The injection of chemical solutions plays an important role in increasing the recovery factor of mature fields. For many reservoirs, polymer or surfactant flooding is an attractive alternative to conventional waterflooding; it can improve the area swept efficiency not only in the macro scale but also in the micro scale.Adsorption of polymer/surfactant on reservoir rock is an extremely important parameter for chemical flooding. Adsorption represents a loss of a chemical agent from solution, and consequently, a net reduction in the surfactant-polymer slug. Therefore, the efficiency of chemical flooding will be significantly diminished not only in technical aspects but also in terms of economics. However, adsorption is usually measured in laboratory scale with high uncertainties, and numerical simulation of multi-component adsorption is still limited. The adsorption process in a polymer/rock system has not yet been well developed, especially for highly heterogeneous reservoirs. In this paper, the polymer and surfactant adsorption processes are modeled by the Langmuir isotherm theory for various chemical flooding approaches including polymer, surfactant, micellar polymer and alkaline/surfactant/polymer flooding. The simulation results indicate that polymer adsorption strongly depends on the polymer concentration, shear rate, pH, salt concentration, and reservoir heterogeneity. An effective controlling of such parameters can reduce the effect of polymer adsorption so that it helps minimize mass of chemical loss and improve economic efficiency of the chemical flooding process.
Low salinity waterflooding (LSW) is an emerging enhanced oil recovery technique in which the salinity of the injected water is controlled to improve oil recovery vs. conventional, higher salinity waterflooding. Despite significant growing interest in LSW, a consistent mechanistic study has not yet emerged, and the mechanisms behind the LSW process have been debated for the last decade due to the complexity of the crude oil-brine-rock interactions. The intent of this paper is to:• Provide a concise review of the current understanding of LSW mechanism and prediction methods;• Address the current development and challenges of LSW modeling and numerical simulation;• Summarize and highlight the success and failur of LSW implementation in pilot tests;• Discuss the potential of a Hybrid LSW in the current and future projects.
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