Modeling Density Effects in CO2 Injection in Oil Reservoirs and A Case Study of CO2 Sequestration in a Qatari Saline Aquifer
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CO2 injection has been used to improve oil recovery for several decades. In recent years, CO2 injection has become even more attractive because of a dual effect; injection in the subsurface 1) allows reduction of CO2 concentration in the atmosphere to reduce global warming, and 2) improves the oil recovery. In this study, the density effect from CO2 dissolution in modeling of CO2 injection is examined. A method to model the increase in oil density with CO2 dissolution using the Peng-Robinson equation of state and the Pedersen viscosity correlation is presented. This method is applied to model the observed increase in oil density with CO2 dissolution in a West Texas crude oil. Compositional simulation of CO2 injection was performed in a 2D vertical cross section and a 3D reservoir with the density effect. The results show that the density increase from CO2 dissolution may have a drastic effect on CO2 flow path and recovery performance. One main conclusion from this work is that there is a need to have accurate density data for CO2/oil mixtures at different CO2 concentrations to ensure successful CO2 injection projects. While CO2 enhanced oil recovery (EOR) is part of the solution, saline aquifers have the largest potential for CO2 sequestration. A literature review of the CO2 sequestration in saline aquifers is performed. The dominant trapping mechanisms and transport processes and the methods used to model them are discussed in detail. The Aruma aquifer, a shallow saline aquifer in southwest Qatar is used as a case study for CO2 sequestration. A compositional simulation model is prepared for the Aruma aquifer using the available log data and flow test data. It was found that the grid size is a key parameter in modeling CO2 sequestration accurately. It affects the propagation of the CO2 plume and amount of CO2 dissolved in brine.