In geological sequestration, CO2 is injected under high pressure into deep underground rock formations, including deep saline aquifers. This paper presents the invading supercritical CO2-brine two-phase numerical model to describe CO2 flow and transport processes in deep saline aquifers. The effects of anisotropy and different kinds of heterogeneity like horizontal and vertical layers and also existence of barriers between layers on the CO2 flow and transport in a saturated porous media with brine are investigated using the presented two-phase model. Following to simulation results, it can be obtained that the permeability of the rock formations and the permeability anisotropy should be considered as the most important parameters in CO2 flowand transport processes and its distribution in the rock formations. Furthermore, the capillary pressure on the buoyancy-driven flow of CO2 is analyzed, and the XFEM is adopted to simulate the injection induced fracturing process of the naturally fractured caprock.
An ever-increasing amount of scientific evidence suggests that anthropogenic release of CO2 has led to a rise in global temperatures over the past hundreds of years, especially since the Industrial Revolution (Crowley, 2000; Bradley, 2011). Among various greenhouse gases, CO2 is the greatest contributor to global warming. Reducing the concentration of CO2 in the atmosphere is a major challenge to migrate greenhouse gas. Carbon Capture and Sequestration (CCS) is one of the options for mitigating CO2 emission contributing to global warming (Gale, 2002; Baines and Worden, 2004; Pacala and Socolow, 2004; White et al., 2004; Schrag, 2007). CO2 emitted by sources such as power plants is separated and captured, and then is stored underground in geological reservoirs in CCS. Three most viable reservoirs for CO2 storage are deep saline formations, unmineable coal bed seems, and oil or gas reservoirs. While from a capacity perspective, deep saline formations offer significant potential. This approach would lock up the CO2 for thousands of years. Studying the migration behavior of supercritical CO2 and its leakage risk after it is injected into deep saline formations is the main concern in this paper.
Injection of CO2 into deep saline formations for the purpose of emission avoidance dates back to the early 1980s. The first large-scale pure CO2 geological sequestration project, Sleipner, was built in 1996. Since then, CO2 geological sequestration has gained increasing attention as a carbon mitigation approach from academia and industry. In the short-term CO2 injection process, the migration of the injected CO2 in geological media is mainly controlled by the buoyancy driven volume flowbecause of its smaller density compared with brine.