Near-Well Pressure Distribution of CO2 Injection in a Partially Penetrating Well

To mitigate global climate change, the atmospheric concentrations of greenhouse gases such as carbon dioxide, carbon monoxide, methane, and nitrous oxide must be reduced. Carbon dioxide (CO2) can be captured and injected into subsurface reservoirs in a process known as geologic carbon sequestration (GCS). Geologic carbon sequestration in saline reservoirs offers the greatest storage capacity in the United States and worldwide. Numerical modeling offers planners a useful tool to evaluate the feasibility of GCS in saline and other reservoirs. With its database of CO2 properties, TOUGH2 and its ECO2N module is an excellent simulator for evaluating the CO2 movement in the subsurface. Radial simulations (along the r-z axis) of brine injected into a thick saline reservoir show a smooth exponential increase in pressure over time near the injection well. However, CO2 injected into a thick saline reservoir does not show the same smooth pressure increase. After some time, the pressure near the injection well levels off, remains steady, and then decreases slightly. The maximum pressure increase at the well is lower for CO2 injection than for brine injection because brine is more viscous. In addition, the maximum pressure increase occurs before the end of the CO2 injection period. Okwen et al. (2011) demonstrated this effect for fully penetrating wells and attributed this pressure response to the contrast in fluid density (native brine versus CO2) and permeability anisotropy (horizontal to vertical permeability). In this paper, we seek to demonstrate that the effect is also observed in partially penetrating wells. Partially penetrating wells are important because they offer a well design that can maximize the storage volume of the buoyant CO2 in thick reservoirs. We used TOUGH2 and the ECO2N module to conduct numerical experiments to evaluate the pressure response of injecting CO2 and brine into saline reservoirs. Preliminary results confirm the results of Okwen et al. (2011) for partially penetrating wells. For a well perforated in the bottom of an anisotropic injection formation, CO2 injection leads to lower pressures near the injection well perforations but higher injection pressures near the top of the injection formation. Apparently, vertical transport is more significant with CO2 injection than brine injection, and it alters the pressure profile near the injection well. These results could inform how partially penetrating wells are completed.