Preliminary Environmental Risk Assessment Study Using US DOE’s National Risk Assessment Partnership on Leakage through Legacy Wells at the Shenhua CCS Demonstration Project

Saline aquifers, among other potential CO₂ storage formations, have been proven to offer the highest storage capacity necessary for commercial-scale carbon capture and storage (CCS) projects. They are an ideal target for emission reduction from coal-fired power plants in the sourcesink model. However, unlike hydrocarbon reservoirs which are typically well developed, these deep formations face the challenge of characterization due to a lack of data and their uncertainty. Spatial reservoir information is critical in understanding CO₂ injectivity, plume dynamics, and pressure management during and after injection operations. In this study, we combine geologic and dynamic data from the Shenhua CCS Demonstration Project in the Ordos Basin, China to provide an improved explanation for the pressure behavior and interesting injectivity at the site as well as presenting a risk assessment study of long-term storage safety. We extend the work of Nguyen et al. (2017a, b) in that a system of interconnected meandering channels are incorporated into our geologic model to account for the pore volume needed to allow high injectivity. CO₂ injection simulations are carried out by varying geologic and rock/fluid parameters to generate scenarios that offer a better understanding of the subsurface spatial heterogeneity which contributed to our observed behavior. Simulation results suggest that the lateral extent of conceptual fluvial channels may not be as extensive as previously thought since the pressure front travels faster than our CO₂ plume, resulting in minimal pressure buildup at the bottom-hole level. Our study also finds that the injection well may have penetrated a sandbody with interconnected permeability which contradicts the notion in previous work that a high permeability area to the Northwest of the injection well may be the cause of low-pressure buildup. Injection rate allocation is an important parameter in explaining the bottom-hole pressure (BHP) response at the injection well. Our models also provide a range of scenarios with the target 300,000 tons of CO₂ being successfully injected into 5 layers of saline aquifers, with the sandstone Liujiagou formation receiving most of the injection. Risk assessment based on these scenarios honoring historical injection data suggests that there is a low probability of CO₂/brine leakage through legacy wellbores in the area, including the injection and two monitoring wells.