The Implementation of Underground CO₂ Sequestration: Analysis of Caprock Leakage on the Todilto Shale of San Juan Basin Available to Purchase

This paper presents comprehensive geological sequestration feasibility studies at the San Juan Basin. The CO₂ injection has targeted over 50 million metric tons of design within 30 years. There is a potential risk of leakage in a caprock due to pressure build-up resulting from CO₂ injection activities. This research aimed to quantify the risk of CO₂ leakage from the caprock to the underground drinking water source. This was achieved by employing different feasibility techniques to calculate the CO₂ saturation area with plume migration upward.

A compositional hydrodynamic simulator predicts the plume migration and pressure changes in the saline aquifer. A fluid model, the relative permeability, and the capillary pressure threshold for the Todilto barrier model were built and joined into an established geological model. The simulation model was initialized by performing a history match with historical water injection and recorded well head pressure (WHP). The fine grid caprock has been modeled as a shale rock barrier that sealed the upward plume migration. The underground CO₂ storage will be trapped under the Todilto shale formation. The first technique to assess the feasibility of caprock integrity was to calculate the capillary pressure threshold that will cause potential caprock failure leakage on Todilto. The effect of increasing pressure was evaluated through various critical storage trapping mechanisms, increasing plume size, and buoyancy effects on the caprock at the end of 100 years of monitoring. This work calculated the potential CO₂ volume that leaks from hypothetically caprock seal failure leakage. The plume surface area was also investigated as the implications of the geological subsurface. Secondly, an uncertainty analysis study was conducted to understand geological, capillary pressure, and rock properties that impact the caprock integrity. The results demonstrated that CO₂ injection on the Entrada geological saline dune has been sealed with ultra-low permeable Todilto Shale. In addition, the long-term CO₂ brine dissolution has a side effect of dissolution that weakens the caprock and then causes CO₂ leakage on the conductive fault. The techniques and analyses used in this study can serve as a guide to produce similar results for other geological dune saline reservoirs with Todilto caprock consisting of limestones and anhydrite.

Keywords: Carbon Capture and Storage; CO₂ Injection; Anhydrite Formation; Caprock; Todilto; Aquifer; Reservoir Simulation; San Juan Basin.