| Description |
The long-term success of Carbon Capture and Storage (CCS) as an industry depends on effective risk management and cost efficiency. Reservoir pressure-buildup associated with injection induces minor seismic events in all subsurface reservoirs, and thus such will necessarily be an outcome of CCS operations, too. Perhaps the simplest approach is to modulate injection rates to maintain bottom hole pressure (BHP) below the theoretical fracture pressure of the reservoir that is assumed to be 80% of the lithostatic pressure. A reservoir model was created in TOUGH-MP for simulating numerous injection well configurations. Due to time constraints, 10 m injection cells were chosen to balance error and computational efficiency. Results of this study include plots of injection volume versus number of injection wells, or "injection curves," for a broad range of reservoir parameters evaluated in a comprehensive sensitivity analysis. One injection well proved to inject the least amount of fluid of the tested well configurations. In all cases, the largest injection coincided with the most wells. Injectivity was most sensitive to permeability; injection volume changed by nearly an order of magnitude for an order of magnitude change in permeability. Effects of less sensitive parameters were summarized by their effects to the permeability injection curves. A cost function was developed and applied to all results from the sensitivity analysis to determine cost efficiency. The full set of results may be interpolated to forecast an optimal number of wells for most scenarios. Generally, the optimal number of wells that facilitates the lowest cost of CO2 per tonne is between four and eight wells. Injection scenarios with a single injection well proved to be the least efficient. Finally, the developed methodology is illustrated via application in a case study of the Rocky Mountain Carbon Capture and Storage (RMCCS) project, a CCS candidate site near Craig, Colorado, USA. The forecasting method provided decent estimates of cost and injection volume when compared to simulated results. All results suggest CCS success may be increased by careful BHP management through optimized well placement strategies. |
