Optimization of CO2 Storage Systems with Constrained Bottom-Hole Pressure Injection

Of concern with CO2 storage in underground aquifers is the potential leakage of mobile CO2 into the regions above or surrounding the storage site. In this study, we perform an optimization study to minimize the mass of mobile CO2 at the top of the formation at the end of a typical CO2 storage project. We define and solve a comprehensive optimization problem involving well placement and control, along with appropriate constraints. The computations are performed within Stanford's Unified Optimization Framework.

We consider two different storage aquifer models - a channelized aquifer and an aquifer characterized by multi-Gaussian statistics. For both models, we perform a heuristic sensitivity study to estimate the required pore volume of the region surrounding the storage aquifer such that the bottom-hole pressure constraint is not violated. We consider different injection scenarios by varying the number of CO2 injection wells. Optimizations are performed using a combination of particle swarm optimization (PSO) and mesh adaptive direct search (MADS). Multiple runs are conducted to account for the stochastic nature of the optimizations. The sensitivity of the optimized objective to the number of injection wells is assessed for both models. We observe a 45% decrease in the objective function value as the number of wells is increased from one to four for the channelized aquifer model. For the Gaussian model, the corresponding decrease in the objective function value is 33%. We also perform a study to determine the minimum pore volume of the surrounding region that allows for a feasible injection strategy (in terms of maximum bottom-hole pressure), for each of the injection scenarios in both of the aquifer models. We observe that with four injection wells, a surrounding region of pore volume 17 times that of the storage aquifer is required for the channelized model, and 10 times that of the storage aquifer is required for the Gaussian model.

Thirugnana Sambandam, Srinikaeth (2018). Optimization of CO2 Storage Systems with
Constrained Bottom-Hole Pressure Injection. Stanford Digital Repository. Available at: https://purl.stanford.edu/wf405hf9275