Evaluating Potential CO2 Injection Capacity of Aquifers Based on Well Testing

Well testing and Pressure Transient Analysis (PTA) are generally used for reservoir characterization. Matching analytical models to pressure and its derivative within PTA is similar to history matching in reservoir simulation. The ultimate goal of reservoir simulation is forecast, but forecast capabilities of PTA models are often underestimated. In this paper, we examine forecast capabilities of such models in application to CO2 storage in saline aquifers. Since the simplest way of characterizing aquifers is a short-term water production or injection followed by well shut-in, such a well test is a basis for injection capacity evaluation. Assuming that a reservoir (PTA) model (analytical in the simplest case) can be assembled and matched to such a test, pressure build-up forecast for water injection may be simulated. The main focus of this paper is converting such forecast for water into the CO2 injection case. Using numerical simulations of synthetic and actual field cases, the ability to account for near wellbore CO2 banking in PTA models employing the well skin concept was confirmed. PTA models can provide a first evaluation of potential CO2 storage capacity requiring substantially less resources compared to conventional reservoir simulation. This evaluation may be further improved by full-field reservoir simulation.