Pressure Transient Effects of CO_2 Sequestration in Faulted Reservoirs: Saline Aquifers

摘要

One of the most critical problems when considering the geologic storage of CO_2 is the risk of leakage which can lead to seepage from the storage area. The model described in this paper examines the injection of CO_2 into faulted reservoirs with some degree of compartmentalization. Presented here are analytical solutions to relate the transmissivity of a fault to the pressure responses in the compartments. The solutions also show the different groups of parameters influencing the migration of injected CO_2 in faulted areas that contain saline aquifers. The amount of cross-fault leakage that can occur is evaluated with respect to basic reservoir parameters that can be easily obtained prior to injection. The model is intended for a type of formation likely to be used for storage in Trinidad. We use the average reservoir pressure and an estimated fault transmissivity from the Mahogany field offshore Trinidad to illustrate the practical application of these analytical solutions. Fluid and rock properties influence the pressure response, and two possible cases are studied for their effects on the reservoir pressure and cross-fault flow. One case that is applicable is at early injection times, when on either side of the fault the water compressibility is dominant. The other case presents a more realistic case that treats the supercritical CO_2 as slightly compressible. A sensitivity analysis shows the effects of fault transmissivity, pore volume and fluid compressibilities. This paper presents a few of the base case scenarios of the pressure response versus cumulative CO_2 injected and also estimates the percent leakage that can occur with time.