Pressure transient model for supercritical CO₂ sequestration in deep saline aquifers and its application in Ordos Basin, China

CO₂ geological sequestration in the deep saline aquifer is considered as a promising technology to reduce CO₂ emissions and prevent global warming. Continuous injection, however, will cause pressurization which may lead to CO₂ leaking from the target zone. For the CO₂ sequestration, the accuracy of formation parameters is the basis for predicting formation pressure and storage capacity. Even though the pressure transient analysis (PTA) method is useful to obtain the reservoir and well properties accurately, the corresponding reports on supercritical CO₂ are rare. Thus, the aim of this work was to address the parameters required to estimate for the supercritical CO₂ sequestration in deep saline aquifers. Based on the well testing theory in petroleum engineering, a two-region composite PTA model is established by introducing a new pseudo-pressure which takes supercritical CO₂ physical properties into consideration. Then, combined with the definition of dimensionless parameters and the Laplace transform method, the analytical solution of the two-region composite model is obtained. The standard log–log typical curves of PTA are drawn and analyzed. The model is further validated by matching the field data from the Ordos Basin of China with type curves. The changes in the reservoir parameters (e.g., permeability and mobility ratio) over time are also analyzed. The results suggest that the method and model are reliable and can be applied in a transient pressure analysis of the CO₂ sequestration in deep saline aquifers to evaluate the flow parameters, to determine the reservoirs properties and to track the location of the CO₂–brine front.