Effect of scCO2-brine mixture on injectivity and storage capacity in rock samples of naturally fractured carbonate formations

ABSTRACT The presence of natural fractures in the formation and its degree of heterogeneity condition the injection of CO2 into the aquifer as they affect the migration processes and its storage capacity. In ATAP experimental facility the petrophysical behavior of two carbonate formations was studied, with different proportions of limestone, dolomite, quartz and anhydrite and fissures sealed mainly by potassium aluminosilicates and iron sulphides. Actual storage conditions (135/141 bar and 44/46 ᵒC) corresponding to a depth of around 1500 m and continuous injection at a constant flow rate of 1cc/min of 10% and 15% of HCl, HCl/Acetic (CH3COOH) 10%/10% and scCO2 (supercritical CO2)/brine 50%/50%, was applied to the brine saturated rock samples (coreflooding). Considering laminar flow through the fractures, the flow injected is proportional to the pressure drop according to the “cubic law” that takes into account the width and length of the fractures. This is used to evaluate the injectivity of the storage. The variations in the pressure drop are due to the dragging of detached fines in the dissolution of the carbonates of the filled fissures that can cause their opening or blocking. The efficacy of pure scCO2 enriched brine injection was determined to dissolve the carbonates of the store formation compared to other methods such as the injection of acids used in the oil industry for the stimulation of producing wells. Scanning Electron Microscope (SEM) studies of the injection surfaces and Computerized Tomography (CT) analysis of the samples before and after injection of the acid mixtures have been performed. The dissolution facilitates the injectivity and increases the capacity favoring the tightness of the storage by the phenomenon of controlled dissolution-precipitation of the carbonates.