An Analytical Model for Water Evaporation During CO2 Injection for Geological Storage

Abstract

Summary Formation damage during CO2 injection into depleted gas or oil reservoirs, or in aquifers, is highly affected by connate water evaporation into injected gas. For example, precipitated salts accumulate into dried-up zone around the well. Dried rock liberates fine clay particles. The aim of the work is creation of an analytical model for connate water evaporation into injected CO2 during coreflood and injection in vertical well. The mathematical model considers non-equilibrium evaporation accounting for changing interfacial area. The interfacial area is derived separately from approximating the porous media as a sphere pack and from the averaging of individual water patches. The resulting model is solved analytically using the method of characteristics, permitting the calculation of the water saturation and vapour concentration profiles during the evaporation process. Finally, we match 5 laboratory tests, determine the typical form of evaporation interface, and upscale the results for injection well conditions. Tuning of laboratory data exhibits high agreement for 5 laboratory tests and allows for characterization of field-scale evaporation dynamics from laboratory testing. The total evaporation time is provided explicitly by the model, and a criterion is presented for determining whether evaporation occurs within finite time. This work provides key insights into the behaviour of CO2 injection wells and can contribute to producing explicit formulae to predict mobilisation of fine clays and precipitation of salts due to rock drying.