Quantitative experimental investigation of multiple P-T effects on primary drainage process during scCO2 storage in deep saline aquifers

Abstract

Deep saline aquifer is the preferred reservoir for CO2 geological storage. However, during the primary drainage process of injecting scCO2 into deep saline aquifers, residual water will form and cannot be drained, which will have adverse effects on the capacity and safety of CO2 storage. This is a new study based on the preliminary exploration, 9 groups of scCO2 drainage experiments in a natural rock core are carried out under multiple pressure (8, 10 and 12 MPa) and temperature (40, 50 and 60 °C) conditions to investigate the formation mechanism of residual water during primary drainage process. A quantitative power function relationship between residual water saturation and drainage time is proposed; a quantitative exponential function relationship between irreducible water saturation and P-T conditions is also presented. The coefficients a, b, c and d of two fitting functions are discussed in detail. In addition, the irreducible water saturation increases with the increase of temperature and decreases with the increase of pressure. Through deep analysis on the interfacial tension, viscosity ratio and logCa-logM stability phase diagram, the interfacial tension of CO2-H2O system, which determines the capillary entry pressure, is regarded as the guiding factor influencing the experimental results, rather than the viscosity ratio. It is worth mentioning that under the given P-T conditions in this study, the influence of temperature on the experimental results is greater than that of pressure.