An experimental evaluation of unique CO2 flow behaviour in loosely held fine particles rich sandstone under deep reservoir conditions and influencing factors

Lack of understanding of CO2 flow behaviour in loosely bonded fine particles (clay and mineral fragments) rich sandstone formations has limited the optimum usage and the operational efficiency of various CO2 injection-related field applications in these formations. A comprehensive experimental study including core flooding tests, XRD and SEM image analysis was therefore conducted precisely to understand the CO2 flow behaviour in sandstone formations rich with loosely bonded clay and detrital particles. 210 mm long sandstone cores obtained from the Marburg Formation, eastern Australia were flooded with CO2 at a range of temperatures (24-54 °C) and confining pressures (10-60 MPa). Pressure developments along the cores were monitored to identify the fluid migration patterns through the samples. According to the results, CO2 permeability in tested sandstone has a high tendency to decrease with increasing injection pressure, depth (confining pressure) and temperature. Increased confining pressure and temperature caused 40-50% and 10-30% reductions in the CO2 permeability. This is because the permeability of fine-rich sandstone is highly affected by fine particle migration associated increased flowing fluid viscosity, pore shrinkage with fine clay particle accumulations and easy compaction of soft clay minerals. Moreover, the closure of micro-cracks under high confining stresses, CO2 adsorption created by clay swelling, the occurrence of electric double layers around clay minerals and a reduced CO2 slip effect are also affect the permeability reduction. Many of these effects were identified in the micro-scale study conducted using SEM image analysis. Interestingly, the injection of CO2 at higher pressures (>6 MPa) caused the pressure development in the sample to be held for a significant time due to the blocking of CO2 flow by the accumulation of transported clay particles in pores. This pressure holding period lasts until sufficient pressure development occurs at the upstream side of the barrier to initiating a fluid flow by breaking that barrier. The findings of the study will be very useful for advances in numerical modelling and analytical equations and worldwide CO2 geosequestration projects in fine-rich sandstone aquifers.