Investigation of Multi-phase Flow Property Hysteresis: Application to Low Salinity Waterflooding, and CO2 Sequestration in Aquifers and Oil Reservoirs

Capillary pressure, relative permeability and electrical resistivity are key parameters to describe multiphase flow in porous media. Their empirical relations with respect to wetting phase saturation demonstrate irreversibility usually referred to as hysteresis. In this dissertation, an experimental setup (Coretest, CP-355) was designed and built to enable measuring hysteresis of capillary as well as two- and four-electrode resistivity (at five different frequencies simultaneously) using reservoir fluids at elevated temperature and pressure; another experimental device used in this study was the core flooding system to conduct unsteady-state coreflooding experiments. Capillary pressure and electrical resistivity hysteresis curves were obtained directly from experiments performed using the CP-355; meanwhile, relative permeability and a hysteresis behavior were obtained by history matching the unsteady-state coreflooding experiments with consideration of capillary hysteresis. Direct determination of relative permeability curves from history matching the capillary pressure experiment failed due to the high resistance of ceramic disk used in the typical quasi-static method that controlled the equilibrium time. This leads to additional testing of new capillary pressure measuring configurations with a degree of success. To investigate the low-salinity effect on hysteresis phenomena, high salinity-high salinity and high salinity-low salinity experiments were carried out on two reservoir rocks (whose properties are quite similar) with reservoir fluids at elevated temperature. Results showed a more noticeable hysteresis for low-salinity brine, which could be explained by higher water-wetness and mineral dissolution induced by low-salinity brine. To further explore low-salinity waterflooding mechanisms, four additional experiments were planned to first investigate the interfacial viscoelasticity effect with exclusion of wettability alteration by conducting experiments at low temperature without aging. We then introduced the effect of wettability alteration by aging the core sample at irreducible water saturation for 3 weeks at high temperature. Furthermore, for these aforementioned experiments, a newly developed dynamic-static method was used to accelerate capillary pressure experiments. Two experimental results on interfacial viscoelasticity effects have been obtained as of now, and two others are still ongoing. Based on all the current results, we conclude that 1) brine with low enough salinity produces a higher viscoelasticity shown before to suppress snap-off with the consequently diminished hysteresis; 2) low salinity can turn the rock more water-wet at high temperature, but resulting in more snap-off and thus more hysteresis; 3) wettability has a noticeable effect on electrical resistivity hysteresis - the more oil-wet, the more hysteresis (resistivity values are higher in imbibition than in drainage). Capillary and relative permeability hysteresis are also crucial for CO2 sequestration in aquifers and oil reservoirs through residual trapping and local capillary trapping. In this dissertation, two separate studies were conducted - a sensitivity analysis on CO2 storage in surrogate Tensleep fractured aquifers using computer experiments and an economic co-optimization study of oil recovery and CO2 sequestration on the 2nd Wall Creek Formation at "East Salt Creek" and the Tensleep Formation at "Teapot Dome". The sensitivity analysis in aquifers shows that fractures play a negative role in CO2 storage, especially when an active aquifer at the bottom is present and dissolution trapping dominates among all the trapping mechanism. Co-optimization of CO2 EOR and storage in oil reservoirs were realized by combining Leach et al.'s rigorous economic model and dynamic reservoir models. The results show that it is necessary to gradually taper the CO2-injection rate to save CO2 recycling costs and thus maximize NPV and paradoxically, cumulative CO2 sequestration is highly insensitive to sequestration subsidies.