Abstract
A series of steady state multiphase flow experiments at a range of fractional flows and flow rates have been conducted using Berea Sandstone. Using the multiphase flow simulator TOUGH2 MP with ECO2N module, carbon dioxide saturation distributions, average saturations, and pressure gradients across the core were calculated to determine the influences of sub-core scale heterogeneity, gravity and flow rate on brine displacement efficiency. It is found that measured CO2 saturation patterns can be replicated using simulation models that include spatially varying porosity, permeability and capillary pressure curves.
The interplay of viscous, capillary and gravity forces in core flood experiments is also investigated at different Gravity and Capillary numbers representative of those expected for a typical sequestration project (Gravity numbers: 0~1000 while Capillary numbers: 10-6~10-10). These dimensionless numbers span the range of conditions expected in the near-well region to leading of the plume which may be up to 5 km or more from the injection well. Simulations show that the efficiency of brine displacement and saturation distributions during vertical displacement fall into three separate regimes. (1) At high flow rates representative of the near-well region, the brine displacement efficiency is nearly independent of flowrate. (2) When the Capillary number drops below 10-7 and the gravity number is 2, both the heterogeneous and homogenous cores display flow rate dependent saturation distributions, with brine displacement efficiency dropping by about 80%. Most of this effect is caused by the influence of gravity, as the decrease in brine displacement efficiency is only slightly smaller for heterogeneous cores. (3) At very low capillary numbers, the brine displacement efficiency appears to asymptotically approach a constant value which is independent of flowrate. In this regime, heterogeneity leads to a large reduction in brine displacement efficiency, which is independent of gravity.
