Two-phase flow behaviour and relative permeability between CO2 and brine in sandstones at the pore and core scales

摘要

In this thesis we have performed an experimental investigation into steady-state two-phase flow behaviour at the core and pore scales and visualised the fluid distributions using medical and fast synchrotron X-ray computed tomography.ududWe performed an experimental study of steady-state, drainage relative permeability curves with CO2-brine and N2-deionised water, on a single Bentheimer sandstone core with a simple two-layer heterogeneity over reservoir conditions of 10.3-20.7 MPa, 38-91??C and 0-5 mol kg-1 NaCl brine. We demonstrate that, if measured in the viscous limit, relative permeability is invariant with changing reservoir conditions, and is consistent with the continuum-scale multiphase flow theory for water wet systems. Furthermore, we show that under capillary limited conditions, the CO2-brine system is very sensitive to heterogeneity in capillary pressure, and by performing core-floods under capillary limited conditions, we produce effective relative permeability curves that are flow rate and fluid parameter dependent. ududWe show that the appropriate conditions for measuring intrinsic or effective relative permeability curves can be selected simply by scaling the driving force for flow by a quantification of capillary heterogeneity and use this methodology to make measurements of CO2-brine relative permeability for target CO2 storage reservoirs in the UK. ududA new type of pore-scale flow behaviour was identified, that we term dynamic connectivity, using fast synchrotron X-ray computed tomography to image the capillary dominated steady-state flow of N2 and 1.5 mol kg-1 KI brine at 50??C and 10 MPa. Non-wetting phase flow occurred via a stable connected pathway at low capillary numbers and through a series of transient connections between a network of static ganglia with a dynamic connectivity at increasing capillary numbers.ududWe speculate that changes observed in the strength and character of hysteresis between drainage and imbibition during capillary and viscous dominated core-scale experiments is a consequence of this pore-scale flow mechanism.