An Experimental Study on the Flood Characteristic and Fluid Rock Interactions of a Supercritical CO2, Brine, Rock System

Abstract

The South West Hub Project is an Australian government funded initiative in partnership with major local industrial CO₂ emitters. The project aims to reduce emissions by storing commercial quantities of CO₂ in a deep saline aquifer, the Triassic Lesueur Sandstone, located in the Perth Basin of Western Australia. This research investigated the multiphase flow characteristics of the Supercritical CO₂ (scCO2)-brine-rock system pertinent to the potential; storage interval. Core-flooding experiments were conducted on four representative core plugs from the Harvey-1well. The experiments were performed using a conventional unsteady-state procedure to obtain relative permeability and residual saturation measurements. Fluids used during the experimental work consisted of dead formation brine, CO₂-saturated brine and vapour-saturated scCO2. Experimental pressure, temperature and brine salinity values were chosen to match the in-situ ones at the sample depths. Petrophysical measurements were carried out on the samples before and after core-flooding (i.e. helium porosity-permeability; pore size distribution by nuclear magnetic resonance (NMR); microstructural and mineralogical investigations) to assess any potential alteration of the samples induced by the flooding procedure. Results show that porosity is not affected by the flooding procedure, but permeability values significantly differ before and after flooding, causing reductions of 25% to 60%. Formation damage (e.g. fines migration) caused by presence of clay minerals in the sample's pore space may induce unusually low end-point relative permeability values measured at the end of the primary imbibitions. The fines migration hypothesis is supported by NMR measurements performed on two of the samples before and after core-flooding. These indicated a negligible variation of total porosity (also indicated by Helium measurements) but a significant difference in the distribution of pore size compatible with the occlusion of larger pores by the fines dislodged by the fluids flowing through the pore space. Note that the migration of any fines, which may result in blockage and/or bridging of the pore throats, may intensify the snap-off trapping mechanism and consequently cause residual scCO2 saturation measurements to be abnormally high. The residual scCO2 saturations for all the samples tested here are within the range of 23%–43% which are to some extent higher than expected for their respective permeability ranges.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015