Hydrogen geo-storage in rock salt formations: petrophysical characterisation and geomechanical testing of a potential host formation in Western Australia

Abstract

We report the evaluation of the potential suitability of a rock salt formation for waste disposal or energy/gas storage. We consider the case of the Frome Rocks salt dome (depth > 600 m) in the Canning basin, Western Australia. This evaluation involves the characterization of the petrophysical, mineralogical and geomechanical properties of rock salt samples from two contrasting facies, identified from recovered core material: a shallower (800m) heterogeneous facies with 40% halite and 38% of dolomite inclusions (mm to cm); and a deeper (1100m) homogeneous, halite-rich facies (98%).

The dataset includes porosity and gas permeability estimation as a function of confining pressure (or depth); and multi-stage triaxial (MTXL) testing at four distinct confining pressures, one of which corresponding to the confining pressure prevailing at the depth of recovery of each sample. MTXL tests allow to simulate the impact on the mechanical properties of depth within the formation; and that of the stress perturbations induced by drilling/excavation operations. During each stage of an MTXL test, gas transmission and creep were also evaluated under hydrostatic and deviatoric stress conditions.

The heterogeneous (homogeneous) salt facies exhibits a porosity of 0.8 - 1.1% (0.2 - 0.3%), and a gas permeability of 50 - 500 µD (1 - 20 µD), within the confining pressure interval 0 - 16 MPa. Each MTXL test lasted about 80 days, essentially due to the time-consuming nature of the gas transmission and creep evaluations. The two salt facies have a remarkably contrasting mechanical and petrophysical response to hydrostatic and deviatoric stresses; both facies, however, behave in a rather ductile manner at their native depth, i.e., plastic yield rather than brittle fracturing/faulting.