Rock Physics for Energy & Environment Solutions
In addition to increase our understanding on the fundamentals of the physics of rocks, non-extensive examples of applications to emerging fields of the Energy challenge can be expected.
Carbon Capture and Sequestration (CCS):
non-extensive exemples of questions in the field, hopefully addressed in the 7IWRP and coming years.
Injecting CO2 in geological reservoirs is a promising strategy to mitigate increases in global warming by taking CO2 directly at the production side and injecting it underground. It however requires research to fully understand the coupled new thermo-chemo-mechanical constrains, e.g. :
Can we precisely track the phase and amount of CO2 present in the reservoir rocks ?
When injected, at depths' P-T conditions, CO2 can be either in gas, supercritical or liquid state. The host reservoir rock is usually saturated by water, from the use of geophysics - and knowledge of the rock physical signature - one can assess the phase of the CO2 at depths. Three main storage cases might exist (i) undissolved CO2 gas as either localised macroscopic plume or homogeneously-distributed bubbles, (ii) dissolved in the water as carbonate anions, (iii) solid phase through precipitation with cations in the solution.
Each state depend on thermodynamics and kinetics, might have its intrinsic geophysical signature and might strongly alter the in-situ rock. From time-lapse 3D geophysics, with the help of seismic and/or electrical methods, one might track changes in saturations and pressures.
How does CO2 storage affect the mechanical properties of host/reservoir and sealing rocks ?
From the storage type and state of CO2, as well as the host/sealing rocks in contact to it, various residence effects might occur, spanning over-pressures, dissolutions of the rock or even precipitation of a secondary mineral phase. One needs the precise knowledge on how much change in geophysical properties are expected from each phenomena in order to invert such information at the field scale.
Do injections strategies, of injection rate and magnitude, affect stability and properties of reservoirs and sealing rocks, as well as at the casings where stresses are largest ?
Independent of the chemical constrain, injections of CO2 in water-saturated reservoir involves the knowledge of - for instance - thermal equilibrium between the injected fluid and host rock. If injection is too fast, and temperature delta too large, thermal stresses might be too localised and large hence induce fracturation. The realm of poro-thermo-elasticity.
What differences might we expect between storage in sedimentary or basaltic rocks ?
Taken from polarpedia & AAPG : Principle and potential targetted reservoir rocks for CO2 injections and storages.
Upper right : Measurements highlighting change in seismic and electrical properties during fluid substitution, from injections of CO2 in a brine-saturated rock (example from NOC, UK).
Lower right : We know that, if CO2 dissolves in water, water acidfies and could dissolve the rock (e.g. calcite or clay minerals in basalts), but could also allow for mineral precipitation (example from CSIRO-ESRE, Perth AU). Such effects can seldom be observed withouth measuring its physical properties.
Geothermal Energy :
non-extensive exemples of questions in the field, hopefully addressed in the 7IWRP and coming years.
Provided that host rocks at temperatures above 100-150°C are reachable at low costs, hence in near surface (e.g. in volcanic zones Island), geothermal energy and powerplants could allow long-term electricity production unaffected by climatic (e.g. sun, wind) conditions. The principle is to create long-term water-cycle loops of injecting in cold water and pumping out hot water. It however is, at current, mainly developed near or at volcanic areas (e.g. Island) as we pretty much know existence of hot water as it permeates to the surface. Developing this energy over a larger scale however involves new and renewed questionnings, e.g. :
Might it occur elsewhere, for instance in zones where volcanism is not observed at the surface ? If so, how could we spot those "bright spots" ?
Do we fully know what physical properties rule heat transfert in water-saturated rocks, e.g. the competition between diffusivity and condcutivity ?
Under construction
Hydrogen storage : Rock physics at the intersection between geomechanics, geophysics, geochemistry…and microbiology.
non-extensive exemples of questions in the field, hopefully addressed in the 7IWRP and coming years.
Do the interactions between the stored hydrogen and the native minerals and pore fluids negatively impact the reservoir, e.g., mechanical stability, permeability, storage capacity, injectivity/productivity,…?
Can conventional shales and evaporites provide adequate caprock sealing for hydrogen storage in depleted gas reservoirs?
How to minimise the contamination of the stored hydrogen with the cushion gas during injection/withdrawal operations
Are aquifers or rock salt caverns suitable for hydrogen storage?
Can microbial activity within the reservoir consume the stored hydrogen, and/or negatively impact the reservoir?
Permafrosts :
non-extensive exemples of questions in the field, hopefully addressed in the 7IWRP and coming years.
Under construction