Geosequestration
Geology, and especially the study of sedimentology, is based on understanding the environment that existed at the time the sediments were deposited. This is the most critical factor for understanding the capacity of depositional basins to retain fluids such as hydrocarbons or supercritical carbon dioxide (SC CO2). Fortunately, extensive reservoirs have been delineated by the oil industry in the search for oil and more recently new gas sources in the form of unconventional coal seam/bed/shale methane gas (CH4), although I do recall having lectures on it at University in 1980. Most of the gas was previously wasted (flared) as it was considered a by-product of the production of oil. However, the US Government was liquefying natural gas from 1920 (100-years), made commercially available from 1940 (80-years), fracking from 1950 (70-years) and first shipment from 1960 (60-years), and from 1990, NG has steadily been increasing and doubled from 1.6 (1990) to 3.2Btoe (2020)[1].
This article is focused on the potential for re-injection of CO2 back into reservoirs returning the combustion pollutant CO2 back into long-term geological storage. For some inexplicable reason, despite the extensive science and engineering that has gone into the study of petroleum geology over the last 100-years, and particularly the use of enhanced oil/gas recovery (EO/GR) in the last 50-years, there is ignorance of the process of reversing production to geological sequestration of CO2.
Let us start at the beginning, in order to understand a previous geological environment, we look to the present as the key to unlocking the past, otherwise known as uniformitarianism. The concept was originally proposed by James Hutton 230-years ago, based on the idea that the earth changes uniformly and critically ‘the present is the key to the past’. The former may not hold-up when we consider major natural disasters that accelerate change such as major earthquakes, volcanic eruptions and tsunamis, that are all be linked, and the outpouring of CO2 changing the climate. Now we are conducting a planetary wide experiment, changing the environment and particularly the climate, increasing natural disasters and the sixth global extinction. Recent events have highlighted what’s install for us all, namely wild/bush fires, droughts, floods, windstorms and the mass exodus of climate refugees from Africa to Europe as the Arab Spring dried-up and governments failed to act.
We have proven technological solutions and at the heart of geo-sequestration is the determination of suitable long-term CO2 storage reservoirs (tanks). Despite having incredible geodata processing technologies, such as Petrel 2020, able to create amazing models of the sub-surface from remotely sensed geophysical (seismic) data it is only by drilling and sampling specific sequences that we can confidently place parameters on models. Despite a myriad of in/down-hole geophysical tools it is only by obtaining cores that we truly understand what sedimentary basins geological capacity is. Being old school, we need to get back to basics, and get our hands-on physical samples that we can see directly and test for suitability. At the heart is the determination of what we learnt in 1980 from a Professor from a Texas University, in the US hydrocarbon heartland, called Facies Models (F-M).
As an example, the University of Queensland’s Surat (Basin) Deep Aquifer Appraisal Project (UQ-SDAAP) in 2019, identified a potential carbon capture and storage (CCS) Hub capable of providing material carbon abatement (MCA). MCA is the safe and secure CCS of more than (>) 5Mtpa (large-scale: l-s) for over (>) 20 years (long-term: l-t). This is equivalent to the greenhouse gas emissions (GHGE) from a local super-critical (coal-fired) power plant (SCPP). However, the study used a reference case of nearly 15Mtpa/1.5GW for 30 years, thereby providing CCS for 3x SCPPs in the area. The geological capacity (geo-cap), sub-surface ‘container’ (tank) and high rates of injectivity (CIC).
The tank was identified at the base of the Surat basin, a ~2.5km deep aquifer storage (DAS), GW safe zone of 10km, within the Precipice Sandstone designated as the Blocky Sandstone Reservoir (BSR).
[1] IEA Total energy supply (TES) by source, World 1990–2018. Btoe: billion tons of oil equivalent.