Development of Methods to Improve Subsurface Injection Project Site-Suitability Assessments Conducted in the Alberta Basin
Creators: Samaroo, Mahendra
Publisher: name: University of Alberta Library
Year: 2023

<p>Drastic changes in the scale and type of fluid injection required to support the implementation of a net-zero energy economy have introduced risks previously not considered in existing site screening processes conducted for industrial-scale injection projects. A scale of injection unprecedented in human history into underexplored injection target formations is being considered, with limited knowledge of potential cumulative or long-term consequences. New methods are required to complement existing site screening and risk assessment procedures for such projects, to account for the potential to impact other (current and future) subsurface users, to trigger induced seismicity and the likelihood of achieving long-term injectivity goals.<br>
This research adapted an existing method (developed for hydrocarbon resource assessment) and used this adaptation along with over 63 million fluid extraction and injection records from over 610,000 wells over the last 60 years to calculate the net fluid balance (a new capacity estimation parameter, equivalent to the upper limit of sustainable injection capacity) at various stratigraphic intervals in the Alberta Basin. This new workflow enables the use of high confidence, publicly available volumetric data to evaluate the in-situ net fluid balance in various geographic locations and stratigraphic intervals in the Alberta Basin. The results indicate that significant sustainable injection capacity may exist within the extensively depleted Mesozoic formations (legacy oil and gas reservoirs) in several geographic locations in the basin, while limited sustainable injection capacity appears to exist in Paleozoic formations in contact with the Precambrian basement. <br>
A novel fluid-injection project site selection screening method was then developed. This method is designed to evaluate and rank the brittleness/ductility and the potential for fault slip associated seismogenicity in geologic formations, based on current in-situ stress state and rock geomechanical properties. The application of this new method to evaluate and rank the potential for seismogenic/aseismic fault slip was then demonstrated, by evaluating over 3,000 laboratory core triaxial tests along with the in-situ (minimum horizontal, vertical) stress and pore pressure measurements available for 51 injection and confining formations in the Alberta Basin. This analysis indicates that most of the major formations evaluated in the Alberta Basin were ductile (at the time of the in-situ measurements) and likely to display low potential for seismogenicity (i.e., fault slip likely to be aseismic), which is consistent with induced seismicity observations in the Alberta Basin over the past decade. <br>
A workflow was then developed for generating high confidence estimates of long-term (20 year) sustained regional-scale carbon dioxide (CO2) injectivity rates in key disposal formations in the Alberta Basin. The utility of this workflow was demonstrated by first using the results of over 3,000 laboratory core tests to construct 22 regional-scale 3D geological, geomechanical and petrophysical models. These models were then calibrated with calculated regional-scale injectivity data obtained from disposal operations conducted in over 4,000 wells over the last 60 years, and the calibrated models used to simulate the effects of 20 years of CO2 injection in these (22) formations. This analysis indicates that several of the ductile (legacy, depleted hydrocarbon reservoir) Mesozoic formations in the Alberta Basin are also capable of supporting sustained CO2 injection at the rates needed to enable commercial-scale sequestration activities (in addition to the main virgin pressure Paleozoic saline aquifer currently targeted) and that CO2 presence and material formation pressure increases can be expected at distances of at least 12 km from the injector.<br>
The three workflows developed and demonstrated in this research may be useful complementary criteria for project proponents and regulators to consider during project site suitability studies conducted at the site screening stages of industrial-scale fluid disposal project development in any sedimentary basin. Consideration of the net fluid balance, brittle-ductile state, and long-term sustained injectivity rates could improve the site selection process, help reduce project risks and thereby enhance the chances of successful commercial-scale CO2 injection project development and operations.</p>