Speaker
Description
Continental Flood Basalts (CFBs) have recently garnered significant attention as a prospective target for geological carbon storage (GCS) due to their vast areal extent, good hydraulic connectivity, and mineralogical composition conducive to trapping CO2 as stable secondary carbonates. However, understanding the complete feasibility of CFBs for GCS requires further studies due to the complexities associated with carbon trapping. Unlike conventional siliciclastic formations, the potential injection intervals of CFBs consist of interbedded vesicular zones. Vesicular intervals range in thickness from a few meters to tens of meters and the pore network properties (range in pore size and pore connectivity) are highly variable. This heterogeneity results in greater uncertainty in the prediction of the CO2 plume extent, the CO2 trapping efficiency and pressure build-up during industrial-scale CO2 injection.
This study highlights the trapping efficiency and geo-mechanical risks associated with injecting CO2 in form of supercritical CO2 (sc-CO2) and CO2-enriched water (CO2-ew) in CFBs. Two 3D reservoir domains (4 meters and 10 meters thick) representing vesicular basalt layers were developed. A range of geological and multiphase flow properties was used to model scenarios that varied from well- to poorly-connected systems. The Van Genuchten-Mualem and Van Genuchten equations were employed to model the effects of relative permeability and capillary pressure. Injection of sc-CO2 and CO2-ew was simulated at three different rates (100 ktpa, 500 ktpa, and 1 mtpa), resulting in a total of 90 simulations. A range of in-situ stress field conditions—spanning normal fault, strike-slip fault, and reverse fault regimes under different tectonic stresses—were analysed to assess their impact on potential rock failure. The Mohr circle, Mohr-Coulomb, and Griffith criteria were utilized to visualize changes in the state of stress.
Our results demonstrated that pore fluid pressure began to increase within approximately one day of injection, with higher pressure buildup observed in sc-CO2 injection scenarios. The thinner domain (4 meters) was found to be geo-mechanically less suitable for efficient injection of both sc-CO2 and CO2-ew phases, particularly at higher injection rates, due to its limited capacity to dissipate pressure. However, limited reservoir thickness was associated with higher pore space utilization (34.4%) at lower injection rates (100 ktpa) compared to the thicker domain (15.8%) (Figure 1a). Notably, some models at higher injection rates (500 ktpa) showed up to 90% pore space utilization for the thinner domain. Conversely, the thicker vesicular domain (10 meters) proved to be better suited for efficient injection of both sc-CO2 and CO2-ew phases in terms of geo-mechanical stability. Moreover, thrust fault regimes under moderate tectonic stress conditions provided more stable environments for CO2 injection (Figure 1b, c), thereby minimizing the likelihood of geo-mechanical failure.
Figure 1: (a) Comparison of pore space utilization in the first (4 meters) and second (10 meters) domain for 100 ktpa injection. Comparison of geo-mechanical failure analyses for the second domain for (b) sc-CO2 and (c) CO2-ew injections under moderate (left panel) and extreme (right panel) tectonic stress in thrust fault regimes.
| Country | Australia |
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