Laboratory and numerical assessment of potential CO2 leakage through the caprock

The emission of huge amounts of anthropogenic CO2 into the atmosphere have given rise to global warming and therefore climate change. Currently, it is widely accepted that geologic storage of CO2 in deep underground formations has to be part of the solution to mitigate these harmful consequences (IPCC, 2018). The injected CO2 is a non-wetting fluid in the reservoir rock and it is also lighter than the in-situ brine, leading to upward buoyant transport of CO2 across the storage reservoir. The migration of CO2 out of the reservoir is supposed to be principally restricted by a low-permeability and high-entry pressure caprock lying immediately above it. Therefore, the successful and safe retainment of CO2 in place over geologic time scales is strongly controlled by the sealing capacity of the caprock. As CO2 gets in contact with the caprock, the concentration gradient of the dissolved CO2 into brine drives molecular diffusion of the non-wetting fluid out of the storage repository through the fluid-filled interconnected pore network of the caprock (Busch et al., 2008). On the contrary, the bulk penetration of CO2 as a free phase into the caprock encounters capillary resistance imposed by fluid-fluid and fluid-rock interfacial forces operating at tight pore throats. The injection-induced excess pressure and buoyancy forces may increase the differential pressure between CO2 and brine at the reservoir-caprock interface. If the overpressure of the non-wetting fluid exceeds the entry capillary pressure P0 acting at the largest pore throats, it starts invading the caprock. Further increase in the differential pressure overcoming another capillary threshold, termed breakthrough pressure Pbrth initiates a continuous filament of CO2 across the pore system. From this point on, the two-phase flow dominates the volumetric displacement of CO2. It is generally believed that the pressure-driven bulk flow of the non-wetting fluid mainly governs the potential leakage through the intact caprock and that molecular diffusive loss toward the surface is negligible (Song and Zhang, 2013). However, to arrive at a fundamental understanding of the CO2 transport behavior and distinguish between the prevailing leakage mechanisms, further experimental investigations under representative reservoir conditions are required. These experimental studies should be accompanied by appropriate interpretation techniques to accurately deal with the CO2-brine-rock system complexities. The main objective of this study is to combine methods from two complementary disciplines of experimental observations and numerical simulations to get a better insight into the dominant leakage mechanisms of CO2 through the caprock. Our focus is on the potential leakage through the rock matrix. Laboratory tests on an analogous caprock sample are first carried out under the in-situ conditions with the primary goal of evaluating CO2 penetration and flow properties across the caprock. Experimental results are then used to parameterize a two-phase flow model for the numerical simulation and interpretation of the core-scale CO2 breakthrough and flow behavior.

Bibliographic Details

Main Authors:	Kivi, Iman Rahimzadeh, Vilarrasa, Víctor, Makhnenko, Roman
Other Authors:	European Research Council
Format:	comunicación de congreso biblioteca
Language:	English
Published:	2020-11-11
Subjects:	CO2 leakage, Caprock,
Online Access:	http://hdl.handle.net/10261/224411 http://dx.doi.org/10.13039/501100000781
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