Assessing Potential Thermo-Mechanical Impacts on Caprock Due to CO2 Injection—A Case Study from Northern Lights CCS

Abstract

Due to significant temperature differences between the injected medium and in situ formation, injection of CO2 (as with water or other cold fluids) at depth induces thermal changes that must be accounted for a complete understanding of the mechanical integrity of the injection/storage system. Based on evaluations for the Northern Lights Carbon Capture and Storage (CCS) project, we focus on thermal effects induced on the caprock via conduction from cooling in the storage sands below. We investigate, using both analytical and numerical approaches, how undrained effects within the low permeability caprock can lead to volumetric contraction differences between the rock framework and the pore fluid which induce both stress and pore pressure changes that must be properly quantified. We show that such undrained effects, while inducing a more complicated response in the stress changes in the caprock, do not necessarily lead to unfavourable tensile conditions, and may, in fact, lead to increases in effective stress. These observations build confidence in the integrity of the caprock/seal system. We also show, through conservative assumptions, that pressure communication between the caprock and storage sands may lead to a localised negative effective stress condition, challenging stability of the base caprock, which will be mitigated for in field development planning.

Impact of the lower Jurassic Dunlin Group depositional elements on the Aurora CO2 storage site, EL001, northern North Sea, Norway

“…Pressure measurements in the well strongly support the suitability of the Drake Formation as cap rock (Meneguolo et al, 2020). Additional characterization of the unit included rock mechanical testing and mineralogical composition and further confirmed that the Drake Formation would act as a robust top seal for the injection targets (Thompson et al, 2022(Thompson et al, , 2021Meneguolo et al, 2021).…”

Third‐order elasticity of transversely isotropic field shales

“…Shales, abundant in the overburden, are known for their low permeability. It is commonly assumed that shales exhibit undrained static stiffness (Bauer et al, 2008;Delle Piane et al, 2011;Islam & Skalle, 2013;MacBeth & Bachkheti, 2021;Sarout & Guéguen, 2008;Soldal et al, 2021;Thompson et al, 2021). In low-permeability formations, the immediate response to reservoir depletion is a heterogeneous undrained pore-pressure change that occurs within a substantial volume surrounding the reservoir, encompassing the entire overburden (Duda et al, 2023;Yan et al, 2023).…”

Thermo-Poromechanical Properties of Pierre II Shale

“…Thus, the temperature of CO 2 is warmed up above 0 °C before its injection to prevent the formation of hydrate or freezing of the pore network and thus the decreasing of injectivity (Hoteit et al 2019;Möller et al 2014). However, even in this case, the temperature of CO 2 at wellhead which can be around 25 °C (or lower) is still lower than that of the in-situ reservoir (around 105 °C or higher) and still lower that of the rock formation behind the casing (Loeve et al 2014;Paterson et al 2010;Thompson et al 2021). This temperature gap between the injected CO 2 and the reservoir as well as the borehole and its surrounding will therefore lead to thermal loadings on the in-situ formations (including the caprock) consisting of cooling during injection and heating back when the injection must be paused (e.g., due to batchwise injection procedure or to technical issues).…”

“…The evaluation of temperature effects on wellbore and insitu formation, which is usually based on theoretical prediction and numerical simulations, requires the knowledge of thermo-poroelastic parameters for their validation, as it can be noticed in investigations (Ghabezloo 2011;Ghabezloo et al 2009;Thompson et al 2021;Vu 2012). The poroelastic parameters derived under isothermal conditions initially derived by Biot (1941Biot ( , 1957 followed by Rice and Cleary (1976), and Zimmerman et al (1986), have been extended to account for temperature effects on the pore fluid and the matrix (Cheng 2016;Ghabezloo et al 2009;McTigue 1986;Palciauskas and Domenico 1982).…”