Abstract

ABSTRACT: As widespread Carbon Capture and Sequestration becomes more relevant, challenges related to thermal cooling upon injection and the potential for significant stress perturbation needs to be accounted for in geomechanical modelling. The current work shows an example of how temperature fluctuations related to CO2 injection can affect the stress changes within a reservoir using a stiff cemented sandstone analogue for deep reservoirs, and further demonstrates how a laboratory test program can be efficiently used to better define thermal aspects of typical geomechanical parameters such as Young's moduli and Poisson's ratio. The current program has shown how elastic moduli can be affected by changes in temperature, and how these changes can affect the estimation of stress changes within a reservoir. This comprehensive triaxial test also displayed a non-linear behavior at lower effective radial stresses during temperature reduction, which can be related to plastic deformation achieved during cooling. 1. INTRODUCTION As carbon capture and Sequestration (CCS) has gained the public's attention, the necessity to demonstrate that CCS can be deployed safely is key to make CCS an accepted solution as a contribution for reducing global emissions. To predict the reservoir response and ensure safe operations, geomechanical models are used to determine the influence of pressure and temperature change due to injection on the in situ stress conditions. To provide accurate predictions, one of the first steps will be the production of relevant laboratory data to both populate numerical models with the relevant parameters, and to validate these models through laboratory experiments simulating pressure and temperature changes expected due to injection. These models will need to accommodate reservoir responses to typical challenges related to CCS. Thermal effects play a significant role in the geomechanical behavior of reservoirs during CCS operations, where cool CO2 is injected into a warmer reservoir. The resulting changes in temperature lead to contraction of the rock matrix and modification of the stress state (Fjær, 2008; Søreide et al., 2014; Thompson et al., 2021). In sandstone reservoirs, cooling is expected to lead to reduction of effective horizontal stress due to thermal contraction of the rock (Søreide et al., 2014). This reduction in horizontal stress can potentially lead to a more critical stress-state. To understand and predict the influence of temperature on stress in the reservoir, it is critical to determine the relative parameters that may be used to model the influence of cooling.