PNNL

Abstract

The impact of temperature variations of the injected CO2 on the mechanical integrity of a reservoir is an important problem but rarely addressed in the design of a CO2 storage site. In this study, a three-dimensional (3D) thermo-geomechanical approach was developed to evaluate the possibility of fracturing the FutureGEN 2.0 site due to injection of supercritical CO2 at different temperatures. The approach sequentially coupled the STOMP-CO2 code for flow and thermal analyses to the ABAQUS® finite element package for performing thermo-geomechanical analyses of this site. The 3D model of the FutureGEN 2.0 site contains four horizontal wells and variable layer thickness and geo-thermomechanical properties. It takes into account the results from modeling the heat exchange between the environment and CO2 during its transport in the pipeline and injection wells before reaching the reservoir, as well as its interaction with the reservoir host rock. Injection temperature in the reservoir was varied, and two cases were simulated and modeled: 28°C, the minimum possible temperature considered as an extreme case since it corresponds to winter conditions maintained during the 20 years of the injection, and 47°C, the annual average temperature. The STOMP-CO2/ABAQUS® analyses indicate lower injection temperatures approaching 28°C could locally induce hydraulic fractures close to the wells and confined to the reservoir. Thermally induced fracturing is not expected for injection temperatures of 47°C or higher. In that temperature range, the injection temperature would be at or above the natural reservoir temperature, and thus we can conclude that thermally induced fracturing should not occur in the FutureGen 2.0 reservoir.