Geomechanical variability within the D-E Member of the lower Tuscaloosa Formation supporting the SECARB Phase III CO2 Injection Program

Abstract:

We characterize the mechanical properties at near in-situ conditions of Lower Tuscaloosa lithologies at the Cranfield-site Southeast Regional Carbon Sequestration Partnership (SECARB) Phase III injection program. Four lithofacies in the injection horizon are chosen for strength testing, including: chlorite-cemented conglomeratic sandstone (CSS); mixed chlorite- and quartz-cemented cross-bedded fine sandstone (XSS); quartz-cemented tabular very fine sandstone (TSS); and quartz-cemented siltstone (SiS). Each lithofacies had 25-mm diameter by at least 50-mm length samples plugged. We performed a suite of compression tests for the sandstone at 100°C and pore pressure of 30 MPa, including near-zero effective confining pressure triaxial test, axisymmetric compression tests, and hydrostatic compression test. Sandstones were saturated with supercritical CO₂-equilibrated brine with 30 MPa pore pressure. SiS samples were equilibrated at a constant relative humidity of 77% at 100°C. TSS had the largest yield and failure envelopes. XSS had slightly smaller yield and failure envelopes. CSS was by far the weakest. The sandy facies' effective unconfined tests showed rounded peaks, indicating viscous deformation during damage. SiS had strengths intermediate to TSS and XSS, and CSS. The chemical environment mechanically changed CSS, with cement type exerting control on strength. Constitutive behavior is modeled with elasto-plastic and viscous models. Essential features describing mechanical behavior include non-associative plasticity, stress-invariant dependent failure, elliptical cap surface, kinematic and isotropic hardening, non linear elasticity and elastic-plastic coupling. We discuss the influence of CO2 injection on geomechanical properties. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.