Three-Dimensional Modeling of the Reactive Transport of CO2 and Its Impact on Geomechanical Properties of Faulted Reservoir Rocks and Seals

Abstract:

This presentation develops a multiscale model to analyze CO₂ faulted reservoirs using the STOMP-CO2-R code that is interfaced with the ABAQUS^® finite element package. The STOMP-CO2-R/ABAQUS^® simulator accounts for the reactive transport of CO₂ causing mineral composition changes that modify the geomechanical properties of reservoir rocks and seals. Rocks’ elastic properties that vary during CO₂ injection and govern the poroelastic behavior of rocks are modeled by an Eshelby-Mori-Tanka approach implemented in ABAQUS^®. A three-dimensional (3D) STOMP-CO2-R model for a reservoir containing an inclined fault is built to analyze a formation containing a reaction network with 5 minerals: albite, anorthite, calcite, kaolinite and quartz. A 3D ABAQUS^® finite element mesh that exactly maps the STOMP-CO2-R grid is developed for coupled hydro-geochemical-mechanical analyses. The model contains alternating sandstone and shale layers. The impact of reactive transport of CO₂ on the geomechanical properties of reservoir rocks and seals are studied in terms of mineral composition changes that affect the rock stiffness, stress and strain distributions, and pressure margin to fracture (PMF). Simulations assuming extensional and compressional stress regimes with and without coupled geochemistry are developed to study the stress regime effect on the risk of hydraulic fracture. The tendency for the fault to slip is examined in terms of stress regime, geomechanical and geochemical-mechanical effects. The results show that the mineralogical changes due to long-term injection of CO₂ reduce the permeability and elastic modulus of the reservoir leading to a reduction of the PMF at and beyond the injection location. Hydraulic fracture and fault slip are not predicted to occur. However, accounting for the geomechemical-mechanical effect in the analysis under the extensional stress regime leads to reduction of the PMF at the injection location and at the seal immediately above this location.