Mechanical Earth Modeling at Farnsworth Unit, Texas, USA: Implications for Caprock Integrity, Fault Reactivation, and Reservoir Forecasting

The Southwest Partnership on Carbon Sequestration administers a CO₂ carbon capture utilization and storage (CCUS) project sponsored by the U.S. DOE. The project is located in a mature waterflood converting to enhanced oil recovery using anthropogenic CO₂. Major project goals are optimizing the storage/production balance, ensuring storage permanence, and developing best practices for CCUS. A key component of this effort is generating detailed geologic and flow models.

This paper presents the development of a 3D coupled Mechanical Earth Model (MEM) for use in assessment of caprock integrity, fault reactivation potential, and stress dependent permeability in reservoir forecasts. Mechanical property estimates computed from geophysical logs at selected wellbores were integrated with 3D seismic elastic inversion products to create a 3D “static” mechanical property model sharing the same geological framework as existing reservoir simulation models including three major faults. Stresses in the MEM were initialized from wellbore stress estimates and reservoir simulation pore pressures. One way and two way coupled simulations were performed.

Coupled simulations were performed on history matched primary, secondary, and tertiary recovery periods, and on an optimized WAG prediction model. These simulations suggest that the field has been operating at conditions which are not conducive to caprock failure or fault reactivation. Two way coupled simulations were performed in which permeability was periodically updated as a function of volumetric strain using the Kozeny-Carmen porosity-permeability relationship. These simulations illustrate the importance of frequent permeability updating when recovery scenarios result in large pressure changes such as in field re-pressurization through waterflood after a long primary depletion recovery period. Conversely, forecasting is less sensitive to permeability update frequency when pressure cycles are short and shallow (WAG).

Funding for this project is provided by the U.S. Department of Energy under Award No. DE-FC26-05NT42591. Additional support has been provided by site operator Perdure Petroleum LLC.