REMINDER: August 11th, 2022 DGS Luncheon Presentation – Tom Bratton

Accounting for Stress Sensitive Formations in Time-Lapse VSP Data while Monitoring for Fluid and Stress Changes in EOR and CCS Projects

Tom Bratton*, Tom Bratton LLC; Lianjie Huang, Los Alamos National Laboratory; William Ampomah, New Mexico Institute of Mining and Technology

Abstract:

The Farnsworth Field Unit (FWU), a mature oilfield in the northeastern Texas panhandle, is currently undergoing CO2-enhanced oil recovery (EOR) with the intent of long-term storage. A high quality time-lapse Vertical Seismic Profile (VSP) was acquired to monitor both P-wave and S-wave velocity changes within an inverted 5-spot pattern with a central injector. The large time-lapse changes observed in the VSP S-wave velocity could not be explained solely by changes in fluid saturation. Core data from the Morrow B injection zone confirmed significant changes in both the P-wave and S-wave velocities that varied with stress loading. The core derived P-wave stress sensitivity was 500 ft/sec/1000 psi change in mean effective stress and the S-wave stress sensitivity was 200 ft/sec/1000 psi. To avoid misinterpreting velocity changes due to stress, a 4D numerical hydrodynamic flow model coupled with geomechanics was used to match the observed changes in the time-lapse VSP. Considering the commonality of stress sensitive formations, this new workflow not only improves the estimates of fluid saturation, but also the changes in in-situ stress.

Tom Bratton is a consultant to the oil and gas industry specializing in geoscience applications for engineering operations. After retiring from a 36-year career with Schlumberger, he was a Visiting Professor and Research Associate in the Petroleum Engineering Department at Colorado School of Mines (CSM). While at CSM, he enrolled as a graduate student and earned his PhD in Geophysics. Before starting his consulting business, Tom was a scientific advisor to Schlumberger’s senior management, specializing in petrophysics, geophysics, and geomechanics with a broad base of experience in drilling, completion, and reservoir engineering. Tom is a full member of the Society of Petroleum Engineers (SPE), Society of Petrophysicists and Well Log Analysts (SPWLA), Society of Exploration Geophysicists (SEG), European Association of Geoscientists and Engineers (EAGE), and the American Rock Mechanics Association (ARMA).