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Meeting Location: 
Churrascos - River Oaks
2055 Westheimer Road
Houston, TX 77098

5:30 to 6:00 PM Happy Hour
6:00 to 7:00 PM Dinner
7:00 to 8:00 PM Presentation
8:00 until ...  Networking

Speaker: Kristoffer Walker, Chevron
Co Authors: Artur Posenato Garcia, Jeff Nunn, Greg Lyman, Tonya Richardson, and Bruno Dujardin, Chevron

The injection of CO2 into saline reservoirs for Carbon Capture and Storage (CCS) displaces relatively dense brine (1.0 to 1.2 g/cc) with less dense supercritical CO2 (0.5 to 0.8 g/cc). Borehole gravity measured from an injection or nearby observation well is potentially an elegant and fit-for-purpose solution for time lapse monitoring of the reservoir for CO2 flow and the overburden aquifers for leaks through the seal. Such gravity signals are relatively inexpensive to measure, have a well-defined and simple repeatability, and return to baseline levels once the CO2 dissolves into the brine. Confirmation of these theoretical findings via field surveys and subsequent optimization of acquisition strategies and inversions is needed for borehole gravity to be applicable for CCS at scale.

Objectives and Methods: The objectives are to show the feasibility, advantages, and limitations of using borehole gravity for CCS conformance and containment monitoring in typical, saline aquifer scenarios. To this end, numerical simulations are utilized to evaluate borehole gravity associated with CO2 flow. Scenarios span thin and thick reservoirs in deep and shallow environments. Forward and inverse modeling are performed that includes the critically important effects of known repeatability. Sensitivity of gravity and inversions to plume diameter, thickness, saturation variation, borehole location, and repeatability uncertainty is analyzed.  

Speaker Biography: Kristoffer Walker, Chevron
Kris Walker is a research scientist and CCS advisor with 20 years of experience in Borehole Acoustics, Anisotropy, Rock Physics, Seismology, Gravity, Fiber Optic Sensor Development, and CCS.  His interests are in providing energy to an energy-hungry world and solving related technical issues.  He’s authored more than 35 journal papers, 75 conference papers, and 10 patents. He develops technology usually through workflows, data processing algorithms, and modeling software applications, with the most recent focus involving CCS and unconventional geomechanics.  At Chevron he has various roles involving leadership, technology development, and computational research, and is the Chevron Technical Center leader for Geophysics and Petrophysics CCS R&D.  Before Chevron he worked at Halliburton for five years in their Wireline Borehole Acoustics Team as a team lead and scientific advisor.  Before Halliburton he worked for 10 years at the University of California, San Diego, as an Associate Research Geophysicist.  He has held various professional society volunteer roles.  Currently he is on the IMAGE conference program committee, secretary for SPWLA Borehole Acoustics SIG, and a member of the organizing committee for Annual AAPG/SEG/SPE CCUS Conference.

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