Time-Lapse Integration at FWU: Fluids, Rock Physics, Numerical Model Integration, and Field Data Comparison

Abstract

We present the current status of time-lapse seismic integration at the Farnsworth (FWU) CO2 WAG (water-alternating-gas) EOR (Enhanced Oil Recovery) project at Ochiltree County, northwest Texas. As a potential carbon sequestration mechanism, CO2 WAG projects will be subject to some degree of monitoring and verification, either as a regulatory requirement or to qualify for economic incentives. In order to evaluate the viability of time-lapse seismic as a monitoring method the Southwest Partnership (SWP) has conducted time-lapse seismic monitoring at FWU using the 3D Vertical Seismic Profiling (VSP) method. The efficacy of seismic time-lapse depends on a number of key factors, which vary widely from one application to another. Most important among these are the thermophysical properties of the original fluid in place and the displacing fluid, followed by the petrophysical properties of the rock matrix, which together determine the effective elastic properties of the rock fluid system. We present systematic analysis of fluid thermodynamics and resulting thermophysical properties, petrophysics and rock frame elastic properties, and elastic property modeling through fluid substitution using data collected at FWU. These analyses will be framed in realistic scenarios presented by the FWU CO2 WAG development. The resulting fluid/rock physics models will be applied to output from the calibrated FWU compositional reservoir simulation model to forward model the time-lapse seismic response. Modeled results are compared with field time-lapse seismic measurements and strategies for numerical model feedback/update are discussed. While mechanical effects are neglected in the work presented here, complementary parallel studies are underway in which laboratory measurements are introduced to introduce stress dependence of matrix elastic moduli.

Quantitative interpretation of time‐lapse seismic data at Farnsworth field unit: Rock physics modeling, and calibration of simulated time‐lapse velocity responses

“…The sequential banks of oil, water, miscible CO 2 –oil mixture, and free phase supercritical CO 2 associated with the CO 2 enhanced oil recovery process create a complex fluid system that requires a suitable fluid model to simulate the fluid phase behavior. Although WAG processes result in better oil recovery, it presents a more challenging thermodynamic condition than immiscible fluid systems where the injected CO 2 forms a distinct phase from the original fluid 8 . For this purpose, an analytical study focused on the complex fluid system was developed.…”

“…Interpreting seismic velocities from the FWU VSP record required estimating the rock elastic properties. This study evaluated the matrix elastic properties by analyzing geophysical logs including dipole sonic, pulsed neutron, and magnetic resonance 8 . The porosity dependence of K dry , G dry , and $${K_s}$$ , $${G_s}\;$$were investigated, and a Krief type characterization was performed, yielding a site‐specific Krief coefficient 39 .…”

“…Extrapolating the relationship of the shear and bulk modulus versus porosity yields the $${G_{smean}}$$ and $${K_{smean}}$$. Figure modified from Will et al 8 …”

“…The SWP dynamic model calibrated for the primary and secondary recovery stage was used as a base case model for the tertiary recovery period. The current static model utilizes the hydraulic flow unit to characterize rock types within the reservoir 8,36,44 . An upscaled reservoir simulation model with 94 $$ \times \;$$89 grid cells present in each layer and a total of 677,646 grid cells was utilized in this study.…”

“…Although WAG processes result in better oil recovery, it presents a more challenging thermodynamic condition than immiscible fluid systems where the injected CO 2 forms a distinct phase from the original fluid. 8 For this purpose, an analytical study focused on the complex fluid system was developed. The thermophysical properties of the hydrocarbon-CO 2 fluid mixture were estimated using the Peng-Robinson equation of state (EOS).…”