Robert D. Benson¹, Thomas L. Davis²

(1) Reservoir Characterization Project - Colorado School of Mines, Golden, CO
(2) Colorado School of Mines, Golden, CO

ABSTRACT: Dynamic Reservoir Characterization Utilizing 4-D, 9-C Seismic Data, Vacuum Field, New Mexico

The Reservoir Characterization Project of The Colorado School of Mines acquired the first time-lapse (4-D), multi-component (9-C) seismic surveys at Vacuum Field, Lea County, New Mexico. Shear wave (S-wave) and compressional wave (P-wave) seismic data were used to monitor reservoir fluid property changes associated with a carbon dioxide (CO2) tertiary recovery project in the Permian San Andres Carbonate. Reservoir fluid properties including viscosity, density, saturation and pressure changes occur in response to CO2 and oil becoming a miscible phase with the oil. These fluid property changes alter the interval velocity and attenuation of S-waves passing through the reservoir interval by up to 10% but cause little (1 to 2%) or no measurable change in P-wave velocity and attenuation on the surface seismic data.

Seismic shear wave anisotropy in the reservoir causes two shear modes to form (S1 and S2) and to propagate with different velocities. This phenomenon is referred to as S-wave splitting, or birefringence. Seismic shear wave anisotropy is key to monitoring fluid property changes in fractured media. At Vacuum Field the miscible flood bank causes the fractured San Andres reservoir to appear more isotropic. As a result, the tertiary flood bank, and its growth over time, can be monitored by this technology. S-wave anisotropy can be applied to monitor a variety of production processes in fractured media from tertiary recovery projects to primary depletion.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado