Laboratory Seismic Methods for Remote Monitoring of Thermal EOR

Abstract

Summary Laboratory measurements of compressional (P) and shear (S) wave velocities and first-arrival amplitudes at ultrasonic frequencies (0.65 to 1.70 MHz [0.65 × 106 to 1.70 × 106 cycles/sec]) in unconsolidated tar and heavy-oil sands indicate that wave-propagation properties in these materials are sensitive to bitumen content. Studies made at elevated temperatures, overburden pressures, and pore pressures revealed that heat and oil content in Venezuelan, Californian, and Canadian reservoir samples had large effects on the measured P and S velocities and amplitudes. Similar results were obtained on well-consolidated sandstones at lower frequencies (1.60 to 3.60 kHz [1.60 × 103 to 3.60 × 103 cycles/sec]). The velocity and relative P-wave attenuation results show that in reservoir sands with high brine-to-oil ratios, the presence of steam or gas is easily detected. In sands with low brine-to-oil ratios, with oil occupying at least half of the available pore space, the presence of steam is not easily detected, but velocities and attenuation are highly sensitive to the temperature of heated oil. Indeed, measurable seismic properties may become a powerful tool for mapping temperature distribution, and therefore viscosity distribution, within heated reservoirs. The results suggest that seismic wave transmission and possibly reflection methods should be highly successful in locating thermal EOR fronts and in monitoring the distribution of heated tar and heavy oils within a reservoir. The application for this technique is evident: because of the potential to track heated oil remotely, field operators may be able to determine optimal placement of future production or injection wells.