Interpretation of multicomponent seismic data across Wister geothermal field, Imperial Valley, California

Abstract

Multicomponent seismic technology has been implemented across Wister geothermal field in southern California to evaluate the potential for further development of geothermal resources. The seismic survey was positioned atop the San Andreas fault system that extends southward from the Salton Sea. An interpretation of Wister Field geology was made using both P-P and P-SV seismic data. Two formation horizons, Canebrake/ Olla/Diablo and Deguynos, were interpreted. Seismic time-structure maps were generated for each horizon. The objective of the study was to determine whether productive geothermal resources could be detected and mapped more reliably with multicomponent seismic data than with single-component P-P data. Complex faults associated with the regional San Andreas Fault system were interpreted across the 13.5 mi 2 3D image space. The structural maps created are thought to be some of the most accurate depictions of subsurface structure publicly available in this area of the Imperial Valley. Particular attention was given to documenting faults that cut across deep strata. Both P-P and P-SV seismic showed evidence of such deep faults. Rock properties were analyzed from well logs. Log data showed that clastic rocks at this site exhibited measurable differences in V P ∕V S velocity ratios for different rock types. Specifically, sand-prone intervals were associated with relatively low V P ∕V S velocity ratios, and shale-dominated intervals had higher V P ∕V S ratios. Using this rock physics behavior, V P ∕V S values derived from seismic traveltime thicknesses were useful for recognizing lithological distributions and identifying favorable reservoir facies. Seismic data across Wister Field, like seismic data across many geothermal fields, have a low signal-to-noise character. We demonstrate that a unified and integrated interpretation of P and S data, even when seismic data quality is not as good as interpreters wish, can still yield valuable information for resource exploitation.

Extracting and Applying SV-SV Shear Modes from Vertical Vibrator Data Across Geothermal Prospects Final Report

“…We particularly recommend the use of the Vp/Vs velocity ratio for estimating the distributions of rock types within a geothermal system. We did not include an example of the value of the Vp/Vs velocity ratio in this paper, but an example is included in our companion paper that appears in this same publication (Wei, et al, 2014). The use of this velocity ratio parameter requires that a dipole sonic log be acquired in one or more local wells to determine how the Vp/Vs velocity ratio varies for the particular rock types found in any geothermal field that is being interpreted.…”

Advanced seismic processing/imaging techniques and their potential for geothermal exploration

“…Steam introduces higher absorption of the seismic wavefield and also has the effect of decreasing the seismic velocity. Wei et al (2014aWei et al ( , 2014b show the benefits of using multicomponent seismic data in the Wister geothermal field, which is a Cenozoic sedimentary basin located in California. The goal of their study was to evaluate potential reservoir units, locate fault, and fracture zones and investigate whether additional value can be gained from multicomponent seismic data.…”