Coso Geothermal Field 2.5D Study

We reprocessed 31 miles of 2-D seismic reflection data from the Coso geothermal field, Inyo County, California. Optim specifically designed the array to take maximize the results that could be obtained from applying SeisOpt® technology. The project was funded by the US Navy Geothermal Program Office.

The objectives of the project were as follows:

Demonstrate effectiveness of advanced processing techniques

• Build on success of a DOE-funded pilot study in Dixie Valley
• Resembles active volcanic, geothermal fields worldwide

Utilize new data acquisition parameters

• Designed to enhance results from advanced processing techniques.
  • Image permeable structures at reservoir depth and image tectonic structures beneath the Coso geothermal field

Constrain down-dip geometry of reservoir structures

• Characterize features that are significant for evaluating subsurface permeability
• Correlate down-dip geometry of features mapped on the surface

Image tectonic structures

• To determine their relationship to faults and fractures controlling the reservoir permeability and production

The results of our study revealed three distinct areas of production within the Coso geothermal field. Following are some examples of our work from Coso.

Figure showing our line geometry for the Coso geothermal field. Optim designed the array to maximize the effectiveness of applying SeisOpt® technology. Specific geographic locations were deleted out of consideration for our client.

High resolution 2D velocity model along one of the lines. SeisOpt® technology clearly images the bounds of the geothermal production area. The production areas are manifested in the velocity model as anomalously deep low velocities. It also images lateral velocity variations across known faults like the Coso Wash fault and other discontinuities. Specific geographic locations were deleted out of consideration for our client. It is important to note that no other data but the seismic data were used to derive velocities using SeisOpt® technology.

Prestack Kirchhoff migration using the high-resolution velocity model derived by using SeisOpt® technology. The migration directly images faults and fractures within the Coso geothermal field. Our imaging revealed the down-dip geometry of structures with surface expression and structures that had no surface expression. The high-amplitude reflector at 6 km depth, imaged using SeisOpt® technology, is thought to be a lens of super-heated fluids that are localized beneath the main production area of the Coso geothermal field. Specific geographic locations were deleted out of consideration for our client.

Velocities derived along individual seismic lines (shown in red and labeled on top) were interpolated to obtain the 2.5D velocity model. The figure shows an east-west slice and a depth slice through the 2.5D model. The model clearly shows three distinct low velocity areas that correlate with areas of production. It is important to note that no other data but the seismic data were used to derive velocities using SeisOpt® technology.

The figure shows slices through the 2.5D volume reveal the emergence of distinctive zones of permeability within the geothermal field. Unlike other geophysical methods, SeisOptŪ reveals target depth. The hatchures show limits of model resolution due to non-availability of data and the red lines are the trace of the 2D seismic lines along which data was recorded. Note how the three distinct low velocity areas form at depth. They correlate with areas of production. Specific geographic locations were deleted out of consideration for our client.

The figure shows an east-west slice and a depth slice through the 2.5D model. The model clearly shows three distinct low velocity areas that correlate with areas of production. It is important to note that no other data but the seismic data were used to derive velocities using SeisOpt technology. Specific geographic locations were deleted out of consideration for our client.