3D Extended Logging for Geothermal Resources: Field Trials with the Geo-Bilt System
Geo-BILT (Geothermal Borehole Induction Logging Tool) is an extended induction logging tool designed for 3D resistivity imaging around a single borehole. The tool was developed for deployment in high temperature geothermal wells under a joint program funded by the California Energy Commission, Electromagnetic Instruments (EMI) and the U.S. Department of Energy. EM1 was responsible for tool design and manufacture, and numerical modeling efforts were being addressed at Lawrence Livermore Laboratory (LLNL) and other contractors. The field deployment was done by EM1 and LLNL. The tool operates at frequencies from 2 to 42 kHz, and its design features a series of three-component magnetic sensors offset at 2 and 5 meters from a three-component magnetic source. The combined package makes it possible to do 3D resistivity imaging, deep into the formation, from a single well. The manufacture and testing of the tool was completed in spring of 2001, and the initial deployment of Geo-BILT occurred in May 2001 at the Lost Hills oil field in southern California at leases operated by Chevron USA. This site was chosen for the initial field test because of the favorable geological conditions and the availability of a number of wells suitable for tool deployment. The second deployment occurred in April 2002 at the Dixie Valley geothermal field, operated by Caithness Power LLC, in central Nevada. This constituted the first test in a high temperature environment. The Chevron site features a fiberglass-cased observation well in the vicinity of a water injector. The injected water, which is used for pressure maintenance and for secondary sweep of the heavy oil formation, has a much lower resistivity than the oil bearing formation. This, in addition to the non-uniform flow of this water, creates a 3D resistivity structure, which is analogous to conditions produced from flowing fractures adjacent to geothermal boreholes. Therefore, it is an excellent site for testing the 3D capability of the tool in a low risk environment. The Dixie Valley site offered an environment where the tool could locate near-well fractures associated with steam development. The Lost Hills field measurements yielded a data set suitable for 3D imaging. The Geo-BLT data corresponded to existing conventional logging data and showed clear indications, in several depth intervals, of near-well 3D structure. Subsequent 3D inversion of these data produced a model consistent with non-planar water flow in specific layers. The Dixie Valley measurements identified structures associated with dike intrusions and water inflow at particular depths. Preliminary analysis suggests these structures are steeply dipping, which is consistent with the geology.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15013490
- Report Number(s):
- UCRL-JC-148552; TRN: US200601%%439
- Resource Relation:
- Conference: Geothermal Resources Council's 2002 Annual Meeting, Reno, NV, Sep 22 - Sep 25, 2002
- Country of Publication:
- United States
- Language:
- English
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