What does it take to build a GT plant? Cobb Mt expansion meeting coverage provides end-to-end details

In California, coverage of a Lake County meeting on a proposed expansion of a geothermal project on Cobb Mountain by Lake County News Reports included a detailed examination of the extensive issues that must be dealt when siting and building geothermal facilities. And this for an expansion of an existing site that resides within The Geysers Known Geothermal Resource Area that hosts a number of operating power plants. The project is inside a leasehold of about 350 acres known as the Francisco Leasehold, Lake County, CA.

According to the report, the project’s owner, Bottle Rock Power GeoResource, has filed an application with the county for a conditional use permit, requiring the county to conduct an environmental review of the steam project. The project itself will involve the construction of two new well pads near the existing Bottle Rock Power generating facility, each with 11 production wells and one injection well, as well as associated access roads and pipelines.

County officials are working with the California Energy Commission and the U.S. Bureau of Land Management in the preparation of an environmental impact report. The Energy Commission has jurisdiction over the licensing of the Bottle Rock plant, but the county has jurisdiction over production and injection wells and associated infrastructure. BLM well permits are required because the new steam field is on private land with federal mineral rights.

The report includes a description of the project and site conditions. Interestingly, the general locations for the two well pads were originally identified during the mid-1980s when the Department of Water Resources held the geothermal rights and had planned to develop the resource. Among the criteria for pad location include: the absence of any landslide potential; minimization of the total area of disturbance; the anticipation of major environmental constraints prior to detailed environmental analysis; and the ability to access all major geothermal resource targets within the lease using currently available directional drilling technologies. All of these issues are to be reviewed once again.

It is noted that the operational area of each well pad would be approximately 3.2 acres in size but construction of the pads would disturb an area of approximately 8.3 acres for the one pad (West pad) and 8 acres for the second (East) pad and that access to the East pad would disturb approximately 5.2 acres. Here, a geotechnical study would be completed prior to construction for slope stability analysis to minimize the chances of landslides and other geologic hazards. Also, well pad preparation will have to meet Lake County Grading Ordinance restrictions. The handling of top soil, cleared organic material, fill and revegitation must be spelled out prior to the start of construction and many of the details can be found in the report.

Drilling and drill rig parameters for the 10,000 to 12,000 ft well are spelled out as well and only a short summary is provided here to give a sense of detail. The wells would be drilled with a rotary drilling rig similar to those used throughout The Geysers. Directional drilling may be conducted based on the location and extent of geothermal resources in proximity to the well site. Geothermal drilling permit applications would be submitted to the BLM for the drilling of these wells. A Drilling Plan would be prepared prior to drilling each well. The Drilling Plan would detail the drilling sequence of operations, the rig well pad layout, a well completion schematic, and a description and specification of the temporary noise barriers that are used for drilling.

Drilling operations would be carried out 24 hours a day, seven days a week, until total depth is reached. An estimated 60 to 90 days would be required to drill and test each well, and approximately 12 to 15 field personnel would be working on each drilling operation at any one time. No camp sites or air strips would be required on the lease site. All support facilities for drilling operations would be located on the well pads. Drilling supervision would also be on site in trailers 24 hours a day.

The report concludes with details on the siting of steam and injection pipelines; equipment and facility improvements (primarily access roads, pipeline extensions and control systems); building new access roads; and potential environmental impacts, which include some things one would expect, as well as aesthetics; air quality; biological resources; cultural resources; noise; population/housing; public services/recreation; transportation/traffic; and utilities/service systems. Follow the link above for the complete, detailed report.