Steam Dominated GreenLoop: Proof of Concept at The Geysers, California


SCH Number
Public Agency
California Energy Commission
Document Title
Steam Dominated GreenLoop: Proof of Concept at The Geysers, California
Document Type
NOE - Notice of Exemption
Document Description
The purpose of this project is to advance the development of the Steam Dominated GreenLoop (SDGL) system (a closed-looped, down bore heat exchanger system), by demonstrating the SDGL system in an existing low-production well at The Geysers geothermal project to confirm the ability of the SDGL system to deliver enthalpy (the total heat content of a system that is equal to the internal energy of the system plus the product of the pressure multiplied by the volume of the system) to the surface without extracting water or reducing well pressure. The ability to produce power from steam dominated resources without losing water or pressure is crucial to future power generation at The Geysers and other steam dominated resources where geothermal production will decline without water injection. This project is a precursor to scaling the technology up for a proposed 100 MW or more commercial expansion project using the SDGL system. This project will confirm the utility of using the SDGL system in actual steam dominated field conditions.

Contact Information

Benson Gilbert
Agency Name
California Energy Commission
Job Title
Mechanical Engineer
Contact Types
Lead/Public Agency


Northern California
Cross Streets
The Geysers Geothermal Area
Other Location Info
Unit 16 steam field - Davies Estate Pad Site

Notice of Exemption

Exempt Status
Categorical Exemption
Type, Section or Code
Cal. Code Regs., tit. 14, § 15301 ; Cal. Code Regs., tit. 14, § 15302
Reasons for Exemption
1. For Cal. Code Regs. (CCR), Title 14, Section 15301(b) (Existing Facilities): Section 15301 exempts the operation, repair, maintenance, permitting, leasing, licensing, or minor alteration of existing public or private structures, facilities, mechanical equipment, or topographical features, involving negligible or no expansion of existing or former use, this includes in subsection (b): “Existing facilities of both investor and publicly-owned utilities used to provide electric power, natural gas, sewerage, or other public utility services.” This project will retrofit an existing geothermal production well to demonstrate the ability of the SDGL system to deliver enthalpy to the surface without extracting water or reducing well pressure. This is an existing facility with no or negligible expansion of an existing use. 2. For Cal. Code Regs. (CCR), Title 14, Section 15302 (c) (Replacement or Reconstruction of Existing Utility Systems): Section 15302 exempts the replacement or reconstruction of existing structures and facilities where the new structure will be located on the same site as the structure replaced and will have substantially the same purpose and capacity as the structure replaced, this includes in subsection (c): “Replacement or reconstruction of existing utility systems and/or facilities involving negligible or no expansion of capacity.” The existing geothermal production well identified for use to act as the proof of concept project well for the SDGL system is an intermittently producing low production well. No new drilling of the well will be performed as part of the project. Instead, a down bore heat exchanger (DBHX) composed principally of vacuum insulated tubing will be inserted into the existing well and a new well head component (a header) will be added on the surface to properly suspend the DBHX in the selected well. Water will be circulated in the DBHX to capture heat from the well, principally from the latent heat of vaporization associated with the condensation of steam from the geothermal resource on the DBHX, which heat will be transported to the surface by the water circulated in the DBHX. At the surface, instrumentation will be added to measure and assess the performance of the SDGL system and the DBHX. Analysis has suggested that with the SDGL system the well will be able to produce consistently, rather than intermittently, but the total power that can be produced from the well at any specific time will not be substantially increased.


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