Downhole Generator for a Geothermal Injection Well

Abstract

The Northern California Power Agency (NCPA) has successfully developed and demonstrated a new technology to recover the hydraulic head energy of reinjection water so that additional electricity can be generated from under-pressured reservoir injection. The innovative approach incorporates an off the shelf 400 hp electrical submersible pump into an existing geothermal injection well to produce electricity and reduce plant house power expenses. This Pump As Turbine Project resulted in a sustainable generation of 250 kw. NCPA applied for and received a California Energy Commission Grant with the objective of modifying one existing off the shelf downhole electrical submersible geothermal pump to operate as a turbinegenerator. Modifications to the downhole system include a valve to control flowrates, downhole pressure monitoring capability, and a protective shroud for the pump/motor. A wellhead landing spool allows for power cables to extend from the well without any release of geothermal fluids. An at-grade electrical facility was constructed to interconnect the turbinegenerator with the local distribution system and provide generator and system protection. The surface electrical equipment includes transformer, switchgear, cabling, relays, and a medium voltage transmission system. The downhole pump was installed at a depth of 1,800 feet in an injection well and performance is being monitored to develop benchmarks. The specific economic objectives of the Project will be presented in this paper. Due to the success of this first downhole Turbine, a second downhole turbine has been planned by NCPA. Other design improvements are discussed.