Arthur S. Seki

Field testing of an optical fiber temperature sensor in a geothermal well

A program has been initiated for developing and field testing optical fiber sensors to monitor in situ physical and chemical parameters in highly corrosive environments, such as geothermal wells, oil wells, and hot-water boiler reactors. The difficulty of sampling hot geothermal fluids or reliably measuring physical and chemical properties of brines in wells limits the authors understanding of in situ conditions in geothermal fields. In this communication, the authors report a test of the concept of utilizing optical fiber based sensors by measuring the temperature profile of a geothermal steam well. The purpose of this paper is not only to demonstrate that a temperature optical chemical sensor (optrode) can be used to obtain realtime information from a geothermal well, but also that great potential of the optrodes can be exploited for measuring physical and chemical parameters in the field. It is believed that this is the first real-time, in situ, geothermal well measurement to have been made using an optical fiber sensor.

The Hawaii geothermal applications program

The Puna Research Center (PRC) will provide a facility next to the Hawaii Geothermal Project for high technology research, development and demonstration in geothermal and related activities. PRC will initiate an industrial park development and examine multi-purpose dehydration, minerals utilization and biomass applications related to this technology. The facility will become operational in autumn 1985.

Hawaii Geothermal Project: HGP-A Reservoir Engineering

Department of Energy, Contract EY-76-C-03-1093; Energy Research and Development Administration, Contract E(04-3)-1093; National Science Foundation, Grant GI 38319; State of Hawaii, Grants RCUH 5774, 5784, 5942; County of Hawaii, Grant RCUH 5773; Hawaiian Electric Company, Grants 5809, 5828.

Geothermal reservoir engineering of HGP-A : a summary report of activities up to October 31, 1976. Technical report No. 19

The initial four holes were drilled in 1961 by the Hawaii Thermal Power Company. Recent measurements have shown that these temperatures have not change significantly. It is interesting to note that TTW #2 shows virtually a continuous increase in temperature with depth, with a sharp gradient from 253 to 262 feet. However, the well had caved in at around 361 feet, when a temperature of 97° was measured at this point in 1975. TTW #3 was measured to the bottom of the well. where a peak temperature of 93°C was measured at around 540 feet. A sharp positive gradient was measured from 460 feet to 540 feet, and a rather sharp negative gradient (not as steep as the positive gradient) from 540 feet to the bottom (Epp and Ha1unen, 1976).