Title:

Characteristics of the Cove Fort - Dog Valley - Twin Peaks Thermal Anomaly, Utah

Authors:

Rick ALLIS, Mark GWYNN, Christian HARDWICK, Stefan KIRBY, Roger Bowers, Joseph MOORE, Stuart SIMMONS, Phil WANNAMAKER

Key Words:

Cove Fort, Dog Valley, Utah, heat flow, thermal regime, pressure regime

Conference:

Stanford Geothermal Workshop

Year:

2017

Session:

Field Studies

Language:

English

Paper Number:

Allis

File Size:

1967 KB

View File:

Abstract:

There has been considerable geothermal exploration in the region of Cove Fort since the 1970s, culminating recently in the construction of ENEL’s 24 MW (gross) binary power plant in late 2013 at Sulphurdale. This paper is a reassessment of more than 160 thermal gradient wells, 8 wells between 500 and 2.3 km depth, and over 20 wells with water level and temperature information from the Utah Division of Water Rights database. Contouring temperatures at 100 m depth indicates a 500 km2 area of anomalously high temperatures (mostly between 20 – 50 °C) extending 20 km northeast and west from near the Cove Fort power plant. Most of the thermal anomaly, including the reservoir beneath Sulphurdale, appears to coincide with Paleozoic formations at relatively shallow depth. These are dominated by fractured carbonates with characteristically high permeability. Typically the mean annual ground temperature indicated by the gradients is 13 ± 2 °C, so 20 °C represents an average gradient of 70 °C/km. Assuming a thermal conductivity of 1.5 W/m°C for the uppermost 100 m of alluvium and volcanics, the 20°C isotherm corresponds to a conductive heat flow of about 100 mW/m2, and the anomalous conductive heat loss inside this contour is 110 MW with a 20% uncertainty. This implies a large thermal system at depth, and if generated by a 150 °C cross-flow of water cooling conductively to 20 °C, this amounts to a flow of about 200 kg/s. Additional cooling by mixing with cold groundwater would increase the total heat loss and the mass flow. By way of contrast, the conductive thermal loss from the Roosevelt geothermal system 25 km to the west is only 50 MW. The cooler temperatures (60 – 90 °C) in the Paleozoic section encountered in the Hunt Energy well north of Dog Valley supports a crossflow from the south (Sulphurdale) to the north and west. The highest recorded temperatures around Cove Fort are in the volcanics overlying the carbonate reservoir, and in a monzonite intrusion beneath the carbonate (170 – 180 °C.) This suggests the carbonates should be considered as a large outflow zone fed from an upflow zone, possibly southeast or southwest of Sulphurdale. The fluid pressure regime is an important aspect of understanding the hydrogeology. The deep wells penetrating the carbonates within the thermal anomaly are under-pressured with respect to a cool, near-surface groundwater aquifer. Their hot water head is at about 1500 - 1600 m asl in contrast to the cold groundwater head between 1700 – 1800 masl. The low pressure hot water within the carbonates requires equilibration with regional groundwater of similar or lower head, which is present around the northern and western boundaries of the thermal anomaly. Twin Peak Spring, near the northwest edge of the thermal anomaly and with a Cl concentration of 2300 mg/kg and a temperature of 28 °C, could have been sourced from Cove Fort geothermal water cooled predominantly by thermal conduction. A well drilled to 1200 m depth in the Tertiary volcanics 5 km west of Sulphurdale (22-2, Amax-Hunt Energy) had a head of 1800 m asl and a thermal gradient of 70 °C/km. This possibly indicates an upflow zone, with a higher temperature and pressure than the carbonate outflow zone, may be present in either a fault zone beneath the volcanics to the southwest, or in fractured monzonite to the southeast of Sulphurdale.


ec2-44-200-210-43.compute-1.amazonaws.com, you have accessed 0 records today.

Press the Back button in your browser, or search again.

Copyright 2017, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.


Attend the nwxt Stanford Geothermal Workshop, click here for details.

Accessed by: ec2-44-200-210-43.compute-1.amazonaws.com (44.200.210.43)
Accessed: Thursday 28th of March 2024 05:19:16 PM