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This factsheet briefly summarizes and clarifies the application of aerial infrared surveys in geophysical exploration for geothermal energy sources and environmental monitoring for potential volcanic hazards.
For the largest producing natural gas fields in the onshore Gulf of Mexico Basin, the relation between temperature versus depth was investigated. Prolific natural gas reservoirs with the highest temperatures were found in the Upper Cretaceous downdip Tuscaloosa trend in Louisiana. Temperature and production trends from the deepest field, Judge Digby field, in Pointe Coupe Parish, Louisiana, were investigated to characterize the environment of natural gas in the downdip Tuscaloosa trend. The average production depth in the Judge Digby field is approximately 22,000 ft. Temperatures as high as 400 degrees F are typically found at depth in Judge Digby field and are anomalously low when compared to temperature trends extrapolated to similar depths regionally. At 22,000 ft, the minimum and maximum temperatures for all reservoirs in Gulf Coast producing gas fields are 330 and 550 degrees F, respectively; the average temperature is 430 degrees F. The relatively depressed geothermal gradients in the Judge Digby field may be due to high rates of sediment preservation, which may have delayed the thermal equilibration of the sediment package with respect to the surrounding rock. Analyzing burial history and thermal maturation indicates that the deep Tuscaloosa trend in the Judge Digby field is currently in the gas generation window. Using temperature trends as an exploration tool may have important implications for undiscovered hydrocarbons at greater depths in currently producing reservoirs, and for settings that are geologically analogous to the Judge Digby fiel
The amplitude level and velocity of seismic noise at The Geysers area in California are different from the average pattern of background noise. The predominant peak in the spectrum of noise occurred at about 1 Hz. This noise was highly coherent over a distance of about 1 km, showed episodic bursts of energy, and appeared to come from the general region of major geothermal activity in the region. The predominant noise velocities were in the 4 to 7 km/sec range.
The Bruneau-Grand View area occupies about 1,100 square miles in southwest Idaho and is on the southern flank of the large depression (possibly a graben) in which lies the western Snake River Plain. The igneous and sedimentary rocks in the area range in age from Late Cretaceous to Holocene. They are transected by a prominent system of northwest-trending faults. For discussion purposes, the aquifers in the area have been separated into two broad units: (1) the volcanic-rock aquifers, and (2) the overlying sedimentary-rock aquifers. The Idavada Volcanics or underlying rock units probably constitute the reservoir that contains thermal water. An audio-magnetotelluric survey indicates that a large conductive zone having apparent resistivities approaching 2 ohm-metres underlies a part of the area at a relatively shallow depth. Chemical analysis of 94 water samples collected in 1973 show that the thermal waters in the area are of a sodium bicarbonate type. Although dissolved-solids concentrations of water ranged from 181 to 1,100 milligrams per litre (mg/l) in the volcanic-rock aquifers, they were generally less than 500 mg/l. Measured chloride concentrations of water in the volcanic-rock aquifers were less than 20 mg/l. Temperatures of water from wells and springs ranged from 9.5 to 83.0 degrees C. Temperatures of water from the volcanic-rock aquifers ranged from 40.0 to 83.0 degrees C, whereas temperatures of water from the sedimentary-rock aquifers seldom exceeded 35 degrees C. Aquifer temperatures at depth, as estimated by silica and sodium-potassium-calcium geochemical thermometers, probably do not exceed 150 degrees C. However, a mixed-water geochemical thermometer indicates that temperatures at depth may exceed 180 degrees C. The gas in water from the volcanic-rock aquifers is composed chiefly of atmospheric oxygen and nitrogen. Methane gas (probably derived from organic material) was also found in some water from the sedimentary-rock aquifers. The thermal waters in the area are believed to be heated by deep circulation in a zone of high geothermal gradient resulting from thinning of the earth?s crust.
The following method of geothermal gas collection meets our needs for chemical and isotopic gas analyses, requires a minimum of special equipment in the field, and provides field analytical data of assistance in a sampling program.
The purpose of the attached bibliography is to supply in one document an annotated listing of the references pertaining to the density of solutions of importance to geothermal exploration and energy production.
About three years ago, at the initiation of a major effort by the U.S. Geological Survey into studies of geothermal systems, a decision was made to evaluate the audio-magnetotelluric, AMT, technique for this application. At that time we had had no real experience with the method nor any equipment. Some prior work by Lebel [1971], and Slankis and others [1972], suggested that field operations might be slow and difficult reducing the advantages of the method. A cautious approach was used in developing equipment and field techniques until some experience was gained with the method. As no commercial equipment was available, design and fabrication of the AMT equipment to cover the frequency range 8 Hz to 18,600 Hz was done in-house. Because of the nature of the method, our approach has been to use AMT surveys for reconnaissance exploration and to follow up with other electrical methods in interesting areas. In this paper some of the results of our research are shown to illustrate the effectiveness of the technique.
In order to explore for economic steam reservoirs, it is important to know the complete, three-dimensional geology which governs such a system. The Geysers-Clear Lake region California (figure 1), has the world's largest production of commercial power from a dry steam geothermal reservoir. This paper describes gravity and magnetic field analysis at The Geysers which defines a possible deep geologic structure and heat source.
This paper was written to (1) illustrate a process of evaluating a geothermal energy prospect from a geochemical point of view, and (2) present a geochemical evaluation of the hydrothermal system at Long Valley, California. Temperatures of aquifers feeding thermal springs and wells in Long Valley, California were estimated using silica and Na-K-Ca geothermometers and warm spring mixing models. The results ranged from 160° to 219°C. This information was then used to construct a diagram showing enthalpy-chloride relationships for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282°C aquifer with water containing about 375 milligrams chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to 219°C Casa Diablo water by mixing with cold water, and to 201°C Hot Creek water by boiling and steam loss. Oxygen and deuterium isotopic data are consistent with this interpretation. An aquifer at 282°C with 375 mg/kg chloride allows the estimated convective heat flow in Long Valley to be increased from 4.3 x 10 7 to 6.6 x 10 7 cal/sec.
During July 1977, forty-nine gravity stations were obtained in the Double Hot Springs Known Geothermal Resource Area and vicinity, northwestern Nevada. Elevations for twenty-two stations were estimated from lake bed topographic contours. Horizontal positions for these stations were determined from topographic maps and vehicle odometer. Elevations for stations DBLD34 and DBLD35 were determined with altimeters. Positions for the remaining stations were taken from spot elevations shown on U.S. Geological Survey topographic maps at scales of 1:24,000.
During July 1977, fifty-one gravity stations were obtained in the Gerlach Extension Known Geothermal Resource Area and vicinity, northwestern Nevada. Elevations for twenty-seven stations were estimated from lake bed topographic contours. Horizontal positions for these stations were determined from topographic maps and vehicle odometer.
During July 1977, forty-four gravity stations were obtained in the Fly Ranch Extension Known-Geothermal Resource Area and vicinity, northwestern Nevada. Elevations for three stations were estimated from lake bed topographic contours. Horizontal and vertical positions for stations FREX33 through FREX43 were determined from plane-table surveying. Positions for the remaining stations were taken from benchmarks or spot elevations shown on U.S. Geological Survey topographic maps at scales of 1:24,000.
An electromagnetic (EM) controlled source survey was made during the period Nov. 30, 1977, to Dec. 13, 1977, in the Randsburg, California, Known Geothermal Resource Area (KGRA). This report summarizes the observed extra-low-frequency (ELF) data and least squares interpretation using a computer program developed by Anderson (1977). The results are given in tabular form along with observed and calculated amplitude and phase plots. In addition, one vertical electrical sounding (VES) was obtained and a graphical solution is included via a Schlumberger inversion program developed by Zohdy (1973).
A 10,365 ft (3,159 m) geothermal test well was drilled in the spring of 1979 at the Idaho National Engineering Laboratory, eastern Snake River Plain, Idaho: The majority of rock types encountered in the borehole are of volcanic origin. An upper section above 2,445 ft (745 m) consists of basaltic lava flows and interbedded .sediments of alluvial, lacustrine, and volcanic origin. A lower section below 2,445 ft (745 m) consists exclusively of rhyolitic welded ash-flow tuffs, air-fall ash deposits, nonwelded ash-flow ruffs, and volcaniclastic sediments. The lithology and thickness of the rhyolitic rocks suggest that they are part of an intracaldera fill.
On October 31, November 1 and 3, 1978, forty-eight gravity stations were established near Helena, in the Broadwater geothermal area, west-central Montana (fig. 1).
Water samples were collected from 31 wells and springs in eastern Idaho and western Wyoming to help evaluate the potential geothermal resources in the Teton River area, Idaho. The water analyses included the common anions and cations, oxygen-18, deuterium, and several minor elements. Actual temperatures of the sampled thermal waters ranged from 23° to 49°C. Estimated aquifer temperatures, as derived from geochemical thermometers, ranged from 45° to 145°C based on silica concentrations and 45° to 205°C based on sodium-potassium-calcium ratios. Using the cation thermometer, two analyses indicated aquifer temperatures that were lower than the actual measured temperatures. Estimated temperatures using a mixing-model method ranged from 205° to 320°C, the higher temperature being of questionable value. The different methods used to estimate aquifer temperatures showed little correlation. On the basis of isotope data, the warm waters may be of local meteoric origin and have not been heated enough to react significantly with the aquifer rocks, or they originated as precipitation at high altitude and great distance from the area.
Thermal water (30.0 to 72.0 degrees Celsius) is produced from 26 wells and 2 springs in the vicinity of Banbury Hot Springs near Buhl, Idaho. Thermal water is used for space heating of private residences, catfish and tropical fish production, greenhouse operation, swimming pools, and therapeutic baths. In 1979, 10 ,300 acre-feet of thermal water was utilized; heat discharged convectively from the geothermal system was about 1.1 x 10 7 calories per second. Decline in artesian head and discharge apparent in recorder charts from two wells may represent seasonal fluctuations or may reflect aquifer response to development of the resource. Thermal waters sampled are sodium bicarbonate in character and slightly alkaline. Mixing of a hot (72 degrees Celsius) water with local, cooler ground water can be shown from various relations between stable isotopes, chloride, and enthalpy. On the basis of concentration of trituim, age of the waters sampled is at least 100 years an perhaps more than 1,000 years. One water (33 degress Celsius) may be as young as 29 years. On the basis of silica, sodium-potassium-calcium, and sulfate-water geothermometers, best estimate of the maximum reservoir temperature for the thermal waters is between about 70 and 100 degrees Celsius.
This report includes drillers ' logs, temperature logs, and water quality analyses from geothermal tests made at 11 sites near Oasis, lower Coachella Valley, California. A map shows the locations of the wells and also included is the location-numbering system for wells. (USGS)