Geophysical exploration for geothermal prospects west of Albuquerque New Mexico
— George R. Jiracek, Edward P. Gustafson, and Mark D. Parker

With more than one-third of New Mexico's inhabitants residing in the Albuquerque area, a vast market exists for direct utilization of geothermal heat. Such utilization is prescribed by expectations of low- to moderate-temperature (<150°C) resources at economic depths. Geo- thermal exploration in the Albuquerque area has concentrated on the western side of the city (fig. 1; for studies on the eastern side of Albuquerque, see Grant, this guidebook). This is an area of anticipated growth where the warmest municipal ground-water temperature (32°C in 360 m deep West Mesa #1, fig. 1) was reported by Bjorklund and Maxwell in 1961. The 32°C reading represents the highest pumped temperature of a city water well despite many recent wells, some drilled near the Albuquerque volcanoes (fig. 1).

The Albuquerque volcanoes are a group of fissure-controlled basaltic volcanoes and spatter cones which have been episodically active from about 200,000 to at least 120,000 years before present (Bachman and others, 1975; Machette, 1978; see Machette, this guidebook). They appear to be related to the Nine Mile (County Dump) fault (fig. 1) described by Kelley (1977) and Machette (1978), respectively. The only other mapped faults in the survey area are the unnamed faults west of Nine Mile fault (fig. 1; Kelley, 1977). Machette (1978) detailed 17 m of vertical displacement on the Nine Mile fault in the past 400,000 years. Only 10 m or so of offset was discussed by Kelley (1977) on the faults to the west.

The escarpments on the east and west of Figure I bound the Ceja Mesa of Kelley (1977), also called the Llano de Albuquerque, which extends beyond the study area illustrated in Figure 1 for a total length of 110 km. Parker and Jiracek (1980) have chosen the name Llano de Atrisco for the segment of the mesa encompassed in Figure 1. The northeastern portion of the Llano in Figure 1 is mantled by basaltic lava flows from the Albuquerque volcanoes. Scarps shown on the rest of the map are formed by resistant, carbonate soil horizons developed in post—Santa Fe gravel and eolian sands. Underlying beds of youngest Santa Fe Group sands and gravel are exposed on the erosional scarps. An oil-test well (the Carpenter #1 Atrisco) drilled in 1948 just north of U.S. Highway 66 (fig. 1) in sec. 28.440, T ION, R1E reached 2,027- m depth before leaving the Santa Fe. Bjorklund and Maxwell (1961) describe the bottom 168 m as having penetrated rocks of "Cretaceous (?) age." The well record on file with the New Mexico Oil Conservation Commission is unclear in this regard. As pointed out by Kelley (1977), a projection of the base of exposed Santa Fe in the Rio Puerco valley only 10 km to the west of the well intersects the well at depths of about 450 to 600 m. Consequently, considerable unexposed faulting or in- crease in easterly dip must exist in the subcrop to the west of the Carpenter #1 Atrisco well. Kelley (1977) has hypothesized that most of the vertical displacement (over 1,600 m) is along the Sand Hill fault about 7.5 km west of the Carpenter #1 Atrisco well. A deeper (5,906 m) oil-test well was drilled in 1981 by Shell Oil Company approximately 2 km west of the northernmost cone of the Albuquerque volcanoes (fig. 1). The lithology of the hole has not been released.

Water-table depths in the area of Figure 1 vary from 65 m at West Mesa #4 (our measurement) to 285 m at the former radar site well (Bjorklund and Maxwell, 1961) about 3 km west-northwest of the Carpenter #1 Atrisco well (fig. 1). Probably the most significant aspect of the absolute elevation of the ground-water table beneath the area is a pronounced north-south trough 10-15 km wide approximately centered over the Llano de Atrisco. The trough described by Bjorklund and Maxwell (1961) is about 10 m lower than the Rio Grande 10 km to the east and perhaps 35 m below the water level at the radar-site well. These values are based on very few data (water wells); however, a more recent compilation by the U.S. Geological Survey (D. Wilkins, personal commun., 1981) confirms a considerable hydraulic gradient on the west side of Figure 1 of approximately 10 m/km. This implies significant eastward water movement on the west side of the Llano de Atrisco.
Electrical resistivity investigations in the Albuquerque area consisted first in 1979 of Schlumberger and combined Schlumberger-equatorial soundings at three locations, S 1 , S2, and S3 (fig. 1). The soundings were followed in the same year by bipole-dipole mapping from two orthogonal bipole transmitter pairs BD1 and BD2 (fig. 1). Two dipole- dipole lines DD1 and DD2 (fig. 1) were measured in 1980. Surface magnetic profiles totaling 171 km were occupied in 1980. These fol- lowed initial measurements of less than 10 km length made in 1979. Shallow (<30 m) temperature-gradient measurements were made on the Llano de Atrisco during 1979-80. Some anomalously high values (>100°C/km) in the shallow drill holes exposed the need for deep gradient values, particularly below the water-table. One such mea- surement has been made in a 372-m deep borehole. Data from this U.S. Geological Survey water monitor well #1 (fig. I), drilled in the summer of 1981 by the survey and the City of Albuquerque with our cooperation, are presented herein.