Desert Peak Well B

Immediately after well B21-2 was determined to be successful the pad for B23-1 was constructed (once again on private land) about 1 !4 miles east of the two previous wells. No prior stratigraphic test data were available for this site and geology was not a factor in this location. The Desert Peak thermal anomaly is so large that these exploratory holes had to be widely spaced for proper evaluation.

Immediately before drilling began in January 1977 the rig was released and a more thorough evaluation of the results from wells B21-1 and B21-2 was undertaken. It was more than two years later when well B23-1 was spudded. However, during this two-year period much additional new data were obtained and interpreted. Ten stratigraphic tests were drilled by Phillips, Supron Energy Corporation, and Thermal Power Company; two reservoir tests were conducted; a detailed geologic map and gravity survey were completed; and attempts were made to further evaluate the MT survey. Much of these new data confirmed that the well B23-1 was a promising location for a large step-out.

Well B23-1 was spudded on March 19, 1979, and the rig was released on May 30, 1979. The well reached a total depth of 9641 feet. Well B23-1 intersected the geothermal reservoir but its production capability is not known. During a nine-day flow test in November 1979 the well produced approximately 100,000 to 140,000 pounds per hour of fluid. As is the case for all the Desert Peak geothermal wells, it was necessary to use nitrogen to displace a portion of the standing fluid and start the well flowing, but once it began flowing it continued without assistance (fig. 24). The low flow rate resulted in a low wellhead temperature of 228°F and a wellhead pressure of 8 psig. After the flow test a temperature survey was attempted, but a sinker bar could not be lowered below the casing shoe at 3000 feet. The extent of hole blockage is unknown; as a result, the true production capability of well B23-1 is unknown.

FIGURE 24. Photographs of Desert Peak well B23-1 flowing. View looking north. Desert Peak is present at the far left.

FIGURE 24. Photographs of Desert Peak well B23-1 flowing. View looking north. Desert Peak is present at the far left.

There are limited data available to conclusively locate the producing zones in the reservoir in well B23-1. The available evidence is discussed in the section of this report on the Desert Peak reservoir. A lithologic log of well B23-1 is shown on figure 25. The major units noted in the previous wells are all present in well B23-1. However, there are substantial lithologic differences within the major units when well B23-1 is compared with the previous wells. Well B23-1 is located about 200 feet south of strat. test no. 7, and as expected both holes reveal the same geology.

The top 40 feet of B23-1 consist of Quaternary sand, gravel, and boulders. From 40 to 225 feet limestone and tuffaceous sediments of the Truckee Formation are present. This sequence and the top of the underlying Chloropagus Formation are well exposed in the hills about Vi mile south and east of well B23-1.

Between 225 and 1325 feet basalt, basaltic andesite, and andesite flows and breccias of the Chloropagus Formation are present. Three lacustrine units are present between 380 and 400 feet, 495 and 570 feet, and 590 and 650 feet. These units are composed of white to green to brown, fine-grained, tuffaceous sediments which have been locally silicified. Pyrite was first observed at a depth of 340 to 350 feet. Below this depth pyrite (in varying quantities) is present throughout most of the hole.

From 1325 to 4225 feet the rhyolitic unit consists of a series of andesitic to rhyolitic ash-flow tuffs and lava flows. Seven major subunits have been noted on the lithologic log. The gamma log suggests that several of

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