Research Drilling in an Active Geothermal System: Salton Sea Scientific Drilling Project (SSSDP)

W. A. Elders

In March 1986 a research borehole, designed to study the processes occurring in an active, high-temperature, magmatically driven hydrothermal system, reached a depth of 3.22 km in the Salton Sea geothermal field at the northern end of the Gulf of California. Only 10% of the borehole was cored; however, an integrated set of drill cuttings, wireline logs, and downhole measurements were obtained using high-temperature tools and cables. Similarly, downhole VSP, gravity, and fluid sampling tools were successfully deployed. The borehole penetrates Pleistocene and upper Pliocene lake and delta sediments with minor extrusive and intrusive igneous rocks, all of which are being progressively altered to greenschist facies hornfelses.

A flow test of a zone at 1,865 m with a temperature of 305°C, produced Na, Ca, and K chloride brines containing 24% of dissolved salts. Flows of up to 200 tonnes/hr of steam and brine were obtained. An even more productive zone, the deepest tested at 3,215 m where the temperature was 355°C, briefly attained a peak flow of 400 tonnes/hr during a 48-hour test. However, this test was marred by interference from other flow zones.

Although the borehole was shut in after the 7-in. (17.78-cm) diameter liner parted, a comprehensive program of laboratory studies is underway in about 40 different institutions. Results to date have more than met our original goals. In the summer of 1987, field operations will resume and will include extensive reservoir engineering. However, drilling deeper to penetrate the magmatic rocks that underlie the explored hydrothermal system must await future funding.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.