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.