Geological Survey MEASUREMENT OF HEAT FLOW BY A DOWNHOLE PROBE TECHNIQUE IN THE SAN JOAQUIN VALLEY, CALIFORNIA by

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature, During the drilling of five shallow (120 to 150 m) wells in the central San Joaquin Valley, 18 successful penetrations were made using the downhole heat-flow probe. Eighteen values of thermal conductivity measured in situ ranged from 1.19 to 2.07 with mean of 1.65 WnT 1 K ' 1 ± 0.23 s.d. When compared with grain conductivity measurements on adjacent ditch samples, the in situ values yielded interpreted values of porosity ranging from 7 % to 44% with mean of 28.8 ± 9.1 s.d. Heat flows at the five sites were between 44 and 64 mWm~2 (1.05 and 1.53 HFU). This is in the same range as heat flows obtained from deep oil wells in the southwestern part of the San Joaquin Valley. It is inconsistent with predictions of high heat flows (85 to 105 mWm 2 and greater) from silica geotemperatures of non-thermal waters presented by C. A. Swanberg and Paul Morgan.- 2