Correlation of Wireline LOG Characteristics with Hydrothermal Alteration and Other Reservoir Properties of the Salton Sea and Westmorland Geothermal Fields, Imperial Valley, California, USA

摘要

A detailed study of wireline logs from 11 wells in the Salton Sea and Westmorland geothermal systems was undertaken in order to determine the effects of hydrothermal alteration on the response of electrical and gamma-gamma density well logs. For the Salton Sea geothermal field, definite correspondence between log responses and hydrothermal mineralogy is evident, which in turn is related to the physical properties of the rocks. Three hydrothermal and one unaltered zone can be identified from log data on shales. These are: (1) the unaltered montmorillonite zone (<100 exp 0 to 190 exp 0 C); (2) the illite zone (100 exp 0 to 190 exp 0 C to 230 exp 0 to 250 exp 0 C); (3) the chlorite zone (230 exp 0 to 250 exp 0 C to 290 exp 0 to 300 exp 0 C); and (4) the feldspar zone (>290 exp 0 to 300 exp 0 C). The characteristic responses on well logs by which these zones are identified result primarily from changes in clay mineralogy of the shales and increases in density with progressive hydrothermal metamorphism. In the Westmorland geothermal field, differentiating mineral zones from log responses was only partially successful. However, analyses of both well log and petrologic data for wells Landers 1 and Kalin Farms 1 suggest that the former is heating up and the latter is cooling. (ERA citation 09:037483)