Well log interpretation of certain geothermal fields in the Imperial Valley, California

This study reviews the wireline log responses of some geothermal fields in the Imperial Valley, California. The fields under study include the Heber, the East Mesa, the Brawley, and the Westmoreland. The well logs used in the study did not include all the wireline surveys obtained by the operators. The selected well logs obtained under special arrangements with the operators were chosen to maintain the anonymity of specific well locations but are only representative of each area. Analysis of the well logs indicates that on an individual field basis, the well logs are excellent for correlation purposes. The presence of extremely saline fluids in some fields precludes the monitoring of Q/sub v/ (cation exchange capacity per unit volume) profile for detection of hydrothermally altered zones. The producing sections in all the fields are characterized by low porosity and high resistivity

Lithology and hydrothermal alteration determination from well logs for the Cerro Prieto Wells, Mexico

The purpose of this study is to examine the characteristics of geophysical well logs against the sand-shale series of the sedimentary column of the Cerro Prieto Geothermal Field, Mexico. The study shows that the changes in mineralogy of the rocks because of hydrothermal alteration are not easily detectable on the existing logs. However, if the behavior of clay minerals alone is monitored, the onset of the hydrothermally altered zones may be estimated from the well logs. The effective concentration of clay-exchange cations, Q/sub v/, is computed using the data available from conventional well logs. Zones indicating the disappearance of low-temperature clays are considered hydrothermally altered formations with moderate to high-permeability and temperature, and suitable for completion purposes