DESIGN, FABRICATION, INSTALLATION, AND TESTING OF AN ADVANCED WELLBORE/RESERVOIR MONITORING SYSTEM AT THE DIXIE VALLEY,NEVADA GEOTHERMAL FIELD

Abstract

A wellbore/reservoir monitoring system consisting of four 0.25" capillary tubing strings banded on the outside of a 1.9" hangdown string was installed in a production well at the Dixie Valley geothermal field. Two optical fibers, one single ended and one looping from the surface to 4900' and back, were installed in sealed capillary tubings to obtain distributed temperature logs to a depth below the flash point. A thermocouple was installed to both assist in calibrating the optical fibers and provide a continuous and independent long-term single point temperature of the wellbore below the flash point. A 0.094" cap tubing was installed inside a 0.25" cap tubing to continuously monitor the pressure below the flash point. The annulus of this 0.25" string is also utilized for injection of a scale inhibition chemical. This system allows the well to be kicked off with compressed air and confirmation logging with small diameter tools inside the hangdown string.

Both optical fibers degraded within days but did provide information suggesting the looped fibers produce higher quality data. The temperature profile of the well to a depth of 4900' was continuously monitored as the well was kicked off with compressed air. The thermocouple, pressure monitoring, and chemical inhibition systems have now successfully operated for six months.