| Abstract |
This report focuses on Sandia National Laboratories' effort to create high-temperature logging tools for geothermal applications without the need for heat-shielding. Presently, tool electronics can operate up to 300?C with a few limiting components operating to only 250?C. An actual well log to 240?C without shielding is discussed. The first prototype high-temperature tool measures pressure and temperature using a wire-line for power and communication. The tool is based around the HT83C51 processor. The HT83C51 processor with 32K RAM has been tested in excess of 300?C within the lab environment. This development is being made possible through the development of Silicon-On-Insulator (SOI) electronics. This new category of electronics allows for manufacturers to qualify silicon electronic components to 225?C for continuous operation with reduced performance and life at 300?C. There is presently a short fall of available SOI components for tool building. Only recently, an SOI analog-to-digital inverter became available. Thus, designing circuits using only SOI components has limited function. In the future, additional components should become available, which will increase design functionality. At temperatures above 225?C there is a loss of performance or accuracy compared to conventional Dewared logging tools. To increase accuracy at temperatures above 225?C will require the creation of second generation electronics for key components. For example, the analog-to-digital conversion can be no better than the voltage reference used. At present, the SOI voltage reference has increased error over 225?C and failure at about 270?C. A second-generation device made from wide-band-gap semiconductors at silicon carbide (SiC) is needed. To power new unshielded tools and instruments downhole will require the development of high-temperature batteries. At Sandia National Laboratories, we are working to develop a new battery using molten salt technology. These batteries, often called thermal batteries, require a minimum temperature to activate the battery. At Sandia National Laboratories, we have developed usable thermal batteries, which start operating below 200?C and continue to operate up to 250-300?C. |