Improved geothermal well logging tools using no downhole electronics. Final report

A geothermal sonde for measuring temperature and pressure using no downhole electronics was designed and tested for operation at temperatures up to 275/sup 0/C (527/sup 0/F) and pressures of at least 10,000 psi. The measurement system uses variable resistance transducers which are powered in series by an uphole constant current supply. The output signals from the transducers are measured with a digital voltmeter having very high common mode and normal mode rejection ratios. The high rejection ratios of the digital voltmeter virtually eliminate any noise or pickup introduced into the measurement system. The system was tested in a hydroclave at temperatures up to 288/sup 0/C (550/sup 0/F) and at pressure up to 8,000 psi. The sonde was also tested in the Los Alamos geothermal well at temperatures up to 186/sup 0/C (366/sup 0/F) and pressures up to 4100 psi. The main problems encountered were associated with pressure transducers and the logging cable or the cable head and connector. The results of this project indicate that this is a feasible method of making geothermal measurements without the use of downhole electronics and that with further development the technique could be extended to higher temperatures and pressures.