To the problem of improving the depth, sensitivity and accuracy of monitoring and oil and gas searching borehole geothermal researches

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To the problem of improving the depth, sensitivity and accuracy of monitoring and oil and gas searching borehole geothermal researches

Journal Title: Геодинаміка - Year 2018, Vol 24, Issue 1

Abstract

Purpose. The purpose of the work is to present important methodological and instrumental solutions to improve the depth, sensitivity, and accuracy of monitoring and oil and gas searching borehole geothermal research. Methodology. The technique includes the analysis of a number of methodological and instrumental factors, which affect the depth, sensitivity, and accuracy of borehole geothermal research using the developed downhole equipment with a quartz thermo-frequency sensor and appropriate methodological and instrumental developments to increase this depth, sensitivity, and accuracy. Results. An analysis of the results of our previous borehole geothermal studies using the developed downhole equipment with a quartz thermo-frequency sensor showed that along with the high overall sensitivity and accuracy of the developed equipment, there are limitations of its depth due to insufficient hermeticity of the well log sonde when it is working in wells on the great depths at operating there high hydrostatic pressures of fluid filling the well. Therefore, we first improve the construction of the well log sonde for the purpose of ensuring its reliable operation at great depths. There is also a depth limitation (in particular, the allowable length of the logging cable) of borehole studies with the "direct" transfer of measurements results by this cable due to the large attenuation of the signal of the high operating frequency of the quartz thermosensitive sensor. Therefore, the operating frequency of the transmission channel (on the logging cable) was significantly reduced by a digital divider. Also we can see the influences of a number of methodological and instrumental factors on the quality of these results, especially when we follow up the rapid changes in the temperature in the well during its thermal profiling (high-speed thermal logging) or regime monitoring. This, in particular, is the thermal inertia of the well log sonde. To neutralize the effect of this inertia, studies were carried out and a method for reducing its influence was proposed by introducing appropriate timings-dependent temperature corrections. Thermal profiling of a number of hydrothermal wells in the west of Ukraine was carried out and the results were corrected taking into account the listed corrections. The method of detection, taking into account the meteorological influences on seismoprognostic monitoring, was developed based on geothermal monitoring of rock massifs. It presented the seasonal thermoelastic deformations with low-amplitude deformation, a precursor to the local Transcarpathian earthquake. Originality. An increase of sensitivity and accuracy was reached using the developed geothermal well equipment with a quartz thermo-frequency sensor, in particular, by studying, determining, and taking into account the timing`s temperature corrections (“interval shifts/delays”) and corrections for the thermal inertia of the well log sonde. The temperature profiles of a number of hydrothermal wells in the west of Ukraine have been studied in detail, and the features of their temperature changes with depth, have been established. Due to the reduction from the extensometer’s data the seasonal thermoelastic deformations of rocks, simulated by the results of geothermal monitoring, a low-amplitude deformation precursor of the local Transcarpathian earthquake was selected. Practical significance. An increase of the depth of geothermal studies using the developed geothermal well equipment has been achieved due to the use of a significantly reduced frequency of transmission of the measured signal on the logging cable and the improvement of the construction and circuitry of the well log sonde.

Authors and Affiliations

A. Nazarevych

Keywords

thermal logging well log sonde quartz thermo-frequency sensor thermal inertia temperature corrections temperature profile of the well dynamic temperature variations precursors of earthquakes

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EP ID EP456027
DOI 10.23939/jgd2018.01.060
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