Description

Through-Casing Resistivity Logging is an accurate and reliable measurement of cased hole formation resistivity, not only can provide higher stratigraphic reservoir saturation evaluation, but also to monitor the reservoir and identify dead reservoir, and measure high-risk-hole formation resistivity and improve field effectiveness. ■Through-Casing Resistivity Logging primarily measures the formation resistivity after casing. ■Working Principle: The instrument’s electrode is charging to the casing, due to the casing and formation are conductors, you can detect electrical potential in other locations of casing. The main current is in the casing, small part inflows to formation. Current volume into the formation is determined by the conductivity of the formation. Electrodes measure the electrical potential difference from casing leakage currents, which is positive proportional to the conductivity of formation. ■The instrument faces the difficulty in the measurement of micro-electric potential. A typical formation resistivity is roughly **9 times the steel casing resistivity. This is a tube resistance and formation resistivity parallel system. Due to the diverting effect of formation, the measured electrical potential is lower than the simple casing electric potential. However, Casing resistivity is only a few dozen micro-ohm, and general leakage current is only a few milliamps, so the instrument obtains the electric potential difference in Nanovolt level. ■The instrument&#**9;s main role is to find cased hole resistivity distribution, and proceed to find the possible leakage of the reservoir.