A method for making calibrated directional electromagnetic logging measurements includes causing an electromagnetic logging tool to make a plurality of voltage measurements while deployed in a subterranean wellbore. A ratio of currents in first and second electromagnetic transmitters is computed and a ratio of gains in first and second electromagnetic receivers is computed. A ratio of selected ones of the measured voltages is processed in combination with the ratio of currents, the ratio of gains, and a test loop calibration coefficient to compute the calibrated directional electromagnetic logging measurement.

Some aspects relate to techniques for calibrating a logging tool. In some implementations, the logging tool may estimate certain unknown properties of a signal based on distances between transmitters and receivers of the logging tool and based on frequencies used by the transmitters and receivers. The logging tool may estimate the unknown properties by interpolating values into a mathematical function related to the above-noted distances and frequencies. After estimating the unknown properties, the logging tool may be deployed into the wellbore, where it may use the estimated properties to process signals received through a subsurface formation.

Some aspects relate to techniques for calibrating a logging tool. In some implementations, the logging tool may estimate certain unknown properties of a signal based on distances between transmitters and receivers of the logging tool and based on frequencies used by the transmitters and receivers. The logging tool may estimate the unknown properties by interpolating values into a mathematical function related to the above-noted distances and frequencies. After estimating the unknown properties, the logging tool may be deployed into the wellbore, where it may use the estimated properties to process signals received through a subsurface formation.

Systems, methods, and devices for evaluation of an earth formation intersected by a borehole using a logging tool. Methods include performing EM logging in a borehole intersecting an earth formation using a measurement signal from an antenna system in the borehole, the measurement signal dependent upon a parameter of interest of the formation and at least one antenna system parameter of the antenna system, comprising feeding a calibration signal into a signal path of the antenna system to generate a resultant signal; estimating at least one value of the at least one antenna system parameter by using the resultant signal; and performing further logging operations in dependence upon the at least one value of the at least one antenna system parameter. The calibration signal comprises at least two calibration subsignals with a first calibration subsignal having a first frequency and a second calibration subsignal having a second frequency.

Systems, methods, and devices for evaluation of an earth formation intersected by a borehole using a logging tool. Methods include performing EM logging in a borehole intersecting an earth formation using a measurement signal from an antenna system in the borehole, the measurement signal dependent upon a parameter of interest of the formation and at least one antenna system parameter of the antenna system, comprising feeding a calibration signal into a signal path of the antenna system to generate a resultant signal; estimating at least one value of the at least one antenna system parameter by using the resultant signal; and performing further logging operations in dependence upon the at least one value of the at least one antenna system parameter. The calibration signal comprises at least two calibration subsignals with a first calibration subsignal having a first frequency and a second calibration subsignal having a second frequency.

An x-ray based cement evaluation tool for measurement of the density of material volumes within single, dual and multiple-casing wellbore environments is provided, the tool including at least an internal length comprising a sonde section, wherein said sonde section further comprises an x-ray source; a radiation shield for radiation measuring detectors; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs, wherein the tool uses x-rays to illuminate the formation surrounding a borehole and a plurality of detectors are used to directly measure the density of the cement annuli and any variations in density within. Detectors used to measure casing standoff such that other detector responses are compensated for tool stand-off and centralization; a plurality of reference detectors is used to monitor the output of the x-ray source, and a shortest-axial offset detector is configured to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

An x-ray based cement evaluation tool for measurement of the density of material volumes within single, dual and multiple-casing wellbore environments is provided, the tool including at least an internal length comprising a sonde section, wherein said sonde section further comprises an x-ray source; a radiation shield for radiation measuring detectors; sonde-dependent electronics; and a plurality of tool logic electronics and PSUs, wherein the tool uses x-rays to illuminate the formation surrounding a borehole and a plurality of detectors are used to directly measure the density of the cement annuli and any variations in density within. Detectors used to measure casing standoff such that other detector responses are compensated for tool stand-off and centralization; a plurality of reference detectors is used to monitor the output of the x-ray source, and a shortest-axial offset detector is configured to distribute incoming photons into energy classifications such that photoelectric measurements may be made.

Memory gauge and method for processing recorded raw data acquired with a memory gauge in a well. The method includes selecting a first calibration table (C.sub.1), of the memory gauge, that has a highest calibration value for the measured parameter; performing a first analysis of the recorded raw data using the first calibration table (C.sub.1) to determine a highest measured value of the measured parameter; comparing the highest measured value of the measured parameter with highest calibration values of the plural calibration tables of the memory gauge; and when a highest calibration value of a second calibration table is closer to the highest measured value of the measured parameter than the highest calibration value of the first calibration table, selecting the second calibration table (C.sub.2); and performing a second analysis of the recorded raw data using the second calibration table (C.sub.2) to generate measured values of the measured parameter.

Memory gauge and method for processing recorded raw data acquired with a memory gauge in a well. The method includes selecting a first calibration table (C.sub.1), of the memory gauge, that has a highest calibration value for the measured parameter; performing a first analysis of the recorded raw data using the first calibration table (C.sub.1) to determine a highest measured value of the measured parameter; comparing the highest measured value of the measured parameter with highest calibration values of the plural calibration tables of the memory gauge; and when a highest calibration value of a second calibration table is closer to the highest measured value of the measured parameter than the highest calibration value of the first calibration table, selecting the second calibration table (C.sub.2); and performing a second analysis of the recorded raw data using the second calibration table (C.sub.2) to generate measured values of the measured parameter.

Methods and devices used to calibrate EM corrosion detection tools may estimate the effects of the presence of a core on measurements to enable more accurate corrosion detection in the well line. The methods may involve sending voltages to a core of a well tool disposed in the well line to obtain signals while the core is in a saturated and unsaturated state. Subsequent measurements using the core may be calibrated using a constant resulting from the division of the signals achieved at the core in the saturated and unsaturated states.