Computalog USA Inc.

Computalog Research, Inc.

Peter J Schoch

Edward Bryant Tickell, Jr

Dwight A Bloomfield

William David Iwanicki

Stephanie A Michels

Lonnie M Moseley

Wade Stewart Maxfield

Using micro-resistivity techniques, an image of the wall of a borehole can be obtained. A downhole tool stack is provided with plural imaging tools, wherein each imaging tool has a set of pads that deploy radially outward to contact the borehole wall to obtain the image thereof. As the pads deploy outwardly, gaps are formed between the pads. The pads of one tool are circumferentially offset relative to the pads of the other tool so that more complete circumferential coverage of the borehole wall is obtained during the imaging process. Furthermore, an adaptive polling technique is utilized to telemeter the large amounts of data generated by the two imaging tools to the surface. Data is obtained from the imaging tools by polling at a particular rate, which rate is modified depending upon the amount of data generated by the imaging tools.

Method and apparatus for full offset resistivity imaging for use in boreholes

An induction logging tool is disclosed for utilization in conjunction with surface electronic equipment for measuring a characteristic of subsurface formations. A transmit signal which is comprised of a repetitive sequential series of at least three transmit frequencies is generated by coupling an oscillator to a transmitter coil and a plurality of selectable tuning capacitors. A signal characteristic of the response of the formation to this transmit signal is detected at a receiver coil array and two phase sensitive detectors are then utilized to generate output signals indicative of the magnitude of the X and R components of the formation signal which is in phase with a reference phase signal. The output signal of each phase sensitive detector is then utilized to accurately determine the X and R component of the receiver coil signal for each frequency by nulling the output of the phase sensitive detector utilizing a closed loop conversion circuit which eliminates errors due to phase and gain variations. The output signal is then compensated by convolving the output of the phase sensitive detector with one of multiple filter coefficient sets which are each associated with a particular transmit frequency, for each portion of the output signal which is attributable to a particular transmit frequency. Each filter coefficient set preferably comprises a Finite Impulse Response (FIR) filter, which is derived by altering each filter coefficient to induce a specified response of the induction tool to a simulated step function.

Multiple transmit frequency induction logging system with closed loop

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Fort Worth, TX, United States of America

Peter J Schoch