Borehole tool

A method of surveying the direction of a borehole comprising the steps of:

• passing a survey probe including a magnetic field measuring device into a borehole;
• dampening the response time of the magnetic field measuring device as the device responds to changes in magnetic fields associated with the probe;
• and
• supplying an electrical current to one end of the probe, with the electrical current changing direction at a rate faster than the response time of the dampened magnetic field measuring device to the changes in the magnetic fields due to such electrical current.

An apparatus for measuring a borehole parameter comprising:

• an instrument housing;
• electrically operated recorder means within said housing;
• magnetic responsive means within said housing for measuring a borehole parameter;
• electrical conductor means passing to both ends of said housing and within the magnetic field proximity of said measuring means;
• power supply means electrically connected to said conductor means for supplying an alternating current to said instrument housing;
• and
• means changing the direction of said alternating current at a rate exceeding the response rate of said magnetic responsive means to changes in the magnetic field in the magnetic field proximity of said measuring means due to the passage of an electrical current.

A method of surveying an earth borehole, comprising:

• supplying an alternating electrical current to the first end of a survey probe and thereafter making a first pass of said probe through the said borehole to thereby generate first signals indicative of a survey characteristic;
• removing the said probe from the said borehole;
• supplying an alternating electrical current to the second end of said survey probe and thereafter, with the said probe inverted from its position during the first pass through the borehole, making a second pass of said probe through the said borehole to thereby generate second signals indicative of a survey characteristic;
• and
• combining said first and second signals to provide a survey of said earth borehole.