The introduction of a rate gyro surveying system was made in the Rocky Mountain area in April 1982. This paper describes that system as well as its accuracy and durability.
It appears there has been a significant increase in accuracy and durability, with a decrease in survey time over conventional free gyro systems. This assessment is made from data accumulated over 100 field surveys, many runs in a 1400 foot test well and hundreds of hours on a laboratory test stand.
The Eastman Whipstock rate gyro system employs a single floated rate integrating gyroscope gimbled with a single precision accelerometer. This configuration is rotated about the tool axis 360° for every survey measurement. From this rotation the gyro measures a component of the earths horizontal spin vector, which by definition points true north, and the accelerometer measures a component of the earths gravity. The information is then processed to provide inclination, borehole azimuth and tool face. This method provides increased accuracy by producing readings which are independent of those taken previously and by eliminating C-independent sensor bias. Additionally this configuration allows a pressure barrel outside diameter of only 1 3/4″ (45.0mm).