ABSTRACT
Tests with a new directional-survey instrument show a significant enhancement in the accuracy of defining a wellbore trajectory. Several prototype systems developed over the previous two years by Gyrodata Inc., in conjunction with Incosym Inc., a developer of guidance systems and components for the aerospace industry, have successfully undergone tests in the laboratory and in the field. The testing period, which included both land and offshore operations, indicates that the original design objective for borehole position uncertainty less than 1.7 feet per 1,000 feet of hole has been met. Although prototype development has been completed to the extent that criteria for manufacturing have been established, an ongoing testing programme is in effect to verify field accuracies and system application in a wider range.
The Gyrodata Wellbore Surveyor employs an inertial grade-rate gyro adapted from the aerospace industry. In combination with its other sensors and electronics, the device can sense the orientation of the earth's spin vector at each independent survey station. As a result, the major systematic errors associated with conventional gyros-geographical reference and unaccountable drift - are eliminated. Other sources of inaccuracy are minimized by the system's measuring techniques and operational procedures, and additional benefits arise from faster survey speed and increased reliability. A true north reference device can also employ a small outside diameter since it requires only one gyro and one accelerometer.
