Institute of Information Theories and Applications FOI ITHEA
Conventional methods in horizontal drilling processes incorporate magnetic surveying techniques for
determining the position and orientation of the bottom-hole assembly (BHA). Such means result in an increased
weight of the drilling assembly, higher cost due to the use of non-magnetic collars necessary for the shielding of
the magnetometers, and significant errors in the position of the drilling bit. A fiber-optic gyroscope (FOG) based
inertial navigation system (INS) has been proposed as an alternative to magnetometer -based downhole
surveying. The utilizing of a tactical-grade FOG based surveying system in the harsh downhole environment has
been shown to be theoretically feasible, yielding a significant BHA position error reduction (less than 100m over a
2-h experiment). To limit the growing errors of the INS, an in-drilling alignment (IDA) method for the INS has been
proposed. This article aims at describing a simple, pneumatics-based design of the IDA apparatus and its
implementation downhole. A mathematical model of the setup is developed and tested with Bloodshed Dev-C++.
The simulations demonstrate a simple, low cost and feasible IDA apparatus.