Precision Inertial Downhole Operation and Mechanizations
Anthony Matthews, Retired, exLitton
Location: Big Sur
In urban environments there is a requirement for Downhole Drilling Operations. Because of land rights and infrastructure limitations, and disturbance, it becomes cost effective to drill close to the surface using inertial technologies. With the development of low cost MEMS, and medium cost higher quality Tuned Rotor Gyros, if the correct geometry is chosen and given the introduction of Inertial mechanizations , accuracies of the order of sub XX feet are possible ,thus greatly reducing infrastructure costs and disturbance to the general public,
This paper will develop geometries and mechanisms that will give a self-contained Heading Determination Unit for two types of gyro sensors namely single axis MEMS and two axes Tuned Rotor Gyros. A typical Horizontal Drilling scenario will be examined and when combined with the self-contained HDU precision survey performance is achieved .With this improved performance the likelihood of doing end trajectory drilling maneuvers can be avoided. It should be noted that the most demanding aspect of any Downhole Inertial Measurement Unit, IMU, is in the determination of Heading, i.e. Azimuth, hence the choice of the HDU terminology.
The Horizontal Drilling scenario encompasses a very limited area and depth, relative to normal fully mechanized Inertial Navigation System, therefore a simplified error model is presented that was used to determine the expected performance of the chosen inertial sensors.
Finally a brief description of a HDU, utilizing the Northrop Grumman G2000 Tuned Rotor Gyro and commercially available MEMS accelerometers is given that gives an indication of the expected size, and performance, of the HDU. It is expected that if MEMS gyros are implemented, in the HDU, the size can be slightly reduced together with a cost reduction.