Testing a new integrated solution for MEMS inertial measurement unit used for measurement-while-drilling in rotary steerable system

Trajectory surveying in drilling application applications in oil fields, especially using the Rotary Steerable System (RSS) require the Measurement-While-Drilling (MWD) tool to have exact attitude measurements. Currently, inertial systems based on gyroscopes and accelerometers are widely used in different fields such as the field of flight navigation and land vehicle positioning. Gyroscopesbased method of measuring orientation is not sensitive to the earth's magnetic field or surrounding magnetic interference which is the main shortage of the current magnetometers-based MWD tools. This is the reason that inertial technology shows great potential for drilling surveying applications. MEMS-based Inertial Measurement Unit (IMU) is regarded as a perfect candidate for MWD because of two reasons. Firstly, due to its small size the MEMS IMU can be installed directly with the RSS package into one collar which makes the MWD tool very close to the drill bit. Secondly, when surveying sensors get close to the drill bit, the harsh environment becomes very challenging where low-cost MEMS makes it affordable to lose and replace the sensors without considerable cost. Unfortunately, current MEMS sensors have low precision which leads to large errors in surveying results that accumulate with time. As known in general, for an inertial system to have good accuracy in long-term navigation, it has to either have precise gyroscopes (but usually expensive), or to benefit from other high precision aiding system (like GPS in land vehicle). However, similar aiding sources are extremely limited in drilling applications. Therefore, an appropriate aiding scheme for MEMS IMU must be carefully explored as well as a suitable solution. This paper aims at studying a practical solution to update the MEMS measurements. A Kalman Filter (KF) scheme is designed to optimally estimate and compensate for inertial errors, where only the forward axial speed of the drill pipe that can be measured at all time is applied as the moving update. Laboratory experiments and emulation results indicated that this new integrated KF solution significantly improved the MEMS performance.