When kicking off at low inclination, static measurement-while-drilling (MWD) surveys are used to confirm the kickoff direction, when free of magnetic interference from offset wells. However, as MWD continuous azimuth and inclination measurements have limited accuracy when near vertical, the directional driller does not have confidence in the kickoff direction with continuous (dynamic) survey while drilling. This requires additional static surveys to be made, taking up precious rig time.
In a novel continuous survey method used in a particular rotary steerable system (RSS), a six-axis survey was taken continuously, both while drilling and when static, with the surveys sensors being housed in a rotation-speed-controlled platform in the RSS. This algorithm was first verified in a software simulator, and it was subsequently implemented in hardware and tested in a hardware-in-the-loop-simulator environment. The effectiveness of the new measurement method was field tested and compared against MWD static survey points. The field test result shows that the new near-bit continuous azimuth and inclination from the RSS is considerably more accurate than that of the MWD continuous measurements at very low inclinations of between 1° and 5°.
This unique measurement method has valuable applications, such as low-angle kickoff without using multiple static surveys as the directional driller can use the continuous azimuth and/or toolface to accurately steer the well. Equally important is that if gyro surveys are required, their number will reduce as the survey measurement point is so close to the bit, reducing the amount of time of exposure to magnetic interference from an offset casing. When drilling out of the shoe, this survey method will allow an accurate kickoff approximately 50 ft earlier than would normally be expected as magnetic interference is cleared. Additionally, the use of a continuous gravity toolface is possible without the need for static surveys, allowing accurate low-side sidetracks to be performed even in areas of high magnetic interference. This surveying method reduces the rig time needed to kick off and provides a more reliable real-time measurement for the directional driller to ensure the desired well trajectory is drilled through crowded platform environments.