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.
The first commercial high-dogleg rotary-steerable systems (RSSs) were introduced in 2011. These systems were specially designed to drill vertical, kick off, build at planned 8 to 12°/100 ft (or even higher), and drill the lateral to lengths of up to 6,000 ft in unconventional reservoirs (such as shale gas applications) in North America. Because of the improved economics and other benefits for efficient drilling a high-build-rate curve and lateral in single run, high-dogleg RSS technology has rapidly gained acceptance for drilling shale wells.The performance of the high-dogleg RSS is greatly enhanced with automated steering mode in vertical and lateral sections by reducing a human-machine interaction and minimizing wellbore tortuosity in these sections. Downhole trajectory-control algorithms make small, but frequent, adjustments to RSS steering parameters, comparing the near-bit continuous survey data against a planned well trajectory. Downhole steering automation is an integral part of the overall drilling system automation that the drilling industry is pushing forward.A new static and continuous (dynamic) survey method has been used in the near-bit sensors of a specific high-dogleg-severity (DLS) RSS. The new survey method significantly improved the inclination and azimuth measurement in near-vertical angles; thus, it not only enhanced the automated vertical drilling feature but also provided more accurate kickoff from a near-vertical position using the RSS near-bit static and continuous survey. In addition, improved continuous measurements around magnetic north and south allowed the closed-loop trajectory-following algorithm of the RSS to drill lateral sections more precisely in these directions.The software simulation and field trials were conducted to test a new survey measurement method implemented in a highdogleg RSS, along with automatic trajectory-following algorithms. In one of the field trials, the RSS drilled more than 10,750 ft (vertical, high-dogleg curve, and lateral) in one run, including 5,000 ft of vertical and 4,500 ft of lateral sections in automated steering mode, saving 4 days (about 30%) compared with the previous non-high-dogleg RSS runs. A unique combination of the new technologies has enabled increased well construction efficiency in shale plays by providing a step change in steering technology, trajectory-following algorithms, and downhole survey method.
High dogleg rotary steerable systems (RSS) were introduced for general industry use in 2011. These systems were developed for high dogleg shale applications in North American land operations. The initial systems were 6 ¾-in. These tools were designed to produce up to 15°/100 ft in 8 ½-in. to 8 ¾-in. hole size. High dogleg tools for different borehole sizes followed. The requirement for high dogleg RSS is now global, and the systems are being used to drill in areas where steerable motors previously dominated because of their higher dogleg capability. A new 4 ¾-in. RSS has been designed for high dogleg (15°deg/100 ft) and dogleg assurance applications. Additionally, a new high dogleg RSS for 5 7/8-in. to 6 ¾-in. hole sizes has been developed and field tested. The new slim-hole high dogleg RSS has proven to perform well and be a cost-effective solution in specific applications, such as difficult formations and multilateral well construction.
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