Mud motors have been used for decades to help steer wells in a desired direction. They are typically oriented with a bent sub in the motor and are pointed in the planned direction to kick-off the well or drilling section. They use a combination of rotating and sliding to keep the well on target and, depending on various drilling and formation parameters, may need to slide the majority of the time to maintain hole projection. Sliding often creates issues with hole cleaning, ledging, and decreased rate of penetration (ROP). Rotary-steerable tools, on the other hand, continuously rotate in the hole eliminating many of the problems associated with an oriented positive displacement motor (PDM). A new system for wellbore directional control has been developed that uses a positive displacement motor and a bent sub to provide continuous rotation throughout the wellbore. This new system offers many advantages of a rotary-steerable system but also capitalizes on the proven technology of a positive displacement mud motor. Steering is accomplished by managing the pressure fluctuations within the drillstring, creating slight oscillations in the flow rate through the mud motor. These controlled undulations in flow rate allow high-frequency variations in drilling parameters to steer the well in any targeted azimuth. If the planned objective cannot be achieved using ROP modulation in rotary mode, then the motor can still be oriented in the desired direction and slid, using the more conventional mud motor orienting technique. This paper will review several operations where the new steering system was used to help drill the well. It will discuss the operational challenges of drilling the wells, as well as how the new system helped overcome those challenges.
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