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Abstract Rotary Steerable drilling systems have led to a step change in drilling performance in many areas of the world. However their use in the Middle East has generally been slower to develop than in other drilling provinces around the world such as The North Sea where the value of rotary steerable drilling has been documented since 1998. Commercial as well as technical issues have limited widespread deployment of these systems in the region. This paper reviews successful rotary steering applications in the Middle East to date and explores areas for potential increased use.
Using case studies the paper looks a range of specific applications where the change from steerable motor to rotary steerable system has been both technically and commercially successful in the Middle East. Through these case histories the paper will demonstrate both tangible and intangible benefits resulting from the use of rotary steerable systems that have led to a step change in overall drilling performance in the Middle East.
Introduction The stratigraphy of the Middle East is relatively uniform over a wide area bringing a commonality to drilling issues and performance across the region. For the last decade or so steerable positive displacement motors have been used for the majority of directional drilling work. Steerable motor drilling is a relatively inefficient process, with associated problems in the Middle East area ranging from trajectory control in unstable shales, pipe sticking in lost circulation zones and slide drilling in carbonate reservoirs. Rotary steerable systems are in many cases able to overcome these difficulties through continuous drillstring rotation and optimized bit and drilling parameter selection. Rotary steerable systems are now in use in all common hole sizes from 6" to 17 1/2" allowing problems to be addressed throughout the well.
Steerable Motor Drilling Steerable motor drilling is inefficient. With a requirement to slide the bottom hole assembly in order to steer the well path drilling becomes slower and potentially more problematical. ROP is impacted as a result of wellbore friction and BHA and drillstring components hanging up. Hole cleaning, without drillstring rotation, is adversely affected, as cuttings will drop out of suspension to the low side of the hole. The transition from slide back to rotate requires rotating the motor bend through the section steered. This can result in hole spiraling.
Steering a steerable motor requires maintaining the orientation of the bend in the desired tool face setting. Reactive torque from the motor itself works against good tool face control with the force turning the string in a counterclockwise direction. The magnitude of reactive torque will depend on the torque being generated at the bit which itself is a function of bit aggressivity, motor torque output and the formation being drilled. Tool face control using a light set PDC bit with large cutter diameter run on a low speed high torque motor can be extremely difficult. As a result a compromise on bit selection is frequently made for steerable motor drilling. It is not unusual for a roller cone bit to be run for a critical directional section of the well due to problems controlling toolface with a PDC bit. Orienting a PDC bit can be time consuming with frequent time spent off-bottom in order to control reactive torque. Significant progress has been made using depth-of-cut control technology whereby steerability and ROP improvements have been documented and indeed these new bit designs have proven excellent for medium radius applications. However the basic inefficiencies of steerable motor drilling remain.
The rotary sections with a steerable motor can also result in inefficient drilling. As with a rotary bottom hole assembly the directional behavior of a steerable motor assembly will be a function of stabilizer gauge and spacing as well as drilling parameters used. As a result the drilling parameters will be set to control the directional tendency of the assembly as opposed to maximizing ROP.
Micro-tortuosity associated with a slide rotate sequence is of particular significance in many regional reservoirs. Coiled tubing accessibility can be severely impacted by a tortuous well path in the reservoir. In 6" hole, today's extended power motors are susceptible to formation effects and can be difficult to stabilize and highly tortuous well path can result in the reservoir, often masked by a survey interval of every stand.
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