Controlling Well Path Trajectory with Rate of Penetration Modulation
- Steven Reid Farley (Weatherford) | Christopher A. Maranuk (Weatherford International) | B.J. Hronek (Weatherford International) | C. Jasper (Weatherford International)
- Document ID
- Society of Petroleum Engineers
- SPE/IADC Drilling Conference and Exhibition, 1-3 March, Amsterdam, The Netherlands
- Publication Date
- Document Type
- Conference Paper
- 2011. SPE/IADC Drilling Conference and Exhibition
- 1.4.1 BHA Design, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.2 Separation and Treating, 1.7 Pressure Management, 1.6 Drilling Operations, 1.6.6 Directional Drilling, 4.3.4 Scale, 5.6.4 Drillstem/Well Testing, 1.1 Well Planning, 1.5 Drill Bits, 1.6.2 Technical Limit Drilling, 1.12.6 Drilling Data Management and Standards, 4.1.5 Processing Equipment, 1.6.3 Drilling Optimisation, 1.6.1 Drilling Operation Management
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The majority of footage drilled directionally is achieved by using bent-housing, positive displacement motors. This established technology uses oriented drilling intervals to maintain well trajectory. These intervals can be difficult and time consuming in many drilling environments; however, the economic advantages of this system often preclude the use of more capable rotary steerable assemblies. Operators have long needed a system that fills the widening gap between the two technologies.
A new system of wellbore directional control has been developed that uses continuous string rotation above a positive displacement motor and bent sub. Path deviation is achieved by brief variations in the rate of penetration (ROP) that occur once during each rotation of the bent sub. Bit advance is increased during each rotation causing the bit to drill faster in the targeted direction. This directed variation in ROP allows manipulation of hole trajectory while the bent housing and drillstring are continuously rotating. Steering is accomplished by managing pressure fluctuations within the drillstring, creating slight oscillations in the flow rate through the mud motor. These controlled fluctuations in flow rate allow variations in drilling parameters to steer the well in any targeted azimuth.
The goal of this system is to eliminate all oriented drilling in applications up to 3 degree per 100 feet by employing a low risk, low cost method that maximizes ROP and hole cleaning. At the Gas Technology Institute (GTI) Catoosa Test Facility in Oklahoma, drilling tests yielded successful well trajectory manipulation, delivering up to 3 degree per 100 feet of controlled directional performance in both 6 1/8" and 8 1/2" hole diameters. Because a standard bent housing assembly was used, oriented drilling was always available as needed. This allowed a redundancy in directional control (oriented or rotary), widening the operational scope and technical capability of the system.
The cost reduction of directional drilling has been at the forefront of downhole drilling technology since the ability to steer a well path was first devised. This is specifically accomplished in two ways. The first is to reduce the cost of whatever directional drilling tools are used, and the second is to expedite the speed with which they drill to their targets.
The overwhelming majority of directional footage drilled today makes use of a mud motor. This assembly uses a bent sub and continuous fluid power to apply some cross-axis pressure to the rotating bit, so that it can drill in any direction at some rate of change of trajectory. The steering is accomplished by sliding the oriented drillstring while only the bit is turned by the mud motor. These units have undergone continuous innovation and improvement for some 50 years and, as such, have become the most reliable means by which directional drilling can be accomplished. A further benefit of their continual use is that of competitive pricing which naturally accompanies any economy of scale. Taken together, these two strengths have given drilling motors a significant edge in both reliability and pricing.
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