Controlling Well Path Trajectory with Rate of Penetration Modulation

Abstract

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.