Low-latency feedback, high bandwidth, and improved sensor placement are key benefits provided by wired-drillpipe (WDP) technology. Improved WDP reliability, based on more than 100 wells of field experience, enables more-aggressive application of the technology, including closed-loop control of drilling processes. Often, there is a requirement to consider multiple variables when attempting to control complex processes, such as drilling in deepwater wells. Such is the case when dynamically optimizing rate of penetration (ROP) in a pressure-critical wellbore environment.
Formerly, ROP and bottomhole pressure (BHP) have been considered separate optimization and automation tasks, respectively. This study combines ROP and BHP into a single comprehensive controller for a managed-pressure-drilling (MPD) application. The controller adjusts mud-pump flow rate, choke-valve position, drillstring-rotation rate, and weight on bit simultaneously and with coordinated actions. The automated operations are guided by an objective function that includes factors relevant to both BHP stabilization and ROP maximization. A preliminary MPD case study is used to assess the performance during different drilling events, including transition into varying formations, causing an unexpected gas influx. For the unwanted-gas-influx case, the controller better stabilizes the pressure when there are low-latency communications by simultaneously adjusting ROP. With WDP and the optimizing controller, there is substantial decrease in time required to control influx events compared with earlier controllers or manual methods. The high-speed data availability affects both the pressure-control reaction time and the resulting severity of the kick. When encountering different formations, there is also noticeable benefit by allowing pressure to fluctuate within an acceptable range to optimize ROP.
Combining ROP control and BHP control minimizes risk, decreases drilling costs, and reduces operator workload. Improvements in drilling performance include higher ROP, lower risk of uncontrolled kick events, and more-uniform cuttings loading. Another benefit of this combined ROP/BHP controller is that the reaction to gas influx is made more consistent and predictable relative to manual operations, reducing the demand for time-consuming remedial efforts.