Managed pressure drilling (MPD) has gained significant traction as an adaptive drilling method for challenging wells with narrow downhole pressure limits. Though a standard set of MPD equipment is used across the oil and gas industry, there has been some debate on what constitutes true MPD integration.
MPD control systems, the combination of engineered software and specialized hardware, are used to help mitigate the difficulty of dealing with such complex drilling approaches. However, National Oilwell Varco (NOV) believes permanent installation and integration with existing rig infrastructure must occur to truly change the MPD business paradigm.
The MPD method has traditionally been perceived as overly complicated, involving many different subsystems and interfaces, and requiring specialist knowledge in both the planning and execution phase. The cost of an MPD project has been prohibitively high to many operators, and MPD has often only been applied in extremely specific scenarios for wells that would be impractical otherwise. Mobilizing a temporary MPD service involves rig modifications, installation, commissioning and potentially third-party certification via organizations such as ABS and DNV GL.
The result of these challenges is that many potential end users have negative associations with MPD, which is problematic if the method is to gain more widespread implementation as a viable drilling technique. The solution to these challenges is deceptively simple. First, MPD equipment must be permanently installed versus used on a job-by-job basis. Second, the systems must be truly integrated with existing rig infrastructure. And third, a more sustainable business model must be developed that ensures the practice remains financially feasible given current oil price equilibrium.
Integration of the MPD control systems is arguably the most important part of a permanent MPD system installation. Not only is such integration crucial for reliability and safety but it paves the way to greatly reduce the number of people required to execute an MPD operation. While most existing MPD control systems have been developed to be run by a specially trained crew, true integration calls for a different model, one where MPD systems can be operated by a driller as part of standard drilling operations.
Most drilling rigs already have a centralized drilling control network that integrates many different drilling tool controllers in one common human-machine interface (HMI) that the driller manages. In a typical drilling network, all major drilling machines share data on a common, high-speed network. All data are logged and stored for post-processing analysis, and all information is available to all the users on the network.
The prevailing method of installing MPD control systems, however, is to set up a separate MPD network outside of the drilling control network. Separate sensors are installed to transfer data to the MPD system, and additional screens are installed in the driller’s cabin to allow the driller to monitor the operation (Figure 1). While this is a strategy for integration, such a strategy may lead to additional operational inefficiencies and increase the potential for making simple mistakes that can significantly impact the operational success of an MPD deployment.
The MPD control system remains independent of the rig’s control system with unique and nonaligned software behavior. If an alarm is turned on or off in one control system and not in the other during an active drilling operation, personnel can be caught by surprise and the operation can be negatively impacted. Terminal and screen proliferation is a typical response to the need to integrate MPD into the driller’s cabin. The driller and other rig personnel are tasked with operating the rig as well as monitoring and operating the MPD control system through its dedicated terminal, co-located in the driller’s cabin. This can become a visual distraction that can impede the human mind from reacting correctly.
Leveraging all systems
MPD control systems should leverage the existing drilling control network and the information available on the network (Figure 2). The driller should be able to monitor all critical systems from the controls chair. This includes not only key control objectives and performance of the MPD control but also other critical information like MPD-related alarms, inlet flowmeters, outlet flowmeters, pressure relief valves and valve alignment. With all relevant MPD control functions seamlessly integrated into the normal HMI, the driller gets an immediate, clear and intuitive visual overview of the complete drilling process, including the MPD system. In this scenario, all information pertaining to the drilling operation is made available in a familiar and easily accessible format.
True MPD rig integration includes one centralized control system that integrates MPD functionality in synchronization with the top drive, drawworks and mud pump control. This enables consistent, optimized performance of the overall drilling operation while accounting for both pressure control accuracy and key performance indicators in drilling. By configuring standard automatic connection sequences that can be activated by a click on a keypad, mud pumps can be ramped up as quickly as possible while ensuring choke control is within the optimal range to minimize deviations in downhole pressure. Tripping operations can be optimized by controlling drawworks speed, in addition to choke actuation to minimize downhole pressure fluctuation caused by surge and swab when running and pulling drillpipe.
To assess the impact of an integrated control system, NOV asked four drillers to perform primary drilling tasks while simultaneously monitoring an MPD control system in a simulated environment. The experiment used one dualscreen setup with a separate dedicated screen displaying MPD events and alarms, and one integrated setup with critical MPD events and parameters displayed on the same driller’s display as the primary driller’s control objective. Results clearly indicated the value of the integrated setup, with the driller performing both MPD and drilling operations with a 33% to 80% improvement in reaction time to events and changes in MPD conditions as compared to a nonintegrated, dual-screen control scenario. These improvements in performance and consistency suggest that a driller can assume additional MPD monitoring responsibilities more efficiently if the integrated rig control system provides essential MPD data on the primary driller’s screen.
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