Closed-loop drilling

An in-depth look at NOV’s closed-loop drilling automation system, which could help develop North Sea and Arctic assets.

Automation is a growing force in the offshore oil and gas industry. Its potential to increase safety, optimize operations, improve quality, and reduce risk is a strong driver for an industry with ever-rising costs.

The drivers for technology adoption are strongest in operations where efficiencies, quality, and consistency are of utmost importance. Tony Pink, vice president, Dynamic Drilling Solutions (DDS) – Services, National Oilwell Varco (NOV), says well construction north of the Atlantic Ocean and in the Arctic is challenging and expensive, as well as being in a harsh environment.

“Automation would enable operators to reduce or eliminate the need for manpower on the rig floor, reduce risks, and improve project economics through enhanced equipment performance,” he says. “By using high-speed downhole data integrated with a comprehensive drilling model, drilling speed can be significantly improved and managed from a remote operations center to offer well consistency and repeatability.”

NOV has developed a closed-loop drilling automation system. Closed-loop systems use sensor output, or feedback, to control the machinery and ultimately processes. Used in drilling automation, the direct closed-loop control of machines performs drilling optimization tasks by using high-speed downhole and surface data. In other words, the system allows surface equipment on the rig to be controlled in response to downhole data.

NOV’s automation system incorporates intelligent applications, or software, using the closed-loop control of the drillstring to improve drilling performance with control of downhole weight on bit (DWOB), automated steering, stick-slip mitigation, equivalent circulating mud density (ECD) management, and mechanical specific energy parameter optimization.

In NOV’s system, downhole data is measured by a downhole drilling dynamics sub and is then transmitted to the surface via wired drillpipe. Surface and downhole acquired data is interpreted and analyzed by software applications, and commands are then distributed to the rig’s control system to adjust the appropriate machine functions. The system also includes along-string drilling dynamics subs. Pressure measurements from this sub enable better understanding of the borehole condition and reduce the risk of breaking down the formation or poor hole cleaning.

Key components in NOV’s automated well construction system are:

• Downhole data acquisition (DAQ) tools

The BlackStream enhanced measurement sub and BlackStream along-string measurement sub tools are drilling dynamics DAQ tools that provide real-time and memory data of the following parameters: DWOB, downhole torque, rotational velocity, lateral/torsional/axial acceleration, internal pressure, annular pressure, and temperature. The drilling dynamics subs are designed for use in the bottomhole assembly (BHA) and the drillstring, respectively. The BlackStream measurement while drilling tool provides real-time inclination, azimuth, and gamma ray measurements.

• High-speed telemetry network

• The IntelliServ high-speed telemetry network consists primarily of wired drillpipe and network boosters subs, enabling bi-directional data flow along the drillstring. The network capacity is 57.6Kbps. Currently, BHA interfaces exist for communication with most of the major service providers.

• Control system add-on and data visualizationNOV offers the Amphion, Cyberbase, and NOVOS control systems that can enable the add-on necessary to facilitate the drilling automation system. The add-on enables the TrueDrill DWOB controller, which is a real-time supervisory control engine that utilizes rig equipment to deliver the desired DWOB.

• Well construction applications

The add-on does more than just enhance control; it enables data visualization and software applications. Current applications deliver rate of penetration (ROP) optimization, risk management, dynamics mitigation (SoftSpeed II stick-slip service), and steering optimization.

The data flow and automation process is as follows:

1. Data from the BHA and drillstring are transmitted to the surface via the telemetry network and combined with surface data in the rig’s control system. The data is validated and analyzed on a fixed time interval.

2. Control logic computes the required SWOB set point to deliver the desired DWOB determined by the drilling program plan or optimization applications. Auto driller parameters such as RPM and differential pressure can also be recommended by the optimization applications.

3. The autodriller receives the SWOB set point as a request, analyzes it in the context of its current operational state and safety case, and makes a decision whether to implement the requested SWOB set point or not.

The NOV DDS optimization team has already demonstrated consistent ROP improvements of 20-30% with occasional improvements of 100% (Pink et al. 2011).

“Drilling automation improves drilling stability, reduces risk, and increases ROP. These improvements will also help extend drill bit and BHA life and reduce the number of expensive trips due to bit or downhole tool failure. In harsh drilling conditions and complex drilling environments, the system can deliver knowledge and performance to help contractors and operators achieve their goals safer and more efficiently,” Pink says.

The system has been through three onshore field tests and it has been used on two onshore commercial wells.

“The early results have demonstrated that these technologies can deliver significant performance improvements,” Pink says. “The largest observed benefit however was more cultural than technical; the high-speed downhole drilling dynamics data allows the driller and the customer representatives to maximize the performance of the rig without compromising safety or the reliability of the equipment. High-speed downhole data means the rig and drilling system can be used in a less conservative way—the equipment can be pushed to a higher limit because of clear visualization of the downhole environment. This safe and controlled lack of conservatism could significantly improve well delivery times and reduce the cost of field development.”

Three major projects are being planned in Norway with Total, ENI, and Lundin.

This article is based on a presentation by Tony Pink, National Oilwell Varco, presented in March 2014 at the SPE workshop, In Arctic Norway, and a presentation at the IADC’s conference in Vienna in June 2014.