Closed-loop automation of DWOB

Today during the development of unconventionals, the lack of knowledge of the downhole dynamics environment creates a culture of conservatism where excessive safety margins need to be applied to prevent damage to the rig equipment, drillbits, drillstring, and sensitive drilling tools. By using downhole data in real time, this risk can be reduced, and drilling performance can be improved.

Automation of the well construction process has the potential to reduce well construction costs by improving performance, increasing consistency, and helping fill the competency gap that exists across the oil and gas industry today. In discussions with operators, it was determined that their expectation is that automation must first deliver consistent performance, and then the consistent delivery must become faster and more precise.

FIGURE 1. The impact of automated DWOB control was evaluated on various assemblies while drilling the curve and laterals of each wellbore. (Images courtesy of National Oilwell Varco)

Open architecture system

An automated drilling system was developed that incorporates an open architecture for both downhole and surface components. The system is customer-configurable and allows surface equipment on the rig to be controlled in response to downhole data streamed through wired drillpipe, mud pulse, or electromagnetic telemetry methods. Data are prioritized and distributed to appropriate applications as they enter the rig control system. The open architecture allows any party to create applications to control any specific part of the drilling process. Damaging downhole vibrations such as stick/slip and bit whirl are not always detectable at the surface. These are just two of the well-documented events that can cause damage not only to the bit but also to the other drillstring components. A downhole automated control system enables operators to react by changing drilling parameters in real time, thus reducing the vibration and improving or optimizing the weight and torque parameters being applied to the bit.

System description

The system components that make up the automated drilling system are shown in Figure 1. One of the key components is the drilling dynamics sub that provides real-time and memory data of downhole weight on bit (DWOB), downhole torque, lateral/angular acceleration, Z (axial) acceleration, external pressure, temperature, and rpm.

The wired pipe consists of a high-speed wired drillpipe telemetry system that allows bidirectional data flow along a drillstring. The current state of wired drillpipe allows a 57.6-kilobyte/sec bidirectional data rate. It also is possible to measure temperature as well as borehole and annular pressures along the string of pipe. Currently, bottom-hole assembly (BHA) interfaces exist for communication with most of the major service providers.

The DWOB controller is a real-time supervisory control system that uses software and rig equipment to deliver a DWOB value desired by the driller. The system components are shown in Figure 2. The DWOB controller was tested during the drilling of three directional wells on a six-well pad. These wells included vertical, curve, and long lateral sections. Rotary drilling, sliding, and “automated pipe rocking system” operations were conducted on all three test wells.

FIGURE 2. The DWOB controller is a real-time supervisory control system. The system diagram shows data flow.

The DWOB controller successfully controlled DWOB while drilling under all conditions encountered in the three wells. While the DWOB controller automatically compensated for both of these effects, it is unlikely that the driller would have been able to constantly apply the optimum DWOB to get the maximum ROP that the controller was able to achieve.

Automated drilling system tests

Field tests were run for a six-well project in eastern Ohio. The test was designed to evaluate the impact of automated DWOB control on various assemblies while drilling the curve and laterals of each wellbore.

The downhole data for the test were measured by a downhole drilling dynamics sub and then transmitted to the surface via wired drillpipe. The downhole data were visualized and analyzed by a surface application. The surface application then sent setpoints through a control interface to the rig’s preexisting control system. The first three wells were drilled using the automation system and conventional assemblies, while the last three wells were drilled using the automation system and a rotary steerable tool. The test also involved looking at the benefits of this system from a stability standpoint and from how having these high-speed drilling dynamics data can influence the behavior pattern on the rig site.

The test first focused on the ROP improvements that occurred while rotating, sliding, and sliding using an automated rocking application. The second focus was on the positive behavioral change that occurs when the downhole environment is fully understood. These technologies bring significant benefit to the industry, especially in the development of unconventional assets where sliding becomes slow and more challenging the longer the horizontal.

The results demonstrated that these technologies significantly improved sliding performance up to 100%, especially when combined with a surface top-drive rocking technology. The high-speed downhole drilling dynamics data allowed the driller and operator representatives to maximize the performance of the rig without compromising safety or reliability of equipment.

Benefits

ROP values also were obtained on both bent motor and rotary steerable system runs. When paired with the rotary steerable system, the DWOB controller experienced stable and reliable performance 24 hours per day, demonstrating its robust design and operational value. While drilling with the rotary steerable system in the curved section of the well, the DWOB controller actively increased the ROP drilling stability by an average of 93%, thus leading to a more efficient drilling process. In the lateral section, a similar increase of 86% was seen.

The automated drilling system provides real-time vibration control via a controlled torque-monitoring system. When the system senses excessive feedback torque spikes under certain drillstring conditions, it automatically creates a log of the risky drilling criteria and runs a series of optimization algorithms to mitigate and avoid these areas of risk. In the same series of rotary steerable tests, a decrease in torsional vibration from 20% to 14% was measured when the DWOB controller was enabled.

The field test proved that the automated DWOB controller delivered improvements in downhole stability. It also delivered stable 24-hour control and improved performance in rotary and sliding modes. Performance was further enhanced when the technology was combined with a rocking system. The high-speed DWOB controller delivered consistent performance on the curve and lateral sections, with all three wells coming in within six hours of each other when normalized for depth.

Optimization of the well construction process has a clear benefit for future economics of both oil and gas projects.