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Condition monitoring of drilling RCDs

Thursday, October 6, 2022

Aramco Researchers have developed a system to do condition monitoring of Rotational Control Devices (RCDs). These 'seal' the well while allowing the drill string to rotate and move up and down in managed pressure drilling

Byline by Krzysztof Machocki - Aramco Overseas, Aberdeen Technology Office; Zahrah Marhoon - Saudi Aramco, EXPEC-ARC; Amjad Shaarawi - Saudi Aramco, EXPEC-ARC; Ossama Sehsah - Saudi Aramco, Drilling & Workover

Aramco Research Teams, based in the UK and Saudi Arabia, have developed a technology solution for monitoring the condition of rotating control devices (RCDs).

These are devices that 'seal' the well during managed pressure drilling while allowing the drill string to rotate and move up and down.

Managed pressure drilling (MPD) is a technology that allows for rapid and precise wellbore pressure control, especially in formations of uncertain geomechanics.

The RCD seal is a crucial part of the MPD equipment but is prone to various failures.

This new technology monitors the condition of various RCD parameters, and allows the users to identify and act on the early indications when the RCD is about to fail during MPD jobs.

The sensors used for condition monitoring measure vibrations, acoustic emissions, rotation, pipe movement, temperatures, and contamination level in the coolant fluid.

This system then displays all the critical measurements, in real-time, to the user. So they provide early indications and warnings to prevent catastrophic RCD failures during the critical parts of drilling activities.

Additionally, all of the recoded data is then used for further processing and analysis to seek statistically significant correlations to predict future time-to-failures using ML techniques.

Background to MPD

When drilling a traditional oil and gas well, the specific drilling mud is used for various critical reasons: to lubricate the bit, clean the well from the cuttings, and provide hydrostatic pressure. The mudflow system, at the surface, is typically open to atmospheric pressure.

Therefore, the majority of the bottom hole pressure is generated by the hydrostatic pressure of the drilling fluid column. In general, the denser the drilling mud, the more pressure will be generated at the bottom of the well.

To drill the well safely, the density of the drilling mud must be carefully selected and monitored throughout the entire drilling process to avoid wellbore instability problems and well control incidents.

These wells are usually drilled with a certain pressure overbalance to allow for safe drilling operations.

Managed Pressure Drilling (MPD)is an alternative method. It allows controlling the bottom hole pressure in a more precise way. It has been developed and successfully adopted and used within the industry to enable drilling of more challenging wells. MPD is currently being more and more widely utilized, especially offshore.

An additional benefit of MPD systems is that they can quickly detect changes in formation pressure while drilling. This gives feedback to the drilling crew on the critical pressure changes. It allows them to rapidly regain control over the well to prevent dangerous hydrocarbon influxes and non-productive time.

MPD systems can also increase the rate of penetration and lower the cost of drilling mud.

The current MPD systems are closed-loop systems. Therefore, they eliminate the risk of any dangerous gases rising to the surface and around the rig crew personnel and equipment.

MPD equipment

The Rotating Control Device (RCD) and choke manifold within the MPD equipment package allow the creation of a closed-loop system and rapid regulation of the downhole pressure.

This closed-loop system, with surface pressure gauges within the MPD equipment, allows monitoring of any formation pressure changes. It is possible to precisely adjust the bottom hole pressure to the corresponding formation pressure profile.

The RCD sealing element is one of the essential features that enable maintaining this pressure. The pressure is applied and adjusted between the RCD seal and the wellbore while permitting pipe movement.

There are various types of RCDs. All of them can be connected to the top of the blow out preventer (BOP) stack. There is a stationary housing, sometimes called the 'RCD bowl', and the sealing element, or bearing assembly, that connects the stationary bowl with the dynamic drill pipe inside. This allows for various pipe manipulations while operating under pressure.

All of the current RCDs are manufactured and tested according to API 16 RCD specifications. The dynamic pressure tests within this specification require to prove the RCD's ability to maintain the pressure during multiple cycles of specific pipe manipulations. These tests significantly improve the standardization and characterization of the general RCD performance.

It is essential to remember that the conditions where the new RCDs are tested are different from the typical MPD job environment. The drilling rig conditions will vary from rig to rig and, on some occasions, can be significantly more challenging.

As a result, there are occasions where premature RCD failures can occur without a significant warning to the operator. Failure to maintain the closed-loop system MPD operations can result in dangerous drilling scenarios, leading to well control issues, well stability issues, and stuck pipes.

RCD failures

Failures of the RCD to maintain the closed-loop and pressurized system can be slow, with small leakage around the sealing element, or very rapid, with a total failure of the sealing component.

While gradual pressure losses can be easier to detect and address by the crew members, both of these failure types can be very dangerous if not addressed in the correct time and manner.

Failures can happen due to many factors, and sometimes, the early signals cannot be detected, even with strict inspection and maintenance procedures and before reaching the recommended hours of operation.

Condition monitoring

For safe MPD operations, it has become important to develop a system that allows monitoring the condition of this crucial MPD element.

The new RCD Condition Monitoring equipment was designed to capture multiple system measurements in good operational conditions. It alerts the operator when the operating conditions and the environment have changed, giving early warnings that a failure might happen to the RCD.

This system was designed to operate in hazardous areas classified as 'Zone 0,' 'Zone 1,' and 'Safe Zones.' It can work in high ambient temperatures and environments with dust particles, which are usually present while drilling in the desert.

It is a non-intrusive system - installation doesn't require any modifications to the existing MPD system.

The system consists of various sensors mounted onto the jacket attached to the RCD (see illustration).

In the initial stage of research, the system was designed to operate in a passive mode. It was collecting data and showing the results on an integrated Human Machine Interface (HMI) in the form of time-series plots. This allowed the user to spot trends and any trend deviations. All the essential measurements are shown in real-time to the operator in the field.

The passive mode for this equipment was chosen to avoid any potential false alarms before sufficient data samples are collected from various jobs and adequately analysed.

This condition monitoring system is now operating in the field and capturing data.

Sensors and measurements

Various non-intrusive sensors are included in this package and attached directly to the RCD and related MPD drilling machinery.

Rotational Speed Sensor - the primary function of this sensor is to take the measurements of the bearing component rotation speed versus the stationary bowl. In the current passive mode, any significant fluctuations in the time-series plots from these measurements provide the operator with the inside of the bearing problems.

In the advanced analytics stage, post job, the measurements from these sensors are then correlated to the rotational speed of the top drive to monitor any slippages between the top drive, drill pipes, and RCD. For example, a difference in rotational speed could suggest a problem with bearings or seals.

Displacement Sensors - these sensors monitor the position of the drill pipe relative to a stationary datum and the change of shape in drill pipes. Proximity sensors measure the drift of drill pipes concerning the top drive and the RCD positions.

In the current operational mode, the operator can notice any potential misalignment between the top drive and the RCD and when the tool joint approaches the RCD sealing element.

The data from these sensors allows tracking the movement of drill pipes into and out of the well and helps understand the unique RCD response for each of the tool joints passing through the seal.

Vibration Sensors - these monitor the vibrational signature from the interactions between the seal and the drill pipes, and help measure the condition of the bearings. Vibration data also offers information on the system's response to the ongoing drilling operations.

Temperature Sensors - by measuring housing temperatures at two different locations, the operator can notice early problems that will result in temperature changes in the specific areas of the RCD. For example, some temperature changes might be expected to come from the change in the friction factor in the bearings and the seals.

Acoustic Emissions sensor - this sensor is mounted on the housing and can measure acoustic emissions inside the RCD bowl. The acoustic emission measurements are related to the ongoing operations and the RCD responses to certain drilling events.

Each sensor then sends the measurements to the data acquisition system for processing and storage.

Data handling

The current design allows storing raw data from the sensing equipment with a corresponding time and date stamp.

The data is saved on various mediums as a backup, including integrated local storage and a removable SD for further data analysis.

Collected data is displayed on an integrated display on the central unit, Human Machine Interface (HMI), allowing the operator to interact with the system, read and adjust the alarm levels, modify graphs for more precise analysis, and set some basic parameters.

The processed data triggers simple alarms and provides operator feedback. These alarms are communicated to the user through visual and sound events. At the early stage, they help with self-troubleshooting the system by detecting any readings significantly off the scale. This is a way to check the system and sensors are functioning correctly.

On completing each job, all the data is transferred directly from the central unit to a dedicated device for more sophisticated analysis.

Installation and deployment

The system was used for an MPD job on a land rig in challenging desert conditions during its first field deployments.

The sensors were pre-attached into an add-on jacket that is easily attachable to the RCD already pre-installed to the BOP stack.

The add-on jacket design was chosen to minimize time spent on sensor installation activities in the field. It made it easy to standardize the positions for each of the sensors, making sure the measurements between all collected data from different jobs can be correlated together in further, advanced data analysis.

The Human-Machine Interface was positioned inside the MPD container to provide shelter against the sand particles and high ambient temperatures that are usually present in desert drilling environments.

A special multicore cable with low signal attenuation properties connected the sensors via a junction box installed on the jacket and the HMI.

Pre-installation, post-installation, and operational checks were followed to ensure that the system was functioning correctly and data was captured appropriately. Post-job tests and maintenance work was also carried out to prepare the condition monitoring system for additional deployments.

This condition monitoring system was designed with the user in mind, ensuring it is easy to set up and safe to use in zone-1 hazardous areas during drilling activities.

Initial field deployment results

During the first field deployments, the condition monitoring system measured, recorded, and displayed various desired parameters to the operator.

Several trend observations were made, and various drilling events were observed, recorded, and displayed to the operator in real-time.

Different vibration levels were observed at various speeds of the running pipe and during running in and out of drill pipes.

The proximity sensors detected events like tool joints passing through the RCD, allowing us to measure the unique RCD response to each tool joint at different pipe running parameters.

These measurements were displayed during the job in the field to the operator in real-time.

Specific trends formed during different drilling-related activities.

Currently, more data is being collected to understand the RCD critical responses while it is approaching closer to the failure.

More data collected in the future is expected to help in improving the advanced data analysis part of this technology. This will help quantify the health of the RCD sealing and bearing components, identify applicable trend deviation limits, and predict a safe operating window for the critical MPD operations.

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» Aramco

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