The continuous circulation of drilling fluids offers many benefits, including the control of bottom hole pressure along with enhanced wellbore cleaning and stability.
In the current oil market scenario, these features become crucial requirements for personnel safety, operational efficiency and cost reduction, particularly in drilling environments with very narrow margins and more extreme deep-water, high-pressure/high-temperature situations.
Drillmec HoD (Heart of Drilling) is an advanced Continuous Circulation System developed and patented where an automated control system provides mudflow switching between the top drive and a side port integrated in each continuous circulation valve (subs) that are made-up on top of drilling stands before starting the drilling phase. A remotely controlled and fully automated clamp provides the opening and closing of the sub side port in a “hands-off” operation.
When a new stand is added to the drilling string, a sub connected to a stand already drilled into the well is positioned in the rotary table, and the clamp carrying a side flowline is engaged to it. Once the hydraulic clamp arms are safely connected to the sub, the rig floor crew can move away from the red zone area and manage the rest of the operative sequence from a remote control panel.
Acting on the clamp commands on the control panel, the operator opens the external plug of the sub side port which remains inside the clamp body during the entire sequence. When the control system confirms the open status of the external plug, the mud flow can be redirected from the top drive to the side port before breaking the top drive connection; mud flow is also switched back to the top drive after adding the new stand.
The flow rate to the well remains always constant during the entire connection sequence, keeping a dynamic condition in the well characterized by constant bottom hole pressure and continuous BHA cleaning. The HoD Continuous Circulation System can be used during the drilling and tripping phases in an identical way.
Some important considerations made during the design process were to prioritize a high level of personnel and equipment safety, convenience in rig integration and the ability to minimize the downtime through the integration of a maintenance management with the control systems.
All the HoD system components are designed in accordance to applicable API standards for a working pressure rating of 7,500 psi and a maximum flow rate during the connection of 1000 gpm. The sub’s design guarantees a double safety barrier to be in place between the pressure inside the drilling string and the outside during connections on the rig floor as well as in the well. Both the barriers are independent and tested to one and a half times the working pressure rating.
The system is designed for onshore and offshore rigs with the diverter manifold, the hydraulic power unit (HPU) and the control system integrated in the same skid having a small footprint. This feature ensures complete flexibility during its installation and safe and fast rig-up operations without the necessity for an expensive mud loop upgrade. The typical installation layout isolates the diverter manifold from the mud pump system during the standard drilling phase. Consequently, pressure drops added to the mud circuit are minimized and the manifold valves’ lifetime can be drastically increased. Furthermore, with the diverter manifold not being pressurized during drilling, checks and routine maintenance tasks can be carried out avoiding system downtime.
The operation during connections is entirely computer controlled from a safe area on the rig floor or directly from the driller’s control cabin. Rig hands are only required to engage and remove the clamp, but the clamp and its flexible hose are not pressurized at that time. A fully automated handling system for the clamp has been developed and it is available for Drillmec brand new rigs, where the advanced Continuous Circulation System can be integrated in the rig packages.
The embedded software allows a complete remote control of the operative sequences as well as providing the status of the system components in real time from the remote control panel. The connection sequence can be performed with a fully automated routine or step by step. In both cases, the control system acquires and elaborates signals from sensors integrated in the main system components, reducing human errors with help text messages and warnings. The software also includes a CMMS “computerized maintenance management system” that helps to keep a historical record of working parameters of each component of the system, schedule and track maintenance tasks, and print operation reports. Maintenance database is also remotely accessible.
After the successful completion of strict testing programs related to pressure and functionality, the HoD Continuous Circulation System has recently completed a field application in a deep onshore reservoir appraisal well in Europe. In details, the HoD Continuous Circulation System has been used to drill the 12in 1/4 phase to keep ECD “equivalent circulation density” constant during connections, improve bottom hole assembly cleaning and hole stability during drilling and pull-out of hole. For this application, “tailor made” subs for H2S containing environment, characterized by very high levels of tensile and torsional strength were studied and built.
The entire HoD package has shown excellent results in terms of components’ functionality and reliability in hard working conditions, represented by heavy mud and high hydraulic parameters. Connections have been made with a maximum stand pipe pressure of 4200 psi and a maximum flow rate of 750 gpm in a complete safe manner.
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