industry’s first active sealing device for deepwater managed pressure drilling
provides greater control and condition monitoring of the wellbore seal,
reducing maintenance costs and rig downtime.
Pressure Drilling (MPD) provides a variety of benefits to a drilling operation.
MPD isolates the wellbore from the atmosphere, enabling rapid adjustments of
wellbore pressure to improve downhole pressure control.
the closed-loop drilling system, advanced flow metering devices are more
readily adapted to measure volumetric and mass flowrates of returns, improving
kick detection and well feedback. With better feedback mechanisms, the rig may
be able to detect kicks faster, leading to reduced kick response time and total
influx volume. Furthermore, upon detecting a kick, the crew may increase the
back pressure to stop kick growth prior to closing the blowout preventer (BOP).
implement an applied surface backpressure (ASBP)-MPD system, rigs have
historically used passive sealing systems, such as a rotating control device (RCD).
RCD systems vary in complexity but share most of the same basic features. An
RCD consists of a housing and a seal assembly. The housing includes a latching
mechanism to retain the seal assembly and ports for the return flow, and it is
integrated into the drilling riser or affixed to the top of a surface BOP
seal assembly consists, in part, of a bearing assembly and an RCD seal element.
The RCD seal element is typically elastomeric, with an opening slightly smaller
than the drill pipe body to grip the drill pipe. One or more seal elements are attached
to the rotating portion of a bearing assembly, while rotary seals seal between
the rotating and non-rotating portions. External static seals are installed on
the outside of the bearing assembly, to seal the space between the bearing
assembly and the housing. The seal element is specially designed to allow the
element to stretch, as drill pipe tool joints pass through.
operating principles govern RCD systems. When circulation commences, the RCD
seal assembly obstructs the annular fluid. The seal element rotates with the
drillstring, to reduce wear on the element. There are no means to adjust the
seal, so if the element fails to maintain a pressure-tight seal, the entire
assembly must be replaced. The design of an RCD does not support direct
monitoring of the seal condition, so the rig must remain ready to stop
operations, to replace a bearing assembly, if required. Furthermore, unexpected
failure of the RCD system to maintain a wellbore seal may occur due to a worn seal
element, torn seal element or failed bearing assembly.
this general design has the advantage of a short stack height, it has the
disadvantage of parallel failure modes between the element, the bearing and all
rotary and static seals. In practice, the operation of passive RCDs in
deepwater drilling is more complex and costly, due to additional protective
sleeves in non-MPD sections and requirements for highly specialized running
tools. In the offshore environment, the stack-up height in the riser is much
less of a constraint, making the primary benefit of RCDs less pronounced. In
deepwater, superior seal life and seal quality are of higher importance, due to
higher daily costs.
developed an active control device (ACD) (Fig. 1) to address the
limitations of passive sealing devices in deep water. The active control device
uses dual spherical annular packer elements—similar to those found in a BOP—to
actuate a dual, non-rotating seal sleeve element. An active control system,
which enables closing pressure monitoring and optimization over the life of the
seal sleeve element, controls the annular packers. Two seal sleeve elements are
made up into a seal sleeve assembly, which drillstring-deployed tools run and
retrieve. The seal sleeve elements use a unique co-molding construction
technique, in which a wear-resistant polytetrafluoroethylene (PTFE) honeycomb
insert is molded with a flexible polyurethane buffer material. The system
contains no rotating parts and uses a durable polymer seal insert to absorb the
wear caused by pipe motion within the element.
active control device is part of a larger MPD system, as illustrated in Fig.
2. An ACD typically forms a portion of an MPD specialty joint that runs in
the drilling riser, just below the termination joint. The MPD specialty joint
includes an ACD, a drillstring isolation tool (DSIT), and a flow spool. When
the ACD or DSIT annular packers are closed, returning drilling fluid is
diverted through a pair of API 17K hoses to the MPD manifold at the surface.
Additional support equipment, such as the hydraulic power unit (HPU) and
umbilical reel, provides power and communications to the subsea joint.
seal sleeve elements run relaxed in the hole. In contrast, passive RCD elements
use an interference fit to create a seal, meaning that the element is subject
to wear from the moment the drill pipe is inserted. When the annular packers
close on the outer surface of the elements, the element elastomers bend inward,
and the wear-resistant PTFE insert makes contact with the drillstring. The
polyurethane supports the PTFE insert and provides a buffer material between
the packer and the seal insert.
closed-loop, direct-hydraulic active control system operates the active control
device. All control valves reside at the surface, within reach when service is
necessary. An umbilical system combines control and communications functions,
using a single termination head. The closed-loop design allows the use of
optimal hydraulic fluids to function the subsea joints while reducing the risk
the seal assembly in place, closing the active control device annular packers
closes the seal sleeve elements against the drillstring. The upper and lower packer closing pressures adjust
independently. Initial closing pressures are prescribed for each packer, based
on the expected wellbore pressure at the surface, and the closing pressure
applied to the seal sleeve elements is adjusted, as needed. The active control
system maintains the required closing force, while the PTFE seal insert
gradually wears. As a seal element wears, a higher closing pressure is applied to
maintain seal integrity, as the annular packer operating it moves to a more
The combined use of the active control system
with the co-molded seal sleeve insert enables the system to detect and alert
the crew when the PTFE seal insert is worn away. The seal wear state indicator
alerts the rig crew that the seal assembly should be replaced soon. A
lubrication system is provided to enable seal condition monitoring. The
lubrication system draws drilling fluid from the active mud system for
injection into the cavity formed between the upper and lower seal sleeves.
During drilling operations, the packer
closing pressures are precisely controlled, to maintain the lubrication chamber
pressure just above the wellbore pressure. Fluid lubricating the lower seal
sleeve element joins the well returns, while fluid lubricating the upper seal
sleeve element collects in the trip tank. As the seal material wears away, the
seal element geometry changes, reducing the wall thickness of the element from
the inside out, as shown in Fig. 3.
the PTFE insert wears through, the PTFE’s contribution to closing pressure
fades. The PTFE insert and the polyurethane buffer material have notably
different material properties; whereas the PTFE is more rigid, the polyurethane
is more flexible. Once the PTFE is worn away, the polyurethane makes contact
with the drillstring. The greater flexibility of the polyurethane requires the application
of higher closing pressure to contain the same lubrication pressure as the
PTFE. This sudden loss of lubrication pressure and the shift in the required
closing pressure inform the system that the PTFE has worn away. However, it is
noteworthy that even when the element reaches a worn state, it can still seal
API Specification 16RCD provides a standardized approach to testing RCDs.
However, API 16RCD tests are designed to test different aspects of rotating pressure-containing
devices separately, so the seal assembly is often replaced between stripping
and rotational tests. This provides limited information on how the system
should perform in the field. Before field operations, design verification
testing of the active control device was performed, in accordance with the
rating test requirements specified in API Specification 16RCD. Under the 16RCD
licensing testing requirements, the active control device holds a 1,500-psi
dynamic pressure rating, at 160 revolutions per minute (RPM) drillstring
rotation, and a 1,000-psi stripping pressure rating.
design verification testing and system optimization of the active control
device were performed at a fit-for-purpose, full-scale test rig in Willis, Texas.
The test rig facility enables the performance of advanced drill mode testing
and stripping mode testing protocols, which far exceed the standard testing
requirements. The performance of these test protocols enables clients to define
an operating envelope and measure system performance and seal wear, prior to
going to the field. This ability helped reduce adoption risks and improve
confidence in the active control device performance before field deployment,
ensuring the equipment was project ready.
drill mode testing provides a standardized and
pragmatic approach to quantifying and optimizing seal performance. The seal
life optimization program uses the drill mode test format to trial alternate
control system modes against previous baseline trials. Drill mode testing also
enables validation of control system functionality and testing of automation
against established benchmark tests.
integration scope for the MPD project included equipment and control system
integration with the rig’s drilling control system and the driller’s chair. Upon
arriving at the rig, the lubrication system feeding the ACD was arranged in an
open loop circuit, in which the lubrication system draws directly from the
active mud pits. Mud is then injected into the chamber between the ACD seal
elements. The operator and drilling contractor selected multiple equipment and
service providers for the project, requiring cooperation between various parties.
completion of the systems integration and commissioning scope, responsibilities
for operation and maintenance were handed over to the rig. As the crew became
more familiar with the system, the commissioning support crew head count gradually
reduced to zero. The framework in Fig. 4 illustrates the general roadmap
for control system integration.
ACD system helped the operator reach the deep success case, allowing the crew
to navigate a narrow and uncertain drilling window, while drilling close to the
maximum permitted depth of the well with zero recordable safety incidents. The
ACD sealing system held annular surface pressure as high as 500 psi while
drilling and 600 psi during connections, as required by the well plan,
performing in line with passive RCD equipment on the first well. In the first
well, the longest single run included 20,000 ft of stripping pipe and nearly 4,000
ft of drilling in the open hole, with the seal sleeve closed. Also, during the
first well, the crew became familiar with the running and retrieval tools, so
replacing the seal assembly took less than 30 min.
after-action review identified lubrication pump life as a focus area. Although
the lubrication was deactivated during portions of the drilling operation, the
ACD system was able to seal the well and allow operations to continue without
downtime. After the first well, alterations to the lubrication system were
implemented. To prevent fluid bypassing the lubrication pump, the lineup of the
lubrication pump was adjusted to gravity feed clean fluid from a trip tank,
while the returns were lined up to the opposite trip tank. This method is
referred to as the closed-loop method.
the supply tank drains, it is periodically refilled, whereas the return tank is
periodically drained back to the shakers, to recycle the mud. The short packer
life of the lubrication pump was also observed in the first well. Between well
testing was performed at the test rig, but it could not replicate the shorter
packing life observed. Instead, emphasis was placed on testing existing
off-the-shelf triplex pump packing designs in the field.
emphasis has been placed on providing a real-time indication of the remaining
seal sleeve life. A new approach to tracking seal performance uses electronic
drilling data to account for the combined effects of pipe motion on the seal
elements in context with the applied closing pressure. This approach compares current
operating conditions to past runs, to provide the rig with an estimate of the seal
element’s remaining life.
the introduction of the ACD in 2019, multiple systems have been deployed
globally in basins in the Black Sea, Gulf of Mexico, and South Atlantic. The
ACD has been used to perform a variety of drilling operations including
drilling, stripping tapered strings, sidetracking, running liners, and
cementing. While passive RCDs are near peak technology after decades of
modification, the ACD system is at the beginning of the development cycle, realizing
performance gains with each new well drilled. The adaptability of the ACD
technology makes it an ideal candidate for closed-loop drilling operations,
including controlled mud level (CML) dual-gradient drilling, and it enables other
next-generation drilling technologies. WO
is the Technology Development manager for NOV’s Managed Pressure Drilling group,
defining and bringing forward the next generation of drilling solutions. He
joined the MPD industry in 2013, helping to develop the non-rotating active
control device sealing technology. He joined NOV through the acquisition of
AFGlobal’s Advanced Drilling Systems business in 2021. Austin holds a B.S. in
Petroleum Engineering from Texas A&M University and an MBA from Rice