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Oilfield Technology
September 2016
in 2016 with the addition of two new darts that extend operator
capabilities beyond what was conventionally possible.
The valve assembly of the DAV MX CircSub operates on a piston
and spring mechanism, engineered to the highest level of quality
and tested to withstand the harshest of formation environments,
including high angle and HPHT drilling where heavy muds are
required. The differential pressure rating of 10 000 psi in both
directions provides the highest possible level of assurance.
The mechanism is activated when a Smart Dart is
pumped down the drill string and lands in the seat of
the CircSub. The piston spring is compressed, aligning
the internal ports of the tool with the external ports of
the assembly thereby making an opening for the drilling
mud to flow into the annulus. The BHA can be either fully
or partially bypassed depending on application and dart
selection.
The system is user-operated and comes with a
range of activating Smart Darts, each designed to
offer a specific functionality depending on application
requirement. The range includes the standard diverter
dart (SDD) which offers 100% bypass, latch and seal
and a nose-lock hold open feature designed to keep the
valve ports open even after pumping has stopped. This
dart is well suited for LCM spotting (case history of up to
224 ppb) and/or dry tripping.
In the situation where partial flow to the BHA is
required, the split-flow dart (SFD) is used. This dart will
give partial flow to the bit, sufficient to allow the pipe
to be rotated and to keep the BHA cool for hole cleaning
applications. It is also well suited for self-filling when
tripping in to hole with closed-end assemblies. For
maximum isolation and non-return applications, the
alternative diverter dart (ADD) offers 100% bypass and
also shuts out in-flow from the annulus when pumping
stops. Each opening dart in the range has extremely high
stability and can be relied upon to stay firmly latched in
place to maintain the setting mode.
Operational advantages
The system features a simple cycling sequence. Operation
begins with selection of the relevant Smart Dart for the
intended application (i.e. loss curing, drying tripping, hole
cleaning etc.) before the dart is then pumped into the
string. Activation is rapid, and the dart will travel at over
1000 ft/min. at 225 - 300 gpm. Upon activation, the tool
will show a clear pressure drop at surface – confirming
that the dart has landed in the activating seat and the
fluid is now flowing into the annulus.
The Smart Dart range is more reliable than ball
activated systems – with each dart featuring latch and
seal and up to 10:1 anti-blow-thru safety factor. The
latched seal of the system offers 100% BHA bypass,
something that cannot be guaranteed with ball systems.
The latched darts are highly stable, providing a much
wider operating envelope for the user to deploy. In
addition, this system is faster to use, as the darts can be
pumped down at high speed with negligible concern of
blow-thru.
When the intended application has been completed,
a Universal Closing Dart (UCD) is pumped down to
deactivate the tool. This lands on the concentrator
button on top of the Smart Dart, releasing the
mechanical extrusion mechanism. The UCD exerts pressure on the
concentrator button to break the shear pins in the darts. These pins
shear at 2000 psi, upon which the Smart Dart and UCD travel down
into the catcher sub below. The decompression of the piston spring
is rapid with the valve ports closing in 0.05 seconds. Shearing is
confirmed by a pressure increase shown at surface and the darts are
stored in the catcher with negligible pressure loss. The catcher sub
can hold multiple cycles of the opening and closing darts.
Pushingtheenvelope
Operators continually push the envelope of what is
possible and Churchill Drilling Tools has responded
to the demand for increased performance and
reliability. DAV 2016 upgrade advances on the
feature set of the valve and introduces several new
enhancements to the tool.
The Ultra Series dart increases speed of
activation by up to 25% to 400 gpm. This dart also
features a low shear closing pressure of 600 psi
– 70% lower than is conventionally available.
This is especially useful when drilling with fragile
formations or in pressure sensitive assemblies.
In one case study in the Norwegian Sector, two
CircSubs were cycled a total of three times during
the 7 in. liner shoe track drillout, and 6 in. x 7 in.
section drill-out operation in a highly deviated
section of a development well. The 5 in. (NC38) DAV
MX sub was used to lift up the cuttings to surface
post drilling. The sub was then closed, before being
activated again to boost displacement to a lighter
fluid (on the shoe track drill-out run) and to screen
the mud (on the reservoir run). The Ultra Series darts
provided the operator with a possibility of pumping
the darts into place with up to 300 gpm.
The Ultra Series dart has shown to be
particularly useful when activations are constrained
by challenging well geometry and or compromised
hydraulics.
As operators increase performance demands,
either intentionally or due to unexpected downhole
events, it is possible to put the valve beyond its
capability. A safeguard against extreme tool use was
developed in the form of the emergency shut-off dart
(ESD). This dart makes the DAV MX the first circulation
valve that can be shut even after it has been damaged
– providing operators the means to force all flow
through to the bit even though the valve has not fully
closed. This allows sections to be completed without
the need to trip out of hole – saving time and allowing
a swift return to the drilling schedule.
In a recent deployment, after cycling in a highly
abrasive milling operation in the Norwegian Sector,
it was suspected that the CircSub might have been
damaged by debris and had not fully closed. The
operator was able to pump an ESD into place in just
15 minutes. Satisfied with the repair, the ESD was
used for over 17 hours, allowing the operator to
successfully complete the 8 ½ in. window section
without any additional trips.
In addition, the DAV 2016 upgrade also includes
compatibility with the HyPR HoleSaver tool. This
tool is the first hydraulic pipe and hole recovery
Figure 1.
Point 1: Valve
openedby selectedSmart Dart
pumped fromsurface. Point 2:
Valve closedwhen Smart Dart
shearedbyUniversal Closing
Dart. Bothmove into catcher.
Multiple open/close cycle.
Drillingmuddivertedaround
catcher suballowing for
operations to continue.
