ONS 2016: Successful use of new version CircSub offers improved performance in Norway
An upgraded version of a popular multi-cycle circulating sub from Churchill Drilling Tools, which has been successfully deployed offshore Norway, is providing operators in the region with access to significant performance and productivity gains.
DAV MX CircSub. Image: Churchill Drilling Tools.
Churchill’s DAV MX circulating sub (CircSub) delivers a faster and more reliable bypass than traditional ball activated tools. Using patented MX (Mechanical Extrusion) Smart Darts for activation, the circsub offers rapid and reliable deployment for applications including loss curing, hole cleaning, displacement, self-filling and dry tripping.
With a 99% opening and closing reliability, the tool has been used by over 60 operators worldwide. It offers 100% bottom hole assembly (BHA) bypass functionality and has been activated at a depth of nearly 30,000 ft.
The valve assembly operates on a piston and spring mechanism, which is activated when a 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, enabling the drilling mud to flow into the annulus. The BHA can be either fully or partially bypassed depending on application and dart selection.
The circsub is user operated and comes with a range of activating darts, each designed for a specific function.
The Standard Diverter Dart offers 100% bypass, latch and seal and a nose-lock hold open feature to keep the valve ports open even after pumping has stopped -- ideal for LCM spotting and/or dry tripping.
Where partial flow to the BHA is required, the Split-Flow Dart is used. This gives partial flow to the bit, sufficient to allow the pipe to be rotated and to keep the BHA cool for hole cleaning. 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 offers 100% bypass and shuts out in-flow from the annulus when pumping stops.
Each opening dart has extremely high stability and is firmly latched in place to maintain the setting mode.
The darts travel at over 1,000 ft/m 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 fluid is flowing into the annulus.
When the application is complete, a universal closing dart (UCD) is pumped down to deactivate the tool. This lands on a 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. The pins shear at 2,000 psi, and the darts fall into the catcher sub below. Shearing is confirmed by a pressure increase shown at surface. The darts are stored in the catcher with negligible pressure loss. The catcher sub can hold multiple cycles of the darts.
The DAV 2016 enhancements to the CircSub are already being used by operators in Norway. The Ultra Series Dart (USD) was activated by an operator at 1,500 lpm in a challenging high deviation environment for hole cleaning, displacement and mud screening. Speed of activation using the Ultra Series Dart is up to 25% faster and the 70% lower shear out pressure allows for use in wells with compromised hydraulics.
In the Norwegian sector of the North Sea, two DAV MX circsubs were cycled 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. A 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 is particularly useful when activations are constrained by challenging well geometry.
The DAV 2016 upgrade also introduces a safeguard against extreme tool use -- 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 -– allowing operators to force all flow through to the bit even though the valve has not fully closed. This enables sections to be completed without the need to trip out of hole -- saving time and allowing a swift return to the drilling schedule. This technology makes the DAV 2016 the world’s first valve with a proven back-up closing mechanism.
For instance, after cycling in a highly abrasive milling operation offshore Norway, an operator 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 min. Satisfied with the repair, the ESD was used for over 17 hr, allowing the operator to successfully complete the section without tripping. Unexpected contamination can occur at any time and the ESD offers a back-up solution to closing the valve.
Furthermore, for the first time in Norway, operators have been able to deploy a fully compatible valve and non-explosive disconnect system as a rapid low cost contingency for differential, mechanical and pack-off stuck pipe situations. DAV 2016 and HyPR HoleSaver are fully compatible when run together in the string. The HyPR HoleSaver is another pioneering Churchill technology. Utilizing ordinary drilling mud, the user-operated HyPR jetting dart can cut through a full strength sub in less than two hours. Drilling engineers can use either a cementing dart which allows for rapid side-tracking after cementing operations or, if an attempt to fish the BHA is preferred, a fishing dart can be pumped down, leaving a clean box to fish once the dart has cut the string free.
The new features in the 2016 version of the DAV MX circulation sub are providing Norwegian operators access to significant performance and productivity gains. These enhanced product capabilities are providing a significant regional boost for Churchill with a number of successful new technology being adopted by operators in the sector.
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