Gents,

Find attached, for your perusal, an overview of the use of a hydraulic disconnect sub in Brunei Shell Petroleum (BSP) from 1999 to early 2001.

Concept

The original idea came from Antos Vos, as I recall, one of our great Senior Drilling Engineers on the Team.  Leaving long lengths of (used) tubing in the well saved time of having to stack multiple (shorter) cement plugs, incl WOC, and saved time in having to lay down the tubing stingers.  On most occasions, our teams would run the sacrificial tubing and hydraulic disconnect sub below a tubing stinger which in turn was used to set a cement kick-off plug above the abandoned zone, for sidetracking.

Experience - Learning

The attached listing includes failure runs.  
We reviewed the failures and with Smith Services optimised the design of their hydraulic disconnect sub, which was used to great effect.  It's key features were: [1] splined tool, to enable transmission of torque to tubing stinger in long horizontal legs, [2] secondary sealing option of drop ball or dart.  
We were able to run hydraulic subs in tandem, using different sized release sleeves and activation balls. 

During the early trials we had problems getting the sacrificial tubing down to planned depth in long horizontal sections and had to add centralisers for better stand-off and to reduce friction.  The splined disconnect sub allowed us to break friction by rotating and get the sacrificial tubing string to bottom.
We experienced a problem, with an earlier designed tool, whereby the activation ball got damaged during dropping it.  The phenolic ball got chipped, we reckon that it hit the sharp edge of the partially opened ball valve, being sucked down hard by falling cement (U-tube effect).  The resulting damage prevented the from achieving an effective seal, or enough of a seal (choking effect) to achieve disconnect.  We then pushed for secondary sealing capability.
We used phenolic balls as we were plugging back long horizontal legs of appraisal wells.  Heavier brass or steel balls could hang up (fall behind) in the tubes of the DP above the stinger in the horizontal leg.

This tool was also used on a HPHT well in the Bugan field.


Notes on HPHT applications

Please NOTE that there is an inherent problem when setting cement plugs using (Synthetic) Oil Based Mud: cement and (S)OBM when mixed generate a goopy thick sludge.  With heavy muds and even heavier cement slurries, spacers are of little use, and foam balls are preferred for shorter plugs.  Please note that the cement will mix with the film of mud left on the inside of the drill string when pumped down, generating this goopy sludge.  Considering the length of the drill string you will find a considerable volume of mud film...  Be aware, be very aware.
Hence you really need to pump a decent size (LARGE) volume of cement in these cases to have any chance of success.  This speaks in favour of using a longer sacrificial abandonment string or HPHT wells drilled with (S)OBM, as most cementing companies limit open hole lengths to 750-800m maximum, which is not a lot of volume in small diameter hole sizes (6" or less).


Good luck, Jorrit

Hi Ruslan and others.
Although I'm aware that sacrificial stingers have been used in the past I wasn't aware that they are still in use. The issue I don't have an answer for is that a cement plug needs to be left above the stinger so that it can be tagged - it would prove nothing to tag the top of the stinger - so how do you know that the cement in and around the stinger was effective rather than simply getting a tag and a test on the cement above the stinger?

Hi, we used the BHKA disconnect sub for an uHPHT appraisal well P&A in the UK sector.  We ended up losing the well.  The 7” DST liner had been cemented in place and a 5-7/8” section drilled out the bottom to appraise a lower formation section.  We were then to use a sacrificial cement stinger on a BHKA sub to cement up the lower section and perform the DST on the 7” liner section.

All went well - or so it was thought.  Spacer & cement was pumped and displaced with the release dart and Magnatec OBM.  After picking up a few stands above the TOC, we WOC.  The rig went to move the drill string after WOC and found it was stuck inside the 7” liner.

A full review of the work revealed that the spacer and mud system had reacted under uHPHT conditions and created a perfect “plug” of hard clay.  This hit the BHKA sub, causing it to disconnect.  We then very successfully circulated the cement inside the 7” liner and around the drill string, leaving the sacrificial stinger completely un-cemented in the 5-7/8” open hole below.....  Hence we had cemented our running string inside the DST liner....  Due to a weak 13-5/8” shoe, we had to sidetrack from the 20” casing shoe.

Since that day, we have not used the BHKA sub for P&A.  This was over 10 years ago now, and was a fluid design issue and not a BHKA sub issue - though there were some thoughts that the BHKA sub also suffered internal erosion due to the high mud weights at 18+ppg.  This may have been a contributory factor to the premature release, but we will never know.  

Hi Ruslan,

I don't have any experience of using a sacrificial stinger in the way you outline.

But it does raise some questions in my mind as to why you need to fill the entire open hole section with cement it in the first place?

If you have several hydrocarbon zones of differing pressure regimes in the open hole, how are you going to prove that you have zonal isolation between them?

If they are all of the same pressure regime, do you need to isolate them because of production from different zones in adjacent wells? If this is the case, then again, how are you going to prove zonal isolation?

At 30 Deg inclination with NC 38 connections in 8 1/2" hole, I would have a hard time believing that you can avoid channelling up the high side, even if you can rotate and reciprocate the string during cementing. 

If neither of the two above cases are valid, then why not just spot a plug across the shoe?

Or are you just going through the motions for the regulatory authorities?

All the best

Scott

All

Dear members

This post by Ruslan triggered quite a lot of responses, especially since there are more than one solution in the market.

Does anyone have updates. I'm particularly interested in:

• Use in HPHT wells (max. BHT)
• Any issues (e.g.Angus McKay response had premature release; chemistry)
• Maximum length run and OD of stinger vs. ID of hole
• It's always useful to be able to rotate stingers to get a better cement job; what was possible
• Best practices

Thanks

Dave

Successfully the single abandon cement plug for 8 ½” pilot hole with +/- 2800 ft length at +/- 65-75 Deg inclination using +/- 2800 ft of 3 ½”, 9.2 ppf, L-80, VAM21, C-75 used tubing string with BHKA disconnect tools.

The job completed within 1.6 days Vs 4 days plan for conventional abandon cement plug

The main advantages of using the single abandon cement plug with BHKA disconnect tools are as follow:

In the olden days, we did use sacrificial strings either of aluminium or more frequently GRP  Glassfiber Reinforced Plastic.

We recently (within last 2 months) used a BHKA to abandon a 8-1/2" pilot hole from our semi-sub in the North Sea. We set a 3,100ft plug using 2,600ft of 4-1/2" tubing, job went well no issues running or cementing and BHKA released as planned. We had a torque capable tool but decided not to attempt rotation.

We had already identified the sacrificial tubing string to use and a bigger issue was actually getting the required crossovers from the BHKA to tubing and back to the TT550 drill pipe. We had prime and back up assemblies made up prior to load out to minimise handling at rig site.

The next operation after dropping off was pulling back to shoe to set a kick off plug on a CST. One thing that came up at the rig site was that there was no known experience of dropping a CST through a BHKA workstring adaptor after disconnecting. Drawings showed no ID or shoulder issues and the CST was dropped successfully to act as base for kick off plug.

My apologies if a bit out of touch on this-kinda made sense looking at on Kurdistan quite a few years ago , but seems expanding- but  for my education:  well, just great you have 1500m or 2500 ft of HCs need cement opposite  !!  as per regulations spreading.
Just seems to be me, that no matter what hole size, these will be very atrocious worthless cement jobs,  but just to satisfy regulations ?  or to get round stupid regulations.and save money... or just to be seen to be doing different ?

Rusian,

We used the Smith Int'l / Red Baron "TUBING ABANDONMENT RELEASE TOOL" to great effect on two P&A's in the Middle East.

I believe these are built to order only, but they're good tools, virtually fool proof.

James

Blackhawk have developed a drillable version of the Stinger Disconnect Tool. And has been deployed successfully for a major independent operator offshore Mediterranean sea, plug depth 15,000ft.

OBJECTIVE

 Permanently abandon 2,500+ ft of 12-1/4" open hole and sidetrack for next casing section

SOLUTION

 Blackhawk’s Drillable Stinger Disconnect System was run with 5-1/2" fiberglass stinger pipe across the open hole interval.

 A custom guide shoe was designed and run to allow the string to be set on bottom and rotated, without packing off, as secondary release option.

 Drillable components of the system were disconnected 250 ft below casing shoe.

 Cement was pumped behind the disconnect dart to place a second balanced plug 65 ft inside the previous casing shoe.

 Successfully kicked off the next open hole section just below the shoe for successful abandonment and sidetrack in single cement pumping operation.

VALUE TO CUSTOMER

 Customer successfully isolated and abandoned the open hole section and sidetracked the well, as planned.

 Customer saved 4.5 days of rig time compared to previous campaigns where multiple plugs had to be pumped and tested.

I just wanted to clarify that the P3 Perfect Cement Plug Placement Disconnect Tool has been available since 2014, and whilst we have not supplied 100's there have been zero operational problems reported. See attached interesting track record of a 2500ft disposable stinger job.

Our tool was specifically designed for disposable stinger cement jobs, not hydraulic disconnect tools borrowed from coiled tubing drilling or inflatable packer running.

Our tool has an emergency rupture disc by-pass in case the tubing plugs and circulation cannot be achieved. The primary release mechanism is hydraulic with a drill pipe wiper dart landing on a seat but a contingency drop ball is supplied again if circulation is not possible.

Due to "what if questions" rather than operational issues we are introducing a mechanical back-up release feature to our tool in the event the dart does not land for some reason or pressure cannot be applied, then mechanical action can be used to leave the stinger in the hole.

Our system can be supplied with a drillable or non drillable disconnect sub left in the hole. We can supply Fibre Glass drillable tubing and have recently developed a stronger higher temperature rated alloy tubing to leave in the well but remain drillable.

Be clear, you don't have be a large Service Company to have good equipment and supply a good service.

Sudelac P3 - Limited tensile & torque rating.

Hi, we used the BHKA sub for P&A of an HPHT well years ago. The sub accidentally disconnected early and we ended up cementing in the drill string leaving the sacrificial
stinger in the uncemented open hole below us. We found afterwards that at the particular hydrostatic pressure and temperature, the spacer and OBM system reacted to form a solid clay plug. This plug was at the lead of the cement job and when the clay plug hit the BHKA sub, it caused it to disconnect. It was so far down thenwell we did not see a pressure spike. Hence we very carefully positioned the cement around the drill pipe and not around the stinger. I hope this is a valuable lesson that you can use. 

Hi Ruslan

Sudelac also have some great tools, drillable cement stingers and great release systems.  Please check out their website

https://www.sudelac.com/files/7015/3944/2079/DrillABLE_Tubing_Information_Sheet_Rev_0.pdf

I hope it helps

Best wishes

Dave