Re: Transocean fire « Reply #201 on May 1, 2010, 6:40pm »
I just listened to"James" again. He says that the bottom plug had been set and that the seal assembly had also been set. He does not mention any malfunction concerning the seal assembly. Then he describes the BOP test, with a top plug job to be done next. For anyone interested, here is a closeup view of a regular generic wellhead assembly. I have no idea what was used on this well.
« Last Edit: May 1, 2010, 6:59pm by cordialdevil »
Right - the interview says they did set the plug then tested the liner ready to displace.
HAL press release says they had not set the plug?
Seam to be contradictory to me, although I could be being dense.
regarding the comments (not by me) way upthread about multiple failures to test the liner seal are obviously not congrugent with the interview.
Well spotted Wired,
I listened to the clip part 1 again. At 0:54 sec he mentions with words to the effect : open BOP, displ w/sw in preparation to unlatch, then again at 01:48 he mentions open BOP to do the top plug. I guess he lost train of thought because he was interrupted - nothing sinister. In any case technically speaking you are right and the interview is not totally consistent with the HAL report.
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Re: Transocean fire « Reply #203 on May 1, 2010, 6:53pm »
Cordial, your image depicts a surface wellhead. Still, it will be useful for some to help them envision how the various casing strings are landed, associated seal assemblies, etc.
-test BOPs assumed test OK OR ELSE NOT OK to open BOP LATER AFTER DISPL RISER TO SW
-displ riser w/sw
-open BOP in prep to unlatch riser
-KICK --------> BLOWOUT
Question: how much time elapsed between the pressure test and the END OF BOP testing ?
Was the well bore isolated before testing BOP ?..how ? ...with what ?
Which Rams were tested and to how much pressure and duration ?
Also, were BOPs low pressure tested ?
The press release from HAL, over on Rigzone, says " At the time of the incident, well operations had not yet reached the point requiring the placement of the final cement plug which would enable the planned temporary abandonment of the well, consistent with normal oilfield practice"
So they say they had not set the final plug, so they were not getting ready to unlatch. Something is not adding up. (or I can't add, something I do not discount)
Where did the comments about the liner seal assembly not testing come from - is that likly to be rumour?
Wired,
Something is most definitely not adding up. Your comments make perfect sense, so personally I don't think it's your maths which is at fault.
On thing appears clear, that being that this 'tapered casing string' as initially reported in fact consists of 7" liner set within 9 5/8". One can safely assume this liner had not been perforated. So why the need to set a cement plug in the liner? It constitutes a mechanical barrier. (cf MMS temporary abandonment requirements, published in a previous post.) Or is it possible that this rumour about the liner lap not testing is true (I'm unclear about the use of the term 'seal assembly' here, are we really talking about a liner packer run above the hanger???), so it was decided simply to set a cement plug across the hanger assembly? That would be unconventional and unwise in the extreme.
Also, your point about the BOP test and displacing the riser before setting the tophole cement plug does indeed raise many questions.
But finally, if the test of the first cement plug, and also the liner 'seal assembly' (or packer) were quite so hunky-dory, where did the gas come from???
I'm going to spend some time reading back over all this thread, because somewhere this story emerged about testing something (the liner lap?) 10 times. Even if it was only a rumour. Because as a rule of thumb, any pressure test of anything should only be attempted a maximum of three times. If an acceptable test cannot be obtained by then, it's time to bite the bullet, find out the cause, and remedy the problem in a safe manner.
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Re: Transocean fire « Reply #206 on May 1, 2010, 7:18pm »
Drillingrep, yes it appears the CHASRT theory doesn't fit because, also, according to "James", the BOP appears to have been function tested without a problem immediately before the well coming in.
« Last Edit: May 1, 2010, 7:23pm by cordialdevil »
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Pupjoint, as far as I can tell, the initial post about a possible seal assembly failure comes from kwcharlie on page one of this thread.
That was me quoting what was said in discussion i posted here http://drillingclub.proboards.com/index.....ol&thread=4840. it was over my head then and now is WAY out of my experience, no wires, SCR's or computers now. I go back to lurking here in the GOM while you Sub SEA boys come to better understanding from all this new info. My info is VERY old now and not first hand.
If a 7" production liner was run, it virtually eliminates the previous speculation that the CHASRT was preventing the blind/shears from closing.
Wired,
Furthermore, I have been back through the various posts on this thread, and am unable to find the reference to multiple failures testing the liner lap. Maybe it was just a rumour. (Or maybe I missed that post. Or its author has retracted it.)
Also, quite correct, Halliburton does not mention setting a plug in or around the liner top.
Or could it actually be that the liner was cemented with an excess designed to cover a certain depth above the hanger, and then the running tool just pulled out, leaving a 'plug' above TOL which the completion rig would then clean out? Normally, nevertheless, in such a circumstance either a pressure test or a weight test (or preferably both, just to check where TOC is) after WOC should be done, prior to POOH.
But enough speculation on my part for now. If a 7" liner was run, it is safe to assume that it covered all the producing zone. And to revert to my prior post, saying "where did the gas come from?", obviously it has to have come from that producing zone. So to do so, either there is a flow path into the liner, which Halliburton states was tested, or it came up the backside and into the upper wellbore via the liner hanger and the liner lap.
Personally my money begins to be put on the latter.
And it still sounds a really odd time to decide to test the BOP. If it was a routine, scheduled test, I'd have put in for a dispensation to delay it, given that the rig was due to move off two days later. Or had a fault already been recognized?
Another thought. The schematic diagrams posted on this site notwithstanding, was this in fact a vertical well?
Information or opinions are solely provided for educational and/or discussion purposes on an informal public forum and should not be interpreted as a recommendation for a specific treatment plan, course of action or product/ service. Use of any of this information does not replace consultations with qualified individuals in these respective fields.
Re: Transocean fire « Reply #211 on May 1, 2010, 8:00pm »
No, prior to my last, just a couple of other thoughts. An 'Inflow' (or underbalance) test. This would require displacement above the line under closely controlled conditions to a lighter fluid, which would be reversed out if there was any sign of it not working. This after WOC, but prior to POOH. Halliburton hasn't mentioned it. Only "James" has, but then maybe only because it's considered a standard operationg procedure. Did it actually take place?
There's also another inconsistency in "James" testemony, though I'm convinced that the guy was talking in good faith, and given the circumstances (recent survivor of a traumatic event, speaking live on the radio under an assumed name, etc.), may have been somewhat stressed. He mentioned displacing the riser to seawater with the Hydril closed. How does one do this? I've never seen a stack setup with a choke or kill line entering the riser above the Hydril. Unless it's another of these newfangled deep-water innovations.
Information or opinions are solely provided for educational and/or discussion purposes on an informal public forum and should not be interpreted as a recommendation for a specific treatment plan, course of action or product/ service. Use of any of this information does not replace consultations with qualified individuals in these respective fields.
Re: Transocean fire « Reply #212 on May 1, 2010, 8:15pm »
Pupjoint, For subsea systems, on installation of the blowout preventer stack, each component including the high pressure connectors should be individually pressure tested at a low pressure (200 psi) and to the greater of 70 percent of rated working pressure or the maximum pressure expected in the upper part of the casing. Subsequent pressure tests may be limited to the lesser of 70 percent of the rated working pressure of the blowout preventers or 70 percent of the minimum internal yield strength rating of the upper part of the casing, provided the test pressure equals or exceeds the maximum pressure expected inside the upper part of the casing. An exception is the annular preventer which may be tested to 50 percent of its rated working pressure to minimise pack-off element wear or damage. A test plug or cup type tester should be used. The periodic actuation test is not required for the blind or blind shear rams. These rams need only be tested when installed and prior to drilling out after each casing string has been set.
Re: Transocean fire « Reply #214 on May 1, 2010, 8:44pm »
Obviously, the Plug 'Bumped' when cementing the 7" Liner, and tested ok. Did they check for backflow? We then have to figure out if the Packer was set. I can't see how pressure testing can take place if the Packer has not been set after completion of the cement job, and if we just kept pumping up10 times it seems to me that the cement between the 7" Liner and the 9 5/8" Casing would be displaced to allow a channel to form. Therefore, there must have been communication between the 7" Liner and the 9 5/8" Casing. Assuming all went acccording to plan and the Packer was considered 'set', the next stage of the well should have been an 'inflow test', which should have been conducted thus. Displace the Choke line to Sea Water, Close a ram and line up the well to the Choke. Observe for pressure build-up. If negative, open up to Trip Tank. Confirm line-up is 100%. If the well was going to flow it would happen at this point. So, let's assume we now have one barrier in the well. We Pooh and while pulling perform a BOP test. Or, Pooh to surface and run BOP test tool. Test BOP, while observing TT volumes throughout the test procedure. Also, volumes being pumped by cementer are critical (especially if testing the Packer and the tests failed). Questions: How long was the Annular closed for during its test? Why are we displacing to SW with only one 'apparent' barrier in the well? Why have we not set the mechanical plug yet? I've heard of situations where plugs are installed and cement dumped on top, but this was to be a temporary abandonment. A mechanical plug would then have been placed in the well.
Too many things don't add up. When testing produces problems these need to be addressed first. Any plan to withdraw primary well control (displacing Riser to SW) when preesure tests confirm that no barrier exists, is surely impossible to do.......in any part of the world.
What about the possibility of Gas migrating and locating itself below the BOP? Normally, after the cement job is performed, and Hanger/Packer set, the running tool is stung out of the PBR and a full circulation of well volume performed. This should 'clean out' any gas which may have become present during the cement job. Let's assume this was done. Where can the gas have come from? Is it possible that when the riser displacement took place no-one was observing the volume of return? Perhaps the BOP was leaking, allowing an underbalanced scenario to unfold. Was there really a BOP function test going on? Perhaps, the driller noticed a large gain and shut the Annular. Depending on how long it was closed, gas migration would collect below the Annular.
Of course, this is all speculation as BP are not issuing details of what was going on in the well, and not all the information from the 'witness' on the rig adds up.
Doesn't the US have regulations specifying the barriers required in circumstances like this?
Re: Transocean fire « Reply #215 on May 1, 2010, 9:18pm »
Alcor, thanks for the many points you raised. I believe that the witness, "James" has contributed some good information and is obviously no fool, but I don't think he is a drilling hand. He leaves too many gaps. I don't think the driller saw any pressure increase and closed in the annular, because he would have had to inform the co man, toolpusher etc., and they would not have opened the hole back up without doing a lot of checking. It appears that this gas hit, which they experienced upon opening the annular (according to "James"), came as a complete surprise. Apart from the question of where did the gas appear from (leak into the wellbore at depth or close to the seabed), why didn't anyone notice a flow rate while not circulating (prior to the BOP test), or a pressure buildup while BOP testing (unless this was just a function test of the annular(s) and pipe rams?). Something does not add up.
« Last Edit: May 1, 2010, 9:19pm by cordialdevil »
Re: Transocean fire « Reply #216 on May 1, 2010, 9:35pm »
HALLIBURTON PRESS RELEASE : Halliburton had completed the cementing of the final production casing string in accordance with the well design approximately 20 hours prior to the incident.
James Interview : -set seal assy top of well
In many cases, the final casing (7" ) is taken to the wellhead level, known as Production Casing and then its not a liner.It is set in the Wellhead with Hanger & Seal Assembly requiring CHASRT to set....
(But James in his opening line also says about 7" Production Liner....then its seals, ie liner hanger seals are not on top of well)
HALLIBURTON PRESS RELEASE : In accordance with accepted industry practice approved by our customers, tests demonstrating the integrity of the production casing string were completed.
While bumping the top plug,which is the completion of displacement, the pressure is held by the casing string and (under present situation) is being termed as Integrity of production string is said.
If we take James version, that all BOP Tests had been concluded, then it must be with Boll Weevil BOP Test Tool, which is set in the wellhead (like CHASRT,its also a full bore tool.have potential to obstruct a Ram) .
But the Tool bottom is open to well and the landing string is filled with water and kept open,such that any leak past test tool seals well kicking, it will be on the top of string, above the rig floor..Hence any well influx during the testing (takes about 6 Hrs atleast with 5min low n 15 mins hp tests for each failsafe valves,rams,annulars etc.), will always show up on the rig floor.
Hence, its doubtful,they had conducted full BOP Test at this point.
BOP Tests are carried out by Cement Units..But Halliburton is silent about it.
Usually, before opening any Annular or Ram,the Choke or Kill line is lined up(all sub sea failsafes opened ) to C& K Manifold with Auto Choke on the rig, the line pressure if any is readout and then the annular is opened...
...Hence like AK has said, something is not adding up. --------------------------------------------------------------------------------------------- In another analysis, lets say they opened Annular(James said),then the blow out,leaving all working hands not available...and blackout, Abondonment order, left other knowledgable crew to leave....Hence the ROV which was being manned not from Rig, tried to close the shear ram.possibly by that time, the Boll Weevil has travelled up and stuck in the bop bore.
-------------------------------------------------------------------------------------------------- Like the ideas for containment, BOP flanges (side outlets) can be accessed , some ROVs, can burn two studs on Clamp 5, and connect another coflexip with new set of failsafes ...Its difficult but possible. Its a better way of having funnel on leaks till the relief well being drilled.
Re: Transocean fire « Reply #217 on May 1, 2010, 9:49pm »
There is a 3rd line, known as Booster line (Generally its a hydraulically/Electrically operated Ball Valve with an nrv ) connected on the first riser,just above the Flex Joint. This is besides Choke & Kill Lines and the booster line gives access to Riser,above the stack....They might have displaced riser volume with sea water through this, when Annular is kept closed....
Re: Transocean fire « Reply #218 on May 1, 2010, 10:00pm »
"Like the ideas for containment, BOP flanges (side outlets) can be accessed , some ROVs, can burn two studs on Clamp 5, and connect another coflexip with new set of failsafes ...Its difficult but possible. Its a better way of having funnel on leaks till the relief well being drilled."
Correction to the last sentence , Its a better way, THAN having funnel on leaks till the relief well being drilled
Means, accessing well at the stack will achieve a fair degree of containment, which is a better and feasible plan than trying out a Funnel (with no or doubtful pressure integrity ) on leaks and to hose it to surface to a tanker.
Re: Transocean fire « Reply #219 on May 1, 2010, 10:47pm »
I don't have any direct experience with oil drilling, so bear with me - I'm trying to figure out a lot of the terminology from context etc... but I think I may have an odd idea of what might have happened: from both the "James" interview and the Halliburton statement, it sounds like the well had been plugged with a cement plug in the bottom of the "final production" casing, (which I guess is the "7 inch" people are mentioning here), and this was sealed to the larger diameter wellhead casing at the seafloor level. So at that point there would have been a continuous column of mud from the surface to the bottom of the bore, so dense as to provide enough pressure at the bottom to prevent any inflow before the bottom plug was placed.
Both statements agree that the installed assembly was then tested for pressure-tightness, which I presume might be done by sealing the BOP and pressurizing the bore below it. So supposedly we have a tightly sealed bore (by the cement plug at the bottom, and the BOP and the annular seals at the casing hangers at the top) - let's assume this was actually true: the testing was valid, the seals didn't leak.
According to "James", the mud in the riser above the BOP was displaced with water, and the next operation was to be to place a cement plug at the top of the bore, preparatory to disconnecting the rig. (This is consistent with the Halliburton comments, which said that the top seal and bottom plug had been set, but not yet a planned cement plug at the top of the bore.)
So we have a bore that's sealed, and full of mud, and there's a major gas kick when the BOP is opened to access the top of the bore for placing the upper plug... and the question is "where did that gas come from"... might it have been dissolved in the mud in the sealed bore, under enough pressure to not form bubbles under the preceding conditions? But when the BOP was reopened to place the cement, the pressure at the wellhead would be less than when it was sealed off, since the riser now contained water rather than mud.
(I've noted some mentions of "oil-based" or "synthetic olefin-based" mud as likely to be used here - I guess for underwater drilling a non-water-miscible mud mixture is preferred? - and this type of mud is described as having some ability to dissolve gas under pressure!)
So what I'm guessing is the change from mud to water in the riser reduced the pressure at the top of the mud column in the bore, enough to let some of the gas bubble out - which starts a cascading effect as water is displaced from the riser by the gas, which reduces the pressure at the top of the remaining mud even more, letting more gas out of solution... could there be enough gas dissolved in the mud that it all would fizz up like a bottle of warm Coke when you unscrew the top quickly, and this would propagate down the bore as the hydrostatic pressure decreased, eventually kicking out all the mud and leaving the bore nearly dry?
At this point the only remaining well control would be the mechanical structure of the casing and the bottom plug... without the weight of the mud, would the external pressure be enough to crush and tear the casing, allowing the supposedly-sealed well to start flowing some oil?
Could this sequence of events also perhaps have compromised the BOP, by damaging the sealing elements or perhaps by a failure of the hold-down feature at the casing hanger assembly, which allowed the inner casing to rise in the well head and interfere with the BOP?
Re: Transocean fire « Reply #220 on May 1, 2010, 11:09pm »
If the 7" Tubing was completed to the Wellhead, then we have other problems to consider. On semi submersible rigs, using Vetco wellheads, confirmation that the Seal Assembly has been set correctly is performed using an 'index line' to reference the position of the drill string before and after setting takes place. I believe this applies to all other Wellheads. Normally an 8" drop is observed. Any less and the possibility of installing Emergency or back-up Seal Assy has to be considered. If the seal Assy failed testing, then I have no idea why displacement of Riser took place. With SW in the riser and gas migrating up the Annulus of the 7" liner there was only one possible outcome. Sounds like the BOP was tested. What for if the Seal Assy failed. I'm beginning to wonder whether the Hanger landed out in the wellhead or not. It's much harder to get a precise 'index' measurement in deeper waters to ensure that landing out is exactly right. But it can be done as long as the same strings are run for pulling Wear Bushing versus running Hanger. It MUST be done! I am baffled that there weren't earlier volume increase signs while circulating/displacing cement, or perhaps there were. I'd like some Wellhead experts to offer their opinion on the possibility of the kick coming from the annulus.
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Re: Transocean fire « Reply #221 on May 1, 2010, 11:19pm »
More wild speculation from me and a couple of comments; After reading the last few posts and listening to James' interview It seems possible they did actually run a 9 5/8" X 7" tapered production string. I know they get run in Norway occasionally, they can be complicated to cement and set, (can be a nightmare actually) but they can save a lot of time. This would explain why they were working with a casing hanger at seabed before the accident.
Another thing- it is pretty unusual to test the stack a couple of days before moving off the well- if they were going to pull the stack in 2 days, they most probably were testing the WH/casing hanger assembly, not the bop.
Unless things have changed over the last 3 years, normally after setting a subsea well liner you would pressure test the whole casing/liner string by closing shear/blinds and pumping down the kill line.
Also About inflow testing: if it was an HPHT well and you were going to underbalance the well by displacing mud to light brine/seawater, you would do an inflow test on the liner lap by running a retrievable packer and setting it just above the liner lap, and just before setting displace the DP to water, set packer and bleed DP to zero, then accurately measure inflow every 5 mins for about 2 hours. you plot the volume inflow V time using a "horner plot" and can determine if the inflow is a leak, or if it is just thermal expansion of well bore fluids.
Another thing-on a deepwater well, it is SOP to circulate below your rams via kill and choke lines if the rams have been closed for longer than an hour to circulate out any trapped gas bubbles before they get into the riser.
Having read a few other comments today I think I should also mention that the riser between the BOP and the surface is not a pressure containing piece of pipe. On the outside of the riser are clamped two smaller pipes (kill and choke lines) rated to 10kpsi or 15kpsi which connect into the well bore in between the various pipe rams.
Anyway, there does not seem to be enough information available to figure out what they were doing and what went wrong- We will find out in a few months what really happened. I'm going to stop trying to second guess what went wrong, I just hope they get it shut in quickly.
Re: Transocean fire « Reply #222 on May 1, 2010, 11:33pm »
Listening to the 'James' interview he is unsure about whether the BOP tests were completed. Why was there a build-up of gas below the Annular? During pressure testing of the BOP, Rams and Annular are opened and closed every 20 to 25 mins. It's possible that soluble gas was constantly migrating up the well in between tests. Then, when the well was being displaced to SW gas returns may have been evident if the well volumes are being monitored, so called 'volume control'. It may be that this volume control was not considered necessary due to succesful tests of Seal Assembly and BOP. One thing is for sure. The well flowed from either the Annulus or from the 7" Production Liner.
Re: Transocean fire « Reply #223 on May 1, 2010, 11:48pm »
One other point to consider: The cement job had finished 22 hours prior to the Blowout. It will be interesting to know whether volume control was maintained during the cementing and displacement procedure. Because, the 'initial' gas must have entered the well either whilst running the Tubing, during the cementing and displacement, or on the previous trip out of the hole. Was a full circulation of the Well performed prior to cementing? This would have taken considerable time, but at least we'd know if the well was gas-free. Another thing worth considering is this: What fluid was used to displace the cement? Did they use a heavy brine in preparation of eventual production. Was this fluid weighted to the same value as the drilling mud.
Joined: Nov 2003 Gender: Male Posts: 193 Location: USA
Re: Transocean fire « Reply #224 on May 2, 2010, 12:12am »
A few things that James is not accurate about in my opinion. He gave the impression that the well pressure is in the range of 30,000 - 40,000 psi. Plain not true. Likely less than 10,000 psi. Also talked about this constant "battle" for well control. I wouldn't have used those words but obviously we lost it here. Whatever happened they thought they had a barrier otherwise would not have opened the BOP! Finally, that mother nature that sneaks up on you sometimes and that's how it is - BULL!!! Where is that taught in well control school?
If it was gas to begin with and then oil then there was time for phase separation and it was right at the surface. The problem would have started right after the cement job and would not have been apparent until they had circulated the riser to sea water, causing the well to become underbalanced.
Measurement is key. Maybe in this case they had a bad gauge but should have been flow checking the well after the test. Maybe a valve wasn't in the right position and it appeared that there was no flow because the valve was closed. Were they checking volume. I would bet they weren't and if they were it was taking less volume than anticipated but just a guess on my part.
A lot of maybe's and guesses. Could have been a mechanical failure too but in any case there was human error and likely by several people to have this type of event. All this will come out in an investigation.
What is important is to get a good look at the stack and see what can be done to divert flow.
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