This does not end operations at the well. Both the original well and the relief well must now follow the procedures for abandonment of the site. The DDII has been preparing for this, but the procedures that must be followed are relatively standard. I am presuming that the plugs that have been discussed are those at the bottom of the well, but there also need to be plugs installed within the well to ensure that there are no possibility of fluids migrating from one horizon to another. To a large extent this has likely been achieved with the filling of the annulus between the end of the lined well and the top of the cement injected earlier this summer. The well is now effectively totally lined on the outside, and there is a plugged production casing in the middle, which retained its integrity over the course of the events.
Nevertheless the regulations will be followed. For your information the relevant bits are, perhaps:
(a) Isolation of zones in open hole. In uncased portions of wells, cement plugs shall be set to extend from a minimum of 100 feet below the bottom to 100 feet above the top of any oil, gas, or freshwater zones to isolate fluids in the strata in which they are found and to prevent them from escaping into other strata or to the seafloor. The placement of additional cement plugs to prevent the migration of formation fluids in the wellbore may be required by the District Supervisor.This means that there will be some continuing work at the well, but not a lot, and thus from now on I shall only be intermittently posting on that topic, and will start to write about the more general topics that have been neglected over the past few months.
(b) Isolation of open hole. Where there is an open hole below the casing, a cement plug shall be placed in the deepest casing by the displacement method and shall extend a minimum of 100 feet above and 100 feet below the casing shoe. In lieu of setting a cement plug across the casing shoe, the following methods are acceptable:
(1) A cement retainer and a cement plug shall be set. The cement retainer shall have effective back-pressure control and shall be set not less than 50 feet and not more than 100 feet above the casing shoe. The cement plug shall extend at least 100 feet below the casing shoe and at least 50 feet above the retainer.
(2) If lost circulation conditions have been experienced or are anticipated, a permanent-type bridge plug may be placed within the first 150 feet above the casing shoe with a minimum of 50 feet of cement on top of the bridge plug. This bridge plug shall be tested in accordance with paragraph (g) of this section.
(c) Plugging or isolating perforated intervals. A cement plug shall be set by the displacement method opposite all perforations which have not been squeezed with cement. The cement plug shall extend a minimum of
100 feet above the perforated interval and either 100 feet below the perforated interval or down to a casing plug, whichever is the lesser.
In lieu of setting a cement plug by the displacement method, the following methods are acceptable, provided the perforations are isolated from the hole below:
(1) A cement retainer and a cement plug shall be set. The cement retainer shall have effective back-pressure control and shall be set not less than 50 feet and not more than 100 feet above the top of the perforated interval. The cement plug shall extend at least 100 feet below the bottom of the perforated interval with 50 feet placed above the retainer.
(2) A permanent-type bridge plug shall be set within the first 150 feet above the top of the perforated interval with at least 50 feet of cement on top of the bridge plug.
(3) A cement plug which is at least 200 feet long shall be set by the displacement method with the bottom of the plug within the first 100 feet above the top of the perforated interval.
(d) Plugging of casing stubs. If casing is cut and recovered leaving a stub, the stub shall be plugged in accordance with one of the following methods:
(1) A stub terminating inside a casing string shall be plugged with a cement plug extending at least 100 feet above and 100 feet below the stub. In lieu of setting a cement plug across the stub, the following methods are acceptable:
(i) A cement retainer or a permanent-type bridge plug shall be set not less than 50 feet above the stub and capped with at least 50 feet of cement, or
(ii) A cement plug which is at least 200 feet long shall be set with the bottom of the plug within 100 feet above the stub.
(2) If the stub is below the next larger string, plugging shall be accomplished as required to isolate zones or to isolate an open hole as described in paragraphs (a) and (b) of this section.
(e) Plugging of annular space. Any annular space communicating with any open hole and extending to the mud line shall be plugged with at least 200 feet of cement.
(f) Surface plug. A cement plug which is at least 150 feet in length shall be set with the top of the plug within the first 150 feet below the mud line. The plug shall be placed in the smallest string of casing which extends to the mud line.
(g) Testing of plugs. The setting and location of the first plug below the surface plug shall be verified by one of the following methods:
(1) The lessee shall place a minimum pipe weight of 15,000 pounds on the cement plug, cement retainer, or bridge plug. The cement placed above the bridge plug or retainer is not required to be tested.
(2) The lessee shall test the plug with a minimum pump pressure of 1,000 pounds per square inch with a result of no more than a 10-percent pressure drop during a 15-minute period.
(h) Fluid left in hole. Each of the respective intervals of the hole between the various plugs shall be filled with fluid of sufficient density to exert a hydrostatic pressure exceeding the greatest formation pressure in the intervals between the plugs at time of abandonment.
(i) Clearance of location. All wellheads, casings, pilings, and other obstructions shall be removed to a depth of at least 15 feet below the mud line or to a depth approved by the District Supervisor. The lessee shall verify that the location has been cleared of all obstructions in accordance with Sec. 250.704 of this part. The requirement for removing subsea wellheads or other obstructions and for verifying location clearance may be reduced or eliminated when, in the opinion of the District Supervisor, the wellheads or other obstructions would not constitute a hazard to other users of the seafloor or other legitimate uses of the area.
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I appreciate all the effort you put in to keep us informed throughout this saga. Thank you.
ReplyDeleteWhy do they they keep adding the word "effectively", as "effectively dead" and "effectively sealed".
ReplyDeleteThis makes it seem as though they are leaving an opening for escape from commitment. It inspires distrust.
They said it was sealed weeks ago, but it turned out not to be sealed. They have said a lot of things that turned out not to be true.
Now they have pulled up the ROV's. "Nothing more to see here, folks. Just move along."
No, thanks. I'll just stay here a while and look around.
HO -- Let me echo Porsena's thanks. Your summaries here have been a great help. Much appreciated!
ReplyDeleteLet's not jump to conclusions about the flow path from reservoir to surface in the Macondo well. By the time the relief well got to the annulus (and found no cement??), the well had been standing static for weeks. Any hydrocarbons in the annulus had long since migrated upwards (above where the relief well intercepted the wellbore), and any mud in the annulus had migrated downwards. No-one should have expected to find any hydrocarbons!
What is clear in retrospect is that BP's risky cost-shaving caused an entirely unnecessary blow-out. The mechanism of that blowout will be under scrutiny for years to come. Detailed future analyses will reveal what actually happened.
Thanks for the kind remarks. In regard to the mud and oil in the annulus, I think that they can do a chemical analysis from the returns to establish whether this was the mud from the Deepwater Horizon, before the disaster, or from the DDII when it did the top kill. I suspect that it was the former, and that this was what led the oversight committee to say, in essence, "we're done."
ReplyDeleteHO -- That's where I get concerned about reading too much into the news releases.
ReplyDeleteFrom what I saw (and admittedly I did not invest the time to hunt down the details), when the relief well intercepted the Macondo wellbore, the mud returns showed (a) no oil, and (b) no cement. Which implies they drilled into a (then) mud-filled annulus.
From earlier documents, it seemed like the cement was supposed to fill the annulus most of the way to the preceeding casing shoe. I have not tried to put the two wells onto a common True Vertical Depth -- since the relief well is deviated, the reported Measured Depth is not directly comparable to depths in the blowout well. But unless they deliberately tried to hit the annulus in the narrow interval above the nominal top of cement, the lack of cement seems to require explanation.
Parties on both sides of the issue have very strong financial incentives to understand the findings from the relief well. I doubt we have the complete picture yet.