I would not be surprised at all if gas hydrates caused the influx of gas in the well bore and the problems with functioning of the BOP because exactly the same thing happened to me in the GOM in 1985. People familiar with deepwater drilling will recall the drillships Sedco 445, Sedco/BP 471 (now the Joides Resolution) and Sedco 472/Esso were pioneers in Deepwater Drilling. They were ships built and operated by Sedco Inc, which eventially became part of Transocean Sedco Forex and now Transocean. I have described below the series of events that happened on the 472. Coming back from a hurricane evacuation we reentered the well and were drilling out a EZSV when we got a gas influx. Extremely erratic BOP C/K line operation, couldn’t pump down the C/K lines with indications the valves were open. Shut in the well on annulat, VBR’s wouldn’t close, gas blew out in riser, couldn’t pump down C/K to fill the riser, got very hairy, finally able to fill riser from top but a close call. Tooks us weeks to sort out the situation and get well back under control. There are several references to this well situation, especially Barker and Gomez book on hydrates in deepwater drilling operations who were the Exxon Engineers on the well. Sounds like this could be exactly what happened on the Deepwwater Horizon. the presence of the gas hydrates (crystallized methane) probably masked the presence of gas in the wellbore until it was too late. I dug up my notes from that time frame, we took the kick at mid day on 12 Sept 1985. When I read my notes that we woke up all hhands at 3:00 Pm for possible evacuation because of gas blowing out the riser, hit a bit close to home. didn’t think about this until Deepwater Horizon incident and I recalled our experience on the 472 almosty 25 years ago. Would have thought hydrates was a much more known phenomena now.
I am finally glad to see that someone is finally focusing on hydrates as the probable cause of the well control situation, blowout and BOP erratic behavior on the Deepwatyer Horizon. Although I suspected this over 6 weeks ago, based on my experience of almost 25 years ago, I have been out of the oilfield for over 20 years and much better minds than mine have been investigating this situation. In Sept 1985 I was rig manager for the drillship Sedco 472, drilling for EXXON on the Bluethroat prospect well OCS-G-7956 #2 on Mississippi Canyon Block 755 in 3,100′ of water. I believe we were under the 11 3/4 ” liner shoe, I think we had just re entered the well after a hurricane move off, took a kick, shut in, vented a lot of gas out of C/K lines. BOP”s functioning very erratically. Were closed in on annular, erratic PSI readings in C/K lines, ie. we weren’t sure if valves open or closed, same with rams, and even upper annular, signal indications good for function, but taking insufficient hydraulic volumes to confirm open or close status on valves or rams. Ran 2 ’7/8″ tubing inside the riser alongside the DP. took weight at 300″ above upper annular, started circing , got gas in returns, diverted, ran in tubing slowly, circing up gas to top of upper annular, Exxon decided we were probably hydrated, we went inside DP with w/line, ran CBL, no cement in liner annulus. cemented in bottom of DP, perfed casing the through DP, squeezed cmt into annulus. For the next few weeks we circulated heated mud, ran coil tubing with steam, a variety methods to get the gas out of the bore. It’s been a while, but I recall we pretty much confirmed we had been hydrated, our rams and valves essentially ice blocked, and I believe we determined the 13 3/8″ hanger seal (last full string of casing in the hole) had leaked, possibly due to hydrate issues. Anyway, Exxon pretty much confirmed that hydrates had caused our well control issues. It snuck up on us because the hydrates (crystallized methane) did not behave as gas in their crystallized form and we did not have conventionl pressure/volume increase indications of gas in the well bore. I just happened to be on the rig the day it blew, on a rig visit, and although I don’t recall the exact details, we may have just reconnected and reentered the well after one of the 4 hurricanes we moved off for that season, I remember clearly that we were in a section of hole we felt safe and had no indications or reason to expect we had gas in the bore, were very surprised when it unexpectedly blew out on us. Thankfully, Exxon was very conservative and we probed the well with the tubing, heated mud, wireline survey, cement squeeze job until we eventually got the well back under control. Fascinating, I dug up my pipe tally book for the 10 days or so I was on the rig for the initial evaluation of the problem and remedial steps taken along with the erratic PSI readings, even the hydraulic volumes recorded when we functioned BOP rams, showing the reduced hyd volumes to open and close functions which essentially indicated to us something was keeping our valves and rams from fully opening and/or closing. Re Reading my detailed hourly notes after 25 years was both fascinating and eery. When we got the well secured, we pulled the BOPS, while pulling them, the last chunks of ice blew out the riser C/K lines. At surface, the BOP’s functioned normally with out need of repair. We went back in the well, and eventually took it to TD with a 7″ liner to 12,163″ by the next March of ’86. 4 hurricane evactuations, a somewhat preventable drive off , this 3-4 week well control operation, it was a heck of a well. Despite the fact we had to move off location for 4 hurricanes, Danny, Elena, Juan and Kilo, we were very fortunate as 2 came before and 2 after the well situation, not sure what would have happened if one came along while we were connected trying to get the well under control. Anyway, I‘ve been out of the oilfield for over 20 years, but when this came up brought back the thought that we thought we were in a safe condition, the hydrates masked the danger we were in, perhaps those very experienced Transocean hands were lulled in by the fact they had functions blocked and thought that indicated well was static. When they reported the negative test that showed DP pressure, and 0 on the Kill line, I would guess the kill line was blocked by hydrates. With the well control issues they had on that well, doesn’t make sense they didn’t run the CBL or at least set the surface plug, almost certainly when they started displacing and dropped hydrostatic the methane reverted to gas phase, and it doesn’t take much gas expanding from 5,000′ to evacuate the riser in a hurry. Ramon Gomez and John Barker were the Exxon engineers on that well in 1985, they wrote a book that chronicled this SEDCO 472 event as well as others that involved gas hydrates in deepwater drilling.
If you find there is any merit to my observations, or interested in the hour to hour log of what we and Exxon did for the first 10 days or so of our well control situation in 1985, please contact me, there are very few oilfield people here in Maryland, no one to really discuss this with, and I’ve been telling anyone who will listen for the past 6 weeks about hydrates, even the oilfield people I keep in touch with discount hydrates. If I had not observed the effect of hydrates myself, I probably wouldn’t listen either. I would be interested to know if my observation has any validity.
Thank you,
Jim Watkins 301-261-6845, Crofton, Md.
