Like many, I have been monitoring The Oil Drum, a technical blog about the oil industry. The Oil Drum has a lot of new (newbie) members since the crisis. One of the regular contributors is ROCKMAN. In this post he does an excellent job of explaining what he thinks happened:
[new] ROCKMAN on June 2, 2010 - 6:58pm Permalink | Subthread | Comments top
FOR ALL NEWBIES
05 (question from previous thread) – For your benefit and that of other newbies showing up daily I’ll offer you my very biased conclusion of the primary cause of the blow out. The regulars can skip the rest of the story…they’ve heard already. I’ll make just one qualification and it’s a big one: IF THE INITIAL REPORTS ARE CORRECT. It will likely be at least 6 months but more likely a year before there’s official confirmation. The following are just my suppositions. But suppositions gleamed from 35 years as a petroleum geologist with a strong background in well site operations. That experience includes working on site on DW GOM wells as a pore pressure analyst. As a PPA I assisted the drillers in determining the magnitude of the rock pressure they had to deal with.
BP drilled thru an oil reservoir at about 13,000’ below the sea floor. The pressure in the reservoir was around 14,000 psi (an educated guess). They ran steel pipe (casing) from the bottom of the hole back up to the wellhead at the sea floor. They then ran the drill pipe to the bottom of this csg string and pumped wet cement up between the csg and the rock. The purpose of the cement isn’t to hold the csg in place…it isn’t going anywhere. The purpose is to isolate the oil reservoir and keep it from flowing along the outside of the csg in either direction…up or down. It appears the cmt job failed to provide this isolation. Opinions vary but IMHO this is not the BIG SMOKING GUN. Cmt jobs fail all the time. You assume that during the course of drilling a well that you’ll have get a bad cmt job or two. That’s why you routinely test the cmt after a period of 18 to 36 hours. The primary and best cmt test is to apply pressure to it. The cmt has to hold a pressure greater than the reservoir pressure. If it doesn’t then you do a “squeeze job”: pump more cmt behind the csg and then test again. There is some question regarding the validity of the pressure tests BP conducted. Opinions vary but the cmt did fail…that’s why the well blew out.
After BP decided the cmt job was sufficient they had to set cmt plugs inside the csg string as required by MMS regs. But before setting the upper cmt plug they began removing the heavy drilling mud (14.5 pounds per gallon) from the csg and the riser (the 20” tube that connected the wellhead to the drill rig 5,000’ above. They did this by going down into the csg with drill pipe and pumping seawater down. The seawater pushed the drill mud back up to the rig. The seawater weighs about 7.5 pounds per gallons. That means the pressure exerted at the bottom of the well was reduced considerably. So low this pressure wasn’t sufficient to keep the oil reservoir from flowing up. This is a normal procedure. Had the cmt job held all would have been fine. The bad cmt job allowed the oil reservoir to flow up the csg. Had they set the top cmt plug first the well would not have blown out when they displace the mud. Even with a bad cmt job a proper upper plug would have held the flow back.
There are any number of circumstances when there’s a valid concern that some reservoir is flowing into a well that’s cased or still drilling. There’s a very basic protocol for checking to see if the well is “kicking (flowing upwards): you turn the mud pumps off and determine if there’s any drilling mud still flowing out of the well. There are some exceptions but in general a reservoir can’t flow up the well unless it pushes the mud out ahead of it. No flow returns and the well is static. Mud flowing out of the well when the mud pumps are off = something pushing it out. This is not an uncommon event. The drill crew has practiced “killing” the flow (stopping it) many times. First all the return lines are closed (shut the well in). Even if this doesn’t prevent the oil/NG from flowing all the way up to the rig it does prevent it from breaching the drill floor (this is the definition of a blow out). Once the well is shut in they can pump a “kill pill” (heavy drilling mud) down the well and put enough back pressure to stop the well flow. I could be wrong but the evidence seems to indicate that the hands on the rig weren’t monitoring the mud returns when they were displacing the mud. They didn’t see the well coming in (flowing) until it was too late and the oil/NG breached the drill floor and exploded. Why weren’t they closely watching the mud returns? I’ll skip that part of my already long store.
When the well blew out every hand on the drill floor knew exactly what was happening at that point. They knew what was likely to happen. Every hand on the rig knows. The hands had two simple choices. Run and give up any chance of killing the well. Or stay in there and try to execute the kill procedure. The 11 hands that died took the second option. They were obviously “top hands”. That’s the highest title you can earn on a drill rig. Doesn’t seem like a very impressive title to most but in the oil patch it says everything you need to know about the guy working next to you.
I’ll pass on the BOP failure. That’s a critical but separate issue. Just as the efforts to stop the flow since the rig sunk. Lot’s of folks on TOD better qualified to handle those discussions. Likewise other knowledgeable TOD folks have other interpretations of what caused the blow out. Listen to them all and you can come up with your own conclusions
This is my interpretation:
Apologies to ROCKMAN if I've got this image wrong, and apologies for reposting the entire description, but this is not a time to mince words or worry about posting rules. This is evidence. An expert in the field has issued a lucid description that can be understood by laymen. Take what you will from it, it should be known. Others may have a different take, and that should be widely expressed and discussed as well.
Right now we are in the middle of the greatest environmental catastrophe of this country's history and maybe the worst environmental catastrophe of all time, at least the worst man-made environmental calamity.
There will be time in the future to investigate and place blame, and that is not the most important thing right now. Stopping this monster is the most important thing right now.
So, it is necessary to know what happened, and it is important that it be understood now. Knowledge is our best ally when confronting such a crisis. Information and understanding is the only way out of this mess.
UPDATE: And from the comments on TOD:
[new] passaloutre on June 2, 2010 - 9:36pm Permalink | Subthread | Comments top
Rockman I read your posting about how the well was drilled. Right on. I worked in the oilfields for over 50 years helped drill a well at Pt Sulphur La in 1954 to 22570. Deepest well in world at that time Old inland barge steam power. Same plan then as now. Pressure Test bottom of casing or liner. If liner pressure test top of liner. The more things change---The company I worked for believed that if the BOPs were to be tested to 5000 lbs for 30 minutes that did not mean 4900 for 29 minutes. Took bad kicks but never had to leave rig with shirt tail on fire Worked on some of the early day “OffShore rigs” 1950 vintage Some of ODECO’s very first. Worked in 30feet WOW Old jackups and platforms with Converted LST as tenders. Worked for years for a wire line service company and did pioneer work on running conductor lines under pressure. The old original “Injector, Grease seal lubricator.” CBL? I have seen CBLs interpreted as “Possible partial cement bond”. What does that mean? Had to work with several “Company men” on Hi Pressure jobs that didn’t want to follow all my companies safety rules. My company all ways backed me up when I told Company man “Sorry but it our way or rig down” I understand from one report on this job that Stumberger told them that and even called in their own helicopter “When told none were available” to bring their hands in. Insult to memory of hands killed in explosion to say “Might have been running” Old time Tool Pusher saying “Wells don’t blow out. “People let wells blow out”