May 24, 2010
http://seattletimes.nwsource.com/html/nationworld/2011938864_oilcement24.htm
By Kevin Spear
The Orlando Sentinel
ORLANDO, Fla. ⤔ Oil company BP used a cheaper, quicker but potentially less dependable method to complete the drilling of the Deepwater Horizon well, according to several experts and documents.
“There are clear alternatives to the methods BP used that most engineers in the drilling business would consider much more reliable and safer,” said F.E. Beck, a Texas A&M University petroleum-engineering professor who testified recently before a Senate committee investigating BP’s blown-out well in the Gulf of Mexico.
He and other petroleum and drilling engineers who reviewed a log of the Deepwater Horizon’s activities described BP’s choice of well design as one in which the final phase called for a 13,293-foot length of permanent pipe, called “casing,” to be locked in place with a single injection of cement that often can turn out to be problematic.
A different approach more commonly used in the hazardous geology of the Gulf involves installing a section of what the industry calls a “liner,” then locking both the liner and a length of casing in place with one or, often, two cement jobs that are less prone to failure.
The BP well “is not a design we would use,” said one veteran deep-water engineer who would comment only if not identified because of his high-profile company’s prohibition on speaking publicly about the April 20 explosion aboard the Deepwater Horizon or the oil spill that started when the drilling rig sank two days later.
He estimated that the liner design, used nearly all the time by his company, is more reliable and safer than a casing design by a factor of “tenfold.”
But that engineer and several others said that had BP used a liner and casing, it would have taken nearly a week longer for the company to finish the well ⤔ with rig costs running at $533,000 a day and additional personnel and equipment costs that might have run the tab up to $1 million daily.
BP PLC spokesman Toby Odone in Houston said the London-based company chooses between the casing and liner methods on a “well-by-well basis” and that the casing-only method is “not uncommon.”
Investigators and Congress already have homed in on a series of suspected instances of recklessness or poor maintenance aboard the Deepwater Horizon ⤔ looking, for example, at why the well’s blowout preventer failed. Those instances, taken together, may have weakened the rig’s defenses and fueled the rig explosion, which killed 11 workers and caused the biggest offshore-drilling spill in U.S. history.
Hunting for enormously rich deposits of oil and natural gas in deep-water regions of the Gulf of Mexico entails some of the most formidable drilling in the world. And BP’s ill-fated Macondo exploratory well had more than its share of trouble and warning signs, according to the rig’s activity log, or “well ticket.”
Drilling began on Oct. 7, 2009, in water 4,992 feet deep and nearly 50 miles southeast of the tip of the Mississippi River Delta.
The first 4,023 feet of drilling was done by the rig Marianas, owned by Switzerland-based Transocean. That rig was damaged by Hurricane Ida a month later and was towed to a shipyard. Transocean’s Deepwater Horizon, fresh from drilling a record-deep well elsewhere in the Gulf, took over by early February.
The Deepwater Horizon, weighing about as much as the 900-foot-long Titanic and considered one of the most capable drilling rigs in the world, almost immediately encountered some of the problems for which the Gulf is known.
Beneath the Gulf’s seafloor is a mush of sand, shale and salt in formations that are geologically young, unsettled and fragile. Coupled with that are layers of sand that hold crude oil and natural gas under high pressure.
While boring into Earth’s crust, a rig pumps a chemical slurry called “mud” down the center of the drill pipe. The mud exits through the drill bit in a blast that washes cuttings out of the freshly cut hole and back up to the rig.
Mud also serves as a kind of liquid plug that can hold pressurized reservoirs of natural gas and crude oil within their formations.
If oil and gas show alarming signs of wanting to “kick” up and out of the well, as they did twice on Deepwater Horizon ⤔ once temporarily and later catastrophically ⤔ drillers can call for heavier mud.
In many of the world’s petroleum regions, heavier mud will counteract the threat of a blowout. In the Gulf, however, it can and often does make matters worse.
The classic and potentially perilous duel for drillers in the Gulf is to maintain a mud weight that keeps pressurized gas and oil underground but doesn’t crack open fragile formations.
According to the Deepwater Horizon’s well ticket, that struggle defined almost every foot of progress made by the rig ⤔ until the Gulf’s geology finally won.
In late February, the rig was losing mud in a weak formation, according to the well ticket. Among the variety of tricks drillers have at their disposal when that happens, the most reliable is to continually reinforce a well with permanent sections of casing or with liner and cement. Deepwater Horizon did that nine times.
In early March, the rig experienced a double dose of trouble, according to the well ticket: The pressure of the underground petroleum temporarily overwhelmed the mud, triggering alarms on the Deepwater Horizon. At nearly the same time, the rig’s drill pipe and drill bit became stuck in the well.
Just one of those occurrences would amount to a bad day.
Deepwater Horizon recovered, but only after losing hundreds of feet of drilling pipe ⤔ likely at an equipment cost of several million dollars ⤔ and losing nearly two weeks of rig time.
After rig workers ran the final section of casing into the well, they opted to fix it in place with cement modified to have foamlike consistency. That makes the cement lighter and less likely to fracture or break weak formations and, as can happen with overly heavy mud, drain away into underground voids.
At that point, said the big-oil engineer who reviewed the ticket, rig workers must have been “jumping for joy” at having completed a stubborn well and discovering petroleum. Based on the array of measuring instruments lowered into the well ⤔ and detailed by the well ticket ⤔ the rig most likely had made a significant discovery.
But among the several possible errors and failures involving the Deepwater Horizon well, that final cement job is widely suspected of having broken down, allowing oil and gas to erupt up into the rig. That is what apparently occurred as rig workers were pumping out the well’s costly and reusable mud ⤔ the liquid plug ⤔ and replacing it with seawater.
The well ticket’s last entry states: “10:00 PM 4-20-10, EXPLOSION & FIRE.”
Engineers interviewed by The Orlando Sentinel said it’s common knowledge among drillers operating in the Gulf of Mexico that final cement jobs rarely are perfect and often badly flawed. That’s a key reason, they said, why many of them rely on a liner to complete a well: It offers more options for injecting, testing and repairing cement, and so is more effective at keeping petroleum under control.
There are three major U.S. cementing companies: Halliburton, Schlumberger and BJ Services. Cementing typically is performed by such rig contractors as part of a broad range of drilling services.
Halliburton, which had the Deepwater Horizon job, mixes in nitrogen to make its slurry more elastic. The nitrogen also helps create a lightweight cement that resembles a gray, foamy mousse and bonds better to the casing.
Cement contractors work closely with oil and gas companies, and the oil and gas companies have the final say on the formulas.
Halliburton says it has used such a mix on scores of wells and told a congressional committee that the cementing on the Deepwater Horizon job was successful.
Information from The Associated Press is included in this report. Special thanks to Richard Charter
