Tests suggest Macondo cement was unstable, spill commission told
Laboratory tests of cement and additives closely resembling what BP PLC used in its Macondo well in the Gulf of Mexico strongly suggest that the mixture was unstable, the chief counsel for US President Barack Obama’s independent commission investigating the Apr. 20 accident and subsequent crude oil spill said on Oct. 28.
OGJ Washington Editor
WASHINGTON, DC, Oct. 29 -- Laboratory tests of cement and additives closely resembling what BP PLC used in its Macondo well in the Gulf of Mexico strongly suggest that the mixture was unstable, the chief counsel for US President Barack Obama’s independent commission investigating the Apr. 20 accident and subsequent crude oil spill said on Oct. 28.
Halliburton Co., which provided the Macondo well’s cement, said several hours later in an initial response that it was reviewing the study, which it felt raised a number of questions. The company said it believed significant differences between its own cement tests and tests performed for the commission may be due to differences in the cement materials tested.
“We have known for some time that the cement used to secure the production casing and isolate the hydrocarbon zone at the bottom of the Macondo well must have failed in some manner. That cement should have prevented hydrocarbons from entering the well,” Fred H. Bartlit Jr., a founding partner of Bartlit Beck Herman Palenchar & Scott LLP in Denver, said in a letter to commission members that also was signed by Sean C. Grimsley, of the same law firm, and Sambhav N. Sankar, of the US Department of Justice.
They said they asked Halliburton to supply commission investigators with samples of materials used in the BP well. The oil field service company provided off-the-shelf cement and additive materials that were used there from its stock. Although they were not from specific batches used at the Macondo well, they were identical in all other ways to the slurry used there, the letter said.
In its response, Halliburton said its internal tests used “the unique blend of cement and additives that existed on the rig at the time Halliburton’s tests were conducted.” It also noted that a federal court preservation order prevented it from providing the commission with cement, additives, and water from the rig, adding that these materials would soon be released to the Marine Board of Investigation.
Chevron did tests
The letter said that Chevron Corp., which “employs some of the industry’s most respected cement experts, and maintains a state-of-the-art testing facility in Houston,” agreed to test the cement slurry on the commission’s behalf. “Halliburton agreed that the Chevron lab was highly qualified for this work,” it added.
“Chevron’s report states, among other things, that its lab personnel were unable to generate stable foam cement in the laboratory using the materials provided by Halliburton and available design information regarding the slurry used at the Macondo well,” the letter continued. “Although laboratory foam stability tests cannot replicate field conditions perfectly, these data strongly suggest that the foam cement used at Macondo was unstable. This may have contributed to the blowout.”
The lawyers noted that when Chevron provided them with preliminary results of the tests, they asked Halliburton, which had publicly stated that it tested the Macondo cement on Apr. 19-20 and those tests indicated it was stable, to provide all the data from those tests. Documents supplied showed that Halliburton conducted at least four such foam stability tests, three of which suggested the mixture was unstable before a final test, using a modified procedure, indicated that the mixture would hold, according to the letter.
Halliburton responded that two of those tests were preliminary pilots conducted in February and did not include, as the letter noted, the same slurry mixture and design as that actually used at the Macondo well because final well conditions were not known at that time. “Additionally, there are a number of significant differences in testing parameters, including depth, pressure, temperature and additive changes, between Halliburton’s February tests and two subsequent tests Halliburton conducted in April,” it said.
“Finally, we want to emphasize that even if our concerns regarding the foam slurry design at Macondo are well-founded, the story of the blowout does not turn solely on the quality of the Macondo cement job,” the letter said. “Cementing wells is a complex endeavor and industry experts inform us that cementing failures are not uncommon even in the best of circumstances. Because it may be anticipated that a particular cement job may be faulty, the oil industry has developed tests, such as the negative pressure test and cement evaluation logs, to identify cementing failures. It has also developed methods to remedy deficient cement jobs.”
Two possible tests
“Halliburton believes that had BP conducted a cement bond log test, or had BP and others properly interpreted a negative-pressure test, these tests would have revealed any problems with Halliburton’s cement,” the oil field service company said in its response.
It said a cement bond log test is the only available means to evaluate a cement bond’s integrity, but that BP, as the well’s owner, chose not to run one and that several of its employees said that one was planned for later and remedial work would be done at that time. The negative pressure test, which evaluates the production casing’s integrity to provide a barrier to the reservoir, was run but did not produce successful results which employees on the rig of BP and Transocean Ltd., which owned the semisubmersible rig drilling the Macondo well, misinterpreted, it added.
Other factors contributing to the Apr. 20 well blowout and explosion that killed 11 workers and BP’s well design decisions have been broadly criticized, Halliburton noted.
The commission will hold its next hearing Nov. 8-9 in Washington, where it is scheduled to discuss causes of the well’s blowout, rig explosion, and subsequent crude oil spill that took months to contain and control. Bartlit, Grimsley, and Sankar attached a copy of the results of Chevron’s laboratory tests to their letter, and said an expert from the company would attend the Nov. 9 hearing to discuss the report.
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