Federal investigators sent a letter Thursday indicating that only one of the four tests Halliburton performed on the cement produced a stable foam.
In a statement, Halliburton said that several tests were conducted but admitted to skipping a critical test prior to the blast that caused the Gulf oil spill.
These tests were conducted before Halliburton knew the conditions in the well. The company used a slurry mixture different from the one that was actually used in the well.
A later test conducted in April was "irrelevant because the laboratory did not use the correct amount of cement blend."
Halliburton also said that BP (BP) was made aware of issues with the April test.
The company highlighted BP's misinterpretation of negative pressure tests and failure to perform cement bond log test as factors in the April 20 disaster, which killed 11 people and left the oil well spewing out crude into the Gulf of Mexico.