No need to wonder what was destroyed if any of you are willing to do so much at 30 seconds of google searching...
According to the government, Halliburton recommended to BP that the Macondo well contain 21 centralizers, metal collars that can improve cementing, but BP chose to use six.
The government said that, during an internal probe into the cementing after the blowout, Halliburton ordered workers to destroy computer simulations that showed little difference between using six and 21 centralizers.
Halliburton Pleads Guilty To Destroying Gulf Oil Spill Evidence
A centralizer is nothing more than a ring that helps to guide a pipe down so that it can place something more precisely, in this case, the pipe that was to pump the cement down into the well. 21 of them would have allowed the cementing to be more precise, but of course, at the cost of a lot more time spent installing the centralizers.
My guess is that the government overreached in this case...the simulations weren't really germane to identify a cause or causes for the blowout, since they indicated that 6 vs. 21 centralizers wouldn't have compromised safety. But anything related to the disaster becomes evidence, and since Halliburton got rid of this information, it makes them appear that they are hiding something.
Also, they are on the hook for a 200k dollar fine, and volunteered to donate $55,000,000 to National Fish and Wildlife Foundation.