The drilling mud is evacuated from the borehole after casing the well by pouring or injecting water into the casing, called backwashing.
42.
This is usually because, in order to reduce the equivalent density of the drilling mud, a compressible gas is injected into the mud.
43.
This involved pumping weighted drilling mud into the well via the wellhead assembly, a method which was ultimately successful in halting the leak.
44.
On 3 August, first test oil and then drilling mud was pumped at a slow rate of approximately per minute into the well-head.
45.
The expansion is crucial because drilling deeper wells means the rig needs to carry more pipe, drilling mud and other equipment, Vecchio said.
46.
Sometimes an inert gas is injected into the drilling mud to reduce its equivalent density and hence its hydrostatic pressure throughout the well depth.
47.
One company also allowed drilling muds to be discharged in the shallow ocean rather than pumping them underground as required along much of Alaska's shore.
48.
Without centralizers, there is a high risk that a channel of drilling mud or contaminated cement will be left where the casing contacts the borehole.
49.
But federal records show that EPA regulators apparently did have concerns that wouldn't have been fully addressed by the new rules governing drilling mud discharges.
50.
The drilling muds, once used, are pumped back to the rig platform and, in most of the Gulf oil fields, simply dumped over the side.
