rozwał - wiert. osypywanie się w czasie wiercenia okruchów skalnych ze ściany otworu wiertniczego.
http://www.teberia.pl/encyklopedia.php?a=ArtShow&ArtId=10785

sloughing - see caving
http://www.boemre.gov/glossary/si-sp.htm#sloughing
caving - collapsing of the walls of the wellbore. Also called sloughing.
http://www.boemre.gov/glossary/c.htm#caving

These clay-containing drilling fluids form a mud cake on the bore hole walls which reduces the sloughing of the incompetent formation as long as the fluid...
http://tinyurl.com/2ekofa9 [+ podobne teksty]

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Note added at 9 hrs (2010-09-17 00:44:09 GMT)
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In such cases, the well bore wall sloughs into the well bore. Sloughing of shale and other similar unstable materials into the well bore can cause the drill...
...to swell and to slough into the well bore. Uncontrolled sloughing may stick drill pipe.
Some well bore problems, such as sloughing of sensitive shales, are virtually...
CASING - Steel pipe used in oil wells to seal off fluids from the bore hole and to prevent the walls of the hole from sloughing off or caving in.