دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: a device installed near the bottom of the casing. It has a valve that keeps mud out of the casing so that the casing can be floated into the hole to lessen the weight on the rigs equipment This valve will, however, automatically open to let mud into the casing when the pressure of the mud outside the casing becomes high enough to collapse the joints of casing near the bottom of the string. Thus, this special collar, with its pressure-sensitive valve, not only allows casing to float, but also keeps it from collapsing.