PROCEDURE FOR UNSTABLE ROCK SIMULTANEOUS OPENING AND CASING AT HOLE DRILLING Russian patent published in 2011 - IPC E21B7/20 

FIELD: gas and oil production.

SUBSTANCE: procedure consists in drilling borehole with bore bit connected with casing string. The casing string is set in the hole, and the bore bit is further extracted from it. A section of the hole with unstable and destructed rock is drilled from a main hole at certain pressure of fluid consumed with an expendable bit connected to the casing string in form of multi-ray expandable tube of length exceeding length of the given section This bit is lowered on a drilling string. Internal diametre of the given section is bigger, than diametre of the main borehole minimum at thickness of wells of the casing string. Upon drilling a section overpressure is created in the casing string exceeding specified pressure and sufficient for complete extension of casing string corrugations. The casing string is fixed relative to walls of hole. Further, the drilling string is disconnected and extracted to surface. A calibrating tool is lowered for final casing string strengthening to diametre equal to diametre of the main borehole. The calibrating tool is equipped with a catcher on a lower end for gripping, disconnection and extraction of bore bit.

EFFECT: raised reliability, reduced expenditures and occurrence of emergency situations.

2 dwg