WELL STRING FOR DRILLING THROUGH LOW PRESSURE ZONE Russian patent published in 2020 - IPC E21B33/127 

FIELD: soil or rock drilling; mining.

SUBSTANCE: group of inventions relates to a well string for drilling in a well through a low pressure zone in a formation, a well system for drilling in a well through a low pressure zone in a formation, a downhole method for drilling in a well through a low pressure zone in the formation. Downhole string for drilling in well through low pressure zone in formation includes lowering casing string having first end closest to well head, and second end and working tool connected with lower end of stepping casing string. Borehole column additionally comprises annular barrier having expanding metal clutch surrounding lowering casing string. Each end of expandable metal coupling is connected to reducing casing. Expanding metal coupling is made with possibility of coming into contact with wall of borehole or other casing string so that possibility of rotation of reducing casing and its sliding relative to annular barrier after expansion of expansion sleeve is provided. Borehole column additionally comprises swivel installed as part of step-down casing string and dividing step-down casing into first part of casing string and second part of casing string to ensure rotation of first part of casing string relative to casing second part.

EFFECT: technical result is creation of improved system of well pumping or drilling.

15 cl, 14 dwg