METHOD FOR ISOLATION OF THIEF ZONE DURING WELL DRILLING Russian patent published in 2016 - IPC E21B33/138 E21B21/00 

FIELD: mining.

SUBSTANCE: invention relates to construction of wells and can be used during well drilling through flushing fluid loss zone. During well construction, a well is drilled with development of absorption interval. Method for isolation of thief zone consists in lowering of drilling string with open end, not reaching to bottomhole, washing face cover of annular space. In pipe string filled with clay solution with density of 1.12-1.16 g/cm³ with filler in form of motes and cordage fibre 10-30 % of volume of solution, flush fluid, gel cement in form of a mixture of cement with 7-9 % clay powder, mixed on technical water with addition of 1.5-2.5 % calcium chloride, and process water. Annular space is opened. At drill string service water is poured partially with rotation and partially with reciprocation of drilling string. Method includes preventing immersion of drill string below initial depth end. Drilling pipe string is lifted at a depth above level of filled volume and residues of cement solution from drill string. Annular space is closed. Process water is pushed on drill string. Process is withheld for cement setting and hardening. Open end of drilling string is lowered and grappling head cement bridge. New operations are repeated as many times as depth sufficient for creation of total cement bridge is not less than absorption interval zone. Drilling pipe string is lifted from well. Cement bridge is drilled, well is drilled to design depth, cased and annular space is cemented.

EFFECT: isolation of a wide absorption interval.

1 cl