METHOD OF ISOLATION OF THIEF ZONE DURING WELL DRILLING Russian patent published in 2015 - IPC E21B21/00 E21B33/138 

FIELD: oil and gas industry.

SUBSTANCE: method of isolation of thief zone during the well drilling includes run in the well of the package including packer and drilling pipes, packer seating, pressing-through under the packer of the isolating materials, holding for the cement setting, packer breakaway, isolation monitoring, package raising from the well, cement bridge drilling-out, and continuation of the well drilling. The package is run with maximum speed 0.5 m/s, after run own weight of the package is registered, prior to the packer seating the drill pump is switched on with completely opened gate in manifold, and mud is pumped through, gradually the gate is closed, and pressure is set to 2-3 MPa as per pressure gauge, simultaneously the packer is set by load 10-12 t for complete sealing of the annulus, annulus is filled with water, isolating materials are pressed through under the packer at maximum pressure 9 MPa, the isolating materials contain the first portion of the cement and water with density 1.6-1.7 g/cm³, second portion of the cement, water with density about 1.6-1.7 g/cm³ and 8-12% (by weight) of sodium carbonate, the third portion of cement and water with density about 1.6-1.7 g/cm³ and 2-4% (by weight) of calcium chloride, and forth portion of cement and water with density about 1.6-1.7 g/cm³, holding for the cement setting is ensured, axial load is removed from the packer, holding for 3-5 minutes is ensured, liquid circulation is ensured in well, upon circulation presence the thief zone is removed from isolation, the package is raised from the well with minimum speed of first 5-6 m.

EFFECT: increased efficiency of isolation of the thief zone during the wells drilling.

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