WELL DRILLING METHOD Russian patent published in 2015 - IPC E21B7/00 E21B21/00 

FIELD: oil and gas industry.

SUBSTANCE: method includes drilling of a well borehole by an assembly with the lower power drive and usage of a circulation fluid as a drilling mud. A loss zone is entered and drilling is transferred to the drilling mud, at entry to the loss zone rotary assembly or the upper power drive is switched, a drill string is rotated with a rate of 60-90 rev/min, consumption rate of the drilling mud is set equal to 18-20 l/s at the wellhead pressure of 1-2.5 MPa, the drilling mud is used with a viscosity of 60-90 CP, at the entry to the loss zone cuttings are introduced in a quantity up to 30% of the drilling mud volume and in the progress of the loss zone the passage quantity of cuttings in the drilling mud is reduced up to 8-12% at the loss zone end, the well is washed by the drilling mud without cuttings with a viscosity of 40-60 CP, with the consumption rate of 30-35 l/s and the wellhead pressure of 1-2.5 MPa and drilling is continued till the design reference mark.

EFFECT: improved reliability of the loss zone isolation, sticking of drilling tools is excluded.