RESTORING METHOD OF SEALING OF CASING STRINGS Russian patent published in 2013 - IPC E21B33/138 

FIELD: oil and gas industry.

SUBSTANCE: restoring method of sealing of casing strings consists in preparation of mixture consisting of cement with aluminosilicate microspheres. Mixture is pumped to the well with water-intake capacity of more than 250 m³/day to the leak interval of casing string and displaced after the casing string so that pressure exceeding the microsphere destruction pressure is created at the end of pumping process, and the well is flushed. Besides, 0.05-0.2% (of cement weight) of fibres with sizes of 3-18 mm long and with diameter of 22-35 mcm are added to mixture composition. Content of microspheres does not exceed 20% in mixture. Besides, after microsphere destruction pressure is achieved, pumping of mixture is stopped, and pressure drop is performed at least in three minutes, but not more than the thickening time of grouting mixture in casing string.

EFFECT: increasing strength and service life of cement stone due to the ratio of aluminosilicate microspheres with cement and by adding reinforcing fibre of the specified length.

2 cl, 1 ex