WELL STAGE CEMENTING METHOD Russian patent published in 2015 - IPC E21B33/14 

FIELD: oil and gas industry.

SUBSTANCE: at stage cementing of the well cementing of the first stage is made, bottom plug is entered to the string in order to open circulating openings of cement collar for stage cementing, periodical washing of the borehole is arranged through circulating openings during waiting-on-cement time at the first stage, cementing of the second stage is arranged with entry of top plug to the string in order to close circulating openings of cement collar for stage cementing. At the first stage cementing oil-well cement is flushed by portions of drill mud, water and drill mud again, with setting of oil-well cement in annular space above the cement collar for stage cementing, and portions of water in the casing pipe within interval of the cement collar; during waiting-on-cement time at the first stage cyclic circulation of drill mud is arranged along the casing pipe through the cement collar with output to the wellhead through annular space until oil-well cement is removed completely within the interval of the cement collar for stage cementing; upon oil-well cement hardening at the first stage, at cementing of the second stage a portion of buffer solution and design volume of oil-well cement is pumped through the casing pipe, the top plug is placed and flushed by service water until it is set in the interval of the cement collar for stage cementing and openings of the latter are covered, pressure is increased in the casing pipe per 0.5-1.5 MPa above the operating pressure at pumping until openings of the cement collar are closed and waiting-on-cement time is started, and at well development the top plug is drilled out. Aqueous solution of surfactant and sodium tripolyphosphate is used as buffer solution.

EFFECT: developing simple and cheap method that guarantees performance of state cementing at high quality level.

2 cl, 3 ex