WELL STAGE CEMENTING METHOD Russian patent published in 2017 - IPC E21B33/14 

FIELD: oil and gas industry.

SUBSTANCE: invention relates to oil industry and can be used when lowering and cementing a production string. Method comprises pumping cement grouting into a column. Bottom plug is introduced into column. Cement grouting is fed in portions of drilling mud, water and mud again with installation of cement grouting in annular space above stage cementing collar, and water portions in column in interval of cement collar of stage cementing. Hardening of cement of first stage is waited for. Drilling mud is circulated in cyclic mode via column through cement collar of stage cementing with output on head through annular space until complete removal of cement grouting in interval of cement collar of stage cementing. Cementing of second stage is carried out. That is ensured by pumping via column a portion of buffer solution and design volume of cement grouting. Upper plug is placed and flushed by process water. Pressure in string is increased above working pressure while pumping until closure of holes of cementing collar of stage cementing. Cementing hardening is waited for. During development of well, upper plug is drilled. Method is characterised by that when lowering column, method includes washing with mud fluid with viscosity of not more than 30 s for 1.5 cycles, starting from depth of 400 m every 300 m and at end of descent. When cementing before pumping cement grouting, viscous buffer liquid is pumped into column. Cement grouting used is a grouting mixture of low density and grouting mixture of higher density. Portions of drilling mud is are pumped until "stop" pressure is achieved. Pressure in column is reduced to atmospheric pressure. Making sure of tightness of check valve. Excess pressure is re-created until circulating openings of stage cementing collar open and washing off excess cement. Process holding is performed for cement hardening with flushing of well every 2 hours with drilling mud. When cementing second stage, method includes consecutively pumping into column viscous buffer fluid, grouting mixture with density from 1.65 to 1.9 g/cm³, containing aluminosilicate hollow microspheres, grouting mixture with low density. Locking plug of stage cementing collar is released and process water is flushed until "stop" is achieved. After outputting grouting mortar to mouth during flushing for 2 hours of waiting for cement hardening, well head is equipped with string on clamp and annular space is filled with grouting mortar to well head.

EFFECT: higher quality of well cementing.

1 cl, 1 ex