METHOD FOR BACK-CEMENTATION OF CASING STRING IN WELL Russian patent published in 1997 - IPC

FIELD: oil and gas production industry. SUBSTANCE: this is used in cementation of casing strings in wells. It cuts time and use of materials, permits injection of plugging compound of any density at any velocity and under any pressure. Mounted on lower end of casing string to be run into well is spring-loaded non-return valve of plate-type. It is made for possible opening under action of axial vertical force directed downwards for example under action of flushing tube string. Holes are made in lower part of string. Annular space between casing string and flushing tube string is filled with liquid. Back pressure is created. During injection of plugging solution into annular space, effected at well head is regulation of back pressure value. Moment of stopping injection of plugging solution into annular space of well is defined at appearance of plugging solution of required composition at well head. EFFECT: high efficiency. 4 dwg