METHOD FOR TENSIONING OF CASING STRINGS Russian patent published in 1999 - IPC

FIELD: mining industry. SUBSTANCE: method can be used for strengthening of gas wells, gas-condensate wells and oil wells. According to method, casing string is lowered into well. Then casing string is subjected to cementation by using two types of slurries with different periods of hardening. Starting time of hardening of upper slurry is larger than starting time of hardening of lower slurry. Starting time of hardening of upper slurry is determined according to formula. It is made up of ending time of hardening of lower slurry multiplied by 1.25 and period of performing operations related to adjustment of tension. These operations include determination of boundary of dividing slurries, calculation of tensioning force and adjustment of tension. Dividing boundary is determined by thermal measurements or according to injected and displaced volumes of slurry. Application of aforesaid method allows for preventing destruction of casing strings at sharp temperature variations along entire length of casing string. EFFECT: higher efficiency.