METHOD OF LOCALISING LEAKAGE ZONES IN PRODUCTION CASING Russian patent published in 2009 - IPC E21B33/14 

FIELD: oil-and-gas production.

SUBSTANCE: n the method of localising leakage zones in a production casing, before lowering the protective casing, a holder is fitted on the protective casing, as well as the required number of devices for sealing the annular space between protective casing and the production casing in the leakage zone of the latter. The supporting column is joined to the protective casing using a disconnecting piece. A valve unit is placed under the disconnecting piece in the protective casing. The protective casing with the disconnecting piece is lowered into the production casing. Excess pressure acts on the valve unit in the protective casing for sealing the top tubing space, linked to the wellhead, separating it from the bottom tubing space, linked to the productive stratum. The protective casing is suspended, increasing pressure in the top tubing space until preliminary engagement of the protective casing with the wall of the production casing through action on the holder, which converts axial force to radial force. The weight of the protective casing on the wall of the production casing is gradually decreased, after which the leakage zones in the production casing are localised using sealing devices, preventing cross-flow in several intervals. The protective column is disconnected using the disconnecting piece from the supporting column without rotating it and the latter is raised. The valve unit comprises a suspended plug, which is forced into a stop ring so as to seal the top tubing space from the bottom tubing space. The disconnecting piece has a connector joined to the supporting column and a socket, joined to the protective column. The connector and the socket of the disconnecting piece are flexibly joined by a restraining bolt and grooves, and are fixed by shear bolts. Grooves are made in the connector and are joined together by an inclined channel. One of the grooves is open and a blind with a holder is fitted on the shear bolts. The second groove is closed and the restraining bolt fixed on the socket can move along the inclined channel and can interact with the blind. The supporting column is disconnected from the protective casing by loading the assembly of supporting pipes to the disconnecting piece through exit of the bolt on the socket from the groove in the connector and sliding the bolt along the inclined channel until the blind covers entrance of the inclined channel and the closed groove until alignment of the bolt in the socket with the open grooves in the connector. The top device for sealing the annular space is positioned on the wellhead using a compressor, and the bottom device - on the bottom hole using a compressor.

EFFECT: longer service life of the well and reduced expenses on repairs.

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