CASING STRING SERVICE METHOD FOR WELLS WITH DEFECTIVE SECTION AND INTERNAL CASING STRING RESTRICTION Russian patent published in 2009 - IPC E21B29/10 

FIELD: oil and gas industry.

SUBSTANCE: invention is applicable to the oil and gas industry and is intended more specifically to roll out collapsed casing strings and restore their tightness. To implement the method the user shall: find out all information about the defective interval; cut out the internal casing string restriction throughout its length; use a directed liquid flow to wash rocks out of the defective interval throughout the length and perimeter of the resulting cutout until the rocks being washed out stop coming out at the well mouth; equip an additional intermediate string with an outward spring-loaded stop with external overflow ducts; lower and install the additional intermediate string so that it is fixed opposite to the defective interval and then cemented. As the string is being lowered the stop is expanding thereby fixing the string against the top edge of the cutout. Thus the entire defective interval is covered by the intermediate string.

EFFECT: expanded functional capabilities, improved service reliability.

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