An examination of cement samples from the top and bottom of liners and statistical studies of all liner cementations since 1982 clearly indicated that for long liners (approx. 1000 m) the cement was of poor quality and that for longer liners (up to 2200 m) cement contamination was so bad that the cement would probably never set.

As a result, a top and bottom wiper plug system was developed to prevent contamination of the cement inside the string while pumping the slurry. Repeated downhole testing and initial field experience resulted in improvements to the system, and the final design has been in field use since mid-1989. By December 1990, twenty-six 1" liners had been cemented using this system with a significant improvement in the quality of the cementation. The weight percentage of cement in samples taken from above the liner top using the old 2-Plug System was between 177» and 867> and for samples taken from the liner collar/shoe it was between 377» and 877» depending upon the length of liner which was run. The use of the new 4-Plug System resulted in a weight percentage of cement of greater than 90% in samples taken from the liner top and the collar/shoe, irrespective of liner length.

This paper deals with the research, development, and field experience associated with the use of a four plug liner cementation system.

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