METHOD AND APPARATUS TO ISOLATE A FORMATION ZONE

摘要

A method and apparatus are disclosed which allow isolation of a plurality of zones for treatment, particularly sand fracturing. The lowermost barrier can be pumped through tubing and anchored in cased or open holes. In the preferred embodiment, the pumped plug has a visco-elastic member which contains a particulate aggregate mixture, such as described in U.S. Pat. No. 5,417,285. The visco-elastic material is subjected to a force which changes its shape so that the material obstructs the wellbore. The shape change also accomplishes dehydration of the material within the visco-elastic enclosure by virtue of fluid displacement, resulting from a volume reduction, hardening it so that a plug using the visco-elastic material is formed. Thereafter, a packer on the tubing string is set to isolate the zone for sand fracturing. The process can be repeated without tripping out of the hole as additional plugs are pumped through tubing and the process is repeated. At the conclusion of the fracturing, the various plugs, which are of simple and economical construction, can be readily milled out.