SELECTIVE ZONAL ISOLATION OF OIL WELLS

摘要

In the horizontal parts of deviated wells arranged within a producing formation, good communication between the formation and the wellbore liner is required, and this may be achieved by using a slotted or perforated liner in the horizontal section without any cementing to bond the liner to the wellbore. However, problems can arise if it is desired to work selectively in a zone in the horizontal section, since with a perforate liner there is no way of isolating the zone from the remainder of the well by using internal packers. This problem can be overcome by providing packers around the outside of the liner; this then allows packers inside the liner to be used to isolate a portion of the well. However, these external casing packers must be sealed against the wellbore, they must be positioned in advance, and they substantially increase the cost of the completion. The present invention suggests novel means of zonal isolation in a well with a perforate liner, this isolation being achieved by using a liquid composition that can be pumped into the relevant annular region between the liner and the wellbore and then set to form a plug that prevents communication from one side to the other except via the liner. More specifically, the invention provides a method of placing a plug around a perforate liner in which: a pair of spaced packers (14, 16) are placed inside the liner (12) to define both a chamber (20) inside the liner which includes a perforation (22) and also a region (24) to be plugged outside the liner; a predetermined volume of plugging fluid is pumped into the chamber and, via the perforation, into the region to be plugged; and after the plugging fluid has set the packers are removed from the liner.