Page 259 - Hydrocarbon

246 Well Completions

polished bore for
liner hanger pre-drilled or
packer later installation of pre-slotted liner
a plug or straddle

external casing packer
or
swellable elastomer packer
Figure 10.17 Openhole completion with zonal isolation.

detonating
cord
case

conical liner

primer

main explosive

Figure 10.18 The shaped charge.

perforated completion is that the engineer can select where to perforate. The
decision will be made on the basis of log data, and water, gas or weak intervals can be
avoided. Perforations can also be later isolated if they produce too much water or gas.
None of the techniques mentioned already can cope with very weak sand
production prone intervals, although if these intervals are few in number a
perforated completion can at least avoid them. Sand control completions can either
be openhole or cased hole. They employ screens (simple wire wrap or more
complex mesh type) which are installed across the openhole or across a cased and
perforated interval. To increase reliability, the annulus between the screen and the
formation is often packed with gravel (a gravel pack). In some openhole
completions, the formation is left to collapse directly onto the screen. More
recently, another method of increasing reliability is to use an expandable screen in
an openhole section. This screen is run across the reservoir section and then
expanded against the borehole wall. In a cased hole, sand control completion, the
annulus and the perforations are always packed with gravel. Cased hole gravel packs