Page 422 - Hydrocarbon Exploration and Production Second Edition

Managing Decline 409

coiled
tubing
pump
acid

(a) (b)
production
tubing
casing

perforations

circulating squeezing
acid down acid away
Figure 17.5 Coiled tubing acid placement.

low permeability oil low permeability oil
high permeability high permeability
water gel
Before After
Figure 17.6 Water shut-o¡ with chemicals.

If water or gas breakthrough occurs (in an oil well) from a high-permeability layer,
it can dominate production from other intervals. Problems such as this can
sometimes be prevented by initially installing a selective completion string, but in
single-string completions on multiple layers, some form of zonal isolation can be
considered. Mechanical options include plugs and casing patches (or ‘scab’ liners),
which can be installed on wireline or pipe, although production tubing has to be
pulled unless a well has a monobore completion. These options were illustrated
in Section 16.1, Chapter 16. Chemical options, which are becoming much more
common, work by injecting a chemical, for instance a polymer gel (Figure 17.6)
which fills pore spaces and destroys permeability in the more permeable layers.
These chemicals can be placed using coil tubing. Squeezing off water or gas
producing zones using cement is a cheap but often unsatisfactory option.
Cross flow inside the casing can also be prevented by isolating one zone. However,
this may still result in reduced production. Installing a selective completion can solve