Page 267 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

238 Xingru Wu

5.4.2.1 Removal of the scaling ions before mixing occurs
This option generally refers to the removal of sulfate from sea water as
injection water. One option is to reduce sulfate concentration through
Sulfate Reduction Unit (SRU). Removing sulfate from the sea water not
only lowers the risk of sulfate scaling issues, but also reduces the reservoir
souring potential. On the operating cost side, this option can reduce or
eliminate scale inhibitor squeeze treatments. Furthermore, this option can
render the production free of LSA scales, which are usually coprecipitants
of sulfate scales. Other technologies such as Reverse Osmosis (RO) can
not only reduce sulfate concentration to a low level, but also remove
other ionic species. For particular formations, injecting low-salinity water
can also improve oil recovery. On the other hand, the technologies of
reducing ionic concentration can require high initial capital expenditure
and long-term operational expenditure because of the sulfate removal
unit commitment.

5.4.2.2 Passive scale treatment in well completion
In well-completion stage, engineers can take preemptive actions to treat
near wellbore condition during the completion process or prior to the
start of well (Tyler et al., 1985). In wells completed over short reservoir
intervals, it is possible to place the treatment effectively by bullheading
the treatment from the surface. For many wells with frac-pack comple-
tion, fracture proppant impregnated with scale inhibitor or solid-scale
inhibitor mixed with proppant are used. Alternatively, liquid-scale inhibi-
tor is deployed with the frac fluid during fracturing operations. With this
technology, large amounts of scale inhibitor, impregnated into proppant
material, can be placed into a hydraulic fracture. However, the technical
challenge of well interventions should not be underestimated.

5.4.2.3 Periodic squeeze treatments
In this method chemical inhibitor is pumped into the near well formation
of a producing well to provide scale control for a limited period after
which the process is repeated. Most of the conventional technology for
the treatment of downhole scaling is essentially one form or another of
batch treatment with scale inhibitor. Squeeze treatments being by far the
most common method to control downhole scale problems (Mackay
et al., 1998). With chemical squeeze inhibition, large volumes of scale
inhibitor are injected into the formation and around the wellbore. An
amount of the scale inhibitor is retained in the formation due to