Page 427 - Hydrocarbon Exploration and Production Second Edition

414 Production De-Bottlenecking

capacity in the form of hydrocyclones may be a technical option, but will increase
existing operating and maintenance costs, at a time when OPEX control is
particularly important. In many mature areas, the treatment of produced water
is becoming a key factor in reducing operating costs. In the North Sea more water is
now produced on a per day basis than oil!
If extra treatment capacity is not cost-effective, another option may be to handle
the produced water differently. The water treatment process is defined by the produc-
tion stream and disposal specifications. If disposal specifications can be relaxed, less
treatment will be required, or a larger capacity of water could be treated. It is unlikely
that environmental regulators will tolerate an increase in oil content, but if much of
the water could be re-injected into the reservoir, environmental limits need not be
compromised.
Injection of produced water is not a new idea, but the technique initially met
resistance due to concerns about reservoir impairment (solids or oil in the water
may block the reservoir pores and reducing permeability). However, as a field
produces at increasingly high water cuts, the potential savings through reduced
treatment costs compared with the consequences of impairment become more
attractive. Local legislation has become the catalyst for produced water re-injection
(PWRI) in some areas.
Rather than attempting to treat increasing amounts of water, it is possible in
some situations to reduce water production by well intervention methods. If there are
several wells draining the same reservoir layer, water cut layers in the ‘wettest’ wells
can sometimes be isolated with bridge plugs or ‘scab’ liners. Unless a well is
producing nothing but water, high water cut wells will also reduce oil production
which may not be made up elsewhere. Similar operations can be considered in
water injectors to shut-off high-permeability zones if water is being distributed
inefficiently (Figure 17.10).

fault

oil
water
perforations
new plug
Figure 17.10 Well intervention to reduce water cut.