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a report by

Anna A ab

President, International Research Institute of Stavanger (IRIS)

In mature fields excessive water production

is a serious problem. Worldwide an average of three

barrels of water are produced for each barrel of

oil, which is also typical for the situation for the

mature fields in the North Sea. Worldwide the

annual cost of disposing of this water has been

estimated at US$40 billion.

The high water production has a negative impact on:

oil production (e.g. reduced oil relative

permeability and reduced hydrostatic lift);

processing costs (the oil industry spends more

money on water than all other major services

combined); and

the environment (e.g. increased disposal to

the sea).

Re sea r c h

Consequently the industry has addressed

the need for research on better methods for

reducing water production. For new field

implementations, action should primarily be

taken to optimise the injection strategy of

water, optimise the sweep or to evaluate

alternatives to water injection. For mature

fields with high water production it

is too late for such actions; therefore other

means are considered, such as re-injection,improved water cleaning, downhole separation

or controlling the water inflow. Of these, the

latter method has been highlighted through

research projects at the International Research

Institute of Stavanger (IRIS), mainly because this

is the only method with the potential to also

improve oil production.

Chem i c a l I n j e c t i on

One of the methods controlling water inflow

is chemical injection. If the chemicals

can be bullheaded, the method will be

cost effective. Bullhead injection is often

the only available option for water control,

especially for subsea installations and complex

multi-branched wells. Chemical systems

that are bullheaded must comprise some

intelligence, either chemicals that reduce the

water permeability significantly more than the

oil or gas permeability (disproportionate

permeability reduction, DPR) or chemicals that

selectively block the water-producing zones (self-

selective placement).

In the last decade there have been a number of

publications and field trials of systems with DPR

properties. Previous success rates have been

variable due to a combination of lack of diagnosis,

the DPR mechanisms not being fully understood

and the chemical systems not being suitable.

DPR is found to be effective in multi-layered

reservoirs without crossflow and with some zones

producing clean oil, or in treating coningproblems. In such situations DPR treatment will

reduce the water cut and may result in increased

oil production.

Water Management Bet te r Methods for Reduc ing Water Product ion

Health, Safety & Environment

44 E X P L O R A T I O N & P R O D U C T I O N : T H E O I L A N D G A S R E V I E W 2 0 0 6

Worldwide an average of three barrels of water are produced

for each barrel of oil, which is also typical for the

situation for the mature fields in the North Sea.

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Water Management

BRP F l u i d s

Generally there are two classes of DPR fluids:

polymers that show retention at the pore surface

or crosslinked gel. The polymer systems are the

most frequently used; they normally have anoptimum at low to medium temperature,

permeability and production rates.

The more robust alternative to polymer is

crosslinked gel, use of which allows the

temperature, permeability and production rate

limits to be increased.

The major obstacle with crosslinked gel is the risk of

total shut-off for both phases. This has been solved by

placing the blocking gel at an oil saturation higher

than residual, e.g. IOR Chemcos patent on making

and injecting the polymer and crosslinker as

an emulsion. When the gelant is injected

as an emulsion one can easily control the water

saturation by the wateroil ratio in the injected

emulsion. Further, the emulsion is made in such a

way that it breaks in the formation during the shut-inperiod. The water phase reacts to gel and the oil phase

secures open pathways for oil to flow.

A programme was undertaken to verify this

DPR method in field tests using a commercial

blocking gel system mixed in base oil and a

suitable emulsifier. The first treatment was

successfully performed at the Statoil operated

Veslefrikk field offshore Norway.

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For new field implementations, action should primarily be

taken to optimise the injection strategy of water, optimisethe sweep or to evaluate alternatives to water injection.