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The Extraction Degree
could be increased to 50%
Researchers and oil companies
are working intensively on the
development of methods to increase
the extraction degree
in the Danish part of the North
Sea. Denmark’s leading oil
researchers at the Technical
Univercity of Denmark and at
Aalborg University (Esbjerg Institute)
expect that the degree
can be increased to 50% – the
double of the actual level.
In the late 80’es the horizontal drilling method
opened up new opportunities for the Danish
oil and gas industry in the North
Sea. Later water injection followed
as an effective method to
stimulate the extraction. CO2 injection
could be the next big step
in the endeavours to increase
the vital extraction degree and
prolong the Danish selfsuffi
ciency.
- People often quote me for saying that I
expect that we can increase the extraction
degree in the Danish part of the North Sea to
50%. Even though it will be diffi cult to reach
such goal, I think that we should consider it as
our national strategy, Denmark’s leading oil
researcher, professor Erling H. Stenby, Department
of Chemical Institute for Engineering,
the Technical University of Denmark (DTU),
informs.
The DTU professor takes us on a journey
to the more than 50 years old Weyburn oil
fi eld, which had reached a worn-down level,
when the oil company EnCana decided to
inject CO2 in order to stretch out the production.
Via a 300 km long pipeline taken from a
coal gasifi cation plant in North Dakota the CO2
residual gas from the natural gas production
was led to the oil fi eld in the middle of
the North American continent, and with a
very promising result: During the following
years, the production increased by 25%.
- Weyburn is of course a land-based fi eld,
however, the geological conditions are not very
different from the Danish section, and provided
10 Offshore Center Danmark
Yearbook 2008
that the CO2 will react as it did in Canada, we
will look at a very promising production for
many years to come, Erling H. Stenby states.
Hesitation in Denmark
and Norway
Supported by the Danish National Advanced
Technology Foundation a series of companies
headed by DONG Energy are conducting a
research project, with the purpose of creating
a basis for a decision regarding a test plant
with CO2 injection. The heavy fi nancial
decision whether CO2 can be introduced in
the Danish oil extraction process cannot be
taken, before the project has been completed.
Marginal Fields
Reservoirs with a limited occurrence of oil and gas.
This could also be larger deposits with an expected low
extraction degree due to the geological conditions.
Finally, larger occurrences with diffi cult production conditions
due to large water debts or poor infrastructure,
which complicates the transportation of the oil/gas.
- Very large quantities of CO2 would have
to be used, and it would furthermore be necessary
to use a pipeline from shore. CO2 has
been successfully used for decades, mainly in
the US, Canada and Hungary, but its employment
is limited mainly by the occurrence of
CO2 . In the US as well as in Hungary the CO2
occurrence is geological, whereas in Canada
it will have to be supplied, which would also
be the case in the North Sea. Neither Denmark
nor Norway use CO2 as yet, Erling H. Stenby
informs.
The Chalk is not the main Reason
The low permeable chalk is often mentioned
as the main reason that the Danish part of the
North Sea is an area where it is diffi cult to
extract oil and gas. This is not the whole truth.
Norway’s largest oil fi eld, Ekofi sk, is also a low
permeable chalk fi eld, and besides, the oil companies
in the Norwegian and the British sector
face diffi culties in sandstone fi elds as well.
- Our job is to develop better technologies to
extract the oil, Enhanced Oil Recovery (EOR),
taking parameters as rock, oil viscosity, pres-
MARGINAL
FIELDS
sure and temperature into consideration, Erling
H. Stenby informs.
The accessibility of a reservoir does not
entirely depend on the thickness of the chalk
layers. E.g., the chalk layer in the DUC’s
Valdemar fi eld is not very thick, but as it covers
a large area, the oil extraction is complicated.
In such reservoir horizontal drillings and
unmanned STAR platforms are indeed an
advantage.
The extraction conditions in the North
Sea differ substantially. The latest prognosis
carried out by the Danish Energy Authority
stating an extraction degree of 24% comprises
big variations, from fi elds with an extraction
degree below 5% to fi elds where
it is possible to extract 35-40%,
e.g. in the DUC’s Skjold fi eld.
Additional advanced
Methods
At the EOR area several methods
are being tested to improve the
oil and gas extraction. One of the
methods is to introduce energy by increasing
the temperature. The procedure is to inject
steam into the oil layers, a method which,
however, cannot be employed on large debts,
as well as in situ combustion - a combustion
process inside the reservoir, where oxygen is
introduced from the surface, in order to form
nitrogen. Nitrogen does not mix with the oil as
is the case with CO2 , but it heats the CO2 and
thereby lowers the viscosity, which allows a
free oil fl ow. In Romania the method has been
used for a number of years, and even though
we for the time being are not conducting any
tests, we have not abandoned the method.
Microbial methods, e.g. to inject active ingredients,
such as detergents, into the oil reservoir
to loosen the oil from the pores, have proved
to be an expensive method to increase the
extraction degree. It would be more cost effective
to introduce microorganisms, which can
reproduce and increase the activity in the reservoir.
Aalborg University (Esbjerg Institute) is
currently researching the consequences such a
method would have on a 5-10 years’ basis. ■