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Oilfield Technology
December
2014
1 million bpd in 2040. The EIA is referring to conventional fields;
a Wood Mackenzie study of emerging technologies predicts that
shale oil EOR could add a further 3 million bpd by 2030.
And, that is just one country. The Middle East, South America,
Asia – indeed virtually every oil‑producing province – has
EOR potential. In BP’s Statistical Review of World Energy 2013,
the report noted that the world’s proved oil reserves stand at
1669 billion bbls. The current recovery factor for oilfields is
approximately 35%; if that were to be increased from 35% to 45%
through EOR, it would book about 1 trillion bbls of oil, or enough
to meet world needs for an additional 30 years.
When first tapped, petroleum reservoirs often contain enough
formation pressure to push oil into the wellbore, where it can be
lifted to the surface by pumps. This is called primary recovery,
and can amount to approximately 15% of oil‑in‑place. The life of
an oilfield can be extended through secondary recovery, which
often takes the form of a water flood, in which water is injected
laterally to push oil toward a production well. Typically, secondary
techniques can double recovery rates, to around 30% or more
(some offshore fields in the North Sea achieve rates of around 60%
with water floods).
Some fields can be further produced using EOR techniques,
including surfactants, polymers and miscible gas injection. In
the latter case, natural gas or CO
2
is injected under high pressure
into a reservoir. The CO
2
acts as a solvent, reducing the viscosity
and the interfacial tension bond between the remaining oil and
the reservoir rock. It also swells the oil, so the reservoir pressure
increases.
CO
2
EOR projects last 10 ‑ 30 years and enhance oil recovery by
7 ‑ 15% of original oil in place. Most of the successful projects of
this type depend on tapping and transporting (by pipeline) carbon
dioxide from underground reservoirs. Major natural CO
2
deposits
(such as McElmo Dome and Sheep Mountain) occur in Texas and
nearby states.
Other EOR technologies involve the injection of various
chemicals in dilute solution. Alkali and caustic solutions act to
create a soapy‑substance that reduces the interfacial tension.
Dilute polymer solutions increase the viscosity of water flooding to
aid in oil recovery. Canadian Natural Resources Limited (CNRL) has
used polymer solutions to increase production at its Pelican Lake
field in northeast Alberta. The company has also experimented
with injecting nano‑spheres, which block the natural flow paths
for the injected water so that it can be diverted to un‑swept parts
of the reservoir.
Win‑win
The vast majority of future EOR projects are expected to be based
on CO
2
floods, partially thanks to the increased concern over
the climate. The Global Carbon Capture and Storage Institute
(GCCSI), an international consortium, reports that manmade
sources amounted to 36 billion t of CO
2
equivalent in 2009. Since
the industrial revolution, the amount of GHGs in the atmosphere
has increased from 280 ppm to over 400 ppm. The UN’s
Intergovernmental Panel on Climate Change (IPCC) has concluded
that, should the level reach 450 ppm, sea rises and other
calamities may ensue. At the current increase rate of 2 ppm/y, that
level will be reached by 2040.
Legislation has been enacted in many jurisdictions to slow
and eventually reduce the amount of manmade GHGs. Most
nations signed the Kyoto protocol, agreeing to an emissions
reduction a 6% below 1990 levels by 2012. The EU established a
‘cap & trade’ system and now has set targets for member countries
to cumulatively reduce the current level of CO
2
emissions by at
least 20% by 2020. Although the US Congress has not passed
carbon legislation, the Environmental Protection Agency (EPA)
and other federal regulators have issued regulations regarding
GHG restrictions on vehicles and large stationary sources.
In North America, low gas prices, spurred by the shale gas
revolution, have induced electricity utilities to switch some of
their baseload production from coal to natural gas (which emits
far less CO
2
per MW produced). Fuel‑efficient cars are reducing
the amount of petrol needed to get from home to work. Many
countries have incentive programmes to encourage the growth
of renewable energy (primarily wind and solar power), and most
sectors of the economy now have programmes to eliminate
fugitive emissions (such as gas leaks at pipeline compressor
stations).
While these steps are important, experts reckon they are
insufficient to stem the global warming trend. In order to make
significant reductions, emissions from large stationary emitters
must somehow be captured. The GCCSI estimates that, in order
to limit a worldwide temperature rise to 2˚C by the end of the
century (a level deemed far less traumatic than 3˚C), as many as
130 large‑scale carbon capture and storage (CCS) projects must be
operational by 2020.
Large‑scale CCS projects rely on a number of different
technologies and processes to capture CO
2
, depending on the
source and generation. In the gas sector, for instance, natural
CO
2
that is comingled with methane must be separated using
membranes or solvents before the latter is sold to customers.
CO
2
is also a side‑product of ammonia manufacture and must be
removed prior to making fertiliser.
The largest CO
2
emissions are generally associated with the
burning of coal and natural gas at electricity, steel mill and cement
plants. One method of capturing GHGs is known as oxy‑fuel
combustion, where pure oxygen is mixed with the fuel. This
produces a flue gas of pure CO
2
, which can then be easily captured.
Most facilities use atmospheric oxygen for combustion, however,
which results in a flue gas composed of a mixture of nitrogen,
oxygen, CO
2
and other gases. In order to capture the CO
2
, complex
modules, including amine absorbers and cryogenic coolers, are
used to separate the GHG from its benign cousins.
For over a decade, manmade CO
2
has been used in EOR at a
handful of fields. In Canada, Cenovus Energy has been operating
a project in the Weyburn Oilfield in southern Saskatchewan
since 2000. The company receives pure CO
2
via pipeline from a
coal gasification plant in North Dakota. Over the 25 year life of
the project, approximately 18 million short tons is expected to be
injected, resulting in an additional 130 million bbls of production.
According to the GCCSI, worldwide, there are over a dozen
projects that use CO
2
for EOR, either underway or under
construction.
Ì
Natural CO
2
from Sandridge Energy’s Century gas processing
plant in Texas was formerly released to the atmosphere. Since
2010, however, Occidental Petroleum has been capturing
approximately 5 million tpy and shipping it through a 260 km
pipe to oilfields for use in EOR floods.
Ì
Since 2004, ExxonMobil and partners have been capturing
natural CO
2
at the Shute Creek gas processing facility in
Wyoming and transporting it to nearby fields for EOR floods.
Following expansions in 2010, the facility now captures
around 7 million tpy.
Ì
Koch Nitrogen Company altered a fertiliser plant in Enid, OK,
so that 680 000 tpy could be captured during the ammonia
manufacturing process. Since 2010, the CO
2
has been
