Pilot demonstration project facilities configuration.
day. For one thing the oil was not particularly
heavy, at 18-21° API, and at reservoir temperature, was not especially viscous, at around
10 centipoise (cP).
The critical parameter in working out how
effective a water flood process will be is the
mobility ratio; that is, the mobility of water divided by the mobility of oil. If that ratio is too
high the sweep efficiency will suffer and the
recovery will be less. Captain’s oil has a reservoir viscosity of about 90 cP, which means
the mobility ratio is about 10 times the Harding mobility ratio, so the expected recovery
factor for its water flood is about 35%, about
half of the Harding recovery factor.
The next generation of heavy oil fields feature oil with reservoir viscosities as high as
1,500 cP. Viscosities that high make a huge
difference to the proportion of oil in the fluids
coming out of the ground. It is not only the
recovery factor that suffers, the water handling capacity required also soars. The ratios
change as viscosity increases. For Bentley,
based on Xcite’s reservoir modeling, the
proportion of oil in the produced fluids is just
4.4%, so the company will have to produce
nearly 6 Bbbl of fluids in order to get over 250
MMbbl of oil out of the ground. That is an
extraordinary volume of fluids and it takes a
huge amount of money and energy to do that.
What is the alternative? The oil is the oil,
you cannot change that, but you can change
its viscosity. Oil viscosity changes dramatically with temperature, and steam happens
to be hot. Indeed at Pilot reservoir pressure,
steam is 600°F (315°C) hot, and at that temperature the oil viscosity is in single digits.
Steam flood procedures
No one disputes the potential for steam
flooding to deliver a very high recovery factor,
if it could only be applied to the high permeability heavy-oil sandstone reservoirs encountered in the North Sea.
The recovery factor case for steam is well
proven. However, the general belief is that the
cost of steam, especially the cost of generating
steam offshore, will far outweigh the benefits.
That is not the case, although you do have to
consider carefully how and when to apply a
steam flood. Most people imagine that steam
flooding is an enhanced oil recovery (EOR)
technique, and EOR techniques tend to come
into consideration after all the easy, inexpensive oil has been captured and the field is on
its last legs, and the operator is desperately
trying to defer decommissioning.
That is how most steam flood projects
have started. But it actually makes no sense
to push water into a heavy oil field to force
some oil out only to have to sweep all that
water out of the reservoir with steam as
you try to boost the recovery factor. No, the
right way to go about it is to steam the reservoir from the start; and to steam it quickly. The key to a successful steam flood is to
minimize the heat losses and the way to do
that is to inject steam at as high a rate as you
can and to sweep the reservoir between injectors and producers as quickly as possible.
The Steam Oil Production Company has
devised a production profile for a steam flood
of the entire Pilot field, based on the thermal
reservoir simulation done so far. The profile
is flat and short and the proportion of oil in
the fluids pumped out of the reservoir is projected to be even higher than for the Harding
field. The field life is just 11 years, not the 35
years required to produce Bentley with a water drive scheme.
That represents a two-thirds saving in operating costs. Combine that with the reductions
in facilities capacities and there is more than
enough capital saved to pay for the steam boilers. The cost of the gas that has to be burned is
not trivial but between a doubling in reserves
and the operating cost savings the economic
case for steam is well made.
But what about the emissions and the carbon
footprint? In a conventional water drive scheme all
that water does not move around the reservoir all
by itself – it takes energy to do that and energy
that is expended for more than 30-odd years.
Based on Xcite’s 2013 environmental state-
ment the carbon footprint of producing Bent-
ley oil was over 60 kg carbon-dioxide (CO2)/
bbl. A gas-fired steam flood of Pilot with a
steam/oil ratio of about 2 bbl of steam for
each barrel of oil would probably have a car-
bon footprint of about 55 kg CO2/bbl. That is
already an improvement on the Bentley plan:
it is a heavier footprint than the 35 kg CO2/
bbl Statoil anticipates for Mariner, but not by
much. It is a gap that technology could bridge.
If the steam/oil ratio for Pilot could be improved, so could the carbon footprint. MEG
Energy has suggested this is possible, having
seen a dramatic improvement in steam/oil ratio
following implementation of a methane co-in-jection scheme at its SAGD project onshore in
Alberta. MEG claims a 70% reduction in steam
requirements. If the Pilot scheme could achieve
a steam/oil ratio of about one, that is a 50% reduction in requirements, the carbon footprint
could be among the best in the UKCS, hopefully as low as 30 kg CO2/bbl. And that makes the
environmental case for steam.
The Steam Oil Production Company plans to
demonstrate that steam flooding can be done
offshore. The company is working on the design of a demonstration steam flood project to
be carried out on a segment of the Pilot field.
The plan is to drill seven wells, three injectors
and four producers, 100 m (328 ft) apart, inject
steam into the reservoir at a rate of around
36,000 b/d of cold water equivalent and produce between 15,000 b/d and 20,000 b/d over
a period of three years. This will be done in the
middle of the North Sea, in 80 m (262 ft) of water, and no-one has attempted anything of this
scale offshore before.
The wells will be drilled from, and tensioned
back to, a jackup with a steam boiler installed
on its deck (yes, it will fit). An FPSO will also
be needed to process and store the oil and to
prepare the boiler feedwater. That sounds like a
lot of equipment, but the key to the project economics is to make use of otherwise idle equipment and to work with contractors and suppliers who have the vision and energy to help
make a technological breakthrough happen.
We believe there are around 2 Bbbl of additional reserves to be recovered in the UK
North Sea if all the applicable fields were
steam flooded, not counting Premier’s recent
Bagpuss discovery. That is a huge prize and if
we can get this demonstration project underway it will make a real contribution to maximizing economic recovery in the UKCS. •
Steve Brown is a founder and the CEO of The Steam Oil
Production Company Ltd. He is a petroleum engineer
with over 30 years of experience. Holding a degree in
Chemical Engineering from Peterhouse, Cambridge,
he started his career as a petrophysicist with BP. He
worked on the Forties Bravo field and the development
of the Harding and Andrew fields as well as in BP’s
corporate planning department. He has also worked for
Halliburton and Petrofac as well as founding Challenge
Energy, Exile Resources, and Setanta Energy.