ENVIRONMENTAL AND TECHNOLOGICAL ISSUES ASSOCIATED WITH
NON-CONVENTIONAL OIL.
Recent Technological Advancements
Claude MANDIL,
Chairman and CEO,
Institut Français du Pétrole, Rueil-Malmaison, France.
Non-conventional oil often result from a bacterial oxidation of conventional oils
inside the reservoir rock, which induces that they have different physical and chemical
properties, generally degraded. Indeed, they have much higher viscosity, higher heavy
metals, sulfur and nitrogen contents. These properties imply specific solutions for
production, transport and refining. Such solutions already exist, but technological
breakthroughs are still needed to make the exploitation of these unconventional crudes
economically more attractiv and to reduce substantially the associated environmental
issues.
I will consider that non-conventional oils are crude with API degree under 20.
Heavy oil have an API degree between 10 and 20. Extra heavy oil and bitumen have an
API degree under 10, distinction being made on their viscosity at the reservoir
temperature: more than 10 000 cp for bitumen and less than 10 000 for extra heavy oils.
Production
Due to their extremely high viscosity at reservoir conditions, heavy oils and
bitumen have a mobility or ability to flow through the porous media which is very low.
Therefore, primary production of these oils is very difficult and the recovery ratio is
generally low, less than 10%.
Most of the reservoirs are producing with enhanced recovery methods, which allow
recovery ratio of 20-25 %. Most of the methods are thermal, to reduce the oil viscosity;
steam injection is the most commonly used. Others technologies have been proposed:
injection of a diluent (lighter oil) or of additives (polymer). Horizontal drilling technology
introduced in the mid-80 in Canada by IFP and Elf Aquitaine, has the greatest impact on
unconventional oil production and it is presently used in all recovery methods, either
primary or enhanced.
Primary production or cold production of some non conventional oil sand
reservoirs, in Canada and Venezuela, entails production rates much higher than
expected from estimates based on conventional theory. To explain these unusual high
rates, several mechanisms have been mentioned. The first production mechanism
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known as "foamy oil" is gas bubble expansion, which gives the oil a foamy aspect as
the bubbles are trapped by the oil and recovery is enhanced by solution gas-drive.
TotalFinaElf on the Sincor project in Venezuela is producing with these mechanism. The
second one is the internal erosion in the unconsolidated sand reservoirs that can create
a network of high-permeability channels, known as “wormholes”. This mechanism can
enhance the drainage by factors of 10 and more, but it involves associated sand
production. This process is essentially limited to vertical or slanted wells where sand
flushes can be performed without major equipment when sanding occurs. However,
wormholes formation and localization are not completely understood, so that it is difficult
to optimize production. Moreover, the produced sand has to be separated from oil and
cleaned, involving additional operating costs.
These primary production methods, as the reservoir characteristics allows it, are
cheaper and most environment friendly than the other extraction methods.
In Canada, some oil deposit lay in unconsolidated sand close to the ground
surface. In that case, the extraction method is a mining one.
IFP has developed an extensive expertise on primary production of
unconventional oils.
Concerning enhanced recovery processes, the most commonly used are steam
injection, where the heat released by the steam condensation increases the oil
temperature and reduces its viscosity. The steam temperature used is mainly 150 to 300
°C and the heavy oil viscosity can be decreased by several orders of magnitude. Cyclic
steam stimulation (CSS) or Huff and Puff consists to inject steam into a well for a few
weeks, then to put this well back in production. When the reservoir is not too deep, as in
Cold Lake for instance, steam is injected above reservoir fracturing pressure, inducing
horizontal fractures that greatly enhance the process efficiency. In the steam assisted
gravity drainage (SAGD), injector and producer wells are different. That method is quite
new and find its best application in very high permeable reservoirs, as those
encountered in oil sands of Western Canada. Its main advantage is a high oil recovery,
up to 65% of original oil in place (OOIP).
Other options could be solvent assisted processes (known as "Vapex" for
Vapor Extraction or "NAGD" for Naphtha Assisted Gravity Drainage), where a solvent is
used instead of steam. Solvent in the Vapex process is propane. This process will be
soon at a pilot scale at the Dover pilot (Devon Canada Company). The drawback with
these processes is that the solvents, propane or naphtha, are high value products and
must be fully recovered at the end of the production for the projects to be economical.
Globally these processes do not require any water thus any water surface separation,
and therefore would be much environment friendly than SAGD. An option is a mix
between SAGD and NAGD by injecting steam with additives.
IFP is working on numerical modeling of SAGD and NAGD, especially on the
preliminary heating and on the optimization of the steam chamber development.
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Some non-thermal-flooding methods could be also used for heavy oil recovery by
injection of polymer or non-miscible CO2. These methods implemented in horizontal
wells are well suited for thin reservoirs where the oil viscosity is limited to a few
thousand of centipoises and where heat injection is not efficient.
There is a new interest nowadays for the old concept technology of in-situ
combustion. Thermal cracking of heavy oil is realized in the porous media, and the high
temperature in the mobile oil zone provides very efficient thermal sweeping of the lighter
oil to the production well. New methods consist in enhancing existing systems, using
different types of wells combining horizontals and verticals and different schemes of
production well-injection well combination. One of these is the “Toe to Heel Air injection”
process, proposed by the University of Bath (in England) and the Petroleum Recovery
Institute in Calgary. This process has been tested in the lab but additional studies are
required before its implementation at the pilot scale or at the reservoir scale.
Other methods of in-situ upgrading are studied, as for example hydrogen injection in the
reservoir.
Transportation
Due to their very high viscosity, heavy crude generate extremely high friction in
pipes and high pressure drop. The high pressure drop has important consequence on
the installation dimensions: diameter and thickness of pipes, pumps and compressors
dimensions, and horse power needed. Most of the existing and future solutions to
transport heavy crude I will present, consist in reducing their viscosity by heating them,
diluting them with a lighter crude, creating an oil emulsion in water or upgrading on-site
the crude before transporting. Others could consist in reducing the friction in the pipe,
without modifying the crude viscosity.
The dilution method consists in diluting the heavy crude with a solvent such as
condensate, natural gasoline or naphtha. This is the most common transportation
technology for heavy oil because it is very easy to achieve. Drawback is that the dilution
involves bigger volume to transport, and larger required pipelines capacities, in fact,
diluent could represent about 35% of the heavy oil volume. Problems could be the
availability of the diluent and its recycling. IFP is today working on the chemical
properties of diluent to increase efficiency of the dilution technology.
An other method to transport heavy crude consists in heating the oil to reduce its
viscosity and isolating the pipe to avoid heat losses. This method is well known and
widely proven in several part of the world. The disadvantage of that method are the high
costs, especially for heating the crude, and the greater corrosion of the internal pipe due
to the temperature.
The partial on-site conversion of heavy oil is commonly used in the case of
mining extraction of heavy crude in Canada. The principle is to realize partial upgrading
of the heavy crude to produce good quality (that means API degree more than 20),
transportable synthetic crude oil, which could be sold to existing refineries to further
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process to finished products. In a such technology, asphalt is produced too, which can
be recovered as a solid or liquid fuel. IFP is working on on-site conversion, which will be
more explain in the upgrading part. A major improvement of that technology would be
partial conversion at the well-head, to avoid completely transportation of the heavy
crude.
Another method is the emulsion one, which principle is that the extra heavy
crude or bitumen is suspended in the water in the form of droplets stabilized by chemical
additives. Emulsion technology is well known to use it as a fuel for electric power plant,
as does the Bitor company in Venezuela. Problem is that this use is under pressure due
to flue gas emissions levels and CO2 issues. Getting round that problem implies to break
the emulsion, but such a process is not available. Moreover, it involves additional
investment for treating and cleaning the used water. IFP is actually conducting research
on that subject, trying to create an efficient and economic process for emulsion breaking.
Recently appear research work on a new method called core annular flow. The
idea is that water acts as a lubricating layer which absorbs the shear stress existing
between the walls of the pipe and the viscous oil, reducing the resistance to about 1.5
the flow resistance of water alone. It allows to reduce drastically the pressure drop
induced by the viscous fluid. The main problem of that technology is that the oil tends to
adhere to the wall of the pipeline upon contact, leading to restriction and an eventual
blockage of the flow system. Such problems are exacerbated when flow must be
stopped for a certain period of time. IFP is actually conducting research program on the
modeling of that transportation method.
Very new idea for the transportation of non-conventional oil is the use of Friction
Reducing Agent in combination with dilution to optimize it. That method is already
used for conventional oil but has to be adapted to the non-conventionals. IFP is today
working on the problem and specially on the chemical stucture of the additives. Such
Friction Reducing Agent could be also used to optimize transportation by heating the
crude.
When comparing the efficiency of the transportation methods in term of pressure
drop induced, the core annular flow is by far the best one, with a pressure drop the
closer to the one of water, followed by emulsion, then heating and finally dilution.
Transportation methods could be also compared in term of investment and
environment matter. In that case, the core annular flow is potentially the cheapest and
the less polluted one. The other methods all have a crucial problem: electricity source for
heating, high investment for dilution and water separation and treatment for the
emulsion.
Upgrading
Heavy and light crude oil processing will give the same range of refined products
but in very different proportions and qualities. Heavy oils give much more vacuum
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residues than the lighter one. These residues have an API degree between one and five
and very high sulfur and metals content, which do not facilitate their treatment. Several
processes exist to convert vacuum residues, they are thermal, catalytic or both. Thermal
conversion methods are mature technologies but generally, the obtained products are of
lower quality than those obtain with catalytic processes. We can mention here
visbreaking and coking.
Solvent deasphalting is a well-proven process which separates vacuum
residues into a low metal/carbon deasphalted oil and a heavy pitch containing most of
the contaminants especially metals. SDA is a subject of much interest from refiners
because it allows to recover a substantial quantity of incremental light feedstock notably
for lubricants oil base production from vacuum residue, which means that the yield of the
refinery can be increased. Moreover, the pitch could be gasified to meet a zero fuel oil
production. IFP has developed one process of solvent deasphalting called Solvahl.
The most of recent works has been therefore turned on various type of
Hydrotreating processes. The principle is to lower product carbon to hydrogen ratio by
adding significant amount of hydrogen, as well as to desulfurise and to remove nitrogen
and heavy metals. Those processes usually require specific catalyst combination and
operate under high pressure. Three types of reactor technology exist: fixed bed,
ebullated bed and slurry reactor.
- Fixed bed process are the first to be developed but their application are limited for
feeds with high metals contents.
- Ebullated bed reactor was first introduced in the 1960s (the ancestor of the H-Oil
process of IFP). In this design, hydrogen and oil enter at the bottom of the reactor,
expanding the catalyst bed. The catalyst performance can be kept constant because
fresh catalyst can be added and part of the aged catalyst withdrawn on line. Recent
R&D has resulted in substantial improvement in the ebullating processes. These
improvements include catalyst and reactor technologies and conversion increases.
Second generation catalysts are available resulting in improved process performance
and product quality.
However, all these processes require large amount of hydrogen which would require
specific production from natural gas and will induce CO2 emissions.
- The slurry reactor, using high concentration of finely divided catalyst. This type of
technology might allow high conversion. No commercial process is presently available.
Recently, the idea is to associate different processes to optimize the heavy
crude conversion. The combination of hydrotreating and solvent deasphalting processes
is particularly studied. Those combination can be used either in refineries or for on-site
partial upgrading. IFP proposes solutions in that field, using Solvahl and T-Star (a
process derived from H-Oil, for feeds free of asphaltenes) or H-Oil and Solvahl. That last
solution allows the refiner to obtain a syncrude of a good quality which could be used as
a feed by a standard refinery, and a dirty heavy asphalt phase which can be recovered
as a solid or liquid fuel for a Integrated Gasification Combined Cycle (IGCC) purpose, or
just for combustion in order to generate steam for upstream applications. The IFP
technology for upgrading are commercialized by the Axens company.
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Another route for upgrading heavy oil is therefore the process of gasification
which consists in conversion by partial oxidation of the feed, liquid or solid, into a
synthesis gas in which the major components are H2 and CO. Gasification is a clean
flexible technology already improved on coke or heavy crude. Gasification is now
receiving a global interest because of the integrated gasification combined cycle (IGCC),
where gasification can process low value refinery streams and raise power with the
lowest SOx and NOx of any liquid/solid feed technology. Major concern will be in the
future on the important CO2 emissions of such processes. Capital costs of integrated
gasification combined cycle has fallen and has been divided by two in ten years.
However, the oxygen production phase is still costly and many researches are going to
improve air separation and integration of this part with the partial oxidation in a single-
step reactor. Moreover, depending on industrial situation, gasification could also be
associated with Gas to Liquids (GTL) projects firstly based on natural gas steam
reforming because of ratio H2/CO (2/1) required for Fisher Tropsh reaction.
CO2 issues
CO2 emissions is clearly a major issue for the exploitation of non-conventional
oils. A recent study realized in IFP underlines that all along the non-conventional
pathway, CO2 emissions are 4 to 6 and even 10 times higher than in the conventional
one, depending on projects (Orinoco type or steam injection type). Moreover, in the field
of energetic yield, the one of project like those in the Orinoco region are about 89% and
those with steam injection of 86% meanwhile yield of conventional oil are close to 98%.
We can see here that technological innovation like horizontal wells allow substancial
improvements in term of CO2 emissions and energetic yield.
Conclusion
We have seen that lots of technical innovations have been made in the field of
heavy oil exploitation but main concerns remain to be solved. They are of three types:
- energetic yield, which is, as we have seen it before, by far lower for
unconventional oil than for the conventional.
- environmental issues: electric power needed for enhanced recovery or for
heating the pipe for transportation, water treatment, sulfur, nitrogen and heavy metals
removal, etc…environmental problems due to non-conventional oils are much higher
than for conventional one,
- CO2 emissions which are, as we have seen, 4 to 6 times higher than those for
conventional crude exploitation.
R&D effort must be focused on those issues, to allow the exploitation of non-
conventional oil to become more competitive as the reserves are very huge.