METHOD OF SHEAR HEATING OF HEAVY OIL TRANSMISSION PIPELINES

METHODE DE CHAUFFAGE DE CISAILLEMENT POUR RESEAUX DE DISTRIBUTION DE PETROLE LOURD

English Abstract

A method aid apparatus for transporting heavy oil in a pipeline using shear
heating. Shear
heating provided by external friction or internal friction acts to heat the
heavy oil to increase or
maintain the temperature of the heavy oil as it flows through the pipeline.
The pipeline may be
designed to enhance shear heating.

Claims

CLAIMS:
1. A method of transportation of heavy oil in a substantially underground
pipeline by
increasing or maintaining the temperature of the heavy oil within the pipeline
using shear heating.
2. The method of claim 1, wherein the shear heating is provided by external
friction within a
pump.
3. The method of claim 1, wherein the shear heating is provide by internal
shear friction
within the flow of the heavy oil.
4. The method of claim 1, wherein the pipeline is substantially non-insulated
or poorly
insulated.
5. The method in claim 1, wherein the heavy oil has an API gravity of less
than 26 degrees
API.
6. The method of claim 1, where shear heating acts to raise the temperature of
the heavy oil
at a rate designed to substantially match, within desired parameters, the
effect of pipeline
conditions in lowering the temperature of the oil, to produce an equilibrium
oil temperature.
7. The method of claim 6, wherein the equilibrium oil temperature, defined as
substantially
the asymptote of the temperature versus time graph, averaged over
substantially the length of the
pipeline is at least about 15°F (8.3°C) above the average ground
temperature at the pipeline's
operating condition.
8. The method of claim 7, further comprising the step of heating the heavy oil
to
substantially the equilibrium oil temperature before using shear heating for
increasing or
maintaining the temperature of the heavy oil.
9. The method of claim 1, wherein a portion of the pipeline comprises a
feature for
increasing shear heating.
6

10. The method of Claim 9, wherein the feature comprises a section of reduced
pipeline
diameter, a flow restriction, a mixer, internal blades or vanes, an uncoated
pipeline wall, a
roughened pipeline wall, or a combination thereof.
11. The method of claim 6, wherein the heavy oil is cooled to keep the heavy
oil substantially
at or below a selected temperature.
12. The method of claim 11 wherein the selected temperature corresponds
substantially to the
design and temperature limits of the pipeline.
13. The method of claim 12, wherein the design temperature limit of the
pipeline is selected
on the basis of an external coating temperature limit or an environmental
design temperature
limit.
14. The method of claim 1, where the shear heating in at least a segment of
the pipeline is
controlled by controlling the pressure drop of the heavy oil within the
pipeline, wherein a larger
pressure drop yields more shear heating of the heavy oil.
15. The method of claim 1, where the shear heating is tailored for at least a
segment of the
pipeline by tailoring flow velocity and pressure drop within the segment
(assuming no change to
other inputs such as constitution of heavy oil, starting temperature and
pressure, pipeline diameter
and environmental conditions), the flow velocity and/or discharge pressure
being tailored by
adjustment of pump horsepower and pump operating pressure range.
16. The method of claim 1, wherein the pipeline has a length of at least 160
miles (266 km)
(i.e, the pipeline is a "long-haul" pipeline).
17. The method of Claim 16, wherein the pipeline has a length of at least 300
miles (500 km).
18. The method of claim 1, wherein selected portions of the pipeline are
thermally insulated
to reduce heat loss in the selected portions.
7

19. The method of claim 18, wherein the selected portions comprise river
crossings, surface
projections (expansion loops, surface valves or piping, meter stations, etc.),
or regions where the
ground has a higher thermal conductivity (e.g. wet soil).
20. The method of claim 1, wherein the heavy oil comprises a blend or mixture
of heavier oil
and a diluent.
21. The method of claim 20, wherein the diluent is a hydrocarbon having five
or fewer
carbon atoms.
22. The method of claim 20, wherein the diluent is a hydrocarbon having six or
more carbon
atoms.
23. The method of claim 20, wherein the diluent is selected from a group of
high
(>atmosphere) vapor pressure products comprising, ethane, propane, n-butane, i-
butane,
ethylene, propylene and butylene.
24. The method of claim 20, wherein the heavy oil has an API gravity of less
than about 26
degrees API.
25. A method of selecting the route of a substantially non-insulated
substantially
underground pipeline in order to facilitate a shear heating effect, comprising
the steps of:
a) assessing a plurality of possible routings, considering at least one
detracting
factor, the at least one detracting factor known to effect or at least
partially overcome the
shear heating effect in achieving or maintaining the pipeline's equilibrium
temperature;
and
b) selecting one of the plurality of possible routings based on the
minimization or
reduction in the at least one detracting factor.
26. The method of claim 25, wherein the at least one detracting factor is
selected from the
group of ground thermal conductivity, river crossing required, or surface
projections (expansion
loops, surface valves or piping, meter stations, etc.).
8

27. The method of claim 26, wherein underground moisture affects the ground
thermal
conductivity.
28. A pipeline for transporting heavy oil, the pipeline adapted to benefit
from shear heating,
the pipeline having a maximum operating pressure (MOP) greater than about 800
psia, an
operational average pressure drop greater than about 10 psi/mile, and a
equilibrium oil
temperature, defined as substantially the asymptote of the temperature versus
time graph,
averaged over substantially the length of the pipeline, of at least about
15°F (8.3°C) above the
average ground temperature, at the pipeline's operating condition.
9

Description

CA 02427544 2003-05-02
Inventor: PEItRY, GLEN F.
Title: l~~IETHOD OF SHEAR HEATING OF HEAVY OIL T1~ANS1VIISSION
PIPELINES
Field of the Invention
The Invention relates to the field of oil and gas. In particular, the
l:nvention, in one
embodiment, is a method of using shear heating effect for the long distance
pipeline
transportation of heavy oil.
Background of the Invention
The state of the prior art can be summarized by the following quotation, taken
from a
paper presented in the October 26, 1998, issue of the Oil and Gas Journal. The
paper is
called "Drive to produce heavy cnzde prompts variety of transportation
methods", by 1~.
Gustavo, H. J. Rivas Nunez and D. D. Joseph. The statement is as follows:
"It is important to note that the external heating of the oil can be partially
frustrated
by heat losses from the pipe walls when the flow velocity is low... Heat
losses will
always occur and the heating method can work only (emphasis added) when the
oil
is reheated in the pumping stations. Direct fired heaters are generally used
to raise
the oil temperature; they can be natural gas or fuel fared."
Summary of the Invention
It is an object of the Invention to overcome limitations in the prior art.
It has been found that it is possible to design a long distance, non-
insulated, heavy
oil transmission pipeline that can be heated using a principle referred to
here as shear
heating. This principle refers to the fact that, using appropriate design
factors, the
temperature in the pipeline will naturally (without the injection of heat)
increase above
ground temperature, and will remain at this elevated state, even when the line
is not
insulated. The increased temperature shows a benefit in reducing the viscosity
of the
heavy oil, and thus allowing for greater throughput at a lower power
requirement. The
temperature can be controlled by varying the design choices of line diameter,
station
spacing, operating pressure range and the viscosity specification of the
transported oil at
ambient temperature.
These and other objects and advantages of the Invention are apparent in the
following description of embodiments of the Invention, which is not intended
to limit in
any way the scope or the claims of the Invention.
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CA 02427544 2003-05-02
l3escription of the Invention
The following described embodiments of the Invention display preferred methods
but are not intended to limit the scope of the Invention. It will be obviou;9
to those skilled
in the art that variations and modifications may be made without departing
from the scope
and essential elements of the Invention.
For heavy oil and bitumen oil involved in long distance pipeline
transportation, the
designed viscosity specification of oil pipelines is usually met by blending
the heavy oil
with a lighter hydrocarbon compound. l~latural gasoline, pentanes plus or
naphtha is
traditionally used because of their low vapor pressure. Traditional oil
pipelines operate
with a low vapor pressure restriction, close to ambient pressure, in order to
maximize their
capacity. This restricts the choice of blending compounds to CS+ or heaviier.
For example,
an older pipeline with a maximum operating pressure ("MOP") of 80C) psia,
operating
down to 25 Asia, has 775 psi.a of useful pressure drop betwf;en pump stations
to define the
throughput. Raising the minimum pressure to 150 psia would reduce throughput
significantly. Increasing the maximum pressure to 925 psia would reestablish
the lost
capacity, however this is not possible with an existing line already operating
at MOP.
When designing a new line, the minimum and maximum operating pressure can be
designed so that the shear heating effect, which permits this Invention's
benefits, can be
predicted and controlled and the range of available blending compounds used to
vary the
base heavy oil or bitumen oil viscosity for transport is broadened. The new
line could, for
example, range between 1400 psia and 150 Asia, allowing for both a greater oil
velocity
between stations and a higher vapor pressure limit.
With a minimum vapor pressure limit of 150 Asia, a new pipeline can use
hydrocarbon compounds lighter than natural gasoline for blending, such as
ethane,
propane or butane. This has an advantage in areas such as Alberta, Canada,
where the
available supply of CS+ is limited, and thus carries an economic penalty as a
diluent, while
the available supplies of C2, C3 and C4 are plentiful, and can be purchased
for a discount
relative to the value of the commodities at the destination of the pipeline.
The resulting system has a pressure drop of 1250 psia between stations,
sufficient
to generate the shear heating effect.
The shear heating effect is initiated by two factors. The first is the small
temperature increase that occurs in the pump through friction, as the o:il is
increased in
pressure. This is dependent on the pressure rise and tends to increase the oil
temperature
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CA 02427544 2003-05-02
by about 1-2 degrees Fahrenheit. The second is the heat generated by internal
shear
friction within the oil as it flows through the pipeline. This shear friction
translates into
heat. When the sum of these two heat inputs exceeds the ability of the non-
insulated pipe
to radiate heat to the surrounding ground, the temperature of the oil will
continuously
increase until an equilibrium temperature is reached, where the heat
generation is equal to
the heat loss. As the temperature of the oil rises, the viscosity and internal
shear friction
reduces and therefore the shear friction heat generation reduces. Also, as the
temperature
rises, the heat loss to the environment increases with the difference in
temperature
between the oil and the environment.
For some of the designs, the net temperature increase can add upwards of 1
degree
Fahrenheit for every 10-20 miles of distance, with an equilibrium temperature
of 150
degrees Fahrenheit.
Rather than wait for this effect to slowly heat the oil as it travels down the
pipelir3e,
and be limited in pipeline capacity by the operating conditions over the
initial distance
traversed, one design using or embodying the invention would include a heater
at the front
end of the pipeline, so that this target equilibrium temperature was induced
in the oil being
injected into the pipeline at the outset. In this fashion, the equilibrium
temperature (and
other operating factors) would be maintained throughout the pipeline systf;m.
In the event that the equilibrium temperature exceeds a maximum design
temperature limit, dictated by other factors such as environmental impact,
external
coating, or steel expansion, the oil can be cooled by the use of low cost
aerial radiators or
similar coolers at selectively spaced pump stations. This is possible because
the heating
effect is quite gradual, usually taking several pump stations to rise by 10
degrees
Fahrenheit.
The key contributing factors to the shear heating effect are summarized below:
1. The higher the oil viscosity, the greater the internal shear friction and
the
more heat is generated. This shear heating effect is not seen with normal
light and
medium gravity oil as the viscosity within the transport system is too low.
The
upper limit on viscosity on long distance pipelines specifically designed for
heavy
oil will usually be dictated by the pipeline's shut down condition. The oil
must be
able to move after an extended shut down, when it has cooled to the ambient
temperature. This would, for example, prevent pure bitumen with a viscosity of
250,000 ep at 50 degrees Fahrenheit from being used, and would dictate the
need
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CA 02427544 2003-05-02
for some blending. In the following examples, a 75%/25% bitumen-to-condensate
blend is assumed. This blend has an assumed viscosity of 310 cp at 50 degrees
Fahrenheit and 108 cp at 80 degrees Fahrenheit. If the shutdown condition is
not a
key design feature, because the cool down time is so long that pipeline
startup can
be guaranteed within the time window, then even higher viscosity oils can be
assumed and the shear heating effect is increased.
2. The higher the velocity and pressure drop per unit distance, the greater
the
heat generation. For practical applications, this means that the pipeline must
be in
turbulent flow or partially turbulent flow. The high velocity is achic;ved
byutilizing
a large pressure drop between pump stations, and in using relatively tight
station
spacing. The following example assumes a pump station outlet of 1400 psia, a
pump station inlet of 150 psia, and station spacing between 60 and 120 miles.
The
resulting velocity is 4-10 feet per second.
3. The greater the pipe diameter, the greater the ratio between oil volume
(radius squared) and heat radiating surface area (radius). The following
example
assumes three pipe sizes of 24", 30" and 36" diameter. The ~fect is seen to be
greater with the larger diameters.
4. The equilibrium temperature is very sensitive to the ground thermal
conductivity. Typical North American soil conditions range from 0.6 to 0.9
BTU/ft-degree F-hour in the summer and 0.8 to 1.1 in the winter. The following
example is based on 0.9 for summer conditions, which would represent a wet,
clay-
like soil, with about the highest heat conductivity of all soils expected to
be
encountered. The equilibrium temperature would be higher with more typically
dryer or insulating soils.
The impact of higher oil temperature on pipeline capacity is to reduce the
viscosity
of the oil. With all else being equal (minimum and maximum pressure, line
size, station
spacing, elevation), at similar throughput, this viscosity reduction reduces
the pressure
drop between stations. Alternatively, at a similar pressure drop between
stations, this
viscosity reduction allows for an increase in throughput. The increase in
throughput for the
60-mile station spacing bettueen using the referenced oil blend at 50 degrees
Fahrenheit
and 310 cp and in using the referenced oil blend at 130 degrees Fahrenheit and
28 cp is
approximately 40%. This requires a 40% increase in pump horsepower, however
all the
other aspects of the system remain the same. As the pump station horsepower
represents
4

CA 02427544 2003-05-02
about 25% of the total system capital and operating cost, one achieves 140% of
the
throughput at 110% of the cost. The unit cost of transportation reduces by
about 21
(30/140). This is one measure ofthe economic value of the invention.
All aspects of the Invention may be comprised of any suitable material or
methods,
including but not limited to: pipeline greater than 300 miles in length; oil
which has an
API gravity of less than 26 degrees API; oil temperature more than 15 degrees
Fahrenheit
hotter than the ground temperature; temperature maintained without the use of
external
heating except at the initiation station; use of aerial coolers to keep the
oil below the
maximum operating temperature.
Figure One (1) displays the results from a hydraulic simulation of am
embodiment of
the Invention.
In the foregoing descriptions, the Invention has been described in known
embodiments. However, it will be evident that various modifications and
changes may be
made without departing from the broader scope and spirit of the Invention.
Accordingly,
the present specifications and embodiments are to be regarded as illustrative
rather than
restrictive.
The descriptions here are meant to be exemplary and not limiting. It is to be
understood that a reader skilled in the art will derive from this descriptive
material the
concepts of the Invention, and that there are a variety of other possible
implementations;
substitution of different specific components for those mentioned here will
not be
sufficient to differ from the Invention described where the substituted
components are
functionally equivalent.