Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR RECOVERY OF STRANDED OIL
CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional Application
No. 60/764,822 filed February 4, 2006.
FIELD OF THE INVENTION
[00021 This invention relates to a method for the recovery of stranded oil
left
behind in an oil reservoir after recovery of oil by conventional means.
BACKGROUND OF THE INVENTION
[0003) Oil fields typically are abandoned after oil can no longer be produced
economically by known secondary or tertiary recovery methods. At this point,
the remaining oil in place often represents as much as two-thirds of the
amount originally in place. Of the remaining oil, about twenty percent is
considered technically recoverable using advanced techniques such as, for
example, carbon dioxide flooding. Unfortunately, for stranded oil in most
U.S. fields, carbon dioxide is not available. Moreover, there is a need to
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recover far more stranded oil than can be recovered by known advanced
methods such as carbon dioxide flooding. It is therefore an object of the
present invention to make possible economic recovery of nearly all the
remaining stranded oil in place.
SUMMARY OF THE INVENTION
[0004] The oil coating on the reservoir minerals can be flushed off much more
effectively than by carbon dioxide flooding. By heating the oil to an elevated
temperature along with reservoir pressurization, the oil can be flushed off of
the sand, for example, in the reservoir. In the present invention, hot fluids
are
injected near the top of the reservoir such that fluid flow is downward toward
the reservoir floor by gravity drainage aided by the downward fluid flow.
Inert gases present in injected fluids provide reservoir repressurization.
Preferably, fluid is injected through a horizontal well to best distribute the
flow across the reservoir ceiling. Advantageously, the hot combustion gases
are produced using a downhole combustor. If available, carbon dioxide is
added to combustion products for sequestration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005J Figure 1 depicts an isometric of horizontal injection well with
branches
protruding into the reservoir.
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DETAILED DESCRIPTION OF THE INVENTION
[00061 In the present invention 10, as shown in Figure 1, hot fluids such as
steam or combustion gases may be produced at the surface and injected
downhole via injection well 12. However, heat losses advantageously may be
reduced by generating the heated fluids downhole as by a downhole
combustor with fuel and air supplied from the surface. Combustion gases
produced by downhole combustion typically are reduced in temperature by
addition of an inert fluid such as nitrogen or carbon dioxide. Steam may be
produced by spraying water into the hot combustion products. Hot fluids also
may be generated by in-situ combustion with air supplied from the surface.
[00071 Hot fluid is provided near the reservoir ceiling 14 using any
conventional method known in the art such that the flow forms a gas blanket
layer which flows downward toward the reservoir floor. Thus heated oil
drains toward the reservoir floor 16. Typically the fluid is injected via a
horizontal well 18. To distribute the fluid over a wider area, the horizontal
well may have horizontal branches 20 as shown in Figure 1.
[0008] Temperature of the injected fluid in most cases is below that which
would result in significant cracking of the oil. However, if significant
reduction in the oil viscosity is desired, the temperature of the injected
fluid is
controlled to a value which will result in cracking of the oil. Temperatures
high enough for cracking can be provided by use of in-situ combustion.
Cracking of the oil is desirable where the viscosity of the stranded oil is
higher
than that originally produced in primary production. Oil draining to the
reservoir floor may be recovered through an existing production well.
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However, it may be advantageous to provide a new horizontal productiori well
located on or near the reservoir floor.
[0009] After the heated fluid has heated an upper portion of the reservoir
flushing the oil downward, heat from oil depleted layers may be utilized to
heat a cold fluid such as nitrogen or carbon dioxide thus providing heated
fluid
for recovery of oil from lower levels.
[0010] While the present invention has been described in considerable detail
with reference to a preferred method for the recovery of stranded oil left
behind in an oil reservoir after recovery of oil by conventional means as
described herein, other methods. exhibiting the characteristics taught herein
are
contemplated. Therefore, the spirit and scope of the invention should not be
limited to the description of the preferred embodiment described herein.
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