METHOD FOR IN-SITU COMBUSTION OF IN-PLACE OILS

METHODE DE COMBUSTION SUR PLACE D'HYDROCARBURES

English Abstract

A novel method is provided for in situ combustion and recovery of oil from underground reservoirs including injecting air into the reservoir at a region near the reservoir floor, withdrawing combustion products from a region near the reservoir ceiling, and collecting oil from a horizontal production well near the reservoir floor.

French Abstract

On propose une nouvelle méthode pour la combustion in situ et la récupération dhuile de réservoirs souterrains, y compris linjection dair dans le réservoir dans une région près du fond du réservoir, le retrait des produits de combustion dune région près du haut du réservoir, et la collecte de lhuile dun puits de production horizontal près du fond du réservoir.

Claims

6
CLAIMS
1. A method of in situ combustion for recovery of oil from an underground
reservoirs oil
reservoir comprising:
a) injecting air into the reservoir via an injection well in a region near
the reservoir floor;
b) establishing a combustion front wherein hot combustion gases rise at the
combustion
front with combustion progressing from heel to toe;
c) withdrawing combustion products from a region near the reservoir ceiling,
wherein heated
oil drains to the reservoir floor; and
d) collecting oil from a horizontal production well near the reservoir floor,
wherein the
horizontal production well defines a heel proximate to the injection well.
2. The method of claim 1 wherein combustion products are withdrawn through
a bleed well located
above an air injection well flow exit.
3. The method of claim 1 wherein withdrawn combustion products are passed
to an expansion turbine
for energy recovery.
4. The method of claim 3 wherein fuel is combusted to heat the combustion
products before
expansion.
5. The method of claim 1 wherein the production well is drilled from the
same platform as an air
injection well.
6. The method of claim 1 wherein the toe of the production well is at a
higher elevation than the
heel.
7. The method of claim 2 wherein the bleed well includes a horizontal
section perpendicular to a
vertical injection well.

7
8. The method of claim 1 wherein the production well is a horizontal well
perpendicular to an
injection well.
9. The method of claim 1 wherein combustion products are withdrawn through
multiple bleed
wells.

Description

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METHOD FOR IN-SITU COMBUSTION OF IN-PLACE OILS
FIELD OF THE INVENTION
[0001] This invention relates to a method for contacting carbonaceous
deposits in
a sub-surface formation with a reactive fluid whereby such deposits may be
mobilized
thus allowing for recovery. More specifically, the invention relates to a
method for
efficient recovery and upgrading of heavy oils.
BACKGROUND OF THE INVENTION
[0002] In-situ combustion is an established method for enhanced oil
recovery. In
a typical application, air is injected into a vertical well resulting in
combustion and
increased oil mobility. Product oil is then recovered via either the injection
well by a
process known as huff-and-puff or via a second vertical well. The process is
not widely
used because it has been difficult to control. Thus attempts have been made to
improve
the process.
[0003] To reduce the problem of gravity segregation, for example, air is
injected
at a high point of the reservoir. U.S. Patent No. 5,211,230 teaches injecting
air at a high
point of the reservoir via a vertical well along with a lower horizontal
production well.
U.S. Patent No. 5,626,191 teaches placing the low horizontal well
perpendicular to the

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vertical well to draw the combustion front along the horizontal well and away
from the
injection well. Although this is an improvement, combustion products are
intended to be
removed with the heated oil and thus injected fresh air also has ready access
to the
horizontal well between the toe and the combustion front. A further
disadvantage is that
the injection well and the horizontal well vertical leg must be located far
apart.
Accordingly, there is still a need for a process which is controllable and
provides
efficient use of injected air.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide an improved
method of
contacting an injected fluid with a reaction front whereby oil may be
recovered
economically. More specifically, it is a further object of the present
invention to enable
more efficient in-situ combustion of in-place heavy oil whereby combustion
products are
more efficiently removed from the combustion zone and thermal cracking is
promoted.
[0005] In the present invention, air is injected near the reservoir floor
allowing
the hot combustion products to over-ride the cooler fresh air. The cooler air
is thus
drawn to the combustion front aided by withdrawal of combustion products via a
bleed
well located at a point well above the reservoir floor. Use of a horizontal
bleed well
permits steering of combustion front travel. Advantageously, oil is recovered
via a
horizontal production well having its heel (the transition from horizontal to
vertical rise
to the surface) near the injection well. This means that the production well
can be

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maintained liquid full throughout the air rich burned out zone blocking loss
of injected
air.
[0006] Combustion product gases may be withdrawn from a region near the top
of the reservoir, preferably at an elevated pressure near the reservoir
pressure. Passage of
the withdrawn gases through a power turbine allows recovery of a portion of
the energy
required for compression of the injection air. Combustion of fuel to utilize
oxidant in the
withdrawn gases increases power output of the power turbine. Fresh air may be
added as
necessary to combust fuel values present in the combustion products.
[0007] An advantage of the present invention is that the oil recovery
well(s) may
be drilled from the same platform as the injection and bleed wells thereby
reducing the
environmental impact. Multiple production wells may be utilized depending upon
the
reservoir geometry. Typically, it will be advantageous to place the injection
well at a low
point in the reservoir. In addition, the required wells need not terminate
directly under
the production platform. If desired, injection and production wells may be
drilled from
separate platforms located some distance apart with the production well toe
(i.e.,
horizontal terminus) located near the injection well.
[0007a] In accordance with an aspect of the present invention there is
provided
a method of in situ combustion for recovery of oil from an underground
reservoirs
oil reservoir comprising:
a) injecting air into the reservoir via an injection well in a region
near the reservoir floor;
b) establishing a combustion front wherein hot combustion gases
rise at the combustion front with combustion progressing from heel
to toe;
c) withdrawing combustion products from a region near the
reservoir ceiling, wherein heated oil drains to the reservoir floor;
and

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d) collecting oil from a horizontal production well near the reservoir
floor, wherein the horizontal production well defines a heel
proximate to the injection well.
BRIEF DESCRIPTION OF THE DRAWINGS
[00081 Fig, 1 is a schematic representation of the state of the art system
of U.S.
Patent No. 5,626,191.
[0009] Fig. 2 is a schematic representation of the present invention.

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DESCRIPTION OF THE INVENTION
[0010] Figure 1 depicts an advanced design in-situ combustion system of
the
prior art. Unlike the system of the present invention, excess combustion gases
are
withdrawn via the horizontal production well 12. Thus the horizontal section
12A of well
12 that lies within burned out zone 14 cannot withdraw combustion gases
without
preferentially bleeding off fresh air. As the combustion front progresses from
location 16
through representative locations 18, 20, etc., loss of fresh combustion air
worsens. To
minimize fresh air loss, the toe section may be at a lower elevation than the
heel so that
the leg between the toe and the combustion front remains liquid full. This
also allows oil
to drain out of the toe into the reservoir. Even so, this is only a partial
solution since hot
gases will still tend to over-ride the cooler fresh air at the withdrawal
point. The result is
energy loss.
[0011] Referring to the drawings, Figure 2 depicts a well pattern 100 for
in-situ
combustion according to the present invention. Air 110 is injected via well
112 at the
bottom of reservoir 114 flowing to combustion front 116. Heated oil 118 drains
to the
reservoir floor on rock bed 120 and is withdrawn at a controlled rate such
that horizontal
well 122 is liquid full throughout burned out zone 124. Hot combustion gases
rise at
combustion front 116 and are withdrawn via concentric well 126 for energy
recovery in a
turbine (not shown). Well 126 need not be concentric with injection well 112
and may be
located as the reservoir structure dictates or may be a horizontal well.
Regardless, it is
typically advantageous to drill all wells from a common platform.

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100121 While the present invention has been described in considerable
detail,
other configurations exhibiting the characteristics taught herein for a method
for in-situ
combustion of in-place oils are contemplated. Therefore, the scope of the
invention should
not be limited to the description of the preferred embodiments described
herein.

Representative Drawing