Note: Descriptions are shown in the official language in which they were submitted.
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B~\CKGROUl`lD OE' T~IE INVE:Mq'IO~i
The present invention relates to recovery of
petroleum from subterranean formations. Particularly,
it relates to recovering relatively heavy petroleum
5 oils, such as tar sands bitumen, from consolidated or
unconsolidated subterranean formations employing a
method wherein light hydrocarbon fractions, steam dis-
tilled from produced bitumen, are reinjected with steam
into the subterranean formations via injection wells,
10 and wherein produced crude, steam, and reinjected light
hydrocarbons are recovered from wells producing from the
same subterranean formations.
It is known, generally, to produce petroleum
oils, tar sand bitumens, and related petroleum hydro-
15 carbons from shale, sandstone, unconsolidated sand, and
t `other subterranean formations by injecting steam into a
` first well for heating the petroleum in such formations
and forcing such petroleum to a second well from which
"~ such petroleum is produced. Particularly when this
20 method is employed for recovering bitumen, or heavy
petroleum, from subterranean formations, a bank of oil
builds up in a cold zone ahead of the advancing steam.
` This bank of restricts flow through the formation,
xequiring high pressures for moving the bitumen to the
25 producing well.
An improvement of the process of recovering
petroleum oils employing steam injection has been
suggested in the prior art. In this improved process, a
vapor mixture of superheated steam and a normally liquid
30 hydrocarbon solvent are injected, via an injection well,
into a subterranean formation for forcing petroleum
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to a second well from which such petroleum is produced. Hydro-
carbon solvents contemplated in this improved process are those
which, when admixed with petroleum to be produced, will reduce
the viscosity of the mixture considerably below that of the
petroleum in place. Such solvents will ordinarily have the
characteristics of such liquids as kerosine, gasoline, jet fuel,
stoddard solvent, benzene, xylene, toluene, etc.
SUMMARY OF THE INVENTION
Now, according to the present invention, we have
discovered an improved method for recovering bitumen, or heavy
petroleum, from subterranean formations. In this application,
"bitumen" will be understood to include heavy crude petroleum.
In accordance with the present invention there is
provided, in a process for recovery of bitumen from a sub-
terranean formation wherein steam is injected via an injection
well into said subterranean formation, wherein bitumen is
produced via a production well from said formation, wherein
injection of steam into said formation is continued until a steam
front reaches said production well such that steam condensate
in admixture with bitumen enters the bore of said production
well, the improvement which comprises:
(a) flashing said mixture of bitumen and steam condensate
produced from said formation at a pressure less than the
pressure of said formation for production of a vapor phase com-
prising steam and steam-distilled hydrocarbon and a liquid phase
comprising bitumen;
(b) injecting at least a portion of said steam-distilled
hydrocarbons from step (a), with additional steam, into said
formation, via said injection well, for enhancing production of
bitumen from said formation via said production well.
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In another aspect the present invention provides a
process for recovering bitumen from a subterranean formation,
which process comprising:
(a) injecting steam into said formation via an injection
well;
(b) producing bitumen from said formation via a production
well,
(c) continuing injection of said steam and production of
said bitumen until communication between said injection well and
said production well is established through said formation such
that a mixture of bitumen and steam condensate enters the bore
of said production well;
(d) flashing said mixture of bitumen and steam condensate : :
for production of a vapor phase comprising steam and steam-
distilled hydrocarbon, and production of a liquid phase compris- ~:
ing bitumen; :
: (e) condensing, in a condensing zone, said vapor phase for :.:
production of a condensate comprising water and condensed hydro-
carbon;
(f) injecting said condensed hydrocarbon with additional
steam into said formation, via said injection well, for enhancing
recovery of additional bitumen from said formation.
In a preferred embodiment of such a process the liquid
volume ratio of injected condensed hydrocarbon to additional
steam is in the range of about 1:1 to about 1:100, and the
volume of injected condensed hydrocarbon is equivalent to about
~ 1-100 percent of the pore volume of that portion of the forma-
`~ tion swept by the injected hydrocarbon and additional steam.
In one embodiment of the present invention, the
improved process comprises:
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a) injecting steam into a bitumen containing
subterranean formation via at least one in-
jection well;
b) producing bitumen from said bitumen
containing subterranean formation via at
least one production well;
c) continuing said steam injection and said
bitumen production for a time sufficient to
establish communication between said injec-
tion well and said production well such that
a mixture of bitumen and steam condensate
enters said production well;
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7 d) flashinc~, in a fl~s~l æone, s~id ~i~ture
of bitumcn and steam condcnsate for production
of a liquid phase comprising bitumen and a
vapor phase comprisiny steam and hydrocarbon
vapor;
e) condensing, in a condenser, said vapor
phase for producing a condensate comprising
water and liquid hydrocarbon;
f) separating, in a gravity separation zone,
~ said condensate into a water phase and a
hydrocarbon phase;
g) injecting said hydrocarbon phase, with
additional steam, into said injection well
for displacing additional bitumen from the
formation.
k In one alternative, the total condensate of
step (e) comprising water and steam distilled hydrocarbon
may be reinjected with additional steam into the sub-
terranean formation. In this alternative, the condensing
step (d) may be dispensed with, ana the flashed vapor
mixed directly with the steam, by means such as a jet
pump.
Under certain conditions, when the produced
fluid is sufficiently hot, flashing of water and steam
~5 distilled hydrocarbons can occur in the well bore of the
producing well. In such situations, vapor from the
producing well head may be xecovered directly for o~tain--
ing steam distillea hydrocarbons suitable for reinjection
into the subterranean formation.
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1 For situations ~7here~ the produc~d Jni~tUre of
bitumen and steam cond~nsate i~ no~ sufficiently hot for
flashin~ of a vapor comprising stearn distilled hydro-
carbon and steam, additional heat may be added to the
produced liquid prior to flashing. Such heat may be
added by indirect heat exchange means. Preferably, how-
ever, steam is added directly to the produced bitumen in
a flash ~one for increasing the amount of steam dis-
tilled hydrocarbons produced.
Advantages of the process of the present
invention over processes of the prior art include: in-
creased displacement of bitumen from a subterranean
formation employing an injected mixture of steam and the
light hydrocarbon steam distilled from the produced
bitumen, as compared to bitumen displacement obtained
`~ using steam-hydrocarbon mixtures of the prior art.
Also, the steam-distilled hydrocarbon for injection with
steam to enhance production of bitumen is obtained at
` the production site, and expensive hydrocarbon solvents
~xom external sources are not required. These, and
other advantages of the process of the present invention
` will be discussed in the detailea description of the
`~ invention which follows.
DETA TED DESCRIPTION OF T~E INVENTION
~ 25 When steam flooding a bitumen bearing reservoir,
`~ such as a subterranean tar sand formation, a steam front
comprising a bank of condensed hot water is often propagated
from the injection well towards the producing well. As
the steam front propagates, steam distillation takes
30 place in the steam zone behind the steam front, evaporating -~
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1 h~drocarbon fractions of the bitumen . Continuous st~arn
distillation behind the steam front cnriches the hydro-
carbon content in the steam phase. Cont~mporaneously,
due to the condensation of the hydrocarbon vapors ahead
of the steam front, a region of solvent bank will be
established. When the steam front reaches the producing
well, the light hydrocarbons in the solvent bank will be
produced to the surface together with the displaced
bitumen. At the producing wellbore, the steam distillation
efficiency may be further increased due to reduced
pressure ~compared to formation pressure) within the
wellbore~ Such pressure reduction will induce steam
distillation conditions and hydrocarbons of lower density
than the bitumen will be evaporated with steam. Conse- -
15 quently, a large amount of light hydrocarbons may be
produced with the produced steam.
We have discovered that this Pteam distilled-
hydrocarbon fraction of the produced bitumen has superior
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solvent properties for enhancing production of additional
bitumen when such light hydrocarbon is reinjected with
additional steam into a subterranean formation. This
" discovery forms the basis of our invention. ~ ;
`~ Hydrocarbon bearing formations for which the
process of the present invention is useful include those
2~ which may be produced emplbying steam flooding techniques. -
` For example, the present invention may be appllea to
ormations which are depressured or underpressured and
which contain heavy (low API gravity) petroleum deposits
or bitumen. Particularly, the pxocess o the present
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invention is applicable to formations near the earth's
surface, such as tar sands which will not contain high
pressures.
The temperature of the steam and steam dis-
tilled hydrocarbon injected into a subterranean forma-
tion for enhancing recovery of bitumen, is selected to
carry sufficient heat into the formation to produce an
advancing steam front with the associated hydrocarbon
bank. The temperature of the injected mixture will be
sufficient to maintain a steam phase at formation
pressures, and usually will be sufficient to provide
some superheat at injection pressures. For example,
temperatures of about 225F may be used for formations
at about atmospheric pressure, and temperatures in the
15 range of 470-600F may be used in formations with
pressures of about 500 psig. Such temperatures of
injected steam and light hydrocarbon may be adjusted for
the injection pressure of a particular subterranean
formation from which bitumen is to be produced.
The proportion of steam distilled hydrocarbon
`` to steam in the injected mixture may vary over a relatively
large range of liquid volume ratios of about 1:1 to
~ about 1:100 steam-distilled hydrocarbon to steam `
`; respectively.
When steam-distilled hydrocarbon comprises
a large proportion of the injected vapor, the solvent
power for reducing viscosity of bitumen in the formation
is increased such that the bitumen will flow more readily
toward the production well. However, the amount of heat
per volume of injected vapor is decreased. When
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1 steam-distilled hydrocarbo~ ompri.SC5 a very sma'l
pLOpOrtion of the injected vapors, its solvent po~/er is
substantially curtailed. Consecluently, liquid volume
ratios of steam-distilled hydrocarbon to steam in the
injected vapor in the range of about 1:10 to about 1:50
respectively are preferred for providing a good balance
of heat input and amount of solvent per volume of injected
vapor for enhancing production of bitumen from the
formation.
In the process of the present invention, the
steam-distilled hydrocarbon may be injected along with
steam at commencement of a steam flood; may be injected
after the steam front has reached the production well;
or may be injected when the steam front is in an inter-
1~ mediate position between the injection well and the
production well.
When the steam-distilled hydrocarbon is injected
a commencement of steam flooding, a solvent bank will
accumulate rapidly, improving the recovery of bitumen.
However, the accumulated solvent bank may increase
` pressure drop through the formation, thus requiring
increased injection pressure to drive the bitumen to the
production well. ~ -
When the steam-distilled hydrocarbon is in-
jected after the steam front has reached the production
~ell, the formation temperature will be increased. - ~-
Thus, solution of hydrocarbon with remaining bitumen
will be increased and the viscosity of the resulting
solution will be decreased.
Recovery of a steam distilled hydrocarbon
fraction, having superior properties over other hydro-
carbon fractions for recovery of additional bitumen or
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heavy petroleum, may be obtained directly from the
production wellbore in the case where the steam front
has reached the production well or may be recovered from
produced bitumen by steam distillation techniques. In
either case, the steam distilled hydrocarbon fraction
exhibits improved solvent ability for production of
additional bitumen, and is advantageously produced at
the production site, such that expensive solvents need
not be imported.
The discussion thus far has been in terms of
reinjecting the steam distilled hydrocarbon fraction
into an injection well associated with a production well
from which the hydrocarbon fraction is obtained. It is
~ to be understood that all or a part of such steam dis-
`~ 15 tilled hydrocarbon fraction may also be injected into
another injection well for the same benefits of enhanced
production of bitumen. Also, within contemplation of
the present invention is the situation where one injection -
~` well serves two or more production wells.
The total volume of steam-distilled hydro-
carbon injected into a subterranean formation according
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to the method of the present invention is sufficient to
result in increased production of bitumen from the
formation, and will be proportional to the pore volume
(volume pores/volume of formation) and the total volume
of the formation swept by the injected hydrocarbon-steam `
mixture flowing to the production well. For practical
~ increased recoveries, the total injected volume of light
`~ hydrocarbon should be in the range of 1-100 percent of ~
30 the total pore volume in that portion of a formation -
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I st~eL~t by the hy~ro-~lrborl ste~m-lnixtur~. Pre~era~1~, the
total amoun-t of steam-distilled hydrocarbon injected
~ill be in the ran~e of about 5-20 percent of the total
pore volume in that portion of a formation swept ~y the
hydrocarbon-steam mixture. Should the total volume of
injected hydrocarbon be less than 1 percent of the total
swept pore volume, no substantial increase in production
will occur over that obtained by steam flooding alone.
Use of a total volume of injected hydrocarbon exceeding
100 percent of the total swept pore volume will not be
economically justified by increased production of
bitumen.
` One embodiment of the improved bitumen recovery
process of the present invention is applied as described
1~ below. Steam is injected into a bitumen containing tar
sands formation via an injection well for a time sufficient
~; for a steam front and an associated ban~ of bitumen to
reach a production well. A hot mixture of bitumen and - -
steam condensate enters the production wellbore rising
toward the well head at the earth's surface. As the hot -~
mixture xises in the production wellbore, pressure
decreases allowing a portion of the steam condensate to
flash into steam, thereby steam distilling a hydrocarbon
vapor fraction from the bitumen. At the production well
heàd, vapor from the wellbore is separated from produced
liguid, and the vapor is condensed in a condenser.
Condensate from the condenser flows into a receiver
~, vessel wherein the condensate separates under the in~
fluence of gravity into a hydrocarbon phase and water
phase. Hydrocarbon phase from the receiver is injected
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w:ith additional steam into the :injection well for pro-
duction of additional bitumen from the suhterranean
formation.
It is to be understood that modifications and
variations of the process described in the foregoing
specification will occur to those skilled in the art,
which modifications and variations are within the spirit
and scope of the present invention. Consequently, the
only limitations of the present invention intended are
those included in the appended claims.
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