U.S. patent application number 11/327874 was filed with the patent office on 2006-07-27 for method for producing viscous hydrocarbon using incremental fracturing.
This patent application is currently assigned to World Energy Systems, Inc.. Invention is credited to Charles H. Ware.
Application Number | 20060162923 11/327874 |
Document ID | / |
Family ID | 36695497 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060162923 |
Kind Code |
A1 |
Ware; Charles H. |
July 27, 2006 |
Method for producing viscous hydrocarbon using incremental
fracturing
Abstract
A method for producing viscous hydrocarbon formations involves
the use of a downhole burner. The well undergoes a mild hydraulic
fracturing process that limits the fractured zone to a relatively
small dimension so as to avoid intersecting any drainage zones of
adjacent wells. The operator pumps fuel, steam and oxygen to the
burner, which bums the fuel, causing the flow of hot, gaseous
fluids into the fractured zone. The steam delivered from the
surface cools the burner and becomes superheated as it enters the
fractured zone. The operator allows the fractured zone to soak,
then produces the oil. After the production declines, the operator
may repeat the fracturing to incrementally increase the fractured
zone, then repeat the injection and soak cycles.
Inventors: |
Ware; Charles H.; (Safety
Harbor, FL) |
Correspondence
Address: |
James E. Bradley
P.O. Box 61389
Houston
TX
77208-1389
US
|
Assignee: |
World Energy Systems, Inc.
|
Family ID: |
36695497 |
Appl. No.: |
11/327874 |
Filed: |
January 9, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60646790 |
Jan 25, 2005 |
|
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Current U.S.
Class: |
166/263 ;
166/302; 166/308.1; 166/59 |
Current CPC
Class: |
E21B 43/2405 20130101;
E21B 43/26 20130101; E21B 36/02 20130101 |
Class at
Publication: |
166/263 ;
166/302; 166/308.1; 166/059 |
International
Class: |
E21B 43/24 20060101
E21B043/24; E21B 43/26 20060101 E21B043/26; E21B 43/25 20060101
E21B043/25 |
Claims
1. A method for producing a viscous hydrocarbon from a well,
comprising: (a) hydraulically fracturing a viscous hydrocarbon
formation surrounding the well, creating a limited fractured zone
surrounded by an unfractured portion of the formation; (b) securing
a downhole burner in the well; (c) pumping a fuel into the burner
and burning the fuel in the burner; (d) creating superheated steam
in the burner and injecting the superheated steam into the
fractured zone to heat the hydrocarbon therein, and impeding the
escape of the superheated steam into the surrounding unfractured
portion of the formation; then (e) flowing hydrocarbon from the
fractured zone up the well; then (f) at a selected time,
hydraulically fracturing the formation again to increase the extent
of the fractured zone, and repeating steps (c), (d) and (e).
2. The method according to claim 1, wherein the extent of the
fractured zone created in step (a) is less than one-half a distance
to any adjacent wells.
3. The method according to claim 1, wherein the extent of the
fractured zone created in step (a) is limited so as to avoid
intersecting any drainage zones of any adjacent wells.
4. The method according to claim 1, further comprising: allowing
the fractured zone to soak for a selected time after step (d) and
before step (e) by stopping steps (c) and (d) other than to
maintain the formation pressure at a desired level until beginning
step (e).
5. The method according to claim 1, wherein: steps (c) and (d)
create a solution gas and causes a formation pressure within the
fractured zone to increase; and wherein step (e) comprises using
the solution gas as a source to force the hydrocarbon into and up
the well in step (e).
6. The method according to claim 1, wherein step (d) comprises
pumping partially saturated steam to the burner and flowing a
portion of the partially saturated steam through a jacket around
the burner to cool the burner and convert the partially saturated
steam to superheated steam.
7. The method according to claim 1, wherein step (f) is performed
without removing the burner.
8. A method for producing a viscous hydrocarbon from two adjacent
wells, both of which extend into the same viscous hydrocarbon
formation, comprising: (a) hydraulically fracturing the hydrocarbon
formation surrounding each of the wells, creating a separate
fractured zone around each of the wells, and limiting the extent of
the fractured zones so that they do not intersect each other,
leaving unfractured portions of the formation surrounding each of
the fractured zones; (b) injecting steam into each of the fractured
zones and impeding the escape of the steam from the fractured zones
into the unfractured portions of the formation surrounding each of
the fractured zones; then (c) flowing hydrocarbon from each of the
fractured zones up the well; and (d) when the flow of hydrocarbon
drops below a selected minimum in each of the wells, hydraulically
fracturing the formation in each of the wells again to create
enlarged fractured zones around each well, and limiting the extents
of the enlarged fractured zones so as to avoid them intersecting
each other; then repeating steps (b) and (c).
9. The method according to claim 8, further comprising allowing the
fractured zones to soak for a selected time after step (b) and
before starting step (c), and while soaking, ceasing step (b) other
than to maintain a desired pressure in each of the fractured
zones.
10. A method for producing a viscous hydrocarbon from a well,
comprising: (a) hydraulically fracturing a viscous hydrocarbon
formation to create a fractured zone, but limiting an extent of the
fractured zone so that the fractured zone is surrounded by an
unfractured portion of the formation; (b) securing a downhole
burner in the well; (c) pumping hydrogen, oxygen and partially
saturated steam down the well to the burner, burning a portion of
the hydrogen, cooling the burner with the partially saturated
steam, and heating the partially saturated steam to create
superheated steam; (d) injecting the steam and unburned portions of
the hydrogen from the burner into the fractured zone to heat the
hydrocarbon and create a solution gas in the fractured zone, the
unfractured portion of the formation impeding the escape of the
heated steam and unburned portions of the hydrogen; then (e)
ceasing step (c) during a selected soak interval except for at
least one repetition of step (c) to maintain a desired pressure in
the fractured zone; then (f) opening a valve at a wellhead and
allowing the heated hydrocarbon to flow up the well driven at least
in part by the solution gas; then (g) repeating steps (a), (c),
(d), (e) and (f).
11. The method according to claim 10, wherein the hydraulic
fracturing of step (a) is limited to have an outer periphery
separated from a drainage zone of any adjacent wells.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of provisional
application Ser. No. 60/646,790 filed Jan. 25, 2005.
FIELD OF THE INVENTION
[0002] This invention relates in general to methods for producing
highly viscous hydrocarbons, and in particular to injecting steam
from a downhole burner into a fractured zone.
BACKGROUND OF THE INVENTION
[0003] There are extensive viscous hydrocarbon reservoirs
throughout the world. These reservoirs contain a very viscous
hydrocarbon, often called "tar", "heavy oil", or "ultraheavy oil",
which typically has viscosities in the range from 3,000 to
1,000,000 centipoise when measured at 100 degrees F. The high
viscosity makes is difficult and expensive to recover the
hydrocarbon. Strip mining is employed for shallow tar sands. For
deeper reservoirs, heating the heavy oil in situ to lower the
viscosity has been employed.
[0004] In one technique, partially saturated steam is injected into
a well from a steam generator at the surface. The heavy oil can be
produced from the same well that the steam is injected by allowing
the reservoir to soak a selected time after the steam injection,
then producing the well. The heavy oil can also be produced by
means of a second well spaced apart from the injector well. When
production declines, the operator repeats the process. A downhole
pump may be required to pump the heated heavy oil to the surface.
If so, the pump has to be pulled from the well each time before the
steam is injected, then re-run after the injection.
[0005] Another techniques uses two horizontal wells, one a few feet
above and parallel to the other. Each well has a slotted liner.
Steam is injected continuously into the upper well bore to heat the
heavy oil and cause it to flow into the lower well bore. Other
proposals involve injecting steam continuously into vertical
injection wells surrounded by vertical producing wells.
[0006] U.S. Pat. No. 6,016,867 discloses the use of one or more
injection and production boreholes. A mixture of reducing gases,
oxidizing gases, and steam is fed to downhole combustion devices
located in the injection boreholes. Combustion of the reducing gas
oxidizing gas mixture is carried out to produce superheated steam
and hot gases for injection into the formation to convert and
upgrade the heavy crude or bitumen into lighter hydrocarbons. The
temperature of the superheated steam is sufficiently high to cause
pyrolysis and/or hydrovisbreaking, which increases the gravity and
lowers the viscosity of the hydrocarbon in situ. The '867 patent
also discloses fracturing the formation prior to injection of the
steam. The '867 patent discloses both a cyclic process, wherein the
injection and production occur in the same well, and a continuous
drive process involving pumping steam down boreholes of wells
surrounding the producing wells. In the continuous drive process,
the '867 patent teaches to extend the fractured zones to adjacent
wells.
SUMMARY OF THE INVENTION
[0007] The well is fractured to create a fractured zone of limited
diameter. The fractured zone extends from the well and preferably
does not intersect any drainage or fractured zones of adjacent
wells. A downhole burner is secured in the well. The operator pumps
a fuel, which may be hydrogen, and oxygen in separate conduits down
the well to the burner, and burns the fuel in the burner. The
operator also pumps partially saturated steam from the surface into
the well The steam flows into and cools the burner. The heat
exchange creates superheated steam, which then flows into the
fractured zone along with residual unburned fuel and other products
of combustion.
[0008] The unfractured formation surrounding the fractured zone
impedes leakage of these gaseous products from the fractured zone.
After injecting the steam and other gaseous products for a selected
time, the operator allows the fractured zone to soak for a selected
time. During the soak interval, the operator may intermittingly
pump fuel and steam to the burner to maintain a desired amount of
pressure in the fractured zone. After the soak interval, the
operator opens valves at the wellhead to cause the hydrocarbon to
flow into the borehole and up the well. The viscous hydrocarbon,
having undergone pyrolysis and/or hydrovisbreaking during this
process, flows to the surface for further processing. Preferably,
the flow occurs as a result of solution gas created in the
fractured zone from the steam and residual hydrogen. A downhole
pump could also be employed,
[0009] When production declines sufficiently, the operator may
repeat the procedure of injecting steam and combustion products
from the burner into the fractured zone. The operator may also
fracture the formation again to enlarge the fracturing zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic illustrating a well and a process for
producing heavy oil in accordance with this invention.
[0011] FIG. 2 is a schematic illustrating the well of FIG. 1 next
to an adjacent well, which may also be produced in accordance with
this invention.
[0012] FIG. 3 is a schematic illustration of a combustion device
employed with the process of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to FIG. 1, well 11 extends substantially
vertically through a number of earth formations, at least one of
which includes a heavy oil or tar formation 15. An overburden earth
formation 13 is located above the oil formation 15. Heavy oil
formation 15 is located over an underburden earth formation 17. The
heavy oil formation 15 is typically a tar sand containing a very
viscous hydrocarbon, which may have a viscosity from 3,000 cp to
1,000,000 cp, for example. The overburden formation 13 may be
various geologic formations, for example, a thick, dense limestone
that seals and imparts a relatively high fracture pressure to the
heavy oil formation 15. The underburden formation 17 may also be a
thick, dense limestone or some other type of earth formation.
[0014] As shown in FIG. 1, the well is cased, and the casing has
perforations or slots 19 in at least part of the heavy oil
formation 15. Also, the well is fractured to create a fractured
zone 21. During fracturing, the operator pumps a fluid down the
casing, which flows through perforations 19 and imparts a pressure
against heavy oil formation 15 that is greater than the parting
pressure of the formation. The pressure creates cracks within
formation 15 that extend generally radially from well 11, allowing
flow of the fluid into fractured zone 21. The injected fluid to
cause the fracturing may be conventional, typically including
water, various additives, and proppant materials such as sand or
ceramic beads.
[0015] The operator controls the rate of injection of the
fracturing fluids and the duration of the hydraulic fracturing
process to limit the extent or dimension of fractured zone 21
surrounding well 11. Fractured zone 21 has a relatively small
initial diameter or perimeter 21a. The perimeter 21a of fractured
zone 21 is limited such that it will not intersect any existing or
planned fractured or drainage zones 25 (FIG. 2) of adjacent wells
23 that extend into the same heavy oil formation 15. Further, in
the preferred method, the operator will later enlarge fractured
zone 21 well 11, thus the initial perimeter 21a should leave room
for a later expansion of fractured zone 21 without intersecting
drainage zone 25 of adjacent well 23. Adjacent well 23 optionally
may previously have undergone one or more of the same fracturing
processes as well 11, or the operator may plan to fracture adjacent
well 23 in the same manner as well 11 in the future. Consequently,
fractured zone perimeter 21a does not intersect fractured zone 25.
Preferably, fractured zone perimeter 21a extends to less than half
the distance between wells 11, 23. Fractured zone 21 is bound by
unfractured portions of heavy oil formation 15 outside perimeter
21a and both above and below fractured zone 21.
[0016] A production tree or wellhead 27 is located at the surface
of well 11. Production tree 27 is connected to a conduit for
directing a mixture of fuel and steam down well 11, as indicated by
the numeral 37 The fuel may be hydrogen, methane, syngas, or some
other fuel. The fuel may be a gas or liquid. Preferably, the steam
is partially saturated steam, having a water vapor content up to
about 20 percent. The water vapor content could be higher, and even
water could be pumped down well 11 in lieu of steam, although it
would be less efficient. A wellhead 27 is also connected to a
conduit for delivering oxygen down well 11, as indicated by the
numeral 39. Preferably the fuel and steam 37 is delivered separate
from the conduit that delivers oxygen 39. The conduits for fuel and
steam 37 and oxygen 39 may comprise coiled tubing or threaded
joints of production tubing. One of the conduits could comprise the
annulus in the casing of well 11.
[0017] A combustion device or burner 29 is secured in well 11 for
receiving the flow of fuel and steam 37 and oxygen 39. As
illustrated in FIG. 3, a packer and anchor device 31 seals and
secures burner 29 to the casing of well 11. Burner 29 has a
combustion chamber 33 surrounded by a jacket 35. Fuel and steam 37
enter combustion chamber 33 for burning the fuel. In this
embodiment, at least some of the steam flows through jacket 35, as
indicated by the arrows 41. If the fuel is hydrogen, some of the
hydrogen can flow through jacket 35 along with steam.
[0018] Burner 29 ignites and burns at least part of the fuel, which
creates a high temperature in burner 29. Without steam or water as
a coolant, the temperature would likely be too high for burner 29
to withstand over a long period. The steam flowing into combustion
chamber 33 reduces that temperature. Also, preferably there is an
excess of fuel flowing into combustion chamber 33. The excess fuel
does not burn, thus also lowers the temperature in combustion
chamber 33. Further, the steam and fuel 41 flowing through jacket
35 cools combustion chamber 33. A downhole burner for burning fuel
and injecting steam and combustion products into an earth formation
is shown in U.S. Pat. No. 5,163,511.
[0019] The steam and excess fuel lower the temperature within
combustion chamber 33, for example, to around 1600 degrees F.,
which increases the temperature of the partially saturated steam
flowing through jacket 35 and through combustion chamber 33 to a
superheated level. The gaseous product 43, which comprises
superheated steam, excess fuel and other products of combustion,
exits burner 29 preferably from about 550 to 700 degrees F. The
hot, gaseous product 43 flows into fractured zone 21. The fractures
within fractured zone 21 increase the surface contact area for
these fluids to heat the formation and dissolve into the heavy oil
to lower the viscosity of the oil and create solution gas to help
drive the produced oil. The unfractured formation 15 is
substantially impenetrable by the gaseous product 43 because the
heavy oil or tar is not hot enough to be displaced. The surrounding
portions of heavy oil formation 15 thus create a container around
fractured zone 21 to impede leakage of hot gaseous product 43.
[0020] In the preferred method, the delivery of fuel, steam and
oxygen into burner 29 and the injection of hot gaseous product 43
into fractured zone 21 occur simultaneously over a selected period,
such as seven days. While gaseous product 43 is injected into
fractured zone 21, the temperature and pressure of fractured zone
21 increases. At the end of the injection period, fractured zone 21
is allowed to soak for a selected period, such as 21 days. During
the soak interval, the operator may intermittingly pump fuel, steam
and oxygen to burner 29 where it burns and the hot combustion gases
are injected into formation 15 to maintain a desired pressure level
in fractured zone 21. Other than pressure maintenance, no further
injection of hot gaseous fluid 43 occurs during the soak
period.
[0021] Then, the operator begins to produce the oil, which is
driven by reservoir pressure and preferably additional solution gas
pressure. The oil is preferably produced up the production tubing,
which could also be the same tubing through which the fuel and
steam or oxygen is pumped. Preferably, burner 29 remains and place,
and the oil flows through burner 29. Alternately, well 11 could
comprise two boreholes a few feet apart, preferably no more than
about 50 feet, with the oil flowing up a separate borehole from the
one containing burner 29.
[0022] The oil production will continue as long as the operator
deems it feasible, which could be up to 35 days or more. When
production declines sufficiently, the operator may optionally
repeat the injection and production cycle either with or without
additional fracturing. It may be feasible to fracture again after
one or more injection and production cycles to increase the
perimeter 21a of fractured zone 21, then repeat the injection and
production cycle described above. Preferably, this subsequent
fracturing operation can take place without removing burner 29. The
process may be repeated as long as fractured zone 21 does not
intersect fractured zones or drainage areas 25 of adjacent wells 23
(FIG. 2). By incrementally increasing the fractured zone 21
diameter from a relatively small perimeter up to half the distance
to adjacent well 23 (FIG. 2), the operator can effectively produce
the viscous hydrocarbon formation 15. With each new fracturing
operation, the previously fractured portion would provide flow
paths for the injection of hot gaseous product 43 and the flow of
the hydrocarbon into the well. Also, the previously fractured
portion retains heat from the previous injection of hot combustion
gases 43. The numeral 21b in FIGS. 1 and 2 indicates the perimeter
of fractured zone 21 after a second fracturing process. The
operator could be performing similar fracturing, injection, soaking
and production cycles on well 23 at the same time, if desired.
[0023] Before or after reaching the maximum limit of fractured zone
21, which would be greater than perimeter 21b, the operator may
wish to convert well 11 to a continuously driven system. This
conversion might occur after well 11 has been fractured several
different times, each increasing the dimension of the perimeter. In
a continuously driven system, well 11 would be either a continuous
producer or a continuous injector. If well 11 is a continuous
injector, downhole burner 29 would be continuously supplied with
fuel and steam 37 and oxygen 39, which burns the fuel and injects
hot gaseous product 43 into fractured zone 21. The hot gaseous
product 43 would force the oil to surrounding production wells,
such as in an inverted five or seven-spot well pattern. Each of the
surrounding production wells would have fractured zones that
intersected the fractured zone 21 of the injection well. If well 11
is a continuous producer, fuel and steam 37 and oxygen 39 would be
pumped to downhole burners 29 in surrounding injection wells, as in
a normal five or seven-spot pattern. The downhole burners 29 in the
surrounding injection wells would burn the fuel and inject hot
gaseous product 43 into the fractured zones, each of which joined
the fractured zone of the producing well so as to force the oil to
the producing well.
[0024] The invention has significant advantages. The unfractured
heavy oil formation surrounding the fractured zone serves as a
container to impede leakage of excess fuel, steam and other
combustion products into adjacent formations or to the surface. The
container maximizes the effects of the excess fuel and other hot
gases flowing into the fractured zone. By reducing leakage from the
fractured zone, the expense of the fuel, oxygen, and steam is
reduced. Also, containing the excess fuel increases the safety of
the well treatment.
[0025] While the invention has been shown in only one of its forms,
it should be apparent to those skilled in the art that it is not so
limited but is susceptible to various changes without departing
from the scope of the invention. For example, although the well is
shown to be a vertical well, it could have a horizontal component
extending through the heavy oil formation The fractured zone could
be one or more vertical fractures in that instance.
* * * * *