U.S. patent application number 11/856566 was filed with the patent office on 2008-05-22 for in situ conversion of heavy hydrocarbons to catalytic gas.
Invention is credited to Frank D. Mango.
Application Number | 20080115935 11/856566 |
Document ID | / |
Family ID | 39615627 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080115935 |
Kind Code |
A1 |
Mango; Frank D. |
May 22, 2008 |
IN SITU CONVERSION OF HEAVY HYDROCARBONS TO CATALYTIC GAS
Abstract
A method of producing natural gas from a heavy
hydrocarbon-containing subterranean formation includes: placing a
catalyst having at least one transition metal into the formation,
injecting an anoxic stimulation gas into the formation, and
collecting the natural gas generated in the formation. The method
may be performed outside the context of a subterranean formation
under controlled conditions. Thus, a method of producing natural
gas from bitumen includes: providing an anoxic mixture of heavy
hydrocarbons and a catalyst having at least one transition metal,
adding an anoxic stimulation gas to the mixture, and heating the
mixture in the presence of the stimulation gas.
Inventors: |
Mango; Frank D.; (Houston,
TX) |
Correspondence
Address: |
WINSTEAD PC
P.O. BOX 50784
DALLAS
TX
75201
US
|
Family ID: |
39615627 |
Appl. No.: |
11/856566 |
Filed: |
September 17, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US07/60215 |
Jan 8, 2007 |
|
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11856566 |
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60757168 |
Jan 6, 2006 |
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Current U.S.
Class: |
166/259 ;
166/260 |
Current CPC
Class: |
C09K 8/70 20130101; C10G
2300/1025 20130101; C10G 11/02 20130101; C09K 8/845 20130101; C09K
8/92 20130101; C10G 2300/4037 20130101 |
Class at
Publication: |
166/259 ;
166/260 |
International
Class: |
E21B 43/243 20060101
E21B043/243 |
Claims
1. A method of producing natural gas from a heavy
hydrocarbon-containing subterranean formation comprising: placing a
catalyst comprising at least one transition metal into the
formation; injecting an anoxic stimulation gas into the formation,
wherein said stimulation gas is not hydrogen; and collecting the
natural gas generated in the formation.
2. The method of claim 1, wherein the catalyst is provided from an
active source rock.
3. The method of claim 1, wherein the catalyst is provided on a
proppant.
4. The method of claim 1, wherein at least one transition metal is
selected from the group consisting of a zero-valent transition
metal, a low-valent transition metal, alloys, and mixtures
thereof.
5. The method of claim 4, wherein the at least one transition metal
is selected from the group consisting of molybdenum, nickel,
cobalt, iron, copper, palladium, platinum, rhodium, ruthenium,
tungsten, osmium, rhenium, and iridium.
6. The method of claim 1, wherein the stimulation gas is at least
one selected from the group consisting of natural gas, natural gas
depleted of methane, carbon dioxide, helium, argon, and
nitrogen.
7. A method of producing natural gas from heavy hydrocarbons
comprising: providing a mixture comprising: heavy hydrocarbons; and
a catalyst comprising at least one transition metal; adding an
anoxic stimulation gas to the mixture; wherein the stimulation gas
is not hydrogen; and heating the mixture in the presence of the
stimulation gas.
8. The method of claim 7, wherein the catalyst is provided from an
active source rock.
9. The method of claim 7, wherein the at least one transition metal
is selected from the group consisting of a zero-valent transition
metal, a low-valent transition metal, alloys, and mixtures
thereof.
10. The method of claim 9, wherein the at least one transition
metal is selected from the group consisting of molybdenum, nickel,
cobalt, iron, copper, palladium, platinum, rhodium, ruthenium,
tungsten, osmium, rhenium, and iridium.
11. The method of claim 7, wherein the catalyst further comprises
salts of at least one main group element selected from the group
consisting of sulfur, phosphorus, arsenic, and antimony.
12. The method of claim 7, wherein the anoxic stimulation gas is at
least one selected from the group consisting of natural gas,
natural gas depleted of methane, carbon dioxide, helium, argon, and
nitrogen.
13. The method of claim 7, wherein heating is carried out in a
range from about 25.degree. C. to about 250.degree. C.
14. The method of claim 13, wherein heating is carried out in a
range from about 100.degree. C. to about 200.degree. C.
15. A method of forming natural gas comprising: providing an anoxic
mixture comprising: heavy hydrocarbons; and a catalyst comprising
at least one transition metal; adding an anoxic stimulation gas to
the mixture; wherein the stimulation gas is not hydrogen; and
heating the mixture in the presence of said stimulation gas.
16. The method of claim 15, wherein the catalyst is provided from
an active source rock.
17. The method of claim 15, wherein the at least one transition
metal is selected from the group consisting of a zero-valent
transition metal, a low-valent transition metal, alloys, and
mixtures thereof.
18. The method of claim 17, wherein the at least one transition
metal is selected from the group consisting of molybdenum, nickel,
cobalt, iron, copper, palladium, platinum, rhodium, ruthenium,
tungsten, osmium, and iridium.
19. The method of claim 15, wherein the anoxic stimulation gas is
at least one selected from the group consisting of natural gas,
natural gas depleted of methane, carbon dioxide, helium, argon, and
nitrogen.
20. The method of claim 15, wherein heating is carried out in a
range from about 25.degree. C. to about 350.degree. C.
21. A method of stimulating natural gas production in a heavy
hydrocarbon-containing subterranean formation comprising:
fracturing the formation in a substantially oxidant free
environment; and adding an anoxic stimulation gas to the fractured
formation.
22. The method of claim 21 further comprising withdrawing gases
generated by the addition of the anoxic stimulation gas.
Description
[0001] This application is a continuation-in-part of PCT
application PCT/US07/60215 filed Jan. 8, 2007 which in turn claims
the benefit of U.S. Provisional Patent Application No. 60/757,168
filed Jan. 6, 2006 and is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates in general to the production
of natural gas from high molecular weight hydrocarbons.
BACKGROUND
[0003] Heavy hydrocarbons such as bitumen, kerogen, Gilsonite.RTM.,
and tars are high molecular weight hydrocarbons frequently
encountered in subterranean formations. These hydrocarbons range
from thick viscous liquids to solids at ambient temperatures and
are generally quite expensive to recover in useful form. Bitumen
occurs naturally in tar sands in locations such as Alberta, Canada
and in the Orinoco oil belt north of the Orinoco river in
Venezuela. Kerogens are the precursors to fossil fuels, and are
also the material that forms oil shales. Kerogens, believed to be
the precursor to bitumens, are frequently found in sedimentary rock
formations.
[0004] Heavy hydrocarbons in general, have been used in a number of
applications such as in asphalt and tar compositions for paving
roads and roofing applications and as an ingredient in
waterproofing formulations. Importantly, they are a potentially
valuable feedstock for generating lighter hydrocarbons. This is
typically accomplished by thermal cracking and hydrogenolysis
processes, for example.
[0005] Recovering heavy hydrocarbons whole or as lighter
hydrocarbons and/or natural gas by thermal cracking in subterranean
formations continues to be a challenge. The excessive temperatures
necessary for thermal (or steam) cracking (about 850.degree. C.)
requires expensive, complex technology due to the special
construction material to sustain high cracking temperatures and
high energy input. Hydrogenolysis has limited utility when the
recovery of lighter hydrocarbons is desirable. This is due to the
difficulty of separating hydrogen from light olefins such as
ethylene, propylene, and natural gas. Therefore, there is a
continuing need for the development of methods for producing light
hydrocarbons and natural gas from high molecular weight hydrocarbon
feedstocks.
SUMMARY OF THE INVENTION
[0006] In view of the foregoing and other considerations, the
present invention relates to a method for the catalytic conversion
of heavy hydrocarbons to natural gas.
[0007] Accordingly, a method of producing natural gas from a heavy
hydrocarbon-containing subterranean formation includes: placing a
catalyst comprising at least one transition metal into the
formation, injecting a stimulation gas containing less than 1 ppm
oxygen (hereafter referred to as `anoxic`) into the formation, and
collecting the natural gas generated in the formation.
[0008] A method of producing natural gas from heavy hydrocarbons
includes: providing a mixture of heavy hydrocarbons and a catalyst
that includes at least one transition metal, adding an anoxic
stimulation gas to the mixture, and heating the mixture in the
presence of the stimulation gas.
[0009] A method of forming natural gas includes: providing a
mixture of heavy hydrocarbons and a catalyst having at least one
transition metal; adding an anoxic stimulation gas to the mixture,
and heating the mixture in the presence of the stimulation gas
[0010] The foregoing has outlined the features and technical
advantages of the present invention in order that the detailed
description of the invention that follows may be better understood.
Additional features and advantages of the invention will be
described hereinafter which form the subject of the claims of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing and other features and aspects of the present
invention will be best understood with reference to the following
detailed description of a specific embodiment of the invention,
when read in conjunction with the accompanying drawings,
wherein:
[0012] FIG. 1 is a plot showing the generation of methane and
ethane over time from Barnett Shale in flowing helium at
250.degree. C.
[0013] FIG. 2 is a plot showing the generation of methane and
ethane over time from Monterey source rock KG-4 in flowing helium
at 250.degree. C.
[0014] FIG. 3a is a plot showing gas chromatographic analyses of
the amount and types of gasses produced from a sample of New Albany
shale subject to an isothermal helium flow, at 100.degree. C. and
350.degree. C. under anoxic helium flow.
[0015] FIG. 3b is a plot showing gas chromatographic analyses of
the amount and types of gasses produced from a sample of New Albany
shale subject to a flow of helium with 10 ppm O.sub.2 at
100.degree. C. and 350.degree. C.
[0016] FIG. 4 is a plot showing gaseous hydrocarbon evolution over
21.7 hours at 50.degree. C. from a sample of shale from Black
Warrior Basin.
DETAILED DESCRIPTION
[0017] Embodiments disclosed herein are directed to a method in
which various transition metal-containing catalysts present as
zero- or low-valent metal complexes, are co-injected with sand or
other proppant into reservoirs rocks under sufficiently high
pressures to fracture the rocks thus creating conduits of porous
sand through which the transition metal complexes can pass into the
regions of the formation containing heavy hydrocarbon materials.
Alternatively, the catalysts may be delivered to
hydrocarbon-containing sites within a formation using muds.
[0018] The method further includes closing the well (after
introduction of stimulation gases) for sufficient time to allow
metal catalyzed decomposition of bitumen (digestion) and gas
generation. Thus, a method of producing natural gas from a heavy
hydrocarbon-containing subterranean formation includes placing a
catalyst which has at least one transition metal into the
formation, injecting an anoxic stimulation gas into the formation
(in some embodiments simultaneous with catalyst introduction), and
collecting the natural gas generated in the formation.
[0019] Heavy Hydrocarbons: Heavy hydrocarbons as used herein
include, but is not limited to all forms of carbonaceous deposits
with sufficient hydrogen to convert to natural gas:
(--CHx--).fwdarw.gas+(--CHy--) where x>y. Examples include
kerogens, solid hydrocarbons (Gilsonite, tars and the like), and
bitumens. Such heavy hydrocarbons may be processed in situ in a
formation. Alternatively, any of the hydrocarbons may also be
reacted outside the context of a subterranean location, for
example, in a batch reactor under carefully controlled conditions.
Such conditions would include, for example, the substantial removal
of oxygen which is prone to poisoning transition metal
catalysts.
[0020] Catalyst: Typical source rocks, usually shales or
limestones, contain about 1% organic matter, although a rich source
rock might have as much as 20%. Source rocks convert their bitumen
to natural gas at moderate temperatures (25 to 200.degree. C.) in
their natural state without hydrogen addition (see Experimental
examples below). They do so chaotically, with random bursts of
activity within periods of little or no activity, a phenomenon not
uncommon in transition metal catalysis. Such behavior has been
observed in a number of hydrogenation reactions including the
hydrogenation of carbon monoxide, ethylene, and nitric oxide over
Ni, Pt, Pd, Ir, Rh, and Ag (Eiswirth, M., 1993. Chaos in
surface-catalyzed reactions. Ch. 6 in Chaos in Chemistry &
Biochemistry, eds. R. J. Field & L. Gyorgyi, World Scientific
Publishing Co., River Edge, N.J., USA, 141-174.) and in the
hydrogenolysis of ethane over Ni and Pd (Kristyan, S., and Szamosi,
J., 1992. Reaction kinetic surfaces and isosurfaces of the
catalytic hydrogenolysis of ethane and its self-poisoning over Ni
and Pd catalysts. Computers in Physics 6, 494-497.). Indeed, such
chaotic behavior is an identifying characteristic of transition
metal catalysis.
[0021] Therefore, in some embodiments, the method of converting
heavy hydrocarbons to natural gas (oil-to-gas) may be accelerated
in situ by injecting transition metals into reservoir rocks. The
catalyst components may be obtained from an active source rock by
isolation of the transition metals from active source rock.
Alternatively, the source rock itself may be used without isolation
of the individual active transition metals by generating a fine
powder form of the source rock. One skilled in the art will
recognize that under heterogeneous conditions high catalytic
activity may be achieved by having catalyst particles with large
surface area to volume ratios. Thus, it may be particularly
beneficial to mill the source rock to very small particle size, for
example, 10 nm-10,000 nm average diameter, though larger particles
may be used as well.
[0022] In yet other embodiments, purified reagent grade transition
metal components may be used and mixed in appropriate
concentrations to reflect the naturally occurring compositions. For
example, active source rocks may contain sufficient low-valent
transition metals (100 to 10,000 ppb) to promote the reaction at
reservoir temperatures (100.degree. C. to 200+.degree. C.) on a
production time scale (days to years). Source rock activities may
be determined experimentally in flowing helium at various
temperatures. An assay procedure has been described by Mango (U.S.
Pat. No. 7,153,688).
[0023] The transition metal may be a zero-valent transition metal,
a low-valent transition metal, alloys, and mixtures thereof. Any
transition metal that serves as a hydrogenation catalyst may be
viable as a catalyst for the disproportionation reaction of heavy
hydrocarbons. Various transition metals catalyze the hydrogenolysis
of hydrocarbons to gas (Somorjai, G. A., 1994. Introduction to
Surface Chemistry and Catalysis. John Wiley & Sons, New York.
pg. 526); for example, C.sub.2H.sub.6+H.sub.2.fwdarw.2 CH.sub.4. It
has also been demonstrated that source rocks are catalytic in the
hydrogenolysis of hydrocarbons (Mango, F. D. (1996) Transition
metal catalysis in the generation of natural gas. Org. Geochem. 24,
977-984.) and that low-valent transition metals are catalytic in
the hydrogenolysis of crude oil (Mango, F. D., Hightower, J. W.,
and James, A. T. (1994) Role of transition-metal catalysis in the
formation of natural gas. Nature, 368, 536-538.). Furthermore,
there is substantial evidence that low-valent transition metals are
active agents in sedimentary rocks (U.S. patent application Ser.
No. 11/006,159). Active source rock may include transition metals
such as molybdenum, nickel, cobalt, iron, copper, palladium,
platinum, rhodium, ruthenium, tungsten, rhenium, osmium, and
iridium.
[0024] The catalyst components may be immobilized and introduced
into the formation on a proppant, in some embodiments.
Alternatively, catalysts may be injected as gases, metal carbonyls,
for example, which could dissolve in the carbonaceous sediments,
decompose with time, thus delivering to the sediments low-valent
active metals such as Ni, Co, Fe. Alternatively, the catalyst may
be introduced at various stages in oil-based muds, for example.
Fine metal particles could also be injected directly with sand in
reservoir fracturing, thus dispersing fine particles of active
catalyst throughout the network of porous sand conduits that carry
hydrocarbons from the reservoir to the surface. Catalysts may be
coated with paraffins (C.sub.8 to C.sub.18) to protect them from
oxygen-poisoning while on the surface and during injection into the
reservoir.
[0025] Stimulation gas: Since active metals in natural sedimentary
rocks are poisoned irreversibly by oxygen (U.S. Pat. No.
7,153,688), it is beneficial that the stimulation be anoxic (<1
ppm O.sub.2). Trace amounts of oxygen picked up in processing can
be easily and inexpensively removed with commercial oxygen
scrubbers. The stimulation gas may include natural gas, gas
depleted of methane, carbon dioxide, helium, argon, and nitrogen.
For natural gas (catalytic gas) production, hydrogen gas may
interfere with separation and therefore is not an ideal stimulation
gas. Again, the stimulation gas may also be used not only for the
fracturing, but also as a means of depositing the catalyst within
the formation. In some embodiments, the stimulation of catalytic
gas generation from bitumen in reservoir rocks may be achieved
through a single well bore in a permeable reservoirs by injecting
and withdrawing gas sequentially to create sufficient turbulence to
stimulate chaotic gas generation or it may be achieved through
multiple injection wells positioned to maximize continuous gas flow
through the permeable reservoir to production wells that collect
the injected gas plus catalytic gas. Production units would collect
produced gas, injecting a fraction to maintain a continuous process
and sending the remainder to market.
[0026] In reservoirs with insufficient permeability to sustain gas
flow such as tight shales like the Mississippian Barnett Shale in
the Fort Worth Basin (TX), fracturing the reservoir may be
beneficial. Fracturing may be accomplished with injected sand or
other appropriate proppant to create interlacing conduits of porous
sand to carry injected gas through the reservoir to conduits of
porous sands that carry the injected gas plus catalytic gas from
the reservoir to production units. The flowing gas injected into
the reservoir stimulates catalytic activity within the shale.
[0027] Fracturing may also be used to expose active catalytic sites
inherent in shales and other heavy hydrocarbon-containing
formations. Care should be taken in the fracturing process to
minimize the exposure of these freshly exposed catalytic sites to
oxygen and other oxidants that may deactivate low valent transition
metal catalysts. Elemental oxygen in excess of 1 ppm can reduce the
effectiveness of the catalytic reaction with heavy hydrocarbons. It
has been observed, however, that this poisoning of catalytic
activity is temperature sensitive. At temperatures lower than about
50.degree. C. catalytic activity may be unaffected by the presence
of oxygen, for example. For the common fracturing fluid water, a
simple degassing procedure prior to fracturing may be sufficient to
protect the nascent catalytic sites exposed during fracturing. In
order to establish natural gas production after fracturing, the
stimulation gas is simply allowed to flow over the newly fractured
formation.
[0028] Injected gas may be natural gas produced from the deposit or
natural gas produced from another deposit elsewhere. The process
could be carried out by sequential injections where the reservoir
is pressured, then allowed to stand and exhaust its induced
pressure over time. This process could be repeated multiple times
until the reservoir was exhausted of heavy hydrocarbons. The
process could also be carried out in a continuous mode where gas is
injected continuously into one well and withdrawn continuously from
another. The two wells (or multiple wells) would be interconnected
through a production unit that withdraws produced gas from the
system sending excess gas to market and re-injecting the remainder
to sustain continuous production.
[0029] Heavy hydrocarbon to natural gas: In addition to methods for
in situ cracking of heavy hydrocarbons in a subterranean location,
one may also produce natural gas from isolated heavy hydrocarbons
in batch reactors, for example. To carry out such production the
method entails mixing isolated heavy hydrocarbons (for example
mined bitumen) with an active catalyst as described above. An
anoxic stimulation gas may be introduced and the mixture heated
under anoxic conditions.
[0030] Again the catalyst may be an active source rock ground into
fine powder as described above. Alternatively, the active
transition metal components may be isolated from the source rock or
stock mixtures prepared from commercially available sources in
proportions identified in high activity source rock.
[0031] The stimulation gas may be natural gas, natural gas depleted
of methane, carbon dioxide, helium, argon, and nitrogen. In the
context of batch reaction, such a stimulation gas may be provided
as a flow while heating the bitumen catalyst mixture. Catalytic
activity may be facilitated by heating in a range from about
25.degree. C. to about 350.degree. C. and from about 25.degree. C.
to about 250.degree. C. in other embodiments. In particular
embodiments, heating may be carried out in a range from about
100.degree. C. to about 200.degree. C. In all embodiments, it is
beneficial that the stimulation gas be anoxic (<1 pp
O.sub.2).
[0032] Methods disclosed herein may be used in the production of
natural gas (catalytic gas). The aforementioned method for the
disproportionation of bitumen and high molecular weight
hydrocarbons may be used in such production. This may be carried
out in batch reactors, or generated directly from tar sand sources
where it may be collected in the field and distributed
commercially.
[0033] The following example is included to demonstrate particular
embodiments of the present invention. It should be appreciated by
those of skill in the art that the methods disclosed in the example
that follows merely represent exemplary embodiments of the present
invention. However, those of skill in the art should, in light of
the present disclosure, appreciate that many changes can be made in
the specific embodiments described and still obtain a like or
similar result without departing from the spirit and scope of the
present invention.
EXAMPLE 1
Barnett Shale, 250.degree. C., Helium
[0034] In a typical anoxic procedure, rocks are ground to powders
(60 mesh) under pure argon to protect their inner surfaces from
oxidation. These powders are then transferred to 5 ml 1/2 inch
tubular brass reactors (new reactors were constructed for most
experiments) that are secured at each end to 1/4 inch copper tubing
through Swagelok fittings. The tubing is attached to gas lines
through valves to open and close the system to gas flow. Reactors
(pressure-tight) are flushed with flowing gas (helium, 12 cc/min)
for 10 minutes at room temperature to remove any air picked up in
reactor assembly. They are pressure flushed (purified helium) five
times by pressuring to 50 psi and venting to one atmosphere to
remove any remaining oxygen and residual light hydrocarbons
(adsorbed in the shales) that might interfere with the analysis.
Reactors (now anoxic) are then heated (12.5.degree. C./min) under
purified helium flow to reaction temperatures where gas flow is
continued at constant temperatures.
[0035] In this example, a sample of Barnett shale (Mississippian,
Ft. Worth Basin Tex.) (3.4 g), ground to a powder in anoxic argon,
was placed in a reactor and purged of any adsorbed oxygen by
flowing anoxic helium (through a commercial oxygen scrubber)
through the reactor at 350.degree. C. for 20 minutes. Helium flow
(12 mL/min) was continued at 250.degree. C. for over one hour while
the effluent (i.e. stimulation) gas was monitored for methane by a
FID as shown in FIG. 1. The first methane peak (presumably adsorbed
and catalytic methane from the 10 min purge at 350.degree. C.)
emerged at 12.5 min (5.8.times.10.sup.-5 g CH.sub.4) followed by a
flat baseline over the next 20 min showing that the sample was no
longer releasing methane. Three sharp peaks of increasing intensity
then appeared at 45 min. (9.9.times.10.sup.-6 g CH.sub.4), 68 min.
(1.6.times.10.sup.-5 g CH.sub.4), and 94 min. (5.6.times.10.sup.-5
g CH.sub.4). The final three peaks constitute 2.2.times.10.sup.-2
mg CH.sub.4/(g rock hr) which is greater than that for this rock
under our usual conditions (in hydrogen) (5.7.times.10.sup.-3 mg
CH.sub.4/(g rock hr).
EXAMPLE 2
Monterey Source Rock, 250.degree. C., Helium
[0036] A sample of Monterey shale (Miocene, Calif.) (KG-4) (1.64 g)
was analyzed under identical conditions under pure helium flow for
about 7 hours (FIG. 2). After the initial peak of adsorbed gas (3
min., 2.7.times.10.sup.-6 g CH.sub.4), three very large peaks
emerged after 5 hours of He flow, the first corresponding to
7.3.times.10.sup.-4 g CH.sub.4, the second (180 min. later) to
2.2.times.10.sup.-4 g CH.sub.4, and the third (285 min. after the
first) to 1.1.times.10.sup.-4 g CH.sub.4, with an overall rate of
0.2 mg CH.sub.4/(g rock hr), not materially different from that
under hydrogen.
EXAMPLE 3
Barnett Shale, 200.degree. C., Helium
[0037] Pure helium (passed through an oxygen scrubber) was passed
over a sample of Barnett Shale (2.88 g) (ground to a powder (60
mesh) in argon) at 200.degree. C. for 140 minutes producing a burst
of methane (4.times.10.sup.-2 mg) corresponding to a rate of
8.3.times.10.sup.-3 mg CH.sub.4/(g rock hr), a rate substantially
greater than that obtained from the same experiment in hydrogen
(3.6.times.10.sup.-5 mg CH.sub.4/(g rock hr)) at this temperature
and only slightly lower than that at 250.degree. C.
[0038] It was observed that activity increases only slightly with
temperature in helium suggesting rate suppression counteracting the
usual Arrhenius exponential rate increase with temperature. The
higher-than-expected activities observed in helium at 200.degree.
C. suggests higher than anticipated activities at subsurface
temperatures and the expectation of promoting the conversion of
heavy hydrocarbon to natural gas at moderate reservoir temperatures
by injecting low-valent active transition metals into these
reservoirs.
EXAMPLE 4
[0039] A Monterey shale (Miocene, Calif.) sample generates methane
at a rate of .about.6.times.10.sup.-6 g C.sub.1/(g rock hr) in
hydrogen gas containing 3% propane under closed conditions (30
minutes) at 250.degree. C. and generates very little methane at
200.degree. C. under the same conditions (30 minutes). Under
flowing helium at 200.degree. C., the same rock converts its
bitumen to gas at a rate of 1.3.times.10.sup.-4 g C.sub.1/(g rock
hr). These results suggest that the mass-transfer stimulation gas
may achieve two positive effects: 1) it transports hydrocarbons
from heavy hydrocarbon deposits to active catalytic sites, and 2)
it removes activity-suppressing agents (products' and adsorbents)
from the active sites catalyst surfaces.
EXAMPLE 5
[0040] Marine shales generate two distinct gases in the laboratory,
one at high temperatures (>300.degree. C.) from kerogen
cracking, and the other at low temperatures (<100.degree. C.)
through the catalytic action of low-valent transition metals as
shown in exemplary FIGS. 3a and 3b. The data in FIGS. 3a and 3b
were obtained from a sample of New Albany shale subject to an
isothermal helium flow, at 100.degree. C. and 350.degree. C.,
sequentially. FIG. 3a shows the system under an anoxic helium flow.
FIG. 3b shows the system with a flow of helium with 10 ppm O.sub.2.
New Albany shale generates catalytic gas dominated by propane.
Thus, the high-propane peaks at 100 and 350.degree. C. are
catalytic gas peaks. Thermal gas from kerogen cracking is
represented by the methane peak (500 ppm vol) at 350.degree. C.
Catalytic gas is 90% of the total gas in FIG. 3a.
[0041] Low-temperature gas generation is unique. Generation rates
are orders of magnitude higher, product compositions are dynamic,
kinetics of generation are non-linear, and gas generation
terminates on exposure to trace levels of oxygen. Equally
surprising, different shales generate gases having different
compositions. Barnett Shale, Fort Worth basin, generates a gas
enriched in methane and near thermodynamic equilibrium in
C.sub.1-C.sub.3 (K=[(C.sub.1)(C.sub.3)]/[C.sub.2).sup.2]), while
New Albany Shale, Illinois basin, generates a gas with mainly
propane, and not at equilibrium, although it approaches equilibrium
over time.
EXAMPLE 6
[0042] Cuttings of marine shale from the Black Warrior Basin were
ground to powders (60 mesh) in argon (1.31 g) and placed in a metal
reactor and prepared for reaction as described before
(pressure-purging the reactor with pure helium, etc). The reactor
was then warmed to 50.degree. C. under anoxic helium flow and the
products in the effluent stream were analyzed by FID. The product
gas stream was passed directly into the FID bypassing all cold
traps. The trace represents the FID signal over time (minutes).
Since the product stream bypassed all cold traps, the four peaks
represent all gaseous hydrocarbons generated from the shale. This
produced four distinct signals of gas production at 308.8, 516.7,
728.6, and 927.9 minutes, as shown in FIG. 4, corresponding to 70
.mu.g gas/g shale. This experiment provides the clearest example of
chaotic kinetics and thus additional evidence of catalytic action
by transition metals (Field & Gyorgyi, Chaos in Chemistry &
Biochemistry, World Scientific Pub. Co, River Edge, N.J., 1993;
Eiswirth, Ch 6 in Chaos in Chemistry & Biochemistry, 1993).
[0043] Low-temperature gas forms at temperatures comparable to
geological reservoir temperatures, but only when there is gas flow
under anoxic conditions. This is achieved in the laboratory by
grinding the shales in pure argon to expose inner anoxic surfaces,
and then passing purified helium over the surfaces at constant
temperature. In a typical example, a Paleozoic marine shale
(Chattanooga/Floyd) from the Black Warrior Basin
(Alabama/Mississippi) generated 70 .mu.g gas/(g shale) in 21.7
hours at 50.degree. C.
[0044] Two things are remarkable about these results. First, is the
robust activity at a very low temperature. Rates of most chemical
reactions diminish with decreasing temperatures. Higher reaction
temperatures may be suppressing activity or otherwise altering the
chaotic kinetics of catalytic gas generation. Without being bound
by mechanism, anoxic gas flow stimulates gas generation at very low
temperatures, in this example at 50.degree. C., and thus, gas-flow
stimulated gas generation may be viable at all subsurface
temperatures. Generating gas without injecting heat may be viable
because of the thermodynamic stability of light hydrocarbons over
the heavier hydrocarbons. The conversion of pentane to methane,
propane, and carbon at 27.degree. C., for example, is exothermic by
-15.81 kcal/mole (Stull et Al., The Chemical Thermodynamics of
Organic Compounds, John Wiley & Sons, N.Y., 1969). Thus the
conversion of bitumen to gas is energetically favorable at most
reservoir temperatures and requires no heat input to drive
conversion. The second remarkable thing is the duration of
sustained high activity, in this case over 22 hours. This means
that a shale like this one in the subsurface at this temperature
would generate about 4 MMcft/(acre-ft year) under gas-flow
stimulation.
[0045] Advantageously, the methods describe herein provide a means
for recovery useful catalytic gas from heavy hydrocarbons in situ
from subterranean formations. When used in situ at the site of a
formation, the conversion of heavy hydrocarbon extends the useful
lifetime of reservoir enhancing the oil recovery process. The same
process may be duplicated under controlled conditions in batch
reactors for commercial production of natural gas. Furthermore, the
availability of certain heavy hydrocarbons, such as bitumen, from
renewable resources may provide an environmentally sound means for
natural gas production.
[0046] All patents and publications referenced herein are hereby
incorporated by reference to the extent not inconsistent herewith.
It will be understood that certain of the above-described
structures, functions, and operations of the above-described
embodiments are not necessary to practice the present invention and
are included in the description simply for completeness of an
exemplary embodiment or embodiments. In addition, it will be
understood that specific structures, functions, and operations set
forth in the above-described referenced patents and publications
can be practiced in conjunction with the present invention, but
they are not essential to its practice. It is therefore to be
understood that the invention may be practiced otherwise than as
specifically described without actually departing from the spirit
and scope of the present invention as defined by the appended
claim.
[0047] From the foregoing detailed description of specific
embodiments of the invention, it should be apparent that a novel
method for converting bitumen to natural gas has been disclosed.
Although specific embodiments of the invention have been disclosed
herein in some detail, this has been done solely for the purposes
of describing various features and aspects of the invention, and is
not intended to be limiting with respect to the scope of the
invention. It is contemplated that various substitutions,
alterations, and/or modifications, including but not limited to
those implementation variations which may have been suggested
herein, may be made to the disclosed embodiments without departing
from the spirit and scope of the invention as defined by the
appended claims which follow.
* * * * *