U.S. patent application number 11/565590 was filed with the patent office on 2007-06-28 for coal bed pretreatment for enhanced carbon dioxide sequestration.
This patent application is currently assigned to HCE, LLC. Invention is credited to Meyer Steinberg.
Application Number | 20070144747 11/565590 |
Document ID | / |
Family ID | 38226486 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144747 |
Kind Code |
A1 |
Steinberg; Meyer |
June 28, 2007 |
COAL BED PRETREATMENT FOR ENHANCED CARBON DIOXIDE SEQUESTRATION
Abstract
A method is claimed for enabling storage of greater volumes of
carbon dioxide for sequestration while simultaneously enhancing
methane recovery from the coal bed. The process is implemented by
injecting hydrogen into a coal bed, such as a depleted underground
coal deposit, at a temperature below about 800 degrees Centigrade
(10); extracting the hydrogen together with methane from the
deposit (20); separating the hydrogen from the methane (30);
delivering the methane as a product of the process (40);
reinjecting the separated hydrogen into the deposit to continue the
process until sequestration of carbon dioxide is desired (50);
optionally producing hydrogen from methane (60) and optionally
injecting carbon dioxide for sequestration (70).
Inventors: |
Steinberg; Meyer; (Melville,
NY) |
Correspondence
Address: |
LOUIS VENTRE, JR
2483 OAKTON HILLS DRIVE
OAKTON
VA
22124-1530
US
|
Assignee: |
HCE, LLC
2483 Oakton Hills Dr.
Oakton
VA
22124-1530
|
Family ID: |
38226486 |
Appl. No.: |
11/565590 |
Filed: |
November 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60597447 |
Dec 2, 2005 |
|
|
|
Current U.S.
Class: |
166/402 |
Current CPC
Class: |
E21B 43/164 20130101;
E21B 43/006 20130101; E21B 41/0064 20130101; E21B 43/16 20130101;
Y02P 90/70 20151101; Y02C 20/40 20200801 |
Class at
Publication: |
166/402 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Claims
1. A process for pretreating an underground coal bed to enhance the
potential for carbon dioxide sequestration and to enhance methane
production comprising the steps of, injecting hydrogen into an
underground coal bed, wherein the hydrogen is at a temperature
below about 800 degrees Centigrade; extracting hydrogen and methane
from the coal bed; separating the hydrogen from the methane;
delivering the methane as a product of the process; and reinjecting
the separated hydrogen into the deposit to continue the process
until the deposit is no longer productive or until sequestration of
carbon dioxide is desired.
2. The process of claim 1 further comprising the step of cleaning
the extracted methane and hydrogen to remove contaminants.
3. The process of claim 1 further comprising the step of injecting
carbon dioxide for sequestration after the last step.
4. The process of claim 1 further comprising the step of producing
hydrogen from a portion of the methane to replenish lost hydrogen
in the process.
5. The process of claim 1 further comprising the step of collecting
the separated hydrogen for resale or reuse after the last step.
6. The process of claim 1 wherein both the step of injecting and
the step of extracting are performed using at least one borehole
into the deposit.
7. The process of claim 1 wherein the step of injecting is
performed using at least one borehole into the deposit and the step
of extracting is performed using at least one borehole different
than any borehole used for injecting the hydrogen.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. section 119(e), the present invention
claims the benefit of the filing date of United States provisional
application No. 60/597,447 filed 02 Dec. 2005, the text of which is
hereby incorporated by reference herein.
FIELD OF INVENTION
[0002] In the field of carbon dioxide sequestration, a coal bed
pretreatment process using hydrogen for increasing the storage
potential of an underground coal deposit and enhancing production
of methane.
DESCRIPTION OF PRIOR ART
[0003] Methods for adjusting the porosity and permeability of an
underground coal bed have been practiced using the injection of
fluids. However, none propose the use of hydrogen alone as a fluid
displacing methane from the pores of an underground coal bed to
enhance the carbon dioxide storage capability of the coal bed.
[0004] Enhanced coal bedded methane recovery is currently under
development using carbon dioxide injection prior to carbon dioxide
sequestration in the coal bed. For enhanced coal bedded methane
recovery, the carbon dioxide is injected into depleted coal bedded
methane coal beds, which are usually located deep underground in
otherwise unminable coal seams. The injected carbon dioxide
displaces methane naturally present in the coal bed, and releases
it for recovery.
[0005] The yield of methane can be about 1 mole of methane for 2
moles of injected carbon dioxide, which is very significant for
sequestering carbon dioxide. However, this yield quickly drops off
because the carbon dioxide tends to swell the coal and tends to
block the passage of the methane out of the coal deposit.
[0006] Coal permeability and porosity is significantly diminished
by the injection of carbon dioxide. The theory is that carbon
dioxide is a large molecule, which gets adsorbed on the surface of
the coal in the pores. This adsorption then blocks the methane from
getting out of the coal once the pressurized and easily displaced
molecules of methane are released, and pumped out of the coal
seam.
[0007] The present invention is a coal bed pretreatment process
that increases the potential of the coal bed to store carbon
dioxide and recover more methane from the coal bed than can be
recovered using carbon dioxide.
[0008] As is the case in the known process of carbon dioxide
sequestration, the present invention preferably uses an injection
well and a production well. Hydrogen is injected into one well and
flushed through the coal bed to exit from a production well along
with methane. The difference is that hydrogen and not carbon
dioxide is used first to flush out methane trapped in the coal bed.
In the process of the invention, methane is separated from the
hydrogen and methane exiting the production well, and then sold.
The main effect of using the method of the invention is that more
methane is harvested and the coal bed has greater storage potential
for carbon dioxide sequestration. When the hydrogen pretreatment
process is completed, the hydrogen is captured and used again at
another location.
[0009] Hydrogen in combination with water has been proposed to
extract oil from depleted wells. For example, U.S. Pat. No.
4,241,790 to Magnie on Dec. 30, 1980 teaches recovery of crude oil
utilizing hydrogen. The '790 patent teaches injection of hydrogen
into an underground petroleum reservoir that is devoid of natural
gas. Hydrogen is diffused into the crude oil within the reservoir,
changing the physical properties of the oil. After the crude oil is
saturated with hydrogen, the pressure is lowered in the reservoir.
Hydrogen then migrates from the tight portions of the reservoir,
sweeping petroleum into the more permeable portions. A water sweep
then displaces the oil to production wells. The present invention
is different in that it uses hydrogen to displace methane a gaseous
energy resource.
[0010] Unlike the '790 disclosure, a coal bed is not devoid of
methane. It is the adsorbed and intersticial methane in the coal
bed that can be displaced with the hydrogen and recovered. Methane
displacement creates greater space within the coal bed for carbon
dioxide storage. In the present invention, hydrogen is used in a
coal bed and not in an oil reservoir to diffuse with oil. The
physical mechanisms are completely different from those in the '790
patent and serve a different function. Also, the method of the
present invention does not use hydrogen in combination with water
as taught in the '790 disclosure.
[0011] Prior art also describes using hydrogen and steam in an oil
deposit to extract petroleum. U.S. Pat. No. 4,597,441 to Ware, et
al. on Jul. 1, 1986 is an example of such prior art. The '411
patent teaches a method of recovering petroleum from underground
formations penetrated by a production well, superheated steam and
then hot hydrogen are injected by way of the well into a preheated
formation zone next to the well. The hydrogen is injected under
sufficient pressure to cause hydrogenation of the petroleum in the
heated zone. The '411 patent does not teach the use of hydrogen to
displace methane and is confined to an oil well to produce oil by a
chemical process, namely hydrogenation. The present invention does
not involve the use of steam or heating of the coal bed. A
significant element of the '411 patent is thus omitted in the
present invention. The present invention is further distinguished
because it not functional through hydrogenation of oil, nor by
extension to the hydrogenation of coal.
[0012] The use of hydrogen as a coal bed pretreatment in the
present invention will maximize recovery of methane from a coal
bedded methane deposit. Enhanced methane recovery is achieved by
avoiding the coal bed swelling, blockage and interference of
methane extraction from a coal bed found to occur when using carbon
dioxide alone.
[0013] Another important fact relative to gas recovery from coal
bed is that, from a processing point of view, injection of any gas,
whether carbon dioxide or hydrogen in a coal seam, will mix with
the displaced methane. When gas is extracted, it is necessary to
separate the methane from the injected gas in order to produce a
methane product and to recycle the displacing gas. This separation
process consumes energy and generally, the larger the difference in
the molecular weight of the gases being separated, the lower the
energy consumption. The energy performance can thus be indicated by
the molecular weight ratio of the gases being separated.
[0014] The molecular weight ratio of methane to hydrogen (MW ratio
16/2) is 8. This compares to a molecular weight ratio of methane to
carbon dioxide (MW ratio 16/44) of 0.36. So, the ratio for methane
to hydrogen is about 22 times that of methane to carbon dioxide.
The much larger molecular weight ratio of methane to hydrogen means
that it takes much less energy to separate the methane from
hydrogen than it takes to separate methane from carbon dioxide. In
fact, hydrogen can be readily separated from the methane by
membrane diffusion. The present invention, therefore, improves on
the energy efficiency of enhanced coal bedded methane extraction
over that obtainable with carbon dioxide.
[0015] While hydrogen is a more expensive gas than carbon dioxide,
hydrogen can be recycled. The actual cost will be limited to the
loss of hydrogen in the resource deposit and in recycling.
[0016] The loss of hydrogen is expected to be minimal. Coal bedded
methane wells are closed systems, otherwise the methane would have
leaked away over the centuries. However, the process optionally
makes up for any loss of hydrogen by reforming some of the methane
produced, so that there is no diminishment in the volume of the
hydrogen working fluid.
[0017] For a gas tight well, hydrogen consumption is expected to be
minimal, since it is all recycled. When methane extraction is
completed, hydrogen filling the depleted well under pressure is
pumped out to recover the hydrogen. This is advantageous because
with the evacuated coal bed at lower pressure, the capacity to
store carbon dioxide is enhanced.
[0018] The invention will, therefore, enhance coal bedded methane
recovery by employing a recycling working fluid, hydrogen, that
does not require the purchase of hydrogen from market sources. More
methane removed from the coal bed means that the coal bed will
store that much more carbon dioxide.
[0019] Water can be an environmental pollution problem in coal
bedded methane recovery, but may not be a significant effluent in
some sites. Water present in a coal seam is usually pumped out with
the methane and some of the enhanced methane recovery working
fluid. In traditional enhanced methane recovery process using
carbon dioxide, the problem is that carbon dioxide is relatively
soluble in the water especially under pressure and it forms
carbonic acid. This presents two sources of pollution, one from the
carbonic acid and the other from the release of carbon dioxide back
to the environment.
[0020] In contrast, the present invention's use of hydrogen as the
enhanced methane recovery working fluid avoids this environmental
pollution problem. Hydrogen is much less soluble and less corrosive
than aqueous carbon dioxide. This means that the hydrogen can be
more easily separated from water than carbon dioxide and its ease
of separation from water are significant advantages to using
hydrogen instead of carbon dioxide for enhanced coal bedded methane
production.
[0021] The invention, therefore, avoids the potential environmental
pollution associated with the dissolution of carbon dioxide in
water and the re-release of dissolved carbon dioxide to the
environment in the enhanced coal bedded methane recovery process.
The invention also minimizes energy consumption in separating the
working fluid from the methane.
[0022] Hydrogen is a less adherent gas on coal surfaces than either
carbon dioxide or methane. One gram of charcoal at 15 degrees
Centigrade can adsorb 48 cubic centimeters of carbon dioxide, 16.2
cubic centimeters of methane and only 4.7 cubic centimeters of
hydrogen, which is indicative of the relative adsorptive capacity
of a coal carbon structure.
[0023] Hydrogen can also reduce the partial pressure of methane in
the coal seam, which is an additional driving force for liberating
methane from the surfaces of the coal.
[0024] Hydrogen has been proposed as a means to chemically react
with the carbon in a coal seam to form methane. U.S. Patent
Publication 2006/021,940 by Steinberg for a pumped carbon mining
process represents this prior art. The present invention is
distinguished from the pumped carbon mining process in that
hydrogen is pumped into the coal seam or oil field at a temperature
below that at which significant quantities of carbon in the coal
will be extracted from the coal seam by chemical combination with
the hydrogen.
[0025] The pumped carbon mining process disclosed in the '940
application removes carbon from the coal seam, creating a much
larger storage space than exists in the coal bed. In the present
invention, minimal quantities of carbon may be removed, but is
fundamentally different because the present invention operates at
much lower temperatures and is primarily directed at displacing and
removing adsorbed and intersticial methane in the coal bed.
[0026] Accordingly, the present invention will maximize carbon
dioxide sequestration potential of an underground coal bed by
recovery of greater quantities of methane than is possible using
carbon dioxide for this purpose. The present invention improves on
the prior art by avoiding the coal bed swelling, blockage and
interference of methane extraction from a coal bed by carbon
dioxide. The present invention improves the energy efficiency of
enhanced coal bedded methane extraction over that obtained with
carbon dioxide. The present invention enhances coal bedded methane
recovery by using a recycling working fluid, hydrogen, that does
not require the purchase of hydrogen from market sources to
continue the process. The present invention permits a maximization
of carbon dioxide storage capacity of a coal seam. The present
invention avoids potential environmental pollution associated with
the dissolution of carbon dioxide in water and the re-release of
dissolved carbon dioxide to the environment in the known enhanced
methane recovery process using carbon dioxide. The present
invention minimizes energy consumption in separating the working
fluid from the methane. The present invention provides a
pretreatment process for an underground coal bed to enable storage
of greater volumes of carbon dioxide for sequestration while
simultaneously enhancing methane recovery from the coal bed.
BRIEF SUMMARY OF THE INVENTION
[0027] A process enables storage of greater volumes of carbon
dioxide for sequestration while simultaneously enhancing methane
recovery from the coal bed. The process is implemented by injecting
hydrogen into a coal bed, such as a depleted underground coal
deposit, at a temperature below about 800 degrees Centigrade;
extracting the hydrogen together with methane from the deposit,
separating the hydrogen from the methane; delivering the methane as
a product of the process; reinjecting the separated hydrogen into
the deposit to continue the process until sequestration of carbon
dioxide is desired; optionally producing hydrogen from methane and
optionally injecting carbon dioxide for sequestration (70).
BRIEF DESCRIPTION OF THE DRAWING
[0028] The drawing is a flow diagram of the preferred embodiments
of the process.
DETAILED DESCRIPTION OF THE INVENTION
[0029] In the following description, reference is made to the
accompanying drawing, which forms a part hereof and which
illustrates several embodiments of the present invention. The
drawing and the preferred embodiments of the process are presented
with the understanding that the present invention is susceptible of
embodiments in many different forms and, therefore, other
embodiments may be utilized and operational changes may be made
without departing from the scope of the present invention.
[0030] The process employs hydrogen for pretreating an underground
coal bed to enhance: (1) the potential for carbon dioxide
sequestration by removing adsorbed methane and methane trapped
within pores of the coal bed, and (2) methane production.
[0031] There are five fundamental steps to the base process. 1.
injecting hydrogen into an underground coal bed, wherein the
hydrogen is at a temperature below about 800 degrees Centigrade; 2.
extracting hydrogen and methane from the coal bed; 3. separating
the hydrogen from the methane; 4. delivering the methane as a
product of the process; and 5. reinjecting the separated hydrogen
into the deposit to continue the process until the deposit is no
longer productive or until sequestration of carbon dioxide is
desired.
[0032] The first step is injecting hydrogen into the underground
coal bed, wherein the hydrogen is at a temperature below about 800
degrees Centigrade (10). For the typical embodiments, the coal bed
is an underground coal deposit that has already undergone coal
bedded methane removal, which typically leaves a significant amount
of methane that is adsorbed on the surface of coal and trapped
within minute pores of the coal bed.
[0033] Hydrogen is injected at a temperature below that in which
significant hydrogasification of the resource occurs, that is
namely about 800 degrees Centigrade. Hydrogen is preferably at any
convenient temperature and no special temperature below the maximum
temperature is required. Hydrogen temperature in a preferred
embodiment is typically at ambient temperature, since the hydrogen
at any convenient temperature will displace bound or adsorbed
methane and will penetrate into the pores of the coal bed
displacing and releasing the methane found in these pores.
Penetration into the pores is facilitated by the low molecular
weight and small molecular size of hydrogen. The upper limit on
hydrogen temperature is specified because a chemical reaction
forming new methane, called hydrogasification, predominates above
about 800 degrees Centigrade. The subject invention is principally
directed at methane displacement and not formation of new methane
from the chemical combination of hydrogen with the carbon in the
coal. The pressure required for hydrogen injection is that needed
to circulate the hydrogen through the underground coal deposit.
[0034] Typically, at least one borehole will be utilized for
injecting hydrogen. There is no limit on the number of boreholes
that may be used to inject the hydrogen into the deposit.
[0035] The second step in the process is extracting hydrogen and
methane from the coal bed (20). The methane released from the
hydrogen injection of the first step mixes with the hydrogen to
create a gaseous product, which is what is extracted from the coal
bed. Extraction is typically accomplished either by simply allowing
the production gas to flow to the surface, or by pumping the gas
mixture to the surface through the same borehole. The hydrogen and
methane mixture is the "production gas," but, as with any such
process, probably includes contaminant gases and unwanted
particulate matter.
[0036] In one embodiment, the step for extracting is performed
using one borehole and this is typically the same borehole used for
injection. In alternate embodiments more than one borehole is used
for extraction, whether or not these are the same boreholes as used
for injecting the hydrogen. For example, in some coal bedded
methane deposits, a single injection borehole is fluidly connected
to numerous surrounding extraction boreholes and these boreholes
may be used in substantially the same manner for the present
invention.
[0037] If the production gas contains contaminant gases, such as
carbon dioxide gas, the production gas may be cleaned using
well-known processes, such as pressure swing adsorption, membrane
diffusion, solvent absorption-stripping, or cryogenic treatment.
Particulate contaminates would typically be removed by filtration,
but other methods are well known in the art.
[0038] The third step is separating the hydrogen from the methane
in the production gas (30). Processes to separate gasses are well
known in the art. For example, hydrogen can be readily separated
from the methane by membrane diffusion. Separation of the hydrogen
from the energy commodities is necessary to enable the recycling of
the hydrogen back into the deposit to continue the process and to
enable production of one or more energy products from the
process.
[0039] The fourth step is delivering the methane as a product of
the process (40). Once separated from the production gas, the
methane is a valuable energy commodity that may be sold or used for
other purposes.
[0040] The fifth step in the basic process is reinjecting the
separated hydrogen into the deposit to continue the process until
the deposit is no longer productive or until sequestration of
carbon dioxide is desired (50). This step in the process is
intended to continue the methane recovery process until it is
determined that the process is not producing sufficient quantities
of methane to merit continuation. However, the process may be
stopped at any time either to halt operations or to begin injecting
carbon dioxide for sequestration.
[0041] Once the methane production operation is stopped, the
deposit may be used for sequestration of carbon dioxide. An
embodiment of the invention therefore includes a step of injecting
carbon dioxide for sequestration (70). Of course, the process might
be used only to provide for enhanced methane recovery and not for
carbon dioxide sequestration. However, while perhaps low in cost,
simple recovery of methane is less than optimal use of this
process. If such an operation were to be desired, it would be far
more efficient and cost effective based on the total resources
available to process the deposit with hot, pressurized hydrogen
using the pumped carbon mining process. While having a larger front
end cost, the pumped carbon mining process would yield far more
methane than with the present invention. However, even though the
present invention would be far less efficient based on the total
resource available, it could still be operated principally as a
means for enhanced methane recovery.
[0042] In an optimized process, an additional step may be needed to
produce hydrogen from the methane to replenish hydrogen lost either
in the deposit or in processing. Thus, in this embodiment, the
process further includes a step of producing hydrogen from a
portion of any separated methane to replenish lost hydrogen in the
process (60). Typically, such step would involve steam reforming
methane produced from the deposit. Steam reforming methods are well
known in the art.
[0043] At the end of the methane recovery process, an embodiment of
the process includes a step of collecting the separated hydrogen
for resale or reuse (80). This is an optional step considering that
one may simply decide to sell the hydrogen with the methane or burn
off or discharge the hydrogen. Considering its cost, however, it
should be economically attractive to capture and sell the hydrogen
separately.
[0044] In an embodiment of the invention where the hydrogen is
collected at the end of the commodity recovery process, a step is
included for injecting carbon dioxide (90) for sequestration.
[0045] The disclosure herein is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the broad aspect of the invention to the
embodiments illustrated. Thus, the scope of the invention is
determined by the appended claims and their legal equivalents
rather than by the examples given.
* * * * *