BIOGENIC FUEL GAS GENERATION IN GEOLOGIC HYDROCARBON
DEPOSITS
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority from co-pending U.S. Non-Provisional Patent
Application No. 12/639,483, filed December 16, 2009. The entire contents of the above-
identified application is herein incorporated by this reference for all purposes.
[0002] This application is related to U.S. App. Ser. No. 12/129,441, filed May 29, 2008, which
was a continuation of U.S. App. Ser. No. 11/343,429, filed Jan. 30, 2006, which was a
continuation-in-part of International Application PCT/US2005/015259, with an international
filing date of May 3, 2005. The entire contents of all the above-identified applications are herein
incorporated by this reference for all purposes.
BACKGROUND OF THE INVENTION
[0003] The formation water present in subterranean geologic formations of oil, coal, and other
carbonaceous materials is normally considered an obstacle to the recovery of materials from
those formations. In coal mining, for example, formation water often has to be pumped out of
the formation and into remote ponds to make the coal accessible to mining equipment.
Similarly, formation water has to be separated from the crude oil extracted from a subterranean
field and disposed of typically underground. The extraction, separation and disposal of the
formation water add costs to recovery processes, and generate a by-product regarded as having
little value.
[0004] Further investigation, however, has revealed that even extracted formation water can
support active communities of microorganisms from the formation. The presence of these
microorganisms in the formation environment were known from previous recovery applications,
such as microbially enhanced oil recovery (MEOR), where the microorganisms naturally
generate surface active agents, such as glycolipids, that help release oil trapped in porous
substrates. In MEOR applications, however, it was generally believed that the microorganisms
were concentrated in a boundary layer between the oil and water phases. The bulk formation
water was believed to be relatively unpopulated, because it lacked the proper nutrients for the
microorganisms. More recent studies have shown that robust populations of microorganisms do
exist in the bulk formation water, and can even survive extraction from the geologic formation
under proper conditions.
[0005] The discovery of active populations of microorganisms in bulk formation water has
come at a time when new applications are being envisioned for these microorganisms. For years,
energy producers have seen evidence that materials like methane are being produced
biogenically in formations, presumably by microorganisms metabolizing carbonaceous
substrates. Until recently, these observations have been little more than an academic curiosity,
as commercial production efforts have focused mainly on the recovery of coal, oil, and other
fossil fuels. However, as supplies of easily recoverable natural gas and oil continue to dwindle,
and interest grows using more environmentally friendly fuels like hydrogen and methane,
biogenic production methods for producing these fuels are starting to receive increased attention.
[0006] Unfortunately, the techniques and infrastructure that have been developed over the past
century for energy production (e.g., oil and gas drilling, coal mining, etc.) may not be easily
adaptable to commercial-scale, biogenic fuel production. Conventional methods and systems for
extracting formation water from a subterranean formation have focused on getting the water out
quickly, and at the lowest cost. This is particularly evident in coal bed methane (CBM)
production. Little consideration has been given to extracting the water in ways that preserve the
microorganisms living in the water, or preserve the water resource. Similarly, there has been
little development of methods and systems to harness microbially active formation water for
enhancing biogenic production of hydrogen, methane, and other metabolic products of the
microbial digestion of carbonaceous substrates. Thus, there is a need for new methods and
systems of extracting, treating, and transporting formation water within, between, and/or back
into geologic formations, such that microbial activity in the water can be preserved and even
enhanced.
[0007] New techniques are also needed for stimulating microorganisms to produce more
biogenic gases. Native consortia of hydrocarbon consuming microorganisms usually include
many different species that can employ many different metabolic pathways. If the environment
of a consortium is changed in the right way, it may be possible to change the relative populations
of the consortium members to favor more combustible gas production. It may also be possible to
influence the preferred metabolic pathways of the consortium members to favor combustible
gases as the metabolic end products. Thus, there.is also a need for processes that can change a
formation environment to stimulate a consortium of microorganisms to produce more
combustible biogenic gases.
BRIEF SUMMARY OF THE INVENTION
[0008] Methods are described for flowing aqueous liquids, such as formation water, through
carbonaceous materials inside anaerobic geologic formations. The flowing liquid may have
functions analogous to a circulatory system in a living organism by delivering nutrients and
removing wastes from microorganisms in contact with the flowing fluid. The flowing liquid
may also function as a transport mechanism that disperses the microorganisms to new areas of
carbonaceous material, which can increase both their rate of population growth and biogenic gas
production. These methods may include inducing fluid flow events on a regular or semi-regular
basis in the anaerobic formation to maintain or increase the rate of biogenic gas production. The
fluid for these fluid flow events may be provided by an external fluid source introduced to the
formation, or fluid already present in the formation (e.g., formation water).
[0009] Embodiments of the invention include methods to enhance biogenic gas production in
an anaerobic geologic formation containing carbonaceous material. The methods may include
the step of accessing the anaerobic formation. They may also include increasing a rate of
production of the biogenic gases in the anaerobic formation, and flowing formation water within
the anaerobic formation after the increase in the production of biogenic gases.
[0010] Embodiments of the invention also include methods to redistribute formation water in
an anaerobic geologic formation containing carbonaceous material. The methods may include
the step of locating a reservoir of the formation water within the anaerobic formation. The
methods may further include forming at least one channel between the reservoir of formation
water and at least a portion of the carbonaceous material, and transporting the formation water
from the reservoir to the carbonaceous material through the channel.
[0011] Embodiments of the invention further include methods of accumulating biogenic gas in
an anaerobic geologic formation to enhance biogenic gas production. The methods may include
the step of holding the accumulating biogenic gas in the anaerobic formation to increase gas
pressure in at least a part of the anaerobic formation. The methods may also include driving
formation water through carbonaceous material in the anaerobic formation in response to the
increased gas pressure. The flow of the formation water through the carbonaceous material may
further increase the. rate of biogenic gas production in the anaerobic formation.
[0012] Additional embodiments and features are set forth in part in the description that
follows, and in part will become apparent to those skilled in the art upon examination of the
specification or .may be learned by the practice of the invention. The features and advantages of
the invention may be realized and attained by means of the instrumentalities, combinations, and
methods described in the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] A further understanding of the nature and advantages of the present invention may be
realized by reference to the remaining portions of the specification and the drawings wherein like
reference numerals are used throughout the several drawings to refer to similar components. In
some instances, a sublabel is associated with a reference numeral and follows a hyphen to denote
one of multiple similar components. When reference is made to a reference numeral without
specification to an existing sublabel, it is intended to refer to all such multiple similar
components.
[0014] Figs. 1A-B show flowcharts with selected steps in methods of enhancing biogenic gas
production according to embodiments of the invention;
[0015] Fig. 2 shows a flowchart with selected steps of in methods of redistributing formation
water in anaerobic geologic formations according to embodiments of the invention;
[0016] Figs. 3 A & B show simplified cross-rsections of a geologic formations containing
formation water reservoirs according to embodiments of the inventions; and
[0017] Fig. 4 shows a flowchart with selected steps in methods of accumulating biogenic gas
in an anaerobic geologic formation to enhance biogenic gas production according to
embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] There is increasing evidence that the circulation of water in an anaerobic geologic
formation increases the rate of biogenic gas production in the formation. While the water itself
may not be a nutrient or activation agent for microorganisms producing the gas, the properties of
flowing water as a transport medium for nutrients, activation agents and other compounds, as
well as a transport medium for the dispersal of microorganisms, plays a role in enhancing
biogenic gas production. Flowing water may also help carry away and dilute the waste products
and other compounds that may have an inhibitory effect on microorganism grown and metabolic
rates.
[0019] The source of the flowing water may come from outside the anaerobic formation, or
may be found within the formation. Sources outside the formation may include treated water
transported to the formation, and formation waters supplied from one or more separate geologic
formations. Sources within the formation may include reservoirs of formation water inside the
anaerobic formation that have limited or no contact with carbonaceous material that can provide
a nutrient substrate for methanogenic microorganisms.
[0020] Referring now to Fig. 1A, selected steps in methods 100 of enhancing biogenic gas
production according to embodiments of the invention are shown. The methods 100 may include
the step of accessing carbonaceous material 102 in an anaerobic geologic formation. The
carbonaceous material may include bituminous coal, subbituminous coal, anthracite, oil,
carbonaceous shale, oil shale, tar sands, tar, lignite, kerogen, bitumen, and peat, among other
carbonaceous materials. The anaerobic geologic formation that holds the carbonaceous material
may be a previously explored formation such as a coal field, oil field, natural gas deposit, or
carbonaceous shale deposit, among other formations. In many instances, the formation may be
accessed through previously mined or drilled access points used to recover carbonaceous
material. For previously unexplored formations, access may involve digging or drilling through
a surface layer to access an underlying site containing carbonaceous material.
[0021] The geologic formation may be a subterranean anaerobic formation. Because sub-
surface formation environments typically contain less free atmospheric oxygen (e.g., O2) than
found in tropospheric air, the formation environment may be described as anaerobic. These
anaerobic formation environments may support microorganisms that can live and grow in an
atmosphere having less free oxygen than tropospheric air (e.g., less than about 18% free oxygen
by mol.). In some instances, microorganisms may operate in a low oxygen atmosphere, where
the O2 concentration is less than about 10% by mol., or less than about 5% by mol., or less than
about 2% by mol., or less than about 0.5% by mol.
[0022] Once the anaerobic formation has been accessed, actions may be taken to increase the
production rate of biogenic gases 104 in the formation. These actions may include introducing a
chemical amendment or nutrient to the formation, such as an acetate-containing compound, a
phosphorous-containing compound, a yeast extract, a hydrogen-containing compound (e.g., H2),
among other compounds and combinations of compounds. These actions may also include
introducing a consortium of microorganisms to the formation, such as a consortium capable of
anaerobic biogenic gas production (e.g., methanogenesis). These actions may further include
introducing water to the anaerobic formation.
[0023] Following an action to increase the production rate of biogenic activity, the rate of
biogenic gas production may be measured to determine if the action was successful in increasing
the production rate.. For example, recovery rates for natural gas (e.g., methane and/or other light
hydrocarbons) at a wellhead having access to the formation may be measured on a periodic basis
(e.g., daily, weekly, monthly, etc.). A significant increase in the recovery rate following the
action is indicative of a successful action to increasing the production rate of biogenic gas.
[0024] Following the increase in the biogenic gas production rate, formation water may be
made to flow within the formation 106. The flowing formation water may maintain or further
increase the biogenic gas production rate in the formation. The source of the formation water
come from outside the formation, or may come from a reservoir within the formation. Sources
of formation water from outside the formation may include formation water supplied from one or
more separate formations (e.g., inter-formation transport) and/or formation water extracted and
resupplied to the same formation (e.g., intra-formation circulation).
[0025] The formation water may be anaerobic formation water. "Anaerobic" formation water
is characterized as having little or no dissolved oxygen, in general no more than 4 mg/L,
preferably less than 2 mg/L, most preferably less than 0.1 mg/L, as measured at 20 °C and 760
mmHg barometric pressure. During application of the present invention, higher levels of
dissolved oxygen, greater than 4 mg/L, can be tolerated without appreciably degrading
microorganism performance, for limited times or in certain locations such as a surface layer in a
storage or settling tank. Dissolved oxygen can be measured by well-known methods, such as by
commercially-available oxygen electrodes, or by the well-known Winkler reaction.
[0026] The formation water may also be tested and/or treated to further enhance biogenic gas
production. For example, the formation water may be tested to measure properties such as
microorganism nutrient levels, pH, salinity, oxidation potential (Eh), and metal ion
concentrations, among other properties. An amendment may be added to correct for an
imbalance, deficiency, or excess in one or more of these properties. Amendments may also be
added that are unprompted by the testing. Formation water treatments may also include filtering
and/or processing the reduce the concentration of one or more chemical and/or biological species
in the formation water.
[0027] Fig. 1B shows selected steps in methods 150 of enhancing biogenic gas production
according toembodiments of the invention. The methods 150 may include the steps of accessing
carbonaceous material 152 in an anaerobic geologic formation, and flowing formation water
through the formation 154. Flowing the formation water may involve circulating the formation
water between a reservoir in the anaerobic formation and carbonaceous material that is also
found in the formation. The circulation of the formation water may involve a continuous or
near-continuous transportation of water between the reservoir and carbonaceous material.
Alternatively, the formation water may be circulated at discontinuous intervals (e.g., periodic
intervals) between the reservoir and carbonaceous material. For example, a portion of the
reservoir water may be transported to the carbonaceous material over a short period of time,
which is followed by a longer period where the formation water stays in contact with the material
before returning to the reservoir. At the end of the longer period, the formation water may be
recirculated to the carbonaceous material.
[0028] As the formation water flows over and/or through the carbonaceous material transports
microorganisms, chemical amendments, nutrients, and other materials across a larger volume of
the carbonaceous material. This increases the contact area (e.g., surface area) between the
carbonaceous material and the migrating microorganisms 156. As the microorganisms are
exposed to more nutrients and activators with less crowding from other microorganisms, the rate
of production of biogenic gases can start to increase 158. Increased biogenic gas production may
also be facilitated by the removal of wastes and other inhibitory substances from the
microorganism living environment.. When the formation water is circulated on a regular or
continuous basis through the carbonaceous material, ability of the circulating water to supply
nutrients, disperse microorganisms, and remove wastes can further enhance the rate of biogenic
gas production in the formation.
[0029] Fig. 2 shows selected steps in methods 200 of redistributing formation water in
anaerobic geologic formations according to embodiments of the invention. As noted above, one
source of formation water is a reservoir within the anaerobic formation. Methods 200 include
the step of locating formation water in such a reservoir in the geologic formation 202. As further
described below with reference to Figs. 3A & 3B, the reservoir may be positioned above or
below carbonaceous material in the formation. Alternatively, the reservoir may longitudinally
traverse the carbonaceous material such that there may be an upper portion of the reservoir above
the carbonaceous material and/or a lower portion of the reservoir below the carbonaceous
material.
[0030] The formation water reservoir may have little or no fluid contact with targeted
carbonaceous material in the formation that may benefit from the flow of the formation water to
enhance biogenic methane production. The methods 200 include the step of forming one or
more channels, between the reservoir and the carbonaceous material 204. The channel may be
formed using drilling equipment that drills the channel through a barrier in the formation (e.g.,
bedrock) that inhibits contact or flow of formation water between the reservoir and carbonaceous
material. Alternatively, the barrier may be fractured by mechanical impact or an explosion to
form an opening or crack that acts as the channel. The channel can act as a conduit for
transporting the formation water from the reservoir to the carbonaceous material 206.
[0031] In an optional step, the partially or fully drained reservoir may be refilled by supplying
additional water to the reservoir 208. The added water in the reservoir may maintain the
transport of the formation water over and/or through the carbonaceous material. The added
water may also further distribute microorganisms, nutrients and other materials over a larger
volume of the carbonaceous material, as well as allowing these materials to penetrate further into
the fractures, cleats, and microchannels of the carbonaceous material. This water may be
formation water that is transported from another part of the same geologic formation (i.e., intra-
formation transport) or from another formation (i.e., inter-formation transport). The water may
also be sourced from outside a geologic formation, such as a surface water source.
[0032] Methods are also contemplated for refilling channels in the formation with water. In
some cases, the channels are in fluid communication with a reservoir of formation water. In
other cases, the channels are not connected.to a reservoir, and may be formed (e.g., drilled)
directly into carbonaceous material in the formation. Examples of these channels may further
include well bores that were previously used to recover natural gas or other carbonaceous
material from the formation. The water used to fill these channels may be formation water, or
water from another source.
[0033] When a reservoir is located above the carbonaceous material like Fig. 3A below, one or
more channels may be formed to permit gravity to transport the reservoir formation water to the
underlying carbonaceous material. In this example, the reservoir may be said to be perforated to
permit a waterfall of the formation water to flow down (or rain down) on the carbonaceous
material. The example may also include transporting the formation water back to the reservoir
using a mechanical pump or other pumping means, so the water can re-circulate to the
carbonaceous material through the one or more channels.
[0034] In another example, the reservoir may be located below the carbonaceous material like
Fig. 3B below. The channel may be formed by drilling through the carbonaceous material and
barrier between the material and underlying reservoir. The drilling may form one or more
channels in the barrier that permits the formation water to be transported through the channel and
contact the carbonaceous material. For example, a plurality of channels may be formed, and at
least one channel or perforation may be coupled to a source of pressure that can force formation
water through the other channels to the carbonaceous material. Alternatively, one or more of the
channels may be fitted with a mechanical pump to transport water against gravity from the
reservoir to the overlying carbonaceous material.
[0035] If there is a headspace above the carbonaceous material, the underlying reservoir may
be sufficiently pressurized to push the formation water above the carbonaceous material before is
showers down on a top surface of the carbonaceous material. The formation water may then be
allowed to fall back down the reservoir before being pumped again over the top of the
carbonaceous material,
[0036] The methods 200 source and circulate the formation water from within the formation,
which can have advantages over supplying the water from outside the formation. Significantly
less energy is required to transport the reservoir formation water to the carbonaceous material,
than water from outside the formation. Outside water may be pumped and/or trucked over
significant distances (e.g., tens to hundreds of miles) before reaching the formation at a
substantial expenditure of energy. In addition, an underground reservoir provides a natural
storage facility for the formation water that may be difficult and expensive to replicate on the
surface. For example, increasingly strict environmental regulations make it difficult to create a
water storage pool or reservoir on land, especially if the water is contaminated with
hydrocarbons.
[0037] Referring now to Fig. 3 A, a simplified cross-section of a portion of a geologic
formation 300 is shown that includes a formation water reservoir 304 positioned above a deposit
of carbonaceous material 308. The relative positions of the reservoir 304 and carbonaceous
material 308 allow for a gravity fall of the formation water when one or more channels are
formed in the layer 306 that separates the reservoir from the carbonaceous material. In Fig. 3A,
a channel 312b is shown formed in the layer 306 that provides a way for the formation water to
travel from the reservoir 304 to the carbonaceous material 308.
[0038] The channel 312b may be formed by drilling through layer 306 until the surface or bulk
of the carbonaceous material 308 is reached. This drilling may be a further extension of a well
bore 310. that also has a first portion of channel 312a extending from the terrestrial surface of the
geologic formation to the top of the formation reservoir 304.
[0039] .In the embodiment shown in Fig. 3A, a single channel 312b is shown between the
reservoir 304 and the carbonaceous material 308. Embodiments may also include a plurality
channels (not shown) formed between reservoir 304 and the carbonaceous material 308. The
plurality of channels may be said to perforate the reservoir 304 to create a gravity induced fall of
formation water onto the carbonaceous material 308.
[0040] Fig. 3B shows another simplified cross-section of a portion of geologic formation 350
containing a formation water reservoir 360 below a layer of carbonaceous material 356. The
reservoir 360 and carbonaceous material 356 are separated by a layer 358 that hinders contact of
the underlying formation water with the overlying carbonaceous material. The carbonaceous
material 356 is buried underneath layer 352 whose upper surface is the terrestrial surface of the
formation 350. One portion of layer 352 is in direct contact with the underlying carbonaceous
material 356, while another portion is separated from the carbonaceous material by a pocket 354.
[0041] The embodiment shown in Fig. 3B has two channels 362 & 364 formed through several
layers of the formation 350, including the layer of carbonaceous material 356 and the layer 358
that separates the reservoir 360 from the carbonaceous material. These channels may be used to
transport formation water from the reservoir 360 up to the carbonaceous material 356. For
example, channel 362 may be pressurized with a gas or fluid to create an increase in pressure in
the formation water in the reservoir 360. This may cause a portion of the formation water to
push upwards through channel 366 at least until coming into contact with the carbonaceous
material 356. In some embodiments, the formation water may be pushed above the top surface
of the carbonaceous material 356 and start filling the pocket 354. As the formation water spills
over the top surface of the carbonaceous material 356, it may penetrate and drift down into the
material with the aid of gravity.
[0042] The top end of channel 364 may include an article 366 to help transport the formation
water from the reservoir 360 to the carbonaceous material 356. The article 366 may be a pump
or other device to create a negative pressure gradient up the channel 364 that helps to pull the
formation water up the channel. Alternatively, the article 366 may be a plug or other device to
stop the flow of fluid out of the formation 350. Such a plug may create a positive pressure
gradient up the channel 364 that encourages the formation water to flow laterally from the
channel into the surrounding formation material, including the carbonaceous material 356.
[0043] Referring now to Fig. 4, methods 400 are described for accumulating biogenic gas in an
anaerobic geologic formation to enhance biogenic gas production according to embodiments of
the invention.. The methods 400 may include the step of holding accumulating biogenic gases in
the geologic formation 402. These accumulating gases may be generated native microorganisms
in the formation without assistance, and/or by stimulatory actions that start or increase the rate of
biogenic gas production in the formation. The accumulating biogenic gas may itself have a
stimulatory effect on the rate of biogenic gas production. For example, the gases produced by
methanogens, such as methane and hydrogen, may alter the gas composition of the formation to
be more anaerobic, which may facilitate more anaerobic microorganism activity like
methanogenesis.
[0044]. The accumulating biogenic gases held in the formation may also increase the overall
gas pressure in the subterranean formation. The increased gas pressure may in turn help drive
formation water through carbonaceous material 404. The flow of the formation water through
the carbonaceous material may have a stimulatory effect on biogenic gas production (e.g.,
methanogenesis) which may further increase the rate of biogenic gas production. As noted
above, flowing formation water can transport microorganism, nutrients, chemical amendments,
and other materials over a wider volume of the carbonaceous materials. The dispersion of the
mircoorganims can increase the contact between the microorganisms and the carbonaceous
material, which can increase their growth rates and/or biogenic gas production rates. Flowing
and/or circulating formation water can also facilitate the removal of microorganism waste
products, toxins, and methanpgenesis inhibitors from the living environment of the
microorganisms.
[0045] The ability of increased gas pressure to drive formation water through carbonaceous
material may depend on nature of the carbonaceous material and also the composition of the
formation. When the carbonaceous material is a relatively porous solid (e.g., lignite coal) the
formation water may more easily penetrate into the material. When the carbonaceous material is
harder (e.g., anthracite coal) the formation water may have more difficulty penetrating the
material, but may still find cracks, fissures, cleats, etc., through which it can traverse the
material. In some instances, the carbonaceous material may be sufficiently hard and non-porous
that the formation water can only flow around exposed surfaces of the material. For purposes of
the present application, driving formation water through the carbonaceous material may include
penetrating a porous material, pushing the water further into cracks, fissures, cleats, etc. in the
material, and flowing or spreading the water over an exposed surface of the material. In
addition, driving formation water through a carbonaceous material does not require the water to
be pushed completely through the material. Advancing the formation water into the material or
spreading it further across a surface of the material is may also be considered examples of
driving the formation water through the material.
[0046] In some embodiments of methods 400, at least a portion of the biogenic gases may be
removed from the formation 406 following the holding period. For example, these gases may be
removed at a wellhead that is fluidly coupled to a natural gas pipeline. The removal of the
biogenic gases may cause a change (e.g., decrease) in gas pressure in the formation. A decrease
in formation gas pressure may be large enough to alter the flow of formation water through the
carbonaceous material 408. In some instances, the decrease in pressure may reverse the direction
of flow of the formation water.
[0047] Following the removal of the biogenic gases from the formation, new biogenic gas may
be allowed to accumulate in the formation. The accumulating gases held in the formation may
cause the gas pressure in the formation to change again (e.g., increase). The gases may be held
until the gas pressure reaches a threshold pressure, such as returning to the pressure in the
formation prior to the previous release of biogenic gases. An increase in the gas pressure may
alter the flow of the formation, water again, and in some instances may reverse the direction of
flow back to the original flow direction before the biogenic gases were removed. In some
embodiments, the removal and re-accumulation of the biogenic gases may be done a plurality of
times. This may result in several reversals in the change of the gas pressure in the formation,
which may result in corresponding alterations, in the direction and/or rate of flow of the
formation water through the carbonaceous material. In some instances the removal and re-
accumulation of the biogenic gases may result in a cyclical, and possibly continuous, change of
flow of the formation water, creating a circulation of the formation water in the carbonaceous
material that may enhance biogenic gas production.
[0048] Having described several embodiments, it will be recognized by those of skill in the art
that various modifications, alternative constructions, and equivalents may be used without
departing from the spirit of the invention. Additionally, a number of well-known processes and
elements have not been described in order to avoid unnecessarily obscuring the present
invention. Accordingly, the above description should not be taken as limiting the scope of the
invention.
[0049] Where a range of values is provided, it is understood that each intervening value, to the
tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the
upper and lower limits of that range is also specifically disclosed. Each smaller range between
any stated value or intervening value in a stated range and any other stated or intervening value
in that stated range is encompassed. The upper and lower limits of these smaller ranges may
independently be included or excluded in the range, and each range where either, neither or both
limits are included in the smaller ranges is also encompassed within the invention, subject to any
specifically excluded limit in the stated range. Where the stated range includes one or both of
the limits, ranges excluding either or both of those included limits are also included.
[0050] As used herein and in the appended claims, the singular forms "a", "an", and "the"
include plural refefents unless the context clearly dictates otherwise. Thus, for example,
reference to "a process" includes a plurality of such processes and reference to "the well"
includes reference to one or more wells and equivalents thereof known to those skilled in the art,
and so forth. '
[0051] Also, the words "comprise," "comprising," "include," "including," and "includes" when
used in this specification and in the following claims are intended to specify the presence of
stated features; integers, components, or steps, but they do not preclude the presence or addition
of one or more other features, integers, components, steps, acts, or groups.
We claim:
1. A method to enhance biogenic gas production in an anaerobic geologic
formation containing carbonaceous material, the method comprising;
accessing the anaerobic formation;
increasing a rate of production of the biogenic gases in the anaerobic formation;
and
flowing formation water within the anaerobic formation after the increase in the
production of biogenic gases.
2. The method of claim 1, wherein accumulating biogenic gases are held in
the anaerobic formation to increase the rate of production of the biogenic gases.
3. The method of claim 1, wherein the carbonaceous material is contacted
with water to increase the rate of production of the biogenic gases.
4. The method of claim 3, wherein the water increases contact between
microorganisms and the carbonaceous material in the anaerobic formation.
5. The method of claim 3, wherein the water transports nutrients to
microorganisms in the carbonaceous material.
6. The method of claim 3, wherein the water removes inhibitory materials
from a living environment of microorganisms in the carbonaceous material, and wherein those
inhibitory materials are selected from the group consisting of microorganism waste products,
microorganism growth inhibitors, and microorganism methanogenesis inhibitors.
7. The method of claim 3, wherein the water is supplied from a source
outside the anaerobic formation, or a reservoir of the formation water within the anaerobic
formation.
8. The method of claim 1, wherein an amendment is added to anaerobic
formation to increase the rate of production of the biogenic gases.
9. The method of claim 1, wherein the amendment comprises an acetate-
containing compound, a phosphorous-containing compound, a yeast extract, or hydrogen.
10. The method of claim 1, wherein the flowing of formation water comprises
circulating the formation water between a reservoir in the anaerobic formation and the
carbonaceous material.
11. The method of claim 1, wherein the flowing of the formation water
comprises pressurizing the anaerobic formation with accumulating biogenic gases to drive
formation water through the carbonaceous material.
12. The method of claim 1, wherein the circulating of the formation water
further increases the rate of production of biogenic gases.
13. A method to redistribute formation water in an anaerobic geologic
formation containing carbonaceous material, the method comprising:
locating a reservoir of the formation water within the anaerobic formation;
forming at least one channel between the reservoir and at least a portion of the
carbonaceous material; and
transporting the formation water from the reservoir to the carbonaceous material
through the channel.
14. The method of claim 13, wherein the reservoir is located above or below
the carbonaceous material in the anaerobic formation.
15. The method of claim 13, wherein the forming of the channel between the
reservoir and the carbonaceous material comprises drilling the channel through formation rock to
fluidly connect the reservoir and the carbonaceous material.
16. The method of claim 13, wherein a plurality of channels are formed
between the reservoir and the carbonaceous material.
17. The method of claim 13, wherein the transporting of the formation water
comprises a gravity flow of the formation water from the reservoir to the carbonaceous material
located below.
18. The method of claim 13, wherein the transporting of the formation water
comprises showering the formation water on the carbonaceous material from the reservoir
located below the carbonaceous material.
19. The method of claim 13, wherein the method further comprises refilling
the reservoir with water after the formation water is transported from the reservoir to the
carbonaceous material through the channel.
20. The method of claim 19, wherein the water comprises additional
formation water.
21. A method of accumulating biogenic gas in an anaerobic geologic
formation to enhance biogenic gas production, the method comprising:
holding the accumulating biogenic gas in the anaerobic formation to increase gas
pressure in at least a part of the anaerobic formation; and
. driving formation water through carbonaceous material in the anaerobic formation
in response to the increased gas pressure, wherein a flow of the formation water through the
carbonaceous material further increases a rate of biogenic gas production in the anaerobic
formation.
22. The method of claim 21, wherein the accumulating biogenic gas is
removed from the anaerobic formation after driving the formation water through the
carbonaceous material.
23. The method of claim 22, wherein the removal of the accumulating
biogenic gas from the anaerobic formation at least partially reverses the flow of the formation
water through-the carbonaceous material.
24. The method of claim 21, wherein the method comprises removing at least
part of the accumulating biogenic gas a plurality of times such that the gas pressure in the
anaerobic formation changes over time.
25. The method of claim 24, wherein the changes in gas pressure over time
change a direction of the flow of formation water through the carbonaceous material.
26. The method of claim 25, wherein the change in direction of flow further
increases the rate of biogenic gas production.
27. The method of claim 21, wherein the method comprises:
measuring gas pressure in the anaerobic formation; and
removing at least a portion of the accumulating biogenic gas from the anaerobic
formation to.adjust the gas pressure in the anaerobic formation to a target pressure.

Methods to enhance biogenic gas production in an anaerobic geologic formation
containing carbonaceous material are described. The methods may include the steps of accessing
the anaerobic formation, increasing a rate of production of the biogenic gases in the anaerobic
formation, and flowing formation water within the anaerobic formation after the increase in the
production of biogenic gases. Also described are methods to redistribute formation water in an
anaerobic geologic formation containing carbonaceous material. The methods may include the
steps of locating a reservoir of the formation water within the anaerobic formation, forming at
least one channel between the reservoir and at least a portion of the carbonaceous material, and
transporting the formation water from the reservoir to the carbonaceous material through the
channel. Further described are methods of accumulating biogenic gas in an anaerobic geologic
formation to enhance biogenic gas production.