US20080236820A1 - Production of natural gas from hydrates - Google Patents

Abstract

Methods and apparatus for producing methane gas from a hydrate formation. A column of modified material substantially filling a wellbore extending into the hydrate formation. The column of modified material is permeable to gases. A heat source extends into the column of modified material and is operable to provide heat to the hydrate formation so as to release methane gas from the hydrate formation. Methane gas flow through the column of modified material to a gas collector, which regulates the flow of gas to a production system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application is a continuation of copending U.S. Ser. No. 11/706,543 filed Feb. 15, 2007 which is a continuation of U.S. Ser. No. 11/315,939, filed Dec. 22, 2005, now abandoned, which in turn is a continuation of Ser. No. 10/890,040, now U.S. Pat. No. 6,978,837, filed Jul. 13, 2004, entitled “Production of Natural Gas from Hydrates”, which in turn claims priority to U.S. Provisional Application No. 60/519,497, filed Nov. 13, 2003, titled “Production of Natural Gas from Hydrates,” all of the above hereby incorporated herein by reference for all purposes.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
• Not Applicable.
FIELD OF THE INVENTION
• The present invention relates generally to methods and apparatus for extracting gaseous hydrocarbons from subterranean formations. More particularly, the present invention relates to extracting gaseous hydrocarbons from gas hydrate formations.
BACKGROUND
• Production of gas from subterranean oil and gas reservoirs by drilling and installation of grouted casings is a well-established practice. Natural gas (methane) production has primarily been achieved through drilling wells into deep reservoirs where natural gas, frequently in association with crude oil and water, may be trapped under a layer of cap rock. The well is lined with a casing that is cemented to the surrounding formation to provide a stable wellbore. The casing is then perforated at the reservoir level to allow gas and reservoir fluids to flow into the casing and then to the surface through tubing inside the casing.
• In these cased well applications, one or more concentric casings are installed to progressively greater depths, down to a pressurized reservoir. Cementing, or grouting, the casing(s) to the formation material, and to adjacent casings, prevents hydrocarbons from escaping from the pressurized reservoir along the exterior of the casing. Gas enters the lower part of the casing via perforations in the casing or, in highly consolidated (rock) reservoir formation material, via an un-cased extension of the drilled hole.
• In most applications, a “packer” is used to isolate the lower part of the casing from the upper part and one or more strings of production tubing hang from the wellhead down to the zone below the packer or between adjacent packers. After entering the casing via the perforations, the gas enters the tubing string(s) where it flows to the surface, through valves, and to a pipeline. The cased well method facilitates control of the flow of gas from a high-pressure reservoir and is well suited for production from porous rock or sand formation material.
• Methane hydrates, or hydrates, are one type of formation material found close to the surface, especially in cold environments. Methane hydrates are similar to water ice and are composed primarily of water, methane, and, to a lesser extent, other volatile hydrocarbons. The frozen water particles form an expanded lattice structure that traps the methane, or other hydrocarbon particles, to form a primarily solid material.
• Methane hydrates have been found to be stable over a range of high pressure and low temperature. Methane hydrates are stable at combinations of temperature and pressure found in onshore arctic regions and beneath the sea floor in water depths greater than approximately 1,500 feet (500 meters). Changes in either the temperature or the pressure can cause methane hydrates to melt and release natural gas. Methane gas may also be trapped below the hydrate layer, much as it is trapped below cap rock layers in deep underground reservoirs.
• The development of viable methods for the commercial production of natural gas from naturally occurring deposits of methane hydrates has been the subject of extensive research. The construction of standard cased wells has been used to reduce the pressure on the underside of the hydrate-bearing zone. This approach collects gas that is trapped below the hydrates and, by reducing the pressure, may cause hydrates in the surrounding formation to release additional natural gas. This release will cease when the formation materials isolate the remaining hydrates from the zone of reduced pressure or when the latent heat of thawing causes the temperature to drop sufficiently to stabilize the remaining hydrates at the reduced pressure. Thawing absorbs heat equal to the latent heat of the hydrates and, if this heat is not replaced, the temperature will drop and conditions will eventually shift into the stability region for hydrates, whereupon release of methane from the hydrates will stop.
• Notwithstanding the above teachings, there remains a need to develop new and improved methods and apparatus, for producing hydrocarbon gases from subterranean hydrates, which overcome some of the foregoing difficulties while providing more advantageous overall results.
SUMMARY OF THE PREFERRED EMBODIMENTS
• The embodiments of the present invention are directed toward methods and apparatus for recovering hydrocarbons from subterranean hydrates. A column of modified material substantially filling a wellbore extends into the hydrate formation. A heat source extends into the column of modified material and is operable to provide heat to the hydrate formation so as to release methane gas from the hydrate formation. Methane gas flows through the column of modified material to a gas collector, which regulates the flow of gas to a production system.
• In one embodiment, a well for producing hydrocarbons from hydrate deposits includes a wellbore containing a column of material modified for permeability and/or heat conductivity. The well also comprises a heat source for heating the hydrate formation to release hydrocarbon gases. The hydrocarbon gases pass through the permeable material up through the wellbore and is captured. Gas captured can be collected and/or processed to provide useful hydrocarbon gas products.
• The embodiments of the present invention include provisions for forcing the release of natural gas from the hydrates and provisions for producing the released gas. These embodiments may also include provisions for delivering produced gas to a chamber suitable for separating gas from water, storing gas, drying gas, and regulating flow. Embodiments may also include comingling gas from multiple wells in a controlled manner and delivering the gas to a pipe or pipeline. These embodiments can be used to produce gas from hydrate formations that are not suitable for production by conventional wells. Certain embodiments can also be used to extend the life of wells used to produce hydrates.
• Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:
• FIG. 1 is a schematic illustration of a hydrate production apparatus constructed in accordance with embodiments of the present invention and illustrating the flow of gas from the formation into the wellbore;
• FIG. 2 is a schematic illustration of a hydrate production apparatus including an impermeable cap constructed in accordance with embodiments of the present invention;
• FIG. 3 is a schematic illustration of a hydrate production apparatus including an impermeable cap and a heat source constructed in accordance with embodiments of the present invention;
• FIG. 4 is a schematic illustration of a gas production system constructed in accordance with embodiments of the present invention;
• FIG. 5 is a schematic illustration of a gas production system constructed in accordance with embodiments of the present invention;
• FIG. 6 is a schematic illustration of a multi-well gas production system constructed in accordance with embodiments of the present invention;
• FIG. 7 is a schematic illustration of a well having a circulating heating system constructed in accordance with embodiments of the present invention;
• FIG. 8 is a schematic illustration of a well having multiple heat sources constructed in accordance with embodiments of the present invention;
• FIG. 9 is a schematic illustration of a well having multiple heat sources constructed in accordance with embodiments of the present invention;
• FIG. 10 is a schematic illustration of a well having a combustion chamber constructed in accordance with embodiments of the present invention;
• FIG. 11 is a cross-sectional schematic illustration of the well ofFIG. 10; and
• FIG. 12 is a schematic illustration of a gas production system constructed in accordance with embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. For example, the concepts of the present invention can be used in deviated, horizontal, and directional wells, as well as the vertical wells used in the following description.
• In particular, various embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art hydrate production systems. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings.
• The embodiments of the present invention are described in the context of the production of natural gas from hydrates that occur naturally in arctic permafrost or within sediments that comprise the deep ocean seabed, typically at water depths of 1,500 feet and deeper. Except where otherwise indicated, it is assumed that the pressure within these hydrate formations is at or near the corresponding ambient pressure for the depth at which the formation is found. Hydrate formations will release hydrocarbon gases as either the temperature of the formation is increased or the pressure on the formation is decreased. The embodiments of the present invention seek to produce hydrocarbon gases from these hydrate formations using novel production apparatus designs and methods.
• Referring now toFIG. 1, a section of awellbore10 is shown disposed in ahydrate formation12. Aswellbore10 is drilled to adiameter14, at least a portion of the formation material is removed from the wellbore and replaced or combined with a selectedmaterial15 to create acolumn16 of modified material that fills the wellbore. The selectedmaterial15 may be chosen to adjust the permeability and/or thermal conductivity of thecolumn16. For example, materials of particular granular size can be used to makewellbore10 permeable to liquids and gases while being relatively impermeable to particulate matter, thus allowing flow of gas while filtering unconsolidated formation materials that might otherwise interfere with gas production.
• Thus, in the following discussion, modifiedmaterial15 should be taken to define a material having a different permeability and/or thermal conductivity than the surrounding formation. The modifiedmaterial15 may be a slurry or a granular solid material that substantially fills a wellbore. In this context, substantially fills is defined as where thematerial15 is in direct contact with thehydrate formation12 and fills wellbore10 irrespective of other wellbore-installed members, such as tubing and casing, or interstitial areas formed between adjacent particles of the modified material.
• The selection of the materials forming the column of modified material may also be made with some consideration to regulating the heat flow from the wellbore into the formation. Thermal conductivity can be regulated by changing the liquid content or by injecting materials having the desired thermal conductivity into modifiedcolumn16. Examples of materials with high thermal conductivity that may be suitable for use include, naturally occurring minerals or ores, refined or processed minerals, metals, or ceramics, and industrial byproducts. Exemplary materials include metal ores and coke breeze. Fabricated devices such as metal fibers, metal particles, metallic oxides, or liquid filled volumes may also be placed incolumn16 to enhance thermal conductivity. The modified material may preferably be a slurry, for which conventional pumping methods can be used to inject the slurry intowellbore10.
• For the purposes of the following description, the modifiedcolumn16 is considered to be permeable to gases and/or have a high thermal conductivity. Thus, ashydrate formation12releases hydrocarbon gases18, the gases flow intowellbore10 and up through modifiedcolumn16 toward the top of the well.
• FIG. 2 shows wellbore10 having acap22 at the top of the well.Wellbore10 is disposed in ahydrate formation12 having anupper layer26 that is impermeable. As inFIG. 1, wellbore10 contains a column of modifiedmaterial28.Cap22 is installed at the top ofwellbore10 to act as a gas collector and stop the flow ofgas18 up through the wellbore.Cap22 may be formed from cement, grout, or some other substantially impermeable material.Cap22 may extend throughupper layer26 to whatever depth is desired to minimized the escape of gases through the surrounding formation.Tubing32 is installed throughcap22 to provide an outlet for removinggas18 fromwellbore10.Valve34 may be installed ontubing32 to allow the tubing to be closed and the well shut-in.
• A heat-injectingwell36 is shown inFIG. 3. Well36 includeswellbore10 drilled intohydrate formation12 and containing a column40 with a first zone42 and asecond zone43 having different compositions of modified material. Well36 also includescap44,tubing46,valve48, andheat source50. Heatsource50 provides heat to wellbore10, which is transferred through modified material42 intohydrate formation12. In the preferred embodiments, modified material42 has thermal conductivity properties that enable a high efficiency in transferring heat fromheat source50 intoformation12. Themultiple zones42,43 may allow selected properties of column40 to vary between the zones. For example, the thermal conductivity of column40 may be lower in first zone42 so as to limit the heat transfer into the upper regions offormation12. In some embodiments, the permeability of column40 may also be varied so as to control the flow of gas through the column.
• When heat is transferred toformation12 by heat-injecting well36, hydrates in close proximity to the well thaw first, with thawing extending farther out as time progresses. Thawing of the hydrates releases hydrocarbon gases, such as methane. Methane released in close proximity to well36 flows toward the inlet oftubing46, on the outside ofheat source50, and through modified material42, which has been disturbed during drilling ofwellbore10 and/or modified to change its permeability or thermal conductivity. Methane liberated at a greater distance from well36 is effectively blocked from vertical upward migration by naturally occurring layers of consolidated materials, and by hydrate ice in the pores and fissures of theundisturbed formation12. Increased pressure resulting from thermal liberation of gaseous methane from solid ice, causes the released methane to flow primarily horizontally or diagonally upward through the thawed zone until it can move vertically throughwell36. Proximity to a heat source helps prevent hydrates from reforming inwellbore10 and accelerates the methane migration through the wellbore to the inlet oftubing46.
• A heat-injecting well causes gas to be released by thawing the hydrates. The thawing generates sufficient pressure to cause the gas to migrate into and through a permeable wellbore from where it can be produced. The heat for the heat-injecting well may be from any available source, including hot fluids, combustion of fuel and oxidizer, hot combustion gases, or electrical resistance heating. Combustion may be at any location remote from the heat-injecting well, or may occur inside the heat-injecting well. An ambient or cooled liquid or gas can also be injected into the well in order to decrease the temperature of the surrounding formation. This decrease in temperature will reduce and eventually stop the hydrates from thawing, thus limiting the release of gas into the wellbore.
• Cap44 not only controls the flow of gas, but also allows further control of thermal effects on the formation in the region around the cap. Reducing the thermal conductivity around the upper part of the well allows the upper levels of sediment to remain cold. Isolation of the upper layers of sediment from heating can help maintain the structural stability of the formation, and help maintain a relatively impermeable cap over the hydrate area to help reduce the escape of methane.
• Once captured in a tubing string, the hydrocarbon gases can be collected and transported via a pipeline, or other means.FIG. 4 illustrates one exemplary system for collecting hydrocarbon gases produced from a hydrate well.Gas collector system51 includeschamber54 disposed over ahydrate well58.Chamber54 may have substantiallyrigid walls60 shaped so that gas collects toward acentral outlet62 at the top of the chamber.Chamber54 contains aliquid region64 and agas region66. Well58, which is drilled intohydrate formation12, includeswellbore10 containing a column of modifiedmaterial72 and acap74. Heatsource76 andtubing78 run throughcap74 into modifiedcolumn72.Tubing78 may includetubing valve80 to control the flow of produced fluids intochamber54.
• Heatsource76 extends from well58 into a region ofchamber54 where it is accessible for connections and control.Tubing78 extends from well58 into eithergas region66 orwater region64 ofchamber54. Gases ingas region66 will tend to circulate up alongheat source76 and then back down alongchamber walls60, which are cooled by unconfined seawater or arctic air on the outside of the wall, effectively serving as a cold plate. Gas circulating down alongwalls60 will be cooled, and moisture in the gas will condense on the wall and fall intoliquid region64. In this manner, excess moisture can be removed from the gas.
• Inchamber54, water is displaced from theliquid region64 through acontrol valve82 as the volume of stored gas increases.Control valve82 may also be used to control the pressure ingas region66 by regulating the volume of liquid inliquid region64. Gas can be removed fromchamber54 throughexport pipe84 by regulating one ormore export valves86 controlled either remotely or by the volume of gas in the chamber, or by both.
• Thus,chamber54, when equipped with suitable valve(s) for controlling the gas and liquids inlet, outlet, and pressure, can serve any or all of the multiple functions of accepting gas from the formation, separating the gas from produced water, removing excess moisture from the gas, storing gas, regulating gas pressure, regulating gas into a pipe or hose, preventing water from entering the pipe or hose, and disposing of produced liquid.Chamber54 is shown inFIG. 4 installed in conjunction with a simple heat-injecting well, but may also be used in conjunction with any of the embodiments presented herein, or any combination thereof.
• Whenchamber54 is installed on theseafloor56, gas enters the chamber at or near ambient sea water pressure so a large quantity of gas can be held in a relatively small volume. For example, if the chamber is located at a water depth of 3,300 feet (1,000 meters), the gas occupies approximately 1% of the volume it would occupy at a pressure of one atmosphere. Securingchamber54 to heatsource76 and/orcap74 allows the weight and soil-skin friction of the casing and cap to be used to react the buoyancy force of the stored gas.
• An alternate chamber embodiment is illustrated inFIG. 5.Chamber120 includes substantially an upper,gas containing portion122 havingrigid walls124 and a lower, liquid containingportion126 having substantiallyflexible walls128.Chamber120 is positioned over well130, which is drilled intohydrate formation12, includeswellbore10 containing a column of modifiedmaterial136 and acap138.Fuel supply140 andoxidizer supply142 are provided to inject combustion gases into well130 that act as a heat source.Tubing144 provides a pathway for the passage of gas from well130 intogas portion122.Water vent143 andgas export line145 are provided to remove water and gas fromchamber120 and may be controlled by valves or other control devices.Chamber120 also includesheating chamber146, whose source of heat may come from lines connected to fuelsupply140 andoxygen supply142.
• As withchamber54 inFIG. 4,chamber120 provides a system for passively removing water from the produced gases. Gases ingas portion122 will tend be cooled onchamber walls124, which are cooled by unconfined seawater on the outside of the wall, effectively serving as a cold plate. Gas circulating alongwalls124 will be cooled, and moisture in the gas will condense on the wall and fall intoliquid portion126. In this manner, excess moisture can be removed from the gas.Liquid portion126 hasflexible walls128, which, when acted on by external pressure, maintain the pressure withinchamber120 at a level equal with the surrounding environment.
• As previously discussed,heating hydrate formation12 will result in both methane and water flowing up throughproduction tubing144 and into the storage andtreatment chamber120. In order to preventchamber120 from filling with water, excess accumulated water must be vented. It is often desirable, both for efficiency and for environmental protection, to strip any dissolved methane from water before it is released. This can be done by routing the vent water throughheating chamber146 to warm it and thereby reduce its ability to hold dissolved gas.FIG. 5 illustrates aheating chamber146 that is heated by reacting a portion of the fuel and oxidizer used to heat the well that are diverted to the heating chamber. In alternate embodiments,heating chamber146 can be heated by heated fluid being circulated into the well or by combustion products flowing out of the well and used to warm the heating chamber.
• Gas driven from the vented water is released into the storage andtreatment chamber120 where it is captured and mixed with the gas products ingas portion122.Heating chamber146 can be placed anywhere in the vent water path but may be preferably placed contiguous with the production tubing as shown inFIG. 5 such that the heating chamber will also raise the temperature of the produced methane intubing144. Heating the produced methane above 350° C. will result in the reaction of any residual oxygen that might be present in the production stream due to combustion exhaust gasses having been injected into the modified column. Introduction of heated methane into the gas volume of the storage andtreatment vessel120 will cause the gas to circulate up, toward a wall, and down a cold wall where moisture will be condensed from the gas as previously described.
• In certain applications, a plurality ofhydrate production systems52, which may be arranged in a circular or rectangular array, can be used in cooperation as shown inFIG. 6.Export pipes84 frommultiple production systems52 combine into a commingledcollection chamber88 that is connected to apipeline90. The pressure incollection chamber88 may be maintained at sufficient pressures to eliminate or reduce the amount of further compression that is required to transport the gas viapipeline90. It is also recognized that there may still be sufficient moisture in the gas to cause hydrate blockage in thepipes84 orpipeline90 if the gas is transported at certain temperatures. To prevent blockage, flow assurance measures, such as methanol injection, may be implemented in the flow path betweenproduction systems52 andpipeline90. Multiple wells, production systems, and collection chambers may be inter-connected in order to increase the production rate and to average out any irregularity of flow that might occur from an individual well.
• The design of the well is one of the most important aspects of any of the above described hydrate production systems. Shown in the above described embodiments is a simple heat-injecting well that produces hydrocarbon gases. Although shown integrated into one well, it is understood that the heat-injecting and the hydrocarbon production functions could be separated into two or more wells. Injecting heat into the hydrate formation releases the hydrocarbon gases from the formation and allows recovery of the gases.
• The hydrate formation is analogous to an insulating blanket wrapped around the heat-injecting well. The heat flow in the formation, for a given thermal conductivity and temperature difference, is directly proportional to the surface area of the formation in contact with the heat-injecting well. It is understood that heat transfer, Q, into the formation can be represented by the equation:
• 
  Q∝C·T_g·A; where
• C is the thermal conductivity of the material, T_gis the temperature gradient, which is the temperature difference between the heat source and the formation, divided by the distance over which the temperature difference is measured, and A is the surface area over which the heat is exchanged between the heat-injecting well and the formation. Heat flow can be increased by increasing the temperature of the heat-injecting well, but the maximum temperature is limited by practical considerations such as the boiling point of water, formation of salt deposits, dehydration of formation materials, strength of the materials from which the apparatus is made, etc.
• Heat transfer can be analyzed by considering the surface of the heat-injecting well as a cylinder, surrounded by concentric cylindrical shells of formation material. Shells further from the well have larger surface area so they conduct the heat more readily. If the thermal conductivity of the heat-injecting well is greater than that of the formation material, then the greatest restriction of heat flow is through the innermost cylindrical shell of formation material, i.e., the one that is in direct contact with the well. Increasing this surface area (such as by increasing the diameter of the heat-injecting well) allows greater heat flow without exceeding the practical limit on maximum temperature.
• In the embodiments in which a single heat source is contained within a centrally located tubular member, the formation is warmed by heat flowing through the wall of the tubular member. The amount of heat that can be transferred through the wall of the tubular member is dependent on the surface area of the tubular member, both in contact with the hot medium inside and the modified column outside. Thus, the maximum heat transfer through the tubular member is dependent on the surface area, and therefore the diameter, of the tubular member. Further, the tubular member is preferably constructed from a material with a high thermal conductivity, such as metal.
• It is preferred that for a desired amount of heat transfer, the limiting parameters that determine the minimum diameter for the tubular member depend primarily on the temperature, specific heat, and mass flow rate of the fluid or combustion gas that moves through the tubular member. Given turbulent subsonic flow inside the tubular member and maintenance of a temperature below the boiling point of water on the outside of the member, the preferred tubular member has an outside diameter of at least 4 inches.
• As discussed earlier, heat transfer is proportional to thermal conductivity times the surface area through which the heat is transferred. Thermal conductivity of the formation depends on local conditions, but a conductivity of 2 Watts/m° C. can be used as representative. If a value of 10 Watts/m° C. is taken as the upper limit on column conductivity, then the ratio of thermal conductivity for the column to the conductivity of the formation is 5. From the proportionality established earlier for heat transfer across a boundary, it is apparent that the outer diameter of the modified column/wellbore must be at least 5 times the diameter of the central heating tubular member. If, as above, the central tubular member has a diameter of 4 inches, the outer diameter of the modified column must be at least 20 inches.
• This calculation ignores the effect of temperature drop along a horizontal radial line through the modified column but this is relatively small because, for the case examined here, the separation is only 8 inches. It is apparent that improvement in thermal conductivity of the modified column, a larger and higher energy central element, or improvement in any of the variables subject to engineering manipulation would make it desirable to increase the outer diameter of the modified column since the thermal conductivity of the formation is the most important limiting parameter that can not be optimized by engineering trade-off of physical constraints.
• Thus, it can be seen that a large diameter wellbore is preferred. Depending on the properties of the hydrate formation being exploited, wellbores having diameters up to and exceeding 60″ are possible. At these large diameters lining the depth of the wellbore with a metal casing is possible but can be cost prohibitive. A metal casing may also create additional challenges with the movement of gas into the wellbore from the formation. Thus, as opposed to lining the wellbore with a casing, the wellbore may be filled with a material that replaces or modifies the formation material to facilitate the movement of gases and the transfer of heat.
• Referring now toFIG. 7, one method for supplying heat to a well100 includes flowing hot gas or fluid throughtubing102 and circulating the fluid back out of thewell100. In certain embodiments, water, or steam, may be heated by any available energy source and brought to the heat injecting well by insulated pipeline. As the heated liquid, or steam, is pumped throughtubing102, heat is transferred from the heated liquid intowellbore10. This heat is then transferred acrosswellbore10 intoformation12.
• In an alternate embodiment, as shown inFIG. 8, heated liquid, or steam, is pumped directly intowellbore10 throughtubing110.Tubing110 may include multiple tubing strings that may be disposed within alarger tubing111 that carries the heated material to the bottom ofwell112. The liquid then cools and is circulated back to the top of well112 with the released hydrocarbon gases.Tubing113 carries the produced gas and liquids out ofwell112. Alternately, in the well ofFIG. 8, combustible materials can be introduced to generate hot gas inside the well with the exhaust gas then flowing out through the well. An independent fuel source can be introduced into the well or used or a portion of the produced gas can be burned with an introduced oxidizer.
• FIG. 9 illustrates another alternate well114 having multiple tubing strings116. Tubing strings116 allow for fluids to be injected at one elevation and extracted at another.Tubing116 can also be used to provide different heating levels at different depths within well114.Tubing116 can also be used to inject materials to control permeability and heat transfer. Thus,multiple tubing strings116 can be used to produce gas, to inject materials, to modify permeability, to modify thermal conductivity, to inject or circulate heated fluid, or to kill the well by circulating cold fluid to remove heat and chill formation materials in proximity to the well.
• FIGS. 10 and 11 illustrate one embodiment of a well200 having aheat source202 including downhole combustion. Well200 includeswellbore10 having a column of modifiedmaterial206 disposed below animpermeable cap208. Heatsource202 includescombustion chamber210,fuel supply212, andoxidizer supply214, all of which may be disposed within a singlelarge diameter tubing222.Tubing222 may also include atemperature sensor221 andintervention tubing218, which provides additional access tocolumn206 and may be used for a variety of purposes.Production tubing220 provides a pathway for produced gas to bypasscap208.
• Fuel212 andoxidizer214 are preferably combusted at select regions alongchamber210 in order to regulate the amount of heat transferred into the formation at varying depths.Combustion chamber210 provides for the reaction of fuel and oxidizer and allows combustion products to flow downward for injection into the modifiedcolumn206 or upward to be vented. One reactant may flow in thecombustion chamber210 and the other in a separate tubing, or each reactant may flow in separate tubing and be injected into the combustion chamber.
• In some embodiments, a well may not be used to produce gas but only to inject heat into the formation in order to facilitate production through other wells. For a non-producing, heat-injecting well the thermally conductive material may be formulated so as to block the migration of gas. Migration can be blocked by, for instance, injecting a material formulated for the desired thermal characteristics, such as grout or resin, that will solidify.
• The heat-injecting wells described above may be used as an alternative to, or in conjunction with, conventional pressure relief production wells that may be used to tap pressurized gas from the hydrate zone. A heat-injecting well can be used to produce natural gas from hydrate deposits while a nearby pressure relief well is producing, or after a nearby pressure relief well has depleted the hydrates that are suitable for production by pressure relief methods. Heat-injecting wells can also be used in conjunction with pressure relief wells such that one or more heat-injecting wells replace the heat absorbed by thawing of hydrates so as to sustain flow in a pressure relief well past the time when gas flow would otherwise decrease and eventually stop.
• Referring now toFIG. 12, another embodiment of ahydrate production apparatus300 is shown in including awellbore10 formed in ahydrate formation12. The wellbore is filled with a column of modifiedmaterial306 and the top of the wellbore is enclosed by agas collector308. Aheat source310 extends into the column of modifiedmaterial306.Gas collector308 includes achamber312 having a water/gas separator318,outlet320, andliquid region316, andgas region314.
• Wellbore10 may be formed by drilling or jetting intohydrate formation12.Wellbore10 may be filled with the column of modifiedmaterial306 as thewellbore10 is formed. In some embodiments, column of modifiedmaterial306 is formed from a granular, or particulate, solid material, such as gravel or sand, that forms interstitial areas between adjacent solid particles. These interstitial areas make the column of modifiedmaterial306 permeable to gases.
• Heatsource310 may be at tubular member that extends into the column of modifiedmaterial306. Heatsource310 provides a conduit through which a heated fluid, such as steam, can be pumped to a desired location within the column of modifiedmaterial306. As heat is injected into the column of modifiedmaterial306, the heat is transferred to the surroundinghydrate formation12. This heat causesmethane gas18 to be released from thehydrate formation12 and flow into the column of modifiedmaterial306. The temperature of the heated fluid can be regulated to control the flow ofgas18 into thecolumn306. In certain embodiments, an ambient or cooled fluid can be injected throughheat source310 to effectively stop the flow ofgas18 intocolumn306.
• Gas18 will flow up through the column of modifiedmaterial306 towardscollector308 located at theseafloor56.Gas18 entersgas region314 where contact with the cool walls ofchamber312 causes water to condense and fall intoliquid region316. Gas/liquid separator318 uses the heat fromheat source310 to remove further gas from the water before excess water is removed throughvent326. Heatsource310 also serves to heat bothgas region314 andliquid region316 to createcirculation currents328 and330.Outlet320 provides fluid communication to a production unit or gas export pipeline.
• While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the system and apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Claims (10)

1-35. (canceled)

36. A system for extracting methane gas from a hydrate formation, said system comprising:

a plurality of wellbores extending into the hydrate formation;

a column of modified material substantially filling wellbores and in direct contact with the hydrate formation;

a heat source operable to provide heat to said modified material, wherein the heat is transferred through said modified material to the hydrate formation so as to release methane gas from said formation; and

gas collector means operable to control the flow of methane gas out of said formation.

37. A system according toclaim 36 wherein said wellbores are arranged in a circular array.

38. A system according toclaim 36 wherein said wellbores are arranged in a rectangular array.

39. A system according toclaim 36 wherein export pipes from multiple gas collectors are combined into a commingled collection chamber connected to a pipeline.

40. A system according toclaim 36 wherein said boreholes filled with modified material and in direct contact with the hydrate formation are used to heat the hydrate formation so as to release methane gas from said formation and recovering said gas from a conventional pressure relief well.

41. A system for extracting methane gas from a hydrate formation, said system comprising:

a wellbore extending into the hydrate formation;

a column of modified material substantially filling said wellbore and in direct contact with the hydrate formation, wherein said column of modified material is in multiple zones;

a heat source operable to provide heat to said column of modified material, wherein the heat is transferred through said column of modified material to the hydrate formation so as to heat the formation and release methane gas into said column of modified material; and

a gas collector in fluid communication with said column of modified material, wherein said gas collector is operable to control the flow of methane gas out of said column of modified material.

42. A system according toclaim 41 wherein the zones of modified material have differing properties.

43. A system according toclaim 41 wherein the zones of modified material have differing thermal conductivity.

44. A method for extracting hydrocarbon gases from a hydrate formation, the method comprising:

drilling a wellbore into the hydrate formation;

substantially filling the wellbore with a modified material that is permeable to gases;

supplying an oxidizer to a heat source in said modified material operable to provide combustion to fuel at said heat source and to heat said modified material so as to heat the hydrate formation and release hydrocarbon gases from the formation; and

collecting at least a portion of the hydrocarbon gases that flow into the wellbore.

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