CA2839136A1

CA2839136A1 - Method of recovering hydrocarbons from carbonate and shale formations

Info

Publication number: CA2839136A1
Application number: CA2839136A
Authority: CA
Inventors: William H. Rogers; Kenneth D. Rogers
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-01-09
Filing date: 2014-01-09
Publication date: 2015-07-09
Also published as: US20150192002A1

Abstract

A method to mobilize for production bitumen, kerogen, heavy oil, other hydrocarbons, and hydrogen contained in a subterranean formation comprised largely of silicate and carbonate minerals that are capable of generating a series of chemical reactions, that once induced are self-sustaining. Such formations include bitumen carbonates, unconventional oil or gas shales and oil shales. The induced silicate-reactions, carbonate-reactions and resulting hydrocarbon-reactions and heat generated in the formation are sufficient to chemically and physically decompose much of the rock structure so that it becomes porous and permeable. These reactions also convert the solid bitumen, heavy oil, kerogen and other hydrocarbons to fluid or gaseous forms and create formation fluids and reservoir pressure to help move hydrocarbons to production wells. Waste heat generated by the method may be used to generate electricity, or for other uses.

Description

METHOD OF RECOVERING HYDROCARBONS FROM CARBONATE AND
SHALE FORMATIONS
Field of the Invention The present invention relates to methods and systems to mobilize and produce hydrocarbons and related by-products from various sub-surface formations, including in particular, hydrocarbon-bearing impermeable carbonate and shale formations.
Background of the Invention New sources of conventional oil reserves have been significantly declining for several decades while the demand for energy has continued to grow. Conventional deposits of gas and oil in North America have essentially been found and largely depleted.
The increasing demand in North America has been generally met by a combination of unconventional oil and gas production and oil sands production.
The unconventional, oil sands and bitumen carbonate hydrocarbons are much more difficult and expensive to produce. Mineable oil sands production is well known and successful, but environmentally is a problem. Deeper oil sands are currently being produced with SAGD and/or solvent methods. Bitumen carbonates, located in the center of oil sands area of Alberta, are huge, solid and impermeable deposits, and have no known economic method of production. Oil shales, such as the Green River formation comprise solid kerogens and likewise have no known economic method of extraction.
Unconventional formations are common and comprise shale and siltstone rock hosting free oil and/or gas that may or may not originate from the same shale formation. The primary known method of producing economic amounts from tight unconventional formations is by drilling long horizontal production wells and fracturing the surrounding rock.
The recovery methods available to date have been unsuccessful in economically recovering hydrocarbons from the vast amounts of heavy hydrocarbons contained in solid impermeable carbonate rock formations such as the Grosmont carbonates and other bitumen carbonates of northern Alberta and the Green River formation oil shales and other unconventional oil shales. The recovery rates for light and medium weight unconventional oils are generally reported to be between 10 and 30 percent, even after enhanced recovery methods. The recovery methods for unconventional natural gas from the Montney, Horn River and Liard formations and other unconventional reservoirs are estimated by Canada's National Energy Board to be able to recover about 15 to percent of the total estimated gas.
The current art for the recovery of heavy hydrocarbons from solid impermeable subterranean formations is largely based on methods currently being used to enable economic recovery of bitumen from the Alberta oil sands, and heavy oils in Alberta and Saskatchewan. These methods are generally relatively expensive and are environmentally poor. The methods used in non-mining situations are some variation of the following:
= Steam Assisted Gravity Drainage (SAGD) and Cyclical Steam Stimulation (CCS) both of which use large amounts of natural gas to create steam to mobilize bitumen, and produce a fluid mixture of hot bitumen and substantial polluted water;
= Heat Assisted Gravity Drainage (HAGD), and Thermal Assisted Gravity Drainage (TAGD), which use heat from down hole electric heaters or other similar means to mobilize bitumen, and produces a mixture of hot bitumen and some polluted water;
= Vapor Extraction (VAPEX), and other solvent-based methods use diluents to mobilize the bitumen and produce a slurry of cool bitumen, diluent and some polluted water.
The above basic recovery methods can be combined in numerous ways and various supplementary processes or substances may be added to these basic processes with the objective of improving the recovery, improving the economics, achieving some in situ upgrading of the bitumen or reducing the pollution or rectifying other problems with the basic recovery methods. Fire flooding or in situ combustion systems, such as toe to heel air injection (THAI), have also been attempted, but with limited success.

2 All of the three initial basic methods have several major economic and environmental drawbacks: a) large amounts of injected energy is required to power the process, which is expensive; b) large amounts of scarce water is used and polluted; and c) large quantities of greenhouse gases are generated and released to the atmosphere.
For unconventional oil or gas production extensive hydraulic fracturing is required, which is expensive and generally has similar or worse environmental problems.
All known methods for in situ mobilizing of hydrocarbons in a bitumen carbonate formation, as well as in all other heavy oil and deeper oil sands formations, have the fundamental requirement that heat or diluents must be applied into the formation from the surface, essentially continuously. The mobilizing process usually takes the form of some variation of steam or diluent injection or some form of electronic or gas heaters being placed in the formation.
Electric heaters, SAGD, HAGD, CSS and combinations thereof and VAPEX involve the continuous or near-continuous injection of large quantities of energy or fuel from the surface in the attempt to mobilize at least some kerogen, bitumen or heavy oil in the formations. The cost to continuously do this is the major reason these processes are so expensive. The process of generating the heat or the solvents required is also one of the primary sources of greenhouse gas emissions to the atmosphere.
Bitumen carbonates (and oil or gas shales or siltstones) are very solid and very impervious rock formations. Heating the formation to typical SAGD/CSS
temperatures of less than 400 C will not make a significant change to these two characteristics. The formations are very solid and generally nothing will flow through them. This means injecting concoctions of fluids will likely also have little effect, as they will generally not penetrate the formation significantly. Injected heat and injected concoctions of chemicals are the essence of all the current bitumen carbonate processes. If they work at all it appears they may be only marginally economic.
All current processes relating to bitumen carbonates are generally focused on the fact that sufficiently heated bitumen will flow. It will, however, only flow if it has an exit path to follow. In their natural state bitumen carbonate and shale formations have few if any such

3 paths. The formation rock structure, including the bitumen, is generally solid and impermeable.
To successfully produce a much greater percentage of contained hydrocarbons from bitumen carbonates it appears that the processes must be focused on attacking and modifying at least some of the rock structure throughout the formation. Then, immediately adjacent released hydrocarbons should find an exit path and be mobilized towards production wells. Talley, US 5,255,740, discloses a process that can theoretically recover some hydrocarbons from impermeable carbonate formations by injecting heat into the formation at temperatures that are high enough to decompose some of the immediate carbonate minerals contacted by the heat and make some of it more permeable. A hot fluid, usually steam, is used to deliver the heat to the rock structure, or a solvent is delivered which causes heat. The decomposition of some of the carbonate minerals is endothermic and cooling takes place. To attack and decompose more of the carbonate minerals to extend the improvement in permeability requires more very expensive on-going injections of heat and/or solvents. Like the bitumen carbonates, the oil shales are definitely less receptive to the methods that have been considered successful in oil sands production.
Shale gas and shale oil are found in sedimentary shale rocks (including siltstone) that are rich in organic material and which are usually both the source rock and the reservoir or trap for the natural gas or oil. The natural gas or oil found in these rocks is referred to as unconventional. They are stored in the host rock in three ways: (i) adsorbed onto insoluble organic matter generally referred to as kerogen, that forms a molecular or atomic film; (ii) free gas trapped in the extremely small pore spaces of the fine grained sediments interbedded with the rock much like conventional reservoirs; and (iii) confined in fractures within the shale itself Gas is also often held within other liquids such as bitumen and oil. These are often referred to as oil-bearing or gas-bearing shales.
With the developments of horizontal drilling, multistage hydraulic fracturing and pad drilling, massive shale formations such as the Bakken for oil and the Montney, Liard and Horn River for natural gas, have become very prolific producing areas. These production methods for oil and gas shales have changed the supply situation in North America. They

4 have also created a number of problems, such as immense fresh water usage and resulting contaminations. Unconventional wells have very rapid decline rates and are very expensive. Only a relatively small portion of the contained hydrocarbons in these shales is currently extractable, estimated by Canada's National Energy Board to be between 10 and 20 percent for natural gas.
With oil or gas-bearing shale formations, the only successful extraction method to date has been a direct attack on the formation, by fracturing parts of the formation. The reach of the fracturing generally does not interconnect with other applied fractures; such that in some formations the number of wells per section has been doubled and there is still little or no interconnecting of fractures. Fracturing is a very expensive process that extracts a relatively small percentage of the hydrocarbons in place. It also has been strongly criticized for its built-in greenhouse gas and other negative environmental impacts.
Oil shales differ from oil-bearing unconventional shales which contain petroleum or gas.
Oil shale is an organic-rich, fine grained sedimentary rock that contains essentially only kerogen. Kerogen is a solid mixture of organic chemical compounds from which liquid hydrocarbons referred to as shale oil can be produced. This process requires high temperatures to cause the chemical process of pyrolysis to yield a vapor, which on cooling produces a liquid shale oil. Kerogens are an early stage in the creation of petroleum through heat and pressure. To date there is no reported means of economically extracting hydrocarbons from these kerogen deposits. The known art includes a process that injects heat into a subterranean oil shale formation at a high enough temperature to decompose some of the rock (Papadopoulos et al., US 3,741,306). However, as is the case for the Talley process for carbonates, this process is essentially theoretical because heat must be injected continuously, thus making any in situ process prohibitively expensive. There are currently no economic extraction solutions for the massive oil shale deposits, such as the Green River formation in Colorado, Utah, and Wyoming.
It would be a major advance in bitumen carbonate and oil shale production if methods of recovery did not require immense on-going injections of heat energy or equivalent. It would be a major improvement in the development of tight oil or gas formations if there were a cheaper and more effective means of attacking the structure such that far more of

5 the contained hydrocarbons may ultimately be recovered. It would be a major environmental advance if production of hydrocarbons could be accomplished with the essential elimination of CO2 or other greenhouse gases being released to the atmosphere.
It would be a major environmental advance if production methods used little or no water.
It would make economic and environmental sense if significant waste heat generated from any production process could be used productively and economically.
Summary of the Invention The invention is a method to mobilize and recover hydrocarbons from impermeable subterranean hydrocarbon formations comprised largely of mixed silicate and carbonate minerals. The method is to induce within the formation a series of complementary and self-sustaining chemical reactions which attack and decompose much of the impermeable solid rock structure, thereby making it more porous and permeable. At the same time the reactions generate considerable heat, pressure and formation fluids, and thereby provide the fluidity and mobility needed for hydrocarbon recovery. An injection well and a production well, or a combined injection/production well, are provided extending into the formation. Heat and carbon dioxide are injected under pressure through the injection well into the formation materials, sufficient to cause (i) chemical reactions that decompose silicate minerals, thereby producing heat, (ii) chemical reactions that decompose carbonate minerals, thereby producing carbon dioxide, and (iii) heating of hydrocarbons, which creates additional chemical reactions plus fluidity of hydrocarbons.
Mobilized hydrocarbons plus CO2, 142, and 02 and pressure, create aggressive formation fluids which move through the decomposed material toward the production well. The pressured injection of heat and carbon dioxide into the formation materials is ceased when the three effects of the continuous injection have taken hold in the formation and the chemical reactions that decompose the silicate and carbonate minerals become self-sustaining.
Resulting formation fluids, including mobilized hydrocarbons, move through the decomposed structure primarily driven by pressure differential and gravity, and are recovered by way of the production well. In another embodiment, formation material immediately adjacent to the injection well is fractured prior to injections to allow the induced reactions to take place quicker and more assuredly. In yet another embodiment, formation material is fractured adjacent to the injection well and to the production well to

6 ensure there is a ready path to the production well. There are many benefits arising from the use of the invention, the two most significant being: (i) reduction of the costs for on-going heat injections during operations, and (ii) increase in the over-all recovery of hydrocarbons in place.
Further aspects of the invention and features of specific embodiments are described below.
Brief Description of the Drawings Figure 1 is a schematic, viewed from above, of an embodiment of layouts of the multi-well pad, injection wells, production wells and heat recovery wells for treating a hydrocarbon-containing formation comprised mainly of silicate and carbonate minerals.
Figure 2 is a schematic, viewed as an elevation, of an embodiment of layouts of the multi-well pad, injection wells, production wells and heat recovery wells for treating a hydrocarbon-containing formation comprised mainly of silicate and carbonate minerals.
Figure 3 is a schematic representation of a flow process for using the method of the invention in a subterranean formation comprised primarily of silicate and carbonate minerals to mobilize and produce hydrocarbons.
Figure 4 depicts a schematic representation of the heat recovery process or the flow process to deliver waste heat or some of the induced heat from the subterranean formation to the surface to generate electricity, or for another use of heat.
Detailed Description The method of the invention is based on three sets of chemical reactions occurring in situ in a subterranean formation comprised, in significant part, of silicate minerals, carbonate minerals and hydrocarbons. The reactions must be induced, but once induced the chemical reactions are complementary and self-sustaining. The method of the invention is referred to herein as the "Induced Reactions process", and the reactions are referred to as the "induced-reactions" while they are occurring in the formation because of injections from the surface.

7 Once the three sets of in situ chemical reactions are self-sustaining in a formation with a mix of minerals appropriate for the Induced Reactions process, they collectively create all, or virtually all of, the permeability, heat, formation fluids and pressure necessary to mobilize hydrocarbons and drive the hydrocarbons to lower pressure production wells.
The chemistry of each of the induced-reactions is well known.
Silicate-Reactions The first set of induced reactions is a species of weathering. Each metal mineral, such as mudstone (an aluminum silicate), has an enthalpy or an amount of energy as a thermodynamic system. When the chemical bonds of the mineral are broken by weathering, some of the enthalpy, in the form of heat, is released to the immediate environment. At normal surface temperatures and pressure this occurs extremely slowly, and is essentially imperceptible. Tuval et al., US 4,491,367, delineates the use of this exothermic chemical reaction to generate substantial subterranean heat. The weathering process, being the decomposition of the silicate minerals, can be artificially accelerated in a contained subterranean formation of the required composition and pressure by an order of 107 to 108 with the generation of large amounts of heat. This process, if 107, would essentially mean that the induced chemical reactions in the subterranean formation will decompose rock in one day that would take 10 million days or over 27,000 years of surface weathering to be similarly decomposed, an immense acceleration.
The types of formations needed to utilize this acceleration, require silicate minerals corresponding to the general formula:
aMx1OrbMz2OycSi02.dH20 where MI and M2 each stand for a metal, each of a, b, c, d, x, y, z, is an integer of Ito 10 and any one of a, b and d may also be zero.
The preferred silicate minerals are aluminosilicates, such as most clays and feldspars, corresponding to the general formula:
aM230.A1203cSi02.dH20

8 where a and c are as in the general formula and M3 is a monovalent metal and d is an integer from 1 to 10.
The accelerated weathering of an aluminosilicates comprises two parts:
dM20.A1203 cSi02.dH20 + dCO2 4 dMC03 + H4Al2S1209 + 4S102 + HEAT
and, because the H4Al2Si209 is unstable: H4Al2Si209 4 2142 + 02 + A1203 +
Si02 (This first group of reactions is referred to herein as "silicate-reactions") The silicate-reactions occur in situ and use CO2 to transform silicate minerals in a relatively solid and impermeable formation rock structure into a more porous and permeable structure, plus generate heat, formation fluids (comprised primarily of free hydrogen (142), free oxygen (02)), and additional reservoir pressure.
Carbonate¨Reactions It is well known that heating a solid piece calcium carbonate rock (limestone) in a test tube results in a white powder (lime) and a gas (CO2).
CaCO3 + heat -> CaO + CO2 The chemical bonds of dolomite, (CaMg)(CO3)2, a major component of the formation rock of the Grosmont carbonates formation, can similarly be decomposed into CO2 and a more porous residual substance replacing the original carbonate mineral.
(This second group of reactions is referred to herein as "carbonate-reactions").
The carbonate-reactions occur in situ and use heat to transform carbonate minerals in a relatively solid and impermeable formation rock structure into a more porous and permeable structure, CO2, and additional reservoir pressure.
Complementary and Self-Sustaining Reactions The silicate-reactions and the carbonate-reactions are complementary and supportive while reacting within the formation. The silicate-reactions generate the heat necessary to keep the carbonate-reactions going, which in turn provide the CO2 necessary to keep

9 silicate-reactions going. In the right balance of silicates and carbonates this is a self-sustaining process. It is expected that a large number of hydrocarbon formations will fit the requirements as silicates and carbonates are abundant and are common together.
Once induced and sustained, the carbonate-reactions and the silicate-reactions in the subterranean formation continue to decompose or break the chemical bonds of the silicate and carbonate minerals which comprise the majority of the rock structure of a formation suitable for the present invention.
Hydrocarbon-reactions, discussed below, start to occur once the hydrocarbons are exposed to the heat and other products of the silicate-reactions and the carbonate-reactions, after which they contribute to creating pathways to enable the silicate-reactions and carbonate-reactions to spread throughout the formation and eventually decompose much of the rock structure.
Because the induced-reactions will so significantly transform the formation rock structure, once they become self-sustaining and expand beyond the region where the reactions are induced, they are referred to collectively as "structure-changing-reactions".
The transformations of the silicate and carbonate minerals and the hydrocarbons, as the structure-changing-reactions spread through the formation, is relatively slow and has an effect like a very slow moving continuous fracturing of the formation.
Each of the silicate, carbonate and hydrocarbon chemical reactions has a role in: a) breaking down the rock structure, which increases the permeability in general and exposes the hydrocarbons in particular, b) creating formation fluids, c) increasing the pressure, and d) creating sufficient heat to liquefy the exposed hydrocarbons which mobilizes them to flow with the other formation fluids through the more permeable parts of the rock formation to lower pressure production wells.
Inducing the Reactions The silicate-reactions and carbonate-reactions cannot be started easily, especially in a solid and impermeable rock structure. They must be artificially started or "induced". The silicate-reactions normally need continuous CO2 to occur and the carbonate-reactions normally need continuous heat to occur.

The essence of the inducement procedure is to inject whatever is needed into the region near the bottom of each injection well of each unique reservoir to cause the reactions to occur until both: (a) the silicate-reactions are on-going using CO2 generated in situ from the carbonate reactions and (b) the carbonate-reactions are on-going using heat generated in situ from the carbonate reactions. The region near the bottom of each injection well where the reactions are to be induced is referred to as an "inducement pocket".
As part of the inducement stage only, target formations could possibly require the injection of only one of either heat or CO2 into the inducement pocket via the injection well. In most cases the inducement will require, or be more easily achieved, with the injection of both heat and CO2 into the inducement pocket. Other procedures that may be required or useful to kick-start the self-sustaining reactions in a particular formation include increasing pressure in the inducement pocket and fracturing the region near the bottom of each injection well to help create a more permeable inducement pocket. For better control of the process the inducement pocket fracturing may be extended to where fluid communication with the production well is created. For most solid and impermeable formations, all four procedures, injecting CO2, heat and pressure and some fracturing will probably be required. All four procedures are known art. The injections must be applied through the injection well until the reactions are induced and then sustained in the unfractured formation.
Injected CO2 passing through or near a down-hole electric heater, as an example, may be sufficient to start the reactive process. There are many known means of heating such a small area. Heating could be done prior to the injection of CO2. Such heating means may include injected steam or combustible fuel, both of which are well known in the art.
Depending on the water content of the formation, some injected steam may also be required as part of the inducement process. Once the silicate-reactions and carbonate-reactions become self-sustaining, all inducement injections of heat, CO2 and H2O would normally cease. Except for the possibility of supplemental injection of CO2 or heat if either silicate or carbonate minerals are inadequate in a portion of the formation, the injection well would subsequently have little purpose as such. It may be utilized as a conduit for monitoring purposes. In some situations it may be used as a production well When the formation is thick, minor vertical fracturing of the formation adjacent to each injection well may assist to establish early exit paths to production wells.
This would enable the early recovery of most quality medium hydrocarbons before higher temperatures change them. The recovery of progressively heavier hydrocarbons proceeds as the temperatures slowly increase through the on-going decomposition of the adjacent silicate minerals.
Hydrocarbon-Reactions Herein, "hydrocarbons" refers to any compound comprised primarily of carbon and hydrogen, including heavy hydrocarbons and accompanying elements, including but not limited to halogen elements, metallic elements, nitrogen, oxygen and sulfur;
and "heavy hydrocarbons" refers to kerogen, bitumen, heavy oil, tar, asphalt, coal, oil shale, natural mineral waxes and asphaltenes, as well as any accompanying smaller concentrations of sulfur, oxygen, nitrogen, and other elements in trace amounts.
The silicate-reactions and carbonate-reactions gradually breakdown the rock structure such that previously encapsulated hydrocarbons are exposed to sufficient of the heat, created by the silicate-reactions, that the hydrocarbons are progressively converted to fluid form. The hydrocarbons are also exposed to, and start to chemically react with, the formation fluids and other products of the decomposition.
The hydrocarbons, including related elements, especially sulfur and nitrogen, become an integral part of the series of chemical reactions that physically and chemically change the rock structure and otherwise help mobilize the hydrocarbons for production.
All petroleum products, including bitumen, heavy oil and other heavy hydrocarbons usually contain small amounts of non-hydrocarbon organic compounds containing sulfur, nitrogen and oxygen, and they also contain small amounts of metals, usually copper, iron, nickel and vanadium. As the solid heavy hydrocarbon component of the rock structure starts to break down into its new components, many of the resulting minerals and other substances will participate in chemical reactions with each other and with the substances created by decomposition of the silicate and carbonate minerals. The possible reactions are numerous and the reactions in each formation will vary with the unique makeup of the respective rock structures. Some reactions will improve permeability and the mobilization and recovery of hydrocarbons, and some may tend to hinder these targeted changes. These hydrocarbon reactions help create exit pathways from inducement-pockets to production wells.
Some of the hydrocarbon substances combine to form strong acids such as nitric acid (T-1NO3) and sulfuric acid (H2SO4) as well as weak acids and bicarbonate (HCO3). Some of the heavy hydrocarbons may be dissolved in available carbon dioxide (CO2) or water.
If a silicate mineral is hydrous, a significant amount of extremely hot water may be created. The strong acids in particular will cause reactions that contribute to the transformation of the resident rock and/or add heat.
The heat from the silicate-reactions ultimately causes some thermal cracking of some of the hydrocarbons. Some catalytic cracking may occur, particularly because a significant amount of hydrogen is created by the silicate-reactions. Some in situ refining occurs.
Increased pressure contributes significantly to the mobility of hydrocarbon-bearing formation fluids, especially gases. Increased pressure also helps move hot gases through the formation in front of the main heat-generating chemical reactions. The gases and other formation fluids are inclined to move toward lower pressure spaces and attack the adjacent rock while doing so. The pressure and chemical reactions help create exits from the inducement pocket and new small spaces referred to as "gas-pockets", to which these hot formation fluids can flow and eventually to production wells.
The chemical reactions arising between the hydrocarbon components and the products of the decomposing rock structure are referred to herein as "hydrocarbon-reactions".
In summary, the features of the Induced Reactions process include: chemically decomposing the rock structure to create all of the required heat, permeability, pressure and formation fluids in situ, rather than from the surface; the inducement of this as a complementary, self-sustaining process to mobilize and produce hydrocarbons;
the partial refining of the hydrocarbons in situ, the creation of considerable extra heat and free hydrogen as valuable by-products; and the lack of inherent environmental problems.

The Induced Reactions process is a genuine in situ process. After inducement, all heat required to mobilize and produce hydrocarbons by way of the silicate-reactions part of the process is generated in situ. This eliminates the large on-going cost required of all existing processes of continually injecting heat and/or solvents from the surface, or of fracturing and re-fracturing the formation.
More heat will be generated than is needed to decompose the carbonate minerals and convert the hydrocarbons to fluid form, even when silicate minerals comprise significantly less of the rock structure than carbonate minerals. Over time normally so much heat will be generated that cheap waste heat will be available for use at the surface using a heat recovery system. One embodiment, shown in Figure 3, recovers this abundant extra heat to produce electricity without generating greenhouse gases, using a method set forth in Rogers et al, US 2013/0234444, referred to as a "Pipes system" and a single module in a Pipes system, a "Pipes Circuit".
The structure-changing-reactions from a modest sized subterranean silicate/carbonate rock deposit (40m thick by 10km2, or 400,000,000 m3) could produce enough heat to run a sizable (approximately 300 MW) electric power plant for 30 years; assuming enthalpy of 230 Kcal/kg of rock, rock with a bulk density of 3, operating 7500 hours/year, recovering 40% of the heat to the surface and plant efficiency of 2700 Kcal/KWh.
In addition to heat, the in situ Induced Reactions process also creates all required permeability, reservoir pressure, and formation fluids necessary to mobilize and produce hydrocarbons. After the chemical reactions have been induced, injections of heat and/or solvents, CO2, pressure, water or other fluids from the surface will usually not be required, because each round of the structure-reactions is caused by some of the products of the previous round. Each new round of structure-reactions generates additional high temperature heat, additional CO2, and additional pressure. They also continually produce additional formation fluids comprised largely of free hydrogen and free oxygen and, carrying in solution or in suspension, additional mobilized kerogen, bitumen, heavy hydrocarbons and other hydrocarbons and coke.
The large quantity of the free hydrogen and free oxygen produced makes these valuable byproducts that can be sold or used on site. The lesser amounts of other valuable substances, such as sulfur, that are carried to the surface in the formation fluids can be accumulated and sold.
The produced formation fluids will also contain polluted water and other noxious substances, but far less than processes like SAGD. CO2 produced can be re-injected into the formation to cause additional silicate-reactions. The lesser amounts of polluted water and other noxious fluids that are produced and that are not valuable may be processed or stored and subsequently reinjected into the reservoir for permanent sequestration.
SAGD processes continuously inject hot water or steam into the reservoir and this water comprises the majority of the formation fluids and it is much polluted when it is produced. The Induced Reactions process essentially does not inject water or solvents, so it does not have a large scale environmental problem relating to its use of water. One embodiment, shown in Figure 3, re-injects any polluted water or other noxious fluids that may be produced so no greenhouse gases are released to the atmosphere, no settling ponds are needed and no release of polluted water into the environment occurs ¨ making the Induced Reactions process essentially pollution free.
The pollution-free dimension of the Induced Reactions process is very important. The Alberta oilsands is generally perceived by the public to be an environmental catastrophe.
With use of the Induced Reactions process in the Bitumen Carbonates much of this image could be changed, and costs of production would be substantially reduced at the same time.
In a formation with the required minerals mix the Induced Reactions process can mobilize and produce a marvelously high percentage of the bitumen and other hydrocarbons in place. In a formation, all but the lighter early-produced hydrocarbons will come in direct contact with the gradually increasing high temperature heat and abundant free hydrogen. This will cause in situ thermal cracking and hydrocracking of much of the remaining hydrocarbons, including solid kerogen, bitumen heavy hydrocarbons and even coke. One embodiment, shown in Figure 3, takes the partly refined bitumen that is produced through an on-site upgrading/refining facility using the byproducts, hydrogen and excess heat, to refine the hydrocarbons so they can avoid or reduce the heavy oil and bitumen price discounts.

As the process moves through a formation significant decomposition of the silicate and carbonate minerals will have taken place, meaning coke, solid heavy ends and other remaining hydrocarbons are no longer locked in as part of the rock structure.
The exposure to heat and hydrogen will liquefy and upgrade some of these. Much of the remaining bitumen, coke and other heavy ends will be carried by the formation fluids, in solution, by suspension or simply by pressure, to the production wells.
By doing minor fracturing in certain locations at the inducement stage, more assured exit paths will be created from the initial inducement pockets and structure-changing-chambers to production wells. This will allow earlier production and better control to be realized. It also allows production without as much heat being applied to the medium weight hydrocarbons.
Silicate and carbonate minerals will rarely be distributed evenly in a formation. In a =
selected formation, if carbonate minerals are lacking in some areas of the formation then supplemental injections of CO2 into those areas will continue the structure-reactions until more carbonates are available in the formation. Similarly, if silicates are lacking in an area then supplemental heat may be injected to keep the structure-reactions process advancing until more silicates are generally available in the formation.
A primary target of the Induced Reactions process is mobilizing and producing bitumen, kerogen and related hydrocarbons from solid impermeable formations such as the Grosmont carbonates and the Green River formations. The Induced Reactions process may also be used to mobilize and recover hydrocarbons from other subterranean hydrocarbon-bearing formations that also comprise a combination of silicate and carbonate minerals capable of supporting accelerated decomposition. These others include, but are not limited to, tight oil shales such as the Bakken formation, tight natural gas shales such as the Montney, Horn River and Liard formations in North East British Columbia, produced reservoirs that have remaining hydrocarbons for which other recovery methods may be less economic and possibly some oilsands formations.
Unconventional formations in which fracturing methods have previously been applied are a target, because a very high percentage of original hydrocarbons in place, particularly heavy hydrocarbons and kerogens, will still be in the formation. The original production wells may continue to be used. Injection wells would likely be established near or in areas previously fractured as these are natural inducement pockets with connection to production wells.
Oil shale formations comprising primarily kerogens are treated very similar to bitumen carbonate formations. The Induced Reactions process attacks the basic structure of the formation. The decomposition of the rock creates heat, permeability, pressure and formation fluids. Kerogens are exposed to the heat and the open exit paths allow the recovery of economic amounts of hydrocarbons from the pyrolyzed kerogen.
The present invention utilizes wells for three different purposes -production, injection and Pipes Circuits. Figures 1 and 2 provide a horizontal and vertical view respectively of one schematic layout of three types of wells - injection wells, production wells and Pipes Circuit wells. A multi-well pad is well known in the art. Several wells start on the surface in close proximity to one another and extend down into the formation via essentially vertical legs and then extend within the formation via essentially horizontal legs. In the preferred embodiment of the present invention, all the production wells 102 in Figure 2 extend vertically, from a multi-well pad 101, at the surface 105, down through the overburden 106, to the lower part of a contained hydrocarbon bearing formation above an underburden 108.
In Figure 1 all the production wells 102 then extend essentially horizontally near the bottom of the formation 107, half one direction from the multi-well pad 101, and half the opposite direction from the multi-well pad 101. The horizontal legs of the production wells 102, in each half, extend essentially parallel to one another. The horizontal legs of production wells 102 may be located at any elevation within the formation depending primarily on the form of hydrocarbon targeted. The injection wells 104 are vertical wells that extend vertically from various locations at the surface 105, down through the overburden 106 into the formation 107.
As seen in Figure 2 the Pipes Circuit wells 103 extend vertically, from the multi-well pad 101 at the surface 105, down through the overburden 106 to the upper part of the contained hydrocarbon bearing formation 107. The Pipes Circuit wells 103 then extend horizontally near the top of the formation 107, half in one direction from the multi-well pad 101, and half in the opposite direction from the multi-well pad 101. The horizontal legs of the Pipes Circuit wells 103, in each half, extend essentially parallel to one another.
The spacing and locations of Pipes Circuit wells will largely depend on the surface form, the use of the heat energy and its scale. Approximately the same number of Pipes Circuit wells as production wells may be the most efficient way to recover the waste heat during and after the period that production wells are economic to operate. However, fewer Pipes Circuit wells than production wells may be most efficient. This is because the hot gases created by the induced reactions will generally migrate toward the upper part of the formation where the Pipes Circuits are located. The injection wells may or may not be in a row running parallel to the production and Pipes Circuit wells as shown in Figure 1.
Figure 3 illustrates the flow process to mobilize and produce hydrocarbons using the Induced Reactions process in a subterranean hydrocarbon-bearing formation 107 comprised primarily of solid silicate and carbonate minerals. The formation may be a relatively compact formation containing bitumen and/or other heavy hydrocarbons that are in relatively solid form and plug the majority of the pores of the resident rock, making the formation relatively impermeable. The Grosmont and other bitumen carbonate formations in Alberta are believed to contain examples of such formations. The Induced Reactions process of the invention starts with two situ chemical reactions, the silicate-reactions and the carbonate-reactions. They will not begin to react in the reservoir without inducement from the surface 105. To start these two reactions and help them continue until they are self-sustaining and on-going will usually require: a) a fractured inducement pocket, and injections from the surface of: b) heat, c) CO2, d) pressure, and possibly e) steam.
In one embodiment of the process, the formation area at the bottom of the injection well 104 may be fractured in advance of the inducement process. In a second embodiment, the formation area adjacent to most of the length of the injection well 104 that is contained in the formation 107 may be fractured in advance of the inducement process. It is expected that normally such fracturing should be done until fluid communication to the production well is made.

As shown in Figure 3, an electric heater 115 is lowered to the bottom of the injection well 104 and is connected to a control mechanism 125. The electric heater 115 creates intense heat in the fractured space at the bottom of the injection well 104, referred to herein as an inducement pocket 126. When sufficient heat has been created in the inducement pocket, CO2 is flowed from a storage facility 120 through a pipe 121 to a compressor 122. The compressed CO2 flows through a pipe 123 to a pump 124. The compressed CO2 is injected under pressure by the pump 124 through the wellhead of the injection well 104 and down to the bottom of each injection well 104, close to, or through, the heater 115 and into the inducement pocket 126.
The prior art includes many methods to fracture and create a down-hole space like the inducement pocket 126 and create heat, pressure, CO2 and water/steam therein.
Any of these prior art methods may replace the above fracturing, use of an electric heater and injection of CO2 under pressure.
The CO2, fracturing and injected pressure starts the accelerated decomposition of the fractured silicate minerals, i.e. the silicate-reactions, in the inducement pocket 126. The pressure and heat created by the electric heater is also sufficient to start the accelerated decomposition of the fractured carbonate minerals, i.e. the carbonate-reactions, in the inducement pocket 126. As the carbonate-reactions commence, some heat is absorbed and CO2 and related pressure is produced. As the silicate-reactions commence, CO2 is absorbed, a great quantity of heat, H2 and 02 fluids and related additional pressure are produced.
The carbonate-reactions generate CO2 and pressure to help cause more silicate-reactions and the silicate-reactions generate heat and pressure to help cause more carbonate-reactions. Progressively less added CO2, heat and pressure will be needed via the injection wells 104 from the surface as the silicate and carbonate reactions themselves gradually generate enough heat, CO2 and pressure to keep the induced-reactions occurring on a self-sustaining basis.
As the silicate and carbonate reactions progress, the inducement pocket 126 progressively changes. The solid and impermeable silicate and carbonate minerals are slowly decomposed and converted or transformed into gases, liquids and more porous and permeable solids. The gases and liquids intermix to become the formation fluids. The solid and impermeable heavy hydrocarbons are freed from the decomposing rock structure and become exposed to the heat and chemically aggressive products of silicate-reactions and carbonate-reactions. Hydrocarbon-reactions commence. As additional silicate-reactions gradually increase the temperature in the inducement pocket 126, the light and medium hydrocarbons become fluids and are thus mobilized to then join the formation fluids.
The formation fluids along with related heat and pressure that migrate through natural fractures 129 to a gas-pocket 128 start to react with some of the components of the rock structure that comprise the edges of the natural fractures and the gas-pocket 128. To the extent induced fracturing above and near the production wells has occurred and/or natural fractures 129 exist between an inducement pocket and a gas-pocket 128 and production wells, some formation fluids, especially gases containing the lightest hydrocarbons, can flow to the production wells 102 at this stage.
As the self-sustaining silicate-reactions and carbonate-reactions progress in tandem with the related hydrocarbon-reactions, each inducement pocket 126 and natural fracture 129 gradually gets hotter and grows in size, enabling progressively heavier hydrocarbons and other formation fluids to flow to the gas-pockets, and to the production wells 102. New gas-pockets 128 are created. Each gas-pocket gradually gets hotter and grows in size as more formation fluids react with its rock structure. Gradually, each gas-pocket 128 is absorbed into a growing inducement pocket 126/130.
As the temperature in an inducement pocket gradually rises, the induced-reactions accelerate the structural transformation of immediately surrounding resident rock. At this stage, the self-sustaining induced-reactions and an inducement pocket are best described as structure-changing-reactions and a structure-changing-chamber 130, respectively.
As the self-generating structure-changing-reactions progress, the heat and the formation fluids in the structure-changing-chambers create more exit paths 127 from each structure-changing-chamber 130 and expand the size of the exit paths in addition to expanding the size of, and raising the temperature in, each structure-changing-chamber. More gas-pockets 128 get absorbed into structure-changing-chambers and new gas-pockets are formed. Acids and other products in the formation fluids react with the rock in the gas-pockets and increase the permeability of the gas-pockets and in particular the exit paths 127, including natural fractures 129, therefrom.
At lower temperatures the lightest hydrocarbons are subjected to pyrolysis and become part of the formation fluids that migrate to the gas-pockets. Given the fracturing around the injection wells, the light hydrocarbons and related less viscous formation fluids will be the first to migrate via new and expanded exit paths 127 and expanded natural fractures 129 to the production wells 102. As the temperatures rise in the structure-changing-chambers 130, pyrolysis and hydrocarbon-reactions cause medium weight hydrocarbons to convert from their solid form and become part of the formation fluids.
The higher temperatures in the structure-changing-chambers and additional products in the formation fluids expand the exit paths from the structure-changing-chamber to then more permeable lower pressure gas-pockets. Structure-changing-reactions begin in exit paths and gas-pockets.
The formation fluids, including medium hydrocarbons and more acids and other products, continue to react with the rock they encounter and further expand the gas-pockets, exit paths and natural fractures. These permeability changes enable the more viscous medium hydrocarbon-bearing formation fluids to migrate to the lower pressure production wells 102.
As the structure-changing-reactions progress further, the bitumen and other heavy hydrocarbons are more easily accessed by the heat and products that cause hydrocarbon-reactions, because more of the rock has been decomposed, and the temperatures and pressure in the structure-changing-chambers are both higher. As a result, the bitumen and heavy hydrocarbons become less viscous fluids and thus more mobile. Eventually temperatures and produced hydrogen will be sufficient in the first reaction areas that thermal cracking and hydrocracking will commence to refine some of the bitumen and heavy hydrocarbons, lower their viscosity and increase the mobility of the related formation fluids bearing these hydrocarbons.
In a progressive and gradual manner the structure-changing-chambers 130 grow and merge and eventually the entire reservoir may become a single large structure-changing-chamber. It is quite possible that virtually all the hydrocarbons will have been liquefied and produced before all of the silicate and carbonate minerals have been converted to gases and more permeable solids. It may be economic to continue to produce the formation fluids with little or no hydrocarbon content if the recoverable trace minerals, heat, hydrogen and oxygen arising from continued silicate reactions are sufficient.
As formation fluids are delivered from the high pressure reservoir 107 through the lower pressure production wells 102 to the wellhead at the surface, the formation fluids may flow in different sequences depending on the content, temperature and pressure of the fluids. A heat exchanger 131 captures heat from the fluids. One or more separators 132 remove the free hydrogen, free oxygen, trace minerals, CO2 and other greenhouse gases and water/steam from the hydrocarbons.
The separated hydrogen flows through a line 133 to a compressor 157 and the compressed hydrogen will flow through a line 134 to a storage facility 135.
Some hydrogen may flow through line 136 to a hydrocarbon upgrading or refining facility 137.
The separated hydrocarbons will flow through a line 138 to the refining facility 137. The refining facility may use waste heat from the Induced Reactions process directly via a Pipes circuit 103, directly from the heat exchanger for formation fluids and/or be powered by electricity delivered by a line 140 from the Pipes based electric power plant 155.
The CO2 flows from the separator(s) 132 through a pipe 139 to the CO2 storage facility 120 where it may flow via pipe 121, compressor 122, pipe 123, pump 124 and pipe 124A
to be injected under pressure down an injection well 104 into the reservoir to chemically cause additional silicate-reactions. Alternately the CO2 may be injected into the reservoir for permanent storage, after the heat has been mined by the Pipes circuits 103.
The other greenhouse gases flow from the separators 132 via a line 142 to a storage facility 143 and then via line 144 to a compressor 145. Via line 146 the compressed greenhouse gases may be injected down an injection well 104 for permanent storage.
Trace minerals of value such as sulfur and vanadium and gases such as oxygen will flow from the separators 132 to storage 160 from which they will be sold or used in a local process.

Referring to Figure 4, each Pipes well 103 has a vertical leg down to the upper part of the formation 107 and a horizontal leg that usually runs along the upper part of the formation to the end of the formation or property being produced. The bore hole 147 is cased 148 for its entire length. The far end of the casing horizontal leg has a plug 149. A pipe 154 is inserted inside the casing creating an annulus 150 between the pipe and casing that has essentially the same cross section area as the cross section of the pipe. The far end 151 of the pipe 154 is open.
A working fluid such as water is stored in facility 152 from which it flows to pump 153.
The working fluid is pumped from the surface 105 down the annulus 150 to the formation 107 where it will be heated and become steam as it flows along the horizontal leg through the formation to the plug 149. The critically hot steam then flows through the open end 151 of the inner pipe 154 to the surface without coming in direct contact with the formation rock or with greenhouse gases and other pollutants or the hydrocarbons in the reservoir 107. The heated fluid delivered by the Pipes system may be used to generate electricity on a major or minor scale from an on-site power plant 155, or for SAGD, or for a refinery 137 or any other use requiring heat.
As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof Accordingly, the scope of the invention is to be construed in accordance with the following claims.

Claims

Claims:

1. A method of mobilizing and recovering hydrocarbons from a subterranean formation comprising hydrocarbons, silicate minerals and carbonate minerals, comprising the steps of:
(a) providing an injection well and a production well extending into the formation;
(b) injecting carbon dioxide and heat under pressure through the injection well into the formation sufficient to cause chemical reactions whereby carbon dioxide decomposes silicate minerals, producing heat, (ii) chemical reactions whereby heat decomposes carbonate minerals, producing carbon dioxide, and (iii) heating of hydrocarbons, giving them greater fluidity;
(c) allowing the effects (i), (ii) and (iii) of step (b) to spread into the formation around the injection location and decompose silicate minerals and carbonate minerals in the formation creating in those areas a more permeable structure and hydrocarbons with greater fluidity;
(d) ceasing the injection of heat and carbon dioxide into the formation when the effects (i), (ii) and (iii) of step (b) have spread into the formation and the chemical reactions that decompose the silicate minerals and the carbonate minerals become self-sustaining; and (e) recovering resulting formation fluids comprising fluid and gaseous hydrocarbons from the production well.

2. A method according to claim 1, wherein, in step (b), the step of injecting heat through the injection well comprises heating a fluid or gas and injecting the hot fluid or gas through the injection well.

3. A method according to claim 2, wherein the hot fluid comprises carbon dioxide.

4. A method according to claim 1, wherein, in step (b), the step of injecting heat through the injection well comprises injecting a combustible fuel through the injection well and igniting the combustible fuel.

5. A method according to claim 1, wherein, in step (b), the step of injecting heat through the injection well comprises injecting a fluid or gas down the injection well through or close by a down hole heater.

6. A method according to any one of claims 1-5, further comprising, in step (b), injecting steam into the formation materials.

7. A method according to any one of claims 1-6, further comprising extracting heat from the formation and delivering it to the ground surface.

8. A method according to claim 7, wherein said step of extracting heat from the formation is continued after ceasing step (e).

9. A method according to any one of claims 1-6, further comprising providing a heat energy extraction system having a wellbore extending into the formation, and extracting heat energy from the formation using the heat energy extraction system.

10. A method according to any one of claims 1-9, further comprising recovering produced fluid or gaseous hydrocarbons from the injection well.

11. A method according to any one of claims 1-10, further comprising recovering heat energy from the produced formation fluids.

12. A method according to any one of claims 1-11, wherein the produced formation fluids further comprise carbon dioxide, and the method further comprising separating and compressing the carbon dioxide.

13. A method according to claim 12, further comprising sequestering the separated carbon dioxide.

14. A method according to any one of claims 1-11, wherein the produced formation fluids further comprise greenhouse gases other than carbon dioxide, and the method further comprises separating, compressing and sequestering said greenhouse gases.

15. A method according to any one of claims 1-14, wherein a portion of the formation contains insufficient carbonate minerals for the chemical reactions that decompose the silicate minerals to be self-sustaining throughout the formation, and the method further comprises using the existing injection well, or providing a second injection well into that portion of the formation, and injecting carbon dioxide under pressure into that portion of the formation, continuing to do so until sufficient carbonate minerals are available such that the chemical reactions that decompose the silicate minerals and the carbonate minerals become self-sustaining.

16. A method according to any one of claims 1-15, wherein a portion of the formation contains insufficient silicate minerals for the chemical reactions that decompose the carbonate minerals to be self-sustaining throughout the formation, and the method further comprises using the existing injection well, or providing a second injection well into that portion of the formation, and injecting heat under pressure into that portion of the formation, continuing to do so until sufficient silicate minerals are available such that the chemical reactions that decompose the silicate minerals and the carbonate minerals become self-sustaining.

17. A method according to any one of claims 1-16, further comprising suppressing the chemical reactions that decompose the carbonate minerals and the silicate minerals in at least a portion of the formation.

18. A method according to claim 17, wherein the suppressing is done by means of (i) injecting a gas other than carbon dioxide into the formation, (ii) injecting a cold liquid into the formation, or (iii) reducing the pressure in the formation.

19. A method according to any one of claims 1-18, wherein the production well includes a generally horizontal portion in the formation

20. A method according to any one of claims 1-19, wherein the production well includes a generally vertical portion in the formation.

21. A method of mobilizing and recovering hydrocarbons from a subterranean formation comprising hydrocarbons, silicate minerals and carbonate minerals, comprising the steps of:
(a) providing an injection well and a production well extending into the formation;
(b) fracturing a portion of the formation to form a region of fractured formation materials in fluid communication with the injection well;
(c) injecting carbon dioxide and heat under pressure through the injection well into the region of fractured formation materials sufficient to cause chemical reactions whereby carbon dioxide decomposes silicate minerals, producing heat, (ii) chemical reactions whereby heat decomposes carbonate minerals, producing carbon dioxide, and (iii) heating of hydrocarbons, giving them greater fluidity;
(d) allowing the effects (i), (ii) and (iii) of step (c) to spread into the formation around the region of fractured formation materials and decompose silicate minerals and carbonate minerals in the formation creating in those areas a more permeable structure and hydrocarbons with greater fluidity;
(e) ceasing the injection of heat and carbon dioxide into the region of fractured formation materials when the effects (i), (ii) and (iii) of step (c) have spread into the formation around the region of fractured formation materials and the chemical reactions that decompose the silicate minerals and the carbonate minerals become self-sustaining; and (f) recovering resulting formation fluids comprising fluid and gaseous hydrocarbons from the production well.

22. A method according to claim 21, wherein, in step (c), the step of injecting heat through the injection well comprises heating a fluid or gas and injecting the hot fluid or gas through the injection well.

23. A method according to claim 22, wherein the hot fluid comprises carbon dioxide.

24. A method according to claim 21, wherein, in step (c), the step of injecting heat through the injection well comprises injecting a combustible fuel through the injection well and igniting the combustible fuel.

25. A method according to claim 21 wherein, in step (c), the step of injecting heat through the injection well comprises injecting a fluid or gas down the injection well through or close by a down hole heater.

26. A method according to any one of claims 21-25 further comprising, in step (c), injecting steam into the region of fractured formation materials.

27. A method according to any one of claims 21-26, further comprising, in step (b), fracturing a portion of the formation to form a region of fractured formation materials in fluid communication with the production well.

28. A method according to any one of claims 21-26, further comprising, in step (b), fracturing a portion of the formation to form a region of fractured formation materials in fluid communication with both the injection well and the production well.

29. A method according to any one of claims 21-28, further comprising extracting heat from the formation and delivering it to the ground surface.

30. A method according to claim 29, wherein said step of extracting heat from the formation is continued after ceasing step (f).

31. A method according to any one of claims 21-28, further comprising providing a heat energy extraction system having a wellbore extending into the formation, and extracting heat energy from the formation using the heat energy extraction system.

32. A method according to any one of claims 21-31, further comprising recovering produced fluid hydrocarbons from the injection well.

33. A method according to any one of claims 21-32, further comprising recovering heat energy from the produced formation fluids.

34. A method according to any one of claims 21-33, wherein the produced formation fluids further comprise carbon dioxide, and the method further comprising separating and compressing the carbon dioxide.

35. A method according to claim 34, further comprising sequestering the separated carbon dioxide.

36. A method according to any one of claims 21-35, wherein the produced formation fluids further comprise greenhouse gases other than carbon dioxide, and the method further comprises separating, compressing and sequestering said greenhouse gases.

37. A method according to any one of claims 21-36, wherein a portion of the formation contains insufficient carbonate minerals for the chemical reactions that decompose the carbonate minerals to be self-sustaining throughout the formation, and the method further comprises providing a second injection well and injecting carbon dioxide under pressure through the second injection well into the formation.

38. A method according to any one of claims 21-37, wherein a portion of the formation contains insufficient silicate minerals for the chemical reactions that decompose the silicate minerals to be self-sustaining throughout the formation, and the method further comprises providing a second injection well and injecting heat through the second injection well into the formation.

39. A method according to any one of claims 21-38, further comprising suppressing the chemical reactions that decompose the carbonate minerals and the silicate minerals in at least a portion of the formation.

40. A method according to claim 39, wherein the suppressing is done by means of (i) injecting a gas other than carbon dioxide into the formation, (ii) injecting a cold liquid into the formation, or (iii) reducing the pressure in the formation.

41. A method according to any one of claims 21-40, wherein the production well includes a generally horizontal portion in the formation.

42. A method according to any one of claims 21-41, wherein the production well includes a generally vertical portion in the formation.

43. A method according to any one of claims 1-42, wherein the hydrocarbons comprise heavy hydrocarbons.

44. A method according to any one of claims 1-42, wherein the hydrocarbons comprise kerogen.

45. A method according to any one of claims 1-44, wherein the injection well and the production well are one and the same well, extending into the formation.