CA3111686A1

CA3111686A1 - Process for downhole gas to liquids (dgtl) conversion

Info

Publication number: CA3111686A1
Application number: CA3111686A
Authority: CA
Inventors: Leonid Surguchev; Michael SURGUCHEV
Original assignee: Hydrogen Source As
Current assignee: Hydrogen Source As
Priority date: 2018-09-06
Filing date: 2019-09-05
Publication date: 2020-03-12
Also published as: GB201814515D0; WO2020049304A1

Abstract

The present invention relates to a process for Downhole Gas to Liquids (DGTL) conversion comprising: introducing a catalyst or precursor for steam reforming (SR) reactions into a hydrocarbon gas-containing zone in a subterranean gas reservoir; raising the temperature in said reservoir to a temperature at which SR reactions occur; draining syngas (hydrogen and carbon monoxide) by means of a production well(s); generating liquid hydrocarbons from syngas (H2 and CO) downhole in the tubing of the production well(s) using catalysts for Fisher-Tropsch (FT) exothermic process in the form of slurry placed in the tubing or coated on the inner surface of the (easily replaceable) tubing in the production well.

Description

Process for Downhole Gas to Liquids (DGTL) conversion This invention relates to a process of Downhole Gas To Liquids (DGTL) conversion, using only vertical or slightly deviated injection and production wells. The process of the invention may be carried out in a field onshore or offshore, e.g. a natural gas field or a coal field, in order to generate and produce hydrogen and carbon monoxide (CO) in situ in the reservoir and to produce hydrocarbon liquid, low-sulfur diesel fuel, and synthetic fuel downhole in the production well.
Hydrogen and carbon monoxide can be generated in sub-terrain from hydrocarbons in the endothermic Steam Reforming (SR) reactions:
CH4 + H20 CO + 3H2 AH = + 206 kJ/mol CnH2n+2 nH20 nC0 + (2n+1)H2 + AH
Alternatively, oxygen may be incompletely reacted with methane (or other hydrocarbons) to produce carbon monoxide and hydrogen in the following exothermic reaction:
20H4 + 02 200 + 4H2 AH = - 75 kJ/mol Similar reactions will also happen with any other type of hydrocarbons, for example for heavier paraffins:
2CnH2n+2 n02 2n00 + (2n+2)H2 - AH
The present invention relates to the performance of a catalytic process of hydrogen and carbon monoxide generation from hydrocarbon-containing gas, e.g. natural gas, in situ within a subterranean geological formation, e.g. in a carbonate reservoir, a sandstone reservoir, a shale reservoir, a tight low permeable reservoir, in a coal field. This in situ production is achieved by placing a catalyst for hydrogen generation or precursor thereto within the reservoir (e.g. within the formation, e.g. rock, other porous or fractured medium, i.e. the material containing the hydrocarbon-containing gas and in most of the fields also water in connate immobile or mobile state), e.g. by means of an injection well, and raising the temperature within the SR catalyst or catalyst precursor-containing zone of the reservoir to a temperature at which SR reaction occurs (Figure 1). Then the generated hydrogen and carbon monoxide (syngas) are drained by the production well installed with tubing with Gas To Liquids (GTL) catalyst placed in a slurry or coated on the inner surface of the tubing pipe (Figure 2). The tubing with GTL catalyst will be easily replaceable in the DGTL production well. This DGTL installation in the production well (e.g. a Fischer-Tropsch (FT) reactor arranged an installed in the production well) will allow a Fischer¨Tropsch (FT) catalytic

2 process to take place downhole in the production well with production of liquid hydrocarbons, such as alkanes:
(2n + 1) H2 n CO ¨> CnH2n+2 n H20 - AH
The FT reactions occur in the presence of metal catalysts (cobalt, alkalized fused iron, other metals) at temperatures of 150-300 C (302-572 F). The process was first developed by Franz Fischer and Hans Tropsch at the Kaiser-Wilhelm-Institut fur Kohlenforschung in Mulheim an der Ruhr, Germany, in 1925. Most of the alkanes produced are straight-chain representing low sulfur diesel fuel. Typical pressures in the FT process range from one to several tens of bars. Higher pressures which will occur downhole in the production well will be favorable for the reactions and make the GTL process more efficient.
Cobalt catalysts are more active for FT synthesis when the feedstock is natural gas.
Alkalized fused iron catalysts can be used in higher temperature FT synthesis (above 300 C) to produce low-molecular-weight synthetic liquid hydrocarbons.
FT reactions are highly exothermic. In order to achieve efficient removal of heat from the well bore, water circulation in the annulus of the production well will be arranged (Figure 2). Heat from the circulated water will be recovered and consumed on the surface, giving extra energy to the process.
At the well head of the production well a simple separation unit can be installed (in case not all syngas has been converted to synthetic liquid fuel along the production tubing with FT catalyst along the well) to separate gas from the liquid fuel and reinject it in the reservoir or downhole to the gas influx coming into the production well.
The catalyst for SR reaction is preferably a metal-based catalyst. The metal-based catalyst that is introduced may be a material which is already catalytically active (e.g. a transition metal), preferably a porous or "sponge" metal (for example Raney nickel), or a material (e.g. a catalyst precursor) which will transform in situ, for example by thermal decomposition, into a catalytically active material. Many materials are known to be catalytically active for converting hydrocarbons to produce hydrogen and may be used in the process of the invention. Preferably, the catalyst should comprise nickel, platinum, and/or palladium, or alloys thereof.
Catalytically active particulates, for example metal or alloy particles, or metals supported on carrier particles, for example silica, alumina or zirconia particles, may be introduced into the reservoir by first fracturing a region of the reservoir around an injection well, for example by overpressure or by use of explosives, and then pumping in a dispersion of the particulate in a carrier liquid, for example water or a hydrocarbon.
Preferably, the catalyst or precursor thereto is introduced into the reservoir by means of an injection well.

3 Particularly preferably, the catalyst or precursor thereto may be applied in the form of a solution, for example in water or in organic solvent (such as a hydrocarbon which itself may be liquid or gaseous at atmospheric pressure). In the case of the precursor, the solution may be one of a metal compound which is decomposable, e.g. thermally decomposable, to form a catalytically active species, e.g. the precursor reacts or decomposes to form the catalyst. The catalyst and/or precursor may be in the form of particles of the material (e.g. metal). Preferably, the catalyst or precursor thereto is dissolved in an aqueous solution. Preferably the catalyst precursor is a metal compound, or a solution thereof, which is thermally decomposable to a catalytically active form or species.
Examples of such metal compounds or precursors include metal salts such as carbonyls, alkyls, nitrates, sulphates, carbonates, carboxylates (e.g.
formates, acetates, propionates, etc), humic acid salt, and such like. Double complexes, e.g. of palladium or platinum and nickel or zinc may, for example, be used. Metal humates are known to thermally decompose in the temperature range 100-1000 C, while double salts with oxalate and ammonium are known to thermally decompose in the range 200-400 C. The use of metal compounds which thermally decompose to produce particles of the catalytically active metal at temperatures in the range of 150-1100 C, especially 200-700 C, is especially preferred. Where a metal compound solution is applied, this may be a solution of a single metal compound or of two or more compounds of the same or different metals, generally transition metals, especially nickel. The concentrations of the metal compound in the solution will preferably be at or close to saturation.
The catalyst or precursor thereto may be applied over as large a horizontal distribution as possible, e.g. using a deviated section of an injection well.
However, a vertical, substantially vertical or near vertical section of an injection and/or production well is preferred for performing various aspects of the process as herein described.
Injection may, and preferably will, be at two or more locations up dip within the reservoir so as to create one or more reaction zones. If desired, injection may be at two or more depths so as to create two or more vertically stacked reaction zones, so that as the reaction progresses vertically it reaches zones of the reservoir that are pre-seeded with fresh catalyst.
Alternatively, the catalyst or precursor thereto may be placed in a well, e.g.
by packing a perforated liner in the hole with a particulate catalyst or by the use of nickel or nickel-coated liners (e.g. with a porosified nickel internal coating) in the dedicated well. Such catalysts or their precursors may be activated by heating in a hydrogen atmosphere and may be maintained in an activated state under nitrogen until the thermal front reaches the liners.
In general, a temperature sensor will be placed within the borehole liner at the catalyst

4 PCT/GB2019/052475 "injection" site (through which can be injected e.g. one or more catalysts and/or catalyst precursors) so as to identify when the local temperature of the reservoir has risen to the level where hydrocarbon-to-hydrogen catalysed conversion will begin, and indeed to identify if and when the combustion front reaches the catalyst "injection" site.
The process of the invention involves raising the temperature of the zone of the reservoir containing the catalyst or a precursor thereto to a temperature at which hydrogen production occurs, typically between 500 C and 1000 C, preferably at least 500-600 C, optimally between 700 to 1000 C. The catalyst or its precursor can, and preferably will, be placed in the reservoir before this temperature is reached; however, catalyst and/or precursor placement may be effected once the local temperature of the reservoir has risen, for example to increase the local concentration of the catalyst in the reservoir or to provide a fresh catalyst. Typically, the catalyst or precursor thereto will be applied in amounts of at least one tonne calculated on the basis of the catalytic metal. Conveniently, the catalyst or precursor thereto can be applied at a concentration of 5 to 400 kg/m3, especially 10 to 200 kg/m3, particularly 50 to 100 kg/m3.
Raising the temperature in the reservoir may be achieved in several ways, e.g.
by the introduction of an agent (e.g. air or water/air mixture, steam) into the reservoir. For shallow reservoirs, particularly on-shore (i.e. under land rather than under sea) reservoirs, e.g. at depths of up to 1700 m, the temperature may be raised by injection of superheated water (steam). However, at greater depths, or, for example, with offshore reservoirs, the temperature loss of the superheated steam on transit to the injection site within the reservoir may be too great. In this event, the temperature within the reservoir can be raised by the injection of oxygen (e.g. as air) and initiation of hydrocarbon combustion within the reservoir.
Combustion may be initiated by electrical ignition down-hole, or self-ignition may occur, for example on oxygen injection into a deep, high temperature, light oil reservoir. Where oxygen is introduced in this way, it is preferred, although not essential, to co-introduce water, e.g. as steam.
The introduction of oxygen and/or water may occur at the same site(s) as catalyst or catalyst precursor introduction. However, more preferably, oxygen/water introduction is effected at sites below the catalyst or catalyst precursor introduction site, for example 10 to 500 m below, e.g. at one or more positions along a deviated well bore section.
However, a vertical, substantially vertical or near vertical section of a bore section is more preferred.
Where oxygen is introduced in this fashion, a high temperature front will pass through the reservoir ahead of the combustion front, thus causing hydrogen production to occur before the arrival of the combustion front. The high temperature front will activate the catalyst where thermal decomposition of the catalyst (or precursor thereto) material is required and will push catalyst (or precursor thereto) material, steam and produced hydrogen ahead of the combustion In general, hydrocarbon reservoirs already contain sufficient water for the steam reformation reaction to occur if a catalyst is present and the temperature is raised to the appropriate level. Accordingly, steam injection in the process of the invention is optional rather than essential if temperature raising is to be effected by hydrocarbon combustion.
Oxygen introduction, e.g. air injection, may conveniently be effected at a rate of up to million cubic metres per day, for example 0.5 to 8 103 m3/day. In this context, cubic metres means volume at standard (atmospheric) pressure and temperature.
Where steam is introduced, this can typically be at rates of 10 to 1000 kL
water per day. Desirably, the injection temperature is at least 300 C, especially at least 400 C;
however, where steam rather than combustion is to be used to raise the local temperature within the reservoir, the injection temperature will preferably be at least 600 C, for example up to 1100 C. Injection of oxygen (e.g. as air) can be alternated with water, if required.
Another energy efficient way to increase reservoir temperature to the required reformation level is a use of downhole heat pumps.
Also electric heating, downhole flameless or non-flameless reactors, non-flameless reactions in situ, or exothermic reactions downhole can be used to increase temperature in situ to the required level for endothermic reactions of hydrogen generation.
Preferably, the temperature in the hydrocarbon gas-containing zone is raised by using non-flameless reactions in situ, a non-flameless reactor, or exothermic reaction(s) in the downhole of an injection well.
The invention is especially economically suitable for use in offshore or onshore remote natural gas fields without existing pipe line transportation infrastructure, in low permeable tight hard to produce natural gas fields or in depleted non-commercial natural gas fields.
Depleted reservoirs, in this context, include reservoirs which have stopped producing or have non-commercial production rates due to decreased reservoir pressure.
In the depleted abandoned fields there often remains 20-30% of the initial gas volume in place, which due to depleted reservoir pressure cannot be commercially recovered.
These reserves are considered as non-commercial with the technologies available today, and are not accounted in reserves statistics. Primary recovery (natural reservoir energy) factor in natural gas fields under natural depletion can be in the range of 70-80% of the Gas Initially In Place (GI I P). Gravity drainage, compaction and water drive mechanisms in the reservoir can increase gas recovery from the field to 85-90% of GI I P. So, the reserves of natural gas in the fields with depleted reservoir pressure amount on average to 10-30% of GIIP
depending on reservoir properties and conditions. In the gas-condensate field, if the reservoir pressure falls below the dew point during production, the condensate will drop out within the reservoir, stick to the rock surface and remain immobile within the pores of the formation until its saturation exceeds the critical saturation to become mobile. From an economic standpoint, fluid and gas trapped within the reservoir pores at low saturations are generally considered a loss to reservoir rock. These remaining gas reserves are not accounted for under the category of technically recoverable resources with existing technologies and will be left abandoned in situ as non-commercial reserves. The subterranean gas reservoir may be situated in a coal field. The reservoir may be a carbonate reservoir, a sandstone reservoir, a shale reservoir, a tight low permeable reservoir or a natural gas reservoir with CO2 content in the gas.
Since the ability of hydrogen, steam and oxygen to pass through the reservoir is greater than that of water or hydrocarbons, the invention is also applicable to so-called "tight gas" reservoirs, i.e. reservoirs from which methane extraction is inefficient due to the low permeability of the reservoir formation and difficulties with reservoir pressure maintenance.
In the world there are known to be many such reservoirs, containing immense resources of hydrocarbon gas, from which hydrocarbon extraction is not currently economically feasible.
Such tight gas reservoirs typically contain dry hydrocarbon gas or hydrocarbon gas and condensate.
In the case of downhole heat pump used to achieve required temperature in the near well bore zone of the natural gas formation for hydrogen generation process may be performed in an energy efficient way.
Where steam is injected in the process of the invention without oxygen injection, the injection site is preferably at a depth of no more than 1700m.
Embodiments of the invention will now be described with reference to the accompanying drawings.
Figure 1 is a schematic illustration of the DGTL process including hydrogen and carbon monoxide generation process with SR reactions taking place in the reservoir and FT
process taking place inside the production well.
Referring to Figure 1, there is shown a subterranean hydrocarbon reservoir in, e.g. a natural gas field or a coal field 1 having two wells (injection well 2 and production well 3) and an injection unit 4. SR catalyst is introduced, e.g. via an aqueous solution of catalyst or catalyst precursor, via injection into the reservoir through the injection well 2. Thereafter an agent (e.g. air or water/air mixture) can be injected by injection unit 4 (compressor and/or compressor-pump) to initiate reactions. Other means of raising the temperature may be used. Low temperature oxidation reactions taking place in situ will establish a thermal front, which will reach the pre-cursor and decompose its compound to produce catalyst (e.g. in particulate form) and initiate SR reactions. Methane converted to syngas (H2 and CO) in SR
reactions will be drained from the reservoir by production well 2. The production well 2 is equipped with downhole equipment and materials 5 for FT process reactions.
Figure 2 shows DGTL in a production well 6 with downhole equipment inside production tubing 7. Water to remove heat from highly exothermic FT reactions is circulated in the annulus 8. Catalyst for FT reactions to take place downhole is placed in a slurry in the tubing or coated on the surface inside the tubing 9. Syngas (H2 and 00) 10 from SR reaction in the reservoir is drained through perforation 11 into the production well with a packer above the perforation interval. Synthetic liquid fuel 12 produced in FT
reaction inside the tubing is produced to the surface through the production well 6. The production well tubing 7 is made easily retrievable for the purpose of placing new catalyst downhole.

Claims

1. A process for Downhole Gas to Liquids (DGTL) conversion comprising:
introducing a catalyst or precursor for SR reactions into a hydrocarbon gas-containing zone in a subterranean gas reservoir;
raising the temperature in said reservoir to a temperature at which SR
reactions occur;
draining syngas (hydrogen and carbon monoxide) by means of a production well(s);
generating liquid hydrocarbons from syngas (H2 and CO) downhole in the tubing of the production well(s) using catalysts for Fisher-Tropsch (FT) exothermic process in the form of slurry placed in the tubing or coated on the inner surface of the (easily replaceable) tubing in the production well.

2. The process as claimed in claim 1, wherein the process is performed in a natural gas field onshore or offshore.

3. The process as claimed in any one of the preceding claims, further comprising recovering heat from the production wells by circulating water in the well annulus.

4. The process as claimed in any one of the preceding claims, wherein the subterranean reservoir is in a coal field.

5. The process as claimed in any one of the preceding claims, wherein the reservoir is a carbonate reservoir, a sandstone reservoir, a shale reservoir, or a tight low permeable natural gas reservoir.

6. The process as claimed in any one of the preceding claims, wherein the SR catalyst precursor is a metal compound which is thermally decomposable to a catalytically active form, or a solution thereof.

7. The process as claimed in any one of the preceding claims, wherein the temperature in said hydrocarbon gas-containing zone is raised by using non-flameless reactions in situ, a non-flameless reactor or exothermic reaction(s) in the down-hole of an injection well.

8. The process as claimed in any one of the preceding claims, wherein the temperature in said hydrocarbon gas-containing zone is raised to a temperature between 500 C and 1000 C, preferably between 700 C and 1000 C.