A method for in-situ gasification of heavy oil based on micro nuclear reactor

Abstract

The present application relates to a kind of methods for in-situ gasification of heavy oil based on micro nuclear reactor, belong to oilfield development field, the method includes: build heating well and horizontal production well;With coolant micro nuclear reactor is placed in heating section, so that heavy oil occurs thermal cracking reaction and produces gas rich in CH4, light oil and coke;Gas and light oil are produced through production well;A straight well is built as injection well directly above the toe of production well, combined with production well into U-shaped well;Through the injection end, micro nuclear reactor is lowered, and through the production end, micro nuclear reactor loaded with catalyst is lowered;CO2 is injected into reservoir, so that coke generates CO by dissolution loss reaction;Cold water is injected through injection end, and water vapor is formed by heating through reactor, mixed with CO at the bottom of U-shaped well and enters production end to react, and mixed gas containing H2 and CO2 is produced.The present application can improve crude oil quality while producing clean fuel, and is low-carbon and environmentally friendly, solving the problem of nuclear waste disposal.

Description

Technical Field

[0001] This invention belongs to the field of oilfield development and relates to a method for in-situ gasification of heavy oil, particularly a method for in-situ gasification of heavy oil based on a micro nuclear reactor. Background Technology

[0002] Of the world's discovered crude oil resources, heavy oil reserves account for more than two-thirds. my country possesses over 20 billion tons of heavy oil resources, but currently only 7% is commercially exploitable. As conventional crude oil resources decrease annually, heavy oil's share in the energy mix will continue to grow. Most of my country's heavy oil reservoirs are terrestrial sedimentary, complex, and highly heterogeneous, with crude oil viscosities exceeding 10,000 mPa·s. Currently, steam injection remains the primary method for heavy oil extraction, but it is only suitable for reservoirs with depths below 1000m. Furthermore, steam extraction suffers from low thermal efficiency, high energy consumption, and high surface water treatment costs in its later stages.

[0003] In order to efficiently and environmentally exploit heavy oil reservoirs, an in-situ gasification test of heavy oil was conducted at Marguerite Lake in the 1980s. This test attempted to use wet combustion to produce fuel gases such as H2 through hydrothermal and thermal cracking reactions of heavy oil. However, the low gasification rate of heavy oil and the low H2 content in the produced mixed gas led to the failure of the wet combustion in-situ gasification project of heavy oil.

[0004] Studies have shown that when the temperature exceeds 300℃, heavy oil begins to vaporize in an anaerobic environment, undergoing a thermal cracking reaction, primarily characterized by free radical polymerization and the breakage of long-chain hydrocarbons. The final products include a mixed gas, light oil, and coke. The vaporization rate of heavy oil increases with temperature. Indoor studies indicate that within the temperature range of 450℃-600℃, the gas yield from heavy oil vaporization is approximately 0.2 g / g-0.3 g / g, the light oil yield is approximately 0.3 g / g-0.4 g / g, and the coke yield is approximately 0.2 g / g-0.3 g / g, which is 1.33-4.36 times that at temperatures of 300-400℃. The mixed gas is mainly composed of CH4, and the resulting light oil has a boiling point below 200℃. Furthermore, researchers have found that when the temperature exceeds 800℃, CO2 can undergo a dissolution reaction with coke (C + CO2 = 2CO). The study also showed that Zn-Cr-Cu oxide can catalyze the reaction between CO and water vapor at a temperature of 300-500℃, producing H2 and CO2 (CO + H2O = CO2 + H2).

[0005] The International Atomic Energy Agency (IAEA) defines nuclear reactors producing less than 20 MW of heat as microreactors. Microreactors are simple in structure, inexpensive, and have lower requirements for the quality of nuclear feedstock. Typically, nuclear waste from large nuclear power plants can be used as feedstock for microreactors. Westinghouse Electric has designed the eVinci™ microreactor with a power output of 0.2MW-5MW, which can operate stably for more than 3 years. Oklo has designed a 1.5MW microreactor that can operate stably for 20 years. Microreactors are extremely small, with diameters as low as 0.24m and heights only a few meters. They use molten metal salts as coolants, and reactor outlet temperatures can reach over 1000°C.

[0006] This invention proposes a method for producing clean fuel by in-situ gasification of heavy oil using a micro nuclear reactor to provide high temperatures. By using a micro nuclear reactor to maintain the process of generating clean energy from heavy oil cracking in the formation, the method eliminates wellbore heat loss and dependence on surface steam injection facilities, and can further expand the reservoir types and depth range for the application of heavy oil thermal recovery technology. Summary of the Invention

[0007] The purpose of this invention is to provide a method for in-situ gasification of heavy oil in an oil reservoir to produce clean gaseous fuels and light oils. This method is reliable in principle, simple to operate, and improves crude oil quality while producing clean fuels. It also boasts advantages such as low carbon emissions, environmental friendliness, and low cost, and has broad market application prospects. This invention can be used in newly discovered oil reservoirs, as well as in the later stages of oilfield development or for tapping and enhancing the remaining oil potential of abandoned old oilfields.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution.

[0009] First, a continuous micro-nuclear reactor is placed in the oil reservoir via a heated well. Control rods are used to control the temperature of the reservoir, promoting the cracking of heavy oil in the pyrolysis zone. Production is then initiated, yielding gaseous fuel and light oil. A vertical well is constructed at the toe of the horizontal production well as an injection well, forming a U-shaped well. The micro-nuclear reactor and a catalyst-loaded micro-nuclear reactor are placed at the injection and production ends of the U-shaped well, respectively. Next, the second stage of production begins, injecting CO2 into the coke layer via the heated well to dissolve the coke. Simultaneously, water is injected at the injection end of the U-shaped well to provide steam for CO conversion. Finally, H2, CO2, and steam are produced from the production end of the U-shaped well.

[0010] A method for in-situ gasification of heavy oil based on a micro nuclear reactor includes the following steps:

[0011] (1) Construct heating wells and production wells separately. The production well is a horizontal well. After completion, perforations are made evenly in the heating section of the heating well and the horizontal section of the production well.

[0012] (2) A miniature nuclear reactor with coolant is placed in the heating section of the heating well in the middle of the reservoir. The miniature nuclear reactor generates high temperature to heat the reservoir, causing the heavy oil to undergo thermal cracking reaction to produce gas rich in CH4, light oil and coke.

[0013] (3) After the thermal cracking reaction in the reservoir is completed, the production well is opened to produce CH4-rich gas and light oil, while the coke produced remains in the reservoir.

[0014] (4) A vertical well is built directly above the toe of the production well as an injection well, which is combined with the production well to form a U-shaped well. The injection well is the injection end and the production well is the production end. The micro nuclear reactor is lowered through the injection end and the micro nuclear reactor loaded with catalyst is lowered through the production end. The reactor core is not sealed in this step, and external fluids are allowed to pass through.

[0015] (5) The heating well continuously heats the reservoir and injects CO2 into the reservoir through the heating well, so that the coke produced by the thermal cracking reaction undergoes a dissolution reaction to generate CO;

[0016] (6) Cold water is injected through the injection end of the U-shaped well, heated by the reactor core to form steam, which mixes with CO at the bottom of the U-shaped well and enters the production end of the U-shaped well. The reaction occurs in the core of the micro nuclear reactor loaded with catalyst, producing a mixed gas containing H2, CO2 and steam.

[0017] (7) H2 enters the ground energy storage device, and CO2 and water vapor are separated by ground separation equipment and recycled.

[0018] Furthermore, in the aforementioned micro nuclear reactor, uranium-rich nuclear material is made into sub-millimeter-sized uranium particles, which are then wrapped with a graphite layer and a silicon carbide ceramic layer to improve the reactor's temperature resistance (withstanding 1760°C) and prevent reactor meltdown.

[0019] Furthermore, the micro nuclear reactor is equipped with a temperature sensor to monitor the temperature in real time. All the control rods of the micro nuclear reactor are connected to a connecting rod. The nuclear fission rate in the nuclear reactor is adjusted by an automatic program to achieve automatic adjustment of the nuclear reactor output temperature.

[0020] Furthermore, the encapsulation material, connecting rods, heating wells, and inner walls of the U-shaped well of the micro nuclear reactor are all coated with high-temperature resistant (1500℃) nanomaterials.

[0021] Furthermore, the coolant is a fluorinated metal salt, and the surface temperature of the micro nuclear reactor is maintained at around 1000°C by control rods, continuously providing sufficient energy for the thermal cracking reaction of heavy oil in the reservoir.

[0022] Furthermore, the thermal cracking reaction of heavy oil produces a large amount of gas and light oil. Due to the sealing property of the caprock, the gas accumulates at the top of the reservoir, forming a gas cap. The lower part of the reservoir contains light oil produced by cracking. This process is accompanied by a continuous increase in formation pressure. When the bottom hole pressure is monitored to be constant, it indicates that the thermal cracking reaction stage of heavy oil has ended.

[0023] Furthermore, after the heavy oil thermal cracking reaction stage is completed, logging is performed through the production well. If the coke severely blocks the reservoir pores, fracturing is carried out in the horizontal section of the production well to reconstruct the seepage channels.

[0024] Furthermore, if the formation pressure is too high, the reactor operating temperature is lowered by control rods, causing the gas to contract and reducing formation energy; if the production rate decreases too rapidly, the reactor operating temperature is raised by control rods, causing the gas to expand and increasing formation energy.

[0025] Furthermore, the core of the micro nuclear reactor at the production end of the U-shaped well is loaded with a catalyst that catalyzes the high-temperature reaction of CO and water vapor.

[0026] Furthermore, the core temperature of the miniature nuclear reactor at the injection and production ends of the U-shaped well is controlled to 500°C using control rods.

[0027] Furthermore, the pressure at the bottom of the U-shaped well is controlled by the rate of water injection at the injection end of the U-shaped well. The pressure at the bottom of the heated well is required to be higher than the pressure at the bottom of the U-shaped well, so that the generated CO can smoothly enter the bottom of the U-shaped well.

[0028] Furthermore, when the CO2 content in the mixed gas produced at the production end of the U-shaped well rises sharply and remains stable, it indicates that the coke produced by the thermal cracking reaction has been consumed and production has stopped.

[0029] Furthermore, after production is completed, the miniature nuclear reactor will be permanently buried underground, and the generated CO2 will be reinjected into the formation.

[0030] Furthermore, cement is reinjected into the formation to restore its structure after high-intensity thermal extraction.

[0031] Furthermore, the heating well can also be an old well that has been abandoned during the middle or late stages of oilfield development or when production has ceased.

[0032] This invention utilizes a miniature nuclear reactor to generate high-temperature heating in the reservoir, causing the heavy oil to undergo thermal cracking reactions to produce gaseous fuel (mainly CH4) and light oil (boiling point below 200℃). CO2 reinjection facilitates coke dissolution, mitigating the damaging effects of coke on the near-wellbore reservoir and burying greenhouse gases underground. Simultaneously, the CO2 injected through the heated well carries some heat, improving heat transfer efficiency and promoting coke dissolution. Cold water injected through the U-shaped well is heated in the reactor core to form steam, which mixes with CO at the bottom of the U-shaped well and enters the catalyst-loaded core, generating H2 and CO2. The CO2 and water vapor are separated by surface separation equipment and recycled.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Miniature nuclear reactors have a simple structure, stable operation, are safe and reliable, and have a low cost;

[0035] (2) The raw materials used in the nuclear reactor are derived from nuclear waste generated by large nuclear power plants, thus solving the problem of nuclear waste disposal;

[0036] (3) The produced gas contains a large amount of CH4 and H2, which are clean fuels; the produced crude oil is of high quality and can be used after simple processing;

[0037] (4) The generated CO2 is recycled and eventually reinjected into the formation along with toxic gases such as H2S, achieving zero CO2 emissions;

[0038] (5) The chemical reactions that occur in surface oil refineries are moved underground to reduce investment in surface facilities and reduce the impact on the ecological environment;

[0039] (6) Energy is transferred directly from the reactor core to the reservoir without the need for intermediate carriers, resulting in low energy loss and high utilization efficiency;

[0040] (7) The present invention has a wide range of applications. It is not limited to newly discovered oil reservoirs, but can also be used to improve the recovery rate of old oil fields. It is applicable to heavy oil reservoirs of any burial depth.

[0041] In summary, this invention achieves in-situ gasification of heavy oil, significantly improving reservoir recovery. While producing clean fuel, this invention reduces energy consumption in crude oil processing, transportation, and manufacturing by decreasing the heavy components in the heavy oil. This invention requires minimal surface infrastructure, saving costs and making it suitable for development scenarios with limited surface space. Attached Figure Description

[0042] Figure 1 This is a structural diagram of a miniature nuclear reactor.

[0043] Figure 2This is a schematic diagram of a miniature nuclear reactor structure with cooling pipes placed inside a well.

[0044] Figure 3 This is a well network layout diagram of a newly discovered oil reservoir.

[0045] Figure 4 This is a schematic diagram of the mechanism of the first production stage of a newly discovered oil reservoir.

[0046] Figure 5 This is a schematic diagram of the mechanism of the second production stage of the newly discovered oil reservoir.

[0047] Figure 6 This is a well network layout diagram for enhancing oil recovery in an old oilfield.

[0048] Figure 7 This is a schematic diagram of the mechanism of the first production stage of enhanced oil recovery in old oilfields.

[0049] Figure 8 This is a schematic diagram of the mechanism of the second production stage of enhanced oil recovery in old oilfields.

[0050] In the diagram: 1- Protective shell of a miniature nuclear reactor core coated with high-temperature resistant nanomaterials; 2- Coolant (can be gas, water, or molten metal salt); 3- Fuel rods containing submicron uranium particles; 4- Connecting rod; 5- Nuclear fission reaction control rod; 6- Wellbore; 7- Cooling pipe coated with high-temperature resistant nanomaterials; 8- Horizontal production well (located at the bottom of the reservoir); 9- Horizontal heating well (located in the middle of the reservoir); 10- Heavy oil accumulated at the top of the reservoir, pyrolyzed to produce CH4-rich gas; 11- Unexploited oil layer; 12- Light oil accumulated at the bottom of the reservoir, pyrolyzed; 13- Heavy oil pyrolysis reaction zone; 14- Coke deposited by the pyrolysis reaction; 15- With cooling... 16-Extension direction of the thermal cracking zone; 17-Flow direction of gas and light oil generated by thermal cracking; 18-CO2 injection; 19-H2O injection; 20-Newly built vertical well after the completion of the first stage of production (combined with production well 8 to form a U-shaped well); 21-CO generated by the dissolution reaction of coke accumulated at the top of the reservoir; 22-Unexploited coke layer; 23-Miniature nuclear reactor; 24-Extension direction of the coke dissolution reaction zone; 25-Coke dissolution reaction zone; 26-Fully dissolved coke zone; 27-Flow direction of CO and water vapor; 28-Miniature nuclear reactor loaded with catalyst; 29-Old wells in the old oilfield; 30-Remaining oil reservoir. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and examples to enable those skilled in the art to understand the invention. However, it should be understood that the present invention is not limited to the specific embodiments described herein. For those skilled in the art, any variations that fall within the spirit and scope of the invention as defined and determined by the appended claims are all within the scope of protection.

[0052] See the structure of the miniature nuclear reactor. Figure 1 , Figure 2 It includes a miniature nuclear reactor core protective shell 1, fuel rods 3 containing submicron uranium particles, and nuclear fission reaction control rods 5. All the control rods of the miniature nuclear reactor are connected to the connecting rods 4, and the core contains coolant 2.

[0053] The well pattern of the newly discovered oil reservoir is shown in [reference]. Figure 3 , 8, a horizontal production well located at the bottom of the reservoir and 9, a horizontal heating well located in the middle of the reservoir.

[0054] For the layout of the well network in the old oilfield, see Figure 6 To further improve the recovery rate of old oilfields, the original old well 29 can be converted into a heating well.

[0055] This invention includes two production stages:

[0056] In the first production stage, a miniature nuclear reactor 15 containing a metal salt coolant is placed in the heating section of heating well 9 (or in the old well 29). Production well 8 is shut down, the nuclear reactor is started, and the control rod 5 is moved via connecting rod 4 to control the reactor temperature (maintained at 1000℃). After the thermal cracking reaction in the reservoir is completed, production well 8 is opened, producing CH4-rich gas and light oil. The reservoir pressure during production can be adjusted via connecting rod 4.

[0057] In the second production stage, a new vertical well 20 is constructed directly above the toe of production well 8, forming a U-shaped well with it. Vertical well 20 serves as the injection end of the U-shaped well. A miniature nuclear reactor 23 is lowered into the injection end of the U-shaped well; its core is not sealed, allowing external fluids to pass through. A catalyst-loaded miniature nuclear reactor 28 is lowered into the production end of the U-shaped well; similarly, its core allows external fluids to pass through. During this stage, heating well 9 (or the existing well 29) is continuously heated. CO2 and cold water are injected into heating well 9 and vertical well 20, respectively, resulting in a catalytic reaction at the production end that produces H2-rich gas. Example

[0058] In-situ gasification of heavy oil production based on a micro nuclear reactor, such as... Figure 4 , Figure 5 , Figure 7 , Figure 8 As shown, the details are as follows:

[0059] (1) In-situ thermal cracking of heavy oil produces CH4-rich gas and light oil:

[0060] The cooling metal salt solution 2 carries heat from the core of the micro nuclear reactor 15, heating the oil layer. A thermal cracking reaction zone 13 forms in the area with temperatures above 300°C. As heat gradually diffuses into the reservoir, the thermal cracking zone extends towards the unexploited oil layer 11. Due to gravitational differentiation, CH4-rich gas is concentrated at the top of the reservoir 10, while the generated light oil accumulates at the bottom of the reservoir 12, and coke remains in situ 14.

[0061] (2) Production of CH4-rich gases and light oils:

[0062] When production well 8 is opened, the CH4-rich gas and light oil produced in situ flow out from production well 8. This process controls the reservoir temperature by adjusting connecting rod 4, and utilizes the principle of gas thermal expansion and contraction to control reservoir pressure, thereby controlling the production rate.

[0063] (3) In-situ CO generation from coke dissolution:

[0064] The miniature nuclear reactor 15 continuously provides high temperatures to the formation. After CO2 injection, a coke dissolution reaction zone 25 is formed in the area with temperatures above 800°C. The CO produced by the reaction accumulates at the top of the oil layer 21, and as the reaction proceeds, the dissolution reaction zone extends towards the unexploited coke layer 22. Eventually, the entire reservoir is filled with CO.

[0065] (4) Production of H2-rich gas:

[0066] The cold water injected into the U-shaped well is heated into steam in the core of the continuous micro nuclear reactor 23. Similar to (2), the reservoir pressure is controlled to be higher than the pressure at the bottom of the U-shaped well by the control rod 5, so that CO and water vapor are mixed and flow into the catalyst-loaded micro nuclear reactor 28, where H2 and CO2 are catalytically generated. The external fluid acts as a coolant; the coolant in the injection end core is the injected water, and the coolant in the production end core is water vapor and CO gas.

Claims

1. A method for in-situ gasification of thick oil based on micro nuclear reactor, comprising the following steps in sequence: (1) build a heating well and a production well respectively, the production well is a horizontal well, and after completion, uniformly perforate the heating section of the heating well and the horizontal section of the production well; (2) place the micro nuclear reactor with coolant in the heating section of the heating well located in the middle of the reservoir, use the micro nuclear reactor to generate high temperature to heat the reservoir, so that the thick oil generates thermal cracking reaction to produce gas rich in CH4, light oil and coke; (3) after the thermal cracking reaction in the reservoir is completed, open the production well, and produce gas rich in CH4 and light oil through the production well, and the generated coke is retained in the reservoir; (4) build a straight well as an injection well directly above the toe of the production well, and combine the injection well and the production well into a U-shaped well, the injection well is an injection end, and the production well is a production end; lower the micro nuclear reactor into the injection end, and lower the micro nuclear reactor loaded with catalyst into the production end, the reactor core of the nuclear reactor in this step is not sealed, and outside fluid is allowed to pass through; (5) continuously heat the reservoir through the heating well, and inject CO2 into the reservoir through the heating well, so that the coke generated by the thermal cracking reaction generates dissolution loss reaction to generate CO; (6) inject cold water through the injection end of the U-shaped well, heat the water vapor through the reactor core, mix with CO at the bottom of the U-shaped well, enter the production end of the U-shaped well, and react in the reactor core loaded with catalyst to produce mixed gas containing H2, CO2 and water vapor; (7) H2 enters the ground energy storage device, and CO2 and water vapor are separated through ground separation equipment and then recycled.

2. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, In the micro nuclear reactor, the nuclear raw material rich in uranium is made into uranium particles with a size of sub-millimeter, which is wrapped with a graphite layer and a silicon carbide ceramic layer.

3. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The control rods of all micro nuclear reactors are connected to a connecting rod, and the nuclear fission rate in the nuclear reactor is adjusted by automatically controlling the connecting rod to automatically adjust the output temperature of the nuclear reactor.

4. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The wrapping material of the micro nuclear reactor, the connecting rod of the control rod, the inner wall of the heating well and the U-shaped well are all coated with high-temperature-resistant nanomaterials.

5. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The coolant adopts metal fluoride salt, and the surface temperature of the micro nuclear reactor is maintained at 1000℃ through the control rod, so as to continuously provide energy for the thermal cracking reaction of thick oil in the reservoir.

6. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The thermal cracking reaction process of thick oil is accompanied by continuous increase of formation pressure, and when it is monitored that the formation pressure tends to be constant, it indicates that the thermal cracking reaction stage of thick oil is completed, and logging is performed through the production well, and if the coke blocks the pores of the reservoir seriously, fracturing is performed in the horizontal section of the production well to rebuild the percolation channel.

7. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The reactor core of the micro nuclear reactor in the production end of the U-shaped well is loaded with a catalyst for catalyzing the high-temperature reaction of CO and water vapor.

8. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The temperature of the reactor core of the micro nuclear reactor in the injection end and the production end of the U-shaped well is controlled to 500℃ through the control rod.

9. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The injection rate of water through the injection end of the U-shaped well controls the pressure at the bottom of the U-shaped well, and the pressure at the bottom of the heating well is required to be higher than that at the bottom of the U-shaped well, so as to ensure that the generated CO can smoothly enter the bottom of the U-shaped well.

10. A method of in situ gasification of heavy oil based on micro nuclear reactors according to claim 1, characterized in that, The heating well adopts an old well abandoned in the middle and late stages of oilfield development or after stopping production.

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