A method for in situ development of oil shale with reduced risk of groundwater contamination

Abstract

This invention discloses a method for in-situ development of oil shale to reduce the risk of groundwater pollution. The method involves in-situ oil shale mining technology, comprising: drilling at least three wells—an injection well, a heating well, and a production well—to the target oil shale formation, with the heating well located between the injection and production wells; installing a heating device in the heating well; introducing ambient temperature gas into the injection well, with a portion of the gas flowing away from the heating well to form a gas barrier preventing groundwater intrusion into the production area; activating the heating device, allowing the ambient temperature gas flowing through the heating well to carry the heat generated by the device to the production well, causing the oil shale to undergo a pyrolysis reaction upon contact with the heat-carrying gas, producing oil and gas, which is then collected in the production well and extracted. This invention, by placing a heating well between the injection and production wells and employing a combination of heat conduction and ambient temperature gas injection, improves heat utilization while simultaneously preventing groundwater contamination, thus reducing the risk of groundwater pollution.

Description

Technical Field

[0001] This invention relates to in-situ oil shale mining technology, and more particularly to an in-situ oil shale development method that reduces the risk of groundwater pollution. Background Technology

[0002] Currently, with the increasing severity of global energy problems, the production capacity of conventional oil and gas reservoirs is insufficient to meet demand, thus the development of unconventional oil reservoirs is receiving increasing attention. Among them, oil shale, with its wide distribution and abundant reserves, has become an important unconventional energy source. Oil shale contains a large amount of kerogen, which mainly exists in a solid, non-flowing form. To facilitate extraction, it is necessary to heat the kerogen to break it down into smaller, flowable hydrocarbon molecules. Therefore, oil shale development requires high-temperature conditions.

[0003] Currently, there are two main methods for oil shale extraction: surface pyrolysis and in-situ underground conversion. Surface pyrolysis is suitable for shallow oil shale formations, but it may generate waste gas, water, and pollutants such as cyanide and sulfides during extraction, causing serious environmental pollution; in addition, surface pyrolysis requires a large surface area. In contrast, the in-situ conversion method directly carries out the pyrolysis reaction of kerogen underground, and transports the cracked small-molecule oil and gas to the surface through a third well. This method requires less surface area and has relatively less environmental pollution.

[0004] Various methods and studies have been conducted on in-situ conversion technologies for oil shale, such as Shell's ICP technology, ExxonMobil's Electrofrac™ technology, Raytheon's electromagnetic radiation heating technology, Chevron's CRUSH technology, and the SCW technology developed by Kang et al. However, in the in-situ heating process of oil shale, a significant portion of the energy is still used to heat groundwater, leading to energy waste and increased costs.

[0005] Therefore, developing an environmentally friendly and energy-saving method for oil shale development is of particular importance. Summary of the Invention

[0006] The purpose of this invention is to provide a method for in-situ development of oil shale that reduces the risk of groundwater pollution, and to solve the problems of serious environmental pollution and high energy consumption for reservoir heating in existing oil shale development technologies.

[0007] The above-mentioned objectives of the present invention can be achieved by the following technical solutions:

[0008] This invention provides a method for in-situ development of oil shale to reduce the risk of groundwater pollution, comprising:

[0009] At least three wells shall be drilled to the target oil shale formation. The three wells include a first well, a second well, and a third well, with the second well located between the first well and the third well.

[0010] A heating device is installed in the well section of the second well located in the target oil shale producing layer to form a heated well with heating function;

[0011] Ambient gas is introduced into the first well, and part of the ambient gas flows to the side away from the second well, forming a gas barrier to prevent groundwater from intruding into the production area.

[0012] Once the gas barrier is formed, the heating device is activated, allowing some of the ambient temperature gas to flow through the heating device of the second well, forming hot gas with a temperature higher than the pyrolysis reaction temperature of the oil shale. At least some of the hot gas, while flowing towards the third well, comes into contact with the oil shale of the target oil shale producing layer, causing the oil shale to undergo a pyrolysis reaction and produce oil and gas. The produced oil and gas are then collected through the third well and extracted.

[0013] In one specific embodiment, the second well and the first well are sequentially arranged in a radially outward direction along the third well.

[0014] In one specific embodiment, multiple second wells and multiple first wells are spaced apart along the circumferential direction of the third well.

[0015] In one specific embodiment, the method for in-situ development of oil shale to reduce the risk of groundwater pollution further includes: obtaining the water-gas ratio in the third well, wherein the water-gas ratio in the third well is less than 2 cubic meters / 10 4 In cubic meter condition, turn on the heating device.

[0016] In one specific embodiment, at least one pressure sensor is provided in the first well. When the pressure obtained reaches the overburden pressure of the formation, the amount of gas introduced into the first well is reduced or gas injection is stopped.

[0017] In one specific embodiment, at least one temperature sensor is installed in the third well. When the obtained temperature does not reach the pyrolysis reaction temperature of the oil shale, the output power of the heating device is increased.

[0018] In one specific embodiment, the room temperature gas is nitrogen at room temperature.

[0019] In one specific embodiment, the method for in-situ development of oil shale to reduce the risk of groundwater pollution further includes: performing three-phase separation of oil, water and gas on the extracted oil and gas, storing and processing the separated oil and water separately, and sending the separated gas into subsequent stages after analysis by a gas analyzer.

[0020] In one specific embodiment, the separated gas, after being purified to a nitrogen concentration exceeding 95%, can be reinjected into the first well.

[0021] In one specific embodiment, when the nitrogen content in the separated gas is greater than 80%, the flow of room temperature gas into the first well is stopped.

[0022] The features and advantages of this invention are:

[0023] The in-situ development method for oil shale provided by this invention, which reduces the risk of groundwater pollution, involves setting up a heating well between the injection well and the production well. It employs a combination of heat conduction and ambient temperature gas injection. After a gas barrier is formed to prevent groundwater from intruding into the production area, a heating device causes ambient temperature gas to condense into hot gas during convective flow. As the hot gas carries heat to the production well, the oil shale comes into contact with it and undergoes a pyrolysis reaction to produce oil and gas. This method improves heat utilization while simultaneously preventing groundwater contamination and reducing the risk of groundwater being polluted by harmful substances in the production area. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the in-situ oil shale development method for reducing groundwater pollution risk according to the present invention;

[0026] Figure 2 This is a water saturation profile of the in-situ oil shale development method for reducing groundwater pollution risk according to the present invention.

[0027] Figure 3 This is a graph showing the changes in bottom hole pressure and oil rate over time for the in-situ oil shale development method of the present invention, which aims to reduce the risk of groundwater pollution.

[0028] Explanation of icon numbers:

[0029] 1. Injection well; 2. Heating well; 3. Production well; 4. Heating device; 5. Air compressor; 6. Temperature and pressure integrated sensor; 7. Gas analyzer; 8. Three-phase separator; 9. Gas phase; 10. Aqueous phase; 11. Gas barrier;

[0030] a. Water purification period; b. Water compression period; c. Water recirculation period. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] like Figure 1 As shown, this invention provides a method for in-situ development of oil shale to reduce the risk of groundwater pollution, comprising the following steps:

[0033] Step S1: Drill at least three wells to the target oil shale formation. The three wells include the first well, the second well, and the third well, with the second well located between the first and the third wells.

[0034] Step S2: Install heating device 4 in the well section of the second well located in the target oil shale producing layer to form a heated well 2 with heating function, and complete the ground power connection after the heating device 4 is installed in place.

[0035] Step S3: Introduce ambient temperature gas into the first well. Some of the ambient temperature gas flows away from the second well, forming a gas barrier 11 at the interface with water to prevent groundwater from intruding into the production area.

[0036] Step S4: After the gas barrier 11 is formed, the heating device 4 is turned on. Some room temperature gas can flow through the heating device 4 of the second well to form hot gas with a temperature higher than the pyrolysis reaction temperature of the oil shale. At least some of the hot gas comes into contact with the oil shale of the target oil shale producing layer during the process of flowing to the third well, causing the oil shale to undergo a pyrolysis reaction to produce oil and gas. The produced oil and gas are collected through the third well and then extracted.

[0037] Among them, when the water-to-gas ratio in production well 3 was measured to be less than 2 cubic meters / 10 under standard conditions of 293.15 K and 101.325 kPa, 4 At cubic meters, an air barrier 11 is formed at the interface between room temperature gas and water.

[0038] During this period, as the pyrolysis reaction of oil shale proceeds, the effective porosity and permeability of the target oil shale producing layer gradually increase, which improves the flow rate of the oil and gas phase produced by the pyrolysis reaction into production well 3, thereby increasing the recovery rate of shale oil and gas. When the shale oil and gas extraction ends, the porosity and permeability of the oil shale producing layer have increased by at least two times.

[0039] Furthermore, based on the numerical simulation results, we can obtain, for example... Figure 2The water saturation profile shown indicates that, using the oil shale in-situ development method of the present invention to reduce the risk of groundwater pollution, groundwater has difficulty crossing the gas barrier 11 at the interface between the gas phase 9 and the water phase 10, and the molar fraction of hydrocarbons that settle at the gas barrier 11 due to molecular diffusion is less than 0.5%.

[0040] Specifically, such as Figure 1 As shown, the first well drilled is injection well 1, used for injecting ambient temperature gas. The gas flow direction of the injected ambient temperature gas in the target oil shale formation is as follows. Figure 1 As shown by the solid arrow in the center line; the second well drilled is heating well 2, used to house heating device 4, which heats the ambient temperature gas injected into gas injection well 1 to form hot gas. The heat transfer direction of heating device 4 in the target oil shale formation is as follows. Figure 1 As indicated by the solid arrow within the dashed line, the third well drilled is production well 3, used to collect shale oil and gas produced by the pyrolysis reaction of oil shale after contact with hot gas, and to form an oil and gas recovery channel. Thus, by using ambient temperature gas in-situ heating instead of high-temperature gas injection, the ambient temperature gas flowing away from injection well 1 forms a gas barrier 11 that prevents groundwater from intruding into the production area. This ensures that the groundwater within the gas barrier 11 is not affected by heating, concentrating the heat used to heat groundwater in existing development methods onto the pyrolysis reaction of the oil shale. This maximizes the use of the heat generated by heating device 4 for the pyrolysis reaction of the oil shale, achieving the goals of energy conservation and improved economic efficiency. The direction of groundwater flow is as follows: Figure 1 As indicated by the hollow arrow in the dashed line. In this embodiment, ambient temperature gas is injected into the oil shale reservoir from the injection well 1 via the air compressor 5. The preferred heating method for the heating device 4 is electric heating; preferably, the heating device 4 uses an electric heating rod.

[0041] The in-situ development method for oil shale of the present invention, which reduces the risk of groundwater pollution, sets up a heating well 2 between the gas injection well 1 and the production well 3. It adopts a combination of heat conduction and room temperature gas injection. After the gas barrier 11 that prevents groundwater from intruding into the production area is formed, the room temperature gas is turned into hot gas during the convection flow through the heating device 4. As the hot gas carries heat to the production well 3, it comes into contact with the oil shale and undergoes a pyrolysis reaction to produce oil and gas. While improving the heat utilization rate, it also achieves the barrier against groundwater and reduces the risk of groundwater being polluted by harmful substances in the production area.

[0042] According to one embodiment of the present invention, a second well and a first well are sequentially arranged in a radially outward direction from the third well. Specifically, the centerlines of the production well 3, the heating well 2, and the gas injection well 1 are in the same plane to maximize the use of the heat generated by the heating device 4 for the pyrolysis reaction of the oil shale.

[0043] Furthermore, multiple second wells and multiple first wells are spaced apart along the circumference of the third well. Specifically, multiple heating wells 2 and multiple gas injection wells 1 are spaced apart along the circumference of the production well 3, and the heating wells 2 and gas injection wells 1 are spaced apart in a radially outward direction from the production well 3. That is, multiple heating wells 2 are spaced apart around the production well 3, and multiple gas injection wells 1 are spaced apart around the heating wells 2.

[0044] According to one embodiment of the present invention, the method for in-situ development of oil shale to reduce the risk of groundwater pollution further includes: obtaining the water-gas ratio in a third well, wherein the water-gas ratio in the third well is less than 2 cubic meters / 10 4 In cubic meter conditions, heating device 4 is activated. Specifically, under standard conditions of 293.15 K and 101.325 kPa, when the water-to-gas ratio in production well 3 is less than 2 cubic meters / 10... 4 When the volume reaches 1 cubic meter, it indicates that the gas barrier 11, which prevents groundwater from intruding into the production area, has been formed. The heating device 4 is then turned on, allowing the ambient temperature gas to enter a heated state, and the harvesting of shale oil and gas begins.

[0045] According to one embodiment of the present invention, at least one pressure sensor is installed in the first well. When the acquired pressure reaches the overburden pressure of the formation, the amount of gas introduced into the first well is reduced or gas injection is stopped to prevent formation fracturing or gas leakage. Operation is resumed only after on-site inspection and risk assessment. Specifically, at least one pressure sensor is located at the bottom of the gas injection well.

[0046] Furthermore, at least one temperature sensor is installed in the third well. When the obtained temperature does not reach the pyrolysis reaction temperature of the oil shale, the output power of the heating device 4 is increased to prevent insufficient heating from affecting the development efficiency of the oil shale. Specifically, at least one temperature sensor is installed at the bottom of the production well. In this embodiment, at least one temperature and pressure integrated sensor 6 for detecting temperature and pressure is installed at the bottom of both the gas injection well 1 and the heating well 2.

[0047] According to one embodiment of the present invention, the ambient temperature gas is nitrogen at ambient temperature. Specifically, using an inert gas such as nitrogen as the injection gas prevents the light oil and gas generated by the pyrolysis reaction of oil shale from dissolving in the nitrogen and being carried by the nitrogen, thus avoiding groundwater pollution during contact with water. In this embodiment, the gas introduced into the injection well 1 can also be carbon dioxide, gaseous hydrocarbons, or other inert gases. Of course, those skilled in the art can also select other gases with good flow properties within the oil shale producing layer according to the actual construction conditions, and the present invention does not limit this.

[0048] According to one embodiment of the present invention, the method for in-situ development of oil shale to reduce the risk of groundwater pollution further includes: performing three-phase separation of oil, water, and gas on the extracted oil and gas; storing and processing the separated oil and water separately; and analyzing the separated gas using a gas analyzer 7 before proceeding to subsequent stages. Specifically, the gas separated by the three-phase separator 8 is detected by the gas analyzer 7. By tracking changes in gas composition, the pyrolysis reaction of the oil shale and the oil and gas generation efficiency are determined. When an abnormal situation is detected, such as an increase in the concentration of harmful gases or a decrease in oil and gas generation efficiency, relevant contingency plans are activated.

[0049] According to one embodiment of the present invention, the separated gas, after being purified to a nitrogen concentration exceeding 95%, can be reinjected into the first well. Specifically, the separated gas, after being analyzed by a gas analyzer 7, is dried, purified to remove impurities, and further purified to a nitrogen concentration exceeding 95% before being reinjected into the injection well 1 for recycling.

[0050] According to one embodiment of the present invention, when the nitrogen content in the separated gas is greater than 80%, the injection of room temperature gas into the first well is stopped. Specifically, when the nitrogen content in the separated gas is greater than 80% as analyzed by the gas analyzer 7, the amount of oil and gas produced by the pyrolysis reaction of the oil shale has decreased to the economic limit. At this time, it is advisable to stop injecting nitrogen into the injection well 1, shut down the heating device 4, close the production well 3, and seal and abandon the oil reservoir.

[0051] During the development of oil reservoirs using the in-situ development method for oil shale that reduces the risk of groundwater pollution according to the present invention, the bottom hole pressure and oil production rate successively go through three stages: water purification period a, water compression period b, and water recirculation period c.

[0052] Please refer to the details below. Figure 3As shown, in the first stage, i.e., the water purification period a, groundwater is driven out of the production area by injected nitrogen. Under the continuous and stable injection of nitrogen, a bound water saturation condition is formed at the nitrogen-water interface under an inert gas environment, i.e., a gas barrier 11 is formed at the nitrogen-water interface. The gas barrier 11 continuously extracts groundwater, causing a decrease in the average reservoir pore pressure and the bottom hole pressure, during which pressure value A appears. In this stage, the pressure wave generated by gas injection does not reach the bottom boundary of the groundwater, and the influence of gravity can be ignored. At the end of the water purification period a, the bottom hole pressure just reaches pressure value B. At this time, the injection... The pressure wave generated by the gas just reaches the bottom boundary of the groundwater. At this time, due to the effect of gravity separation, the pressure wave accumulates at the bottom boundary of the groundwater, which is slightly higher than that of the wellbore area. At the same time, heating well 2 starts to heat continuously, and the injected nitrogen gas is heated into hot gas with a temperature higher than the pyrolysis reaction temperature of oil shale. During the process of hot gas contacting oil shale, kerogen in oil shale begins to decompose into oil and gas, pre-coke and coke. The oil and gas diffuse and flow to production well 3 and are extracted after collection. At this time, the effective porosity increases, but because pre-coke and coke are also solid products, they will not reach the initial total porosity.

[0053] In the second stage, also known as the water compression period (b), the composition of the porous medium in the production area changes, the temperature in the production area rises, and the average reservoir pore pressure increases. To ensure continuous and smooth gas injection, the nitrogen injection pressure is increased, leading to a corresponding increase in bottom hole pressure and oil production, culminating in a peak production rate. The bottom hole pressure corresponding to this peak production rate is denoted as pressure value C. During this period, water continues to be compressed, and the propagation direction of the pressure wave remains from the near-wellbore area to the bottom boundary of the groundwater. The greater the distance between production well 3 and injection well 1, the more kerogen can be consumed in the oil shale, and the longer the duration of the bottom hole pressure rise.

[0054] In the third stage, also known as the water recirculation period c, after the peak oil production, the overall pore pressure of the reservoir begins to decrease, the nitrogen injection pressure decreases, and the pressure wave propagates from the bottom boundary of the groundwater towards the near-wellbore area, causing groundwater to attempt to flow into the production area, which is blocked by the gas barrier 11 formed by the injected room-temperature nitrogen. In the later stage of the water recirculation period c, the bottom hole pressure gradually stabilizes at pressure value D.

[0055] The above descriptions are merely a few embodiments of the present invention. Those skilled in the art can make various modifications or variations to the embodiments of the present invention based on the content disclosed in the application documents without departing from the spirit and scope of the present invention.

Claims

1. A method for in situ development of oil shale with reduced risk of groundwater contamination, characterized in that, The methods for reducing the risk of groundwater pollution in in-situ development of oil shale include: At least three wells shall be drilled to the target oil shale formation. The three wells include a first well, a second well, and a third well, with the second well located between the first well and the third well. The second well and the first well shall be sequentially arranged in a radial direction outward from the third well. Multiple second wells and multiple first wells shall be spaced apart along the circumference of the third well. A heating device is installed in the well section of the second well located in the target oil shale producing layer to form a heated well with heating function; Ambient gas is introduced into the first well, and part of the ambient gas flows to the side away from the second well, forming a gas barrier to prevent groundwater from intruding into the production area. The water-gas ratio in the third well was obtained. Under standard conditions of 293.15 K and 101.325 kPa, when the water-gas ratio in the third well is less than 2 cubic meters / 10... 4 When the volume reaches cubic meters, it indicates that an air barrier preventing groundwater from intruding into the production area has been formed; Once the gas barrier is formed, the heating device is activated, allowing some of the ambient temperature gas to flow through the heating device of the second well, forming hot gas with a temperature higher than the pyrolysis reaction temperature of the oil shale. At least some of the hot gas, while flowing towards the third well, comes into contact with the oil shale of the target oil shale producing layer, causing the oil shale to undergo a pyrolysis reaction and produce oil and gas. The produced oil and gas are then collected through the third well and extracted.

2. The method for in-situ development of oil shale to reduce groundwater pollution risk according to claim 1, characterized in that, The first well is equipped with at least one pressure sensor. When the pressure reaches the overburden pressure of the formation, the amount of gas introduced into the first well is reduced or the gas injection is stopped.

3. The in situ oil shale development method that reduces the risk of groundwater contamination of claim 1, wherein, The third well is equipped with at least one temperature sensor. When the temperature obtained does not reach the pyrolysis reaction temperature of the oil shale, the output power of the heating device is increased.

4. The in situ oil shale development method that reduces the risk of groundwater contamination of claim 1, wherein, The gas at room temperature is nitrogen at room temperature.

5. The in situ oil shale development method that reduces the risk of groundwater contamination of claim 4, wherein, The method for in-situ development of oil shale to reduce the risk of groundwater pollution also includes: separating the extracted oil and gas into three phases (oil, water, and gas), storing and processing the separated oil and water separately, and analyzing the separated gas with a gas analyzer before proceeding to subsequent stages.

6. The method for in-situ development of oil shale to reduce groundwater pollution risk according to claim 5, characterized in that, The separated gas, after being purified to a nitrogen concentration exceeding 95%, can be reinjected into the first well.

7. The in situ oil shale development method that reduces the risk of groundwater contamination of claim 4, wherein, When the nitrogen content in the separated gas exceeds 80%, stop introducing room temperature gas into the first well.

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