CN118442043A - Method and experimental device for improving shale oil recovery ratio by air injection and laser and magnetic field - Google Patents

Abstract

The present invention provides a method and experimental device for improving shale oil recovery rate by air injection in coordination with laser and magnetic field. The method cooperates with laser technology, air injection technology and electromagnetic induction technology, and activates the injected air and reservoir retention fluid through high-energy laser, providing a large number of active ions in a high-energy state at the initial stage of combustion, enhancing the diffusion and adsorption capacity of surface oxygen atoms in the initial stage of combustion of reservoir organic matter, and improving the combustion rate. Based on the electromagnetic induction theory, an external constant magnetic field is formed by direct current, which prompts the excited state plasma to move in a directional manner, enhances the plasma existence time, expands the expansion area of the combustion front, and improves the combustion stability. Finally, the method is verified by an experimental device to ensure its feasibility. The method and experimental device for improving shale oil recovery rate by air injection in coordination with laser and magnetic field provided by the present invention can improve the recovery rate of shale oil reservoirs and are easy to use.

Description

Method and experimental device for improving shale oil recovery by air injection, laser and magnetic field

Technical Field

The invention relates to the technical field of shale oil development, and in particular to a method and an experimental device for improving shale oil recovery rate by air injection in coordination with laser and magnetic field.

Background technique

China is rich in shale oil resources and has great development potential. According to statistics, 16 sets of shale formations have been discovered in more than 10 basins. According to preliminary estimates by different institutions, the geological resources of shale oil are (100-3772)×10 ⁸ tons, and the recoverable resources are (30-900)×10 ⁸ tons. They are mainly distributed in the Ordos, Songliao, Junggar, Bohai Bay and Sichuan basins. Efficient development of shale oil reservoirs is an important area to ensure the security of national oil supply and support the stable production of 2×10 ⁸ tons of crude oil. Shale reservoirs are dense, with low porosity and permeability, rich in solid organic matter, and low proportion of movable oil, so conventional development methods are difficult to carry out. The current development of shale oil mainly relies on large-scale volume fracturing of horizontal wells, but there are still problems such as rapid decline in oil production rate and low oil production; in addition, part of the fracturing fluid is retained in the reservoir and is difficult to reverse. According to on-site statistics, the hydraulic fracturing reverse rate of shale reservoirs is extremely low, most of which are less than 30%, and some reservoirs are even less than 10%. How to further expand the extension of hydraulic fractures, improve the recovery rate of shale oil reservoirs and the utilization rate of reservoir retained fracturing fluid has become an urgent problem to be solved in the development of shale oil reservoirs. Air injection technology has been introduced into the development of shale oil reservoirs as a high-efficiency thermal recovery technology in recent years. However, after hydraulic fracturing of shale oil reservoirs, the cracks are unevenly distributed, and it is difficult for the injected air to fully contact the organic matter in the reservoir, resulting in the inability to form a stable and advancing combustion front. To solve the above problems, the Chinese invention patent with publication number CN108252692A provides a method for improving the recovery rate of shale oil reservoirs by using air oxidation thermal fracture. The core step of this method is to inject air into the target block for well soaking, so as to promote the full contact between the organic matter in the shale reservoir and the injected air, thereby improving the exothermic effect of the oxidation of organic matter in the reservoir. However, shale reservoirs are highly heterogeneous, and it is difficult to establish a stable combustion cavity by directly injecting air to soak the well. The Chinese invention patent with publication number CN113216918A provides a method for improving the recovery rate of shale oil reservoirs by catalytic oxidation combustion and fracturing reservoirs. The core step of this method is to inject a mixture of oil-soluble catalyst and organic solvent into the shale oil reservoir through a horizontal well, and then carry out air injection and well suffocation operations. Under the action of the catalyst, the initial combustion efficiency of organic matter in the reservoir is enhanced, which promotes the stable advancement of the combustion chamber. However, this method has the following problems: 1) The oil-soluble catalyst is expensive and difficult to use in large quantities; 2) The injected oil-soluble catalyst is unevenly distributed, so the overall catalytic effect is poor. The above problems have limited the application of air injection technology in shale oil reservoirs. Therefore, it is necessary to innovate shale oil air injection efficient development technology.

In recent years, with the continuous maturity and improvement of femtosecond, picosecond and nanosecond laser technologies, their reliability, stability and controllability in practical applications have gradually improved. At the same time, with the development and maturity of microelectronics, micromechanics, micro-optics and other technologies, laser transmitters have been miniaturized. The development of these technologies has promoted the application of laser technology in shale oil reservoirs. For example, Chinese invention patents with publication numbers CN106437633A and CN114810041A have applied laser technology to the field of shale oil fracturing and development. However, the distribution of organic matter in actual reservoirs is highly heterogeneous, and the existence time of high-energy plasma is short. Therefore, the effective space only exists near the laser transmitter, which still needs further improvement. Therefore, it is very necessary to design a method and experimental device for improving shale oil recovery by air injection, coordinated laser and magnetic field.

Summary of the invention

The purpose of the present invention is to provide a method and experimental device for improving shale oil recovery rate by air injection coordinated with laser and magnetic field, which coordinates laser technology, air injection technology and electromagnetic induction technology, activates injected air and reservoir retained fluid through high-energy laser, provides a large number of active ions in a high-energy state at the initial stage of combustion, enhances the diffusion and adsorption capacity of surface oxygen atoms in the initial stage of combustion of reservoir organic matter, and improves the combustion rate. Based on the electromagnetic induction theory, an external constant magnetic field is formed by direct current, which promotes the directional movement of excited plasma, enhances the existence time of plasma, expands the expansion area of the combustion front, and improves combustion stability.

To achieve the above object, the present invention provides the following solutions:

A method for improving shale oil recovery by air injection, laser and magnetic field, comprising the following steps:

Step 1: A pair of parallel horizontal wells are installed at the upper and lower positions of the hydraulic fracturing well, the upper well is used as a magnetic pole well, and the lower well is used as a gas injection well. A laser emission device is set in the gas injection well, a sampling device, a temperature detection device and an electromagnet are set in the magnetic pole well, and a sampling device, a sound wave emission device and a temperature detection device are set in the hydraulic fracturing well;

Step 2: Start the laser emitting device to emit a laser beam at a predetermined power toward the shale surface near the hydraulic fracturing well;

Step 3: At fixed intervals, the formation acoustic wave data is obtained by an acoustic wave transmitting device, and whether the fracture structure between the gas injection well and the hydraulic fracturing well has changed is determined by the formation acoustic wave data;

Step 4: If a change occurs, the laser emission device is turned off, and air is injected into the formation. When the formation pressure reaches a first preset pressure threshold, the gas injection operation is stopped;

Step 5: Perform well soaking operation to collect temperature change data at the hydraulic fracturing well. If the temperature is lower than the first preset temperature threshold, start the laser emitting device to emit a laser beam at a constant power. If the temperature is higher than the first preset temperature threshold, the laser emitting device intermittently radiates the reservoir with a low-frequency laser.

Step 6: If the temperature at the hydraulic fracturing well is higher than the second preset temperature threshold, the temperature change data at the magnetic pole well is collected; if the temperature at the magnetic pole well is lower than the third preset temperature threshold, the laser emitting device and the electromagnet are started, wherein the laser emitting device intermittently irradiates the reservoir with a low-frequency laser, and the electromagnet irradiates the reservoir with a high magnetic flux; if the temperature at the magnetic pole well is higher than the third preset temperature threshold, only the electromagnet is started, and the electromagnet irradiates the reservoir with a high magnetic flux;

Step 7: If the temperature at the magnetic pole well is higher than the second preset temperature threshold, the electromagnet is turned off, and the oxygen concentration data at the gas injection well is collected. When the oxygen concentration in the produced gas is lower than the first preset concentration threshold, the well is opened for depletion production. When the temperature at the magnetic pole well is lower than the third preset temperature threshold, production is stopped.

Step 8: Start the next round of throughput, where the soaking time is set to 1-1.5 times of the previous cycle, and start multiple rounds of throughput according to steps 4-6;

Step 9: When the periodic oil change rate of the huff-and-puff well is less than 0.4, the huff-and-puff well is replaced with a hydraulic fracturing well for production.

Optionally, the first preset temperature threshold is 250°C, the second preset temperature threshold is 300°C, and the third preset temperature threshold is 150°C.

Optionally, the first preset pressure threshold is 1-1.5 times the original formation pressure.

Optionally, the first preset concentration threshold is 5%.

The present invention also provides an experimental device for improving shale oil recovery rate by air injection in coordination with laser and magnetic field, which is applied to the above-mentioned method for improving shale oil recovery rate by air injection in coordination with laser and magnetic field, and includes: an air compressor, a high-temperature and high-pressure combustion experimental device, a laser ignition device, an electromagnetic induction device, a gas-liquid separator, a gas collecting bottle, a liquid collecting bottle and a gas analyzer. The air compressor is connected to the gas storage tank through a pressure gauge and a first six-way valve, the gas storage tank is connected to the flow meter, the flow meter is connected to the input end of the high-temperature and high-pressure combustion experimental device through a second six-way valve, the second six-way valve is provided with a pressure gauge, a core is provided inside the high-temperature and high-pressure combustion experimental device, the laser ignition device and the electromagnetic induction device are connected to the high-temperature and high-pressure combustion experimental device, the output end of the high-temperature and high-pressure combustion experimental device is connected to the input end of the gas-liquid separator, the gas outlet end and the liquid outlet end of the gas-liquid separator are respectively connected to the gas collecting bottle and the liquid collecting bottle, and the gas collecting bottle is connected to the gas analyzer.

Optionally, the high-temperature and high-pressure combustion experimental device includes a combustion tube body and a thermocouple, the second six-way valve is connected to the input end of the combustion tube body, the output end of the combustion tube body is connected to the gas-liquid separator, a core is arranged inside the combustion tube body, a laser ignition window is arranged on the combustion tube body, and the laser ignition device performs laser ignition through the laser ignition window, a plurality of the thermocouples are arranged on the combustion tube body, and the electromagnetic induction device is connected to the combustion tube body.

Optionally, the laser ignition device includes a laser emitter, an energy receiving device, a spectroscope and a focusing mirror. The laser emitter radiates laser light into the interior of the combustion tube body through the spectroscope, the focusing mirror and the laser ignition window, and the laser light split by the spectroscope is input into the energy receiving device.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the method and experimental device for improving shale oil recovery rate by air injection coordinated with laser and magnetic field provided by the present invention, the method will coordinate laser technology, air injection technology and electromagnetic induction technology, firstly, the shale near the hydraulic fracture is instantly heated by laser, so as to promote the formation of thermal fractures, thereby communicating and expanding with the hydraulic fractures, in this process, the retained fluid near the fracture forms hot steam under the action of heat, and the minerals in the shale reservoir are dissolved under the action of hot steam, so as to promote the formation of dissolution pores, further enhance the reservoir conductivity, and then inject air, and activate the gas by laser to form plasma, so as to enhance the connection with the reservoir The oxidation reaction activity of organic matter in the reservoir is increased. In this process, hot steam can also provide more active groups, accelerate the diffusion and adsorption of injected air on the surface of organic matter in the reservoir, and further enhance the thermal effect of organic matter oxidation. Finally, the direction of plasma movement is controlled by the magnetic field, which not only increases the existence time of plasma, but also enhances the probability of collision between high-energy electrons in plasma and organic matter; Finally, the direction of plasma movement is controlled by the magnetic field, which not only increases the existence time of plasma, but also enhances the probability of collision between high-energy electrons in plasma and organic matter; Compared with the electric ignition method, the laser ignition method has the advantages of precise control of ignition time, high ignition energy, reduced heat loss during ignition and reduced _NOx emissions. Introducing it into the ignition application of air/crude oil mixture in the reservoir can reduce the flameout rate in the initial stage of combustion; The experimental device can verify this method and ensure the feasibility of this method.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

FIG1 is a schematic diagram of the structure of a hydraulic fracturing well, a magnetic pole well and a gas injection well;

FIG2 is a schematic diagram of the experimental device structure of the air intake and exhaust experiment (electric ignition);

FIG3 is a schematic diagram of the structure of an experimental device for improving shale oil recovery by air injection in cooperation with laser and magnetic field according to an embodiment of the present invention;

FIG4 is a schematic diagram of shale binarization after air huff and puff (electric ignition);

FIG5 is a schematic diagram of shale binarization after air huff and puff (laser ignition);

FIG6 is a schematic diagram of shale binarization after laser and magnetic field assisted air huff and puff;

FIG7 is a schematic diagram of a binary image of shale after air huff and puff (electric ignition) and median filtering;

FIG8 is a schematic diagram of a binary image of shale after air huff and puff (laser ignition) and median filtering;

FIG9 is a schematic diagram of a binary image of shale after laser and magnetic field assisted air huff and puff and median filtering processing;

FIG10 is a schematic diagram showing the comparison of recovery factors of different rounds of air injection huff and puff (electric ignition), air injection huff and puff (laser ignition) and laser and magnetic field assisted air huff and puff;

FIG11 is a schematic flow chart of a method for improving shale oil recovery by combining air injection with laser and magnetic field according to an embodiment of the present invention.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

The purpose of the present invention is to provide a method and experimental device for improving shale oil recovery rate by air injection coordinated with laser and magnetic field, which coordinates laser technology, air injection technology and electromagnetic induction technology, activates injected air and reservoir retained fluid through high-energy laser, provides a large number of active ions in a high-energy state at the initial stage of combustion, enhances the diffusion and adsorption capacity of surface oxygen atoms in the initial stage of combustion of reservoir organic matter, and improves the combustion rate. Based on the electromagnetic induction theory, an external constant magnetic field is formed by direct current, which promotes the directional movement of excited plasma, enhances the existence time of plasma, expands the expansion area of the combustion front, and improves combustion stability.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG11 , the method for improving shale oil recovery by air injection in coordination with laser and magnetic field provided in an embodiment of the present invention includes the following steps:

Step 1: A pair of parallel horizontal wells are installed at the upper and lower positions of the hydraulic fracturing well, the upper well is used as a magnetic pole well, and the lower well is used as a gas injection well. A laser emission device is set in the gas injection well, a sampling device, a temperature detection device and an electromagnet are set in the magnetic pole well, and a sampling device, a sound wave emission device and a temperature detection device are set in the hydraulic fracturing well;

Step 2: Start the laser emission device to emit a laser beam at a predetermined power to the shale surface near the hydraulic fracturing well, so as to promote the formation of thermal cracks and enhance the connectivity between the gas injection well and the hydraulic fracturing well;

Step 3: At fixed intervals, the formation acoustic wave data is obtained by an acoustic wave transmitting device, and whether the fracture structure between the gas injection well and the hydraulic fracturing well has changed is determined by the formation acoustic wave data;

Step 4: If a change occurs, the laser emission device is turned off, and air is injected into the formation. When the formation pressure reaches a first preset pressure threshold, the gas injection operation is stopped;

Step 5: Perform well soaking operation and collect temperature change data at the hydraulic fracturing well. If the temperature is lower than the first preset temperature threshold, start the laser emission device to emit a laser beam at a constant power to ionize the injected air to form plasma, thereby enhancing the initial reaction activity of combustion. At the same time, in this process, the retained fluid near the hydraulic fracturing well is activated into active groups under the radiation of high-energy laser, which accelerates the diffusion and adsorption of the injected air on the surface of organic matter in the reservoir and enhances the thermal effect of organic matter oxidation. If the temperature is higher than the first preset temperature threshold, the laser emission device intermittently radiates the reservoir with low-frequency laser to enhance the combustion reaction rate.

Step 6: If the temperature at the hydraulic fracturing well is higher than the second preset temperature threshold, the temperature change data at the magnetic pole well is collected; if the temperature at the magnetic pole well is lower than the third preset temperature threshold, the laser emitting device and the electromagnet are started, wherein the laser emitting device intermittently radiates the reservoir with a low-frequency laser, and the electromagnet radiates the reservoir with a high magnetic flux, so that it can generate sufficient magnetic field force to cause the plasma to move in a directional manner, accelerate the overall movement of the plasma cloud, and thus enhance the air injection range of the shale oil reservoir; if the temperature at the magnetic pole well is higher than the third preset temperature threshold, only the electromagnet is started, and the electromagnet radiates the reservoir with a high magnetic flux to form a magnetic field to cause the high-energy active groups formed under the action of the combustion heat to move in a directional manner, thereby enhancing the combustion exothermic activity;

Step 7: If the temperature at the magnetic pole well is higher than the second preset temperature threshold, the electromagnet is turned off, and the oxygen concentration at the gas injection well is collected. When the oxygen concentration in the produced gas is lower than the first preset concentration threshold, the well is opened for depletion production. When the temperature at the magnetic pole well is lower than the third preset temperature threshold, production is stopped.

Step 8: Start the next round of throughput, where the soaking time is set to 1-1.5 times of the previous cycle, and start multiple rounds of throughput according to steps 4-6;

Step 9: When the periodic oil change rate of the huff-and-puff well is less than 0.4, the huff-and-puff well is replaced with a hydraulic fracturing well for production.

The first preset temperature threshold is 250°C, the second preset temperature threshold is 300°C, and the third preset temperature threshold is 150°C.

The first preset pressure threshold is 1-1.5 times of the original formation pressure.

The first preset concentration threshold is 5%.

This application first introduces the conventional air throughput experiment, including electric ignition and laser ignition, wherein the air throughput experiment (electric ignition) is:

As shown in FIG2 , the experimental device includes a high-temperature and high-pressure combustion experimental device, a gas compressor, an intermediate container, a booster pump, etc., wherein the high-temperature and high-pressure combustion device includes a combustion tube body, a thermocouple, an igniter, etc.;

The shale air injection huff-and-puff experiment was carried out. After the shale core was assembled, air was injected into the combustion system at an injection rate of 0.2 mL/min. After 0.1 PV of air was injected, the electric igniter was turned on (the ignition temperature was set to 350 °C). When a stable combustion cavity was formed (temperature>350 °C), the ignition system was turned off and the well was soaked. After soaking for 6 hours, the _O2 content in the produced gas was monitored. When the _O2 content in the produced gas was less than 5%, the outlet was opened for production, and the degree of huff-and-puff recovery was recorded. Then a new round of air huff-and-puff was carried out, and a total of 3 rounds of huff-and-puff were carried out.

The air intake and exhaust experiment (laser ignition) is:

As shown in FIG3 , the disassembled electromagnetic induction device is the experimental device for the air intake and exhaust experiment (laser ignition), which includes a high-temperature and high-pressure combustion experimental device, a gas compressor, an intermediate container booster pump, a laser ignition device, etc. Among them, the high-temperature and high-pressure combustion device includes a combustion tube body, a thermocouple and an igniter, etc., and the laser ignition device mainly includes a laser transmitter, a spectroscope, a focusing mirror, an energy receiving device, etc.;

The shale air injection huff and puff experiment was carried out. The electromagnetic induction device was turned off and air was injected into the combustion system at an injection rate of 0.2 mL/min. After 0.1 PV of air was injected, the laser transmitter was turned on to radiate the laser ignition window with constant energy. The laser emission beam energy can be adjusted by the external energy attenuator of the transmitter. The laser beam emission energy is mainly measured by the spectroscope and the energy receiving device. By measuring the energy of the beam received at the spectroscope, the energy wavelength of the laser beam entering the combustion device can be known. The focal length of the focusing mirror is set to 250 mm. When a stable combustion cavity is formed (temperature>350°C), the laser transmitter is turned off and the well is started. After 6 hours of well, the _O2 content in the produced gas is monitored. When the _O2 content in the produced gas is less than 5%, the outlet is opened for production and the huff and puff recovery degree is recorded. A new round of air huff and puff was then carried out, with a total of 3 rounds of huff and puff.

As shown in FIG3 , the present invention further provides an experimental device for improving shale oil recovery by air injection in coordination with laser and magnetic field, which is applied to the above-mentioned method for improving shale oil recovery by air injection in coordination with laser and magnetic field, and includes: an air compressor, a high-temperature and high-pressure combustion experimental device, a laser ignition device, an electromagnetic induction device, a gas-liquid separator, a gas collecting bottle, a liquid collecting bottle and a gas analyzer, wherein the air compressor is connected to the gas storage tank via a pressure gauge and a first six-way valve, the gas storage tank is connected to the flow meter, the flow meter is connected to the input end of the high-temperature and high-pressure combustion experimental device via a second six-way valve, the second six-way valve is provided with a pressure gauge, a core is provided inside the high-temperature and high-pressure combustion experimental device, the laser ignition device and the electromagnetic induction device are connected to the high-temperature and high-pressure combustion experimental device, the output end of the high-temperature and high-pressure combustion experimental device is connected to the input end of the gas-liquid separator, the gas outlet end and the liquid outlet end of the gas-liquid separator are respectively connected to the gas collecting bottle and the liquid collecting bottle, and the gas collecting bottle is connected to the gas analyzer;

The high-temperature and high-pressure combustion experimental device comprises a combustion tube body and a thermocouple, the second six-way valve is connected to the input end of the combustion tube body, the output end of the combustion tube body is connected to the gas-liquid separator, a core is arranged inside the combustion tube body, a laser ignition window is arranged on the combustion tube body, and the laser ignition device performs laser ignition through the laser ignition window, a plurality of the thermocouples are arranged on the combustion tube body, and the electromagnetic induction device is connected to the combustion tube body;

The laser ignition device comprises a laser emitter, an energy receiving device, a beam splitter and a focusing mirror. The laser emitter radiates laser light into the combustion tube body through the beam splitter, the focusing mirror and the laser ignition window, and the laser light split by the beam splitter is input into the energy receiving device.

The electromagnetic induction device is realized by AC power supply;

Conduct shale air injection huff-and-puff experiments, turn on the electromagnetic induction device, set the magnetic induction intensity range to 0.1-2T, inject air into the combustion system at a gas injection rate of 0.2mL/min, and after injecting 0.1PV of air, turn on the laser emitter to radiate the laser ignition window with constant energy. When a stable combustion cavity is formed (temperature>350℃), turn off the laser emitter and the electromagnetic induction device and start soaking the well. After soaking the well for 6 hours, monitor the _O2 content in the produced gas. When the _O2 content in the produced gas is less than 5%, open the outlet for production, record the degree of huff-and-puff recovery, and then carry out a new round of air huff-and-puff, with a total of 3 rounds of huff-and-puff.

In order to quantitatively characterize the changes in the microscopic pore structure of shale, the SEM images of shale produced from different fire flooding experiments were firstly subjected to binarization and median filtering noise reduction (as shown in Figures 4 to 9), and then the microscopic pore structure parameters in the processed images were statistically analyzed (as shown in Table 1). It can be found that after the laser and magnetic field assisted air huff and puff, the maximum pore size of the shale increased to 6.88 μm, and the porosity increased to 10.2%. As shown in Figure 10, the recovery factors of the first round of air huff and puff (electric ignition), air huff and puff (laser ignition), and air huff and puff assisted by laser and magnetic field were 21.6%, 25.8%, and 28.5%, respectively. The second round of throughput recovery factors were 15.3%, 18.4% and 20.3% respectively, and the third round of throughput recovery factors were 6.7%, 9.6% and 12.6% respectively. It can be seen that under the action of high-energy laser and magnetic field, the recovery factor of the third round of air throughput is still higher than 10%, indicating that the laser and magnetic field assisted air throughput method has the best effect in enhancing the recovery factor. Combining the changes in shale pore structure and recovery factor, it can be considered that under the synergistic action of laser and magnetic field, the diffusion and adsorption of high-energy electrons in plasma on the surface of reservoir organic matter are improved, the reaction activity of solid-phase organic matter is improved, and the heat release capacity of shale air injection oxidation is enhanced.

Table 1 Statistical results of pore structure parameters

The method provided in this application makes full use of the advantages of laser technology and electromagnetic induction technology to achieve the purpose of assisting in enhancing the thermal effect of air injection oxidation. First, the injected gas is activated by a high-energy laser to quickly form a high-energy plasma, enhance the reaction activity of organic matter in the early stage of combustion, and enhance the heat release of the oxidation reaction; in this process, the reservoir retained fluid forms active gases under the action of high-energy laser and oxidation heat, which quickly diffuse into the shale matrix to dissolve rock minerals, and expand the pore-fracture structure in the shale under the synergistic oxidation heat. Under the action of the magnetic field, on the one hand, the plasma density and average free energy are enhanced, which promotes the diffusion and adsorption capacity of high-energy electrons in the plasma on the surface of organic matter in the reservoir, and improves the reaction activity of solid-phase organic matter; on the other hand, the charged ions of the plasma move in a directional manner under the action of a high magnetic flux magnetic field, which enhances the existence time of the plasma and promotes the range of high-energy plasma in the shale reservoir.

The present invention provides a method and experimental device for improving shale oil recovery rate by injecting air in coordination with laser and magnetic field. The method coordinates laser technology, air injection technology and electromagnetic induction technology. First, the shale near the hydraulic fracture is instantly heated by laser to promote the formation of thermal fractures, thereby communicating and expanding with the hydraulic fractures. In this process, the retained fluid near the fracture forms hot steam under the action of heat. Under the action of hot steam, minerals in the shale reservoir are dissolved, promoting the formation of dissolution pores, further enhancing the reservoir conductivity. Subsequently, air is injected, and the gas is activated by laser to form plasma, thereby enhancing the oxidation reaction activity with organic matter in the reservoir. In this process, water vapor can also provide more active groups, accelerate the diffusion and adsorption of injected air on the surface of organic matter in the reservoir, and further enhance the thermal effect of organic matter oxidation. Finally, the direction of plasma movement is controlled by magnetic field, thereby increasing the existence time of plasma and enhancing the collision probability of high-energy electrons in plasma and organic matter. Compared with the electric ignition method, the laser ignition method has the advantages of precise control of ignition time, high ignition energy, reduced heat loss during ignition and reduced NO _x emission and other advantages. Introducing it into the ignition application of air/crude oil mixture in the reservoir can reduce the flameout rate in the early stage of combustion. The experimental device can verify the method and ensure the feasibility of the method.

The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of the present invention. At the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (7)

1. A method for improving shale oil recovery ratio by air injection cooperated with laser and magnetic field is characterized by comprising the following steps:

Step 1: a pair of parallel horizontal wells are arranged at the upper and lower positions of a hydraulic fracturing well, the upper well is used as a magnetic pole well, the lower well is used as a gas injection well, a laser emission device is arranged in the gas injection well, a sampling device, a temperature detection device and an electromagnet are arranged in the magnetic pole well, and a sampling device, a sound wave emission device and a temperature detection device are arranged in the hydraulic fracturing well;

Step 2: starting a laser emission device to emit a laser beam to the shale surface near the hydraulic fracturing well at a preset power;

step 3: acquiring stratum acoustic data through an acoustic wave transmitting device at fixed time intervals, and determining whether a crack structure between the gas injection well and the hydraulic fracturing well is changed or not through the stratum acoustic data;

Step 4: if the pressure of the stratum reaches a first preset pressure threshold value, stopping gas injection operation;

Step 5: performing well-flushing operation, collecting temperature change data at the hydraulic fracturing well, starting a laser emission device to emit laser beams with constant power if the temperature is lower than a first preset temperature threshold value, and intermittently irradiating the reservoir layer by the laser emission device with low-frequency laser if the temperature is higher than the first preset temperature threshold value;

Step 6: acquiring temperature change data of the magnetic pole well if the temperature of the hydraulic fracturing well is higher than a second preset temperature threshold value, and starting a laser emitting device and an electromagnet if the temperature of the magnetic pole well is lower than a third preset temperature threshold value, wherein the laser emitting device irradiates the reservoir with low-frequency laser intermittently, the electromagnet irradiates the reservoir with high magnetic flux, and only the electromagnet is started if the temperature of the magnetic pole well is higher than the third preset temperature threshold value, and irradiates the reservoir with high magnetic flux;

Step 7: if the temperature of the magnetic pole well is higher than a second preset temperature threshold, closing the electromagnet, collecting oxygen concentration data of the gas injection well, when the oxygen concentration of the produced gas is lower than the first preset concentration threshold, opening the well to carry out failure production, and when the temperature of the magnetic pole well is lower than a third preset temperature threshold, stopping production;

Step 8: starting the next round of throughput, wherein the time of well stewing is set to be 1-1.5 times of the previous period, and starting the multiple rounds of throughput according to the steps 4-6;

step 9: and when the periodic oil change rate of the huff-puff well is smaller than 0.4, the huff-puff well is replaced by a hydraulic fracturing well for production.

2. The method of claim 1, wherein the first predetermined temperature threshold is 250 ℃, the second predetermined temperature threshold is 300 ℃, and the third predetermined temperature threshold is 150 ℃.

3. The method for improving shale oil recovery by air injection and laser and magnetic field according to claim 1, wherein the first preset pressure threshold is 1-1.5 times of the original stratum pressure.

4. The method of claim 1, wherein the first predetermined concentration threshold is 5%.

5. An experimental device for improving shale oil recovery ratio by air injection cooperated with laser and magnetic field, which is applied to the method for improving shale oil recovery ratio by air injection cooperated with laser and magnetic field according to any one of claims 1-4, and is characterized by comprising the following steps: the high-temperature high-pressure combustion experimental device comprises an air compressor, a high-temperature high-pressure combustion experimental device, a laser ignition device, an electromagnetic induction device, a gas-liquid separator, a gas collecting bottle, a liquid collecting bottle and a gas analyzer, wherein the air compressor is connected with the air storage tank through a pressure gauge and a first six-way valve, the air storage tank is connected with the flowmeter, the flowmeter is connected with the input end of the high-temperature high-pressure combustion experimental device through a second six-way valve, a pressure gauge is arranged on the second six-way valve, a core is arranged inside the high-temperature high-pressure combustion experimental device, the laser ignition device and the electromagnetic induction device are connected with the high-temperature high-pressure combustion experimental device, the output end of the high-temperature high-pressure combustion experimental device is connected with the input end of the gas-liquid separator, the gas outlet end and the liquid outlet end of the gas-liquid separator are respectively connected with the gas collecting bottle and the liquid collecting bottle, and the gas collecting bottle is connected with the gas analyzer.

6. The experimental device for improving shale oil recovery ratio by air injection cooperated with laser and magnetic field according to claim 5, wherein the high-temperature high-pressure fuel experimental device comprises a combustion tube body and thermocouples, the second six-way valve is connected with the input end of the combustion tube body, the output end of the combustion tube body is connected with the gas-liquid separator, a core is arranged in the combustion tube body, a laser ignition window is arranged on the combustion tube body, the laser ignition device performs laser ignition through the laser ignition window, a plurality of thermocouples are arranged on the combustion tube body, and the electromagnetic induction device is connected with the combustion tube body.

7. The experimental device for improving shale oil recovery ratio by air injection and laser and magnetic field according to claim 6, wherein the laser ignition device comprises a laser transmitter, an energy receiving device, a spectroscope and a focusing mirror, wherein the laser transmitter irradiates laser to the inside of the combustion tube body through the spectroscope, the focusing mirror and a laser ignition window, and the laser is input into the energy receiving device through spectroscope beam splitting.