System and method for exploiting shale oil in situ based on ultrasonic and convection heating method

Abstract

The invention relates to the technical field of in-situ mining of shale oil in underground reservoirs, in particular to a system and a method for in-situ mining of shale oil based on an ultrasonic and convection heating method. The system comprises a production well (1), a heat injection well (2), a horizontal well (10), an ultrasonic transducer assembly, a water injection assembly, a steam injection assembly and an oil gas collection assembly. Wherein the water injection assembly is used for injecting water into an oil shale layer (15) through a horizontal well (10) and is also used for cooling the ultrasonic transducer assembly according to a water cooling principle; the ultrasonic transducer assembly is used for transmitting an ultrasonic signal to the water-injected oil shale layer (15) through the horizontal well (10), so that the oil shale layer (15) forms a crack network consisting of cracks; the steam injection assembly is used for injecting steam into the seam net of the oil shale layer (15) and enabling kerogen of the oil shale layer (15) to be pyrolyzed to form oil gas in cooperation with the nonlinear effect of ultrasound; oil gas moves to the floral tube (4) from the seam net and is discharged out of the ground through the production well (1).

Description

Technical Field

[0001] The present invention relates to the technical field of in-situ exploitation of shale oil in underground reservoirs, and in particular to a system and method for in-situ exploitation of shale oil based on ultrasound and convection heating. Background Art

[0002] Shale oil is a typical example of unconventional oil and gas resource development, with huge potential reserves and steadily increasing production capacity. However, challenges such as generally poor resource quality and low single-well production still restrict the effective exploitation of shale oil.

[0003] Traditional in-situ mining technologies such as pure steam pyrolysis, hydraulic fracturing and chemical methods still have shortcomings such as high cost, high energy consumption, low heat utilization rate and potential risk of groundwater pollution. Ultrasonic in-situ mining technology has the advantages of being green, energy-saving and widely applicable. The cavitation effect, mechanical effect, thermal effect and strong shock wave and micro-jet phenomenon derived from ultrasound have the effects of fracturing, pore expansion, permeability enhancement and improving crude oil properties on shale reservoirs. It is a potential and efficient method to improve shale oil recovery. However, the application of ultrasonic technology in in-situ shale oil mining is still in its early stages, and there is no unified conclusion on the mechanism. Summary of the invention

[0004] The purpose of the present invention is to overcome the difficulties in shale oil extraction in the prior art and the problems of underground pollution and high cost caused by traditional group well fracturing technology, thereby providing a system and method for in-situ extraction of shale oil based on ultrasound and convection heating.

[0005] In order to solve the above technical problems, the technical solution of the present invention provides a system for in-situ extraction of shale oil based on ultrasound and convection heating, comprising:

[0006] Production well 1, heat injection well 2, horizontal well 10, ultrasonic transducer assembly, water injection assembly, steam injection assembly and oil and gas collection assembly; wherein,

[0007] The production well 1 and the heat injection well 2 extend from the ground into the oil shale layer 15;

[0008] The horizontal well 10 is located between the production well 1 and the heat injection well 2, and is also located in the oil shale layer 15;

[0009] The water injection assembly is used to inject water into the oil shale layer 15 through the horizontal well 10, and is also used to cool the ultrasonic transducer assembly through the water cooling principle;

[0010] The ultrasonic transducer assembly is used to transmit ultrasonic signals to the oil shale layer 15 after water injection through the horizontal well 10, so that the oil shale layer 15 forms a fracture network composed of fractures;

[0011] The steam injection assembly is used to inject steam into the seams of the oil shale layer 15, and cooperate with the nonlinear effect of ultrasound to pyrolyze the kerogen in the oil shale layer 15 to form oil and gas; the oil and gas are transported from the seams to the flower pipe 4 and discharged to the ground through the production well 1.

[0012] As an improvement of the above system, the production well 1 and the heat injection well 2 are arranged perpendicular to the horizontal line; and the horizontal well 10 is arranged parallel to the horizontal line.

[0013] As an improvement of the above system, the ultrasonic transducer assembly includes: an ultrasonic generator 7, a power amplifier 3, an ultrasonic transducer array 9 and a cable 8 connected in sequence; wherein the ultrasonic generator 7 and the power amplifier 3 are located on the ground; the ultrasonic generator 7 is used for high-frequency alternating current signals, and the power amplifier 3 is used to amplify the electrical signals and transmit them to the ultrasonic transducer array 9 through the cable 8; the ultrasonic transducer array 9 includes: a plurality of ultrasonic transducers located in the horizontal well 10, which are used to convert the electrical signals into ultrasonic signals and transmit them to the oil shale layer 15.

[0014] As an improvement of the above system, the water injection assembly includes: a water injection tank 11, a water injection pipe 19, a water injection pipe stop valve 13, a plurality of water outlet pipe stop valves 21, a water outlet tank 12 and a water outlet pipe 20; wherein, the water injection tank 11 is located on the ground and is connected to the water injection pipe 19; the water injection pipe 19 enters the horizontal well 10 from the hot injection well 2 and extends in the horizontal well 10; the water injection pipe stop valve 13 is used to control the connection between the water injection pipe 19 and the water injection tank 11; a plurality of the water outlet pipe stop valves 21 are arranged on the water injection pipe 19 and are located in the horizontal well 10, and are used to control the connection between the water injection pipe 19 and the oil shale layer 15; the water outlet pipe 20 extends in the horizontal well 10, and extends from the hot injection well 2 to the ground and is connected to the water outlet tank 12 located on the ground.

[0015] As an improvement of the above system, the steam injection component includes: a steam injection pipeline 18; wherein the steam injection pipeline 18 extends from the hot injection well 2 to the oil shale layer 15.

[0016] As an improvement of the above system, the production well 1 extends from the ground to the top of the oil shale layer 15; the oil and gas collection assembly includes: a flower pipe 4 and a double-layer annulus pipe 5; wherein the flower pipe 4 extends from the bottom of the oil shale layer 15 to the top of the oil shale layer 15 and is connected to the seam network; the double-layer annulus pipe 5 is connected to the top of the flower pipe 4 and extends in the production well 1.

[0017] As an improvement to the above system, the temperature range of the water injected by the water injection assembly is 5-25°C.

[0018] As an improvement to the above system, the temperature range of the steam is 400-700°C.

[0019] To achieve another object of the present invention, the present invention also provides a method for in-situ production of shale oil based on ultrasound and convection heating, which is implemented based on the above-mentioned system for in-situ production of shale oil based on ultrasound and convection heating, comprising:

[0020] Open the water stop valve 13 of the water injection pipeline and the water stop valve 21 of the water outlet pipeline, and the water in the water injection tank 11 flows into the water injection pipeline 19, circulates to the water outlet pipeline 20 through the horizontal well 10, and then flows into the water outlet tank 12, so as to cool down the ultrasonic transducer array 9 based on the water cooling principle;

[0021] Open the water stop valve 21 of the water outlet pipe to allow the water injection pipe 19 to inject water into the oil shale layer 15;

[0022] Turning on the ultrasonic generator 7, the power amplifier 3 and the ultrasonic transducer array 9, transmitting ultrasonic signals to the water-injected oil shale layer 15 through the ultrasonic transducer array 9, so that the oil shale layer 15 forms a fracture network composed of fractures;

[0023] Close the water stop valve 21 of the water outlet pipe, open the valve of the steam injection pipe, and inject steam into the seam network of the oil shale layer 15 through the steam injection pipe 18, so as to cooperate with the nonlinear effect of ultrasound to pyrolyze the kerogen in the oil shale layer 15 to form oil and gas; the oil and gas are carried to the seam network by condensed water or low-temperature steam, and enter the flower pipe 4, and are discharged from the double-layer annulus pipe 5.

[0024] Compared with the prior art, the advantage of the present invention is that it utilizes the ultrasonic nonlinear effect to form interconnected fracture channels in the reservoir, and combines the convection heating method to accelerate the cracking of kerogen in the shale, thereby achieving the purpose of oil and gas exploitation and improving the efficiency of shale oil exploitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the system for in-situ extraction of shale oil based on ultrasound and convection heating.

[0026] Figure ID

[0027] 1. Production well 2. Heat injection well 3. Power amplifier

[0028] 4. Flower pipe 5. Double-layer annular pipe 6. Cement

[0029] 7. Ultrasonic generator 8. Cable 9. Ultrasonic transducer array

[0030] 10. Horizontal well 11. Water injection tank 12. Water outlet tank

[0031] 13. Water injection pipeline water stop valve 14. Oil shale bottom plate 15. Oil shale layer

[0032] 16. Oil shale roof 17. Non-oil shale formation 18. Steam injection pipeline

[0033] 19. Water injection pipe 20. Water outlet pipe 21. Water outlet pipe water stop valve DETAILED DESCRIPTION

[0034] The technical solution provided by the present invention is further illustrated below in conjunction with embodiments.

[0035] Example 1

[0036] In order to improve the extraction efficiency of shale oil, this embodiment provides a system for in-situ extraction of shale oil based on ultrasound and convection heating method, which uses the cavitation effect, mechanical effect, thermal effect derived from ultrasound, and strong shock waves and micro-jet phenomena to increase the pressure and temperature in the oil shale formation instantly, resulting in the formation of numerous micro-cracks in a short period of time. Under the accumulated stress, the micro-cracks can expand into a fracture network, providing a good channel for oil and gas migration; at the same time, the high-frequency vibration of ultrasound can destroy the boundary layer, causing the blocking particles to fall off, thereby reducing the internal surface tension of the pores and roar channels, causing capillary expansion and contraction, and increasing the flow capacity of oil and gas. In addition, the comprehensive effect of ultrasound when acting on shale oil can reduce the viscosity of shale oil, perform in-situ modification on shale oil, thereby enhancing the fluidity of shale oil, and the heat energy converted from acoustic energy, the temperature increase caused by mechanical friction, and the heat energy released by cavitation can promote the cracking of kerogen in conjunction with the convection heating method, and the cracked oil and gas are discharged to the ground from the production well 1 along with the condensed water.

[0037] Among them, the mechanism of ultrasonic in-situ modification of shale oil is mainly related to the ultrasonic cavitation effect. When ultrasonic waves propagate in liquids, they release huge energy, and the source of energy is the collapse of cavitation bubbles. When the compressibility of the liquid is considered, the vibration of the bubbles can be described by the Keller-Miksis equation:

[0038]

[0039] Where R represents the bubble radius, and They represent the first and second derivatives of R, c represents the speed of sound in the liquid, ρ is the density of the liquid, t represents time, and p 1 It represents the sound pressure, and its calculation formula is:

[0040]

[0041] Where κ is the adiabatic coefficient of the liquid, p 0 represents the static pressure in water, represents the water vapor pressure in the bubble, σ represents the surface tension coefficient of water, R 0is the initial radius of the bubble, and μ is the viscosity coefficient of water. Represent the gas pressure inside the bubble, ambient pressure, surface tension, and viscous stress respectively. In ultrasonic cavitation, the sound pressure p s (t) is often abbreviated as:

[0042] p s (t) = p a sin(2πft)

[0043] In the formula, p a represents the sound pressure amplitude, f and t are frequency and time respectively.

[0044] First, based on Keller-Miksis, the initial conditions are set as:

[0045] t=0,R=R 0 ,dR / dt=0

[0046] Meanwhile, the heat and mass transfer on the wall and the multi-bubble interaction during the growth of cavitation bubbles are ignored. Based on the fourth-order Rung-Kutta method, the motion characteristics of cavitation bubbles in aged oil under different parameters are calculated by MATLAB.

[0047] Then the cavitation radius is compressed to the van der Waals hard core radius R 0 / 8.54 is used as the standard for the collapse of the cavitation bubble, and based on the adiabatic law, the temperature T inside the cavitation bubble when the cavitation bubble collapses is calculated. bubble With pressure P bubble :

[0048]

[0049]

[0050] Where, T ∞ is the liquid temperature, P start represents the ambient pressure and γ represents the adiabatic index.

[0051] Then, based on the above results, the basic types of free radical reactions in the process of ultrasonic aging oil are estimated, and based on the initial amount of each substance and the chemical kinetic equation, the reaction rate and cumulative content of different types of free radicals during cavitation collapse are calculated; finally, the change law of the type and content of free radicals under different conditions is obtained. The above method can reveal the mechanism of ultrasonic in-situ shale oil modification from the perspective of cavitation dynamics and free radical reaction kinetics.

[0052] This embodiment provides a system for in-situ extraction of shale oil based on ultrasound and convection heating method, the system comprising: a production well 1, a heat injection well 2, a power amplifier 3, a flower pipe 4, a double-layer annulus pipe 5, cement 6, an ultrasonic generator 7, a cable 8, an ultrasonic transducer array 9 composed of a plurality of ultrasonic transducers, a horizontal well 10, a water injection tank 11, a water outlet tank 12, a water injection pipeline stop valve 13, an oil shale bottom plate 14, an oil shale layer 15, an oil shale top plate 16, a non-oil shale formation 17, a steam injection pipeline 18, a water injection pipeline 19, a water outlet pipeline 20, and a water outlet pipeline stop valve 21. The system structure is as follows:

[0053] (1) Preparation for drilling work: A heat injection well 2 and a production well 1 are built vertically downward from the ground, ensuring that the positions of the two wells are accurate and the depths reach the predetermined formation; then a horizontal well 10 is drilled between the two vertical wells.

[0054] (2) Installation of equipment in the well and formation treatment: A water injection pipeline 19 is installed in the heat injection well 2, and the ultrasonic working device is connected to the ultrasonic transducer array 9 in the horizontal well 10 through the heat injection well 2; at the same time, a flower pipe 4 that allows fluid to pass is installed in the set formation treatment layer section of the production well 1, and double-layer annular pipes 5 are installed in all other formations and mineral layers, and cementing operations are carried out along the outer layer pipe. This layout is intended to effectively utilize the formation characteristics and prepare for subsequent shale oil production.

[0055] (3) Water injection circulation and temperature control: Open the water injection pipeline stop valve 13, start to inject water from the water injection tank 11 into the water injection pipeline 19, keep the water injection pipeline stop valve 13 open during operation, and strictly control the temperature of the water in the water injection pipeline 19; the water flows through the horizontal well 10 to the water outlet pipeline 20 and finally flows into the water outlet tank 12. The water temperature of the water injection pipeline 19 is: 5-25°C. This step not only helps to keep the temperature of the transducer array 9 constant, but also creates favorable conditions for subsequent ultrasonic treatment through water temperature regulation.

[0056] (4) Ultrasonic treatment and fracture formation: Open all the water stop valves 21 of the water injection pipeline 19 in the horizontal well 10 to inject water into the formation; then turn on the power supply of the ultrasonic generator 7 to emit high-frequency AC signals. After being amplified by the power amplifier 3, these electrical signals are transmitted along the cable 10 to the ultrasonic transducer array 9, causing it to start emitting ultrasonic signals. The combined effect of ultrasonic waves destroys the boundary layer, reduces the surface tension in the pores, causes the capillary to expand and contract, and then forms a fracture network in the oil shale formation, so that the pore channels are interconnected.

[0057] (5) High-temperature steam injection, in-situ cracking of shale oil: When all the segmented fractures in the oil shale layer 15 are connected, the water stop valve 21 of the water outlet pipeline is closed, the steam injection pipeline 18 is opened, and steam at about 400-700°C is injected into the fractures along the steam injection pipeline 18 in the hot injection well 2. The steam enters the rock pores along the fractures and heats them, and the combined effect of the ultrasonic wave pyrolyzes the kerogen in the oil shale layer 15 to form oil and gas.

[0058] (6) Oil and gas collection and transportation: Open the water stop valve 21 of the water outlet pipeline and close the steam injection pipeline 18; the oil and gas are carried by condensed water or low-temperature steam to the fracture channel, the channel is connected by the flower pipe 4, and finally produced by the production well 1. Among them, opening the water stop valve 21 of the water outlet pipeline can input condensed water into the oil shale layer 15, thereby forming low-temperature steam.

[0059] Specifically, a high-frequency alternating current signal is emitted by the ultrasonic generator 7 and transmitted along the cable 10 to the ultrasonic transducer array 9, driving the ultrasonic transducer 7 to generate an ultrasonic signal, thereby realizing the conversion of the electrical signal into an acoustic signal.

[0060] Specifically, the water stop valve 13 of the water injection pipeline is opened, and water is injected into the water injection pipeline 19 from the water outlet tank 12, which can not only reduce the temperature of the ultrasonic transducer array 9 to prevent the ultrasonic transducer array 9 from being damaged due to excessive temperature, but also inject water into the formation to form a medium for interaction between ultrasound and rock.

[0061] Specifically, local high temperature, high pressure, shock waves and microjets formed by ultrasound are used to form fractures in the oil shale formation 15, and the shale oil is modified in situ.

[0062] Specifically, steam at about 400-700°C is injected into the oil shale formation along the heat injection well 2, the steam enters the rock pores along the cracks, and synergistically promotes the cracking of kerogen into oil and gas with the combined effect of ultrasound, and then the oil and gas are transported to the cracks through condensed water.

[0063] Specifically, the flower pipe 4 is used to connect the fractures in the oil shale formation, which is helpful for the migration and exploitation of shale oil and gas.

[0064] Specifically, the oil shale bottom plate 14 , the oil shale top plate 16 and the non-oil shale formation 17 are connected by a double-layer annulus pipe 5 along the wellbore direction, and the lower part of the double-layer annulus pipe 5 is connected to the flower pipe 4 .

[0065] Specifically, the outer wall of the production well 1 is cemented with cement 6 that can withstand a high temperature of 700°C.

[0066] Specifically, the horizontal distance between the heat injection well 2 and the production well 1 is 50 meters, and an ultrasonic transducer is placed every 1 meter to form an ultrasonic transducer array 9.

[0067] Specifically, a heat-insulating layer is provided on the pipe wall of the water injection pipe 19 , and a heat-insulating layer is provided on the pipe wall of the water outlet pipe 20 .

[0068] Example 2

[0069] This embodiment provides a method for in-situ extraction of shale oil based on ultrasound and convection heating, comprising the following steps:

[0070] 1. Drill a heat injection well 2 and a production well 1 vertically along the ground, and then drill a horizontal well 10. Clean the gravel in the well to make the well environment clean. Figure 1 Arrange the well instruments.

[0071] 2. Open the water injection pipe stop valve 13 and inject water into the water injection pipe 19. During the operation, the water injection pipe stop valve 13 is not closed to circulate; then open the outlet pipe stop valve 21 of the water injection pipe 19 in the horizontal well 10 to inject water into the formation.

[0072] 3. Connect the power supply of the ultrasonic generator 7 and the power amplifier 3, turn on the working switch, and the ultrasonic transducer array 9 converts the input electrical signal into ultrasonic waves, and utilizes the high temperature, high pressure, shock waves and microjets generated by ultrasonic waves to form a large number of interconnected fractures in the oil shale layer 15.

[0073] 4. Steam at a temperature of about 400-700°C is injected into the oil shale layer 15 through the steam injection pipe 18 along the hot injection well 2. The steam enters the rock pores along the cracks and, together with the composite thermal effect generated by the ultrasonic wave, promotes the cracking of the kerogen in the oil shale layer 15 into oil and gas. The cracked oil and gas are transported to the flower pipe 4 along with the condensed water or low-temperature steam.

[0074] 5. Finally, the oil and gas are discharged to the ground from production well 1, thus realizing efficient and green exploitation of shale oil.

[0075] From the above specific description of the present invention, it can be seen that:

[0076] 1. The present invention is combined with the convection heating method. Compared with the pure steam method, this method only needs a short heating time and reduces energy consumption, while also avoiding the heat loss that may occur during the steam transfer process. The two methods achieve collective advantages through complementary advantages.

[0077] 2. The condensed water in the device of the present invention plays a dual role: on the one hand, as a medium, it enables ultrasound to form a highly energetic nonlinear effect in a liquid environment to act on the oil shale; on the other hand, the condensed water can quickly reduce the steam temperature, achieve the effect of oil and gas condensation, effectively carry and discharge the decomposed oil and gas, and reduce the risk of groundwater pollution and subsequent treatment costs.

[0078] 3. The present invention can reveal the mechanism of ultrasonic in-situ modification of shale oil from the perspectives of cavitation dynamics and free radical reaction dynamics.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A system for in-situ extraction of shale oil based on ultrasound and convection heating, comprising: A production well (1), a heat injection well (2), a horizontal well (10), an ultrasonic transducer assembly, a water injection assembly, a steam injection assembly and an oil and gas collection assembly; wherein: The production well (1) and the heat injection well (2) extend from the ground into the oil shale layer (15); The horizontal well (10) is located between the production well (1) and the heat injection well (2), and is also located in the oil shale layer (15); The water injection assembly is used to inject water into the oil shale layer (15) through the horizontal well (10), and is also used to cool the ultrasonic transducer assembly through the water cooling principle; The ultrasonic transducer assembly is used to transmit ultrasonic signals to the oil shale layer (15) after water injection through the horizontal well (10), so that the oil shale layer (15) forms a fracture network composed of fractures; The steam injection component is used to inject steam into the seam network of the oil shale layer (15), and cooperate with the nonlinear effect of ultrasound to pyrolyze the kerogen in the oil shale layer (15) to form oil and gas; the oil and gas are transported from the seam network to the flower pipe (4) and discharged to the ground through the production well (1).

2. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The production well (1) and the heat injection well (2) are arranged perpendicular to the horizontal line; and the horizontal well (10) is arranged parallel to the horizontal line.

3. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The ultrasonic transducer assembly comprises: an ultrasonic generator (7), a power amplifier (3), an ultrasonic transducer array (9) and a cable (8) connected in sequence; wherein the ultrasonic generator (7) and the power amplifier (3) are located on the ground; the ultrasonic generator (7) is used for high-frequency alternating current signals, and the power amplifier (3) is used for amplifying the electrical signals and transmitting them to the ultrasonic transducer array (9) through the cable (8); The ultrasonic transducer array (9) comprises: a plurality of ultrasonic transducers located in a horizontal well (10) and used for converting electrical signals into ultrasonic signals and transmitting them to an oil shale layer (15).

4. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The water injection assembly comprises: a water injection tank (11), a water injection pipeline (19), a water injection pipeline water stop valve (13), a plurality of water outlet pipeline water stop valves (21), a water outlet tank (12) and a water outlet pipeline (20); wherein: The water injection tank (11) is located on the ground and connected to the water injection pipeline (19); The water injection pipeline (19) enters the horizontal well (10) from the heat injection well (2) and extends inside the horizontal well (10); The water injection pipeline water stop valve (13) is used to control the connection and disconnection between the water injection pipeline (19) and the water injection tank (11); A plurality of water outlet pipe stop valves (21) are arranged on the water injection pipe (19) and located in the horizontal well (10) to control the connection and disconnection between the water injection pipe (19) and the oil shale layer (15); The water outlet pipeline (20) extends in the horizontal well (10), and extends from the heat injection well (2) to the ground to be connected to the water outlet tank (12) located on the ground.

5. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The steam injection assembly comprises: a steam injection pipeline (18); wherein the steam injection pipeline (18) extends from a hot injection well (2) to an oil shale layer (15).

6. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The production well (1) extends from the ground to the top of the oil shale layer (15); The oil and gas collection assembly comprises: a flower tube (4) and a double-layer annulus tube (5); wherein: The flower tube (4) extends from the bottom of the oil shale layer (15) to the top of the oil shale layer (15) and is connected to the seam network; The double-layer annulus pipe (5) is connected to the top of the flower pipe (4) and extends inside the production well (1).

7. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The temperature range of the water injected by the water injection assembly is 5-25°C.

8. The system for in-situ extraction of shale oil based on ultrasound and convection heating method according to claim 1, characterized in that: The temperature range of the steam is 400-700°C.

9. A method for in-situ shale oil production based on ultrasound and convection heating, implemented based on the system for in-situ shale oil production based on ultrasound and convection heating according to any one of claims 1 to 8, comprising: The water stop valve (13) of the water injection pipeline and the water stop valve (21) of the water outlet pipeline are opened, and the water in the water injection tank (11) flows into the water injection pipeline (19), circulates to the water outlet pipeline (20) through the horizontal well (10), and then flows into the water outlet tank (12), so as to cool the ultrasonic transducer array (9) based on the water cooling principle; Opening the water stop valve (21) of the water outlet pipeline to allow the water injection pipeline (19) to inject water into the oil shale layer (15); Turning on the ultrasonic generator (7), the power amplifier (3) and the ultrasonic transducer array (9), emitting ultrasonic signals to the oil shale layer (15) after water injection through the ultrasonic transducer array (9), thereby forming a fracture network composed of fractures in the oil shale layer (15); The water stop valve (21) of the water outlet pipeline is closed, the valve of the steam injection pipeline is opened, and steam is injected into the seam network of the oil shale layer (15) through the steam injection pipeline (18), so as to cooperate with the nonlinear effect of ultrasound to pyrolyze the kerogen in the oil shale layer (15) to form oil and gas; the oil and gas are carried to the seam network by condensed water or low-temperature steam, enter the flower pipe (4), and are discharged from the double-layer annulus pipe (5).

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