Integrated experimental system and method for fracturing flowback fluid clean treatment and heavy oil thermal recovery

Abstract

The present invention discloses an integrated experimental system and method for fracturing flowback fluid clean treatment and heavy oil thermal recovery. The system primarily includes a flowback fluid holding tank, a photocatalyst suspension tank, an intermittent peristaltic pump, a solar simulator, a focusing lens, a photoreactor, a photothermal chamber, a constant-temperature vaporization furnace, an insulation tank, a sand-filled pipe, and a metering container. The system aims to provide researchers and professionals in related fields with a coupled process for fracturing flowback fluid degradation treatment and heavy oil viscosity reduction recovery using hot steam. This facilitates researchers' exploration of mechanisms for optimizing internal process parameters and reaction component structures to enhance the comprehensive utilization of solar energy or enhance the recovery rate of heavy oil through thermal recovery. Furthermore, the system can provide a cutting-edge application paradigm for the tiered allocation and comprehensive utilization of solar energy in oil and gas field development. The system offers advantages such as high integration, ease of use, reliability, and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field development, and in particular relates to an integrated experimental system and method for clean treatment of fracturing flowback fluid and thermal recovery of heavy oil. Background Art

[0002] During the development of oil and gas wells in a mine, injecting fracturing fluid into the underground rock formation through high-pressure equipment to create cracks is one of the key processes in the drilling project. The addition of fracturing fluid can increase the internal space and pore structure of the rock formation, reducing the flow resistance of natural gas, oil, etc. in the formation. At the same time, the proppant components such as sand and alumina mixed in the fracturing fluid can maintain the high-fracture characteristics in the rock formation, which is conducive to the sustainable development of fixed-point gas reservoirs. However, since fracturing fluid usually has the characteristics of high mineralization, high viscosity and high COD, the treatment of fracturing backflow fluid has always been a difficult problem in the oil and gas industry. At present, the main treatment methods for it are discharge to meet the standards, reinjection and utilization, and standby after treatment. Because the backflow fluid contains a lot of organic and inorganic impurities and usually a lot of bacteria, whether it is directly discharged or recycled, batch treatment through oxidation process to reduce its COD value and pollution hazards is one of the essential steps.

[0003] Typically, land areas rich in oil and gas deposits are located in remote areas with abundant solar energy resources. Solar-driven photocatalytic technology is currently a cutting-edge technology, recognized by many technical experts for its mild reaction conditions, environmental friendliness, and low cost. Its main principle is to utilize highly active photocatalysts (such as TiO2, C3N4, CdS, and CuZnS) to generate a large number of highly oxidizing hydroxyl radicals in solution under the stimulation of photons in the ultraviolet and near-infrared regions of solar energy. These radicals effectively convert organic matter in aqueous pollutant solutions into low-carbon carbon dioxide, water, or other inorganic substances, thereby reducing the COD value of the pollutants. This technology has widespread applications in water purification and oilfield chemical reagents.

[0004] Furthermore, in the oil and gas recovery process, fracturing is followed by oil and gas extraction. For crude oil with a high viscosity, such as heavy oil with an average viscosity of 100 mPas, the most widely used method for heavy oil recovery is to inject water vapor to heat the reservoir and significantly reduce its viscosity. However, heavy oil development requires significant amounts of water vapor, which can account for over 75% of the total process cost. Previous methods have mostly relied on direct use of fuel, gas boilers, or grid-electric heating to vaporize water, resulting in significant carbon emissions. Furthermore, in arid regions, obtaining water resources at the source remains a significant challenge. Therefore, developing green and clean heating methods and generating recyclable water locally for sustained and efficient viscosity reduction of heavy oil downstream of the extraction process remains a significant technical bottleneck in oil and gas field development. Summary of the Invention

[0005] The purpose of the present invention is to provide an integrated experimental system and method for the clean treatment of fracturing flowback fluid and thermal recovery of heavy oil. While utilizing photocatalytic technology to effectively degrade and purify organic matter, bacteria, and deep oil contamination in fracturing flowback fluid, the system directly utilizes purified water as a water source to vaporize water vapor for heating and viscosity reduction of heavy oil. The above-mentioned photoreaction and thermal reaction are based on the cascaded complementary absorption and utilization of solar energy, without the need for additional energy input, greatly reducing the technical cost of heavy oil thermal recovery and the pressure on environmental carbon reduction. It can provide researchers and practitioners in related fields with a coupled process for fracturing flowback fluid degradation treatment and coordinated heavy oil hot steam viscosity reduction recovery, facilitating researchers' exploration of internal process parameters and the structural optimization mechanism of reaction components. It can also provide an application paradigm for the cascaded allocation and comprehensive utilization of solar energy in oil and gas reservoirs.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The integrated experimental system for clean treatment of fracturing flowback fluid and thermal recovery of heavy oil includes a flowback fluid quiescent tank, an axial flow pump is provided at the downstream end of the flowback fluid quiescent tank, a differential pressure flow meter is provided at the downstream end of the axial flow pump, a photocatalyst suspension tank is provided at the downstream end of the differential pressure flow meter, an intermittent peristaltic pump is provided downstream of the photocatalyst suspension tank, and a photoreactor is provided downstream of the intermittent peristaltic pump; a sapphire window is provided on the top middle layer of the photoreactor, and an array of prisms is provided on the bottom layer; a separation tank is provided at the downstream end of the photoreactor, and a solar simulator is provided on the top of the photoreactor. and a focusing lens; a diaphragm pump is provided downstream of the separation tank, the diaphragm pump is directly connected to the photothermal cavity, a first state monitor is provided at the downstream end of the photothermal cavity, a constant temperature vaporization furnace is provided at the downstream end of the first state monitor, and a mixing buffer cavity is provided at the downstream end of the constant temperature vaporization furnace; a high-pressure nitrogen bottle and an explosion-proof gas flow meter are provided at the upstream end of the mixing buffer cavity; a second state monitor is provided at the downstream end of the mixing buffer cavity, a sand filling pipe is provided at the downstream end of the second state monitor, the sand filling pipe is placed inside the insulation box, and a metering container is provided at the tail end of the sand filling pipe.

[0008] A further improvement of the present invention is that the fracturing flowback fluid retrieved from the oil field is left to stand in a flowback fluid standing tank for 1 hour to ensure that solid impurities in the flowback fluid are removed.

[0009] A further improvement of the present invention is that a TiO2 photocatalyst particle water suspension with a concentration of 1 mg / mL is placed in the photocatalyst suspension tank, an axial flow pump draws the supernatant from the backflow liquid holding tank into the pipeline, and a differential pressure flow meter selects to compound backflow liquid and photocatalyst particle suspension in different volume ratios according to actual degradation performance.

[0010] A further improvement of the present invention is that the solar photons emitted by the solar simulator are further transmitted to the sapphire window through the focusing effect of the focusing lens, and the focusing ratio is above 100; the intermittent peristaltic pump is used to control the flow rate of the backflow liquid and the photocatalyst particle mixed liquid flowing from the photocatalyst suspension tank, and at the same time, the start and stop time ratio of the intermittent peristaltic pump is controlled according to the actual degradation performance feedback; the height of the arrayed prism in the photoreactor is 5 mm, which is used to form a local micro-turbulence environment when the mixed liquid flows through the arrayed prism.

[0011] A further improvement of the present invention is that the mixed liquid that completes the photoreaction in the photoreactor completes the solid-liquid separation process in the downstream separation tank, and the supernatant after degradation treatment completes the vaporization process in the photothermal chamber. The diaphragm pump needs to control the flow rate below 20mL / min; a black carbon gel film is placed at the bottom of the photothermal chamber to enhance the photothermal absorption and thermal conversion effects; and a first state monitor is used to monitor the temperature, pressure and water content information of the steam in the photothermal chamber in real time.

[0012] A further improvement of the present invention is that the photoreactor and the photothermal cavity form a complementary relationship in utilizing the solar energy spectrum, and absorb the spectrum ranges of 250nm-500nm and 500nm-2500nm respectively.

[0013] A further improvement of the present invention is that the constant temperature vaporization furnace is used to further adjust the temperature and pressure of the steam according to the experimental parameter requirements; the core compressed by quartz sand is used in the sand filling tube to simulate the underground rock layer, and the core treated with saturated water and saturated oil is placed in the sand filling tube, and the insulation box is used to simulate the real-time temperature of the underground environment in situ, and the temperature range that can be set is 25 o C-1000 o Between C.

[0014] A further improvement of the present invention is that inert nitrogen is used as a carrier gas to be injected into the sand filling pipe; an explosion-proof gas flow meter is used to control the high-pressure nitrogen released from the high-pressure nitrogen bottle, and the mixed gas of nitrogen and water vapor enters the rear end together after being evenly mixed in the mixing buffer chamber; a second state monitor is used to detect the gas pressure and temperature at the inlet end of the sand filling pipe.

[0015] A further improvement of the present invention is that the volume flow rate of heavy oil thermal recovery is obtained based on a metering container, and the thermal recovery performance under characteristic parameter conditions is measured by comparing the produced oil volume with the total saturated oil volume.

[0016] Fracturing flowback fluid clean treatment and heavy oil thermal recovery integrated experimental methods, including:

[0017] A 1mg / mL TiO2 photocatalyst particle water suspension is placed in a photocatalyst suspension tank and stirred continuously. The fracturing backflow fluid retrieved from the site is poured into the backflow fluid standing box as an experimental sample and left to stand for more than 24 hours to ensure that the gravel therein is completely settled. For the experimental core, silica particles with a mesh size of 40-100 are compressed as simulated cores, which are then saturated with water and oil and placed in a sand filling tube. The total oil content in the simulated core is recorded. When the system starts running, the backflow fluid is The fracturing backflow liquid in the static box is pumped into the photocatalyst suspension tank by an axial flow pump, and the volume ratio and corresponding concentration of the two liquids are adjusted by a differential pressure flowmeter; the mixed liquid is transported to the photoreactor by an intermittent peristaltic pump to participate in the photochemical reaction, and the arrayed prisms set therein form a local micro-turbulence environment when the mixed liquid flows through the arrayed prisms; the solar simulator emits a full-band spectrum, and the emitted full-band photons are concentrated by the focusing lens and radiated to the reaction suspension through the sapphire window, under the effect of ultraviolet light and some visible light photons. Under excitation, the photocatalyst TiO2 generates holes and correspondingly generates hydroxyl radicals in the base liquid; the reaction liquid after the reaction enters a separation tank for static separation. After the photocatalyst settles, a diaphragm pump pumps the supernatant in the separation tank into the photothermal chamber for photothermal conversion. The unused spectrum of the photoreactor is used to drive the photothermal conversion and convert low-flow liquid water into water vapor. The first state monitor is used to monitor the temperature and pressure state of this test section; the constant temperature vaporization furnace further adjusts the temperature and pressure range of the steam according to the test requirements of the experiment; At the same time, nitrogen stored in a high-pressure nitrogen cylinder passes through an explosion-proof gas flowmeter and enters a mixing buffer chamber to mix with hot steam, serving as a carrier gas and boosting the pressure. The mixed gas exiting the mixing buffer chamber is directly injected into the sand-filling pipe, and an insulation box controls the temperature range of the sand-filling pipe. A second state monitor monitors the temperature and pressure of the mixed gas at the inlet of the sand-filling pipe. After being heated and treated to reduce viscosity by steam, the heavy oil pre-filled in the sand-filling pipe is continuously displaced. The volume of the displaced heavy oil is measured in a metering container, and the performance under different operating parameters is compared.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0019] 1. The present invention achieves clean photocatalytic treatment of oil and gas reservoir fracturing return fluid and stable vaporization of purified water through cascade distribution of solar energy, and uses it in the thermal recovery and displacement process of heavy oil. The entire experiment forms a complementary resource, greatly reducing the cost of heavy oil thermal recovery while solving the problem of return fluid treatment.

[0020] 2. The system of the present invention can be used for a wide range of experimental studies, not limited to a specific type of photocatalyst. The regional and downhole conditions of the fracturing flowback fluid can vary. The simulated underground core properties and the state of the steam used can be simultaneously controlled over a wide range of parameters, making the system highly adaptable.

[0021] 3. The system of the present invention directly simulates the efficient use of solar energy, utilizes the spectral absorption differences of light reaction and thermal conversion, forms a complementary integrated system, improves the comprehensive utilization efficiency of solar energy and expands the technical application of solar energy in the field of oil and gas field development, greatly alleviating the carbon emission pressure in actual oil and gas field development. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the process flow of the experimental system of the present invention;

[0024] Figure 2 This is a schematic diagram of the local structure of the photoreactor in the experimental system of the present invention.

[0025] Description of reference numerals:

[0026] 1 is a backflow still box, 2 is an axial flow pump, 3 is a differential pressure flowmeter, 4 is a photocatalyst suspension tank, 5 is an intermittent peristaltic pump, 6 is a solar simulator, 7 is a focusing lens, 8 is a sapphire window, 9 is a photoreactor, 10 is a photothermal cavity, 11 is a separation tank, 12 is a diaphragm pump, 13 is a first state monitor, 14 is a constant temperature vaporization furnace, 15 is a high-pressure nitrogen bottle, 16 is an explosion-proof gas flowmeter, 17 is a mixing buffer cavity, 18 is a second state monitor, 19 is an insulation box, 20 is a sand-filling tube, 21 is a measuring container, and 22 is an array-type prism. DETAILED DESCRIPTION

[0027] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be considered as illustrative in nature and not restrictive.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0030] In the present invention, unless otherwise expressly specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0031] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0032] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0033] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0034] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0035] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0036] Example 1

[0037] like Figure 1 and Figure 2 As shown, the integrated experimental system for fracturing flowback fluid cleanup and heavy oil thermal recovery provided by the present invention includes a flowback fluid stabilization tank 1. An axial flow pump 2 is provided at the downstream end of the flowback fluid stabilization tank 1. A differential pressure flowmeter 3 is provided at the downstream end of the axial flow pump 2. A photocatalyst suspension tank 4 is provided at the downstream end of the differential pressure flowmeter 3. An intermittent peristaltic pump 5 is provided downstream of the photocatalyst suspension tank 4. A photoreactor 9 is provided downstream of the intermittent peristaltic pump 5. A sapphire window 8 is provided on the top middle layer of the photoreactor 9, and an array of prisms 22 is provided on the bottom layer. A separation tank 11 is provided at the downstream end of the photoreactor 9. A solar simulator 6 and a focusing lens 7 are provided on the top of the photoreactor 9. A diaphragm pump 12 is provided downstream of the separation tank 11 and is directly connected to a photothermal chamber 10. A first state monitor 13 is provided at the downstream end of the photothermal chamber 10. A constant temperature vaporization furnace 14 is provided downstream of the first state monitor 13. A mixing buffer chamber 17 is provided downstream of the constant temperature vaporization furnace 14. A high-pressure nitrogen cylinder 15 and an explosion-proof gas flowmeter 16 are installed at the upstream end of the mixing buffer chamber 17. A second state monitor 18 is installed at the downstream end of the mixing buffer chamber 17. A sand filling pipe 20 is installed downstream of the second state monitor 18. The sand filling pipe 20 is placed inside the insulation box 19 and has a measuring container 21 at the end of the sand filling pipe 20.

[0038] In this embodiment, fracturing flowback fluid retrieved from the oil field site is allowed to rest in a flowback holding tank 1 for one hour to ensure the removal of solid impurities such as grit. A photocatalyst suspension tank 4 contains a 1 mg / mL aqueous suspension of TiO2 photocatalyst particles. An axial flow pump 2 pumps the supernatant from the flowback holding tank 1 into the pipeline. A differential pressure flowmeter 3 selects different volume ratios of flowback fluid and photocatalyst particle suspension based on actual degradation performance.

[0039] In this embodiment, the solar photons emitted by the solar simulator 6 are further transmitted to the sapphire window 8 through the focusing effect of the focusing lens 7, and the focusing ratio is above 100. The optical transmittance of the sapphire window 8 is above 98%. The intermittent peristaltic pump 5 can control the flow rate of the backflow liquid and the photocatalyst particle mixed liquid flowing from the photocatalyst suspension tank 4. At the same time, the start and stop time ratio of the intermittent peristaltic pump 5 needs to be controlled according to the actual degradation performance feedback. The height of the arrayed prism 22 in the photoreactor 9 is 5 mm. Its main function is to form a local micro-turbulence environment when the mixed liquid flows through the arrayed prism 22, so as to avoid the aggregation and sedimentation of the photocatalyst particles.

[0040] In this embodiment, the mixed liquid that completes the photoreaction in the photoreactor 9 undergoes solid-liquid separation in the downstream separation tank 11. The supernatant after degradation is vaporized in the photothermal chamber 10. The diaphragm pump 12 controls the flow rate to below 20 mL / min. A black carbon gel film is placed at the bottom of the photothermal chamber 10 to enhance photothermal absorption and thermal conversion. A first status monitor 13 provides real-time monitoring of the temperature, pressure, and water content of the vapor in the photothermal chamber 10.

[0041] In this embodiment, the photoreactor 9 and the photothermal chamber 10 form a complementary relationship in the utilization of the solar energy spectrum, and the absorption spectrum ranges are 250nm-500nm and 500nm-2500nm respectively. The constant temperature vaporization furnace 14 can further adjust the temperature and pressure of the steam according to the experimental parameter requirements. In the sand filling tube 20, the core compressed with quartz sand can be used to simulate the underground rock layer. The core treated with saturated water and saturated oil is placed in the sand filling tube 20. The insulation box 19 can simulate the real-time temperature of the underground environment in situ. The temperature range that can be set is 25 o C-1000 o Between C.

[0042] In this embodiment, to enhance the water vapor injection capability, inert nitrogen is used as a carrier gas to inject water into the sand-filling tube 20. An explosion-proof gas flowmeter 16 controls the flow of high-pressure nitrogen from a high-pressure nitrogen cylinder 15. The nitrogen and water vapor mixture is then mixed uniformly in a mixing buffer chamber 17 and then enters the rear end. A second status monitor 18 monitors the gas pressure and temperature at the inlet of the sand-filling tube 20.

[0043] In this embodiment, the volume flow rate of heavy oil thermal recovery can be obtained according to the metering container 21, and the thermal recovery performance under the characteristic parameter working condition can be measured by comparing the produced oil volume with the total saturated oil volume.

[0044] Example 2

[0045] like Figure 1 and Figure 2 As shown, the present invention provides an integrated experimental method for fracturing flowback fluid clean treatment and heavy oil thermal recovery, comprising:

[0046] First, before the experimental system is put into operation, it is necessary to prepare a water suspension of TiO2 photocatalyst particles with a concentration of 1 mg / mL and place it in the photocatalyst suspension tank 4, and stir it continuously. In addition, the fracturing backflow liquid retrieved from the site is poured into the backflow liquid standing box 1 as an experimental sample, and left to stand for more than 1 hour to ensure that the gravel therein is completely settled. For the experimental core, silica particles between 40 mesh and 100 mesh can be compressed and used as simulated cores, and then saturated with water and saturated with oil and placed in the sand filling pipe 20, and the total oil content in the simulated core is recorded. When the system starts running, the fracturing backflow liquid in the backflow liquid standing box 1 is pumped into the photocatalyst suspension tank 4 by the axial flow pump 2, and the volume ratio and corresponding concentration of the two liquids can be adjusted by the differential pressure flowmeter 3. Furthermore, the mixed liquid is transported to the photoreactor 9 via an intermittent peristaltic pump 5 to participate in the photochemical reaction. The array of prisms 22 provided therein can form a local micro-turbulence environment when the mixed liquid flows through the array of prisms, thereby preventing the aggregation and sedimentation of the photocatalyst particles. The solar simulator 6 can emit a full-band spectrum, and its own light intensity can also be adjusted by its corresponding controller. The emitted full-band photons are concentrated by the focusing lens 7 and radiated to the reaction suspension through the sapphire window 8. Under the excitation of ultraviolet light and some visible light photons, the photocatalyst TiO2 will produce abundant holes and correspondingly produce hydroxyl radicals with extremely strong oxidizing properties in the base liquid, which can oxidize and degrade organic matter and bacteria in the backflow liquid into non-toxic and harmless low-carbon molecules or inorganic substances. After the reaction, the reaction liquid enters the separation tank 11 for static separation. After the photocatalyst settles, the diaphragm pump 12 pumps the supernatant of the separation tank 11 into the photothermal chamber 10 for photothermal conversion. The unused spectrum of the photoreactor 9 is used to drive the photothermal conversion and convert the low-flow liquid water into water vapor. The first state monitor can be used to monitor the temperature and pressure state of this test section. The constant temperature vaporization furnace 14 can further adjust the temperature and pressure range of the steam according to the test requirements of the experiment. At the same time, the nitrogen stored in the high-pressure nitrogen bottle 15 enters the mixing buffer chamber 17 after passing through the explosion-proof gas flowmeter 16 and mixes with the hot steam to serve the purpose of carrier gas and pressurization. The mixed gas coming out of the mixing buffer chamber 17 is directly injected into the sand filling tube 20, and the insulation box 19 can control the temperature range of the sand filling tube 20. The second status monitor can be used to monitor the temperature and pressure of the mixed gas at the inlet of the sand filling pipe 20. After the steam is heated to reduce viscosity, the heavy oil pre-filled in the sand filling pipe 20 is continuously displaced. The volume of the displaced heavy oil is measured in the metering container 21, and the performance under different operating parameters is compared.

[0047] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from all points of view, the embodiments should be regarded as illustrative and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and range of equivalents of the claims are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

[0048] In addition, it should be understood that although this specification describes the embodiments, not every embodiment contains only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for the purpose of illustrating the technical concept of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made based on the technical solution in accordance with the technical concept proposed by the present invention fall within the scope of protection of the claims of the present invention.

Claims

1. Integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery, characterized by: The invention comprises a backflow liquid quiescent box (1), an axial flow pump (2) is provided at the downstream end of the backflow liquid quiescent box (1), a differential pressure flow meter (3) is provided at the downstream end of the axial flow pump (2), a photocatalyst suspension tank (4) is provided at the downstream end of the differential pressure flow meter (3), an intermittent peristaltic pump (5) is provided downstream of the photocatalyst suspension tank (4), and a photoreactor (9) is provided downstream of the intermittent peristaltic pump (5); a sapphire window (8) is provided on the top middle layer of the photoreactor (9), and an array prism (22) is provided on the bottom layer; a separation tank (11) is provided at the downstream end of the photoreactor (9), a solar simulator (6) and a focusing lens (7) are provided on the top of the photoreactor (9); a diaphragm pump (12) is provided downstream of the separation tank (11), and a diaphragm pump (12) is provided downstream of the separation tank (11). ), a diaphragm pump (12) is directly connected to the photothermal chamber (10), a first state monitor (13) is provided at the downstream end of the photothermal chamber (10), a constant temperature vaporization furnace (14) is provided at the downstream end of the first state monitor (13), and a mixing buffer chamber (17) is provided at the downstream end of the constant temperature vaporization furnace (14); a high-pressure nitrogen bottle (15) and an explosion-proof gas flow meter (16) are provided at the upstream end of the mixing buffer chamber (17); a second state monitor (18) is provided at the downstream end of the mixing buffer chamber (17), a sand filling pipe (20) is provided at the downstream end of the second state monitor (18), the sand filling pipe (20) is placed inside the heat preservation box (19), and a metering container (21) is provided at the tail end of the sand filling pipe (20).

2. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The fracturing flowback fluid retrieved from the oil field is left to stand in the flowback fluid standing tank (1) for 1 hour to ensure that solid impurities in the flowback fluid are removed.

3. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: A TiO2 photocatalyst particle water suspension with a concentration of 1 mg / mL is placed in the photocatalyst suspension tank (4). The axial flow pump (2) draws the supernatant from the backflow liquid holding tank (1) into the pipeline. The differential pressure flow meter (3) selects and mixes different volume ratios of backflow liquid and photocatalyst particle suspension according to actual degradation performance.

4. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The solar photons emitted by the solar simulator (6) are further transmitted to the sapphire window (8) through the focusing effect of the focusing lens (7), and the focusing ratio is above 100; the intermittent peristaltic pump (5) is used to control the flow rate of the backflow liquid and the photocatalyst particle mixed liquid flowing from the photocatalyst suspension tank (4), and at the same time, the start and stop time ratio of the intermittent peristaltic pump (5) is controlled according to the actual degradation performance feedback; the height of the array prism (22) in the photoreactor (9) is 5 mm, which is used to form a local micro-turbulence environment when the mixed liquid flows through the array prism (22).

5. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The mixed liquid that completes the photoreaction in the photoreactor (9) completes the solid-liquid separation process in the downstream separation tank (11), and the supernatant after degradation treatment completes the vaporization process in the photothermal chamber (10). The diaphragm pump (12) needs to control the flow rate to be below 20 mL / min; a black carbon gel film is placed at the bottom of the photothermal chamber (10) to enhance the photothermal absorption and thermal conversion effects; the first state monitor (13) is used to monitor the temperature, pressure and water content information of the steam in the photothermal chamber (10) in real time.

6. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The photoreactor (9) and the photothermal cavity (10) form a complementary relationship in utilizing the solar energy spectrum, and their absorption spectrum ranges are 250nm-500nm and 500nm-2500nm respectively.

7. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The constant temperature vaporization furnace (14) is used to further adjust the temperature and pressure of the steam according to the experimental parameter requirements; the core compressed by quartz sand is used to simulate the underground rock formation in the sand filling tube (20), and the core treated with saturated water and saturated oil is placed in the sand filling tube (20). The insulation box (19) is used to simulate the real-time temperature of the underground environment in situ. The temperature range that can be set is 25 o C-1000 o Between C.

8. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: Inert nitrogen is used as a carrier gas to be injected into the sand filling tube (20); an explosion-proof gas flow meter (16) is used to control the high-pressure nitrogen released from the high-pressure nitrogen bottle (15); the mixed gas of nitrogen and water vapor is mixed evenly in the mixing buffer chamber (17) and then enters the rear end together; a second state monitor (18) is used to detect the gas pressure and temperature at the inlet end of the sand filling tube (20).

9. The integrated experimental system for fracturing flowback fluid clean treatment and heavy oil thermal recovery according to claim 1, characterized in that: The volume flow rate of heavy oil thermal recovery is obtained based on the metering container (21), and the thermal recovery performance under the characteristic parameter conditions is measured by comparing the produced oil volume with the total saturated oil volume.

10. An integrated experimental method for fracturing flowback fluid clean treatment and heavy oil thermal recovery, characterized in that: The method is based on the integrated experimental system for clean treatment of fracturing flowback fluid and thermal recovery of heavy oil according to any one of claims 1 to 9, comprising: A 1 mg / mL TiO2 photocatalyst particle water suspension is placed in a photocatalyst suspension tank (4) and continuously stirred; the fracturing backflow fluid retrieved from the site is poured into the backflow fluid standing box (1) as an experimental sample, and is left to stand for more than (1) hour to ensure that the gravel therein is completely settled; for the experimental core, silica particles between 40 mesh and 100 mesh are compressed as a simulated core, which is then saturated with water and oil and placed in a sand filling pipe (20), and the total oil content in the simulated core is recorded; when the system starts running, the fracturing backflow fluid in the backflow standing box (1) passes through the shaft The liquid is pumped into the photocatalyst suspension tank (4) by a flow pump (2), and the volume ratio and corresponding concentration of the two liquids are adjusted by a pressure differential flow meter (3); the mixed liquid is transported to the photoreactor (9) through an intermittent peristaltic pump (5) to participate in the photochemical reaction, wherein the arrayed prism (22) forms a local micro-turbulence environment when the mixed liquid flows through the arrayed prism; the solar simulator (6) emits a full-band spectrum, and the emitted full-band photons are concentrated by a focusing lens (7) and radiated to the reaction suspension through a sapphire window (8). Under the excitation of ultraviolet light and part of visible light photons, the photocatalyst TiO2 The reaction liquid after the reaction is put into the separation tank (11) for static separation. After the photocatalyst settles, the diaphragm pump (12) pumps the supernatant of the separation tank (11) into the photothermal chamber (10) for photothermal conversion. The unused spectrum of the photoreactor (9) is used to drive the photothermal conversion and convert the low-flow liquid water into water vapor. The first state monitor (13) is used to monitor the temperature and pressure state of this test section. The constant temperature vaporization furnace (14) further adjusts the temperature and pressure range of the steam according to the test requirements of the experiment. At the same time, the high-pressure nitrogen gas is stored in the high-pressure nitrogen bottle (15). The stored nitrogen passes through the explosion-proof gas flow meter (16) and enters the mixing buffer chamber (17) to mix with the hot steam, serving as a carrier gas and boosting the pressure. The mixed gas from the mixing buffer chamber (17) is directly injected into the sand filling pipe (20), and the heat preservation box (19) controls the temperature range of the sand filling pipe (20). The second state monitor (18) monitors the temperature and pressure of the mixed gas at the inlet of the sand filling pipe (20). After the steam is heated to reduce the viscosity, the heavy oil pre-filled in the sand filling pipe (20) is continuously displaced. The volume of the displaced heavy oil is measured in the metering container (21), and the performance under different operating parameters is compared.

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