Exploitation method for in-situ modification of shale oil through cooperation of radio frequency heating and fusible proppant

Abstract

The invention provides a mining method for in-situ modification of shale oil through cooperation of radio frequency heating and a fusible proppant. The nano-catalyst is packaged in a fusible plastic proppant, so that deep transportation of the nano-catalyst is realized; and after the plastic is melted, nanoparticles are released to catalyze kerogen pyrolysis, so that the radio frequency heating efficiency is improved, and a high flow guide channel is provided. The preparation method comprises the following specific steps: S1, preparing a fusible proppant composed of plastic and nanoparticles; s2, injecting the mixed propping agent into the reservoir through hydraulic fracturing; s3, improving the radio frequency heating efficiency by using the strong wave absorbing characteristic of the nanoparticles in the proppant; s4, melting the fusible proppant to release the nano-catalyst and hydrogen free radicals, and promoting kerogen in-situ modification; and S5, efficient recovery of the modified oil gas is achieved through a high flow guide channel formed through melting. The technology solves the problems that the migration of the nano-catalyst is limited, the electromagnetic wave absorption capacity of the shale reservoir is weak, and the percolation resistance of the modified oil gas is large, and provides a new way for the development of the shale oil with medium and low maturity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of unconventional oil and gas development, and particularly relates to a method for exploiting in-situ modified low-maturity shale oil by radio frequency heating in cooperation with meltable proppant. BACKGROUND

[0002] As a global manufacturing power, oil supply security is crucial to China's economic development. China has abundant shale oil and gas resources, mainly distributed in key areas such as Sichuan, Ordos and Songliao Basin. Accelerating the development of domestic shale oil and gas resources can alleviate energy supply pressure.

[0003] Shale oil is hosted in shale formations rich in sedimentary organic matter, and the reservoir has typical characteristics of low porosity and low permeability, and low thermal evolution degree and complex accumulation mechanism. Low-maturity shale oil is hosted in the form of kerogen in the reservoir, and the development difficulty is greater. When the temperature of kerogen is >300℃, it will crack into oil, gas, water and petroleum coke and other products.

[0004] In-situ heating modification is a key technology for the development of low-maturity shale oil. According to the heating method, the current main development technologies include: electric heating, steam heating and electromagnetic radiation heating. Electric heating uses resistance heating, which can use downhole installed resistance elements or set multiple wells as positive and negative electrodes to form a loop to heat the reservoir, mainly in the form of heat conduction to the reservoir, and the heating speed is slow. Steam heating technology injects steam into the reservoir to heat the reservoir, which has the problems of high heat loss at the wellbore, low steam injection capacity due to the tightness of the reservoir, and reservoir damage caused by steam condensate water swelling shale clay. The principle of electromagnetic radiation heating is that the polar molecules in the medium are ionized under the action of an external electric field, and the molecules vibrate at high frequency with the alternating electromagnetic field, generating heat between the molecules, and converting electrical energy into heat energy. Compared with other methods, electromagnetic radiation heating has the advantages of fast speed and no need to consider the problems of heat loss along the wellbore and fluid injection difficulty caused by poor reservoir permeability.

[0005] According to the radiation frequency, electromagnetic radiation heating can be divided into microwave heating and radio frequency heating. The microwave frequency range is 300MHz-300GHz, the wavelength is small, and the penetration ability is weak, with a penetration depth of less than 1m in shale reservoirs, and the action range is concentrated in the near wellbore zone. The radio frequency range is 300kHz-300MHz, which greatly improves the penetration depth in shale, which can reach tens of meters. Radio frequency heating has unique advantages in in-situ modification of shale oil: first, radio frequency heating is fast, which can quickly raise the reservoir temperature and provide the energy required for kerogen pyrolysis; second, the transmission of electromagnetic waves is less affected by reservoir properties, and is suitable for low-permeability, thin-layer and strongly heterogeneous reservoirs. Finally, radio frequency heating heats the reservoir by electromagnetic waves, without the need for injecting hot fluids, reducing reservoir damage.

[0006] However, there are the following problems in the development of shale oil by using radio frequency heating alone: (1) Dry kerogen is a weak electromagnetic wave absorbing medium with low dielectric loss, and the efficiency of converting electrical energy into heat energy is not high, which needs to be further improved; (2) Although low radio frequency can increase the wavelength, its effective range is still limited, and the influence area of radio frequency heating needs to be expanded; (3) Radio frequency heating can improve the quality of shale oil and gas, but the effect of reservoir reconstruction is not effective, and high permeation channels need to be established in the reservoir for the flow of oil and gas. Therefore, how to develop a method for in-situ upgrading of low-maturity shale oil that can heat the shale reservoir in a large range, catalyze the kerogen upgrading reaction and improve the oil and gas permeation capacity is a problem to be solved in the field.

[0007] Technical solution of prior art one Patent CN111594119A discloses a method for in-situ heating and mining oil shale by microwave ladder. The method sets up a microwave heating well in the oil shale reservoir, heats the reservoir by microwave radiation, and makes the generated oil and gas flow out from the lead-out seam. At the same time, temperature sensors are installed to detect the temperature of the heating well, and when the temperature reaches the upper limit, the microwave power is reduced in a ladder form to prevent the reservoir from overheating.

[0008] Disadvantages of prior art one: The penetration depth of microwave heating on shale reservoir is limited, which cannot effectively heat the distant reservoir area; although reducing the power can prevent the temperature from being too high, it will also slow down the heating speed of the reservoir and reduce the overall heating efficiency.

[0009] Technical solution of prior art two Patent CN110593835A discloses a method for in-situ upgrading and mining shale oil by heating shale reservoir with electric field. The method selects shale reservoir with high organic matter abundance, drills straight wells or horizontal wells with specific well spacing in the reservoir, connects the adjacent casings with power supply as positive and negative electrodes through external cable, uses shale reservoir as resistance, and heats the reservoir by Joule heating effect.

[0010] Disadvantages of prior art two: The heating effect of this method is affected by the size of the shale reservoir resistance, and the non-uniformity of the reservoir causes uneven resistance distribution, resulting in uneven heating; the low porosity and low permeability of shale make the oil and gas flow resistance large; in addition, the increase of the distance between the electrodes will weaken the electric field intensity, limiting the effective heating range.

[0011] Technical solution of prior art three Patent CN116335608A discloses a device and method for in-situ upgrading of low-maturity shale oil. The method designs an underground electric heating device, which divides the cable into cold and hot sections through a heat insulation device: the cold section remains in the tubing, and the hot section extends out of the tubing with a length of 2 / 3 of the horizontal well length. The cable connects the hot section with the power supply, and the heat source in the hot section is composed of alloy resistance wire, which heats the shale reservoir for in-situ upgrading by heat conduction, and the separated oil and gas are produced from the production well.

[0012] Disadvantages of prior art three: The method uses resistance heating, mainly by heat conduction, with slow heating rate and limited heating range, which cannot effectively cover the reservoir area far from the wellbore. Meanwhile, the complex structure of the device increases the difficulty of installation and maintenance.

[0013] Technical solution of prior art four Patent CN117328846A discloses a method for in-situ thermal huff and puff upgrading and production of low-maturity shale oil. The method first measures the heat transfer properties of the target reservoir through core experiments, and then performs in-situ upgrading based on these parameters. The specific steps are to sequentially inject hydrogen donor, catalyst and other fluids into the wellbore, inject them into the formation through perforation holes, inject high-thermal-conductivity fluid to establish a high-thermal-conductivity environment between the wellbore and the formation, and finally install a resistance heating device downhole to heat the reservoir for in-situ upgrading.

[0014] Disadvantages of prior art four: Due to the low permeability of shale reservoirs, it is difficult to inject hot fluid, and the injection process of multiple fluids is complex and difficult to operate. The migration distance of catalyst in the reservoir is limited, affecting the overall action range of catalysis. Summary of the invention

[0015] The present invention aims to solve the defects of the prior art and proposes a method for in-situ upgrading of shale oil by radio frequency heating and soluble proppant. Specifically, the method solves the problems of limited migration distance of nanometer catalyst in the reservoir during in-situ upgrading of low-maturity shale oil, low electric-thermal conversion efficiency under the weak electromagnetic wave absorption ability of casein, and poor upgrading oil and gas migration ability due to low porosity and low permeability of shale reservoirs.

[0016] The implementation steps of the present application are as follows: first, a plastic mixed dielectric response type nano-catalyst extracted from waste is used to prepare a fusible proppant; second, the shale reservoir is hydraulically fractured, and the fusible and conventional (high thermal conductivity) proppant is pumped into the artificial fracture at a certain ratio, and the lighter plastic carries the nanoparticles to the deep part of the reservoir; third, a radio frequency heating device such as a dipole antenna is installed at the downhole fracture to heat the reservoir and the fracture, and the strong wave-absorbing nanoparticles in the fusible proppant enhance the electromagnetic wave absorption capacity of the reservoir and the fracture and improve the heating efficiency; finally, when the temperature exceeds a certain threshold, the fusible proppant melts and releases the nanoparticles, catalyzing the kerogen upgrading reaction, and at the same time forming a high conductivity channel in the propped fracture, so that the oil and gas generated by upgrading can be produced along the high conductivity fracture. The method takes the fusible proppant as the core, combines the advantages of radio frequency heating and hydraulic fracturing technology, and forms a "in-situ upgrading-nano-catalysis-channel fracturing" three-in-one development technology for low-maturity shale layers.

[0017] The fusible proppant is composed of plastic, strong wave-absorbing nanoparticles and nano-catalyst. The preparation process includes: mixing carbon-based wave-absorbing nanoparticles with metal or alloy nano-catalyst; extracting polyethylene from plastic waste, mixing the mixed nanoparticles with the extracted polyethylene, and thermoplastically forming 100-mesh small particles to form the fusible proppant. The proppant has three major functions: (1) the plastic melts when the temperature exceeds its melting temperature (polyethylene material is about 120°C), which converts into polyethylene hydrogen donor, enhancing the hydrogen supply reaction in the kerogen pyrolysis process; at the same time, the nanoparticles are released to catalyze the kerogen upgrading reaction and increase the proportion of light components in the upgraded oil and gas. (2) Because the density of plastic is relatively light, about 0.95 g / cm 3 , the fusible proppant mixed with nanoparticles can penetrate deep into the fracture during the fracturing process, expanding the migration distance and range of action of the nanoparticles. (3) After the fusible proppant melts, a high conductivity channel is formed inside the fracture, promoting the seepage and recovery of the upgraded fluid.

[0018] Because of the poor physical properties of shale, it is necessary to improve the permeability through reservoir reconstruction to achieve the purpose of industrial oil flow. Compared with conventional shale fracturing, low-maturity shale fracturing requires the use of special proppant, including the fusible proppant proposed in the present application and conventional proppant mixed together. In addition, high thermal conductivity proppant can be used to replace conventional proppant to promote heat transfer in the fracture and heat exchange between the fracture and the matrix, thereby expanding the range of radio frequency heating. At the same time, the proppant containing plastic can reduce the settling speed of the conventional proppant and increase the migration distance of the proppant when mixed with conventional ceramic or quartz sand and injected.

[0019] After fracturing and flowback, a radio frequency heating device (usually a dipole antenna or leaky wave antenna) is lowered into the well, and the antenna is powered through a cable to heat the reservoir. Under the action of radio frequency heating, the unflowed water can quickly increase the temperature of the reservoir as a strong electromagnetic wave absorbing medium. As the temperature further increases, the fusible proppant melts and releases nanoparticles, among which the dielectric nanoparticles enhance the absorption capacity of the reservoir to electromagnetic waves, improving the efficiency of radio frequency heating. When the temperature rises above about 350°C, the kerogen is cracked into oil, gas, water and residue. The nanoparticles catalyze the kerogen pyrolysis process, reduce the activation energy required for the reaction, regulate the product distribution, and increase the proportion of light components. The modified oil and gas flow along the high permeability channels formed by the melting of the fusible proppant to the bottom of the well, and are finally produced to the ground.

[0020] The present application adopts the following technical solutions: A radio frequency heating method for in-situ upgrading of shale oil by fusible proppant, comprising: Step S1. Preparation of fusible proppant. The fusible proppant is composed of polyethylene plastic, strong wave-absorbing nanoparticles and nanocatalyst.

[0021] The fusible proppant is composed of 93.6wt%-95.2wt% polyethylene plastic, 2.4wt%-3.2wt% activated carbon and 2.4wt%-3.2wt% Fe3O4 thermoplastic molding, which has strong electromagnetic wave absorption capacity and catalytic effect.

[0022] The polyethylene plastic in the proppant can be replaced by common plastic products such as polypropylene; the activated carbon can be replaced by carbon-based nanomaterials such as carbon nanotubes and graphene; and the Fe3O4 nanocatalyst can be replaced by metal or alloy-based nanomaterials such as nickel, molybdenum and cobalt.

[0023] Step S2. Inject mixed proppant into artificial fractures by hydraulic fracturing. 10%-15% of the mixed proppant is fusible proppant, and 85%-90% is conventional proppant. The conventional proppant can be quartz sand, artificial ceramic or high thermal conductivity proppant.

[0024] Step S3. Install a radio frequency heating device to heat the shale reservoir downhole. The radio frequency heating device is mainly composed of a power supply system, a cable and a dipole antenna, and the dipole antenna is powered through the cable. The dipole antenna can emit electromagnetic waves with multiple frequencies such as 13.56MHz, 27.12MHz or 40.68MHz. The dipole antenna can be arranged into a dipole antenna array to improve the efficiency of radio frequency heating.

[0025] The dipole antenna heats the shale reservoir by generating an alternating electromagnetic field. The fusible proppant melts at around 120°C, releasing nanocatalysts and hydrogen donors, and the activated carbon in the mixed nanoparticles improves the absorption capacity of electromagnetic waves, improving the efficiency of radio frequency heating and the temperature of the reservoir.

[0026] Step S4. Radio frequency heating kerogen in-situ upgrading. When the temperature reaches above 350℃, kerogen begins to pyrolysis to produce oil and gas. In this process, nano Fe3O4 particles as catalysts effectively reduce the temperature required for kerogen cracking and promote the reaction to proceed; at the same time, the polyethylene plastic component in the meltable proppant as a hydrogen donor promotes the hydrogenation reaction of kerogen to generate more small molecule saturated hydrocarbons.

[0027] Step S5. Oil and gas recovery. After the melting of the meltable proppant, a high conductivity channel is formed in the fracture, increasing the conductivity of the fracture, and the oil and gas migrate through the fracture to the wellbore and are produced to the ground.

[0028] The beneficial effects of the present application are: The present application combines radio frequency heating with meltable proppant in-situ upgrading of kerogen, which combines the multiple advantages of radio frequency heating, nano-catalysis and channel fracturing. The specific gains include: (1) The nano particles are transported to the deep part of the reservoir by the way of plastic mixed with nano particles, which effectively overcomes the problem of uneven distribution and limited range of action caused by the adsorption and agglomeration of nano particles on the surface of the rock. (2) The shale reservoir is heated by radio frequency, and because the electromagnetic wave transmission is not affected by the reservoir properties and the radio frequency wavelength is larger, it can heat a wider range of shale reservoirs. (3) The strong wave-absorbing nano particles are released after the melting of the meltable proppant, which improves the efficiency of radio frequency heating and solves the problem of weak dielectric response of shale reservoirs; at the same time, the released nano catalysts reduce the activation energy required for kerogen pyrolysis reaction, and increase the proportion of light components in the upgraded oil and gas. (4) The cracks filled with meltable proppants are formed by hydraulic fracturing, which expands the range of radio frequency heating, and after the melting of the proppant, a high conductivity channel is formed in the crack for the seepage of upgraded oil and gas. (5) Combined with green electricity generated by clean energy such as wind energy, solar energy, tidal energy, etc., and using waste materials to prepare meltable proppants based on plastics, this method can promote the efficient and green development of low-maturity shale oil, which is a difficult-to-develop and high-energy-consumption unconventional oil and gas resource. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Flow chart of radio frequency heating combined with meltable proppant upgrading shale oil recovery method.

[0030] Figure 2 Schematic diagram of radio frequency heating combined with meltable proppant in-situ upgrading shale oil recovery device.

[0031] Figure 3 Final temperature of kerogen sample after radio frequency heating of electromagnetic waves with different frequencies.

[0032] Figure 4 Weight loss rate of kerogen sample under different nano particle concentrations in meltable proppant after radio frequency heating.

[0033] Figure 5The radio frequency heating weightlessness rate of the dry kerogen sample under different proportions of different fusible proppants in the mixed proppant.

[0034] Figure 6 The radio frequency heating weightlessness rate of the dry kerogen sample under different sand paving concentrations.

[0035] In the figure: 1-power supply system, 2-frequency converter, 3-wellbore, 4-cable, 5-dipole antenna, 6-electromagnetic wave, 7-artificial fracture, 8-conventional proppant, 9-fusible proppant, 10-hydrogen radical, 11-nano catalyst, 12-high conductivity channel, 13-production tree. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme in the present application is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0037] The technical scheme of the present application will be described below in detail with reference to the accompanying drawings. Figures 1-2 to realize the present application.

[0038] As Figure 1 shown, a radio frequency heating method for in-situ upgrading shale oil by fusible proppant, comprising the following steps: Step S1. Fusible proppant 9 is prepared by using polyethylene extracted from plastic waste and dielectric response type nano catalyst, which has strong electromagnetic wave absorption capacity and catalytic effect.

[0039] Step S2. Hydraulic fracturing of shale reservoir. The fusible proppant 9 is mixed with the conventional proppant 8 and pumped into the artificial fracture 7. The conventional proppant 8 mainly supports the fracture and prevents the fracture from closing under the closure pressure of the formation, while the fusible proppant 9 carries nano particles and provides polyethylene material as a hydrogen donor. After mixing, they can simultaneously support the artificial fracture and enhance the wave absorption capacity of the reservoir and the artificial fracture. At the same time, the low density of the fusible proppant 9 can reduce the density of the mixed proppant after mixing with the conventional proppant 8, which can penetrate deep into the fracture during the fracturing process, and expand the migration distance and range of action of the nano particles.

[0040] Step S3. Arrange the radio frequency heating device to heat the reservoir using the radio frequency heating device.

[0041] As Figure 2The radio frequency heating device is composed of a power supply system 1, a frequency converter 2, a cable 4, and a dipole antenna 5. The power supply system 1 provides power for the heating system. The frequency converter 2 can provide multiple industrial frequencies such as 13.56 MHz, 27.12 MHz, and 40.68 MHz. The cable 3 transmits power. The dipole antenna 5 emits high-frequency electromagnetic waves 6 to perform radio frequency heating on the shale reservoir. The cable 4 enters the wellbore 3 through a channel in the Christmas tree 13. The end of the cable 4 is the dipole antenna 5. The other end of the cable 4 is connected to the frequency converter 2. The frequency converter 2 is connected to the power supply system 1.

[0042] As shown in Figure 2 The fusible proppant 9 melts and breaks at about 120℃, releasing the nano catalyst 11. The active carbon in the nano catalyst 11 and Fe3O4 are electromagnetic wave absorption media, which can significantly improve the wave absorption capacity of the reservoir and rapidly heat the reservoir.

[0043] Step S4. In-situ upgrading of shale oil under high temperature environment. When the temperature is greater than 350℃, the pyrolysis of kerogen produces small molecular oil and gas, and forms a hydrogen-donating reaction with the hydrogen radicals 10 generated by the fusible proppant 9 at 350℃ to promote the thermal cracking of kerogen. Meanwhile, the metal Fe atoms in the nano catalyst 11 reduce the activation energy required for the thermal cracking of kerogen, catalyzing the cracking of kerogen.

[0044] Step S5. The oil and gas generated after upgrading seeps into the artificial fracture 7 through the matrix, and is then produced to the ground through the wellbore 3.

[0045] Further, the Christmas tree 13 is located at the wellhead and is used for hanging the oil casing, controlling and adjusting production. In the present application, the cable 4 enters the wellbore 3 through a channel in the Christmas tree 13. The end of the cable 4 is the dipole antenna 5. The other end of the cable 4 is connected to the frequency converter 2. The frequency converter 2 is connected to the power supply system 1.

[0046] Further, the conventional proppant 8 can be quartz sand, artificial ceramic proppant, or high-thermal-conductivity proppant.

[0047] As shown in Figure 2 The fusible proppant 9 melts in the high-conductivity channel 12 formed in the artificial fracture 7. The oil and gas migrates through the fracture to the wellbore 3 and is then produced to the ground.

[0048] Example 1 Preparation of fusible proppant The preparation steps of the fusible proppant can be divided into three processes: first, cleaning and crushing the plastic waste; second, preparing the mixture according to the formula; and third, thermoplastic molding of the mixture.

[0049] Step 1: Plastic waste (common polyethylene plastic or polypropylene plastic) is cleaned and crushed. If a discarded mineral water bottle is selected, first clean the surface with anhydrous ethanol and then rinse with distilled water. The cleaned plastic is crushed and sieved to obtain plastic particles of about 0.1 mm in size.

[0050] Step 2: Preparation of mixture according to the formula According to the formula, a certain amount of activated carbon, Fe3O4 nanoparticles and plastic particles in step 1 are weighed and placed in a beaker and stirred thoroughly. The specific formula is shown in Table 1:

[0051] Table 1: Soluble proppant formula with different Fe3O4 nanoparticle concentrations

[0052] Step 3: Thermoforming The mixture of plastic and nano-catalyst is thermoformed, and the particles with a particle size of about 100 mesh are separated through a screen to prepare the soluble proppant 9.

[0053] Example 2 Experimental method for modifying kerogen by radio frequency heating in cooperation with soluble proppant.

[0054] Step 1: Preparation of kerogen sheet. Select a low maturity shale sample from the target reservoir, extract the kerogen powder according to the method of GB / T19144-2010, and load the kerogen powder into a core compression instrument. Set the simulated formation pressure to 30 MPa and continuously compress for 10 hours to obtain a kerogen sheet with a diameter of 2.54 cm.

[0055] Step 2: Radio frequency heating experiment. Place different kerogen / proppant systems in a radio frequency heating reaction chamber and conduct radio frequency heating experiments. Set the heating time to 30 minutes, the heating power to 2 kW, and the maximum temperature to not exceed 600°C. After the experiment, clean the samples with n-heptane, dry the samples after cleaning, and finally weigh them. Based on the above experimental method, radio frequency heating experiments at frequencies of 13.56 MHz, 27.12 MHz and 40.68 MHz are conducted to select the optimal radio frequency heating frequency.

[0056] Step 3: Preferable parameters of the meltable proppant. Based on the method in Table 1 of Example 1, different proportions of nanoparticles of the meltable proppant 9 were prepared, the proportion of the conventional proppant 8 and the heat-meltable proppant 9 was changed, and the proppant with different sanding concentrations was selected to fill between two cheese root sheets; the radio frequency heating experiment was carried out for different cheese root / proppant systems; the parameters of the proppant were preferred through the thermogravimetric data of the cheese root samples obtained by the experiment, including the composition of the meltable proppant, the proportion of different types of proppants, and the sanding concentration. The specific experimental scheme is shown in Table 2. The mass proportion of nanoparticles such as activated carbon and Fe3O4 in the formula is 1:1. For the convenience of display, the nanoparticle concentration shown in Table 2 is the concentration of one of them, for example, the concentration of activated carbon. The specific formula is shown in Table 1. For example, the nanoparticle concentration shown in Table 2 is 1.6wt%, and the specific formula of the meltable proppant is 1.6wt% activated carbon, 1.6wt% Fe3O4, and 96.8wt% plastic.

[0057] Table 2 Experimental scheme of radio frequency heating in cooperation with meltable proppant to modify cheese root

[0058] Step 4: Experimental results of the preferred parameters of the proppant. The preferred frequency is shown in Figure 3 . The higher the frequency, the higher the temperature, but the frequency is related to the penetration depth, and the actual selection needs to be combined with the reservoir conditions. The preferred nanoparticle composition of the meltable proppant 9 is shown in Figure 4 . The meltable proppant 9 is composed of nanoparticles and plastic, for example, 2.4wt% AC, 2.4wt% Fe3O4, and 95.2wt% polyethylene. The increase of the proportion of nanoparticles increases the weight loss rate of the cheese root and gradually tends to be stable. When the proportion of nanoparticles increases from 2.4wt% to 3.2wt%, the increase is only 4%. The preferred proportion of the meltable proppant 9 in the mixed proppant is shown in Figure 5 . The increase of the proportion of the meltable proppant 9 increases the weight loss rate of the cheese root, but the trend tends to be stable. When the proportion increases from 10% to 15%, the increase of the weight loss rate is 5.6%, and when the proportion increases from 15% to 20%, the increase of the weight loss rate is only 0.8%. The preferred sanding concentration of the mixed proppant is shown in Figure 6 . With the increase of the sanding concentration, the weight loss rate of the cheese root increases but the change tends to be stable. When the concentration increases from 10kg / m² to 15kg / m², the increase is only 2%. In the selection of the parameters of the proppant, the part with smaller increase can be selected.

[0059] Example 3 In-situ modification of low-mature shale oil exploitation site by radio frequency heating in cooperation with meltable proppant.

[0060] Step 1: Taking a low maturity shale oil reservoir as an example, the vertical depth of the layer is 2549.0-2559.1 m, and the thickness is 10.1 m. A horizontal well is drilled and completed in the target layer. A horizontal well is set in the middle of the target reservoir section, and an electromagnetic wave penetrating downhole string is installed in the target heating section during completion to enable electromagnetic waves to penetrate the oil layer, casing and cement sheath to act on the reservoir or fracture.

[0061] Step 2: Hydraulic fracturing operation. The construction process and flow are consistent with conventional fracturing, and the preflush, sand-carrying fluid and displacement fluid are injected into well X in turn. The difference is that the mixed sand fluid is prepared using the preferred soluble proppant parameters in Example 2, and the flowback operation is carried out after fracturing is completed.

[0062] Step 3: Install downhole radio frequency device. According to the preferred radio frequency heating frequency, dipole antenna 5 is selected, dipole antenna 5 is arranged in the fracturing section, and electromagnetic wave heating of the shale reservoir is generated by power cable, as shown in Figure 2 .

[0063] Step 4: Develop in-situ radio frequency heating of shale oil. According to the experimental results, first use the radio frequency working frequency of 27.12 MHz and the power of 50 kW to preheat the reservoir for 30 days. After preheating, the target reservoir is continuously heated using a working frequency of 13.56 MHz and a power of 120 kW. During the heating process, the soluble proppant 9 melts to release nanoparticles, while improving the heating efficiency and catalyzing the modification of the kerogen. The solid-phase kerogen is pyrolyzed into flowable oil and gas, which flows into the wellbore along the high-conductivity fracture, and is finally produced to the ground.

[0064] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for extracting shale oil by in-situ modification using radio frequency heating and fusible proppant, characterized in that... ,include: Step S1. Prepare a fusible proppant, wherein the fusible proppant has strong electromagnetic wave absorption capability and catalytic effect; Step S2. Hydraulic fracturing of shale reservoirs: Mix fusible proppant with conventional proppant and inject the mixed proppant into artificial fractures; Step S3. Deploy a radio frequency heating device to heat the reservoir; Step S4. Promote in-situ upgrading of shale oil under high temperature conditions; Step S5. Oil and gas recovery: After the fusible proppant melts, it forms a high conductivity channel in the artificial fracture. Oil and gas are transported to the wellbore through the artificial fracture and finally extracted.

2. The method according to claim 1, characterized in that, In step S1, the fusible support is thermoplasticized from 93.6-95.2 wt% polyethylene plastic, 2.4-3.2 wt% activated carbon, and 2.4-3.2 wt% Fe3O4 nanoparticles.

3. The method according to claim 1, characterized in that, In step S1, the fusible support is thermoplasticized from 95.2 wt% polyethylene plastic, 2.4 wt% activated carbon, and 2.4 wt% Fe3O4 nanoparticles.

4. The method according to claim 1, characterized in that, In step S2, the conventional proppant is made of quartz sand or artificial ceramic particles.

5. The method according to claim 1, characterized in that, In step S2, the fusible proppant is mixed with conventional proppant and added to the fracturing fluid along with the hydraulic fracturing fluid for injection into the fracturing fracture. 10%-15% is fusible proppant and 85%-90% is conventional proppant.

6. The method according to claim 1, characterized in that, In step S3, the radio frequency heating device consists of a dipole antenna or a dipole antenna array. The dipole antenna or dipole antenna array in the well is connected by a cable, and the other end of the cable is connected to the power supply system.

7. The method according to claim 6, characterized in that, The dipole antenna is used to transmit electromagnetic waves at frequencies of 13.56MHz, 27.12MHz, or 40.68MHz.

8. The method according to claim 7, characterized in that, The radio frequency heating device was adjusted to a working frequency of 27.12MHz and a power of 50KW to preheat the reservoir for 30 days. After preheating, the target reservoir was continuously heated at a working frequency of 13.56MHz and a power of 120KW.

9. The method according to claim 1, characterized in that, In step S4, as the temperature rises to 120°C or above, the polyethylene plastic component in the fusible support acts as a hydrogen donor, promoting the hydrogenation reaction of kerogen and generating more small-molecule saturated hydrocarbons. At the same time, Fe3O4 nanoparticles act as a catalyst, effectively reducing the temperature required for kerogen pyrolysis and promoting the reaction.

10. The mining method according to claim 1, characterized in that, In step S5, the fusible proppant will completely decompose at 350-500℃, while the conventional proppant continues to support the crack.

Images