Preparation method and application of sand control fluid in outer annular space of oil-string casing

Abstract

The invention discloses a preparation method and application of sand control fluid in an outer annular space of an oil-string casing, and belongs to the technical field of oil-gas field development. The preparation method comprises the steps that S1, the perforation aperture of the oil-string casing and the sand grain size and temperature of a sand production oil layer are obtained; s2, uniformly mixing a non-metallic mineral material, pulverized coal and natural organic compound particles, adding water, and roasting to prepare porous microspheres; s3, paraffin is added, and microspheres wrapping the paraffin are prepared; and S4, adding water and cement to prepare a primary sand control fluid, and adding a retarder or an accelerator to enable the primary sand control fluid to meet the set initial setting time to prepare the sand control fluid. After the prepared sand prevention fluid is solidified, the paraffin can be melted and discharged at the oil layer temperature, so that a sand prevention barrier is formed in an annular space outside an oil-string casing, and due to the fact that the microspheres are porous, a wellbore in the casing is communicated with a sand outlet oil layer, oil gas can enter an oil pipe through pores to be normally exploited and produced, and sand grains are isolated outside. The method is suitable for oil layer sand prevention in oil-gas field exploitation.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, and relates to a sand control method outside the casing of an oil reservoir, specifically a method for preparing and applying sand control fluid in the annular space outside the casing of an oil reservoir. Background Technology

[0002] my country has a wide distribution of shallow and medium-depth loose sandstone oil reservoirs. These reservoirs are shallow, have weak compaction, and complex deposition processes. During oil and gas drilling and production, the compaction vibration of the drill bit, the impact and fracturing effect of the ammunition shock wave or high-pressure gas during perforation, and the stress release, shear expansion, hydraulic impact, and solid phase migration near the wellbore during production cause the continuous shedding and collapse of rock sand particles in the formation skeleton within the annular space outside the casing, forming new fractures and cavities. Sand particles detached from the fractures are washed out with the fluid and transported out of the perforation holes, resulting in the continuous formation of cavities and fractures outside the casing, leading to formation depletion. Over time, this can cause casing deformation or damage. Sand particles entering the casing can easily cause sand jamming and blockage of the lift pump, as well as pump wear. The problem of sand burying the oil layer is also very prominent. Sand particles lifted to the surface can also damage the oil and water treatment system and external transportation.

[0003] Traditional sand control methods all have various problems. In response, a Chinese invention patent, published under the number CN117757454A and titled "A Preparation Method and Application of Sand Control Fluid for Near-Well Oil Layers," describes a method that involves injecting a sand control fluid made of porous particles encapsulating paraffin wax into near-wellbore sand-producing oil layers. After solidification, the paraffin wax melts and is expelled from the solidified cement body at the oil layer temperature, thus modifying the sand-producing oil layer and preventing sand production. However, subsequent practical applications have shown that this method results in low oil layer permeability, leading to low daily oil production and low economic efficiency, and this improvement is difficult to achieve. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing sand control fluid in the annular space outside the casing of an oil layer, so as to solve the problem of low permeability in existing sand control fluid technology.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a sand-control fluid in the annular space outside the casing of an oil layer includes the following steps: S1. Obtain the perforation diameter of the oil layer casing, the sand particle size and temperature of the sand-producing oil layer; S2. Take non-metallic mineral materials, coal powder and natural organic compound particles, mix them evenly, add water, and calcine to make porous microspheres; S3. Drain the residual liquid or residue from the pores of the porous microspheres, add paraffin wax with a melting point lower than the temperature of the sand-exposed oil layer, and make microspheres coated with paraffin wax. S4. Water and cement are added to the paraffin-coated microspheres to make a preliminary sand-preventing liquid. A retarder or accelerator is added to make the preliminary sand-preventing liquid meet the set initial setting time to make a sand-preventing liquid. The porous microspheres have a particle size of 1 / 5 to 1 / 3 of the perforation pore size, a pore size and throat size less than the sand particle size, a porosity greater than 30%, and a pore connectivity greater than 50%.

[0006] As a limitation, the weight percentages of the non-metallic mineral materials, coal powder, and natural organic compound particles are 70%, 10%-15%, and 15%-20%, respectively.

[0007] As a further definition, the non-metallic mineral materials include clay and / or earth clay, and the natural organic compound particles include grain flour, soybean flour, straw flour, grass flour, and wood flour. The particle sizes of the non-metallic mineral materials, coal powder, and natural organic compound particles are all smaller than the particle size of the sand particles in the sand-producing oil layer.

[0008] As another limitation, the roasting is carried out at a temperature of 900-950℃ for a time of 30-40 minutes.

[0009] As a third limitation, residual liquid or residue in the pores of porous microspheres is removed by high-temperature drying or calcination drying.

[0010] As a fourth limitation, the amount of paraffin used is 1-1.5 times the total pore volume of the porous microspheres, and the melting point temperature is 8-10°C lower than the temperature of the sand-exposed oil layer.

[0011] As a fifth limitation, the amount of cement used is 1.2 to 1.5 times the empty volume in the surface volume of the paraffin-coated microspheres.

[0012] The present invention also provides the application of the sand control fluid prepared by the above preparation method, wherein the sand control fluid is injected into the annular space outside the casing of the sand-producing oil layer in the oil well.

[0013] As a limitation, it specifically includes: Pre-fluid is injected to cool the sand-producing oil layer. Xanthan gum or guar gum solution with added paraffin microspheres is injected. Sand-preventing fluid is injected. Displacement fluid is injected after calculation to ensure that all sand-preventing fluid is squeezed into the annular space outside the sand-producing oil layer casing. After 72 hours of curing, the cement plug of the oil layer casing and the casing wall are removed from the sand-preventing fluid. At the initial stage of well opening, water with a temperature higher than the melting point of paraffin is continuously circulated into the casing for 3-5 hours to accelerate the melting and discharge of paraffin in the solidified sand-control fluid in the annular space outside the casing of the sand-producing oil layer. After the paraffin is melted and discharged, normal oil production operations can be carried out.

[0014] As a further limitation, the amount of the pre-treatment liquid injected is 3-5 times the surface volume of the sand-producing oil layer; the surface volume of the paraffin-coated microspheres in the xanthan gum or guar gum solution is 0.2-0.25 times the surface volume of the sand-producing layer; the surface volume of the paraffin-coated microspheres in the xanthan gum or guar gum solution plus the surface volume of the paraffin-coated microspheres in the sand-control liquid equals the surface volume of the sand-producing layer.

[0015] In this application, the table volume, the empty volume within the table volume, the true volume, and the total pore volume are defined as follows: Within 100 cm² 3 After filling the container with 2mm diameter foreskin microspheres (i.e., non-porous microspheres that cannot be immersed in water), you can add 35cm of [unclear text - possibly a typo, should be "35cm"]. 3 Water. Therefore, the surface volume of a microsphere with a diameter of 2 mm is defined as 100 cm³. 3 The empty volume in the table is 35 cm³. 3 The actual volume is 65cm. 3 (i.e. (100-35)cm) 3 When microspheres have pores, the total pore volume of the microspheres = true volume * porosity.

[0016] By adopting the above technical solution, the technical progress achieved by this invention compared with the prior art is as follows: ① This invention provides a method for preparing sand-proof fluid in the outer annular space of an oil layer casing. Due to the small and unadjustable porosity of natural porous activated carbon particles or fly ash particles, the seepage rate is slow in actual production, which is difficult to improve and results in low production efficiency. Therefore, non-metallic mineral materials, coal powder, and natural organic compound particles are specially selected to be sintered into porous microspheres: natural organic compound particles are basically composed of carbon, hydrogen, and oxygen elements, which are easy to burn. During the sintering process, they form gas volatilization and leave permeable spaces; while coal powder can provide heat for preheating and roasting of raw materials. During combustion, it releases gas to form a microporous structure, and at the same time, it can increase the toughness of the microspheres to prevent them from cracking. Thus, the pore size, porosity, and connectivity of the microspheres can be controlled by human intervention. ② The present invention provides an application of sand-control fluid in the outer annular space of the oil layer casing. A sand-control fluid made of porous microspheres coated with paraffin is injected into the outer annular space of the oil layer casing. After the sand-control fluid solidifies, the paraffin can melt and be discharged at the oil layer temperature, thereby forming a sand-control barrier in the outer annular space of the oil layer casing. Furthermore, due to the porous nature of the microspheres, the wellbore inside the casing is connected to the sand-producing oil layer, allowing oil and gas to enter the tubing through the pores for normal production, while sand particles are isolated from the outside. ③ The application of sand-preventing fluid in the annular space outside the casing of an oil layer provided by this invention avoids the oil layer from continuing to produce sand during oilfield development, causing sand burial, sand blockage, and sand plugging of the oil well, resulting in production stoppage, and over time, causing the collapse around the bottom of the oil well, casing deformation, and even the abandonment of the oil well. ④ The application of sand-control fluid in the outer annular space of the oil layer casing provided by this invention is simple to operate, safe and reliable, and low in cost. It solves the problem of sand production in the oil layer, improves the production rate of oil wells, and further enhances the oilfield development effect. In actual production, the production efficiency has increased by an average of more than 76%, generating huge economic benefits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the oil layer casing and annular space in Example 2; Figure 2 This is a schematic diagram of the oil layer casing and annular space in Example 2 where sand-resistant fluid was injected.

[0018] In the diagram: 1. Oil well; 2. Sand-producing oil layer; 3. Oil layer casing; 4. Sand surface; 5. Bridge plug; 6. Sand injection string; 7. Sand control fluid; 8. Annular space; 9. Sand surface. Detailed Implementation

[0019] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are only for explaining the present invention and do not limit the present invention.

[0020] Example 1 This embodiment discloses a method for preparing sand-control fluid in the annular space outside the casing of an oil layer. The sand-control fluid is prepared according to the actual production conditions of a certain work area, and specifically includes the following steps: S1. Obtain the perforation diameter of the oil layer casing, the sand particle size of the sand-producing oil layer, and the temperature. For measuring the diameter of casing perforations in sand-producing oil layers, the following two methods can be used: First, check the perforation history records and determine the perforation diameter by referring to the bullets used during oil testing perforation; second, confirm the perforation diameter during oil testing perforation by taking bottom hole photographs. In this embodiment, the perforation diameter of the oil layer casing is obtained by querying the perforation history. During the operation, a sand flushing string is first run into the wellbore to flush the oil layer sand. The oil layer sand flushed into the surface sand flushing tank is analyzed, including: the volume and quantity of oil layer sand, average particle size, morphological characteristics, and distribution. The cumulative volume and quantity of oil layer sand flushed out during the development of the sand-producing oil layer are also analyzed. The average particle size, morphological characteristics, and distribution of oil layer sand from each flushing are statistically analyzed to determine the size and morphology of the natural organic compound particles to be filled into the porous microspheres. (If the particle size of the oil layer sand retrieved from the sand flushing tank in the previous operation is different from that in the last operation, for example, if the average particle size of the oil layer sand in the previous operation is 65μm, 65μm and 55μm respectively, then the smallest particle size is selected as the standard as the particle size of the natural organic compound particles to be filled when making the porous microspheres, that is, the particle size of the natural organic compound particles is less than 55μm at this time.) Analysis and calculations showed that the average particle size of the sand in the oil-bearing layer was 60 μm, and the volume of sand discharged during the first sand flushing operation was 8 m³. 3 ; To obtain the temperature of the sand-producing oil layer, the temperature of the oil layer in the well can be measured, or the fluid temperature in the same oil layer of a neighboring well can be obtained, so as to select paraffin with a melting point that matches the temperature of the sand-producing oil layer. In this embodiment, the temperature of the oil layer was measured to be 65°C.

[0021] S2. Mix non-metallic mineral materials, coal powder, and natural organic compound particles evenly, add water, and calcine to form porous microspheres. 1) Determine the particle size of porous microspheres Extensive experimental verification has shown that the particle size of porous microspheres should be between 1 / 5 and 1 / 3 of the perforation aperture on the oil layer casing. This particle size can ensure that the porous microspheres can pass smoothly through the perforation aperture on the oil layer casing and enter the annular space, karst cave, or fracture outside the casing, while maximizing the strength and permeability of the sand control zone in the annular space outside the casing, thus ensuring the quality of sand control. The perforation diameter of the casing in the oil layer has been determined to be 7 mm, so the particle size of the porous microspheres can be selected between 1.4 and 2.3 mm. In this embodiment, the particle size of the porous microspheres is selected to be 2 mm. 2) Determine the raw materials for porous microspheres The raw materials for making porous microspheres include non-metallic mineral materials, coal powder and natural organic compound particles with weight percentages of 70%, 10%-15% and 15%-20%, respectively. Fluxes, sintering aids, thickeners and other materials may also be added appropriately. The particle size of the materials should be smaller than the average particle size of the oil layer sand. Here, raw materials with a particle size <60μm are selected, comprising 70%, 12%, and 18% by weight of non-metallic mineral materials, coal powder, and natural organic compound particles, respectively. Non-metallic mineral materials, including clay and / or earth, provide skeletal support for porous microparticles; clay is chosen here. Natural organic compound particles include plant protein particles, cellulose particles, and lignin particles, such as grain flour, soybean flour, straw flour, grass flour, and wood flour. They are basically composed of carbon, hydrogen, and oxygen elements, are easily combustible, and during the firing process of porous microspheres, they are oxidized and volatilized into gases, leaving permeable spaces. The shape of natural organic compound particles can be determined according to the shape of the sand produced from the oil layer, and can be spherical, flake, strip, rod, bar, or other physical shapes. Considering cost factors, spherical straw flour particles are selected here. Powdered coal can provide heat for preheating and calcining raw materials. During combustion, it can release gas to form a microporous structure, while increasing the toughness of microspheres and preventing them from cracking. After calcination, it increases the porosity and connectivity of porous microspheres. 3) Preparation of porous microspheres Take clay, coal powder and straw powder particles with a weight ratio of 70:12:18, mix them evenly, add water, and use a granulator to form microspheres that meet the specifications (i.e., the average particle size is 2mm). Then, put them into a roasting furnace and roast them at 950℃ for 30 minutes to make porous microspheres. After cooling, take them out for use. Experiments show that if the calcination temperature is too high, the porous microspheres are prone to deformation; if the temperature is too low, the porous microspheres lack sufficient strength. If the calcination time is too long, it not only wastes energy but also affects the shape of the porous microspheres. Experiments have verified that a temperature of 900-950℃ and a time of 30-40 minutes are the suitable calcination environment. 4) Detection of the pass rate of porous microspheres Porous microsphere samples were extracted and cut in three directions (horizontal, horizontal, and vertical): the front vertical plane, the horizontal plane, and the side vertical plane. The porosity and connectivity of the microspheres were observed using an electron microscope to determine their qualification: the pore size and throat of the microspheres were less than the sand particle size, the porosity was greater than 30%, the pore connectivity was greater than 50%, and the strength did not break down under the maximum mining intensity. Testing revealed that the porous microspheres prepared in this embodiment had an average porosity of 39%, with pore size and throat size both smaller than the average particle size of the sand particles in the sand-producing oil layer (i.e., <60μm), and a pore connectivity of 58%. According to GB / T 19139-2012 Oil Well Cement Test Method, the breaking pressure of the core of the sand-producing oil layer was 0.8MPa, while the breaking pressure of the porous microspheres was 2.1MPa, meeting the design requirements and proceeding to the next step.

[0022] S3. Remove residual liquid or residue from the pores of the porous microspheres, add paraffin wax with a melting point lower than the temperature of the sand-exposed oil layer, and form microspheres coated with paraffin wax. 1) Selection of paraffin wax Experiments have shown that when the amount of paraffin wax is 1-1.5 times the total pore volume of the porous microspheres, it ensures that the pores of the porous microspheres are filled with paraffin wax and that the outer wall is coated with a layer of paraffin wax. This facilitates the connectivity between the porous microspheres when sand-control fluid is injected into the casing of the oil layer, thereby improving the permeability of the annular space outside the casing. Furthermore, the melting point of paraffin wax is generally 8-10°C lower than the temperature of the sand-exiting oil layer, which helps the paraffin wax to melt and be discharged at the oil layer temperature, forming pores. At 100cm 3 After filling the container with 2mm diameter foreskin microspheres (i.e., non-porous microspheres that cannot be immersed in water), you can add 35cm of [unclear text - possibly a typo, should be "35cm"]. 3The water content indicates that the surface volume of the 2mm diameter microspheres is 100cm³. 3 At that time, the true volume was 65 cm³. 3 The average porosity of the 2mm porous microspheres prepared in this embodiment was measured to be 39%, therefore the total pore volume of the porous microspheres is 25.35 cm³. 3 (65cm) 3 *39%); In this embodiment, the volume of paraffin melted into the pores is selected as 1.3 times the total pore volume. In this embodiment, paraffin wax with a melting point of 55℃ (10℃ lower than the temperature of the sand-extracting oil layer) was selected; 2) Fabrication of paraffin-encapsulated microspheres The porous microspheres that meet the standard requirements are heated to 110°C and dried for 60 minutes to remove residual liquid or residue from the pores, so as to maximize the effectiveness and connectivity of the pores of the porous microspheres and facilitate the melting of paraffin. After the paraffin melts, the aforementioned dried porous microspheres with a particle size of 2 mm are placed into the molten paraffin and stirred thoroughly to ensure that the paraffin is fully melted into the porous microspheres, thus forming microspheres coated with paraffin. After cooling, the adhered microspheres are ground apart.

[0023] S4. Water and cement are added to the paraffin-coated microspheres to prepare a preliminary sand-controlling liquid. A retarder or accelerator is then added to ensure the preliminary sand-controlling liquid meets the set initial setting time, thus completing the sand-controlling liquid product. 1) Raw material dosage of initial sand control fluid In the previous step, we calculated that at 100cm 3 After filling the container with 2mm diameter foreskin microspheres (i.e., non-porous microspheres that cannot be immersed in water), you can add 35cm... 3 The water is 35cm high. 3 The gaps need to be filled, meaning the empty volume within the microsphere surface is 35 cm³. 3 ; Experiments show that the ideal amount of cement in the initial sand-control liquid is 1.2-1.5 times the empty volume of the surface of the paraffin-coated microspheres. Here, we take 1.2 times. This ensures both the consolidation strength of the microspheres and good connectivity between them. 2) Preparation of sand-control liquid Cement and an appropriate amount of water were added to microspheres coated with paraffin wax to prepare a fluid-like preliminary sand control fluid (an appropriate amount of quartz sand, silica powder, or resin materials can also be added to improve tensile, compressive, and erosion resistance properties). The initial setting time of the preliminary sand control fluid was simulated based on the temperature, pressure, and acid / alkali environment of the sand-producing oil layer. According to the requirements of the sand control scheme, a retarder or accelerator was added to ensure that the preliminary sand control fluid met the set initial setting time (5h) to prepare the sand control fluid. After testing, the sand control fluid met the requirements of "GB / T10238-2015 Oil Well Cement".

[0024] Example 2 This embodiment discloses the application of a sand control fluid. The sand control fluid prepared in Example 1 is used for sand control in this work area. Due to the oil layer pressure difference, oil layer expansion, and oil layer heterogeneity during continuous production, cracks, collapses, and caverns occur, resulting in a voided annular space outside the oil layer casing. The specific steps include: Schematic diagram of oil layer casing and annular space as shown below Figure 1 As shown in the diagram, after the sand-control fluid is injected... Figure 2 As shown, specifically, a sand-producing oil well 1 in this work area is selected. During sand control, sand is filled at the bottom of the oil layer casing 3 to a height equal to the sand surface 4. A lower bridge plug 5 is used at the top of the oil layer casing 3. Then, the bottom of the injection string 6 is inserted into the bridge plug 5. Finally, a high-pressure pump truck is used to inject the prepared sand control fluid 7 from the wellhead of the oil well 1 into the annular space 8 outside the oil layer casing 3. The specific steps for injecting the sand control fluid include: 1) Inject pretreatment solution and partially paraffin-coated microspheres. Low-temperature (5-7℃) clean water or oil layer water (preferably oil layer water to ensure compatibility with the oil layer) is used as the pre-flushing fluid in a high-pressure pump truck. The volume is typically 3-5 times the volume of the sand-producing oil layer; in this example, it is 4 times. The sand-producing volume of this oil layer was calculated to be 8m³ in Example 1. 3 That is, the pre-injected liquid volume is 32m³. 3 The ash is injected into the sand-producing oil layer 2 from the ash injection pipe column 6 to cool the sand-producing oil layer 2. Alternatively, a high-pressure pump truck can be used to inject low-temperature (5-7℃) crude oil as a pre-fluid. The amount used is the same as that of clean water or oil layer water. This serves two purposes: first, it lowers the temperature of the sand-producing oil layer 2, preventing the paraffin in the porous microspheres of the sand-control fluid 7 from melting and being discharged before the cement slurry solidifies; second, it allows an oil-soluble film to form in the outer annular space 8 of the oil layer casing 3, preventing the cement in the water-soluble cement slurry of the sand-control fluid 7 from penetrating into the sand-producing oil layer 2 and forming a dense film, thus affecting the permeability of the outer annular space 8 of the oil layer casing 3. Add paraffin-coated microspheres to a low-temperature (5-7℃) aqueous solution of 0.5wt%-2wt% xanthan gum (guar gum can also be used). Here, 1wt% xanthan gum is selected to form a fluid state. Then, use a high-pressure pump to inject the fluid into the annular space 8 outside the oil layer casing 3 from the injection pipe string 6. The surface volume of the paraffin-coated microspheres injected in this process is the surface volume of the sand produced (8m³). 3 The optimal value is between 0.2 and 0.25 times that of the paraffin-coated microspheres; here, 0.2 times is chosen, meaning the surface volume of the microspheres is 1.6 m³. 3 This can increase the porosity between the sand-extracting oil layer and the injected sand-control liquid without affecting the strength of the sand-control liquid after solidification. 2) Inject sand control fluid A pump truck is used to inject sand-control fluid into the casing 3 of the oil layer, allowing it to enter the annular space 8 outside the casing of the sand-producing oil layer. In the previous step, 1.6m has already been driven in. 3 Microspheres encapsulated in paraffin were injected using a pump truck, containing 6.4 mg / L of paraffin. 3 The surface volume of paraffin-coated microspheres in xanthan gum or guar gum solution plus the surface volume of paraffin-coated microspheres in sand-control solution equals the surface volume of sand discharge. Therefore, the surface volume of paraffin-coated microspheres in sand-control solution is: (8-1.6) m³. 3 Low-temperature sand-resistant liquid (5-7℃); Because the cement slurry in the sand control fluid and the microspheres encapsulating paraffin are two incompatible systems, namely, the cement slurry is water-soluble and the paraffin is oil-soluble, when they are solidified in the annular space 8 outside the oil layer casing 3, they repel each other and belong to two interconnected network bodies. 3) Inject displacement fluid After calculating the amount of displacement fluid in the oil casing 3 and the ash injection string 6, a low temperature (5-7℃) displacement fluid can be injected from the ash injection string 6 using a high-pressure pump truck to replace and squeeze the sand control fluid 7 into the annular space 8 outside the oil casing 3. Special attention should be paid to ensuring that the sand control fluid 7 retains a ash surface 9 inside the oil casing 3. The purpose of injecting low-temperature displacement fluid into the injection pipe 6 is twofold: first, to squeeze the sand-preventing fluid 7 inside the injection pipe 6 into the annular space 8 outside the oil layer casing 3; and second, to keep the annular space 8 in the sand-preventing fluid 7 at a low temperature before the cement solidifies, so as to ensure that the paraffin in the porous microspheres remains in a solid, static state. Because cement grout has a bleeding property, a grout surface 9 that is 2m higher than the top of the sand-exiting oil layer 2 should be retained in the oil layer casing 3. This way, after the sand-preventing liquid 7 solidifies, a new solidification cross-section can be formed by drilling through the oil layer casing 3, so that the sand-preventing liquid 7 will not solidify into a dense surface due to the bleeding property of cement, which would affect the permeability of the sand-preventing body. The low-temperature displacement fluid can be water, oil-water mixture, or other low-temperature harmless liquids; After initial solidification, remove bridge plug 5 and backwash the well with low-temperature (5-7℃) clean water. Immediately close the main gate valve and casing gate valve of the oil wellhead to maintain the stability of the wellbore fluid column. Allow the sand-producing oil layer 2 to solidify at low temperature for 72 hours. Then, retrieve bridge plug 5 and use drilling, scraping, and well washing techniques to remove the cement plug and sand-prevention fluid contamination from the casing wall and the casing wall. 4) Well opening and production After the production tubing is run into the well, water containing a gas-liquid mixture with a temperature 20-30°C higher than the melting point of paraffin or a temperature exceeding 100°C is continuously circulated into the oil layer casing 3 for 3-5 hours to accelerate the melting and discharge of paraffin inside the porous microspheres that have solidified outside the oil layer casing 3. As the paraffin melts and is discharged, the microspheres become unobstructed, and the casing and the sand-producing oil layer are connected. This allows oil and gas to enter the tubing through the pores of the porous microspheres for normal extraction and production, while the sand particles are kept out. This ensures normal production and achieves the purpose of sand control.

[0025] Through indoor three-phase flow physical model experiments, under simulated oil reservoir temperature of 65℃ and pressure of 12MPa, the method provided in this embodiment measures an average seepage flow rate of 15 mL / min for crude oil from different oilfields. In contrast, the method disclosed in Chinese invention patent CN117757454A, entitled "A Preparation Method of Near-Well Sand Control Fluid for Oil Reservoirs and Its Application," measures an average seepage flow rate of 8.5 mL / min. This embodiment demonstrates a 76.47% increase in production efficiency compared to the previous method, indicating that this method has higher permeability, higher daily crude oil production, and significantly improved production efficiency.

Claims

1. A method for preparing sand-control fluid in the annular space outside the casing of an oil layer, characterized in that, Includes the following steps: S1. Obtain the perforation diameter of the oil layer casing, the sand particle size and temperature of the sand-producing oil layer; S2. Take non-metallic mineral materials, coal powder and natural organic compound particles, mix them evenly, add water, and calcine to make porous microspheres; S3. Drain the residual liquid or residue from the pores of the porous microspheres, add paraffin wax with a melting point lower than the temperature of the sand-exposed oil layer, and make microspheres coated with paraffin wax. S4. Water and cement are added to the paraffin-coated microspheres to make a preliminary sand-preventing liquid. A retarder or accelerator is added to make the preliminary sand-preventing liquid meet the set initial setting time to make a sand-preventing liquid. The porous microspheres have a particle size of 1 / 5 to 1 / 3 of the perforation pore size, a pore size and throat size less than the sand particle size, a porosity greater than 30%, and a pore connectivity greater than 50%.

2. The preparation method according to claim 1, characterized in that, The weight percentages of the non-metallic mineral materials, coal powder, and natural organic compound particles are 70%, 10%-15%, and 15%-20%, respectively.

3. The preparation method according to claim 2, characterized in that, The non-metallic mineral materials include clay and / or earth clay, and the natural organic compound particles include grain flour, soybean flour, straw flour, grass flour, and wood flour. The particle sizes of the non-metallic mineral materials, coal powder, and natural organic compound particles are all smaller than the particle size of the sand particles in the sand-producing oil layer.

4. The preparation method according to any one of claims 1-3, characterized in that, The roasting process is carried out at a temperature of 900-950℃ for 30-40 minutes.

5. The preparation method according to any one of claims 1-3, characterized in that, The residual liquid or residue in the pores of the porous microspheres is removed by high-temperature drying or sintering.

6. The preparation method according to any one of claims 1-3, characterized in that, The amount of paraffin wax used is 1-1.5 times the total pore volume of the porous microspheres, and its melting point temperature is 8-10℃ lower than the temperature of the sand-extracting oil layer.

7. The preparation method according to any one of claims 1-3, characterized in that, The amount of cement used is 1.2-1.5 times the empty volume in the surface volume of the paraffin-coated microspheres.

8. The application of a sand-control liquid prepared by the preparation method according to any one of claims 1-7, characterized in that, The sand control fluid is injected into the annular space outside the casing of the sand-producing oil layer in the oil well.

9. The application according to claim 8, characterized in that, Specifically, it includes: Pre-fluid is injected to cool the sand-producing oil layer. Xanthan gum or guar gum solution with added paraffin microspheres is injected. Sand-preventing fluid is injected. Displacement fluid is injected after calculation to ensure that all sand-preventing fluid is squeezed into the annular space outside the sand-producing oil layer casing. After 72 hours of curing, the cement plug of the oil layer casing and the casing wall are removed from the sand-preventing fluid. At the initial stage of well opening, water with a temperature higher than the melting point of paraffin is continuously circulated into the casing for 3-5 hours to accelerate the melting and discharge of paraffin in the solidified sand-control fluid in the annular space outside the casing of the sand-producing oil layer. After the paraffin is melted and discharged, normal oil production operations can be carried out.

10. The application according to claim 9, characterized in that, The amount of pre-treatment fluid injected is 3-5 times the surface volume of the sand-producing oil layer; the surface volume of the paraffin-coated microspheres in the xanthan gum or guar gum solution is 0.2-0.25 times the surface volume of the sand-producing layer; the surface volume of the paraffin-coated microspheres in the xanthan gum or guar gum solution plus the surface volume of the paraffin-coated microspheres in the sand-preventing fluid equals the surface volume of the sand-producing layer.

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