Oil and gas well stratum leakage prevention sand washing fluid and preparation method and sand washing method thereof

Abstract

The invention belongs to the technical field of oil and gas field chemistry, and particularly relates to an oil and gas well stratum leakage prevention sand washing fluid and a preparation method and a sand washing method thereof. According to the total volume of the sand washing fluid for preventing oil and gas well stratum leakage, the sand washing fluid for preventing oil and gas well stratum leakage comprises, by mass volume, 0.1%-0.5% of bentonite, 1.5%-5% of a surfactant, 0.7%-2% of xanthan gum, 0.2%-1.2% of a foaming agent, 1.5%-8% of an anti-swelling agent, 0.4%-2% of polyacrylamide and the balance water. A cross-linking agent with a mass volume ratio of 2%-8%; and the balance of clear water. Nitrogen needs to be introduced during sand washing, and the problem that sand washing fails due to the fact that liquid does not return during sand washing of the stratum leakage well is solved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field chemical technology, and specifically relates to a sand flushing fluid for preventing formation loss in oil and gas wells, its preparation method, and sand flushing method. Background Technology

[0002] Currently, during oil and gas well production, due to insufficient reservoir energy, formation void blockage, formation sand production, or other factors, it is necessary to carry out sand flushing, unblocking, and well washing operations. However, due to geological reasons or casing corrosion and misalignment, during sand flushing, unblocking, and well washing operations, there is often a discharge rate at the inlet, but due to formation leakage, circulation cannot be established, and no fluid return is observed in the casing. Especially during sand flushing operations, because sand flushing circulation cannot be established, the formation sand flushed back during the sand flushing operation will generally accumulate at the oil, gas, and water well leakage point, causing downhole accidents where the working tubing gets stuck.

[0003] Current technologies generally employ a process of first controlling the well and plugging the leaking membrane before proceeding with subsequent operations. This results in prolonged construction periods, increased production costs, and reduced economic benefits for oil and gas wells, while also causing formation contamination and impacting gas well production. The common methods for plugging leaking membranes involve two approaches: controlling the leakage pathway and reducing the pressure differential. The technical means involve first plugging the leaking membrane to increase the formation's pressure-bearing capacity, and then increasing the drilling fluid density to stabilize the wellbore and balance formation pressure. While non-target formation leaks can be plugged, plugging the target formation implies reservoir damage.

[0004] A search revealed patent document CN 109722231 A, which discloses a low-pressure lost circulation well sand-flushing foam fluid and its preparation method. The raw materials include a composite foaming agent, polyacrylamide, a stabilizer, a surfactant, and water. The composite foaming agent comprises sodium dodecyl sulfate, triethanolamine, and water. Sodium dodecyl sulfate may hydrolyze or degrade under certain conditions, affecting the stability of its foaming performance. Hydrolysis may cause changes in the concentration of the foaming agent, thus affecting foam generation and stability. Triethanolamine may also be affected by factors such as temperature and pH, undergoing chemical changes that affect its role in the composite foaming agent. Different oil wells have varying geological conditions and fluid characteristics, and this specific composite foaming agent may not be suitable for some wells. For example, in high-salinity oil well environments, sodium dodecyl sulfate may interact with ions in water, reducing the foaming effect. This can easily lead to sand-flushing failure in wells with formation loss, resulting in no fluid return during sand flushing. Summary of the Invention

[0005] The purpose of this invention is to provide a sand flushing fluid for preventing formation loss in oil and gas wells, as well as its preparation method and sand flushing method, which solves the problem of sand flushing failure caused by the failure of the flushing fluid to return after formation loss.

[0006] This invention is achieved through the following technical solution:

[0007] This invention also discloses a sand-flushing fluid for preventing formation loss in oil and gas wells, comprising, based on the total volume of the sand-flushing fluid used to prevent formation loss in oil and gas wells:

[0008] The composition consists of 0.1%–0.5% bentonite by mass and volume, 1.5%–5% surfactant by mass and volume, 0.7%–2% xanthan gum by mass and volume, 0.2%–1.2% foaming agent by mass and volume, 1.5%–8% anti-swelling agent by mass and volume, 0.4%–2% polyacrylamide by mass and volume, and 2%–8% crosslinking agent by mass and volume; the balance is water.

[0009] Furthermore, the foaming agent is a heteropolar molecular surface-active substance composed of polar and nonpolar groups.

[0010] Furthermore, the foaming agent is a carboxylate, sulfonate, sulfate, nitrile salt, or phosphonate.

[0011] Furthermore, the anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride or acrylamide trimethyl monoallyl ammonium chloride.

[0012] Furthermore, the crosslinking agent is dicumyl peroxide, benzoyl peroxide, or di-tert-butyl peroxide.

[0013] Furthermore, the di-tert-butyl peroxide is either potassium di-tert-butyl peroxide or sodium di-tert-butyl peroxide.

[0014] Furthermore, the surfactant is polyoxyethylene dehydrated sorbitan fatty acid ester, sodium lauryl sulfate, or sodium alkylbenzene sulfonate.

[0015] Furthermore, the total volume of the sand-flushing fluid used to prevent formation loss in oil and gas wells includes:

[0016] The composition consists of 0.2%–0.4% bentonite by mass and volume, 1.5%–3% surfactant by mass and volume, 1%–1.5% xanthan gum by mass and volume, 0.5%–1% foaming agent by mass and volume, 1%–3% anti-swelling agent by mass and volume, 0.5%–1% polyacrylamide by mass and volume, and 3%–7% crosslinking agent by mass and volume; the balance is water.

[0017] This invention also discloses a method for preparing a sand-flushing fluid for preventing formation loss in oil and gas wells, comprising the following steps:

[0018] Determine the volume and amount of clean water needed, and add bentonite, surfactant, xanthan gum, anti-swelling agent, polyacrylamide and crosslinking agent to the clean water to prepare the sand flushing solution stock solution; the foaming agent will be added when used on site.

[0019] This invention also discloses a sand flushing method for the sand flushing fluid used to prevent formation loss in oil and gas wells, comprising the following steps:

[0020] Determine the volume and amount of clean water needed, and add bentonite, surfactant, xanthan gum, anti-swelling agent, polyacrylamide and crosslinking agent to the clean water in advance to prepare the sand flushing solution stock solution;

[0021] After mixing the sand flushing fluid concentrate and the foaming agent, the mixture is processed into foam liquid through a foam generator and then injected into the wellbore.

[0022] Upon encountering a sandy surface, nitrogen gas is introduced.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] In oil and gas wells with formation leakage, when using low-damage, solids-free flushing fluid for positive circulation flushing, if the wellhead does not return fluid due to the geological structure of the wellbore, the flushing fluid formula of this invention is used to prepare a foamed flushing fluid. The specific technical solution is to first add 0.1% to 0.5% bentonite, 1.5% to 5% surfactant, 0.7% to 2% xanthan gum, 0.2% to 1.2% foaming agent, 1% to 5% ammonium chloride, 1.5% to 8% anti-swelling agent, 0.4% to 2% polyacrylamide, and 2% to 8% crosslinking agent to a certain amount of clean water.

[0025] The bentonite mentioned above is mainly composed of montmorillonite. Its main function is to increase the viscosity of the flushing fluid, thereby increasing the fluid's ability to carry formation sand. At the same time, it also helps to plug leaks in the formation during the flushing process.

[0026] The main function of surfactants is to reduce the surface tension of sand-washing fluids.

[0027] Alternatively, sodium alkylbenzene sulfonate or alkyl sulfonate can be selected as alternative surfactants in this invention, and are also optional materials in the formulation of this invention.

[0028] The xanthan gum has unique rheological properties, good water solubility, stability to heat and acids and alkalis, and good compatibility with a variety of salts. As a thickener and suspending agent, it improves the stability of the sand flushing fluid in this formula and enhances its sand-carrying capacity, thus ensuring the efficiency of sand flushing.

[0029] The addition of the foaming agent makes the flushing fluid more stable, and with the addition of bentonite and other materials, it improves the sand-carrying capacity and forms a barrier against the lost circulation zone, so as to promote the flushing fluid to reach the wellhead return outlet along the wellbore return channel and ensure the success rate of flushing.

[0030] The anti-swelling agent inhibits the swelling of bentonite in water by reducing the negative charge on the surface of bentonite. Its main function is to reduce the volume of foam flushing liquid and prevent the foam flushing liquid from overflowing and polluting the environment.

[0031] The polyacrylamide aqueous solution has a high viscosity and plays a role in flocculation of the sand flushing fluid in this invention, thereby improving the ability of the sand flushing process to carry over bottom particles.

[0032] In this invention, the crosslinking agent is used to generate chemical bonds between the polymer material and the linear molecules to form a network structure, which ultimately forms a leak-proof bottom layer during the sand flushing process, while also allowing the sand flushing fluid to return upwards.

[0033] In practice, the formula and process of this invention can reduce the density of the sand-washing fluid to 0.59 g / cm³. 3 -0.83g / cm 3 This ensures that the fluid column pressure in the wellbore is less than or equal to the formation pressure, providing technical and process support for sand flushing in lost circulation wells. In oil, gas, and water wells with low formation pressure coefficients and energy absorption phenomena at the bottom of the wellbore, it can improve the performance of the flushing fluid, acting as a suspending, emulsifying, and stabilizing agent, reducing the surface tension of water to form foam. This allows air bubbles in the aerated flotation slurry to adhere to selectively floating sand particles in the wellbore, ultimately accelerating the upward return speed during the flushing process, improving sand carrying capacity, and protecting the formation. The formula of this invention reduces the surface tension of water to form foam, allowing air bubbles in the aerated flotation slurry to adhere to selectively floating sand particles in the wellbore, ultimately accelerating the upward return speed during the flushing process and preventing energy absorption effects caused by reduced formation energy. This creates significant economic and social benefits, especially in oil, gas, and water wells with low bottom pressure coefficients, achieving a total efficiency of 96% and increasing sand carrying capacity by 100%.

[0034] This invention also discloses a sand flushing method that requires the introduction of nitrogen gas on-site. The injection of nitrogen increases the agitation and disturbance of the flushing fluid, enabling it to better carry sand particles. Nitrogen forms microbubbles in the flushing fluid; these bubbles generate buoyancy and agitation as they rise, helping to carry sand particles from the well bottom to the surface. Compared to traditional flushing fluids, the addition of nitrogen improves the fluidity and suspension properties, reducing sand particle settling and accumulation, thereby increasing flushing efficiency. The injection of nitrogen allows the flushing fluid to form a wider flow area at the well bottom, expanding the flushing coverage. The expansion and rise of nitrogen bubbles propel the flushing fluid to diffuse outwards, reaching corners and fractures that are difficult to reach with traditional flushing methods, thus more thoroughly removing sand particles from the well bottom.

[0035] In addition, nitrogen is a low-density gas, and introducing it into the flushing fluid can reduce the overall density of the fluid. A lower-density flushing fluid reduces pressure on the formation and lowers the risk of formation loss. Especially in low-pressure, low-loss formations, using nitrogen-assisted flushing can effectively control the amount of flushing fluid loss and protect the integrity of the formation.

[0036] During sand flushing, nitrogen bubbles can form a temporary sealing layer between the wellbore and the formation. This sealing layer prevents the flushing fluid from further penetrating the formation, reducing leakage. Simultaneously, the sealing layer also supports the formation, preventing formation collapse and fracture propagation. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0038] The detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0040] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0041] This invention discloses a leakage-proof flushing fluid, the main components of which include bentonite, xanthan gum, surfactant, foaming agent, anti-swelling agent, polyacrylamide, crosslinking agent and water.

[0042] Bentonite is a non-metallic mineral with montmorillonite as its main mineral component. It has a 2:1 crystal structure consisting of two silicon-oxygen tetrahedra sandwiching a layer of aluminum-oxygen octahedra. It has good ion exchange properties and can swell into a paste when water is added.

[0043] Xanthan gum is a versatile microbial extracellular polysaccharide produced by *Xanthomonas aurantiacus* using carbohydrates as the main raw material through fermentation engineering. It possesses unique rheological properties, good water solubility, stability to heat and acids / alkalis, and excellent compatibility with various salts. In the formulation of this invention, it acts as a suspending agent, emulsifier, and stabilizer. In the petroleum industry, due to its strong pseudoplasticity, a low-concentration xanthan gum (0.5%) aqueous solution can maintain the viscosity of drilling fluid and control its rheological properties. Therefore, the viscosity is extremely low at high-speed drill bit locations, saving power and enhancing the performance of the formulation of this invention. It also strengthens the sand-carrying capacity of this formulation and reduces the friction between returned material and the wellbore.

[0044] The surfactant is polyoxyethylene dehydrated sorbitan fatty acid ester, which has an amphoteric structure: one end is a hydrophilic group and the other end is a hydrophobic group. The hydrophilic group is often a polar group, such as carboxylic acid, sulfonic acid, sulfuric acid, amino or amine groups and their salts. Hydroxyl groups, amide groups, ether bonds, etc. can also be used as polar hydrophilic groups, while the hydrophobic group is often a nonpolar hydrocarbon chain. In the formulation of this invention, it can reduce the surface tension and interfacial tension between liquid and gas and between liquid and solid.

[0045] Surfactants may also include sodium lauryl sulfate, sodium alkylbenzene sulfonate, or alkyl sulfonates.

[0046] Frothing agents are surfactants that reduce the surface tension of water to form foam, allowing air bubbles in aerated flotation slurry to adhere to selectively floating mineral particles. Frothing agents are typically surface-active substances composed of dissimilar molecules consisting of polar and nonpolar groups. One end of the molecule is a polar group, and the other end is a nonpolar group.

[0047] The polar groups of foaming agents are attracted to solids (minerals), while the non-polar groups are attracted to air. Conversely, the polar groups of foaming agents are attracted to water, while the non-polar groups are attracted to air. They align at the water-air interface, reducing the surface tension of water, thus producing a foaming effect.

[0048] Example 1

[0049] In the specific implementation process, the amount of flushing fluid required for construction is determined according to the construction design requirements, and then the amount of clean water required for flushing is determined according to the mass-volume ratio; in the actual flushing process, a nitrogen generator truck should be equipped to provide the amount of nitrogen used for flushing.

[0050] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.1% bentonite, 1.5% surfactant, 0.7% xanthan gum, 0.2% foaming agent, 1.5% anti-swelling agent, 0.4% polyacrylamide, and 2% crosslinking agent by mass and volume, with the balance being water.

[0051] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium carboxylate, the anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride, and the crosslinking agent is dicumyl peroxide.

[0052] In the application process, 0.1% bentonite is first added to clean water, which expands into a paste. Then, 0.7% xanthan gum is added to act as a suspending, emulsifying, and stabilizing agent, improving the sand-carrying capacity of the flushing fluid and reducing the friction between the returned material and the wellbore. Next, 1.5% polyoxyethylene dehydrated sorbitan fatty acid ester is added, as its hydrophilic groups can reduce the surface tension and interfacial tension between liquid and gas, and between liquid and solid. Then, 0.2% foaming agent, 1.5% anti-swelling agent, 0.4% polyacrylamide, and 2% crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The flushing fluid stock solution is transported to the site by tanker truck. After mixing the flushing fluid stock solution and foaming agent, the flushing fluid is hydraulically stirred using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0053] The sand flushing fluid prepared in this embodiment was applied on-site at #1. The specific construction process was as follows:

[0054] October 21, 2023 - 5:00 PM: Due to significant leakage, perforation will be required later. We contacted the construction company to carry out leak sealing work.

[0055] 2023.10.22 -04:00 Organize the preparation of leak-sealing materials and clean water, using 60.00m³ of clean water. 3 4.25t of powdered plugging and shielding temporary plugging agent (polyacrylamide type HS-1) was prepared and pumped into the oil pipeline at a rate of 60.00m. 3 Pump pressure: 0-1.0MPa, discharge rate: 200-250L / min, but the leak-sealing effect is not ideal;

[0056] October 22, 2023 - 10:00 AM: 40.00 ml of the flushing fluid prepared in this embodiment was prepared. 3 The measured density is 0.83 g / cm³. 3 A density of 0.83 g / cm³ was used. 3 The sand-washing fluid prepared in this embodiment is 30.00m 3 At a well depth of 1078.03m, positive circulation was used to control the well until the inlet and outlet fluid properties were consistent, and fluid returned from the outlet, indicating successful plugging. Circulation was established, and at -14:00, the density of the returned fluid at the circulation outlet was measured to be 0.83 g / cm³. 3 The density did not change after 4 hours of circulation.

[0057] Example 2

[0058] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.2% bentonite, 1.5% xanthan gum, 0.5% foaming agent, 2% ammonium chloride, 8% anti-swelling agent, 0.5% polyacrylamide, and 3% crosslinking agent by mass and volume, with the balance being water.

[0059] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium sulfonate, the anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride, and the crosslinking agent is benzoyl peroxide.

[0060] In the application process, 0.2% bentonite is first added to clean water, which expands into a paste. Then, 1.5% xanthan gum is added to act as a suspending, emulsifying, and stabilizing agent, improving the sand-carrying capacity of the flushing fluid and reducing the friction between the returned material and the wellbore. Next, 2.5% polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups can reduce the surface tension and interfacial tension between liquid and gas, and between liquid and solid. Then, 0.5% foaming agent, 8% anti-swelling agent, 0.5% polyacrylamide, and 3% crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The flushing fluid stock solution is transported to the site by tanker truck. After mixing the flushing fluid stock solution and foaming agent, the flushing fluid is hydraulically stirred using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0061] The flushing fluid prepared in this embodiment was applied on-site at #2. The application process was from October 19, 2023 to October 21, 2023, with a density of 1.00 g / cm³. 3 The low-damage, solids-free well control operation failed due to a hydraulic well that could not return fluid and suffered severe leakage, resulting in well control failure. Positive leakage control materials were prepared and applied three times, using 10.00 tons of powdered plugging and shielding temporary plugging agent (polyacrylamide type HS-1) and 110.00 cubic meters of clean water. 3 The leak could not be successfully plugged, so it was decided to use the sand-flushing fluid prepared in this embodiment.

[0062] October 22, 2023 - 11:00 AM: 40.00 ml of the sand-washing fluid prepared in this embodiment was prepared. 3 The measured density was 0.70 g / cm³. 3 Use a density of 0.70 g / cm³ 3 The sand-washing fluid prepared in this embodiment is 40.00m 3 At a well depth of 1038.75m, positive circulation was used to control the well until the inlet and outlet fluid properties were consistent, and fluid returned from the outlet. Circulation was established, and the leak was successfully plugged. At -15:00, the density of the returned fluid at the circulation outlet was measured to be 0.70 g / cm³. 3 The density did not change after 4 hours of circulation.

[0063] Example 3

[0064] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid, it includes 0.3% bentonite, 1.5% surfactant, 0.6% xanthan gum, 1.2% foaming agent, 2% anti-swelling agent, 1.5% polyacrylamide, and 5% crosslinking agent by mass and volume, with the balance being water.

[0065] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium sulfate, the anti-swelling agent is acrylamide trimethyl monoallyl ammonium chloride, and the crosslinking agent is di-tert-butyl peroxide.

[0066] In the application process, bentonite is first added to clean water, expanding into a paste. Xanthan gum is then added, acting as a suspending, emulsifying, and stabilizing agent to improve the sand-carrying capacity of the flushing fluid and reduce friction between the returned material and the wellbore. Next, polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups reduce surface and interfacial tension between liquid and gas, and between liquid and solid. Then, a foaming agent, anti-swelling agent, polyacrylamide, and crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The stock solution is transported to the site by tanker truck. After mixing the stock solution and foaming agent, the flushing fluid is hydraulically agitated using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0067] The sand flushing fluid prepared in this embodiment was applied on-site at #3. The specific construction process was as follows:

[0068] 2023.10.10 -23:00 Using a density of 1.00 g / cm³ 3 After the low-damage, solids-free well-killing fluid was circulating positively to flush sand at a depth of 1322.50m and then lost power and returned to the well at a depth of 1400.18m, the well was plugged after communication with the construction party and plugging materials were organized.

[0069] 2023.10.11 -01:00 30.00m³ of sealing agent was pumped into the oil pipeline while being prepared. 3 (Contains 3.00t of HS-Ⅰ polyacrylamide), pump pressure: 0-2.00MPa, discharge rate: 350-400L / min, if the plugging fails, use the sand flushing fluid prepared in this example;

[0070] 2023.10.11 -11:00 40.00m of the sand-washing fluid prepared in this embodiment was prepared. 3 Use a density of 0.83 g / cm³. 3 The sand-washing fluid prepared in this embodiment is 40.00m3 At a well depth of 1400.18m, positive circulation was used to control the well until the inlet and outlet fluid properties were consistent, and fluid returned from the outlet, indicating successful plugging. Circulation was established, and at -14:00, the density of the returned fluid at the circulation outlet was measured to be 0.83 g / cm³. 3 The density did not change after 4 hours of circulation.

[0071] Example 4

[0072] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.4% bentonite, 2% surfactant, 2% xanthan gum, 0.5% foaming agent, 3% anti-swelling agent, 2% polyacrylamide, and 8% crosslinking agent by mass and volume, with the balance being water.

[0073] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium phosphonate, the anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride, and the crosslinking agent is di-tert-butyl peroxide.

[0074] In the application process, bentonite is first added to clean water, expanding into a paste. Xanthan gum is then added, acting as a suspending, emulsifying, and stabilizing agent to improve the sand-carrying capacity of the flushing fluid and reduce friction between the returned material and the wellbore. Next, polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups reduce surface and interfacial tension between liquid and gas, and between liquid and solid. Then, a foaming agent, anti-swelling agent, polyacrylamide, and crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The stock solution is transported to the site by tanker truck. After mixing the stock solution and foaming agent, the flushing fluid is hydraulically agitated using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0075] The sand flushing fluid prepared in this embodiment was applied on-site at #4. The specific construction process was as follows:

[0076] Construction process: October 8, 2023 - 17:00, density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 40.00m 3 At a depth of 1245.55m, during positive circulation well control, no fluid returned from the wellhead, making it impossible to establish circulation. We contacted the construction party to use the sand flushing fluid prepared in this embodiment.

[0077] The density measured at 18:00 on October 8, 2023 was 0.8 g / cm³. 3 With a density of 0.80 g / cm³ 3 The sand-washing fluid prepared in this embodiment is 20.00m 3At a well depth of 1245.55m, positive circulation was used to control the well until the inlet and outlet fluid properties were consistent. Pump pressure: 0, discharge rate: 350-400L / min, fluid returned from the outlet, circulation was established, and the next step of operation was continued. At 23:00, the density of the returned fluid at the circulation outlet was measured to be 0.80g / cm³. 3 The density did not change after 5 hours of circulation.

[0078] Example 5

[0079] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.5% bentonite, 3% surfactant, 1% xanthan gum, 1% foaming agent, 5% anti-swelling agent, 1% polyacrylamide, and 7% crosslinking agent by mass and volume, with the balance being water.

[0080] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium phosphonate, the anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride, and the crosslinking agent is dicumyl peroxide.

[0081] In the application process, bentonite is first added to clean water, expanding into a paste. Xanthan gum is then added, acting as a suspending, emulsifying, and stabilizing agent to improve the sand-carrying capacity of the flushing fluid and reduce friction between the returned material and the wellbore. Next, polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups reduce surface and interfacial tension between liquid and gas, and between liquid and solid. Then, a foaming agent, anti-swelling agent, polyacrylamide, and crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The stock solution is transported to the site by tanker truck. After mixing the stock solution and foaming agent, the flushing fluid is hydraulically agitated using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0082] The sand flushing fluid prepared in this embodiment was applied on-site at #5. The specific construction process was as follows:

[0083] Construction process: 2023.09.27 -11:00, using a density of 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 20.00m 3 The positive circulation milling reached a depth of 808.32m, but the wellhead lost its return flow. The construction party was contacted to use the sand flushing fluid prepared in this embodiment.

[0084] 20.09.27 - 13:00 20.00m of plugging agent was pumped into the oil pipeline. 3 The density is 0.83 g / cm³, pumped from the oil pipe. 3 The sand flushing fluid displacement solution prepared in this embodiment is 5.30m. 3The measured density is 0.83 g / cm³. 3 With a density of 0.95 g / cm³ 3 Low-damage, solids-free well-killing fluid 25.00m 3 Positive circulation was used for well control until the inlet and outlet fluid properties were consistent. The system was then allowed to stand and the leakage velocity was measured; the measured leakage velocity was 1.00 m / s². 3 / h, -15:00 measured the return liquid density at the circulation outlet to be 0.83 g / cm³. 3 After 2 hours of circulation, the density did not change, meeting the construction requirements for liquid return at the outlet. Circulation was then established, and the next step of operation continued.

[0085] Example 6

[0086] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.1% bentonite, 1.8% surfactant, 1.2% xanthan gum, 0.3% foaming agent, 2% anti-swelling agent, 1% polyacrylamide, and 2% crosslinking agent by mass and volume, with the balance being water.

[0087] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium nitrile, the anti-swelling agent is acrylamide trimethyl monoallyl ammonium chloride, and the crosslinking agent is di-tert-butyl peroxide.

[0088] In the application process, bentonite is first added to clean water, expanding into a paste. Xanthan gum is then added, acting as a suspending, emulsifying, and stabilizing agent to improve the sand-carrying capacity of the flushing fluid and reduce friction between the returned material and the wellbore. Next, polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups reduce surface and interfacial tension between liquid and gas, and between liquid and solid. Then, a foaming agent, anti-swelling agent, polyacrylamide, and crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The stock solution is transported to the site by tanker truck. After mixing the stock solution and foaming agent, the flushing fluid is hydraulically agitated using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0089] The sand flushing fluid prepared in this embodiment was applied on-site at #6. The specific construction process was as follows:

[0090] Construction process: August 7, 2023, 14:00, using a density of 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 25.00m 3 No fluid returned from the outlet, indicating well leakage. The matter was reported to the construction company, and a hydraulic well with anti-leakage and pressure loss was used.

[0091] 2023.08.07 - 23:00 Density used: 0.83 / cm³3 30m of anti-leakage and pressure loss well fluid 3 At a well depth of 762.21m, the positive circulation well control outlet did not backflow, and the construction party was contacted to organize plugging materials;

[0092] 2023.08.08 -04:00 Used 3.00T of polyacrylamide sealant and 30.00m³ of clean water. 3 33.00m³ of sealant was pumped in. 3 Then continue pumping in 2.50 ml of displacement fluid. 3 Let it stand to seal the leak;

[0093] 2023.08.08 -14:00 Density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 25.00m 3 When the fluid properties of the inlet and outlet are consistent during positive circulation well control, the leakage plugging is successful; however, the leakage prevention well control fluid plugging fails.

[0094] The density was measured at 17:00 on August 13, 2023, and was 0.82 g / cm³. 3 A density of 0.82 g / cm³ is used. 3 The sand-washing fluid prepared in this embodiment is 40.00m 3 The well was circulated until the inlet and outlet fluid properties were consistent, indicating successful plugging. The next step was to proceed. At -21:00, the density of the returned fluid at the circulation outlet was measured to be 0.82 g / cm³. 3 The density did not change after 5 hours of circulation.

[0095] Example 7

[0096] This embodiment discloses a sand flushing fluid for preventing formation loss in oil and gas wells. Based on the total volume of the sand flushing fluid for preventing formation loss in oil and gas wells, it includes 0.1% bentonite, 1.5% surfactant, 1.5% xanthan gum, 0.5% foaming agent, 1.5% anti-swelling agent, 0.8% polyacrylamide, and 2% crosslinking agent by mass and volume, with the balance being water.

[0097] The surfactant used is polyoxyethylene dehydrated sorbitan fatty acid ester, the foaming agent is sodium sulfonate, the anti-swelling agent is acrylamide trimethyl monoallyl ammonium chloride, and the crosslinking agent is dicumyl peroxide.

[0098] In the application process, bentonite is first added to clean water, expanding into a paste. Xanthan gum is then added, acting as a suspending, emulsifying, and stabilizing agent to improve the sand-carrying capacity of the flushing fluid and reduce friction between the returned material and the wellbore. Next, polyoxyethylene sorbitan fatty acid ester is added, as its hydrophilic groups reduce surface and interfacial tension between liquid and gas, and between liquid and solid. Then, a foaming agent, anti-swelling agent, polyacrylamide, and crosslinking agent are added sequentially to prepare the flushing fluid stock solution. The stock solution is transported to the site by tanker truck. After mixing the stock solution and foaming agent, the flushing fluid is hydraulically agitated using a pump truck and foam generator to form the required flushing fluid, which is then injected into the wellbore. Upon encountering sand, nitrogen gas is introduced.

[0099] The sand flushing fluid prepared in this embodiment was applied on-site at #7. The specific construction process was as follows:

[0100] Construction process:

[0101] 2023.08.01-13:00 Density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 40.00m 3 At a depth of 762.59m, the well was controlled with positive circulation, but no return fluid was observed at the outlet. It was determined that the well was severely leaking, and the construction party was notified to carry out leak plugging operations.

[0102] August 1, 2023, 18:00: 3.00T of powdered sealing and shielding temporary plugging agent was used, and 30.00m of plugging agent was pumped into the oil pipeline. 3 Close the well and let it stand still;

[0103] 2023.08.01 - 22:00 Density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 40.00m 3 At a depth of 762.59m, positive circulation was used for well control, but no return fluid was observed at the outlet, indicating that the leak plugging was unsuccessful. The construction company was contacted to replace the leak-proof and pressure-loss-resistant well fluid for plugging.

[0104] 2023.08.02 -0:00 Density used: 0.76 / cm³ 3 30.00m of well fluid for preventing leakage and pressure loss. 3 At a well depth of 762.59m, positive circulation was used for well control, but the casing did not return fluid, and the plugging was unsuccessful. The construction party was contacted to request that the leakage prevention and pressure loss well fluid be used to plug the leak. If the plugging is unsuccessful, the plugging agent should be used to plug the leak.

[0105] 2023.08.02 -15:00 Density 0.70 / cm³ 3 40m of anti-leakage and pressure loss well fluid 3 At a well depth of 762.59m, positive circulation was used for well control and leak plugging. No fluid returned to the casing, and the plugging was unsuccessful. Plugging materials were then prepared.

[0106] 2023.08.02 - 20:00 1.00T of powdered sealing and shielding temporary plugging agent was used, and 10.00m of plugging agent was pumped into the oil pipeline while being prepared. 3 Close the well and let it stand still;

[0107] 2023.08.03 - 15:00 4.00T of powdered sealing and shielding temporary plugging agent was used, and 40.00m of plugging agent was pumped into the oil pipeline while being prepared. 3 Close the well and let it stand still;

[0108] 2023.08.03 - 18:00 Density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 40.00m 3 At a depth of 762.59m, positive circulation was used for well control, but no fluid returned to the outlet, indicating that the plugging was unsuccessful.

[0109] 2023.08.04 -00:00 Use 4.00T of powdered sealing and shielding temporary plugging agent, and simultaneously pump 40.00m of plugging agent into the oil pipeline. 3 Close the well and let it stand still;

[0110] 2023.08.04 -03:00 Density 1.00 g / cm³ 3 Low-damage, solids-free well-killing fluid 40.00m 3 At a well depth of 762.59m, positive circulation was used to control the leak until the inlet and outlet fluid properties were consistent, resulting in successful plugging. However, the attempt to plug the leak using anti-loss-of-transmission well fluid failed midway. A total of 1.00 g / cm³ density well fluid was used in this plugging operation. 3 Low-damage, solids-free well-killing fluid 160.00m 3 12.00T of powdered sealing and temporary plugging agent with a density of 0.76 g / cm³ was used for leak sealing. 3 30.00m of well fluid for preventing leakage and pressure loss. 3 The formation is severely depleted, making plugging the leak extremely difficult.

[0111] The density was measured at 06:00 on August 4, 2023, and was 0.60 g / cm³. 3 With a density of 0.60 g / cm³ 3 The sand-flushing fluid used in this embodiment for reverse pressure well control has a pump pressure of 1.00 MPa, a flow rate of 300-400 L / min, and a pump injection volume of 10.00 m³ of kill fluid. 3 Leak sealing successful. Proceed to the next step. At 10:00, the density of the returned liquid at the circulation outlet was measured to be 0.60 g / cm³. 3 The density did not change after 4 hours of circulation.

[0112] In practice, the formula and process of this invention can reduce the density of the sand-washing fluid to 0.59 g / cm³. 3 ~0.83g / cm 3This ensures that the fluid column pressure in the wellbore is less than or equal to the formation pressure, providing technical and process support for sand flushing in lost circulation wells. When the formation pressure coefficient of oil, gas and water wells is low and energy absorption occurs at the bottom of the wellbore, it can improve the performance of the sand flushing fluid, playing a role in suspending, emulsifying and stabilizing the sand flushing fluid and its liquid properties, reducing the surface tension of water to form foam, so that the air bubbles in the aerated flotation slurry can adhere to the selectively floating sand particles in the wellbore, ultimately accelerating the upward return speed during the sand flushing process, improving the sand carrying capacity, and protecting the formation.

[0113] The formulation of this invention reduces the surface tension of water to form foam, allowing air bubbles in the aerated flotation slurry to adhere to selectively floating wellbore sand particles. This ultimately accelerates the upward flow during the sand flushing process and prevents the energy absorption effect caused by the reduction of formation energy in the wellbore. This results in significant economic and social benefits, particularly in oil, gas, and water wells with low bottom pressure coefficients, achieving an overall efficiency of 96% and increasing sand carrying capacity by 100%.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A sand-flushing fluid for preventing formation loss in oil and gas wells, characterized in that, The total volume of the sand-flushing fluid used to prevent formation loss in oil and gas wells includes: The composition consists of 0.1%–0.5% bentonite by mass and volume, 1.5%–5% surfactant by mass and volume, 0.7%–2% xanthan gum by mass and volume, 0.2%–1.2% foaming agent by mass and volume, 1.5%–8% anti-swelling agent by mass and volume, 0.4%–2% polyacrylamide by mass and volume, and 2%–8% crosslinking agent by mass and volume; the balance is water.

2. The anti-formation loss flushing fluid for oil and gas wells according to claim 1, characterized in that, Foaming agents are heteropolar molecular surface-active substances composed of polar and nonpolar groups.

3. A sand-flushing fluid for preventing formation loss in oil and gas wells according to claim 2, characterized in that, The foaming agent is a carboxylate, sulfonate, sulfate, nitrile salt or phosphonate.

4. The anti-formation loss flushing fluid for oil and gas wells according to claim 1, characterized in that, The anti-swelling agent is acrylamide dimethyl diallyl ammonium chloride or acrylamide trimethyl monoallyl ammonium chloride.

5. A sand-flushing fluid for preventing formation loss in oil and gas wells according to claim 1, characterized in that, The crosslinking agent is dicumyl peroxide, benzoyl peroxide, or di-tert-butyl peroxide.

6. A sand-flushing fluid for preventing formation loss in oil and gas wells according to claim 5, characterized in that, Di-tert-butyl peroxide is made from potassium di-tert-butyl peroxide or sodium di-tert-butyl peroxide.

7. A sand-flushing fluid for preventing formation loss in oil and gas wells according to claim 1, characterized in that, The surfactant is polyoxyethylene dehydrated sorbitan fatty acid ester, sodium lauryl sulfate, or sodium alkylbenzene sulfonate.

8. A sand-flushing fluid for preventing formation loss in oil and gas wells according to claim 1, characterized in that, The total volume of the sand-flushing fluid used to prevent formation loss in oil and gas wells includes: The composition consists of 0.2%–0.4% bentonite by mass and volume, 1.5%–3% surfactant by mass and volume, 1%–1.5% xanthan gum by mass and volume, 0.5%–1% foaming agent by mass and volume, 1%–3% anti-swelling agent by mass and volume, 0.5%–1% polyacrylamide by mass and volume, and 3%–7% crosslinking agent by mass and volume; the balance is water.

9. A method for preparing a sand-flushing fluid for preventing formation loss in oil and gas wells as described in any one of claims 1-8, characterized in that, Includes the following processes: Determine the volume and amount of clean water needed, and add bentonite, surfactant, xanthan gum, anti-swelling agent, polyacrylamide and crosslinking agent to the clean water to prepare the sand flushing solution stock solution; The foaming agent should be added when the product is used on-site.

10. The sand flushing method for the sand flushing fluid used to prevent formation loss in oil and gas wells according to any one of claims 1-8, characterized in that, Includes the following processes: Determine the volume and amount of clean water needed, and add bentonite, surfactant, xanthan gum, anti-swelling agent, polyacrylamide and crosslinking agent to the clean water in advance to prepare the sand flushing solution stock solution; After mixing the sand flushing fluid concentrate and the foaming agent, the mixture is processed into foam liquid through a foam generator and then injected into the wellbore. Upon encountering a sandy surface, nitrogen gas is introduced.