A plant-based high-strength self-degradable isolation temporary plugging agent and its preparation and use method

Abstract

The present invention relates to a plant-based high-strength self-degradable isolation temporary plugging agent and its preparation and use method, the preparation method comprising the following steps: S1: fresh sweet potatoes are steamed and beaten, kelp powder is added while beating, aminosulfonic acid is added for acidolysis, and a sweet potato and kelp paste is made through a sieve; S2: sodium acrylate liquid is prepared; S3: sodium acrylate solution is added to the sweet potato and kelp paste and stirred to mix, N, N-methylenebisacrylamide and ammonium persulfate are added to make acrylic jelly; S4: the jelly is sliced, dried, crushed, and sieved to obtain water-expanded particles; S5: polylactic acid is dissolved in light oil, configured to form a coating slurry, and the water-expanded particles are coated to obtain coated water-expanded particles; S6: xanthan gum powder is mixed with coated temporary plugging agent particles at a ratio of 1:50 to 60 to obtain a plant-based high-strength self-degradable isolation temporary plugging agent finished product. The present invention is used for well washing, sand flushing or well killing of lost oil and gas wells, and has the advantages of low cost, simple synthesis, low pollution, convenient construction, and good effect.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploitation, in particular to a plant-based high-strength self-degradable isolation temporary plugging agent for preventing well fluid from invading low-pressure formations in oil (gas) wells and a preparation method thereof. Background Art

[0002] During oil and gas field exploitation, a certain amount of wellbore fluid needs to be added to the well and circulated in order to wash the well, flush sand, or kill the well. However, due to the low formation pressure, the wellbore fluid cannot be returned to the wellbore to circulate and directly enters the lower layer, thus failing to achieve the construction goal.

[0003] In existing technologies, to prevent wellbore fluid from invading low-pressure formations, one approach is to pre-inject a certain amount of acid-soluble or oil-soluble temporary plugging agent into the well to temporarily seal the low-pressure formation and isolate it from the oil well system. However, as existing temporary plugging agents cannot self-degrade and become ineffective, they require specific media such as acid or oil for unblocking. This process is not only complex but also expensive. Another approach is to inject a cross-linking agent into the formation for plugging, and then inject a gel breaker for unblocking after the construction is completed. This method is not only costly and causes serious formation contamination, but also involves a complex process. Summary of the Invention

[0004] In order to solve the problems of the prior art temporary plugging agents requiring unblocking, complex process, high cost, serious pollution, etc., the present invention provides a plant-based high-strength self-degradable isolation temporary plugging agent and its preparation and use methods.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing a plant-based high-strength self-degradable isolation and temporary plugging agent, characterized by comprising the following steps:

[0007] S1: steaming fresh sweet potatoes, adding water, beating the cooked sweet potatoes with a beater, shortening the fibers in the sweet potatoes, adding kelp powder while beating, then adding sulfamic acid for acid hydrolysis, continuing beating for 120-180 minutes, and sieving to prepare a sweet potato and kelp paste, wherein the mass ratio of the fresh sweet potatoes, kelp powder, and sulfamic acid is 98-102:4-6:1;

[0008] S2: Take acrylic acid, the mass ratio of fresh sweet potato to acrylic acid is 1:0.8-1.2, dissolve it in water to form a 25-40% solution, stir it to form an acrylic acid solution, and neutralize the acrylic acid in the acrylic acid solution with sodium hydroxide to form a sodium acrylate liquid;

[0009] S3: adding the sodium acrylate solution to the sweet potato and kelp paste, stirring and mixing, and heating to 50-75° C., adding 0.1-0.15% N,N-methylenebisacrylamide by weight of acrylic acid and 0.3-0.4% ammonium persulfate by weight of acrylic acid to the mixture while stirring, and reacting for 3-4 hours after the addition is completed to prepare acrylic jelly;

[0010] S4: Slice the gel, dry it, crush it, and sieve out 5-20 mesh particles, which are the water-swollen particles;

[0011] S5: dissolving polylactic acid in light oil to prepare a coating slurry, wherein the mass ratio of polylactic acid to light oil is 0.8-1.2:2, and the amount of the coating slurry is 25-35% of the mass of the water-expanded polytetrafluoroethylene particles. The water-expanded polytetrafluoroethylene particles are coated in a coating machine, and the coating slurry is sprayed while rotating to gradually form a layer of polylactic acid coating on the surface of the water-expanded polytetrafluoroethylene, namely the coated water-expanded polytetrafluoroethylene particles;

[0012] S6: Mix the xanthan gum powder and the coated temporary plugging agent particles at a ratio of 1:50 to 60 to obtain a finished product of a plant-based high-strength self-degradable isolation temporary plugging agent.

[0013] Preferably, in step S1, tap water 5 times the mass of fresh sweet potatoes is added; the mass of kelp powder is 5% of the mass of fresh sweet potatoes; the mass of aminosulfonic acid is 1% of the mass of fresh sweet potatoes; and the sweet potato and kelp slurry is made by passing through a 20-mesh sieve.

[0014] Preferably, in step S2, acrylic acid of the same mass as the mass of fresh sweet potato is taken; the acrylic acid is neutralized with 30% sodium hydroxide solution, and the end point pH is 7.5.

[0015] Preferably, in step S5, polylactic acid and light oil are prepared in a mass ratio of 1:2 to form a coating slurry; and the water-expanded particles are coated in a coating machine with the coating slurry accounting for 30% of the mass of the water-expanded particles.

[0016] A plant-based high-strength self-degradable isolation and temporary plugging agent prepared by the above method.

[0017] The method for using the aforementioned plant-based high-strength self-degradable isolation temporary plugging agent is characterized in that the plant-based high-strength self-degradable temporary plugging agent is used in an amount of 10 to 15 kg per meter of oil layer in the oil well, mixed with water in a ratio of 1:50 to 100 to form a mixed liquid, which is then injected into the wellbore by a cement truck or circulated to achieve plugging of the low-pressure oil layer.

[0018] The plant-based high-strength self-degradable temporary plugging agent of the present invention is used for well washing, sand flushing or well killing of lost oil and gas wells, and its beneficial technical effects are as follows:

[0019] 1. The preparation process of the plant-based high-strength self-degradable temporary plugging agent of the present invention does not require the conditions of starch and nitrogen deoxidation and low temperature control, the synthesis process is simple, and the cost of raw materials is greatly reduced.

[0020] 2. The fresh sweet potato, kelp powder, polylactic acid and xanthan gum powder used in the preparation of the present invention are all plant or biological preparations. The raw materials are easy to obtain, the dosage is small, the cost is low, the degradation speed is fast, and no secondary pollution is caused to the oil layer.

[0021] 3. The fresh sweet potatoes and kelp used in the preparation of the present invention contain starch, alginate, protein, cellulose, etc., and the strength of the water-expanded body made from them is higher than that made with starch.

[0022] 4. After the temporary plugging agent of the present invention is coated with polylactic acid, it will not absorb water during the construction process, the liquid concentration is higher, and less sewage is lost to the formation, which is not only more convenient for construction, but also more conducive to the protection of the oil layer.

[0023] 5. After the temporary plugging agent of the present invention is coated with polylactic acid, it not only isolates the water-expanded particles from external pollutants and improves the stability and storage resistance of the product; but also the colloid formed by the xanthan gum and water can better suspend the coated water-expanded particles. The on-site construction liquid preparation is very convenient, and no specific medium such as acid or oil is required to deblock the temporary plugging agent, and the construction is simple.

[0024] 6. Plant-based high-strength self-degradable temporary plugging agent, only 10 to 15 kg of temporary plugging agent is needed for each meter of oil layer to be plugged, with small dosage, low cost and good effect. DETAILED DESCRIPTION

[0025] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0026] In the following embodiments, the dry matter content and starch content of the fresh sweet potatoes used are not less than 36% and 23% respectively; the particle size of the kelp powder used is 100-150 mesh.

[0027] Example 1

[0028] A plant-based high-strength self-degradable temporary plugging agent is prepared by the following method:

[0029] (1) Take 100 kg of fresh sweet potatoes, steam them in a steamer, let them cool, and add them into a pulper. At the same time, add 500 kg of tap water, start the pulper to pulp, and add 5 kg of kelp powder and 1 kg of aminosulfonic acid while pulping. After adding the kelp powder and aminosulfonic acid, continue to use the pulper to pulp for 120 minutes, and pass through a 20-mesh sieve to obtain sweet potato and kelp slurry.

[0030] (2) 100 kg of acrylic acid was dissolved in tap water to obtain a 25% acrylic acid solution, which was then neutralized with a 30% aqueous sodium hydroxide solution to an end point pH of 7.5 to prepare a sodium acrylate liquid.

[0031] (3) Add the sweet potato and kelp paste to a stirred polymerization kettle and heat it to 50±5°C. Add the sodium acrylate solution to the polymerization kettle while stirring. After the sodium acrylate solution is added, stir for 30 minutes. Then, add 0.1 kg of N,N-methylenebisacrylamide and 0.3 kg of ammonium persulfate to the polymerization kettle in sequence. After the addition is completed, react for 3 hours to form a gel.

[0032] (4) Slice the gel, dry it, crush it, and sieve out 5-20 mesh particles to make water-expanded particles.

[0033] (5) Take 20 kg of polylactic acid, dissolve it in 40 kg of light oil, and prepare a coating slurry. Use the coating slurry, which is 30% of the mass of the water-expanded polytetrafluoroethylene particles, to coat the water-expanded polytetrafluoroethylene particles in a coating machine, forming a layer of polylactic acid coating on the surface of the water-expanded polytetrafluoroethylene, namely the coated water-expanded polytetrafluoroethylene particles.

[0034] (6) 1 kg of xanthan gum powder was mixed with 50 kg of coated temporary plugging agent granules to obtain a finished product of a plant-based high-strength self-degradable temporary plugging agent.

[0035] Example 2

[0036] A plant-based high-strength self-degradable temporary plugging agent is prepared by the following method:

[0037] (1) Take 100 kg of fresh sweet potatoes, steam them in a steamer, let them cool, and add them into a pulper. At the same time, add 500 kg of tap water, start the pulper to pulp, and add 5 kg of kelp powder and 1 kg of aminosulfonic acid while pulping. After adding the kelp powder and aminosulfonic acid, continue to use the pulper to pulp for 180 minutes, and pass through a 20-mesh sieve to obtain sweet potato and kelp slurry.

[0038] (2) 100 kg of acrylic acid was dissolved in tap water to prepare a 40% acrylic acid solution, and the acrylic acid solution was neutralized with a 30% sodium hydroxide aqueous solution to an end point pH of 7.5 to prepare a sodium acrylate liquid.

[0039] (3) adding the sweet potato and kelp paste to a stirred polymerization kettle and heating it to 70±5° C., adding the sodium acrylate solution to the polymerization kettle while stirring, stirring for 30 minutes after the sodium acrylate solution is added, and then adding 0.15 kg of N,N-methylenebisacrylamide and 0.4 kg of ammonium persulfate to the polymerization kettle in sequence, and reacting for 4 hours after the addition is completed to form a gel;

[0040] (4) Slice the gel, dry it, crush it, and sieve out 5-20 mesh particles to make water-expanded particles.

[0041] (5) 20 kg of polylactic acid was dissolved in 40 kg of light oil to prepare a coating slurry. The coating slurry was 30% of the mass of the water-expanded particles, and the water-expanded particles were coated in a coating machine to form a layer of polylactic acid coating on the surface of the water-expanded particles, namely the coated water-expanded particles;

[0042] (6) Add 1 kg of xanthan gum powder to 40 kg of coated water-expanded particles, continue stirring in a coating machine, and mix evenly to obtain a finished product of a plant-based high-strength self-degradable temporary plugging agent.

[0043] Example 3

[0044] Used for oil well sand flushing: KSxx-4 well, well depth 5200m, oil layer production well section thickness 27.5m, oil well static pressure 49MPa, original daily liquid production 12.5 tons, daily oil production 7.2 tons, production is low and it is judged as sand plugging. According to the conventional sand flushing operation requirements, there is no liquid return phenomenon after the sand flushing liquid, the oil layer is seriously leaked, and the conventional sand flushing operation cannot be completed. Take 300kg of the plant-based high-strength self-degradable temporary plugging agent prepared in Example 1, add it to a 20-cubic-meter mixing tank to make a mixed liquid, and after it is driven into the oil well by a cement truck, a sand flushing cycle can be established. The sand is flushed using the conventional sand flushing process, and the cycle is normal. 2.7 cubic meters of formation sand are flushed out. After production is resumed, the well produces 37 tons of liquid and 28 tons of oil per day.

[0045] Example 4

[0046] Used for hot washing of oil wells: TKSxx well is a pumping well with a well depth of 3600m and a production well section thickness of 45.6m. The original daily liquid production was 7.8 tons and the daily oil production was 3.5 tons, which was more than 30% lower than the normal production output. It was judged that the oil well was seriously blocked by wax. Conventional hot water was used to wash the well and remove the wax. Due to the low pressure of the oil well, the well washing fluid had no return liquid phenomenon, the oil layer was seriously lost, and normal hot washing was impossible. The plant-based high-strength self-degradable temporary plugging agent prepared in Example 2 was used to plug the stratum. 650kg was taken and added to a 50-square-meter mixing tank to make a mixed liquid. After being driven into the oil well by a cement truck, a sand flushing cycle was established, and normal hot washing operation was completed. After hot washing, it returned to a higher production capacity 2 days later, with a daily liquid production of 65 tons and a daily oil production of 48 tons. It was judged that the plant-based high-strength self-degradable temporary plugging agent of the present invention also had the function of water blocking.

[0047] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined in the claims.

Claims

1. A method for preparing a plant-based high-strength self-degradable isolation and temporary plugging agent, characterized in that The following steps are involved: S1: steam fresh sweet potatoes, add water, beat the cooked sweet potatoes with a beater, add kelp powder while beating, then add sulfamic acid for acid hydrolysis, continue beating for 120-180 minutes, and sieve to prepare sweet potato and kelp paste, wherein the mass ratio of fresh sweet potatoes, kelp powder, and sulfamic acid is 98-102:4-6:1; S2: Take acrylic acid, the mass ratio of fresh sweet potato to acrylic acid is 1:0.8-1.2, dissolve it in water to form a 25-40% solution, stir it to form an acrylic acid solution, and neutralize the acrylic acid in the acrylic acid solution with sodium hydroxide to form a sodium acrylate liquid; S3: adding the sodium acrylate solution to the sweet potato and kelp paste, stirring and mixing, and heating to 50-75° C., adding 0.1-0.15% N,N-methylenebisacrylamide by weight of acrylic acid and 0.3-0.4% ammonium persulfate by weight of acrylic acid to the mixture while stirring, and reacting for 3-4 hours after the addition is completed to prepare acrylic jelly; S4: Slice the gel, dry it, crush it, and sieve out 5-20 mesh particles, which are the water-swollen particles; S5: dissolving polylactic acid in light oil to prepare a coating slurry, wherein the mass ratio of polylactic acid to light oil is 0.8-1.2:2, and the amount of the coating slurry is 25-35% of the mass of the water-expanded polytetrafluoroethylene particles. The water-expanded polytetrafluoroethylene particles are coated in a coating machine, and the coating slurry is sprayed while rotating to gradually form a layer of polylactic acid coating on the surface of the water-expanded polytetrafluoroethylene, namely the coated water-expanded polytetrafluoroethylene particles; S6: Mix the xanthan gum powder and the coated temporary plugging agent particles at a ratio of 1:50 to 60 to obtain a finished product of a plant-based high-strength self-degradable isolation temporary plugging agent.

2. The method according to claim 1, characterized in that In step S1, tap water 5 times the mass of fresh sweet potatoes is added; the mass of kelp powder is 5% of the mass of fresh sweet potatoes; the mass of aminosulfonic acid is 1% of the mass of fresh sweet potatoes; and the sweet potato and kelp paste is prepared by passing through a 20-mesh sieve.

3. The method according to claim 1, characterized in that In step S2, acrylic acid having the same mass as that of fresh sweet potato is taken; the acrylic acid is neutralized with 30% sodium hydroxide solution to an end point pH of 7.

5.

4. The method according to claim 1, characterized in that In step S5, polylactic acid and light oil are prepared in a mass ratio of 1:2 to form a coating slurry.

5. The method according to claim 1, characterized in that In step S5, the water-expanded particles are coated in a coating machine with a coating slurry that is 30% by weight of the water-expanded particles.

6. A plant-based high-strength self-degradable isolation and temporary plugging agent prepared by the method according to any one of claims 1 to 5.

7. The method for using the plant-based high-strength self-degradable isolation and temporary plugging agent according to claim 6, characterized in that The dosage of the plant-based high-strength self-degradable temporary plugging agent for each meter of oil layer in the oil well is 10-15 kg, which is mixed with water in a ratio of 1:50-100 to form a mixed liquid, which is injected into the wellbore by a cement truck or circulated to achieve the plugging of the low-pressure oil layer.