Vegetable high-strength self-degradation isolation temporary plugging agent as well as preparation and use methods thereof

Abstract

The invention relates to a botanical high-strength self-degradation isolation temporary plugging agent as well as a preparation method and a use method thereof. The preparation method comprises the following steps: S1, steaming and pulping fresh sweet potatoes, adding kelp powder while pulping, adding sulfamic acid for acidolysis, and screening to prepare sweet potato and kelp pulp; s2, preparing a sodium acrylate liquid; s3, adding a sodium acrylate solution into the sweet potato and kelp pulp, stirring and mixing, and adding N, N-methylene bisacrylamide and ammonium persulfate to prepare acrylic jelly; s4, slicing, drying, crushing and sieving the jelly to obtain water-swelling particles; s5, dissolving polylactic acid in light oil to prepare coating slurry, and coating the water-swellable particles to obtain coated water-swellable particles; and S6, mixing the xanthan gum powder with the coated temporary plugging agent particles according to the ratio of 1: (50-60) to obtain the botanical high-strength self-degradable isolation temporary plugging agent finished product. The drilling fluid is used for well washing, sand washing or well killing and the like of leakage oil and gas wells, and has the advantages of low cost, simplicity in synthesis, small pollution, convenience in construction, good effect and the like.

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] In order to wash the well, flush the sand or kill the well during oil and gas field exploitation, it is necessary to add a certain amount of well fluid into the oil and gas well and establish circulation. Sometimes, due to the low formation pressure, the well fluid cannot be returned to the wellbore to establish circulation and directly enters the lower layer, failing to achieve the construction goal.

[0003] In the existing technology, in order to prevent the intrusion of well fluid into the low-pressure formation, the first method is to inject a certain amount of acid-soluble or oil-soluble temporary plugging agent into the well in advance to temporarily seal the low-pressure formation and isolate the formation from the oil well system. Since the existing temporary plugging agent cannot be degraded and become ineffective by itself, a specific medium such as acid or oil is required for unblocking. This not only has complicated procedures but also has high construction costs. Another method is to inject a cross-linking agent into the formation for plugging, and then inject a degelling agent for unblocking after the construction is completed. This is not only costly and causes serious formation pollution, but also has complex processes. Summary of the invention

[0004] In order to solve the problems that the temporary plugging agent in the prior art needs to be unblocked, has a complex process, high cost, and serious pollution, the present invention provides a plant-based high-strength self-degradable isolation temporary plugging agent and a preparation and use method thereof.

[0005] The technical solution of the present invention is as follows:

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

[0007] S1: steam fresh sweet potatoes, add water, beat the cooked sweet potatoes with a beater, cut the fibers in the sweet potatoes, add kelp powder while beating, then add aminosulfonic acid for acid hydrolysis, continue beating for 120 to 180 minutes, and sieve to make sweet potato and kelp paste, wherein the mass ratio of fresh sweet potatoes, kelp powder and aminosulfonic acid is 98-102:4-6:1;

[0008] S2: Take acrylic acid, wherein 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 kelp paste, stirring and mixing, and heating to 50-75° C., adding 0.1-0.15% of N,N-methylenebisacrylamide by weight of acrylic acid and 0.3-0.4% of 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 gel;

[0010] S4: Slice, dry and crush the gel, and sieve out particles with a mesh size of 5 to 20, which are 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 particles. The water-expanded 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 particles, i.e., coated water-expanded 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 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 through a 20-mesh sieve.

[0014] Preferably, 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, 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 amount of the plant-based high-strength self-degradable temporary plugging agent used per 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 then driven 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 potatoes, 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 rate is fast, and no secondary pollution to the oil layer is caused.

[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 of them is higher than that made of 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 leaks into 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 achieves the isolation of the water-expanded particles from external pollutants, but also improves the stability and storage resistance of the product; and the colloid formed by the xanthan gum and water can better suspend the coated water-expanded particles, and the on-site construction liquid preparation is very convenient, and no specific medium such as acid or oil is required to remove 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 for plugging, with small dosage, low cost and good effect. DETAILED DESCRIPTION

[0025] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out 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%; the particle size of the kelp powder used is 100-150 meshes.

[0027] Example 1

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

[0029] (1) 100 kg of fresh sweet potatoes were steamed in a steamer, cooled and added to a pulping machine, and 500 kg of tap water was added at the same time. The pulping machine was started for pulping, and 5 kg of kelp powder and 1 kg of aminosulfonic acid were added while pulping. After the kelp powder and aminosulfonic acid were added, the pulping machine was continued for 120 min, and the mixture was passed through a 20-mesh sieve to obtain a sweet potato and kelp slurry.

[0030] (2) 100 kg of acrylic acid was dissolved in tap water to obtain a 25% 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.

[0031] (3) Add the sweet potato and kelp paste into a stirred polymerization kettle and heat it to 50±5°C. Add the sodium acrylate solution into 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 into 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, and crush it, and sieve out particles of 5 to 20 mesh to prepare 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 that accounts for 30% of the weight of the water-expanded particles to coat the water-expanded particles 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.

[0034] (6) 1 kg of xanthan gum powder was mixed with 50 kg of coated temporary plugging agent particles 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) 100 kg of fresh sweet potatoes were steamed in a steamer, cooled and added to a pulping machine, and 500 kg of tap water was added at the same time. The pulping machine was started for pulping, and 5 kg of kelp powder and 1 kg of aminosulfonic acid were added while pulping. After the kelp powder and aminosulfonic acid were added, the pulping machine was continued for 180 min, and the mixture was passed 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 into a stirred polymerization kettle and heating it to 70±5° C., adding the sodium acrylate solution into 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 into the polymerization kettle in sequence, reacting for 4 hours after the addition is completed to form a gel;

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

[0041] (5) 20 kg of polylactic acid is dissolved in 40 kg of light oil to prepare a coating slurry, and the coating slurry is 30% of the weight of the water-expanded particles. The water-expanded particles are 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 sand flushing in oil wells: KSxx-4 well, well depth 5200m, oil layer production section thickness 27.5m, oil well static pressure 49MPa, original daily liquid production 12.5 tons, daily oil production 7.2 tons, the production is low and it is judged as sand plugging. According to the conventional sand flushing operation requirements, there is no return of liquid after sand flushing, the oil layer is seriously leaking, 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 with a conventional sand flushing process, and the cycle is normal. 2.7 cubic meters of formation sand are flushed out. After resuming production, the well produces 37 tons of liquid per day 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. 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, there was no return of the well washing liquid, and the oil layer was seriously leaked, so it was impossible to perform normal hot washing. The plant-based high-strength self-degradable temporary plugging agent prepared in Example 2 was used to plug the formation. 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 could be established to complete the normal hot washing operation. After hot washing, it recovered 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 implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined in the claims.

Claims

1. A method for preparing a plant-based high-strength self-degradable isolation 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 aminosulfonic acid for acid hydrolysis, continue beating for 120-180 minutes, and sieve to make sweet potato and kelp paste, wherein the mass ratio of fresh sweet potatoes, kelp powder and aminosulfonic acid is 98-102:4-6:1; S2: Take acrylic acid, wherein 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 kelp paste, stirring and mixing, and heating to 50-75° C., adding 0.1-0.15% of N,N-methylenebisacrylamide by weight of acrylic acid and 0.3-0.4% of 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 gel; S4: Slice, dry and crush the gel, and sieve out particles with a mesh size of 5 to 20, which are 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 particles. The water-expanded 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 particles, i.e., coated water-expanded 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 of 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 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, and the end point pH is 7.

5.

4. The method according to claim 1, characterized in that In step S5, polylactic acid and light oil in a mass ratio of 1:2 are prepared into 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 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 10-15kg, which is mixed with water in a ratio of 1:50-100 to form a mixed liquid, which is then driven into the wellbore by a cement truck or circulated to achieve plugging of the low-pressure oil layer.