Preparation method of self-degradable plugging agent and reservoir protection drilling fluid

Abstract

The application relates to a preparation method of a self-degradation plugging agent and a reservoir protection drilling fluid, and belongs to the technical field of oil and natural gas exploitation. The preparation method of the self-degradation plugging agent comprises the following steps: reacting 16.5-31.3 parts of polyethylene glycol, 50-68 parts of a lactide monomer and 7.5-20.7 parts of a carbonate under the condition of 0.056-0.084 parts of a catalyst; and the temperature of the reaction is 135-150 DEG C. The self-degradation plugging agent prepared by the application can realize dense plugging in the drilling process, reduce the invasion risk of drilling fluid liquid phase and solid phase particles, and play a reservoir protection role. Moreover, the self-degradation plugging agent can automatically undergo physical and chemical degradation under the formation temperature, is an intelligent material capable of being completely automatically degraded, ensures that the filter cake is automatically removed efficiently, realizes extremely low damage to an oil and gas reservoir, maximally restores the permeability of the oil and gas reservoir, and significantly improves the reservoir protection effect.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a self-degradation plugging agent and a reservoir protection drilling fluid, and belongs to the technical field of oil and gas exploitation. BACKGROUND

[0002] In recent years, in order to ensure the safety of domestic oil and gas supply and the contradiction between supply and demand, the exploration and development of oil and gas resources in China are continuously developing towards complex, low-permeability, fractured and unconventional oil and gas reservoirs, and higher requirements are put forward for efficient, rapid and economic exploitation of oil and gas. Strengthening the protection of oil and gas reservoirs and reducing the damage to oil and gas reservoirs are key means to ensure efficient exploitation of oil and gas resources.

[0003] Drilling is the first step to open the oil and gas reservoir, and therefore how to effectively prevent or reduce the damage to the reservoir during the oil and gas drilling process so as to improve the oil and gas exploitation efficiency of a single well is a key technology to realize efficient development of oil and gas. In the process of drilling, the oil and gas reservoir is first contacted with the drilling fluid after being opened, and different types and sizes of solid particles in the drilling fluid can easily invade the natural pores near the well wall to cause pollution and damage to the oil and gas reservoir. The existing plugging removal technology is relatively complex and has limited effect, is easy to form new chemical and mechanical plugging, reduces the permeability of the formation, causes secondary pollution of the reservoir, and is difficult to contact the solid plugging particles in the deep part of the reservoir pore to completely remove the plugging and seriously reduce the permeability of the oil and gas reservoir, thereby reducing the production of the oil and gas well and increasing the oil and gas production cost. How to minimize the invasion of solid particles in the drilling fluid and efficiently remove the invaded solid particles is a key to the protection of the oil and gas reservoir.

[0004] In recent years, domestic and foreign scholars have developed many different reservoir protection methods and plugging removal technologies, mainly by scientifically and reasonably selecting the pre-screening temporary plugging and post-acidizing plugging removal, biological enzyme plugging removal technology and the like according to different plugging and reservoir conditions, so as to reduce the damage degree of the oil and gas reservoir, thereby increasing the production of the oil and gas well and improving the economic benefit. However, the subsequent treatment of the formation plugging still needs to use the conventional plugging removal technologies such as the chemical method, the physical method, the microbial method and the composite plugging removal method. These plugging removal processes are complex, and if the plugging removal measures are not properly handled, new chemical plugging and mechanical plugging can be caused, thereby reducing the permeability of the formation.

[0005] At present, the oil and gas reservoir drilling fluid protection materials in the drilling process mainly include acidifiable materials, oil-soluble materials, biodegradable materials, biodegradable polymers and temperature-sensitive polymer materials, which need auxiliary conditions to unblock and do not have good self-degradation characteristics. The temperature resistance, plugging performance and degradation performance of the materials still need further research. Therefore, in view of the contradiction between plugging and reservoir protection in the drilling process of the oil and gas reservoir, it is very urgent to develop a self-unblocking plugging agent, which can meet the requirements of efficient plugging in the drilling process and realize efficient self-degradation after drilling, and is the key of the current oil and gas reservoir protection technology. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of a self-degradable plugging agent, which solves the problem that the plugging agent in the prior art needs auxiliary conditions to unblock.

[0007] The second purpose of the present application is to provide a reservoir protection drilling fluid, which solves the problem that the plugging and reservoir protection in the drilling process of the oil and gas reservoir in the prior art are difficult to reconcile.

[0008] In order to achieve the above purposes, the technical scheme of the preparation method of the self-degradable plugging agent of the present application is as follows:

[0009] A preparation method of a self-degradable plugging agent, comprising the following steps: reacting 16.5-31.3 parts of polyethylene glycol, 50-68 parts of lactide monomer and 7.5-20.7 parts of carbonate under the condition of 0.056-0.084 parts of catalyst; the temperature of the reaction is 135-150 DEG C. The parts refer to the weight parts.

[0010] The present application improves the hydrophilicity and dispersibility of the polylactide material by introducing the ethylene glycol functional group into the polylactide molecular structure. The prepared self-degradable plugging agent is easy to disperse in the drilling fluid, has good compatibility with the drilling fluid, realizes dense plugging in the drilling process, reduces the invasion risk of the drilling fluid liquid phase and solid phase particles, and plays a role in protecting the reservoir.

[0011] The self-degradable plugging agent is a granular material in which a carbonate is wrapped in a polymer by introducing a glycol functional group, a carbonate and molecular structure optimization, improves the degradation efficiency of the self-degradable plugging agent, and can automatically undergo physical and chemical degradation under the temperature and pressure conditions of a formation within a certain time range to generate small molecules of organic acids, inorganic salts and the like, is an intelligent material that can be completely automatically degraded, ensures that the filter cake is automatically removed efficiently, realizes extremely low damage to an oil and gas reservoir, maximally restores the permeability of the oil and gas reservoir, and significantly improves the reservoir protection effect. The self-degradable plugging agent can be self-degraded at 50-120 DEG C, improves the applicable temperature range of the self-degradable plugging agent, and enables the self-degradable plugging agent to be applicable to more oil and gas reservoir conditions. The self-degradable plugging agent has good compression resistance, high strength and low cost, and is convenient for mechanical crushing, wherein the carbonate can react and degrade with the organic acid generated by polymer decomposition.

[0012] Further preferably, the self-degradable plugging agent comprises 20-30 parts of polyethylene glycol, 60-65 parts of lactide monomers, 8-15 parts of carbonate and 0.075-0.08 parts of catalyst.

[0013] Preferably, the molecular weight of the polyethylene glycol is 2000-3000 g / mol.

[0014] Preferably, the reaction time is 5-6 h for better plugging.

[0015] Preferably, the catalyst is a combined catalyst system of compound A and compound B; wherein compound A is selected from one of stannous octoate and stannous isooctoate, and compound B is selected from one of stannous dichloride and boron trichloride, for better reaction of the polyethylene glycol, lactide monomers and carbonate.

[0016] Preferably, the mass ratio of compound A to compound B is (70-75):(25-30) for improving the reaction efficiency.

[0017] Preferably, the carbonate is a structural unit containing formula (I), wherein R1 is one of H atom, sodium, potassium, calcium, lithium and magnesium atom, and R2 is one of sodium, potassium, calcium, lithium, magnesium, zinc and iron atom.

[0018]

[0019] Further preferably, the carbonate is one or more of potassium carbonate, lithium carbonate, zinc carbonate, sodium bicarbonate, calcium bicarbonate, magnesium carbonate and ferrous carbonate.

[0020] Preferably, the preparation method further comprises drying and crushing after the reaction. The drying temperature is 70-80 DEG C, and the drying time is 12-24 h.

[0021] The technical scheme of the reservoir protection drilling fluid of the present application is as follows:

[0022] The reservoir protection drilling fluid contains the plugging agent prepared by the preparation method of the self-degradable plugging agent.

[0023] The self-degradable plugging agent contained in the reservoir protection drilling fluid of the present application can be processed and crushed into particles of different sizes, and the particle size distribution is wide, which is beneficial to reasonably selecting the particle size of the self-degradable plugging agent according to the pore structure and size characteristics of the oil and gas reservoir, adding the self-degradable plugging agent to the drilling fluid to form a dense filter cake, achieving a strong plugging effect, and playing a good effect of preventing permeation, invasion, leakage and plugging, thereby reducing and preventing the leakage of the drilling fluid in the oil and gas reservoir, and ensuring normal drilling and reducing the damage to the oil and gas reservoir.

[0024] The self-degradable plugging agent contained in the reservoir protection drilling fluid of the present application has a better plugging effect and a complete automatic degradation characteristic, can achieve a dense plugging effect during drilling, and the dense filter cake can be automatically and efficiently degraded and unblocked after drilling is completed, without the need for other treatment measures such as acidification, biological enzyme and gel breaking fluid, thereby saving the operation procedure and cost, fundamentally improving the traditional oil and gas reservoir protection concept and method, achieving the target of extremely low pollution and damage to the oil and gas reservoir, realizing the target of safe drilling, maximum protection and simplification of the oil and gas reservoir, and having a good application prospect.

[0025] In order to achieve a better plugging effect, preferably, the mass percentage of the plugging agent in the reservoir protection drilling fluid is 0.85-6.2%.

[0026] Preferably, the reservoir protection drilling fluid mainly consists of water and the following components with the following mass percentages: 0.2-0.5% thickening agent, 1.0-2.0% fluid loss additive, 2.6-3.3% KCl and 0.85-6.2% plugging agent. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Figure is the self-degradation performance diagram of the self-degradable plugging agent of Example 1 of the present application;

[0028] Figure 2 Figure is the self-degradation performance diagram of the self-degradable plugging agent of Example 2 of the present application;

[0029] Figure 3 Figure is the self-degradation performance diagram of the self-degradable plugging agent of Example 3 of the present application;

[0030] Figure 4 Figure is the self-degradation performance diagram of the reservoir protection drilling fluid of Example 4 of the present application;

[0031] Figure 5The diagram shows the reservoir protection performance of drilling fluids in Examples 4-6 and the comparative examples of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0033] I. Specific embodiments of the preparation method of the self-degradable plugging agent of the present invention are as follows:

[0034] Example 1

[0035] The self-degradable plugging agent of this embodiment is composed of the following components in parts by weight: 31.3 parts of polyethylene glycol with a molecular weight of 2000 g / mol, 0.0836 parts of stannous isooctanoate and boron trichloride catalyst in a mass ratio of 72:28, 50 parts of lactide monomer, 2.5 parts of potassium carbonate, 2.5 parts of sodium bicarbonate and 2.5 parts of calcium bicarbonate.

[0036] The preparation method of the self-degradable plugging agent in this embodiment is as follows: 31.3 parts by mass of polyethylene glycol with a molecular weight of 2000 g / mol were weighed and placed in a reactor, heated to 128°C, and vacuumed for 15 min. The reaction solution was allowed to cool naturally. After the temperature of the reaction solution dropped to 25°C, 0.0836 parts by mass of a catalyst consisting of stannous isooctanoate and boron trichloride mixed in a mass ratio of 72:28 was added. Then, 50 parts by mass of lactide monomer and 7.5 parts by mass of carbonate were added. Vacuuming was carried out for 25 min, maintaining the vacuum degree of the reaction solution at 70 Pa. The temperature was raised to 135°C and the reaction was stirred for 5 hours. After drying the reaction product in a drying oven at 70°C for 24 hours, it was mechanically pulverized to prepare a self-degradable plugging agent with a particle size of 100 mesh.

[0037] Example 2

[0038] The self-degradable plugging agent of this embodiment is composed of the following components in parts by weight: 26 parts of polyethylene glycol with a molecular weight of 2000 g / mol, 0.075 parts of stannous octoate and boron trichloride catalyst in a mass ratio of 75:25, 63 parts of lactide monomer, 11 parts of lithium carbonate and 6.5 parts of magnesium carbonate.

[0039] The preparation method of the self-degrading plugging agent of the embodiment is as follows: 26 parts by mass of polyethylene glycol with a molecular weight of 2000 g / mol is placed in a reactor, heated to 128℃, vacuumized for 15 min, and then naturally cooled. After the temperature of the reaction solution is reduced to 25℃, 0.075 parts by mass of a catalyst mixed by stannous octoate and boron trichloride at a mass ratio of 75:25 is added, followed by addition of 63 parts by mass of lactide monomer and 17.5 parts by mass of carbonate. The reaction solution is vacuumized for 25 min, and then heated to 140℃ and stirred for 5 hours. After the reaction product is dried in a drying box at 70℃ for 24 hours, mechanical crushing is performed to obtain the self-degrading plugging agent with a particle size of 100 mesh.

[0040] Example 3

[0041] The self-degrading plugging agent of the embodiment is composed of the following components in mass percentage: 16.5 parts of polyethylene glycol with a molecular weight of 3000 g / mol, 0.056 parts of a catalyst of stannous iso-octoate and stannous dichloride at a mass ratio of 75:30, 68 parts of lactide monomer, 15 parts of zinc carbonate and 5.7 parts of ferrous carbonate.

[0042] The preparation method of the self-degrading plugging agent of the embodiment is as follows: 16.5 parts by mass of polyethylene glycol with a molecular weight of 3000 g / mol is placed in a reactor, heated to 130℃, vacuumized for 15 min, and then naturally cooled. After the temperature of the reaction solution is reduced to 25℃, 0.056 parts by mass of a catalyst mixed by stannous iso-octoate and stannous dichloride at a mass ratio of 70:30 is added, followed by addition of 68 parts by mass of lactide monomer and 20.7 parts by mass of carbonate. The reaction solution is vacuumized for 25 min, and then heated to 150℃ and stirred for 6 hours. After the reaction product is dried in a drying box at 75℃ for 24 hours, mechanical crushing is performed to obtain the self-degrading plugging agent with a particle size of 100 mesh.

[0043] Second, the embodiment of the reservoir protection drilling fluid of the present application

[0044] In the following examples, the viscosity enhancer MC VIS and the fluid loss additive Dual Flo are provided by Sinopec North China Petroleum Engineering Co., Ltd.

[0045] Example 4

[0046] The reservoir protection drilling fluid of the embodiment is composed of the following components in mass percentage: 0.3% of the viscosity enhancer MC VIS, 1.5% of the fluid loss additive Dual Flo, 2.6% of KCl and 0.85% of the self-degrading plugging agent of Example 1, and the balance is water.

[0047] The self-plugging reservoir protection drilling fluid was prepared according to the standard GB / T 16783.1-2014 "Drilling Fluid Field Testing Part 1: Water-based Drilling Fluid", and was marked as YS1.

[0048] Example 5

[0049] The reservoir protection drilling fluid of this example was composed of the following components in mass percentage: 0.3% thickening agent MCVIS, 1.5% fluid loss agent Dual Flo, 3% KCl and 3.1% self-degradable plugging agent of Example 2, and the balance was water.

[0050] The reservoir protection drilling fluid of this example was prepared by the same method as Example 4, and was marked as YS2.

[0051] Example 6

[0052] The reservoir protection drilling fluid of this example was composed of the following components in mass percentage: 0.3% thickening agent MCVIS, 1.5% fluid loss agent Dual Flo, 3.3% KCl and 6.2% self-degradable plugging agent of Example 3, and the balance was water.

[0053] The reservoir protection drilling fluid of this example was prepared by the same method as Example 4, and was marked as YS3.

[0054] III. Comparative Example

[0055] Comparative Example 1

[0056] The drilling fluid of this comparative example was basically the same as Example 4, except that calcium carbonate plugging material was used instead of the self-degradable plugging agent of Example 1. Among them, the particle size range of the acid-soluble material calcium carbonate was 2.0-200 μm.

[0057] The drilling fluid of this comparative example was prepared by the same method as Example 4, and was marked as DS1.

[0058] Comparative Example 2

[0059] The plugging agent of this comparative example did not contain carbonate, and was composed of the following components in mass percentage: 16.5 parts of polyethylene glycol with a molecular weight of 3000 g / mol, 0.056 parts of isooctanoic acid stannous catalyst with a mass ratio of 75:30 and dichloro stannous catalyst, 68 parts of lactide monomer.

[0060] The preparation method of the self-degrading plugging agent of the embodiment is as follows: 16.5 parts by mass of polyethylene glycol with a molecular weight of 3000 g / mol is placed in a reactor, heated to 130°C, vacuumized for 15 min, and then naturally cooled. After the temperature of the reaction solution is reduced to 25°C, 0.056 parts by mass of a catalyst of stannous isooctoate mixed with stannous dichloride at a mass ratio of 70:30 is added, followed by the addition of 68 parts by mass of lactide monomers. The reaction solution is vacuumized for 25 min, the vacuum degree is maintained at 75 Pa, and the temperature is increased to 150°C for stirring reaction for 6 hours. After the reaction product is dried in a drying box at 75°C for 24 hours, mechanical crushing is performed to prepare a self-degrading plugging agent with a particle size of 100 mesh.

[0061] The drilling fluid of the comparative example is prepared by adding 0.3% of a viscosity enhancer MC VIS, 1.5% of a fluid loss additive Dual Flo, 2.6% of KCl, and 0.85% of the plugging agent of the comparative example, and the balance is water.

[0062] The self-degrading plugging reservoir protection drilling fluid is prepared according to the standard GB / T 16783.1-2014 “Drilling Fluid Field Test Part 1 Water-based Drilling Fluid”, and is marked as DS2.

[0063] Comparative Example 3

[0064] The plugging agent of the comparative example is composed of the following components by mass percentage: 16.5 parts of polyethylene glycol with a molecular weight of 3000 g / mol, 0.056 parts of stannous isooctoate catalyst, 68 parts of lactide monomers, 15 parts of zinc carbonate, and 5.7 parts of ferrous carbonate.

[0065] The preparation method of the self-degrading plugging agent of the embodiment is as follows: 16.5 parts by mass of polyethylene glycol with a molecular weight of 3000 g / mol is placed in a reactor, heated to 130°C, vacuumized for 15 min, and then naturally cooled. After the temperature of the reaction solution is reduced to 25°C, 0.056 parts by mass of a catalyst of stannous isooctoate mixed with stannous dichloride at a mass ratio of 70:30 is added, followed by the addition of 68 parts by mass of lactide monomers. The reaction solution is vacuumized for 25 min, the vacuum degree is maintained at 75 Pa, and the temperature is increased to 150°C for stirring reaction for 6 hours. After the reaction product is dried in a drying box at 75°C for 24 hours, mechanical crushing is performed to prepare a self-degrading plugging agent with a particle size of 100 mesh.

[0066] The drilling fluid of the comparative example is prepared by adding 0.3% of a viscosity enhancer MC VIS, 1.5% of a fluid loss additive Dual Flo, 2.6% of KCl, and 0.85% of the plugging agent of the comparative example, and the balance is water.

[0067] The self-degrading plugging reservoir protection drilling fluid is prepared according to the standard GB / T 16783.1-2014 “Drilling Fluid Field Test Part 1 Water-based Drilling Fluid”, and is marked as DS3.

[0068] IV. Experimental Examples

[0069] Experimental Example 1: Self-degradation properties of the plugging agent

[0070] This experiment involved adding 6% (by mass) of the self-degrading sealing agent from Example 1 (particle size 100 mesh) to 100 parts of clean water and testing its degradation performance at 60°C and 0.1 MPa. The results are as follows: Figure 1 As shown.

[0071] according to Figure 1 The results show that the self-degrading plugging agent of Example 1 can effectively self-degrade at 60°C. In the first two days, the degradation rate is very slow, only 16.8%, during which time it can effectively plug reservoir pores and protect the reservoir. As time progresses, the degradation reaction gradually penetrates deeper into the interior, increasing the contact area and allowing more substances to participate in the degradation reaction. This synergistically accelerates the degradation rate of the self-degrading plugging agent of Example 1, achieving near-complete degradation at 60°C for 20 days, with a self-degradation rate approaching 100%.

[0072] Therefore, in terms of degradation effect, the self-degrading plugging agent of Example 1 of the present invention has a strong degradation ability at 60°C and can achieve complete self-degradation within a certain time range.

[0073] Experimental Example 2: Self-degradation performance of the plugging agent

[0074] This experiment involved adding 6% (by mass) of the self-degrading sealing agent from Example 2 (particle size 100 mesh) to 100 parts of clean water and testing its degradation performance at 90°C and 0.1 MPa. The results are as follows: Figure 2 As shown.

[0075] according to Figure 2 The results show that the self-degrading plugging agent of Example 2 can effectively self-degrade at 90℃. In the first two days, the degradation rate is relatively slow, below 24.6%, during which time it effectively plugs reservoir porosity. As time progresses, its degradation pattern is basically the same as that of the self-degrading plugging agent of Example 1. However, due to the increased temperature, the degradation rate of the self-degrading plugging agent of Example 2 accelerates, reaching 100% degradation rate after 17 days.

[0076] Therefore, in terms of degradation effect, the self-degrading plugging agent of Example 2 of the present invention has a strong self-degradation ability at 90°C and can be basically completely self-degraded within a certain time range.

[0077] Experimental Example 3: Self-degradation properties of the plugging agent

[0078] This experiment involved adding 6% (by mass) of the self-degrading sealing agent from Example 3 (particle size 100 mesh) to 100 parts of clean water. The degradation performance was tested at 120°C and 2.0 MPa. The results are as follows: Figure 3 As shown.

[0079] according to Figure 3 The results show that the self-degrading plugging agent of Example 3 can effectively self-degrade at 120℃. In the first 24 hours, the degradation rate is relatively slow, below 29.2%, during which time it effectively plugs reservoir pores. As time increases, the degradation rate accelerates, reaching over 90% after 4 days and 100% degradation within 7 days. This demonstrates that increased temperature significantly accelerates the degradation rate of the self-degrading plugging agent.

[0080] Therefore, in terms of degradation effect, the self-degrading plugging agent of Example 3 of the present invention has extremely strong self-degradation ability at 120°C and can completely self-degrade in a short time.

[0081] Experiment Example 4: Self-degradation properties of reservoir protection drilling fluid

[0082] This experiment measures the self-degradation properties of the filter cake formed by the reservoir protection drilling fluid in Example 4.

[0083] This experimental example uses the standard GB / T 29170-2012 "Laboratory Testing of Drilling Fluids for Petroleum and Natural Gas Industry" to test the filter cake formed by the reservoir protection drilling fluid in Example 4. The self-degradation of the filter cake was observed in clean water at 90℃ and 0.1 MPa. The results are as follows: Figure 4 As shown.

[0084] according to Figure 4 The results show that the filter cake formed by the reservoir protection drilling fluid in Example 4 can undergo significant self-degradation at 90°C. After 5 days, the filter cake degradation rate can reach more than 99%. This indicates that the filter cake formed by the reservoir protection drilling fluid of the present invention still has excellent self-degradation ability, which can significantly reduce the damage to oil and gas reservoirs and achieve the effect of protecting oil and gas reservoirs.

[0085] Experimental Example 5: Reservoir Protection Performance

[0086] This experiment tests the reservoir protection performance of the drilling fluids used in Examples 4-6 and Comparative Examples 1-3.

[0087] The core of the present experimental example adopts the natural sandstone reservoir core of the field oilfield of Sinopec North China Petroleum Engineering Co., Ltd. According to the People's Republic of China Oil and Natural Gas Industry Standard SY / T 6540-2021 “Drilling Fluid Completion Fluid Damage to Oil Reservoir Indoor Evaluation Method”, the reservoir protection drilling fluid YS1-YS3 of Examples 4-6 is tested for the degree of formation pollution damage by dynamic pollution experiment, and is compared with the drilling fluid DS1-3 system prepared in Comparative Examples 1-3, and the results are shown in Table 1 and Figure 5

[0088] Table 1 Comparison of reservoir protection performance of drilling fluids

[0089]

[0090] From the data in Table 1 and Figure 5 It can be seen that: for the field sandstone reservoir, the reservoir protection drilling fluid formed by the self-degrading plugging agent of the present application can effectively plug the core, and the plugging rate can reach 98.17%, and the plugging permeability recovery value after 10 days of backflushing displacement is 98.7% at 10 days. The calcium carbonate plugging in the comparative examples is difficult to unplug, the plugging rate of the self-unplugging plugging agent in Comparative Example 2 is reduced, and the self-unplugging plugging agent in Comparative Example 3 only uses one catalyst and the reaction is not sufficient, and the single catalyst does not have catalytic effect on all chemical reactions in the preparation of the self-unplugging plugging agent, resulting in a decrease in the plugging performance of the plugging agent and a too fast degradation rate, so the catalyst in the present application should be a combined catalyst system; the comparison shows that: the self-degrading plugging agent and the reservoir protection drilling fluid formed by it in the present application can automatically degrade after the drilling is completed, automatically realize backflushing unblocking, maximize the release of oil and gas production capacity, without the need for additional acid washing to remove filter cake and other operation processes, avoiding secondary damage to the oil and gas reservoir, saving operation procedures and time, effectively shortening the completion cycle, and being a simple, efficient, economical and side-effect-free new reservoir protection technology. The degradation of the organic acid formed helps to remove some particulate matter in the formation, which can effectively improve the connectivity between the reservoirs and improve the permeability of the oil and gas reservoir, improve the flowability of the oil and gas in the reservoir, and is a simple, efficient, economical and side-effect-free new reservoir protection technology.​

Claims

1. A method for preparing a self-degrading plugging agent, characterized in that, Includes the following steps: 16.5-31.3 parts of polyethylene glycol, 50-68 parts of lactide monomer and 7.5-20.7 parts of carbonate were reacted under the condition of 0.056-0.084 parts of catalyst; the reaction temperature was 135-150℃; the molecular weight of the polyethylene glycol was 2000-3000 g / mol; The catalyst is a combined catalyst system of compound A and compound B; wherein, compound A is selected from stannous octoate and stannous isooctanoate, and compound B is selected from stannous dichloro and boron trichloride; the mass ratio of compound A to compound B is (70~75):(25~30); The self-degrading plugging agent is a polymer-encapsulated particulate material containing carbonates.

2. The method for preparing the self-degrading plugging agent according to claim 1, characterized in that, The reaction time is 5-6 hours.

3. The method for preparing the self-degrading plugging agent according to claim 1, characterized in that, The carbonate is one or more of potassium carbonate, sodium bicarbonate, calcium bicarbonate, lithium carbonate, magnesium carbonate, zinc carbonate, and ferrous carbonate.

4. A reservoir protection drilling fluid, characterized in that, The reservoir protection drilling fluid contains a plugging agent prepared by the method for preparing the self-degrading plugging agent as described in any one of claims 1-3.

5. The reservoir protection drilling fluid according to claim 4, characterized in that, The plugging agent has a mass percentage of 0.85-6.2% in the reservoir protection drilling fluid.

6. The reservoir protection drilling fluid according to claim 5, characterized in that, The reservoir protection drilling fluid is composed of water and the following components by mass percentage: 0.2-0.5% viscosifier, 1.0-2.0% filtration reducer, 2.6-3.3% KCl and 0.85-6.2% plugging agent.

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