Low-temperature controllable expanded graphite blocking agent as well as preparation method and application thereof

Abstract

The invention relates to a low-temperature controllable expanded graphite blocking agent as well as a preparation method and application thereof. The low-temperature controllable expanded graphite blocking agent comprises the following raw materials in parts by mass: 5-15 parts of crystalline flake graphite, 10-75 parts of an oxidizing agent, 10-45 parts of an intercalating agent and 10-45 parts of a pretreating agent. The low-temperature controllable expansion graphite blocking agent provided by the invention has low-temperature (about 200 DEG C) controllable expansion capacity, and overcomes the defects that the traditional expandable graphite can be fully expanded only when the temperature reaches 900 DEG C or above, and the expansion capacity is difficult to regulate and control. And the graphite material shows excellent stability in a high-temperature environment of 200 DEG C or above, which is benefited from the excellent temperature resistance of the graphite material. Experimental results show that the plugging agent can maintain the stable performance for at least three months under the simulated high-temperature stratum condition, and the long-term plugging requirement of oil and gas wells is met.

Description

Technical Field

[0001] The invention relates to a low-temperature controllable expanded graphite plugging agent and a preparation method and application thereof, in particular to a controllable expanded graphite plugging agent which can be prepared under low temperature conditions and applied in high-temperature formations above 200°C, belonging to the technical field of oil and gas exploitation. Background Art

[0002] As an important component of global energy, oil and gas resources occupy a pivotal position in the energy structure. With the gradual depletion of traditional oil and gas resources, the demand for the exploitation of deep and ultra-deep oil and gas resources is increasing. However, the problem of microcracks in deep and ultra-deep formations has become one of the key factors restricting the efficiency and safety of oil and gas extraction. The presence of microcracks will not only lead to drilling fluid leakage, but also may cause safety accidents such as well wall collapse, seriously affecting the construction progress of drilling operations.

[0003] At present, there are a variety of plugging materials and technologies on the market that have been used for crack plugging in oil and gas wells, including but not limited to cement slurry, resin, polymer gel, etc. These traditional plugging materials have a certain plugging effect under normal temperature conditions, but their performance drops sharply in high-temperature formations above 200°C, making it difficult to meet the plugging needs under high-temperature conditions. In addition, these materials have limitations in controlling the expansion rate and expansion speed, making it difficult to achieve precise plugging, and may have an adverse effect on the long-term stability of oil and gas wells.

[0004] Low-temperature expanded graphite is a graphite material prepared by chemical intercalation and low-temperature heat treatment processes, characterized by the ability to achieve significant interlayer expansion at relatively low temperatures. After entering the formation fracture space, low-temperature expanded graphite can quickly form a stable bridge due to its unique two-dimensional lamellar structure, and then expand under the action of the formation temperature, squeeze and fill the fracture space to form an effective plugging layer, thereby improving the plugging performance of the drilling fluid. In addition, the chemical stability and temperature resistance of low-temperature expanded graphite enable it to remain effective for a long time in harsh underground environments, reduce environmental pollution, and improve the safety and economy of drilling operations.

[0005] However, deep and ultra-deep formations often have micro-cracks of varying sizes. The controllability of the expansion parameters of traditional low-temperature expanded graphite is poor, and the plugging effect on formations with larger fracture scales is not good. In order to play an effective plugging role in deep and ultra-deep fracture spaces, at least the following three problems need to be overcome: ① The problem of too high initial expansion temperature. At present, most of the expanded graphite products on the market have an initial expansion temperature above 400°C, which is difficult to meet the target formation temperature requirements; ② The expansion effect in the actual application environment, that is, the problem of how the expansion effect is in the high-temperature water phase. At present, most of these products are instantaneously heated and expanded in a high-temperature environment to measure their expansion capacity. There is a lack of experimental data in the high-temperature water phase that fits the actual application environment, making it difficult to evaluate their plugging effect in the actual application process; ③ The expansion effect is poorly controllable. The modification process and method of the expanded graphite products currently on the market are relatively single. After reaching the initial expansion temperature, the expansion effect is difficult to control, and the adaptability to the situation of different fracture scales in the actual formation environment is poor.

[0006] In addition, it should be noted that expandable graphite and graphene products are essentially different. From the perspective of physical size, the size of expandable graphite is generally at the micron level, while graphene products are generally at the nanometer level; from the perspective of application characteristics, graphene products have no expansion effect. Therefore, when graphene products are used in the field of drilling fluids, they can only play a physical bridging and plugging role, and have no expansion effect.

[0007] Therefore, the development of a new type of expanded graphite plugging agent suitable for high-temperature formation environment, with excellent thermal stability and controllable expansion performance, has important practical significance and broad application prospects for improving oil and gas production efficiency and ensuring the safety of oil and gas wells. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a low-temperature controllable expansion graphite plugging agent and its preparation method and application. The preparation method provided by the present invention is simple to operate and convenient for mass preparation. The prepared graphite plugging agent not only has the characteristics of low-temperature expansion of traditional graphite plugging agents, but also can achieve controllable expansion and broad-spectrum plugging effects through simple regulation.

[0009] The technical solution of the present invention is as follows:

[0010] A low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 5 to 15 parts of flake graphite, 10 to 75 parts of an oxidant, 10 to 45 parts of an intercalation agent, and 10 to 45 parts of a pretreatment agent.

[0011] Preferably according to the present invention, the low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 5 to 10 parts of flake graphite, 20 to 60 parts of oxidant, 20 to 40 parts of intercalant, and 20 to 40 parts of pretreatment agent.

[0012] Further preferably, the low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 8 parts of flake graphite, 40-60 parts of oxidant, 20-30 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of oxidant to intercalant is (1-3):1.

[0013] According to the preferred embodiment of the present invention, the mesh size of the flake graphite is 50 mesh, 100 mesh, 150 mesh or 300 mesh;

[0014] Further preferably, the specification of the flake graphite is 150 mesh;

[0015] According to the preferred embodiment of the present invention, the oxidant is a combination of any two or more of an aqueous solution of ammonium persulfate, an aqueous solution of potassium persulfate and an aqueous solution of potassium permanganate;

[0016] Further preferably, the oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is (2-4):1, more preferably 3:1.

[0017] Further preferably, the mass concentration of the ammonium persulfate aqueous solution is 40-60%, more preferably 50%; the mass concentration of the potassium permanganate aqueous solution is 2-6%, more preferably 4%;

[0018] Preferably according to the present invention, the intercalant is concentrated sulfuric acid, concentrated nitric acid or perchloric acid.

[0019] Further preferably, the intercalant is concentrated sulfuric acid.

[0020] Preferably according to the present invention, the pretreatment agent is glacial acetic acid, aqueous hydrogen peroxide solution or hypochlorous acid.

[0021] More preferably, the pretreatment agent is an aqueous solution of hydrogen peroxide.

[0022] According to the present invention, the preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent comprises the following steps:

[0023] 1) adding flake graphite to a pretreatment agent, stirring continuously at room temperature, washing with deionized water and filtering to obtain pretreated flake graphite, and then placing the pretreated flake graphite in a blast drying oven and drying to constant weight;

[0024] 2) The dried flake graphite is placed in an oxidant, heated and stirred uniformly for the first time, and then an intercalation agent is added. After stirring uniformly for the second time, the mixture is washed with deionized water and filtered, and then placed in a blast drying oven and dried to constant weight to obtain a low-temperature controllable expanded graphite plugging agent.

[0025] Preferably according to the present invention, in step 1), the stirring rate is 600-1000 rpm, the stirring time is 10-30 min, the mixture is washed with deionized water until the pH value is 4-7, and the drying oven temperature is 30-70°C.

[0026] Further preferably, the stirring rate is 600-800 rpm, the stirring time is 10-20 min, the solution is washed with deionized water until the pH value is 6-7, and the drying oven temperature is 40-60°C.

[0027] Preferably according to the present invention, in step 2), the first uniform stirring rate is 200-500 rpm, the stirring time is 20-40 min, and the stirring temperature is 40-80°C; the second uniform stirring rate is 400-800 rpm, the stirring time is 40-80 min, and the stirring temperature is 30-60°C; washing with deionized water to a pH of 4-7, and the drying oven temperature is 30-70°C.

[0028] Further preferably, the first uniform stirring rate is 300-500 rpm, the stirring time is 30-40 min, and the stirring temperature is 50-70°C; the second uniform stirring rate is 500-700 rpm, the stirring time is 50-70 min, and the stirring temperature is 40-60°C; washing with deionized water to a pH of 6-7, and the drying oven temperature is 40-60°C.

[0029] According to the present invention, the application of the low-temperature controllable expanded graphite plugging agent is used for crack plugging in oil and gas wells. The low-temperature controllable expanded graphite plugging agent of the present invention can obtain plugging agents with different expansion capabilities by adjusting the ratio of the oxidant and the intercalation agent, and effectively plug a larger range of micro cracks.

[0030] Preferably, according to the present invention, in the application, the applicable temperature of the low-temperature controllable expanded graphite plugging agent is 200-300°C, preferably 200-260°C; the applicable formation microcrack range is 150-500 μm, preferably 200-400 μm.

[0031] The low-temperature controllable expanded graphite plugging agent prepared according to the present invention has a simple application and regulation method. When used, it only needs to be added to the drilling fluid in a certain proportion without other processes. When plugging larger-scale microcracks within a certain range, it only needs to regulate the proportion of relevant components during preparation to obtain a plugging agent with stronger expansion ability.

[0032] The technical features of the present invention are as follows:

[0033] The low-temperature controllable expanded graphite plugging agent prepared by the present invention is from the preparation principle. First, nanographene is peeled off the graphite sheet by "gasification" of low-boiling point substances at high temperature to obtain graphene sheets separated from each other, while low-temperature controllable expanded graphite is to fill the graphite sheet with small molecule low-boiling point acid as an intercalation substance through electrostatic action, and the obtained product is essentially a "sandwich" structure; secondly, when preparing nanographene, it is necessary to maintain a high temperature environment for a long time to provide enough energy for the reaction system to "gasify" and peel off the graphite sheet, while preparing low-temperature controllable expanded graphite requires more accurate temperature and time restrictions to ensure that the intercalation substance is accurately inserted and will not escape excessively from the interlayer space. Therefore, the low-temperature controllable expanded graphite plugging agent provided by the present invention is essentially different from the preparation process of nanographene in the selection of modification methods and modified materials.

[0034] The beneficial effects of the present invention are as follows:

[0035] 1. The low-temperature controllable expandable graphite plugging agent provided by the present invention has controllable expansion ability at low temperature (about 200°C), which overcomes the defects that traditional expandable graphite can only fully expand at a temperature of more than 900°C and the expansion ability is difficult to control.

[0036] 2. The plugging agent prepared by the present invention exhibits excellent stability in a high temperature environment above 200°C due to the modified graphite matrix, which is due to the excellent temperature resistance of the graphite material itself. The experimental results show that the plugging agent can maintain stable performance for at least 3 months under simulated high-temperature formation conditions, meeting the needs of long-term plugging of oil and gas wells.

[0037] 3. The plugging agent of the present invention can achieve controllable expansion at a specific temperature by simply adjusting the ratio of the oxidant and the intercalant. The smaller the proportion of the intercalant, the weaker the expansion ability of the prepared plugging agent. This is because its expansion ability mainly comes from the effective content of the low-boiling point intercalant inserted between the graphite sheets. Therefore, a regulatory relationship can be established between the ratio of the oxidant and the intercalant and the expansion ability of the product.

[0038] 4. The plugging agent prepared by the present invention has strong stability. The boiling point of the selected intercalation agent is above 150°C. When stored and transported at room temperature or added to drilling fluid for use, the plugging agent will not expand and fail. At the same time, the plugging agent prepared by the present invention has little effect on the rheological properties of the drilling fluid. Due to its special lamellar structure, it has a certain degree of lubrication. Therefore, the plugging agent prepared by the present invention has the characteristics of convenient transportation and storage, simple operation, and safe slurry preparation. DETAILED DESCRIPTION

[0039] The present invention is further described below with reference to specific examples, but is not limited thereto. The raw materials used in the examples are all conventional raw materials and can be obtained commercially; the methods described are all prior art unless otherwise specified.

[0040] The purity of the flake graphite used in the examples is above 90%, and the flake graphite is purchased from Qingdao Hengrunda Graphite Products Co., Ltd.

[0041] Example 1

[0042] A low-temperature controllable expanded graphite plugging agent A1 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of an oxidant, 20 parts of an intercalating agent, and 20 parts of a pretreatment agent, wherein the mass ratio of the oxidant to the intercalating agent is 3:1.

[0043] The specification of the flake graphite is 150 mesh;

[0044] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0045] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0046] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent comprises the following steps:

[0047] 1) adding flake graphite to the pretreatment agent according to the ratio, stirring continuously for 15 min at room temperature and a stirring rate of 700 rpm, repeatedly washing with deionized water and filtering until the pH value of the filtrate is 7, to obtain pretreated flake graphite, and then placing the pretreated flake graphite in a blast drying oven and drying at 50° C. to constant weight;

[0048] 2) The dried flake graphite was placed in an oxidant, heated to 60°C, and stirred at a stirring rate of 400 rpm for 30 min for the first time, and then an intercalation agent was added. After stirring at a stirring rate of 600 rpm for a second time for 60 min, the mixture was repeatedly washed with deionized water and filtered until the pH value of the filtrate was 7, and then placed in a forced air drying oven at 50°C to dry to constant weight, to obtain a low-temperature controllable expanded graphite plugging agent A1.

[0049] Example 2

[0050] A low-temperature controllable expanded graphite plugging agent A2 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 40 parts of an oxidant, 20 parts of an intercalating agent, and 20 parts of a pretreatment agent, wherein the mass ratio of the oxidant to the intercalating agent is 2:1.

[0051] The specification of the flake graphite is 150 mesh;

[0052] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0053] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0054] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and a low-temperature controllable expanded graphite plugging agent A2 is obtained.

[0055] Example 3

[0056] A low-temperature controllable expanded graphite plugging agent A3 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 20 parts of oxidant, 20 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 1:1.

[0057] The specification of the flake graphite is 150 mesh;

[0058] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0059] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0060] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and a low-temperature controllable expanded graphite plugging agent A3 is obtained.

[0061] Example 4

[0062] A low-temperature controllable expanded graphite plugging agent A4 comprises the following raw materials in parts by mass: 12 parts of flake graphite, 60 parts of oxidant, 20 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3:1.

[0063] The specification of the flake graphite is 150 mesh;

[0064] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0065] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0066] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and a low-temperature controllable expanded graphite plugging agent A4 is obtained.

[0067] Example 5

[0068] A low-temperature controllable expanded graphite plugging agent A5 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of oxidant, 20 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3:1.

[0069] The specification of the flake graphite is 150 mesh;

[0070] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0071] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0072] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and a low-temperature controllable expanded graphite plugging agent A5 is obtained.

[0073] Example 6

[0074] A low-temperature controllable expanded graphite plugging agent A6 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 70 parts of oxidant, 20 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3.5:1.

[0075] The specification of the flake graphite is 150 mesh;

[0076] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0077] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0078] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A6 is obtained.

[0079] Example 7

[0080] A low-temperature controllable expanded graphite plugging agent A7 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 10 parts of oxidant, 20 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 1:2.

[0081] The specification of the flake graphite is 150 mesh;

[0082] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0083] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0084] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A7 is obtained.

[0085] Example 8

[0086] A low-temperature controllable expanded graphite plugging agent A8 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of oxidant, 40 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3:2.

[0087] The specification of the flake graphite is 150 mesh;

[0088] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0089] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0090] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A8 is obtained.

[0091] Example 9

[0092] A low-temperature controllable expanded graphite plugging agent A9 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of oxidant, 10 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 6:1.

[0093] The specification of the flake graphite is 150 mesh;

[0094] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0095] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0096] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A9 is obtained.

[0097] Example 10

[0098] A low-temperature controllable expanded graphite plugging agent A10 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of oxidant, 20 parts of intercalant, and 40 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3:1.

[0099] The specification of the flake graphite is 150 mesh;

[0100] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0101] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0102] The preparation method of the above-mentioned low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A10 is obtained.

[0103] Embodiment 11

[0104] A low-temperature controllable expanded graphite plugging agent A11 comprises the following raw materials in parts by mass: 8 parts of flake graphite, 60 parts of oxidant, 20 parts of intercalant, and 10 parts of pretreatment agent, wherein the mass ratio of the oxidant to the intercalant is 3:1.

[0105] The specification of the flake graphite is 150 mesh;

[0106] The oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is 3:1, the concentration of the aqueous ammonium persulfate solution is 50%, and the concentration of the aqueous potassium permanganate solution is 4%;

[0107] The intercalation agent is concentrated sulfuric acid; the pretreatment agent is aqueous hydrogen peroxide solution.

[0108] The preparation method of the low-temperature controllable expanded graphite plugging agent is as described in Example 1, and the low-temperature controllable expanded graphite plugging agent A11 is obtained.

[0109] Comparative Example 1

[0110] An expanded graphite plugging agent B1 is as described in Example 1, except that the specification of the flake graphite is 32 mesh, and other conditions are the same as in Example 1.

[0111] In this comparative example, the preparation method of the expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B1.

[0112] Comparative Example 2

[0113] An expanded graphite plugging agent B2 is as described in Example 1, except that the mass fraction of flake graphite is 20 parts, and other conditions are the same as in Example 1.

[0114] In this comparative example, the preparation method of the expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B2.

[0115] Comparative Example 3

[0116] An expanded graphite plugging agent B3 is as described in Example 1, except that the mass fraction of the oxidant is 80 parts, and other conditions are the same as in Example 1.

[0117] In this comparative example, the preparation method of the expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B3.

[0118] Comparative Example 4

[0119] An expanded graphite plugging agent B4 is as described in Example 1, except that the mass fraction of the oxidant is 5 parts, and other conditions are the same as in Example 1.

[0120] In this comparative example, the preparation method of the above expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B4.

[0121] Comparative Example 5

[0122] An expanded graphite plugging agent B5 is as described in Example 1, except that the mass fraction of the intercalating agent is 50 parts, and other conditions are the same as in Example 1.

[0123] In this comparative example, the preparation method of the expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B5.

[0124] Comparative Example 6

[0125] An expanded graphite plugging agent B6 is as described in Example 1, except that the mass fraction of the intercalating agent is 5 parts, and other conditions are the same as in Example 1.

[0126] In this comparative example, the preparation method of the above expanded graphite plugging agent is as described in Example 1 to obtain expanded graphite plugging agent B6.

[0127] Test example

[0128] The graphite plugging agents obtained in Examples 1 to 11 and Comparative Examples 1 to 6 were first tested for thermal expansion capacity, and then added to the base slurry at a dosage of 3%, and the rheological properties before and after hot rolling at 200°C / 16h and the changes in high temperature and high pressure filtration properties were examined.

[0129] The base slurry has the following components: 300 parts by mass of water+1.5 parts by mass of sodium carbonate+21 parts by mass of bentonite.

[0130] Thermal expansion capacity test: accurately weigh 4.0g of the sample, measure the volume using the drainage method, and then place it in an aging tank filled with 400mL of deionized water, hot-roll at 200°C for different times, take it out and cool it to room temperature, then filter it. The filtered sample is dried at 60°C to constant weight, and the volume after thermal expansion is measured using the drainage method. The ratio of the volume after thermal expansion to the volume before hot rolling is the thermal expansion ratio at this stage. The experimental results are shown in Table 1.

[0131] Rheological properties test: Pour the prepared drilling fluid into the prepared sample cup, turn on the power, put the slurry cup in the test position, and make the drilling fluid level at the rotor engraved position. Press the switch to adjust the high and low speed gears, and record the readings of 600 rpm, 300 rpm, 200 rpm, 100 rpm, 6 rpm, and 3 rpm respectively. The experimental results are shown in Table 2.

[0132] High temperature and high pressure filtration performance evaluation: Install the filter paper and filter screen to the bottom of the filtration instrument, take 350mL of the aged drilling fluid and pour it into the filtration instrument, fix the upper and lower bottom covers to ensure good sealing. At the beginning of the experiment, the filtration pressure difference is guaranteed to be 3.5MPa and the temperature is set to 200℃. After 30 minutes, the volume of the filtrate is measured, and the filtrate volume is multiplied by 2 to obtain the high temperature and high pressure filtration loss. The experimental results are shown in Table 3.

[0133] Table 1. Thermal expansion data of graphite plugging agent at 200°C

[0134]

[0135]

[0136] Table 2. Rheological data of drilling fluid with graphite plugging agent after aging for 16 h at room temperature and 200 °C

[0137]

[0138]

[0139] Table 3. High temperature and high pressure filtration data of drilling fluid with graphite plugging agent after aging at 200℃ for 16h and 90 days

[0140]

[0141]

[0142] It can be seen from the data in Table 1 that the low-temperature controllable expanded graphite plugging agent of Example 1 of the present invention has an expansion rate of 3.1 for 2h and 5.9 for 16h in hot water at 200°C, indicating that the graphite plugging agent prepared according to the provided method has a low-temperature expansion characteristic; combined with the experimental results of Examples 2 and 3, it is shown that the graphite plugging agent prepared according to the provided method has a low-temperature controllable expansion characteristic; combined with the experimental results of Example 4, the expansion rate for 16h is 3.9, indicating that when the mass fraction of flake graphite is high, the expanded graphite prepared by effective intercalation accounts for The thermal expansion rate is relatively small, resulting in a small thermal expansion rate; combined with the experimental results of Example 5, the expansion rate of 16h is 5.8, indicating that when the mesh number of flake graphite is small, its thermal expansion effect is not greatly affected, because the graphite particle size becomes larger, and its intercalation effect is not greatly affected; combined with the experimental results of Example 6 and Example 7, when the mass proportion of the oxidant is large, the expansion rate of 16h is 5.1, and when the mass proportion of the oxidant is small, the expansion rate of 16h is 4.9, indicating that when the mass proportion of the oxidant is large or small, the final expansion rate will decrease, because the use of the oxidant When the amount is too large, the graphite sheets will be over-opened, and the intercalant will easily escape from the sheets. When the amount of oxidant is too small, the graphite sheets are not fully opened, which will reduce the effective intercalation material and lead to a small expansion rate. Combined with the experimental results of Example 8 and Example 9, when the mass proportion of the intercalant is too large, the expansion rate of 16h is 6.3, and when the mass proportion of the intercalant is too small, the expansion rate of 16h is 4.1, indicating that when the intercalant is excessive, the final expansion rate will slightly increase, but considering the cost, the increased expansion amount is not proportional to the consumption of the intercalant, and the amount of the intercalant is When the amount is too small, it will directly lead to a decrease in the amount of effective intercalation, resulting in a decrease in the final expansion rate. Combined with the experimental results of Example 10 and Example 11, when the mass proportion of the pretreatment agent is too large, the expansion rate of 16h is 5.9, and when the mass proportion of the pretreatment agent is too small, the expansion rate of 16h is 5.6, indicating that an excessive amount of the pretreatment agent has little effect on the experimental results. From an economic point of view, it is more appropriate to choose a smaller amount within the effective range. However, when its amount is too small, it will lead to insufficient removal of impurities between graphites, consume the amount of oxidant and intercalation agent, and reduce the final expansion rate.

[0143] It can be seen from the data in Table 2 that the expanded graphite plugging agent prepared in either the embodiment or the comparative example has little effect on the rheological properties of the base slurry before and after hot rolling. This is because both the flake graphite and the expanded graphite prepared by intercalation have a lamellar structure, which is prone to slippage when stacked, thus having little effect on the dynamic shear force of the base slurry. At the same time, the graphite material itself will not be hydrated and expanded, so it has little effect on the viscosity of the base slurry.

[0144] It can be seen from the data in Table 3 that the low-temperature controllable expanded graphite plugging agent prepared in Example 1 of the present invention has a good plugging effect. After adding 3% of the plugging agent, the filtration loss of the base slurry after hot rolling at 200°C for 16 hours is reduced from 135mL to 37mL, and the plugging rate is as high as 72.59%. At the same time, it has good long-term stability. The filtration loss of the base slurry after hot rolling at 200°C for 90 days is reduced from 187mL to 82mL, and the plugging rate is as high as 56.15%. This is because the lamellar structure of the graphite plugging agent is stacked on each other to make the mud cake formed thin and smooth. At the same time, it has a certain expansion capacity, so that the pores in the original structure are filled and become denser, and the pore diameter in the mud cake medium is further reduced, thereby enhancing the filtration reduction effect of the plugging layer; Combining Examples 2, 3, 4, 6, 7, 8, 9, 10, 11 and Comparative Examples 2, 3, 4, 5, 6, it can be seen that as the expansion capacity of the plugging agent decreases, its plugging effect will also decrease accordingly, because the pore diameter in the mud cake formed by it also increases accordingly, and conversely, as the expansion capacity of the plugging agent increases, its plugging effect will also increase accordingly, because the pore diameter in the mud cake formed by it also decreases accordingly; Combining Example 5 and Comparative Example 1, it can be seen that although the expansion capacity of the plugging agent has not changed significantly, the graphite particle sizes of 50 mesh and 32 mesh are large, and it is difficult to form a denser mud cake, so the plugging effect is poor.

[0145] From the above, it can be seen that the low-temperature controllable expanded graphite plugging agent prepared by the embodiment of the present invention has a good expansion effect in hot water, has little effect on the rheological properties of the base slurry, and has a good high-temperature and high-pressure filtration loss reduction ability. The above data show that the graphite plugging agent of the present invention has a low-temperature (200°C) controllable expansion ability and long-term stability, and has important research value in solving the problems such as well wall collapse encountered in high-temperature deep oil and gas drilling.

[0146] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A low-temperature controllable expanded graphite plugging agent, characterized in that: The low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 5 to 15 parts of flake graphite, 10 to 75 parts of oxidant, 10 to 45 parts of intercalation agent, and 10 to 45 parts of pretreatment agent.

2. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 5 to 10 parts of flake graphite, 20 to 60 parts of oxidant, 20 to 40 parts of intercalation agent and 20 to 40 parts of pretreatment agent.

3. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The low-temperature controllable expanded graphite plugging agent comprises the following raw materials in parts by mass: 8 parts of flake graphite, 40-60 parts of oxidant, 20-30 parts of intercalant, and 20 parts of pretreatment agent, wherein the mass ratio of oxidant to intercalant is (1-3):

1.

4. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The mesh specification of the flake graphite is 50 mesh, 100 mesh, 150 mesh or 300 mesh; Further preferably, the specification of the flake graphite is 150 mesh.

5. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The oxidant is any two or more of an aqueous solution of ammonium persulfate, an aqueous solution of potassium persulfate and an aqueous solution of potassium permanganate; Further preferably, the oxidant is a combination of an aqueous ammonium persulfate solution and an aqueous potassium permanganate solution, wherein the mass ratio of the aqueous ammonium persulfate solution to the aqueous potassium permanganate solution is (2-4):1, more preferably 3:1; The mass concentration of the ammonium persulfate aqueous solution is 40-60%, more preferably 50%; the mass concentration of the potassium permanganate aqueous solution is 2-6%, more preferably 4%.

6. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The intercalant is concentrated sulfuric acid, concentrated nitric acid or perchloric acid; Further preferably, the intercalant is concentrated sulfuric acid.

7. The low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The pretreatment agent is glacial acetic acid, aqueous hydrogen peroxide solution or hypochlorous acid; More preferably, the pretreatment agent is an aqueous solution of hydrogen peroxide.

8. The method for preparing the low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: The following steps are involved: 1) adding flake graphite to a pretreatment agent, stirring continuously at room temperature, washing with deionized water and filtering to obtain pretreated flake graphite, and then placing the pretreated flake graphite in a blast drying oven and drying to constant weight; 2) The dried flake graphite is placed in an oxidant, heated and stirred uniformly for the first time, and then an intercalation agent is added. After stirring uniformly for the second time, the mixture is washed with deionized water and filtered, and then placed in a blast drying oven and dried to constant weight to obtain a low-temperature controllable expanded graphite plugging agent.

9. The preparation method according to claim 8, characterized in that: In step 1), the stirring rate is 600 to 1000 rpm, the stirring time is 10 to 30 min, the mixture is washed with deionized water until the pH value is 4 to 7, and the drying oven temperature is 30 to 70° C.; Further preferably, the stirring rate is 600-800 rpm, the stirring time is 10-20 min, the mixture is washed with deionized water until the pH value is 6-7, and the drying oven temperature is 40-60° C.; In step 2), the first uniform stirring speed is 200-500 rpm, the stirring time is 20-40 min, and the stirring temperature is 40-80°C; the second uniform stirring speed is 400-800 rpm, the stirring time is 40-80 min, and the stirring temperature is 30-60°C; washing with deionized water until the pH is 4-7, and the drying oven temperature is 30-70°C; Further preferably, the first uniform stirring rate is 300-500 rpm, the stirring time is 30-40 min, and the stirring temperature is 50-70°C; the second uniform stirring rate is 500-700 rpm, the stirring time is 50-70 min, and the stirring temperature is 40-60°C; washing with deionized water to a pH of 6-7, and the drying oven temperature is 40-60°C.

10. The use of the low-temperature controllable expanded graphite plugging agent according to claim 1, characterized in that: Used for crack sealing in oil and gas wells; Further preferably, in the application, the applicable temperature of the low-temperature controllable expanded graphite plugging agent is 200-300°C, more preferably 200-260°C; the applicable formation microcrack range is 150-500 μm, more preferably 200-400 μm.

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