A method for evaluating the aqueous expansion performance of ultra-high temperature resistant expanded graphite plugging agent

Abstract

The present invention relates to a method for evaluating the aqueous expansion performance of an ultra-high temperature resistant expanded graphite plugging agent, and belongs to the technical field of drilling fluid treatment agents. The present invention provides a method for evaluating the aqueous expansion performance of an ultra-high temperature resistant expanded graphite plugging agent. The method first obtains a high-definition distribution map of expanded graphite in an aqueous phase using an optical microscope, then performs image processing on the map using Image J software and performs data analysis on the map using Origin drawing software, thereby obtaining thermal expansion data of the expanded graphite in an aqueous phase. Based on the 1 / 3 bridging rule, the 2 / 3 bridging rule, and target layer fracture information, an accurate mesh size specification suitable for the formation is given, thereby improving the matching degree between the plugging material and the formation fracture, reducing drilling fluid leakage, and reducing the risk of wellbore instability during the drilling process. In addition, the method is closer to the actual construction process, and the measurement results have stronger guiding significance for actual engineering applications.

Description

Technical Field

[0001] The invention relates to a method for evaluating the aqueous phase expansion performance of an ultra-high temperature resistant expanded graphite plugging agent, and belongs to the technical field of drilling fluid treatment agents. Background Art

[0002] Wellbore stability is a critical factor in ensuring smooth oil and gas exploration and production. It directly impacts the safety, production efficiency, and economic benefits of oil and gas wells. Wellbore stability issues can lead to wellbore collapse, reduced wellbore diameter, or even complete wellbore blockage, increasing operational risks and costs.

[0003] Plugging agents play a vital role in oilfield chemistry, particularly in ensuring wellbore stability. They are primarily used to control drilling fluid loss and prevent excessive erosion and collapse of the wellbore rock. By effectively blocking rock pores and cracks, plugging agents help maintain wellbore integrity and stability, reducing nonproductive time (NPT) during drilling. The selection and use of plugging agents should be based on factors such as rock type, wellbore conditions, and drilling fluid properties. High-quality plugging agents can improve drilling fluid stability and reduce damage to the wellbore, thereby increasing oil and gas well production and efficiency. Plugging agents can also reduce environmental impact and avoid potential pollution caused by wellbore instability.

[0004] Expanded graphite, a potential plugging agent in drilling fluids, has attracted attention due to its unique physical and chemical properties. Its high compressive strength, excellent thermal stability, and superior adsorption capacity effectively seal rock pores and cracks, reducing drilling fluid loss. Expanded graphite's superior plugging performance is primarily due to its layered structure and high expansibility, which enable it to form stable plugging bridges in drilling fluids, thereby enhancing wellbore stability.

[0005] However, the feasibility of expanded graphite as a plugging agent requires further research and experimental verification. Because its plugging effect in drilling fluid systems primarily occurs through expansion in an aqueous environment, the crack matching relationship caused by particle size increase due to thermal expansion in the wellbore before entering the formation must also be considered. Currently, research on the expansion properties of expanded graphite primarily refers to the National Standard of the People's Republic of China, GB / T 10698-1989, "Expandable Graphite." This standard provides expansion performance measurement methods in a gaseous environment, and the data obtained have certain limitations in guiding the practical application of expanded graphite in drilling fluids.

[0006] Therefore, providing a method for measuring the expansion performance of expanded graphite in an aqueous environment has an important guiding role in the evaluation of the plugging effect of expanded graphite in the field of drilling fluid and its actual field application, so as to better solve the problem of wellbore instability in ultra-high temperature formations. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention provides a method for evaluating the aqueous expansion properties of ultrahigh-temperature resistant expanded graphite plugging agents. This method better reflects the real-world application of expanded graphite as a drilling fluid plugging agent. It also mitigates the impact of increased cavity volume caused by the stacking of expanded particles in traditional gas-phase evaluation methods. The data obtained using this method provides greater practical guidance.

[0008] The technical solutions of the present invention are as follows:

[0009] A method for evaluating the aqueous phase expansion performance of an ultra-high temperature resistant expanded graphite plugging agent comprises the following steps:

[0010] (1) Weigh k parts of expanded graphite with a mass of m0, place them under an optical microscope for observation and take pictures, and obtain optical pictures P1~P k ; Then put it into a volume of deionized water V0, and heat it at a temperature of T0 for t0 hours;

[0011] (2) After the hot-rolled expanded graphite is cooled to room temperature, it is stirred evenly, placed under an optical microscope for observation and photographing, and an optical picture P is obtained. k+1 ~P 2k ;

[0012] (3) Use Image J software to process optical images P1~P k and optical images P k+1 ~P 2k , get the measurement data after Image J processing;

[0013] (4) Based on the measured data processed by Image J, the particle size distribution diagram of expanded graphite was drawn using Origin drawing software to obtain the particle size data d0 and d t and standard deviations σ0, σ t ;

[0014] (5) Repeat steps (2) to (4) k times to obtain k particle size data d0, d1 before and after thermal expansion of the expanded graphite in the aqueous phase. t and standard deviation σ0, σ t Calculate the average particle size data d0' and d t ' and standard deviation mean σ0', σ t ';

[0015] (6) First, according to the average value of expanded graphite particle size data d0', d t ' and standard deviation mean σ0', σ t', calculate the average expansion ratio r; then according to the average expansion ratio r and the size of the formation fracture to be blocked d m After calculation, the required mesh size of expanded graphite plugging agent is determined based on the size of the formation fracture and the expansion performance of the expanded graphite phase.

[0016] Preferably, according to the present invention, in step (1), 80<V0 / m0<120, 25℃<T0<300℃, 0h<t0<16h; the unit of mass m0 is g, the unit of volume V0 is mL, the unit of temperature T0 is ℃, and the unit of time t0 is h.

[0017] According to the preferred embodiment of the present invention, in step (1), the stirring condition is: stirring at 1800-2200 r / min for 10-20 min.

[0018] According to a preferred embodiment of the present invention, in step (3), the specific method of processing the optical image using Image J software is as follows:

[0019] a. Open Image J software and click File→Open to import optical images P1~P k and optical images P k+1 ~P 2k ;

[0020] b. Select Straight Line in the optical image P1~P k and optical images P k+1 ~P 2k Draw a straight line between the starting point and the end point in the scale;

[0021] c. Click Analyze → Set Scale to open the scale setting window;

[0022] d. Enter the actual length of the line in Known distance and the length unit w in Unit of length.

[0023] e. Click Analyze → Tools → ROI Manger to open the measurement interface. Use the line tool to select at least y sample points. After adding, click Measure to obtain the measurement data processed by Image J in .csv format.

[0024] According to the preferred embodiment of the present invention, in step (4), the specific method of using Origin drawing software to draw the particle size distribution diagram of expanded graphite is as follows:

[0025] 1) Open the measured data processed by Image J, copy the Length column data into the Origin drawing software, open the drawing tab, select the distribution chart in the statistical chart to draw, and obtain the particle size distribution chart;

[0026] 2) Click the Statistics tab and select Column Statistics in Descriptive Statistics to obtain the particle size data d0 and d t and standard deviations σ0, σ t .

[0027] According to the preferred embodiment of the present invention, in step (5), the average values ​​of the particle size data d0' and d0' of the expanded graphite before and after thermal expansion in the aqueous phase are calculated. t ' and standard deviation mean σ0', σ t The formula for ' is as follows:

[0028]

[0029] Where d0 is the particle size of expanded graphite before thermal expansion in water phase, d t is the particle size of expanded graphite after thermal expansion in water phase, σ0 is the standard deviation of expanded graphite before thermal expansion in water phase, σ t is the standard deviation of expanded graphite after thermal expansion in water phase, and k is the number of expanded graphite.

[0030] According to the preferred embodiment of the present invention, in step (6), the formula for calculating the average expansion ratio r is as follows:

[0031]

[0032] Where d0' is the average particle size of expanded graphite before thermal expansion in water phase, d t ' is the average particle size of expanded graphite after thermal expansion in water phase, σ0' is the average standard deviation of expanded graphite before thermal expansion in water phase, σ t ' is the average standard deviation of expanded graphite after thermal expansion in water phase.

[0033] According to the preferred embodiment of the present invention, in step (6), according to the average expansion ratio r and the size d of the formation crack to be plugged m After calculation, the method to determine the required mesh size of expanded graphite plugging agent under the results of the formation fracture size and the expansion performance of the expanded graphite phase is: according to the 1 / 3 bridging and 2 / 3 bridging rules, in d m / 3 and 2d m / 3 Rigid particles within the particle size range can be used to penetrate the formation cracks m Form an effective plugging; combined with the calculated expansion ratio r, the required expanded graphite plugging agent particle size d is obtained m / 3r and 2d m / 3r, according to this particle size range, the required mesh size of expanded graphite plugging agent is obtained.

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

[0035] 1. The present invention provides a method for evaluating the aqueous expansion performance of an ultra-high temperature resistant expanded graphite plugging agent. The method comprises the following steps: first, obtaining a high-definition distribution map of expanded graphite in an aqueous phase using an optical microscope, performing image processing on the map using Image J software, and performing data analysis on the map using Origin drawing software, thereby obtaining the thermal expansion data of the expanded graphite in an aqueous phase. Based on the 1 / 3 bridging rule, the 2 / 3 bridging rule, and information on target layer fractures, an accurate mesh size specification applicable to the formation is given, thereby improving the matching degree between the plugging material and the formation fractures, reducing drilling fluid loss, and reducing the risk of wellbore instability during drilling.

[0036] 2. The evaluation method for the aqueous phase expansion performance of the expanded graphite plugging agent provided by the present invention is mainly obtained by image processing of Image J software, combined with the data analysis function and statistical principles of Origin software to obtain the expansion data of the expanded graphite plugging agent in the aqueous phase. Compared with the traditional method, it has the following advantages: First, the traditional method is to measure the expansion ratio of the sample in the gas phase, which is different from the actual application environment of the expanded graphite plugging agent. The measured data has limited guiding significance for the actual application process, while the evaluation method of the present invention can measure the expansion data of the graphite plugging agent in the aqueous phase, which is closer to its actual use environment; Second, the measurement unit of the traditional method is mL / g, and the expanded graphite plugging agent has a large number of cavities generated by particle accumulation after thermal expansion in the gas phase, so that the measured data is much larger than the actual The evaluation method of the present invention uses an optical microscope to collect particle size data of the expanded graphite plugging agent before and after thermal expansion in the aqueous phase, and processes and analyzes the data based on statistical principles, so that the measurement results are closer to the actual values. Third, in the traditional method test, the environment must be preheated first, and the temperature rises rapidly during the test. In the actual application environment, the expanded graphite plugging agent gradually heats up as the drilling fluid is transported from the ground to the target formation. During this process, the agent inserted into the graphite sheet will be partially lost due to diffusion, which directly affects the final expansion effect. The evaluation method used in the present invention is closer to the actual construction process, and the measurement results have stronger guiding significance for actual engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the process of measuring the particle size of the expanded graphite plugging agent in the water phase before thermal expansion;

[0038] In the figure, (a) Image J is used to import high-definition images, (b) the scale is set, (c) points are selected to measure particle size, and (d) Orgin is used to draw and process data.

[0039] Figure 2 This is the process of measuring the particle size of expanded graphite plugging agent in water phase after thermal expansion;

[0040] In the figure, (a) Image J is used to import high-definition images, (b) the scale is set, (c) points are selected to measure particle size, and (d) Orgin is used to draw and process data.

[0041] Figure 3 The structure diagram of the natural core flooding device for evaluating the plugging effect of expanded graphite plugging agent;

[0042] In the figure, 1. Deionized water storage tank, 2. Constant flow pump, 3. First intermediate container, 4. Second intermediate container, 5. Core holder, 6. Computer data acquisition system, 7. Waste liquid barrel, 8. Inlet pressure gauge, 9. Confining pressure gauge. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, they will be described in detail below with reference to the accompanying drawings and specific embodiments, but are not limited thereto. Matters not fully described in the present invention shall be based on conventional techniques in the art.

[0044] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

[0045] The high temperature resistant modified expanded graphite used in the examples was purchased from Qingdao Hengrunda Graphite Co., Ltd.

[0046] Example 1

[0047] A method for evaluating the aqueous phase expansion performance of an ultra-high temperature resistant expanded graphite plugging agent comprises the following steps:

[0048] (1) First, 100 g of 300-mesh expanded graphite was poured onto kraft paper, stirred evenly with a glass rod, and placed in a Petri dish. Five portions of 4 g of expanded graphite were taken out using the point-taking method, and each portion was observed and photographed under an optical microscope. High-definition images with scale bars were derived to obtain optical images P1 to P5. The resulting mixture was then placed in 400 mL of deionized water and hot-rolled at 200°C for 2 hours.

[0049] (2) After the hot-rolled expanded graphite is cooled to room temperature, it is stirred at 2000 r / min for 15 min. After the stirring stops, the sample in the middle is taken with a rubber-tipped dropper, and two drops are dropped on a glass slide. The sample is covered with a cover glass and placed under an optical microscope for observation and photography. A high-definition picture with a scale bar is exported to obtain optical pictures P6 to P 10 ;

[0050] (3) Figures 1-2 As shown, the optical images P1 to P 10 , get the measurement data after Image J processing;

[0051] The specific method of using Image J software to process optical images is as follows:

[0052] a. Open Image J software and click File→Open to import optical images P1~P k and optical images P k+1 ~P 2k ;

[0053] b. Select Straight Line in the optical image P1~P k and optical images P k+1 ~P 2k Draw a straight line between the starting point and the end point in the scale;

[0054] c. Click Analyze → Set Scale to open the scale setting window;

[0055] d. Enter the actual length of the line in Known distance and the length unit w in Unit of length.

[0056] e. Click Analyze → Tools → ROI Manager to open the measurement interface. Use the line tool to select at least y sample points. After adding, click Measure to obtain the Image J-processed measurement data in .csv format.

[0057] (4) Based on the measured data processed by Image J, the particle size distribution diagram of expanded graphite was drawn using Origin drawing software to obtain the particle size data d0 and d t and standard deviations σ0, σ t ;

[0058] The specific method for drawing the particle size distribution diagram of expanded graphite using Origin drawing software is as follows:

[0059] 1) Open the measured data processed by Image J, copy the Length column data into the Origin drawing software, open the drawing tab, select the distribution chart in the statistical chart to draw, and obtain the particle size distribution chart;

[0060] 2) Click the Statistics tab and select Column Statistics in Descriptive Statistics to obtain the particle size data d0 and d t and standard deviations σ0, σ t ;

[0061] (5) Repeat steps (2) to (4) for a total of 5 times to obtain the particle size data d0, d1, and d2 of the expanded graphite before and after thermal expansion in the aqueous phase. t and standard deviation σ0, σ t The average particle size data d0' and d t ' and standard deviation mean σ0', σ t ';

[0062] Calculate the average particle size data d0' and d0' of expanded graphite before and after thermal expansion in water phase t ' and standard deviation mean σ0', σ t The formula for ' is as follows:

[0063]

[0064] Where d0 is the particle size of expanded graphite before thermal expansion in water phase, d t is the particle size of expanded graphite after thermal expansion in water phase, σ0 is the standard deviation of expanded graphite before thermal expansion in water phase, σ t is the standard deviation of expanded graphite after thermal expansion in water phase, k is the number of expanded graphite;

[0065] The average particle size data d0' of the expanded graphite before thermal expansion in the aqueous phase is 41.10 μm, and the average particle size data after thermal expansion is 327.21 μm, and the corresponding standard deviation average σ0' is 4.3 μm and σ t ' is 8.7μm;

[0066] (6) First, according to the average value of expanded graphite particle size data d0', d t ' and standard deviation mean σ0', σ t ', the average expansion ratio is calculated to be about 6.97 times, and the calculation formula is as follows:

[0067]

[0068] Where d0' is the average particle size of expanded graphite before thermal expansion in water phase, d t' is the average particle size of expanded graphite after thermal expansion in water phase, σ0' is the average standard deviation of expanded graphite before thermal expansion in water phase, σ t ' is the average standard deviation of expanded graphite after thermal expansion in water phase.

[0069] In this example, a natural rock core with a formation fracture size of 900 μm is used for plugging. Based on the 1 / 3 bridging and 2 / 3 bridging rules, the required mesh size of the expanded graphite plugging agent is 300 mesh, given the formation fracture size (900 μm) and the expansion ratio of the expanded graphite phase (6.97 times). The specific calculation method is as follows:

[0070] The particle size of the expanded graphite plugging agent required in this embodiment is d m / 3r and 2d m / 3r. Combining the formation fracture data (900 μm) and the expanded graphite phase expansion ratio (6.97x) in this example, it can be determined that the required expanded graphite plugging agent particle size range is approximately between 43 μm and 86 μm, that is, approximately between 200 mesh and 325 mesh. Considering the mesh size specifications of existing expanded graphite plugging agents, the required expanded graphite plugging agent mesh size is 300 mesh. The relevant data calculation results are shown in Table 1.

[0071] Table 1. Parameters and experimental conditions required to calculate the average expansion ratio of graphite plugging agent in water phase

[0072]

[0073]

[0074] Example 2

[0075] A method for evaluating the aqueous expansion performance of an ultrahigh temperature resistant expanded graphite plugging agent. The experimental operation and calculation method are similar to those in Example 1, except that the mesh size of the expanded graphite plugging agent used in the test is 200 mesh.

[0076] According to the test and calculation results, the average particle size data d0' of the expanded graphite before thermal expansion in the aqueous phase is 71.20μm, and the average particle size data after thermal expansion is 570.70μm, and the corresponding standard deviation average σ0' is 5.7μm and σ t ' is 12.3 μm, first according to the average value d0' and d t ' and standard deviation mean σ0', σ t ', the calculated average expansion ratio is about 7.02 times.

[0077] In this example, the natural rock core to be plugged has a formation fracture size of 1.5 mm. Based on the 1 / 3 bridging and 2 / 3 bridging rules, the required mesh size of the expanded graphite plugging agent is 200 mesh, given the formation fracture size (1.5 mm) and the expansion ratio of the expanded graphite phase. The specific calculation method is as follows:

[0078] According to the aforementioned invention method, the required expanded graphite plugging agent particle size is d m / 3r and 2d m / 3r. Combining the formation fracture data and the expansion ratio of the expanded graphite phase in this example, it can be determined that the required expanded graphite plugging agent particle size range is approximately between 71.23 μm and 142.45 μm, that is, approximately between 100 mesh and 200 mesh. Based on the mesh size specifications of existing expanded graphite plugging agents, the required expanded graphite plugging agent mesh size is 200 mesh. The relevant data calculation results are shown in Table 2.

[0079] Table 2. Parameters and experimental conditions required to calculate the average expansion ratio of graphite plugging agent in water phase

[0080]

[0081]

[0082] Comparative Example 1

[0083] This comparative example takes the expansion test method of 300-mesh expanded graphite in the gas phase as an example, and adopts the traditional method to evaluate the expansion capacity of the graphite plugging agent. The specific steps are as follows:

[0084] (1) First, pour 100g of 300-mesh expanded graphite on kraft paper, stir it evenly with a glass rod, place it in a petri dish, and take out five samples of 4g each using the point sampling method;

[0085] (2) Take one of the samples and place it in a quartz beaker that has been burned at 200°C for 5 minutes. Immediately place it in a high-temperature furnace at 200°C. Take it out after 2 hours and read the volume V after the sample expands. i (Read the average value of the corresponding scales of the highest and lowest points on the top surface);

[0086] (3) The same operation is performed on the other four samples. The average expansion ratio r0 of the samples is calculated according to formula (6):

[0087]

[0088] The calculation results are shown in Table 3.

[0089] As can be seen from the data in Table 3, the traditional method can only determine the volume after expansion. At the same time, the expansion ratio measured based on this method has limited guiding role in the actual application of graphite plugging agents.

[0090] Table 3. Parameters and experimental conditions required to calculate the average expansion ratio of graphite plugging agent in the gas phase

[0091]

[0092]

[0093] Test example

[0094] This test example uses a natural core flooding experimental device to measure the effect of the expanded graphite plugging agent evaluated in Example 1 on plugging a 900 μm natural core. The structure of the natural core flooding experimental device is as follows: Figure 3 As shown, it includes a deionized water storage tank 1, a constant flow pump 2, a first intermediate container 3, a second intermediate container 4, a core clamp 5 and a waste liquid barrel 7 connected in sequence by pipelines; wherein the first intermediate container 3 and the second intermediate container 4 are connected in parallel, the tops of the two are connected to the side of the core clamp 5, and an inlet pressure gauge 8 and a pipeline valve are provided on the connected pipeline, and the bottoms of the two are connected to the bottom of the core clamp 5, and a confining pressure gauge 9 and a pipeline valve are provided on the connected pipeline; the natural core displacement experimental device also has a computer data acquisition system to receive and process information data from the inlet pressure gauge 8 and the confining pressure gauge 9.

[0095] The specific measurement steps are as follows:

[0096] 1) Adjust the oven temperature to 200°C;

[0097] 2) Place a natural core with an average microcrack size of 900 μm into the core holder 5, connect the pipeline, and apply a ring pressure to 10 MPa;

[0098] 3) Fill the first intermediate container 3 with base slurry (prepared with 4% bentonite), close the valve of the plugging agent injection pipeline, open the valve of the base slurry injection pipeline, and saturate the fracture core with base slurry at an injection rate of 9.0 mL / min until base slurry continuously flows out of the outlet;

[0099] 4) Add 400 mL of drilling fluid containing the 300-mesh expanded graphite plugging agent described in Example 1 (prepared with 4% bentonite and a 300-mesh expanded graphite plugging agent mass concentration of 1%) after high-temperature rolling at 200° C. for 2 h to the second intermediate container 4, maintaining a stirring rate of 200-300 r / min;

[0100] 5) Close the valve of the base slurry injection pipeline, open the valve of the plugging agent injection pipeline, and inject the plugging agent into the fracture core at an injection rate of 5.0 mL / min until continuous drilling fluid flows out of the outlet. Use a computer data acquisition system to record and process pressure changes in real time. The results are shown in Table 4.

[0101] Table 4. HTHP displacement test results

[0102] Serial number <![CDATA[Average microfracture size of natural core, d m > HTHP flooding test results Example 1 900μm Maximum pressure bearing capacity 6.8MPa Example 2 1.5mm Maximum pressure bearing capacity 6.4MPa

[0103] The data in Table 4 show that when a natural core with an average microcrack of 900 μm was used for the high-temperature and high-pressure displacement experiment, the maximum pressure bearing capacity was 6.8 MPa. When a natural core with an average microcrack of 1.5 mm was used for the high-temperature and high-pressure displacement experiment, the maximum pressure bearing capacity was 6.4 MPa. This indicates that the expansion performance measurement method of the expanded graphite plugging agent in the aqueous phase evaluated in Examples 1 and 2 of the present invention has certain guiding significance for its actual plugging effect and on-site construction.

[0104] The above describes the specific embodiments of the present invention in detail, but the present invention is not limited thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the aqueous expansion performance of an ultra-high temperature resistant expanded graphite plugging agent, characterized in that: The following steps are involved: (1) Weigh k parts of expanded graphite with a mass of m0, place them under an optical microscope for observation and take pictures, and obtain optical pictures P1~P k ; Then put it into a volume of deionized water V0, and heat it at a temperature of T0 for t0 hours; (2) After the hot-rolled expanded graphite is cooled to room temperature, it is stirred evenly, placed under an optical microscope for observation and photographing, and an optical picture P is obtained. k+1 ~P 2k ; (3) Use Image J software to process optical images P1~P k and optical images P k+1 ~P 2k , get the measurement data after Image J processing; (4) Based on the measured data processed by Image J, the particle size distribution diagram of expanded graphite was drawn using Origin drawing software to obtain the particle size data d0 and d t and standard deviations σ0, σ t ; (5) Repeat steps (2) to (4) k times to obtain k particle size data d0, d1 before and after thermal expansion of the expanded graphite in the aqueous phase. t and standard deviation σ0, σ t The average particle size data d0' and d t ' and standard deviation mean σ0', σ t '; (6) First, according to the average value of expanded graphite particle size data d0', d t ' and standard deviation mean σ0', σ t ', calculate the average expansion ratio r; then according to the average expansion ratio r and the size of the formation fracture to be blocked d m After calculation, the required mesh size of expanded graphite plugging agent is determined based on the size of the formation fracture and the expansion performance of the expanded graphite phase.

2. The evaluation method according to claim 1, wherein In step (1), 80<V0 / m0<120, 25℃<T0<300℃, 0h<t0<16h; the unit of mass m0 is g, the unit of volume V0 is mL, the unit of temperature T0 is ℃, and the unit of time t0 is h.

3. The evaluation method according to claim 1, wherein In step (1), the stirring condition is: stirring at 1800-2200 r / min for 10-20 min.

4. The evaluation method according to claim 1, wherein: In step (3), the specific method of using Image J software to process the optical image is as follows: a. Open Image J software and click File→Open to import optical images P1~P k and optical images P k+1 ~P 2k ; b. Select Straight Line in the optical image P1~P k and optical images P k+1 ~P 2k Draw a straight line between the starting point and the end point in the scale; c. Click Analyze → Set Scale to open the scale setting window; d. Enter the actual length of the line in Known distance and the length unit w in Unit of length. e. Click Analyze → Tools → ROI Manger to open the measurement interface. Use the line tool to select at least y sample points. After adding, click Measure to obtain the measurement data processed by Image J in .csv format.

5. The evaluation method according to claim 1, wherein: In step (4), the specific method of using Origin drawing software to draw the particle size distribution diagram of expanded graphite is as follows: 1) Open the measured data processed by Image J, copy the Length column data into the Origin drawing software, open the drawing tab, select the distribution chart in the statistical chart to draw, and obtain the particle size distribution chart; 2) Click the Statistics tab and select Column Statistics in Descriptive Statistics to obtain the particle size data d0 and d t and standard deviations σ0, σ t .

6. The evaluation method according to claim 1, wherein: In step (5), the average values ​​of the particle size data d0' and d t ' and standard deviation mean σ0', σ t The formula for ' is as follows: Where d0 is the particle size of expanded graphite before thermal expansion in water phase, d t is the particle size of expanded graphite after thermal expansion in water phase, σ0 is the standard deviation of expanded graphite before thermal expansion in water phase, σ t is the standard deviation of expanded graphite after thermal expansion in water phase, and k is the number of expanded graphite.

7. The evaluation method according to claim 1, wherein: In step (6), the formula for calculating the average expansion ratio r is as follows: Where d0' is the average particle size of expanded graphite before thermal expansion in water phase, d t ' is the average particle size of expanded graphite after thermal expansion in water phase, σ0' is the average standard deviation of expanded graphite before thermal expansion in water phase, σ t ' is the average standard deviation of expanded graphite after thermal expansion in water phase.

8. The evaluation method according to claim 1, wherein: In step (6), according to the average expansion ratio r and the size d of the formation crack to be plugged m After calculation, the method to determine the required mesh size of expanded graphite plugging agent under the results of the formation fracture size and the expansion performance of the expanded graphite phase is: according to the 1 / 3 bridging and 2 / 3 bridging rules, in d m / 3 and 2d m / 3 Rigid particles within the particle size range can be used to penetrate the formation cracks m Form an effective plugging; combined with the calculated expansion ratio r, the required expanded graphite plugging agent particle size d is obtained m / 3r and 2d m / 3r, according to this particle size range, the required mesh size of expanded graphite plugging agent is obtained.

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