Device and method for measuring sedimentation characteristic of micro-proppant in rock crack by using laser

Abstract

The invention relates to a device and a method for measuring the sedimentation characteristic of a micro-proppant in a rock crack by using laser, and belongs to the field of unconventional oil and gas development. The device mainly comprises a laser transmitter, a light source sensor, a rock crack model, a settling tank and a data transmission and collection system. The method comprises the following steps: determining the relationship between the particle size of the micro-proppant and the optical signal intensity; preparing rock fracture models with different parameters and micro-proppant sand mixing liquid; a laser transmitting and receiving system is arranged along the crack laser path, and optical signals are monitored; and determining the migration trajectory of the proppant according to the signal intensities of different positions, and inverting the dynamic particle size distribution under the interaction of the crack-micro proppant. According to the method, the position of the micro-proppant is positioned through disturbance of the laser signal in the rock crack, the problems that the micro-proppant is difficult to clearly identify and the test error is large in a visualization method are solved, accurate description of the sedimentation track of the micro-proppant in the rock crack is realized, and the method is suitable for characterizing the sedimentation behavior of the micro-proppant in the real rock crack.

Description

Technical Field

[0001] The invention relates to a device and a method for measuring the settlement characteristics of micro-proppant in rock cracks by utilizing laser, and belongs to the technical field of oil and gas field development. Background Art

[0002] The development of unconventional oil and gas, such as shale oil and gas, tight oil and gas, and coalbed methane, is an important way to alleviate my country's energy supply and demand. Due to the poor physical properties, low porosity and low permeability of unconventional reservoirs, hydraulic fracturing is needed to form a high-permeability fracture network to provide channels for fluid flow. Currently, fracturing operations mostly use proppants of 100 mesh and below, resulting in a large number of fractures with a width of less than 150μm (100 mesh) not being effectively supported, reducing the effective reservoir reconstruction volume. To improve the fracturing effect, domestic and foreign scholars have proposed using microproppants (greater than 200 mesh) to fill microfractures and expand the effective support volume of fractures. Palisch et al. added 113.4 tons of 325 mesh microproppants during hydraulic fracturing operations in a well in the Bakken oil field, increasing production by approximately 15%.

[0003] The sedimentation velocity of the proppant affects its migration and placement within the fracture, determines the proportion of effectively supported fractures, and is a key indicator affecting the effectiveness of fracturing transformation. Currently, visualization methods are mostly used to study the sedimentation patterns of proppants in smooth measuring cylinders or sedimentation tanks and simulated rough fractures. The sedimentation velocity of the proppant is calculated by measuring the sedimentation distance and time of the proppant particles. However, due to the small particle size of the microproppant and its interaction with the fracture wall, conventional characterization methods are difficult to accurately characterize the sedimentation behavior of microproppants in rock fractures. For example, the particle sizes of 300-mesh and 800-mesh microproppants are 48 microns and 18 microns, respectively. It is difficult to clearly capture the sedimentation trajectory of the proppant through high-speed cameras or direct observation. Focusing the microproppant with various microscopes will result in a smaller field of view and increase the measurement error. For rough fractures, in order to meet the needs of visualizing proppant sedimentation, the industry often uses etching, 3D printing and other methods to prepare transparent fracture models for experiments. The simulated fracture materials are usually translucent materials such as glass or transparent plastic, ignoring the effects of fracturing fluid loss, rock wettability and adsorption properties on proppant sedimentation. Summary of the Invention

[0004] The purpose of the present invention is to address the problems existing in the prior art and provide a device and method for measuring the settlement characteristics of microproppants in rock fractures using laser. The position of the microproppant is located by perturbation of the laser signal, which overcomes the problem that visualization methods cannot clearly identify the microproppant and have large test errors, and realizes the accurate characterization of the microproppant settlement trajectory.

[0005] The present invention provides a technical solution to solve the above technical problems: a device for measuring the settlement characteristics of microproppants in rock fractures using laser, comprising a laser emitter, a light source sensor, a rock fracture model, a settlement tank, fixing bolts, wires, a power supply, a data cable and a computer;

[0006] The rock fracture model is fixed in the sedimentation tank by fixing bolts, and the laser emitter and light source sensor are arranged on both sides of the sedimentation tank relative to each other;

[0007] The laser emitter and light source sensor are connected to the power supply and computer via electric wires and data cables respectively;

[0008] The bottoms of the light source sensor, the sedimentation tank and the laser emitter are respectively provided with a base I, a base II and a base III.

[0009] A method for measuring the settlement characteristics of microproppants in rock fractures using laser, comprising the following steps:

[0010] Step S10: assembling a device for measuring the settlement characteristics of microproppants in rock fractures using laser, and setting up an experimental device;

[0011] Step S20: Conducting sedimentation calibration experiments on microproppants with different particle sizes to obtain a relationship between particle size d and normalized light signal intensity P;

[0012] Step S30: preparing rock fracture models with different lithologies, fracture widths, branch fractures, and complex fracture networks, and conducting microproppant settling experiments to obtain optical signal intensity data at different fracture locations;

[0013] Step S40: According to the relationship between the light signal intensity data at different fracture positions, the particle size d and the normalized light signal intensity P, the dynamic particle size distribution under the fracture-microproppant interaction of different fracture inversions is determined, and the influence of fracture parameters on the microproppant sedimentation is determined.

[0014] A further technical solution is that the specific process of setting up the experimental device in step S10 is:

[0015] Step S11, filling the sedimentation tank with liquid to make the liquid level level;

[0016] Step S12: a laser transmitter is arranged on the side of the sedimentation tank, and the laser transmitter emits a laser beam toward the sedimentation tank;

[0017] Step S13: Arrange a light source sensor on the other side of the sedimentation tank so that the light source sensor 2 receives the laser emitted by the laser transmitter, and the computer records the initial light signal intensity P0.

[0018] A further technical solution is that the laser emitted by the laser emitter in step S12 is perpendicular to the side of the sedimentation tank.

[0019] A further technical solution is that the specific process of the microproppant sedimentation calibration experiment in step S20 is as follows: measuring in a smooth sedimentation tank, selecting microproppant of a single particle size to prepare a low sand ratio sand mixing liquid, and using ultrasonic vibration to reduce the influence of particle agglomeration, and finally releasing the sand mixing liquid below the liquid surface of the sedimentation tank; when the microproppant is completely irradiated by the laser, recording the light signal intensity P at this time i .

[0020] A further technical solution is that the particle size range of the micro-proppant in step S20 is: 200-800 mesh.

[0021] A further technical solution is that the relationship between the particle size d and the normalized light signal intensity P is obtained by the following steps: i Normalization is performed to obtain the normalized light signal intensity, and a curve of the normalized light signal intensity and the particle size is drawn; the curve is then fitted to obtain a relationship between the normalized light signal intensity and the particle size, and converted into a relationship between the particle size d and the normalized light signal intensity P.

[0022] A further technical solution is that the calculation formula of the normalized optical signal intensity is: P = P i / P0.

[0023] A further technical solution is that the specific process of the microproppant sedimentation experiment in step S50 is as follows:

[0024] Step S51: Create cracks in the rock through Brazilian splitting or hydraulic fracturing experiments, cut the rock into cubes using a cutting machine, retain the cracked parts, and prepare a rock crack model;

[0025] Step S52: Place the rock fracture model in a sedimentation tank, so that the light source sensor receives the laser light emitted by the laser transmitter and penetrates the fracture, and the computer records the position of each laser beam that can penetrate the fracture and the light signal intensity;

[0026] Step S53: preparing micro-proppant sand-mixing fluids with different sand ratios, and releasing the sand-mixing fluids below the fracture liquid surface;

[0027] Step S54: The micro-proppant particles continue to settle and disturb the laser beam when passing through it, changing the intensity of the light signal received by the light source sensor at that position. The computer monitors the laser signal in real time and obtains the laser beam light signal change time Δt at each position. i ;

[0028] Step S55: After the micro-proppant is settled, the computer calculates the laser beam signal change time Δt according to the laser diameter D and each position.i , calculate the sedimentation velocity v of the microproppant when it passes through each laser beam i =D / △t i , clarify the evolution law of the settlement velocity of microproppant at different positions in the rock fracture model, and obtain the average settlement velocity of microproppant by arithmetic average.

[0029] The beneficial effects of the present invention are as follows: the device and method for determining the settlement of microproppants in rock fractures proposed in the present invention can be used to characterize the settlement velocity of microproppants below 800 mesh. Combined with the rock fracture model, it can carry out settlement experiments of proppants under different lithologies, fracture widths, branch fractures and complex fracture networks. The device and method have the characteristics of high test accuracy, economical and practical, and convenient operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0031] Figure 2 is a graph showing the relationship between normalized light signal intensity and particle size;

[0032] Figure 3 is a flow chart of the method of the present invention;

[0033] Figure 4 Schematic diagram of multiple laser points used to determine microproppant settling time based on laser signal changes;

[0034] Figure 5 This is a curve diagram showing the deviation between the calculated and measured values ​​of the settling velocity of microproppants with different mesh sizes.

[0035] As shown in the figure: 1-laser transmitter; 2-light source sensor; 3-rock crack model; 4-sedimentation tank; 5-laser beam; 6-fixing bolt; 7-adjustment knob I, 8-adjustment knob II, 9-adjustment knob III; 10-base I, 11-base II, 12-base III; 13-electric wires; 14-power supply; 15-data cable; 16-computer; 17-primary crack; 18-secondary crack; 19-front. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0037] Example 1

[0038] like Figure 1As shown, the present invention is a device for measuring the settlement characteristics of micro-proppants in rock fractures using laser. The device consists of three parts: a laser transmitting and receiving module, a rock fracture module, and a data acquisition and analysis module.

[0039] The laser emission and receiving module includes a laser emitter 1 and a light source sensor 2; the rock crack module includes a rock crack model 3 and a sedimentation tank 4; and the data acquisition and analysis module includes a computer 16;

[0040] The sedimentation tank 4 is a rectangular transparent container with an open top. The container is larger than the rock fracture model 3 to ensure that the fractures of the rock fracture model 3 are filled with fracturing fluid and prevent liquid leakage. The sedimentation tank 4 is made of a transparent material such as acrylic or PVC, which has good light transmittance and low refractive index. The laser transmitter 1 is 40 cm high, has a power of 100 mW, and can emit up to 10 laser beams. The laser spacing is 2 cm and the laser diameter is 2 mm. The rock fracture model 3 is a cube of rock with a side length of 30 cm.

[0041] The rock crack model 3 is installed in the sedimentation tank 4 by fixing bolts, wherein the crack width of the rock crack model 3 can be changed by adjusting the bolts 6; the laser emitter 1 and the light source sensor 2 are relatively arranged on both sides of the sedimentation tank 4; the light source sensor 2 is connected to the computer 16 via a data line 15, and can transmit laser signal data in real time; the laser emitter 1 is connected to the power supply 14 via an electric wire 13, and can simultaneously emit multiple laser beams to monitor laser signals at different positions, and the laser beam spacing is greater than 2 cm.

[0042] In this embodiment, light source sensor 2 receives the light signal emitted by laser emitter 1 and transmits the signal value to computer 16 via data line 15, recording the changes in the light signal at different times and locations in real time. When the microproppant passes through laser beam 5, the disturbance of the solid-phase microproppant causes changes in the laser signal at the receiving end, allowing the sedimentation time and particle size of the microproppant at that laser beam location to be determined. Similarly, when the microproppant passes through laser beams at different locations, the microproppant sedimentation parameters at each location can be obtained. Based on the sedimentation time and particle size of the microproppant at different locations, the sedimentation velocity and particle size change of the microproppant in the core fracture can be determined.

[0043] like Figure 1 As shown, in this embodiment, the light source sensor 2, the sedimentation tank 4, and the laser emitter 1 are respectively provided with a base I10, a base II11, and a base III12 at the bottom; their function is to adjust the horizontal position of the device; at the same time, in order to adjust the vertical position of the device, an adjusting knob I7, an adjusting knob II8, and an adjusting knob III9 are respectively provided on the base I10, the base II11, and the base III12.

[0044] The operating principle of this embodiment is as follows: a laser emitter 1 emits multiple laser beams, and a light source sensor 2 receives the light signals, using the light flux as an indicator. The microproppant scatters after passing through the laser beam, causing changes in the light signal. Furthermore, proppants of different particle sizes have different light signals. Based on these light signals, the microproppant's position in the rock fracture is accurately located, and the dynamic particle size distribution under the fracture-microproppant interaction is inverted.

[0045] The microproppant settling velocity v is calculated by dividing the settling distance △x by the settling time △t. The settling distance △x is the laser diameter D, and the settling time △t is the time period of laser signal change (e.g. Figure 4 ), the sedimentation velocity of the microproppant at different positions can be obtained, and the average sedimentation velocity can be obtained by arithmetic or weighted average.

[0046] The dynamic particle size of the microproppant during sedimentation is calculated by normalizing the relationship between the light signal intensity and the particle size. The light signal intensity of the laser in clear water is the maximum value P0, and the minimum light signal intensity P is when the microproppant particle is completely within the laser diameter. i , for P i Normalization processing is P i / P0, based on P of microproppants with different particle sizes i The relationship between normalized optical signal intensity and particle size is obtained. The normalized optical signal intensity at different fracture locations during the microproppant settling process is then inserted into the relationship to invert the dynamic particle size distribution under fracture-microproppant interaction.

[0047] Example 2

[0048] like Figure 3 As shown, a method of measuring the settlement characteristics of microproppants in rock fractures using laser light of the present invention specifically comprises the following steps:

[0049] Step S10, assembling the device for measuring the settlement characteristics of microproppants in rock fractures using laser as described in Example 1;

[0050] Step S20: Fill the sedimentation tank 4 with liquid to make the liquid level horizontal; then place a laser emitter 1 on the side of the sedimentation tank 4 to emit a laser beam, and make the laser beam emitted by the laser emitter 1 perpendicular to the side of the sedimentation tank 4; then place a light source sensor 2 on the other side of the sedimentation tank 4 so that the light source sensor 2 receives the laser emitted by the laser emitter 1, and the computer records the initial light signal intensity P0;

[0051] Step S30: Conducting sedimentation calibration experiments on microproppants with different particle sizes to obtain a relationship between particle size d and normalized light signal intensity P;

[0052] Step S40: preparing rock fracture models with different lithologies, fracture widths, branch fractures, and complex fracture networks, and conducting microproppant settling experiments to obtain optical signal intensity data at different fracture locations;

[0053] Step S50: According to the relationship between the light signal intensity data at different fracture locations, the particle size d and the normalized light signal intensity P, the dynamic particle size distribution under the fracture-microproppant interaction of different fracture inversions is determined, and the influence of fracture parameters on the microproppant sedimentation is determined.

[0054] Example 3

[0055] The experimental method for calibrating the sedimentation of microproppants of different particle sizes of the present invention specifically comprises the following steps:

[0056] S1. Measure in a smooth sedimentation tank 4. Use micro-proppant of a single particle size to mix with a low sand ratio. Use ultrasonic vibration to reduce the effect of particle agglomeration. Finally, release the mixed sand below the liquid surface in the sedimentation tank. When the micro-proppant is completely irradiated by the laser, record the minimum light signal intensity P at this time. i ;

[0057] S2. Change the particle size of the microproppant and repeat step S1 to measure the minimum light signal intensity P during the sedimentation of microproppant with different particle sizes. i ;

[0058] S3, light signal strength P i Performing normalization processing to obtain normalized optical signal intensity;

[0059] S4. Draw a curve of normalized light signal intensity and particle size (e.g. Figure 2 shown);

[0060] S5. Fitting the curve to obtain a relationship between the normalized light signal intensity P and the particle size d, thereby obtaining a relationship between the particle size d and the normalized light signal intensity P;

[0061] according to Figure 2 The relationship between the normalized light signal intensity P and the particle size d obtained by curve fitting of the normalized light signal intensity and particle size is:

[0062] P = 1.03273-0.02613e 0.03528d

[0063] That is, the relationship between particle size d and normalized light signal intensity P is obtained:

[0064] d=28.34467ln(39.52277-38.27019P).

[0065] Example 4

[0066] The experimental method for microproppant sedimentation in rock fractures of the present invention specifically comprises the following steps:

[0067] Step 1: Create cracks in the rock by Brazilian splitting or hydraulic fracturing experiments, cut the rock into cubes using a cutting machine, and retain the cracked parts to prepare a rock crack model 3;

[0068] Step 2: Place the rock fracture model 3 in the sedimentation tank 4, so that the light source sensor 2 receives the laser light emitted by the laser transmitter 1 and penetrates the fracture, and the computer 16 records the position of each laser beam that can penetrate the fracture and the light signal intensity;

[0069] Step 3: Prepare micro-proppant sand-mixing fluids with different sand ratios and release the mixed fluids below the fracture liquid surface;

[0070] Step 4: The micro-proppant particles continue to settle and disturb the laser beam when passing through it, changing the intensity of the light signal received by the light source sensor 2 at that position. The computer 16 monitors the laser signal in real time and obtains the laser beam light signal change time Δt at each position. i ;

[0071] Step 5: After the micro-proppant is settled, the computer calculates the laser beam light signal change time Δt according to the laser diameter D and each position. i , calculate the sedimentation velocity v of the microproppant when it passes through each laser beam i =D / △t i , clarify the evolution law of the settlement velocity of microproppant at different positions in the rock fracture model, and obtain the average settlement velocity of microproppant by arithmetic average.

[0072] The present invention mainly solves two problems: first, it locates the position of microproppants through laser signal perturbation, overcoming the problem that visualization methods cannot clearly identify microproppants and have large test errors, and realizes the accurate characterization of the microproppant settlement trajectory; second, it combines the rock fracture model and considers the influence of the interaction between microproppants and fracture walls on settlement. The settlement environment is closer to the real fracturing fracture and can be used to characterize the settlement characteristics of microproppants under different lithologies, fracturing fluids and fracture conditions.

[0073] The present invention combines the rock fracture model and considers the effect of the interaction between microproppant and fracture wall on settlement. The settlement environment is closer to the real fracture, which can be used to characterize the settlement characteristics of microproppant under different lithology, fracturing fluid and fracture conditions. The settlement velocity calculated based on the Stokes sedimentation formula is compared with the measured value (such as Figure 5), the conventional proppant sedimentation test method has a large error compared with the prediction formula. The sedimentation velocity measured in real core fractures deviates more than that measured in a smooth graduated cylinder. The test accuracy of the conventional method affects the prediction of microproppant sedimentation, migration and placement, which in turn affects the design of microproppant fracturing construction and the effect of reconstruction.

[0074] The above description does not limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can use the technical content disclosed above to make some changes or modifications to equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A device for measuring the settlement characteristics of microproppants in rock fractures using laser, characterized in that: It includes a laser transmitter (1), a light source sensor (2), a rock fracture model (3), a sedimentation tank (4), a fixing bolt (6), an electric wire (13), a power supply (14), a data line (15) and a computer (16); The rock fracture model (3) is fixed in the sedimentation tank (4) by means of fixing bolts (6), and the laser emitter (1) and the light source sensor (2) are arranged on both sides of the sedimentation tank (4) relative to each other; The laser emitter (1) and the light source sensor (2) are connected to a power source (14) and a computer (16) via an electric wire (13) and a data line (15) respectively; The bottoms of the light source sensor (2), the sedimentation tank (4), and the laser emitter (1) are respectively provided with a base I (10), a base II (11), and a base III (12).

2. A method for measuring the settlement characteristics of microproppants in rock fractures using laser, characterized in that: The method uses the device for measuring the settlement characteristics of microproppants in rock fractures using laser as described in claim 1, and specifically comprises the following steps: Step S10, assembling the device for measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 1, and setting up an experimental device; Step S20: Conducting sedimentation calibration experiments on microproppants with different particle sizes to obtain a relationship between particle size d and normalized light signal intensity P; Step S30: preparing rock fracture models with different lithologies, fracture widths, branch fractures, and complex fracture networks, and conducting microproppant settling experiments to obtain optical signal intensity data at different fracture locations; Step S40: According to the relationship between the light signal intensity data at different fracture positions, the particle size d and the normalized light signal intensity P, the dynamic particle size distribution under the fracture-microproppant interaction of different fracture inversions is determined, and the influence of fracture parameters on the microproppant sedimentation is determined.

3. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 2, characterized in that: The specific process of setting up the experimental device in step S10 is: Step S11, filling the sedimentation tank (4) with liquid to make the liquid level horizontal; Step S12: Then, a laser emitter (1) is arranged on the side of the sedimentation tank (4), and the laser emitter (1) emits a beam of laser toward the sedimentation tank (4); Step S13: Arrange a light source sensor (2) on the other side of the sedimentation tank (4) so ​​that the light source sensor 2 receives the laser emitted by the laser emitter (1), and the computer records the initial light signal intensity P0.

4. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 3, characterized in that: In step S12, the laser emitted by the laser emitter (1) is perpendicular to the side of the sedimentation tank (4).

5. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 3, characterized in that: The specific process of the microproppant sedimentation calibration experiment in step S20 is as follows: measuring in a smooth sedimentation tank, selecting microproppant of a single particle size to prepare a low sand ratio sand mixing solution, and using ultrasonic vibration to reduce the influence of particle agglomeration, and finally releasing the sand mixing solution below the liquid surface of the sedimentation tank; when the microproppant is completely irradiated by the laser, the light signal intensity P at this time is recorded. i .

6. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 5, characterized in that: The particle size range of the micro-proppant in step S20 is 200-800 mesh.

7. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 5, characterized in that: The relationship between the particle size d and the normalized light signal intensity P is obtained by the following steps: i Normalization is performed to obtain the normalized light signal intensity, and a curve of the normalized light signal intensity and the particle size is drawn; the curve is then fitted to obtain a relationship between the normalized light signal intensity and the particle size, and converted into a relationship between the particle size d and the normalized light signal intensity P.

8. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 7, characterized in that: The calculation formula of the normalized optical signal intensity is: P = P i / P0.

9. The method of measuring the settlement characteristics of microproppants in rock fractures using laser according to claim 2, characterized in that: The specific process of the microproppant sedimentation experiment in step S50 is as follows: Step S51: Create cracks in the rock through Brazilian splitting or hydraulic fracturing experiments, cut the rock into cubes using a cutting machine, retain the cracked parts, and prepare a rock crack model (3); Step S52: Install the rock fracture model (3) in the sedimentation tank (4), so that the light source sensor (2) receives the laser light emitted by the laser transmitter (1) and penetrating the fracture, and the computer (16) records the position of each laser beam that can penetrate the fracture and the light signal intensity; Step S53: preparing micro-proppant sand-mixing fluids with different sand ratios, and releasing the sand-mixing fluids below the fracture liquid surface; Step S54: The micro-proppant particles continue to settle and disturb the laser beam when passing through it, changing the intensity of the light signal received by the light source sensor (2) at that position. The computer (16) monitors the laser signal in real time and obtains the laser beam light signal change time Δt at each position. i ; Step S55: After the micro-proppant is settled, the computer calculates the laser beam signal change time Δt according to the laser diameter D and each position. i , calculate the sedimentation velocity v of the microproppant when it passes through each laser beam i =D / △t i , clarify the evolution law of the settlement velocity of microproppant at different positions in the rock fracture model, and obtain the average settlement velocity of microproppant by arithmetic average.

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