Visual crack competitive shunting test experiment device, experiment system and method

Abstract

The invention discloses a visual crack competitive shunting test experimental device, an experimental system and a method, which are used for simulating and visually monitoring competitive distribution of fluid among a plurality of cracks in a hydraulic fracturing process and influence of the fluid on crack expansion. The experimental device comprises a crack propagation and proppant migration module, a light source module and a visual monitoring module, and is matched with a true triaxial large-scale physical simulation system for use, so that observation and quantitative analysis of real-time distribution of fracturing fluid and a proppant in different cracks in a hydraulic fracturing multi-crack competitive propagation process are realized; and a support is provided for hydrofracture balance transformation optimization.

Description

Technical Field

[0001] The invention belongs to the technical field of underground oil and gas exploitation, and relates to a visual fracture competition diversion test experimental device, an experimental system and a method. Background Art

[0002] Hydraulic fracturing is one of the methods to improve the flow conditions of underground oil and gas reservoirs, and is also one of the main technologies to increase the production of a single well. Hydraulic fracturing injects a large amount of fluid into the wellbore to form cracks in the formation and pumps solid particles into it to provide support for the cracks. During the expansion of hydraulic fracturing cracks, the fracturing fluid continues to accumulate in the formed cracks and increases the crack opening, thereby further expanding the cracks. However, the crack expansion process will generate stress in the formation around the cracks, which will limit the further expansion of the cracks, and even make it impossible to initiate the cracks, and further limit the flow of fluids in the cracks. On the other hand, during the process of fracturing fluid backflow, the net pressure in the cracks decreases, while the formation is always in a high confining pressure state and will cause the confining pressure to increase continuously as production proceeds. The confining pressure will cause the cracks to close continuously, resulting in a decrease in oil and gas production. In order to maintain the crack opening as much as possible, it is necessary to pump proppant particles into the cracks in the later stage of fracturing, and keep the proppant particles in the cracks to provide support for the cracks. However, since the internal space of the wellbore is much larger than the fracture, the fluid flow conditions inside the wellbore are much better than those in the fracture, which leads to large differences in the distribution of proppant particles between the wellbore and the fracture, and between different fractures, causing the downhole fluid balance effect to be disrupted.

[0003] However, there is currently a lack of technology that can accurately describe the migration of proppant particles in the wellbore, the distribution between the wellbore and the fractures, and the distribution process between multiple fractures, which makes it difficult to scientifically and effectively design and optimize the fracturing parameters during the fracturing process. Therefore, the present invention discloses a visual fracture competition diversion test experimental device, system and method. Summary of the invention

[0004] The purpose of the present invention is to provide a visual crack competition diversion test experimental device, experimental system and method.

[0005] The present invention is achieved through the following technical solutions:

[0006] A visualization device for a crack competition and diversion test experiment comprises a crack expansion and proppant migration module, a light source module and a visualization monitoring module, wherein the crack expansion and proppant migration module comprises a transparent equivalent formation, a wellbore is arranged at the inner center of the transparent equivalent formation, a plurality of prefabricated cracks are connected at different positions on the wellbore through perforation holes, the prefabricated cracks are arranged parallel to each other, and the axis of the wellbore is perpendicular to the plane where the prefabricated cracks are located; the light source module is used to provide a stable light source that completely covers the crack expansion and proppant migration module, and the visualization monitoring module is used to shoot the expansion of the prefabricated cracks in the crack expansion and proppant migration module and the migration of the proppant in the prefabricated cracks in real time.

[0007] In order to better realize the present invention, further, the light source module includes a light source body, a light source adjustment seat, and a light source adjuster. The light source adjustment seat is arranged on one side of the transparent equivalent stratum, and the light source body is arranged on the light source adjustment seat. The light source adjustment seat can adjust the light coverage angle of the light source body, and the light source body is connected to the light source adjuster.

[0008] In order to better realize the present invention, further, the visual monitoring module includes a camera device, a camera adjustment seat, and a camera controller. The camera adjustment seat is arranged on one side of the transparent equivalent formation. The camera device is arranged on the camera adjustment seat. The camera adjustment seat can adjust the shooting angle of the camera device, and the camera device is connected to the camera controller.

[0009] The system of the fracture competition and diversion test experiment includes a visualization device of the fracture competition and diversion test experiment and a true triaxial physical simulation device. The true triaxial physical simulation device includes a stress loading module and an injection module. The injection module is connected to the wellbore and fluid is injected into the wellbore through the injection module. The stress loading module is used to apply a load to the transparent equivalent formation.

[0010] The method of crack competition diversion test experiment, based on the system implementation of crack competition diversion test experiment, includes the following steps:

[0011] Step 1: Place the visualization device as a sample into a triaxial chamber of a true triaxial physical simulation device, and preload triaxial stress on the sample through the true triaxial physical simulation device;

[0012] Step 2: injecting colored equivalent fracturing fluid into the wellbore through the injection module of the true triaxial physical simulation device, and using the visualization monitoring module to capture in real time the flow of the colored equivalent fracturing fluid between the prefabricated cracks and the expansion of the prefabricated cracks under pressure;

[0013] Step 3: when it is monitored that any prefabricated fracture has expanded to the first position between the center and the edge of the transparent equivalent formation, the viscosity of the colored equivalent fracturing fluid is increased, and proppant particles are injected into the wellbore at the same time, and the migration of the proppant particles in the wellbore, between the wellbore and the prefabricated fracture, between the prefabricated fractures and the prefabricated fractures, and within the prefabricated fractures are photographed in real time through the visualization monitoring module;

[0014] Step 4: when it is monitored that any prefabricated fracture extends to the edge of the transparent equivalent formation, the loaded triaxial stress is increased, and the opening change of the fracture surface is monitored through the visual monitoring module until the fracture surface where the prefabricated fracture is located is closed; the triaxial stress is unloaded, and the breakage rate of the proppant particles under the triaxial stress is monitored through the visual monitoring module; the excess proppant particles at the fracture surface are cleaned, and the embedding condition of the proppant particles in the prefabricated fracture is detected through a three-dimensional scanner;

[0015] Step 5: Establish the corresponding relationship between the triaxial stress environment and the change in opening, crushing rate, and embedding condition, and evaluate the supporting effect of the proppant particles under different stress environments through the corresponding relationship.

[0016] In order to better implement the present invention, further, the step 2 specifically includes:

[0017] Step 2.1, injecting a colored equivalent fracturing fluid into the wellbore through the injection module of the true triaxial physical simulation device, wherein the experimental injection displacement of the colored equivalent fracturing fluid is converted according to the width of the prefabricated fracture, the height of the prefabricated fracture, and the actual flow displacement of the prefabricated fracture on site;

[0018] Step 2.2, using a visualization monitoring module to take real-time photos of the length, width, height, and front geometry of the prefabricated fracture under the pressure of the colored equivalent fracturing fluid as expansion conditions, and calculating the fluid volume of the colored equivalent fracturing fluid inside the prefabricated fracture as flow conditions based on the length, width, and height of the prefabricated fracture;

[0019] Step 2.3, record the time-varying curve of the injection pressure of the colored equivalent fracturing fluid, and establish a quantitative relationship between the expansion of the prefabricated cracks and the injection pressure of the colored equivalent fracturing fluid at the same time.

[0020] In order to better implement the present invention, further, the conversion formula of the experimental injection displacement of the colored equivalent fracturing fluid in step 2.1 is:

[0021]

[0022] Where: Q M Indicates the experimental injection displacement of the colored equivalent fracturing fluid; Q F Indicates the actual flow displacement on site; w MIndicates the experimental crack width of the prefabricated crack; h M Indicates the experimental crack height of prefabricated cracks; w F Indicates the actual width of the prefabricated crack on site; h F It represents the actual on-site crack height of prefabricated cracks; α represents the empirical coefficient.

[0023] In order to better implement the present invention, further, the step 3 specifically includes:

[0024] Step 3.1, when any prefabricated fracture is monitored to extend to the first position between the center and the edge of the transparent equivalent formation, a thickening additive is added to the colored equivalent fracturing fluid so that the viscosity of the colored equivalent fracturing fluid is greater than or equal to 40 mPa.s, and proppant particles are injected into the wellbore at the same time;

[0025] Step 3.2, using the visualization monitoring module to photograph the volume of the proppant particles inside the wellbore in real time as the migration of the proppant particles inside the wellbore; photograph the volume of the proppant particles remaining between the wellbore and the seam opening of the prefabricated fracture and the volume of the proppant particles inside the seam opening of the prefabricated fracture as the migration of the proppant particles between the wellbore and the prefabricated fracture; photograph the difference in the volume of the proppant particles inside each prefabricated fracture as the migration of the proppant particles between the prefabricated fractures; photograph the volume change of the proppant particles distributed along the fracture surface in the prefabricated fracture as the migration of the proppant particles inside the prefabricated fracture;

[0026] Step 3.3: Continue to inject proppant particles until any prefabricated fracture expands to the edge of the transparent equivalent formation in the fracture length direction, and then stop injecting proppant particles.

[0027] In order to better implement the present invention, further, the step 4 specifically includes:

[0028] Step 4.1, when any prefabricated crack is monitored to extend to the edge of the transparent equivalent formation, the triaxial stress of the loading is increased until the opening of all the crack surfaces is less than or equal to 0.1 mm, which can be regarded as the crack surface being closed;

[0029] Step 4.2, unloading the triaxial stress, monitoring the total number of proppant particles and the number of broken proppant particles in a single prefabricated fracture through a visual monitoring module, and calculating the breakage rate of the proppant particles under the triaxial stress through the total number of proppant particles and the number of broken proppant particles;

[0030] Step 4.3, take the sample out of the triaxial chamber of the true triaxial physical simulation device, clean the excess proppant particles on the fracture surface, and then scan the fracture surface with a three-dimensional scanner to obtain the deformation quantitative discrete parameters, and calculate the embedding range and average embedding amount of the proppant particles in the prefabricated fractures based on the deformation quantitative discrete parameters as the embedding situation.

[0031] In order to better implement the present invention, further, in step 1, the true triaxial physical simulation device needs to convert the preloaded triaxial stress of the sample according to the actual reservoir triaxial stress, and the conversion formula is as follows:

[0032]

[0033] Where: Δσ e It represents the stress of the specimen preloaded by the true triaxial physical simulation device; represents the experimental maximum horizontal principal stress; represents the experimental minimum horizontal principal stress; σ′ h2 represents the maximum horizontal principal stress in the real reservoir; σ′ h1 represents the minimum horizontal principal stress in the real reservoir; n represents the proportionality coefficient.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The present invention has the following advantages:

[0036] (1) The present invention uses transparent high-strength PMMA material and cooperates with a reasonable light source module and a visual monitoring module. It can accurately observe the flow of fluid in the wellbore, the change of wellhead pressure, the initiation and expansion of cracks, the deformation of the formation, etc., under the premise of ensuring that the sample is close to the rock mechanical characteristics of the formation being studied, thus solving the problem that traditional artificial cement samples or natural samples cannot be accurately and directly observed when simulating the expansion of hydraulic fracturing cracks;

[0037] (2) The present invention is based on a true triaxial fracturing environment to accurately observe the flow of fracturing fluid in the fracture, the flow of proppant particles in the wellbore, the distribution between the wellbore and the fracture, and the distribution between multiple fractures in real time. It not only takes into account the flow and distribution of fracturing fluid and proppant particles in the coupling space between the wellbore and the fracture, but also takes into account the interaction between fracture expansion and formation deformation. It overcomes the defect that hydraulic fracturing experiments based on traditional artificial cement samples or natural samples cannot observe the distribution of liquid and solid phases in real time, and overcomes the defect that the planar multi-fracture simulation device cannot restore the formation conditions.

[0038] (3) The present invention adopts transparent high-strength PMMA material and cooperates with a reasonable light source module and a visual monitoring module, which overcomes the problem that the traditional API standard conductivity test device and method cannot observe the embedding and breakage of the proppant in real time;

[0039] (4) The transparent sample of the present invention can accurately record the crack expansion process by cooperating with the light source module and the visual monitoring module. Compared with the traditional large-scale physical simulation experiment of fracturing, which requires ultrasonic emission, optical fiber intervention and other methods to restore the dynamic expansion process of the crack, its cost is much lower, which greatly saves experimental expenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the visualization device for the crack competition diversion test experiment;

[0041] Figure 2 It is a structural schematic diagram of the fracture extension and proppant migration module;

[0042] Figure 3 A schematic diagram of the system structure for the crack competition diversion test experiment;

[0043] Figure 4 A top view of the system for the crack competition diversion test experiment;

[0044] Figure 5 It is a schematic diagram of the flow of colored equivalent fracturing fluid in the fracture extension and proppant migration module;

[0045] Figure 6 Schematic diagram of proppant particle migration in the fracture extension and proppant migration module;

[0046] Figure 7 This is a schematic diagram of the morphology of the fracture extension and proppant migration module captured by the visualization monitoring module;

[0047] Figure 8 It is a schematic diagram of the fitting relationship between the prefabricated crack opening and stress;

[0048] Fig. 9 Schematic diagram of the fitting relationship between the average embedding depth of proppant particles and stress;

[0049] Fig.10 It is a schematic diagram of the fitting relationship between the proppant particle breakage rate and stress;

[0050] Fig.11 Schematic diagram of the experimental method steps for visualizing crack competition diversion test.

[0051] Among them: 1-crack extension and proppant migration module; 2-light source module; 3-visual monitoring module; 4-true triaxial physical simulation device; 11-transparent equivalent formation; 12-wellbore; 13-perforation hole; 14-prefabricated cracks. DETAILED DESCRIPTION

[0052] The following detailed descriptions are all illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0053] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise explicitly stated in the present invention, singular forms are also intended to include plural forms. In addition, it should be understood that when the terms "include" and / or "include" are used in this specification,

[0054] When , it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0055] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0056] Terminology explanation section: The terms "install", "connect", "connect", "fixed" and the like in the present invention should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two elements, or an interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0057] Embodiment 1:

[0058] A visualization device for crack competition flow diversion test experiment in this embodiment, such as Figure 1 and Figure 2 As shown, it includes a fracture extension and proppant migration module 1, a light source module 2, and a visualization monitoring module 3. The fracture extension and proppant migration module 1 includes a transparent equivalent formation 11, a wellbore 12 is arranged at the inner center of the transparent equivalent formation 11, and a plurality of prefabricated fractures 14 are connected at different positions on the wellbore 12 through perforation holes 13. The prefabricated fractures 14 are arranged parallel to each other, and the axis of the wellbore 12 is perpendicular to the plane where the prefabricated fractures 14 are located; the light source module 2 is used to provide a stable light source that completely covers the fracture extension and proppant migration module 1, and the visualization monitoring module 3 is used to capture the expansion of the prefabricated fractures 14 in the fracture extension and proppant migration module 1 and the migration of the proppant in the prefabricated fractures 14 in real time.

[0059] The transparent equivalent formation 11 is prepared using PMMA material. In order to ensure that the mechanical properties of the transparent equivalent formation 11 are equivalent to those of the actual underground rock formation, it is necessary to conduct a mechanical property test on the actual underground rock formation to obtain the Young's modulus, Poisson's ratio, tensile strength, compressive strength, fracture toughness and other mechanical parameters of the actual underground rock formation. Then, the PMMA material is adjusted and tested under the same conditions until the error between the mechanical properties displayed by the transparent equivalent formation 11 prepared by the PMMA material under the same conditions and the mechanical properties of the actual underground rock formation is less than or equal to 5%. The transparent equivalent formation 11 can be regarded as equivalent to the actual underground rock formation.

[0060] Specifically, the mechanical properties of the standard columnar core in the target formation are tested, and the Young's modulus, Poisson's ratio, tensile strength, compressive strength, fracture toughness and other mechanical parameters of the standard core are obtained under the corresponding reservoir stress conditions. The test specimens with the same size and specifications as the standard columnar core are made by PMMA injection molding process, and the mechanical properties of the test specimens are tested under the same reservoir stress conditions to obtain the Young's modulus, Poisson's ratio, tensile strength, compressive strength, fracture toughness and other mechanical parameters of the test specimens. The mechanical properties parameters of the test specimens are compared with those of the standard columnar core. If the error between the two is less than 5%, the test specimen is considered to be equivalent to the standard columnar core; if the error between the two is greater than or equal to 5%, the parameters such as the injection molding machine pressure, sol temperature, injection temperature, and residence time in the PMMA injection molding process are adjusted, and the above detection and comparison process is repeated until the error between the mechanical properties of the test specimen and the mechanical properties of the standard columnar core is less than 5%.

[0061] The wellbore 12, the perforated holes 13, and the prefabricated fractures 14 are all located inside the equivalent formation 11. The wellbore 12 is placed at the center of the equivalent formation 11, and one end of the wellbore 12 passes through the top edge of the equivalent formation 11 and is connected to an external pipeline. The perforated holes 13 are distributed at different positions of the wellbore 12, and all the prefabricated fractures 14 are arranged parallel to each other. The axis of the wellbore 12 is also perpendicular to the plane where all the prefabricated fractures 14 are located. The prefabricated fractures 14 are connected to the wellbore 12 through the perforated holes 13. The fracture extension and proppant migration module 1 needs to be used in conjunction with the stress loading module and the injection module in the true triaxial physical simulation device 4. The triaxial stress is applied to the transparent equivalent formation 11 through the stress loading module, and the fluid is injected into the wellbore 12 through the injection module, so that the fluid enters the prefabricated fractures 14 through the perforated holes 13 on the wellbore 12. Cooperate with the light source module 2 to provide uniform and sufficient illumination to the transparent equivalent formation 11, and at the same time, through the visualization monitoring module 3, the initial stress state of the transparent equivalent formation 11, the flow of the fluid in the wellbore 12, the change of the wellhead pressure, the initiation and expansion of the prefabricated fractures 14, the deformation of the transparent equivalent formation 11, the flow of the fluid inside the prefabricated fractures 14, the flow of solid particles in the wellbore 12, the fluid distribution between the wellbore 12 and the prefabricated fractures 14, and the fluid distribution between each prefabricated fracture 14 are visualized and photographed in real time under transparent and observable conditions, so as to intuitively and visually obtain the competition and diversion of fractures under different stress conditions and injection conditions.

[0062] Furthermore, the light source module 2 includes a light source body, a light source adjustment seat, and a light source adjuster. The light source adjustment seat is arranged on one side of the transparent equivalent layer 11. The light source body is arranged on the light source adjustment seat. The light source adjustment seat can adjust the light coverage angle of the light source body. The light source body is connected to the light source adjuster.

[0063] A transparent inner groove is provided at one side edge of the transparent equivalent stratum 11 as a light source groove. The light source adjustment seat is fixedly installed inside the light source groove by adhesive or connectors, and the light source adjustment seat itself can be adjusted in the pitch direction. The light source body is connected to the light source adjuster through the wire groove on one side of the light source groove, and then the light source body is driven by the light source adjustment seat to adjust the inclination angle in the pitch direction, thereby finally realizing the adjustment of the light coverage angle of the light source body, ensuring that the light of the light source body can completely cover the entire transparent equivalent stratum 11.

[0064] Further, the light source adjustment seat includes a fixed plate, an adjustment support plate, and a connecting member. The fixed plate is fixedly installed on the lower surface of the light source slot by adhesive or a connecting member. The fixed plate is installed with the adjustment support plate by the connecting member. The connecting member has a pitch angle adjustment mechanism to ensure that the pitch angle of the adjustment support plate can be adjusted between 0-90°. The adjustment support plate includes an adjustment caliper, which can drive the adjustment support plate to move with a stroke of 0-15mm. The light source body is installed on the adjustment support plate. The dimensions of the fixed plate and the adjustment support plate are length×width×height: 30mm×30mm×5mm.

[0065] Furthermore, the brightness of the light source body is 0-2000 lumens.

[0066] Furthermore, the visual monitoring module 3 includes a camera device, a camera adjustment seat, and a camera controller. The camera adjustment seat is arranged on one side of the transparent equivalent stratum 11. The camera device is arranged on the camera adjustment seat. The camera adjustment seat can adjust the shooting angle of the camera device. The camera device is connected to the camera controller.

[0067] A transparent inner groove is provided at one side edge of the transparent equivalent formation 11 as an observation groove, a camera adjustment seat is fixed in the observation groove with adhesive or a connector, and the camera adjustment seat itself can flexibly adjust the pitch angle, and the camera device adopts a micro high-speed camera, which is in the observation groove and fixed on the camera adjustment seat, and the micro high-speed camera is connected to the camera controller through a wire groove on one side of the observation groove. The visual monitoring module 3 needs to be used in conjunction with the light source module 2, and is mainly used to observe and record the crack expansion and proppant migration process in real time in the true three-axis physical simulation device 4.

[0068] Furthermore, the shooting and monitoring viewing angle of the miniature high-speed camera is greater than or equal to 155°, the video definition is not less than 1080P, the shooting frame rate is less than or equal to 25s, the captured image definition is not less than 2000 pixels, and the captured image size of length × width × height is less than or equal to 15mm × 15mm × 40mm.

[0069] Furthermore, the camera adjustment seat includes a fixed plate, an adjustment support plate, and a connecting member. The fixed plate is fixedly installed on the lower surface of the observation slot by adhesive or a connecting member. The fixed plate is installed with the adjustment support plate by the connecting member. The connecting member has a pitch angle adjustment mechanism to ensure that the pitch angle of the adjustment support plate can be adjusted between 0-90°. The adjustment support plate includes an adjustment caliper, which can drive the adjustment support plate to move with a stroke of 0-15mm. The camera device is installed on the adjustment support plate. The dimensions of the fixed plate and the adjustment support plate are length×width×height: 20mm×20mm×60mm.

[0070] Embodiment 2:

[0071] A crack competition diversion test experiment system of this embodiment is as follows: Figure 3 and Figure 4 As shown, it includes a visualization device for the fracture competition diversion test experiment and a true triaxial physical simulation device 4, wherein the true triaxial physical simulation device 4 includes a stress loading module and an injection module, wherein the injection module is connected to the wellbore 12, and fluid is injected into the wellbore 12 through the injection module, and the stress loading module is used to apply a load to the transparent equivalent formation 11.

[0072] The visualization device of the crack competition and diversion test experiment and the true triaxial physical simulation device 4 are connected to an external control computer, and the external control computer is used to control the start and stop of the light source module 2 and the visualization monitoring module 3 in the visualization device of the crack competition and diversion test experiment in real time, and to control the pitch angle of the light source module 2 and the visualization monitoring module 3. The stress loading module and the injection module in the true triaxial physical simulation device 4 are controlled in real time by the external control computer, that is, the magnitude of the triaxial stress applied to the sample by the stress loading module is controlled, and the type, flow rate, and displacement of the fluid injected into the sample by the injection module are controlled.

[0073] The other parts of this embodiment are the same as those of Embodiment 1, and thus will not be described in detail.

[0074] Embodiment 3:

[0075] A crack competition flow diversion test experiment method of this embodiment is based on the system implementation of the crack competition flow diversion test experiment, such as Fig.11 As shown, the following steps are included:

[0076] Step 1: Place the visualization device as a sample into the triaxial chamber of the true triaxial physical simulation device 4, and preload the triaxial stress on the sample through the true triaxial physical simulation device 4;

[0077] Step 2: Figure 5 As shown, colored equivalent fracturing fluid is injected into the wellbore 12 through the injection module of the true triaxial physical simulation device 4, and the flow of the colored equivalent fracturing fluid between each prefabricated fracture 14 and the expansion of the prefabricated fracture 14 under pressure are photographed in real time through the visualization monitoring module 3;

[0078] Step 3: When it is detected that any prefabricated fracture 14 extends to a first position between the center and the edge of the transparent equivalent formation 11, the viscosity of the colored equivalent fracturing fluid is increased, and at the same time, Figure 6 As shown, proppant particles are injected into the wellbore 12, and the migration of the proppant particles inside the wellbore 12, between the wellbore 12 and the prefabricated fractures 14, between the prefabricated fractures 14 and the prefabricated fractures 14, and inside the prefabricated fractures 14 are photographed in real time by the visual monitoring module 3;

[0079] Step 4: when it is monitored that any prefabricated fracture 14 extends to the edge of the transparent equivalent formation 11, the loaded triaxial stress is increased, and the opening change of the fracture surface is monitored through the visual monitoring module 3 until the fracture surface where the prefabricated fracture 14 is located is closed; the triaxial stress is unloaded, and the breakage rate of the proppant particles under the triaxial stress is monitored through the visual monitoring module 3; the excess proppant particles at the fracture surface are cleaned, and the embedding condition of the proppant particles in the prefabricated fracture 14 is detected through a three-dimensional scanner;

[0080] Step 5: Establish the corresponding relationship between the triaxial stress environment and the change in opening, crushing rate, and embedding condition, and evaluate the supporting effect of the proppant particles under different stress environments through the corresponding relationship.

[0081] Before performing step 1, a transparent equivalent stratum 11 needs to be prepared in advance. The process steps for preparing the transparent equivalent stratum 11 are as follows:

[0082] Step A1, conduct mechanical property test on the actual underground rock formation to obtain mechanical parameters such as Young's modulus, Poisson's ratio, tensile strength, compressive strength, fracture toughness, etc. of the actual underground rock formation, and then adjust and test the PMMA material under the same conditions until the error between the mechanical properties of the transparent equivalent formation 11 prepared by the PMMA material under the same conditions and the mechanical properties of the actual underground rock formation is less than or equal to 5%, and the transparent equivalent formation 11 can be regarded as equivalent to the actual underground rock formation;

[0083] Step A2, make a sample casting box with a length × width × height of 400mm × 400mm × 200mm, insert a stainless steel pipe at the center of the sample casting box to simulate the wellbore 12, seal the bottom end of the stainless steel pipe, and cut 3-4 groups of bilaterally symmetrical perforation holes 13 with a diameter greater than or equal to 3mm at different positions on the stainless steel pipe. The top of the stainless steel pipe is open and extends to the outside of the sample casting box, and the opening is connected to the injection module of the true triaxial physical simulation device 4. Place a piece of paper with a thickness of less than or equal to 0.1mm at the perforation hole 13 perpendicular to the wellbore 12, and then evenly pour the PMMA material debugged in step A1 into the sample casting box until the PMMA material is completely solidified to form a transparent equivalent formation matrix; the size of the transparent equivalent formation matrix is ​​length × width × height: 400mm × 400mm × 100mm.

[0084] Furthermore, the closed end of the wellbore 12 is greater than or equal to 10 mm from the bottom of the transparent equivalent formation matrix, the inner diameter of the wellbore 12 is greater than or equal to 5 mm, the wall thickness of the wellbore 12 is greater than or equal to 1 mm, and the steel grade of the stainless steel pipe used to simulate the wellbore 12 should correspond to the steel grade of the wellbore steel used in the actual underground rock formation.

[0085] Further, the perforation holes 13 are distributed at different positions on the wellbore 12, and the number of the perforation holes 13 is consistent with the number of the prefabricated fractures 14. The perforation holes 13 correspond to the prefabricated fractures 14 in pairs and are located in the same plane. The perforation holes 13 located in the same plane as the prefabricated fractures 14 are grouped as a cluster. The number of perforation holes 13 belonging to a cluster is calculated according to the on-site completion perforation phase angle. If the phase angle is 90°, the number of perforation holes 13 in a cluster is 2; if the phase angle is 60°, the number of perforation holes 13 in a cluster is 3; if the phase angle is 45°, the number of perforation holes 13 in a cluster is 4; if the phase angle is 30°, the number of perforation holes 13 in a cluster is 6, and the length of the perforation holes 13 is less than or equal to 5 mm, and the inner diameter of the perforation holes 13 is less than the inner diameter of the wellbore 12.

[0086] Furthermore, all prefabricated cracks 14 are arranged parallel to each other, and the axis of the wellbore 12 is perpendicular to the plane where all the prefabricated cracks 14 are located. The prefabricated cracks 14 are connected to the wellbore 12 through perforation holes 13. The surface size of the prefabricated cracks 14 is length × height = 400 mm × 200 mm. The thickness of the cast crack surface is less than or equal to 0.01 mm. The crack surfaces are adjacent to each other by glue. The strength of the crack surface is required to not slip or stretch under triaxial confining pressure conditions.

[0087] Step A3, continue pouring the debugged PMMA material on the left side of the transparent equivalent stratum substrate until it solidifies on the left side of the transparent equivalent stratum substrate to obtain a light source sample with a length × width × height of 400 mm × 400 mm × 100 mm, then open a light source slot on one side of the light source sample, and set at least two groups of light source modules 2 from top to bottom in the light source slot, debug the illumination angle of the light source module 2, and ensure that the light emitted by the light source module 2 can evenly and completely cover the entire transparent equivalent stratum substrate;

[0088] Furthermore, the dimensions of the light source slot are length×width×depth: 50mm×50mm×20mm, and a wire slot with a width greater than or equal to 5mm and a depth greater than or equal to 5mm is opened on one side of the light source slot.

[0089] Step A4, continue pouring the debugged PMMA material on the right side of the transparent equivalent formation substrate until it solidifies on the right side of the transparent equivalent formation substrate to obtain an observation sample with a length × width × height of 400mm × 400mm × 100mm, then open an observation groove on one side of the observation sample, and set at least two sets of visualization monitoring modules 3 from top to bottom in the observation groove, debug the shooting angle of the visualization monitoring module 3, and ensure that the shooting area of ​​the visualization monitoring module 3 can evenly and completely cover the entire transparent equivalent formation substrate.

[0090] Furthermore, the dimensions of the observation groove are length×width×depth: 60mm×40mm×60mm, and a wire groove with a width greater than or equal to 5mm and a depth greater than or equal to 5mm is opened on one side of the observation groove.

[0091] Furthermore, in step 1, the sample is lowered into the triaxial chamber of the true triaxial physical simulation device 4, and the sample is subjected to true triaxial preloading so that the sample gradually reaches a preset triaxial stress environment. The magnitude of the triaxial stress needs to be converted into a stress ratio based on the actual reservoir triaxial stress, and it should satisfy the condition that the magnitude of the triaxial stress loaded by the true triaxial physical simulation device 4 under the experimental conditions is greater than or equal to one-fifth of the magnitude of the actual reservoir triaxial stress.

[0092] The specific conversion process is as follows:

[0093] First, determine the maximum horizontal geostress that can be loaded under experimental conditions. In this embodiment, the maximum horizontal geostress must not be less than 10Mpa. Then calculate the difference between the actual reservoir horizontal two-dimensional geostress: Δσ′=σ′ h2 -σ′ h1 ; Where: Δσ′ represents the difference in the actual horizontal two-dimensional geostress in the reservoir.

[0094] Then set the ratio of the horizontal stress difference between the actual reservoir and the experimental process:

[0095] Wherein: n represents the proportionality coefficient, and in this embodiment, n=1 is preferred.

[0096] Then calculate the difference of horizontal two-direction ground stress under experimental conditions:

[0097]

[0098] Where: Δσ e It represents the stress of the specimen preloaded by the true triaxial physical simulation device; represents the experimental maximum horizontal principal stress; represents the experimental minimum horizontal principal stress; σ′ h2 represents the maximum horizontal principal stress in the real reservoir; σ′ h1 represents the minimum horizontal principal stress in the real reservoir; n represents the proportionality coefficient.

[0099] Furthermore, the step 2 specifically includes:

[0100] Step 2.1, injecting a colored equivalent fracturing fluid into the wellbore 12 through the injection module of the true triaxial physical simulation device 4, wherein the experimental injection displacement of the colored equivalent fracturing fluid is converted according to the width of the prefabricated fracture 14, the fracture height of the prefabricated fracture 14, and the actual flow displacement of the prefabricated fracture 14 on site;

[0101] Step 2.2, using the visualization monitoring module 3 to photograph in real time the length, width, height, and geometry of the front edge of the prefabricated fracture 14 under the pressure of the colored equivalent fracturing fluid as the expansion situation, and calculating the fluid volume of the colored equivalent fracturing fluid inside the prefabricated fracture 14 as the flow situation according to the length, width, and height of the prefabricated fracture 14;

[0102] Step 2.3, record the time-varying curve of the injection pressure of the colored equivalent fracturing fluid, and establish a quantitative relationship between the expansion of the prefabricated cracks 14 and the injection pressure of the colored equivalent fracturing fluid at the same time.

[0103] The conversion formula for the experimental injection displacement of the colored equivalent fracturing fluid in step 2.1 is:

[0104]

[0105] Where: Q M Indicates the experimental injection displacement of the colored equivalent fracturing fluid; Q F Indicates the actual flow displacement on site; w M Indicates the experimental crack width of the prefabricated crack; h M Indicates the experimental crack height of prefabricated cracks; w F Indicates the actual width of the prefabricated crack on site; h F represents the actual on-site crack height of the prefabricated crack; α represents the empirical coefficient, and α=0.1 is preferably selected in this embodiment.

[0106] Furthermore, the step 3 specifically includes:

[0107] Step 3.1. When it is monitored that any prefabricated fracture 14 extends to the first position between the center and the edge of the transparent equivalent formation 11, a thickening additive is added to the colored equivalent fracturing fluid so that the viscosity of the colored equivalent fracturing fluid is greater than or equal to 40 mPa.s. The thickening additive is preferably guar gum, and proppant particles are injected into the wellbore 12 at the same time; the first position refers to the position area between the edge of the transparent equivalent formation 11 and the range of 100 mm from the edge of the transparent equivalent formation 11.

[0108] Step 3.2, using the visualization monitoring module 3 to photograph the volume of the proppant particles inside the wellbore 12 in real time as the migration of the proppant particles inside the wellbore 12; photographing the volume of the proppant particles remaining between the wellbore 12 and the seam opening of the prefabricated fracture 14 and the volume of the proppant particles inside the seam opening of the prefabricated fracture 14 as the migration of the proppant particles between the wellbore 12 and the prefabricated fracture 14; photographing the difference in the volume of the proppant particles inside each prefabricated fracture 14 as the migration of the proppant particles between the prefabricated fracture 14 and the prefabricated fracture 14; photographing the volume change of the proppant particles distributed along the fracture surface in the prefabricated fracture 14 as the migration of the proppant particles inside the prefabricated fracture 14;

[0109] Step 3.3: Continue to inject proppant particles until any prefabricated fracture 14 expands to the edge of the transparent equivalent formation 11 in the fracture length direction, and then stop injecting proppant particles.

[0110] Furthermore, the step 4 specifically includes:

[0111] Step 4.1, when it is monitored that any prefabricated crack 14 extends to the edge of the transparent equivalent formation 11, the triaxial stress loaded is increased until the opening of all the crack surfaces is less than or equal to 0.1 mm, which can be regarded as the crack surface being closed;

[0112] Step 4.2, unload the triaxial stress, such as Figure 7 As shown, the total number of proppant particles and the number of broken proppant particles in a single prefabricated fracture 14 are monitored by the visual monitoring module 3, and the breakage rate of the proppant particles under the triaxial stress is solved by the total number of proppant particles and the number of broken proppant particles;

[0113] Step 4.3, take the sample out of the triaxial chamber of the true triaxial physical simulation device 4, clean the excess proppant particles on the crack surface, and then scan the crack surface with a three-dimensional scanner to obtain the deformation quantitative discrete parameters, and obtain a three-dimensional scanning image, that is, the embedding depth of the proppant particles is 0 (the crack surface is not deformed) as the benchmark, and the depth of the arc pit left after the proppant particles are embedded in the crack surface is used as the embedding depth of the proppant particles. Based on the deformation quantitative discrete parameters, the embedding range and average embedding amount of the proppant particles in the prefabricated cracks 14 are calculated as the embedding situation.

[0114] The triaxial stress parameters applied to the sample were changed by the true triaxial physical simulation device 4, and the type of proppant particles was changed. The change curve of the prefabricated fracture opening, the embedding and crushing of the proppant particles in the fracture surface under the corresponding triaxial stress parameters were observed, and then the relationship between the stress parameters and the average opening of the prefabricated fracture, the average embedding depth of the proppant particles, and the crushing rate of the proppant particles was established as shown in Table 1:

[0115] Table 1. Relationship between different stress parameters and crack extension and migration

[0116]

[0117]

[0118] Based on Table 1, the fitting curves of stress parameters related to the average opening of prefabricated fractures, the average embedding depth of proppant particles, and the breakage rate of proppant particles are obtained as follows: Figure 8-Figure 10 As shown in the figure, the fitting relationship between the stress parameters and the average opening of the prefabricated fractures, the average embedding depth of the proppant particles, and the breakage rate of the proppant particles when the proppant particles are ceramsite is as follows:

[0119]

[0120] The fitting relationship between the stress parameters and the average opening of prefabricated fractures, the average embedding depth of proppant particles, and the breakage rate of proppant particles obtained by fitting is as follows:

[0121]

[0122] Where: σ′ h represents the horizontal principal stress in the real reservoir; a f Indicates the precast crack opening; d pe represents the average embedding depth of proppant particles; cr p Indicates the breakage rate of proppant particles.

[0123] The evaluation results are then obtained as follows:

[0124] When expanded clay is used as the proppant particles, when the stress reaches 15Mpa, the opening of the prefabricated fracture decreases rapidly, the average embedding depth of the proppant particles increases, and the supporting effect decreases. At this time, the particle size of the proppant particles should be increased or expanded clay with higher strength should be used to maintain the width of the prefabricated fracture and the supporting effect.

[0125] When quartz sand is used as the proppant particles, when the stress reaches 25Mpa, the average embedding depth of the proppant particles and the increase in the crushing rate of the proppant particles suddenly increase, and the rate of decrease of the fracture opening increases. At this time, the particle size of the proppant particles should be increased or the proppant particles should be replaced with expanded clay.

[0126] The other parts of this embodiment are the same as those of Embodiment 1 or 2, and thus will not be described in detail.

[0127] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the present invention.

Claims

1. A visualization device for crack competition diversion test experiment, characterized in that: The invention comprises a fracture extension and proppant migration module (1), a light source module (2), and a visual monitoring module (3). The fracture extension and proppant migration module (1) comprises a transparent equivalent formation (11). A wellbore (12) is arranged at the inner center of the transparent equivalent formation (11). A plurality of prefabricated fractures (14) are connected at different positions on the wellbore (12) through perforation holes (13). The prefabricated fractures (14) are arranged parallel to each other, and the axis of the wellbore (12) is perpendicular to the plane where the prefabricated fractures (14) are located. The light source module (2) is used to provide a stable light source that completely covers the fracture extension and proppant migration module (1). The visual monitoring module (3) is used to capture the extension of the prefabricated fractures (14) in the fracture extension and proppant migration module (1) and the migration of the proppant in the prefabricated fractures (14) in real time.

2. The visualization device for crack competition flow diversion test experiment according to claim 1, characterized in that: The light source module (2) comprises a light source body, a light source adjustment seat, and a light source adjuster. The light source adjustment seat is arranged on one side of the transparent equivalent stratum (11). The light source body is arranged on the light source adjustment seat. The light source adjustment seat can adjust the light coverage angle of the light source body. The light source body is connected to the light source adjuster.

3. The visualization device for crack competition flow diversion test experiment according to claim 1, characterized in that: The visual monitoring module (3) comprises a camera device, a camera adjustment seat, and a camera controller. The camera adjustment seat is arranged on one side of the transparent equivalent stratum (11). The camera device is arranged on the camera adjustment seat. The camera adjustment seat can adjust the shooting angle of the camera device. The camera device is connected to the camera controller.

4. A system for crack competition diversion test experiment, comprising the visualization device according to any one of claims 1 to 3, characterized in that: It also includes a true triaxial physical simulation device (4), which includes a stress loading module and a liquid injection module. The liquid injection module is connected to the wellbore (12) and fluid is injected into the wellbore (12) through the liquid injection module. The stress loading module is used to apply a load to the transparent equivalent formation (11).

5. A method for crack competition diversion test experiment, based on the system implementation of the crack competition diversion test experiment according to claim 4, characterized in that: The following steps are involved: Step 1: Place the visualization device as a sample into a triaxial chamber of a true triaxial physical simulation device (4), and preload triaxial stress on the sample through the true triaxial physical simulation device (4); Step 2: injecting colored equivalent fracturing fluid into the wellbore (12) through the injection module of the true triaxial physical simulation device (4), and photographing the flow of the colored equivalent fracturing fluid between the prefabricated fractures (14) and the expansion of the prefabricated fractures (14) under pressure in real time through the visual monitoring module (3); Step 3: when it is monitored that any prefabricated fracture (14) extends to a first position between the center and the edge of the transparent equivalent formation (11), the viscosity of the colored equivalent fracturing fluid is increased, and proppant particles are injected into the wellbore (12) at the same time, and the migration of the proppant particles inside the wellbore (12), between the wellbore (12) and the prefabricated fracture (14), between the prefabricated fractures (14) and the prefabricated fractures (14), and inside the prefabricated fractures (14) are photographed in real time through the visual monitoring module (3); Step 4: when it is detected that any prefabricated crack (14) extends to the edge of the transparent equivalent formation (11), the triaxial stress of the loading is increased, and the opening change of the crack surface is monitored through the visual monitoring module (3) until the crack surface where the prefabricated crack (14) is located is closed; Unloading the triaxial stress, monitoring the breakage rate of the proppant particles under the triaxial stress through a visual monitoring module (3); cleaning the excess proppant particles on the fracture surface, and detecting the embedding status of the proppant particles in the prefabricated fracture (14) through a three-dimensional scanner; Step 5: Establish the corresponding relationship between the triaxial stress environment and the change in opening, crushing rate, and embedding condition, and evaluate the supporting effect of the proppant particles under different stress environments through the corresponding relationship.

6. The method for crack competition flow diversion test experiment according to claim 5, characterized in that: The step 2 specifically includes: Step 2.1, injecting a colored equivalent fracturing fluid into the wellbore (12) through the injection module of the true triaxial physical simulation device (4), wherein the experimental injection displacement of the colored equivalent fracturing fluid is converted according to the width of the prefabricated fracture (14), the fracture height of the prefabricated fracture (14), and the actual flow displacement of the prefabricated fracture (14) on site; Step 2.2, using the visualization monitoring module (3), in real time, photographing the length, width, height, and geometry of the front edge of the prefabricated fracture (14) under the pressure of the colored equivalent fracturing fluid as the expansion status, and calculating the fluid volume of the colored equivalent fracturing fluid inside the prefabricated fracture (14) as the flow status according to the length, width, and height of the prefabricated fracture (14); Step 2.3, record the time-varying curve of the injection pressure of the colored equivalent fracturing fluid, and establish a quantitative relationship between the expansion of the prefabricated fracture (14) and the injection pressure of the colored equivalent fracturing fluid at the same time.

7. The method for crack competition flow diversion test experiment according to claim 6, characterized in that: The conversion formula for the experimental injection displacement of the colored equivalent fracturing fluid in step 2.1 is: Where: Q M Indicates the experimental injection displacement of the colored equivalent fracturing fluid; Q F Indicates the actual flow displacement on site; w M Indicates the experimental crack width of the prefabricated crack; h M Indicates the experimental crack height of prefabricated cracks; w F Indicates the actual width of the prefabricated crack on site; h F It represents the actual on-site crack height of prefabricated cracks; α represents the empirical coefficient.

8. The method for crack competition flow diversion test experiment according to claim 5, characterized in that: The step 3 specifically includes: Step 3.1, when it is monitored that any prefabricated fracture (14) extends to a first position between the center and the edge of the transparent equivalent formation (11), a thickening additive is added to the colored equivalent fracturing fluid so that the viscosity of the colored equivalent fracturing fluid is greater than or equal to 40 mPa.s, and proppant particles are injected into the wellbore (12); Step 3.2, using the visual monitoring module (3) to photograph in real time the volume of the proppant particles inside the wellbore (12) as the migration of the proppant particles inside the wellbore (12); photographing the volume of the proppant particles remaining between the wellbore (12) and the seam opening of the prefabricated fracture (14) and the volume of the proppant particles inside the seam opening of the prefabricated fracture (14) as the migration of the proppant particles between the wellbore (12) and the prefabricated fracture (14); photographing the difference in the volume of the proppant particles inside each prefabricated fracture (14) as the migration of the proppant particles between the prefabricated fractures (14) and the prefabricated fractures (14); photographing the volume change of the proppant particles distributed along the fracture surface in the prefabricated fracture (14) as the migration of the proppant particles inside the prefabricated fracture (14); Step 3.3: Continue to inject proppant particles until any prefabricated fracture (14) expands to the edge of the transparent equivalent formation (11) in the fracture length direction, and then stop injecting proppant particles.

9. The method for crack competition flow diversion test experiment according to claim 5, characterized in that: The step 4 specifically includes: Step 4.1, when it is monitored that any prefabricated crack (14) extends to the edge of the transparent equivalent formation (11), the triaxial stress of the loading is increased until the opening of all the crack surfaces is less than or equal to 0.1 mm, and the crack surface is considered to be closed; Step 4.2, unloading the triaxial stress, monitoring the total number of proppant particles and the number of broken proppant particles in a single prefabricated fracture (14) through the visual monitoring module (3), and calculating the breakage rate of the proppant particles under the triaxial stress through the total number of proppant particles and the number of broken proppant particles; Step 4.3, take the sample out of the triaxial chamber of the true triaxial physical simulation device (4), clean the excess proppant particles at the fracture surface, and then scan the fracture surface with a three-dimensional scanner to obtain the deformation quantitative discrete parameters, and calculate the embedding range and average embedding amount of the proppant particles in the prefabricated fracture (14) based on the deformation quantitative discrete parameters as the embedding situation.

10. The method for crack competition flow diversion test experiment according to claim 5, characterized in that: In step 1, the true triaxial physical simulation device (4) needs to convert the preloaded triaxial stress of the sample according to the actual reservoir triaxial stress, and the conversion formula is as follows: Where: Δσ e It represents the stress of the specimen preloaded by the true triaxial physical simulation device; represents the experimental maximum horizontal principal stress; represents the experimental minimum horizontal principal stress; σ′ h2 represents the maximum horizontal principal stress in the real reservoir; σ′ h1 represents the minimum horizontal principal stress in the real reservoir; n represents the proportionality coefficient.

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