A method for measuring the depth of proppant embedment within a hydraulic fracture in a virgin reservoir
By laying proppant on test and control samples and simulating formation stress for loading-unloading tests, the problem of inaccurate measurement of proppant embedment depth in existing technologies is solved, achieving efficient and accurate evaluation of embedment depth and providing a reliable basis for proppant selection.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHONGQING UNIV
- Filing Date
- 2026-04-02
- Publication Date
- 2026-07-10
AI Technical Summary
Existing technologies are unable to accurately reflect the roughness and microstructure of fracture surfaces in unconventional reservoirs, and cannot efficiently and cost-effectively test the embedding depth of multiple proppants, resulting in inaccurate proppant embedding evaluations that affect fracture conductivity and recovery rates.
By placing proppant on test specimens and control specimens, loading-unloading tests were conducted to simulate formation closure stress. Load-displacement curves were recorded, the elastic-plastic deformation values of the proppant were analyzed, the embedment depth was obtained, and a triaxial mechanical testing machine was used to simulate the real stress state.
This method enables accurate measurement of the embedding depth of multiple proppants, reduces experimental errors, provides a reliable basis for proppant selection, and is simple to implement with readily available equipment, making it easy to promote and apply.
Smart Images
Figure CN122361081A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas field development and fracturing evaluation technology, and in particular to a method suitable for measuring the embedment depth of multiple proppants in the hydraulic fractures of the original reservoir. Background Technology
[0002] Unconventional reservoirs such as coal seams, shale formations, and tight sandstone formations typically have low permeability, making efficient extraction difficult through natural seepage alone. Therefore, production enhancement measures such as hydraulic fracturing are needed to create artificial fractures in the formation, which further develop into a complex fracture network, into which proppant is injected. During this process, the proppant's ability to maintain stable support within the fractures over the long term is crucial to the final recovery rate. It is important to emphasize that if the proppant embeds into the fracture face, it reduces the effective fracture width, thereby weakening the fracture conductivity and leading to decreased production.
[0003] Currently, commonly used methods for evaluating proppant embedding generally include: conducting single-particle proppant embedding tests on processed and polished rock blocks, and then observing the indentation using microscopes and profilometers to estimate the indentation depth; or measuring the proppant embedding depth using CT scans. These methods generally suffer from the following problems: they often use artificially cut fracture surfaces, making it difficult to accurately reflect the roughness and microstructure of the original reservoir fracture surface; most schemes can only test single-particle proppant at a time, making it difficult to test multiple proppant particles in the construction site; under different pressure points, a repetitive "loading-stopping-measuring-reloading" operation is often required, meaning a measurement is needed after each pressure point, resulting in a cumbersome and inefficient testing process; some methods require complex pretreatment or expensive equipment, leading to high operating and time costs, which hinders widespread adoption. Therefore, it is necessary to propose a method that uses the original reservoir hydraulic fracture surface as the object and can test the embedding values of multiple proppant particles. Summary of the Invention
[0004] Technical Problem: The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for measuring the embedment depth of multiple proppants in original reservoir hydraulic fractures. First, proppant is laid on the fracture surface of the test sample to make the contact state, stress path, and interparticle interaction of the proppant in the fracture consistent with the field conditions. Then, normal pressure is applied to the fracture by simulating formation closure stress to obtain the load-displacement curve of the whole process. This enables the testing of the entire process of proppant embedding, providing a reliable basis for evaluating the reduction of effective fracture width caused by proppant embedding depth and for proppant selection.
[0005] Technical solution: The present invention provides a method for measuring the embedment depth of multiple proppants in original reservoir hydraulic fractures, comprising the following steps:
[0006] S1: Extract hydraulically fractured blocky rock from the target reservoir;
[0007] S2: Cut and grind the blocky rock to prepare square or cylindrical rock samples with consistent lithology and crack characteristics. The upper and lower end faces of the rock sample are parallel, and the crack surface is located in the middle of the sample and parallel to the upper and lower end faces.
[0008] S3: Take two rock samples and label them as the test sample and the control sample, respectively;
[0009] S4: A proppant is laid on the crack surface of the test specimen, while no proppant is laid on the control specimen. Then, heat shrink tubing is placed around the outer periphery of the test specimen and the control specimen and heated to shrink and fix them.
[0010] S5: Place the test specimen and the control specimen in a mechanical testing machine and perform axial loading and unloading tests under the same loading and unloading conditions. Record the data corresponding to the load-displacement curves of the test specimen and the control specimen during the loading and unloading process.
[0011] S6: Analyze the load-displacement curves of the test specimen and the control specimen. Subtract the initial displacement value from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the loaded displacement value of the test specimen and the loaded displacement value of the control specimen. Then subtract the loaded displacement value of the control specimen from the loaded displacement value of the test specimen to obtain the elastic-plastic deformation value of the test specimen.
[0012] S7: Subtract the displacement value when unloaded to zero load from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the unloading displacement value of the test specimen and the unloading displacement value of the control specimen. Then subtract the unloading displacement value of the control specimen from the unloading displacement value of the test specimen to obtain the elastic deformation value of the test specimen.
[0013] S8: Subtract the elastic deformation value of the test specimen from the elastic-plastic deformation value of the test specimen to obtain the plastic deformation value generated during the proppant embedding process, i.e., the proppant embedding value.
[0014] The proppant is one of quartz sand, resin-coated sand, or ceramsite, and its particle size range includes one of 20 / 40 mesh, 30 / 50 mesh, 40 / 70 mesh, and 70 / 100 mesh.
[0015] The cylindrical rock samples had a diameter of 10–50 mm and a height of 20–100 mm.
[0016] The square rock sample has a length of 10–100 mm, a width of 10–100 mm, and a height of 20–100 mm.
[0017] The loading-unloading condition involves continuously applying an axial load at a loading rate of 1 to 10 kN / min until the maximum load is reached, and then unloading the sample at the same rate as the loading stage until the load is reduced to zero, in order to obtain a complete load-displacement curve. The maximum load is determined as needed based on the formation pressure of the reservoir being tested.
[0018] The aforementioned mechanical testing machine is a triaxial mechanical testing machine capable of simultaneously applying confining pressure and axial load to simulate the proppant embedding behavior under actual stress conditions in reservoir fractures.
[0019] Beneficial Effects: This invention uses the original fracture surface formed by hydraulic fracturing as the test object, which can preserve the true roughness, waveform undulation, and weak surface structure of the fracture surface, making the stress contact and embedding process of the proppant on the fracture wall more closely resemble the original reservoir environment. Propane is laid on the fracture surface, ensuring that the contact state, stress path, and interparticle interaction of the proppant within the fracture are consistent with field conditions. By preparing test specimens with proppant and control specimens without proppant, the deformation values of the two sets of specimens are obtained under the same loading-unloading conditions. The proppant embedding value is obtained by subtracting the deformation value of the control specimen from the deformation value of the test specimen. During loading, normal pressure is applied to the fracture by simulating formation closure stress, obtaining the load-displacement curve for the entire process, thus achieving full-process testing of proppant embedding. Because the control specimen can effectively eliminate the influence of factors such as specimen compression, fracture surface closure, and deformation of the experimental device itself, the accuracy of the embedding value measurement is significantly improved. Compared with existing technologies, this invention can avoid the result deviations caused by traditional flat samples or idealized crack surfaces while preserving the true roughness, waveform undulation, and weak surface structure of the hydraulic crack surface. It can test the embedding depth of multiple proppants and provides a reliable testing method for evaluating the attenuation of effective crack width caused by proppant embedding depth and for proppant selection. The method has a clear logic and simple data processing; the required equipment can rely on common mechanical testing machines; the sample preparation and experimental operation procedures are well-defined, facilitating rapid implementation in ordinary mechanics laboratories and university research platforms, and possessing good engineering applicability and promotional value. Attached Figure Description
[0020] Figure 1 This is a flowchart of the method for measuring the embedding depth of multiple proppants in the original reservoir hydraulic fractures according to the present invention.
[0021] Figure 2 This is a schematic diagram of the cylindrical rock test specimen containing proppant according to the present invention.
[0022] In the diagram, 1-upper rock, 2-heat shrink tubing, 3-proppant, 4-lower rock.
[0023] Figure 3This is a schematic diagram of the load-displacement curve during the loading and unloading process of the test specimen of this invention.
[0024] Figure 4 This is a schematic diagram of the load-displacement curve during the loading and unloading process of the control sample of this invention.
[0025] Figure 5 for Figure 2 A schematic diagram of the geometric shape of a single proppant particle embedded in rock during loading (elastoplastic embedding).
[0026] Figure 6 for Figure 2 A schematic diagram of the geometric morphology of the proppant particles after unloading and plastic embedding. Detailed Implementation
[0027] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings:
[0028] The method for measuring the embedment depth of multiple proppant in original reservoir hydraulic fractures according to the present invention comprises the following steps:
[0029] S1: Extract hydraulically fractured blocky rock from the target reservoir;
[0030] S2: Cut and grind the blocky rock to prepare square or cylindrical rock samples with consistent lithology and crack characteristics. The upper and lower end faces of the rock samples are parallel, and the crack surfaces are all located in the middle of the sample and parallel to the upper and lower end faces. The diameter of the cylindrical rock sample is 10-50 mm and the height is 20-100 mm. The length of the square rock sample is 10-100 mm, the width is 10-100 mm, and the height is 20-100 mm.
[0031] S3: Take two rock samples and label them as the test sample and the control sample, respectively;
[0032] S4: A proppant of the same concentration as that under actual working conditions is laid on the crack surface of the test specimen, while no proppant is laid on the control specimen. Then, heat shrink tubing is placed around the outer periphery of the test specimen and the control specimen and heated to shrink and fix them. The proppant is one of quartz sand, resin-coated sand, or ceramsite, and its particle size range includes one of 20 / 40 mesh, 30 / 50 mesh, 40 / 70 mesh, and 70 / 100 mesh.
[0033] S5: Place the test specimen and the control specimen in a mechanical testing machine and perform axial loading and unloading tests under the same loading and unloading conditions. Record the data corresponding to the load-displacement curves of the test specimen and the control specimen during the loading and unloading process.
[0034] The axial loading-unloading condition involves continuously applying an axial load at a loading rate of 1 to 10 kN / min until the maximum load is reached, and then unloading the sample at the same rate as the loading stage until the load is reduced to zero, in order to obtain a complete load-displacement curve; the maximum load is determined as needed to test the formation pressure of the reservoir.
[0035] The aforementioned mechanical testing machine is a triaxial mechanical testing machine capable of simultaneously applying confining pressure and axial load to simulate the proppant embedding behavior under actual stress conditions in reservoir fractures.
[0036] S6: Analyze the load-displacement curves of the test specimen and the control specimen. Subtract the initial displacement value from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the loaded displacement value of the test specimen and the loaded displacement value of the control specimen. Then subtract the loaded displacement value of the control specimen from the loaded displacement value of the test specimen to obtain the elastic-plastic deformation value of the test specimen.
[0037] S7: Subtract the displacement value when unloaded to zero load from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the unloading displacement value of the test specimen and the unloading displacement value of the control specimen. Then subtract the unloading displacement value of the control specimen from the unloading displacement value of the test specimen to obtain the elastic deformation value of the test specimen.
[0038] S8: Subtract the elastic deformation value of the test specimen from the elastic-plastic deformation value of the test specimen to obtain the plastic deformation value generated during the proppant embedding process, i.e., the proppant embedding value.
[0039] Example 1
[0040] S1: Take blocky rock with hydraulic fractures from the target rock stratum;
[0041] S2: Cut the blocky rock into square rock samples with a length, width and height of 60 mm along the direction of crack extension. Grind and trim the end faces to make them parallel. The crack surface is located in the middle of the sample and parallel to the upper and lower end faces.
[0042] S3: Take two rock samples and label them as test sample and control sample, respectively.
[0043] S4: Lightweight ceramsite with a particle size of 40 / 70 mesh is selected as the proppant, at a concentration of 3.5 kg / m³. 2 The concentration was applied to the crack surface of the test sample, such as... Figure 2 The test specimen was fitted with proppant 3; the control specimen was not fitted with proppant, and then heat shrink tubing 2 was placed over both the test specimen and the control specimen. Figure 2 As shown, heating causes it to shrink;
[0044] S5: Place the test specimen in a mechanical testing machine for axial compression using a loading-unloading method. The loading rate is 1 kN / min, and the unloading rate is the same as the loading rate, loading to the maximum load of 108 kN. After reaching the maximum load, unload the specimen. When the load drops to 0 kN, record the load-displacement curves for the entire loading and unloading process. Subsequently, test the control specimen under the exact same loading and unloading conditions to obtain the load-displacement curve of the control specimen. The single loading and unloading load-displacement curves of the test specimen and the control specimen are shown below. Figure 3 Figure 4 As shown.
[0045] S6: Analyze the load-displacement curve, and subtract the initial displacement value when the load is zero from the displacement value when the maximum load is reached to obtain the loaded displacement of the test specimen. Displacement compared to control sample At this time, the elastic-plastic deformation value of the test specimen is ,like Figure 3 and Figure 4 As shown; the unloading displacement value of the test specimen is obtained by subtracting the displacement value when unloaded to zero load from the displacement value when the maximum load is reached. Unloading displacement value compared with control sample At this time, the elastic deformation value of the test specimen is ,like Figure 3 and Figure 4 As shown;
[0046] S7: Use the elastic-plastic deformation value of the test specimen. Subtract the elastic deformation value of the test specimen Obtain the plastic deformation value of the test specimen. That is, the total embedment depth of the proppant; the unilateral embedment depth of proppant 3. .
[0047] Example 2
[0048] To more closely approximate the original hydraulic fracture stress conditions of the reservoir, confining pressure and axial load were simultaneously applied to the test specimen and the control specimen in a mechanical testing machine.
[0049] S1: Take blocky rock with hydraulic fractures from the target rock stratum;
[0050] S2: Cut the blocky rock along the direction of crack extension into cylindrical rock samples with a diameter of 50 mm and a height of 100 mm. Grind and trim the two ends to make the ends parallel, with the crack surface located in the middle of the sample height and parallel to the upper and lower ends.
[0051] S3: Take two rock samples and label them as test sample and control sample, respectively.
[0052] S4: Proppant 3 is selected from quartz sand with a particle size of 40 / 70 mesh, at 5.0 kg / m³. 2 The concentration was applied to the surface of the test crack, such as... Figure 2 The proppant 3 is placed in the middle; then heat shrink tubing 2 is placed over the test specimen and the control specimen, as shown. Figure 2 As shown, heating causes it to shrink;
[0053] S5: The test specimen was placed in a mechanical testing machine for axial compression using a loading-unloading method. The loading rate was 1 kN / min, and the unloading rate was the same as the loading rate, until the maximum load of 108 kN was reached. After reaching the maximum load, the specimen was unloaded, and the load-displacement curves of the entire loading and unloading process were recorded when the load reached 0 kN. The confining pressure was kept constant at 3 MPa. Subsequently, a control specimen was tested under the same loading and unloading conditions, and the load-displacement curves of the control specimens were obtained, as shown below. Figure 3 Figure 4 As shown.
[0054] S6: Analyze the load-displacement curve, and subtract the initial displacement value when the load is zero from the displacement value when the maximum load is reached to obtain the loaded displacement of the test specimen. Displacement compared to control sample At this time, the elastic-plastic deformation value of the test specimen is ,like Figure 3 and Figure 4 As shown; by subtracting the displacement value when unloaded to zero load from the displacement value when the maximum load is reached, the unloading displacement value ΔL3 of the test specimen and the unloading displacement value ΔL4 of the control specimen are obtained. At this time, the elastic deformation value of the test specimen is... ,like Figure 3 and Figure 4 As shown;
[0055] S7: Use the elastic-plastic deformation value of the test specimen. Subtract the elastic deformation value of the test specimen Obtain the plastic deformation value of the test specimen. That is, the total embedding depth of proppant 3, and the single-sided embedding depth h = / 2.
[0056] Example 3
[0057] S1: Extract blocky rock containing hydraulic fractures from the target rock stratum.
[0058] S2: Cut the blocky rock into square rock samples with dimensions of 60 mm each, along the direction of the crack extension. Grind and trim both ends to make the ends parallel, with the crack surface located in the middle of the sample height and parallel to the upper and lower ends.
[0059] S3: Take two rock samples and label them as test sample and control sample, respectively.
[0060] S4: Propane 3 is selected from lightweight ceramsite with a particle size of 20 / 40 mesh, at a concentration of 4.0 kg / m³. 2 The concentration was applied to the crack surface of the test sample; then heat shrink tubing 2 was placed over the test sample and the control sample and heated to shrink it.
[0061] S5: Place the test specimen in a mechanical testing machine for axial compression using a loading-unloading method. The loading rate is 1 kN / min, and the unloading rate is the same as the loading rate, loading to the maximum load of 108 kN. After reaching the maximum load, unload the specimen. When the load drops to 0 kN, record the load-displacement curves for the entire loading and unloading process. Set the confining pressure on the transverse side perpendicular to the axial plane to 3 MPa, and the confining pressure on the other side to 5 MPa. Test the control specimen under the exact same loading and unloading conditions and obtain the load-displacement curve of the control specimen.
[0062] S6: Analyze the load-displacement curve, and subtract the initial displacement value when the load is zero from the displacement value when the maximum load is reached to obtain the loaded displacement of the test specimen. Displacement compared to control sample At this time, the elastic-plastic deformation value of the test specimen is ,like Figure 3 and Figure 4 As shown; by subtracting the displacement value when unloaded to zero load from the displacement value when the maximum load is reached, the unloading displacement value ΔL3 of the test specimen and the unloading displacement value ΔL4 of the control specimen are obtained. At this time, the elastic deformation value of the test specimen is... ,like Figure 3 and Figure 4 As shown;
[0063] S7: Use the elastic-plastic deformation value of the test specimen. Subtract the elastic deformation value of the test specimen Obtain the plastic deformation value of the test specimen. That is, the total embedding depth of proppant 3 in each cycle; the unilateral embedding depth of proppant 3 is .
Claims
1. A method for measuring the embedment depth of multiple proppants within a primary reservoir hydraulic fracture, characterized in that, Includes the following steps: S1: Extract hydraulically fractured blocky rock from the target reservoir; S2: Cut and grind the blocky rock to prepare square or cylindrical rock samples with consistent lithology and crack characteristics. The upper and lower end faces of the rock sample are parallel, and the crack surface is located in the middle of the sample and parallel to the upper and lower end faces. S3: Take two rock samples and label them as the test sample and the control sample, respectively; S4: A proppant is laid on the crack surface of the test specimen, while no proppant is laid on the control specimen. Then, heat shrink tubing is placed around the outer periphery of the test specimen and the control specimen and heated to shrink and fix them. S5: Place the test specimen and the control specimen in a mechanical testing machine and perform axial loading and unloading tests under the same loading and unloading conditions. Record the data corresponding to the load-displacement curves of the test specimen and the control specimen during the loading and unloading process. S6: Analyze the load-displacement curves of the test specimen and the control specimen. Subtract the initial displacement value from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the loaded displacement value of the test specimen and the loaded displacement value of the control specimen. Then subtract the loaded displacement value of the control specimen from the loaded displacement value of the test specimen to obtain the elastic-plastic deformation value of the test specimen. S7: Subtract the displacement value when unloaded to zero load from the displacement value when the test specimen and the control specimen reach the maximum load to obtain the unloading displacement value of the test specimen and the unloading displacement value of the control specimen. Then subtract the unloading displacement value of the control specimen from the unloading displacement value of the test specimen to obtain the elastic deformation value of the test specimen. S8: Subtract the elastic deformation value of the test specimen from the elastic-plastic deformation value of the test specimen to obtain the plastic deformation value generated during the proppant embedding process, i.e., the proppant embedding value.
2. The method for measuring the embedment depth of multiple proppants in original reservoir hydraulic fractures according to claim 1, characterized in that: The proppant is one of quartz sand, resin-coated sand, or ceramsite, and its particle size range includes one of 20 / 40 mesh, 30 / 50 mesh, 40 / 70 mesh, and 70 / 100 mesh.
3. The method for measuring the embedment depth of multiple proppants in original reservoir hydraulic fractures according to claim 1, characterized in that: The cylindrical rock samples had a diameter of 10–50 mm and a height of 20–100 mm.
4. The method for measuring the embedment depth of multiple proppants in a primary reservoir hydraulic fracture according to claim 1, characterized in that: The square rock sample has a length of 10–100 mm, a width of 10–100 mm, and a height of 20–100 mm.
5. The method for measuring the embedment depth of multiple proppants in hydraulic fractures of a primary reservoir according to claim 1, characterized in that: In step S5, the loading-unloading condition is to continuously apply axial load at a loading rate of 1 to 10 kN / min until the maximum load is reached, and then unload the sample at the same rate as the loading stage until the load is reduced to zero, so as to obtain a complete load-displacement curve; the maximum load is determined according to the formation pressure of the reservoir to be tested.
6. The method for measuring the embedment depth of multiple proppants in a primary reservoir hydraulic fracture according to claim 1, characterized in that: In step S5, the mechanical testing machine is a triaxial mechanical testing machine that can simultaneously apply confining pressure and axial load to simulate the embedding behavior of proppant under real stress state in reservoir fractures.