Method for determining size of bridging particles in temporary plugging of sand-shale fracture based on lithofacies classification
By using lithofacies classification and 3D printing technology, the particle size of temporary plugging and bridging particles in sandstone and conglomerate fractures was determined, which solved the problem of poor sealing effect of temporary plugging and fracturing in sandstone and conglomerate fractures, achieved a more efficient and stable temporary plugging effect in fractures, and reduced experimental costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2022-07-29
- Publication Date
- 2026-07-03
AI Technical Summary
Existing technologies lack methods for determining the particle size of temporary plugging and bridging particles in sandstone and conglomerate fractures for different lithofacies, resulting in poor sealing effects of temporary plugging and fracturing in sandstone and conglomerate fractures, mainly manifested as "unable to plug", which affects the transformation effect.
A lithofacies-based classification method was used to classify sandstone and conglomerate by the gravel content ratio (VG) and the matrix cement strength ratio (RC). Combined with 3D printing technology, a realistic crack model was prepared, and a temporary plugging test was carried out to determine the most suitable bridging particle size.
It improves the effectiveness and stability of temporary plugging in sandstone and conglomerate fractures, enhances the fracturing effect, reduces experimental costs, and reflects the true fracture morphology and surface roughness.
Smart Images
Figure CN117538220B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of oil and gas development technology, specifically relating to a method for determining the particle size of temporary plugging and bridging particles in sandstone and conglomerate fractures based on lithofacies classification. Background Technology
[0002] Temporary plugging fracturing involves pumping in a biodegradable plugging agent during the fracturing process to bridge and seal the fracture, increasing the net pressure within the fracture, opening new fractures, and increasing the complexity of the fractures. It is an important means of improving the volume and effectiveness of hydraulic fracturing.
[0003] The propagation pattern of fractures in conglomerate and sandstone is influenced by factors such as gravel and cementation strength, differing from that of conventional sandstone and shale. The complex lithofacies of conglomerate and the significant differences in fracture propagation across different lithofacies result in poor sealing effects from temporary plugging fracturing within fractures, primarily manifesting as "inability to plug," i.e., poor bridging stability, which severely impacts the effectiveness of temporary plugging fracturing within fractures. The particle size of the bridging particles largely determines the stability of the bridging, and bridging stability is the foundation and core prerequisite for successful temporary plugging fracturing within fractures.
[0004] Currently, the selection of particle size for temporary plugging and bridging particles in conglomerate fractures relies mainly on construction experience or semi-empirical formulas. There is a lack of methods for determining the particle size of temporary plugging and bridging particles in conglomerate fractures for different rock facies, which limits the effectiveness of temporary plugging and modification in conglomerate fractures.
[0005] To improve the pertinence and scientific rigor of temporary plugging in sandstone and conglomerate fractures, it is necessary to establish a method for determining the particle size of bridging particles used for temporary plugging in sandstone and conglomerate fractures based on lithofacies classification. Summary of the Invention
[0006] This invention aims to address the aforementioned deficiencies of existing technologies by providing a method for determining the particle size of temporary plugging and bridging particles in sandstone and conglomerate fractures based on lithofacies classification. This method solves the problems of complex lithofacies, significant differences in fracture propagation characteristics, and the inability of conventional single-mode methods to effectively plug fractures, thereby enabling targeted temporary plugging of fractures in different lithofacies and improving the effectiveness of temporary plugging.
[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:
[0008] A method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification, the method comprising the following steps:
[0009] Step S101: Collect full-diameter core samples from the target layer of this well or the same layer of an adjacent well, and perform gravel composition analysis on the full-diameter core samples to obtain gravel content characteristic parameters. The gravel content characteristic parameters are the gravel content percentage (VG). The higher the gravel content, the larger the VG value.
[0010] Step S102: The strength of gravel and cement in sandstone and conglomerate reservoir samples is obtained by micron indentation test to obtain strength comparison parameters. The strength comparison parameters are the ratio of the strength of the matrix cement to the strength of the gravel, RC. The greater the strength of the matrix cement, the greater the RC value.
[0011] Step S103: Based on RC and VG as the main controlling factors, the sandstone and conglomerate are divided into four types: gravel-supported cemented loose conglomerate, matrix-supported cemented loose conglomerate, matrix-supported cemented dense conglomerate, and gravel-supported cemented dense conglomerate.
[0012] Step S104: Prepare a real fracture model using a full-diameter core as a sample, and obtain the fracture morphology and surface roughness of different rock phase samples by laser scanning.
[0013] Step S105: Based on the crack morphology and surface roughness of different rock phase samples obtained in step S104, crack models of different rock phase samples are obtained by 3D printing to ensure that the crack models have a realistic degree of tortuosity and wall roughness. The crack models are used to carry out repeated comparative tests without being damaged.
[0014] Step S106: Using the crack model obtained by 3D printing in step S105, conduct a temporary plugging test inside the crack to obtain the best matching bridging particle size for cracks under different rock facies.
[0015] Furthermore, in step S103, using RC and VG as the main controlling factors, the sandstone and conglomerate are divided into four categories, specifically including:
[0016] The relationship between the VG and RC values of sandstone and conglomerate reservoir samples and the fracture wall tortuosity of the samples was statistically analyzed to determine the boundary value of VG as a and the boundary value of RC as b.
[0017] If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented loose conglomerate.
[0018] If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is greater than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented conglomerate.
[0019] If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented loose conglomerate.
[0020] If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is greater than b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented dense conglomerate.
[0021] Furthermore, in step S103, the range of the boundary value a of VG is: a∈[0.35,0.45], and the range of the boundary value b of RC is: b∈[25,35].
[0022] Furthermore, in step S104, a real crack model is prepared using a full-diameter core as a sample. Specifically, this includes: using a wire cutting device to cut the full-diameter core into standard rock slabs, and using a Brazilian splitting test device to split the rock slabs to obtain a real crack model as a sample.
[0023] Furthermore, in step S104, obtaining the crack morphology and surface roughness of different rock phase samples by laser scanning specifically includes:
[0024] Three laser scanners are placed on fixed extension arms in the X, Y, and Z directions, respectively. The X, Y, and Z distance matrices of the crack are obtained by measuring the distance between the fixed extension arms and the crack wall of the sample. The X, Y, and Z coordinate values of the crack recorded in the matrix are transmitted to the data acquisition device and the computer. The computer reconstructs the three-dimensional crack morphology and surface roughness of the sample based on the coordinate values acquired by the data acquisition device.
[0025] Furthermore, in step S105, the 3D printing material is selected as a high-strength resin rock plate with strength comparable to that of the reservoir rock.
[0026] Furthermore, in step S105, the 3D printing instrument selected is the RSPro 450 3D printer.
[0027] Furthermore, in step S106, the maximum pumping pressure for conducting the interstitial plugging test is set to 5 MPa, the constant flow pump injection rate is 40 ml / min, and the pump is stopped when the pumping pressure reaches 5 MPa. The formulas of the temporary plugging agent for plugging different rock facies fracture models with fracture widths of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, and 8 mm are obtained, and the particle size of the interstitial plugging bridging particles is determined according to the plugging speed.
[0028] Compared with the prior art, the beneficial effects of the present invention are:
[0029] (1) Existing methods for determining the particle size of temporary plugging bridging particles in sandstone and conglomerate fractures are mostly based on the assumption that the fracture walls are straight and the fracture width does not change. For sandstone and conglomerate, the fracture propagation under different lithofacies differs greatly from the actual situation, resulting in poor plugging and fracturing effects, which are "unblockable". In contrast, this invention classifies sandstone and conglomerate into lithofacies. Different lithofacies have different gravel content ratios, and their corresponding inherent fracture propagation trends are also different. This invention uses the gravel content ratio (VG) and the ratio of matrix cement to gravel strength (RC) as the main controlling factors to divide sandstone and conglomerate into four categories. For each lithofacies, temporary plugging and fracturing tests are carried out to obtain the most suitable bridging particle size for fractures under different lithofacies. This method can reflect the real fracture morphology and surface roughness, approximate the real situation of fractures in different lithofacies of sandstone and conglomerate to the greatest extent, significantly improve the poor bridging stability, improve the effect of temporary plugging and fracturing, and achieve "blocking".
[0030] (2) This invention applies 3D printing technology to the method of determining the particle size of temporary plugging and bridging particles in sandstone fractures. It can truly reflect the tortuousness of hydraulic fractures and the roughness of the wall. The 3D printed fracture model has high strength and can carry out comparative and repeatable experiments without damaging the fracture model, ensuring the reuse of the fracture model and reducing experimental costs. Attached Figure Description
[0031] Figure 1 This is a flowchart illustrating a method for determining the particle size of temporary bridging particles within fractures of sandstone and conglomerate based on lithofacies classification.
[0032] Figure 2 The diagram shows the setup for a micrometer indentation experiment, where left figure a is the setup and right figure b is the test sample.
[0033] Figure 3 A map showing the classification of sandstone and conglomerate reservoirs of different lithofacies;
[0034] Figure 4 In the figure, Figure a shows a physical image of the fracture surface of the matrix-supported cemented dense sandstone and conglomerate in Well A; Figure b shows a physical image of the fracture surface of the gravel-supported cemented dense sandstone and conglomerate in Well B.
[0035] Figure 5 In the figure, Figure a is a laser scanning reconstruction of the fracture surface morphology of matrix-supported cemented dense sandstone and conglomerate in well A; Figure b is a laser scanning reconstruction of the fracture surface morphology of gravel-supported cemented dense sandstone and conglomerate in well B.
[0036] Figure 6 In the figure, Figure a shows the 3D printed fracture model of matrix-supported cemented dense sandstone and conglomerate in Well A, and Figure b shows the 3D printed fracture model of gravel-supported cemented dense sandstone and conglomerate in Well B. Detailed Implementation
[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0038] Combination Figure 1-6 As shown, embodiments of the present invention provide a method for determining the particle size of temporary bridging particles within fractures of sandstone and conglomerate based on lithofacies classification, such as... Figure 1 As shown, the method includes the following steps:
[0039] Step S101: Collect full-diameter core samples from the target layer in wells A and B, and perform gravel composition analysis on the full-diameter core samples from both wells. The gravel content characteristic parameters VG of the full-diameter core samples from wells A and B are 0.2 and 0.8, respectively. VG is the gravel content percentage. The higher the gravel content, the larger the VG value.
[0040] Step S102: Micrometer indentation test (see...) Figure 2 The strength of gravel and cement in the sandstone and conglomerate reservoir samples was obtained respectively. The comparison parameters of the full-diameter core strength of well A and well B were RC, which were 183 and 73 respectively. RC is the ratio of the strength of the matrix cement to the strength of the gravel cement. The greater the strength of the matrix cement, the greater the RC value.
[0041] Step S103: Using RC and VG as the main controlling factors, the conglomerate is divided into four categories: gravel-supported cemented loose conglomerate, matrix-supported cemented loose conglomerate, matrix-supported cemented dense conglomerate, and gravel-supported cemented dense conglomerate. Specifically, 100-150 full-diameter core samples from several wells in the target block are taken, and their VG and RC values are tested. Fracture propagation experiments are conducted, and the relationship between the VG and RC values and the fracture wall tortuosity is statistically analyzed. Then, the boundary value of VG, a, and the boundary value of RC, b, are determined.
[0042] If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented loose conglomerate.
[0043] If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is greater than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented conglomerate.
[0044] If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented loose conglomerate.
[0045] If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is greater than b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented dense conglomerate.
[0046] The VG and RC boundary values obtained for different target blocks show slight deviations, but the deviations are not significant. The range of the VG boundary value 'a' is a∈[0.35,0.45], and the range of the RC boundary value 'b' is b∈[25,35]. In this embodiment of the invention, the classification boundary value VG = 0.4, RC = 30, and the classification result is as follows: Figure 3 As shown. Based on the classification threshold, the full-diameter core of well A is matrix-supported cemented dense sandstone and conglomerate; the full-diameter core of well B is gravel-supported cemented dense sandstone and conglomerate.
[0047] Step S104: For the full-diameter core samples from wells A and B, a wire cutting device was used to cut the core samples into standard rock plates. A Brazilian fracturing test device was then used to split the rock plates, creating a realistic fracture model. (See [link to relevant documentation]). Figure 4 Figure a shows a physical image of the fracture surface of matrix-supported cemented dense sandstone and conglomerate in well A; Figure b shows a physical image of the fracture surface of gravel-supported cemented dense sandstone and conglomerate in well B; and the fracture morphology and surface roughness of different rock phase samples were obtained by laser scanning.
[0048] Specifically, in step S104, the crack morphology and surface roughness of different rock phase samples are obtained by laser scanning. Specifically, three laser scanners are placed on fixed extension arms in the X, Y, and Z directions, respectively. The X, Y, and Z distance matrices of the cracks are obtained by measuring the distance between the fixed extension arms and the crack walls of the samples. The X, Y, and Z coordinate values of the cracks recorded in the matrix are transmitted to a data acquisition device and a computer. The computer reconstructs the three-dimensional crack morphology and surface roughness of the samples based on the coordinate values acquired by the data acquisition device. (See [link to relevant documentation]). Figure 5 Figure a shows the laser scanning reconstruction of the fracture surface morphology of matrix-supported cemented dense sandstone and conglomerate in well A; Figure b shows the laser scanning reconstruction of the fracture surface morphology of gravel-supported cemented dense sandstone and conglomerate in well B.
[0049] Step S105: Based on the crack morphology and surface roughness of the different lithofacies samples obtained in step S104, 3D printing is used to obtain crack models of different lithofacies samples with realistic tortuosity and wall roughness. See [link to step S105]. Figure 6 Figure a shows a 3D-printed fracture model of matrix-supported cemented dense sandstone and conglomerate in well A, and Figure b shows a 3D-printed fracture model of gravel-supported cemented dense sandstone and conglomerate in well B; the fracture models are used to conduct repeated comparative tests without damage.
[0050] In step S105, the RSPro 450 3D printer is selected as the 3D printing instrument, and the preferred 3D printing material is a high-strength resin rock plate with strength comparable to that of the reservoir rock.
[0051] Step S106: Using the crack model obtained by 3D printing in step S05, conduct a temporary plugging test inside the crack. The maximum pumping pressure is set to 5MPa, the constant flow pumping speed is 40ml / min, and the pump is stopped when the pumping pressure reaches 5MPa.
[0052] In step S106, the width of the 3D-printed fracture model of the matrix-supported cemented dense sandstone and conglomerate in well A is 4 mm. The sealing formula is set as follows: 2% fiber + 1% 1 mm particles + 2% 2 mm particles, 2% fiber + 1% 1 mm particles + 2% 2.5 mm particles, 2% fiber + 1% 1 mm particles + 2% 3 mm particles, and 2% fiber + 1% 1 mm particles + 2% 3.5 mm particles. The sealing times to reach 5 MPa are 21.23 min, 18.56 min, 13.17 min, and 14.87 min, respectively. Therefore, the optimal bridging particle size for sealing the 4 mm fracture in well A is 3 mm.
[0053] In step S106, the width of the 3D-printed fracture model of the gravel-supported cemented dense sandstone and conglomerate fracture in well B is 4mm. The sealing formula is set as follows: 2% fiber + 1% 1mm particles + 2% 2mm particles, 2% fiber + 1% 1mm particles + 2% 2.5mm particles, 2% fiber + 1% 1mm particles + 2% 3mm particles, and 2% fiber + 1% 1mm particles + 2% 3.5mm particles. The sealing times to reach 5MPa are 20.18min, 12.33min, 15.39min, and 16.24min, respectively. Therefore, the optimal bridging particle size for sealing the 4mm fracture in well A is 2.5mm.
[0054] The above description is merely an embodiment of this application and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the scope of this application should be included within the protection scope of this invention.
Claims
1. A method for determining the particle size of temporary bridging particles within fractures of sandstone and conglomerate based on lithofacies classification, characterized in that, The method includes the following steps: Step S101: Collect full-diameter core samples from the target layer of this well or the same layer of an adjacent well, and perform gravel composition analysis on the full-diameter core samples to obtain gravel content characteristic parameters. The gravel content characteristic parameters are the gravel content percentage (VG). The higher the gravel content, the larger the VG value. Step S102: The strength of gravel and cement in sandstone and conglomerate reservoir samples is obtained by micron indentation test to obtain strength comparison parameters. The strength comparison parameters are the ratio of the strength of the matrix cement to the strength of the gravel, RC. The greater the strength of the matrix cement, the greater the RC value. Step S103: Based on RC and VG as the main controlling factors, the sandstone and conglomerate are divided into four types: gravel-supported cemented loose conglomerate, matrix-supported cemented loose conglomerate, matrix-supported cemented dense conglomerate, and gravel-supported cemented dense conglomerate. Step S104: Prepare a real fracture model using a full-diameter core as a sample, and obtain the fracture morphology and surface roughness of different rock phase samples by laser scanning. Step S105: Based on the crack morphology and surface roughness of different rock phase samples obtained in step S104, crack models of different rock phase samples are obtained by 3D printing to ensure that the crack models have a realistic degree of tortuosity and wall roughness. The crack models are used to carry out repeated comparative tests without being damaged. Step S106: Using the crack model obtained by 3D printing in step S105, conduct a temporary plugging test inside the crack to obtain the best matching bridging particle size for cracks under different rock facies.
2. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 1, characterized in that, In step S103, RC and VG are the main controlling factors, and the sandstone and conglomerate are divided into four categories, specifically including: The relationship between the VG and RC values of sandstone and conglomerate reservoir samples and the fracture wall tortuosity of the samples was statistically analyzed to determine the boundary value of VG as a and the boundary value of RC as b. If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented loose conglomerate. If the VG of the sandstone and conglomerate reservoir sample is less than or equal to a and the RC is greater than or equal to b, then the sandstone and conglomerate reservoir sample belongs to matrix-supported cemented conglomerate. If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is less than or equal to b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented loose conglomerate. If the VG of the sandstone and conglomerate reservoir sample is greater than a and the RC is greater than b, then the sandstone and conglomerate reservoir sample belongs to gravel-supported cemented dense conglomerate.
3. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 2, characterized in that, In step S103, the range of the boundary value a of VG is: a∈[0.35,0.45], and the range of the boundary value b of RC is: b∈[25,35].
4. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 1, characterized in that, In step S104, a real crack model is prepared using a full-diameter core as a sample. Specifically, this includes: using a wire cutting device to cut the full-diameter core into standard rock slabs, and using a Brazilian splitting test device to split the rock slabs to obtain a real crack model as a sample.
5. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 1, characterized in that, In step S104, the crack morphology and surface roughness of different rock phase samples are obtained by laser scanning, specifically including: Three laser scanners are placed on fixed extension arms in the X, Y, and Z directions, respectively. The X, Y, and Z distance matrices of the crack are obtained by measuring the distance between the fixed extension arms and the crack wall of the sample. The X, Y, and Z coordinate values of the crack recorded in the matrix are transmitted to the data acquisition device and the computer. The computer reconstructs the three-dimensional crack morphology and surface roughness of the sample based on the coordinate values acquired by the data acquisition device.
6. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 1, characterized in that, In step S105, the 3D printing material is selected as a high-strength resin rock plate with a strength comparable to that of the reservoir rock.
7. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 6, characterized in that, In step S105, the 3D printing instrument selected is the RSPro 450 3D printer.
8. The method for determining the particle size of temporary bridging particles in sandstone and conglomerate fractures based on lithofacies classification according to claim 1, characterized in that, In step S106, the maximum pumping pressure for conducting the interstitial plugging test is set to 5 MPa, the constant flow pump injection rate is 40 ml / min, and the pump is stopped when the pumping pressure reaches 5 MPa. The formulas of the temporary plugging agent for plugging different rock facies fracture models with fracture widths of 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, and 8 mm are obtained, and the particle size of the interstitial plugging bridging particles is determined according to the plugging speed.