Dense glutenite reservoir hydraulic fracturing crack track judgment method

Abstract

The invention provides a dense glutenite reservoir hydraulic fracturing crack track judgment method, which comprises the following steps: on the basis of a particle flow method, considering gravel characteristics of dense glutenite, and constructing a glutenite numerical value description model for a dense glutenite reservoir; on the basis of the glutenite numerical description model, establishing a glutenite hydraulic fracturing model to simulate fracturing progress conditions at different moments in the fracturing process; and on the basis of the glutenite hydraulic fracturing model, in combination with the hydraulic fracture track influence factors, the track extension mode of the hydraulic fracturing fracture encountering gravel is judged. According to the method, the main control factors and the track rule of glutenite crack extension are known, the glutenite crack track change is revealed from the microcosmic perspective, the purposes of optimizing construction parameters and controlling the optimal crack form are achieved, and guidance is provided for glutenite hydraulic fracturing engineering design.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a method for determining hydraulic fracturing crack trajectories in a dense sandy conglomerate reservoir. Background Art

[0002] Sandy conglomerate oil and gas reservoirs are low-permeability and tight reservoirs with low natural productivity. They require horizontal well staged fracturing technology to be industrially exploited. There are a large number of gravel particles in the sandy conglomerate reservoir. The reservoir as a whole is characterized by diverse sedimentary types, complex spatial distribution, poor physical properties, and severe heterogeneity. The uneven distribution of gravel and the large differences in the mechanical properties of gravel and matrix make it difficult to predict the fracture extension trajectory. Therefore, for sandy conglomerate reservoirs, the influence of gravel on the fracture extension trajectory cannot be ignored. There are few types of sandy conglomerate reservoirs abroad, so there are few studies on the fracture extension trajectory of sandy conglomerate.

[0003] The methods that can study the extension of gravel fractures at a microscopic scale mainly include RFPA (Rock Failure Process Analysis) and CDEM (Continuous-Discontinuous Element Method). Among them, the RFPA method has poor computational stability, cannot effectively simulate the distribution of fracture width and the evolution of stress field, cannot be redeveloped, and assumes that the gravel particles are circular in the model. The constructed reservoir model is relatively simple and inconsistent with the actual situation. The CDEM method can be effectively combined with the three-dimensional heterogeneous model of gravel, but this method cannot truly depict the actual gravel distribution of gravel in gravel reservoirs. Due to the low permeability and density of gravel reservoirs, there are gravel particles that interfere with the extension of fractures. The extension morphology of hydraulic fractures after encountering gravel is diverse. Previous researchers have failed to fully reveal the relationship between the geological parameters of gravel reservoirs and the extension morphology of fractures encountering gravel.

[0004] In view of the problems of the prior art, the present invention provides a method for determining the trajectory of hydraulic fracturing cracks in a tight sandy conglomerate reservoir. Summary of the invention

[0005] In order to overcome the defects of the prior art, the present invention provides a method for determining the trajectory of hydraulic fracturing cracks in a dense sandy conglomerate reservoir, the method comprising:

[0006] Based on the particle flow method and considering the gravel characteristics of tight conglomerate, a numerical description model of conglomerate for tight conglomerate reservoir is constructed.

[0007] Based on the sandstone numerical description model, a sandstone hydraulic fracturing model is established to simulate the fracturing progress at different times during the fracturing process;

[0008] Based on the sandstone hydraulic fracturing model and combined with the factors affecting the hydraulic fracture trajectory, the trajectory extension mode of the hydraulic fracture encountering gravel is determined.

[0009] According to one embodiment of the present invention, the gravel characteristics include the size, shape, distribution and mechanical properties of gravel particles, and the numerical description model of the conglomerate reservoir is constructed by the following steps:

[0010] According to the geometric size and number of particles of the dense sandy conglomerate sample, a rock matrix model containing rock matrix but not gravel is constructed;

[0011] According to the size, shape and distribution characteristics of gravel particles, a gravel profile is generated on the basis of the rock matrix model to form a gravel particle cluster;

[0012] Based on the mechanical properties of gravel particles, the mechanical parameter amplitudes of the rock matrix and the gravel particle clusters are calculated to obtain a numerical description model of the sandstone reservoir.

[0013] According to one embodiment of the present invention, the gravel particle clusters are formed by the following steps:

[0014] When randomly reconstructing the two-dimensional microstructure of gravel, the shape of the gravel is simplified, irregular polygons are used to replace gravels with complex geometric shapes, and the length of the long axis of the gravel is used to describe the particle size of the gravel.

[0015] If the gradation relationship of gravel particle size is unknown, it is assumed that the particle size of gravel satisfies normal distribution and the spatial distribution of gravel satisfies random distribution;

[0016] The gravel content is expressed by the ratio of the total gravel area of ​​the sample to the sample area.

[0017] According to one embodiment of the present invention, the conglomerate hydraulic fracturing model is established by the following steps:

[0018] By adopting fluid-solid coupling hydraulic fracture numerical simulation, confining pressure is applied to the model boundary of the sandstone numerical description model to simulate reservoir in-situ stress;

[0019] Setting an injection point in the sandstone numerical description model, and pumping a fluid of preset viscosity into the injection point at a preset fracturing fluid injection rate to simulate a hydraulic fracturing process;

[0020] The fracturing progress at different times during the simulated fracturing process is recorded, wherein the fracturing progress includes the geometric dimensions of the fracturing crack, bottom hole pressure, stress field, particle displacement field, and fluid distribution in the fracturing crack.

[0021] According to one embodiment of the present invention, the factors affecting the hydraulic fracture trajectory include: conglomerate reservoir geological factors and engineering factors, wherein the conglomerate reservoir geological factors include: gravel strength, gravel content, gravel particle size, and ground stress difference, and the engineering factors include: fracturing fluid viscosity and fracturing fluid injection rate.

[0022] According to one embodiment of the present invention, the trajectory extension mode includes: a through extension mode, a crack stop extension mode, an embedding extension mode, and a gravel extension mode, wherein the gravel extension mode includes: a turning extension mode, a forked extension mode, and an attraction extension mode.

[0023] According to one embodiment of the present invention, the trajectory extension mode of hydraulic fracturing cracks encountering gravel is determined by the following steps:

[0024] When the dense sandy conglomerate contains only low-strength gravels, within the preset stress difference range, it is determined that the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is the through extension mode, wherein the gravel strength of the low-strength gravels is less than or equal to 9.5 Gpa, and the preset stress difference range is 5 MPa-15 MPa;

[0025] When the dense sandy conglomerate contains only high-strength gravels, within the preset stress difference range, it is determined that the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is the gravel-circling extension mode and the embedded extension mode including the turning extension mode and the attraction extension mode, wherein the gravel strength of the high-strength gravels is greater than or equal to 16.2 GPa;

[0026] When the dense sandy conglomerate contains only high-strength gravel, within the preset gravel content range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravel is judged to be the attraction extension mode, the penetration extension mode, and the embedding extension mode, wherein the preset gravel content range is 25%-55%;

[0027] When the dense sandy conglomerate contains only high-strength gravels, within the preset gravel particle size range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is judged to be the gravel-around extension mode, the through extension mode, and the embedded extension mode, wherein the preset gravel particle size range is 2 mm-10 mm;

[0028] When the dense sandy conglomerate contains only high-strength gravels, under the condition of low injection rate of the fracturing fluid, within the preset stress difference range, the trajectory extension mode of the hydraulic fracturing crack encountering gravels is judged to be the gravel extension mode and the through extension mode, wherein the low injection rate of the fracturing fluid is 1×10 -5 m 2 / s;

[0029] When the dense sandy conglomerate contains only high-strength gravel, within the preset stress difference range and the preset fracturing fluid viscosity range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravel is judged to be the passing extension mode and the bifurcation extension mode, wherein the preset fracturing fluid viscosity range is 3mPa·s-50mPa·s.

[0030] According to an embodiment of the present invention, the method further comprises: analyzing the main controlling factors and trajectory rules of the extension of the gravel rock cracks, and providing feedback to modify the construction parameters so as to control the target optimal crack morphology.

[0031] According to another aspect of the present invention, a storage medium is provided, which contains a series of instructions for executing the method steps as described in any one of the above.

[0032] According to another aspect of the present invention, there is also provided a device for determining the trajectory of hydraulic fracturing cracks in a tight sandy conglomerate reservoir, which executes the method described in any one of the above items, and the device comprises:

[0033] The description model module is based on the particle flow method, taking into account the gravel characteristics of tight conglomerate, and constructing a conglomerate numerical description model for tight conglomerate reservoirs;

[0034] A fracturing model module, which is used to establish a sandstone hydraulic fracturing model based on the sandstone numerical description model to simulate the fracturing progress at different times during the fracturing process;

[0035] The trajectory extension module determines the trajectory extension mode of hydraulic fracturing cracks encountering gravel based on the sandstone hydraulic fracturing model and the factors affecting the hydraulic fracture trajectory.

[0036] The present invention provides a method for determining the fracture trajectory of hydraulic fracturing in a tight conglomerate reservoir, which has the following advantages over the prior art:

[0037] 1) Based on the particle flow method, the size, shape, distribution and mechanical properties of gravel particles are fully considered to establish a numerical description model of sandstone that is closer to the real reservoir;

[0038] 2) A conglomerate hydraulic fracturing model is established based on the conglomerate numerical description model, which can simulate the fracture geometry, bottom hole pressure, stress field, particle displacement field and fluid distribution in the fracture at different times during the fracturing process;

[0039] 3) Analyze the influence of sandstone reservoir geological factors (gravel strength, gravel content, gravel size, ground stress difference) and engineering factors (fracturing fluid viscosity, displacement) on the trajectory of hydraulic fractures, and determine the six possible extension modes of hydraulic fractures encountering gravel, namely: through extension mode, arrest extension mode, embedded extension mode, turning extension mode, bifurcation extension mode and attraction extension mode;

[0040] 4) Through the understanding of the main controlling factors and trajectory laws of conglomerate fracture extension, the changes in the trajectory of conglomerate fractures are revealed from a microscopic perspective, so as to optimize the construction parameters and control the optimal fracture morphology, providing guidance for the design of conglomerate hydraulic fracturing projects.

[0041] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0043] Figure 1 A flowchart showing the steps of a method for determining a hydraulic fracturing fracture trajectory of a tight conglomerate reservoir according to an embodiment of the present invention is shown;

[0044] Figure 2(a)-Figure 2(c) A flowchart of establishing a sandstone core numerical model based on a particle flow method according to an embodiment of the present invention is shown;

[0045] Figure 3 A diagram showing a numerical model of fracture extension of sandstone fractures established based on a particle flow method according to an embodiment of the present invention is shown;

[0046] Figure 4(a)-Figure 4(f) A schematic diagram of a hydraulic fracture extending in gravel according to an embodiment of the present invention is shown;

[0047] Figure 5(a)-Figure 5(c) A diagram showing the extension morphology of cracks in low gravel strength sandstone with different stress differences according to an embodiment of the present invention is shown;

[0048] Figure 6(a)-Figure 6(c) A diagram showing the extension morphology of cracks in high gravel strength conglomerate with different stress differences according to an embodiment of the present invention is shown;

[0049] Figure 7(a)-Figure 7(c) A diagram showing the extension morphology of fractures in glutenite with different gravel contents according to an embodiment of the present invention is shown;

[0050] Figure 8(a)-Figure 8(c) A diagram showing the extension morphology of sandstone fractures with different gravel grain sizes according to an embodiment of the present invention is shown;

[0051] Figure 9(a)-Figure 9(c) The low injection rate (1×10 -5 m 2 / s) condition;

[0052] Figure 10(a)-Figure 10(f) A diagram showing the extension morphology of sandstone fractures with different fracturing fluid viscosities according to an embodiment of the present invention is shown;

[0053] Fig.11 A screenshot of the two-dimensional display and parameter setting of the sweetness of the J72-9-P2 well according to an embodiment of the present invention is shown.

[0054] In the accompanying drawings, the same reference numerals are used for the same components. In addition, the accompanying drawings are not drawn according to the actual scale. DETAILED DESCRIPTION

[0055] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0056] For conglomerate reservoirs, the influence of gravel on fracture extension trajectory cannot be ignored. There are few types of conglomerate reservoirs abroad, so there are few studies on conglomerate fracture extension trajectory.

[0057] Luo Pan and others in China determined the direction of fracture extension by calculating the critical energy release rate, and determined the position of gravel particles according to the fluctuation of critical fracture pressure. Li Ning and others analyzed the results of rock sample experiments and believed that the tortuosity and branching fractures generated by fractures encountering gravel will cause a sharp increase in pumping pressure during the fracture extension stage. Liu Xiangjun and others established a two-dimensional wellbore model based on the gravel distribution of the real sandstone core cross section, thereby simulating the intersection of fracture extension and gravel particles. Liu Xiangjun and others used the grey correlation method and the hierarchical analysis method to comprehensively consider factors such as gravel characteristics and horizontal ground stress differences, and established a calculation model for the evaluation coefficient of the fracturability of sandstone reservoirs. The dimensionless fracturing fracture area and the meter-level liquid production index were positively correlated with the fracturability evaluation coefficient.

[0058] Wang Hao used RFPA software to establish a 1000mm×1000mm sandstone reservoir model and studied the effects of gravel content and gravel size on the extension morphology of sandstone fractures. The results showed that after fracturing, multiple branch fractures were generated in the sandstone reservoir and distributed in a network, which was consistent with the physical simulation results. Zhao Zhihong used the plane stress analysis method to find that the extension pressure increased with the increase of gravel size, and the extension pressure of round gravels was higher than that of elliptical gravels. Ju Yang et al. reconstructed the CT scanning results of sandstone in three dimensions, established a three-dimensional heterogeneous numerical model, and simulated the extension of sandstone fractures using the continuous medium-discrete element method (CDEM). Yu Donghe et al. combined the theories of damage mechanics and fracture mechanics and established a mathematical model of sandstone fracture extension using the micro-damage finite element method.

[0059] In summary, the methods that can study the extension of gravel fractures at a microscopic scale mainly include RFPA (Rock Failure Process Analysis) and CDEM (Continuous-Discontinuous Element Method). Among them, the RFPA method has poor computational stability, cannot effectively simulate the distribution of fracture width and the evolution of stress field, cannot be secondary developed, and the gravel particles in the model are assumed to be circular, so the constructed reservoir model is relatively simple and inconsistent with the actual situation. The CDEM method can be effectively combined with the three-dimensional heterogeneous model of gravel, but this method cannot truly depict the actual gravel distribution of gravel in gravel reservoirs. Due to the low permeability and density of gravel reservoirs, there are gravel particles that interfere with fracture extension, and the extension morphology of hydraulic fractures after encountering gravel is diverse. Previous researchers have failed to fully reveal the relationship between the geological parameters of gravel reservoirs and the extension morphology of fractures encountering gravel.

[0060] In order to solve the problems of the current existing technology, the present invention involves understanding the laws of fracturing cracks in sandstone gravel reservoirs and improving the transformation effect. Based on the PFC (Particle Flow Code) method, the size, shape, distribution and mechanical properties of gravel particles are fully considered to establish a numerical model of gravel that is closer to the real reservoir. The stress field, pressure field and the evolution and distribution of the geometric shape of hydraulic fractures during hydraulic fracturing are simulated, and the changes in the fracture trajectory of gravel are revealed from a microscopic perspective. Taking irregular polygonal gravel as an example, six possible extension modes of hydraulic fractures encountering gravel are given, namely: passing, stopping, embedding, turning, bifurcation and attraction. Among them, the latter three situations can be summarized as "around gravel" extension. The influence of ground stress difference, gravel strength, gravel content, gravel particle size, gravel ratio, fracturing fluid injection rate and fracturing fluid viscosity on the fracture trajectory of gravel is analyzed, and the main controlling factors of hydraulic fracturing fracture extension in gravel reservoirs are studied, which provides a theoretical basis for guiding the optimization of gravel fracturing construction parameters.

[0061] Figure 1 A flowchart of the steps of a method for determining hydraulic fracturing fracture trajectories in a tight conglomerate reservoir according to an embodiment of the present invention is shown.

[0062] like Figure 1 As shown, in step S101, based on the particle flow method and taking into account the gravel characteristics of the tight conglomerate, a conglomerate numerical description model for the tight conglomerate reservoir is constructed.

[0063] In one embodiment, in step S101, the gravel characteristics include the size, shape, distribution and mechanical properties of the gravel particles, and a numerical description model of the sandstone reservoir is constructed through steps S1011-S1013. Specifically, to establish a gravel model, it is necessary to construct a gravel contour according to certain constraints, and the particles within the contour are gravel particles, and the particles outside the contour are matrix particles.

[0064] In step S1011, a rock matrix model including rock matrix but not gravel is constructed according to the geometric size and number of particles of the dense conglomerate sample. Specifically, a rock matrix model without gravel is generated according to the geometric size and number of particles of the conglomerate core sample, as shown in FIG2(a).

[0065] In step S1012, gravel contours are generated based on the rock matrix model according to the size, shape and distribution characteristics of the gravel particles, and gravel particle clusters are formed. Specifically, gravel contours are generated based on the established rock matrix model according to the geometric distribution characteristics of the gravel, and gravel particle clusters are formed, as shown in FIG2(b).

[0066] In step S1013, based on the mechanical properties of gravel particles, the mechanical parameter amplitudes of the rock matrix and gravel particle clusters are calculated to obtain a numerical description model of the sandstone reservoir. Specifically, the mesoscopic mechanical parameters of gravel and matrix particles are assigned, as shown in Figure 2(c).

[0067] In one embodiment, in step S1012, gravel particle clusters are formed by the following steps: when randomly reconstructing the two-dimensional microstructure of gravel, the shape of the gravel is simplified, irregular polygons are used to replace gravel with complex geometric shapes in fact, and the length of the major axis of the gravel is used to describe the particle size of the gravel; if the grading relationship of the gravel particle size cannot be known, it is considered that the particle size of the gravel satisfies the normal distribution, and the spatial position distribution of the gravel satisfies the random distribution; the gravel content is represented by the ratio of the total area of ​​the sample gravel to the sample area.

[0068] Specifically, the geometric shape of gravels in sandy conglomerate reservoirs is relatively complex. When randomly reconstructing the two-dimensional microstructure of gravels, the shape of gravels needs to be simplified. Irregular polygons are used to approximate gravels with more complex geometric shapes. The length of the major axis of gravels is used to describe the size of gravels. If the grading relationship of gravel particle size cannot be given, when constructing a random structure model of sandy conglomerate, it is generally believed that the size of gravels approximately satisfies the normal distribution, that is, the number of medium-sized gravels is the largest, and the spatial position distribution of gravels is also highly random. The gravel content can be expressed by the ratio of the total gravel area to the sample area.

[0069] In the prior art, the methods that can study the extension of sandstone fractures at a microscopic scale mainly include RFPA and CDEM methods, but both have corresponding defects. The present invention adopts a particle flow method, which can fully consider factors such as the size, shape, distribution and mechanical properties of gravel particles, and establish a numerical description model of sandstone that is closer to the real tight sandstone reservoir.

[0070] like Figure 1 As shown, in step S102, a conglomerate hydraulic fracturing model is established based on the conglomerate numerical description model to simulate the fracturing progress at different times during the fracturing process. Specifically, a fluid-solid coupling hydraulic fracturing model (conglomerate hydraulic fracturing model) is established based on the conglomerate reservoir model (conglomerate numerical description model), a confining pressure is applied to the model boundary to simulate the reservoir in-situ stress, and then a fluid with a certain viscosity is pumped into the injection point at a certain fracturing fluid injection rate to simulate the hydraulic fracturing process, and the fracture geometry, bottom hole pressure, stress field, particle displacement field, and fluid distribution in the fracture at different times during the fracturing process are recorded.

[0071] In one embodiment, in step S102, a conglomerate hydraulic fracturing model is established by the following steps: using fluid-solid coupling hydraulic fracture numerical simulation, applying confining pressure at the model boundary of the conglomerate numerical description model to simulate reservoir in-situ stress; setting injection points in the conglomerate numerical description model, pumping fluid of preset viscosity into the injection points at a preset fracturing fluid injection rate to simulate the hydraulic fracturing process; recording the fracturing progress at different times during the simulated fracturing process, wherein the fracturing progress includes the geometric size of the fracturing crack, bottom hole pressure, stress field, particle displacement field, and fluid distribution in the fracturing crack.

[0072] Specifically, a conglomerate hydraulic fracturing model is established based on the established conglomerate numerical description model, such as Figure 3 The model size is 50 mm × 50 mm, the rock porosity is 9.98%, the particle size follows a random uniform distribution model, the ratio of the maximum radius to the minimum radius of the particle is 1.66, the average particle radius is 0.24 mm, and the particle density is 2600 kg / m 3, the total number of particles is 31145. An injection point is set in the middle of the model to simulate the injection of fracturing fluid. The fluid-solid coupling hydraulic fracture extension numerical simulation is adopted. The confining pressure is applied to the model boundary to simulate the reservoir stress. Then, a fluid with a certain viscosity is pumped into the injection point at a certain fracturing fluid injection rate to simulate the hydraulic fracturing process. The fracture geometry, bottom hole pressure, stress field, particle displacement field and fluid distribution in the fracture are recorded at different times during the fracturing process.

[0073] like Figure 1 As shown, in step S103, based on the sandstone hydraulic fracturing model and in combination with the factors affecting the hydraulic fracture trajectory, the trajectory extension mode of the hydraulic fracture encountering gravel is determined.

[0074] In one embodiment, factors affecting hydraulic fracture trajectory include: gravel reservoir geological factors and engineering factors, wherein the gravel reservoir geological factors include: gravel strength, gravel content, gravel particle size, and ground stress difference; and the engineering factors include: fracturing fluid viscosity and fracturing fluid injection rate.

[0075] In one embodiment, the track extension mode includes: a through extension mode, a crack stop extension mode, an embedding extension mode, and a boulder-around extension mode, wherein the boulder-around extension mode includes: a turning extension mode, a bifurcated extension mode, and an attraction extension mode.

[0076] Specifically, taking irregular polygonal gravel as an example, the present invention proposes six possible extension modes of hydraulic fractures encountering gravel, namely: penetration (Figure 4(a)), arrest (Figure 4(b)), embedding (Figure 4(c)), turning (Figure 4(d)), bifurcation (Figure 4(e)) and attraction (Figure 4(f)). Among them, the last three situations can be summarized as "around gravel" extension.

[0077] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only low-strength gravel, within a preset stress difference range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be a through extension mode, wherein the gravel strength of the low-strength gravel is less than or equal to 9.5 Gpa, and the preset stress difference range is 5 MPa-15 MPa.

[0078] Specifically, the fracturing fluid injection rate is 10-4m 2 / s, the fracturing fluid viscosity is 10mPa·s, the gravel content is 40%, the gravel particle size is 2-6mm, the gravel major-minor axis ratio is 1.2-1.8, and it is assumed that the sandstone contains only low-strength gravel (E*=9.5GPa). The simulated fracture extension morphology is as follows Figure 5(a)-Figure 5(c) .

[0079] It can be seen that under different stress difference conditions (Figure 5(a) is a stress difference of 5MPa, Figure 5(b) is a stress difference of 10MPa, and Figure 5(c) is a stress difference of 15MPa), the hydraulic fractures show a "penetrating gravel" extension mode no matter at what angle they encounter gravel, indicating that gravel with low fracture toughness and low strength has almost no shielding effect on hydraulic fractures, and can even promote the uniform extension of fractures. As the stress difference increases, the straighter the fracture, the smaller the curvature. In addition, tensile microcracks are almost generated under different stress difference conditions, but a small amount of shear microcracks are generated under higher stress difference conditions (10MPa and 15MPa), indicating that high confining pressure is more likely to cause shear failure.

[0080] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only high-strength gravel, within a preset stress difference range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be a gravel-circling extension mode and an embedding extension mode including a steering extension mode and an attraction extension mode, wherein the gravel strength of the high-strength gravel is greater than or equal to 16.2 GPa.

[0081] Specifically, the fracturing fluid injection rate is 10-4m 2 / s, the viscosity of the fracturing fluid is 10mPa·s, the gravel content is 40%, the gravel particle size is 2-6mm, the gravel major-minor axis ratio is 1.2-1.8, and it is assumed that the sandstone contains only high-strength gravel (E*=16.2GPa). The simulated fracture extension morphology is as follows Figure 6(a)-Figure 6(c) .

[0082] It can be seen that under different stress difference conditions (Figure 6(a) shows a stress difference of 5MPa, Figure 6(b) shows a stress difference of 10MPa, and Figure 6(c) shows a stress difference of 15MPa), the dominant left-wing cracks have obvious "turning" and "attraction" phenomena, while the right-wing cracks have all experienced "embedding" phenomena. Analysis shows that the elastic modulus and fracture toughness of gravel are much greater than those of the matrix, which makes it difficult for hydraulic fractures to "penetrate gravel" when encountering gravel. Even if they enter the gravel, the extension resistance is large, the energy at the crack tip is insufficient, and it is easy to embed, resulting in a higher tip pressure at the end of the simulation. In addition, the left-wing cracks appear to pass through the edge of the gravel. Analysis shows that this is because it is difficult to turn and truly bypass the gravel due to the limitations of two dimensions, while in three-dimensional situations, the cracks can bypass the gravel. Therefore, in this project, passing through the edge of the gravel can be approximately regarded as "circling the gravel" or having a "trend to bypass the gravel."

[0083] It can be seen that large-size gravels have a significant attraction to the fractures, and they are more likely to turn after being attracted. This is due to the stress concentration of large-size gravels, which leads to the weakening of the stress field around the gravels. Therefore, the extension mode of hydraulic fractures encountering gravels is manifested as an obvious "around gravel" extension mode, indicating that gravels with high fracture toughness and high strength have a certain shielding effect on hydraulic fractures. When the stress difference is 5MPa and 10MPa, the left-wing cracks show obvious around-gravel extension in both the near field and the far field, while under the condition of high stress difference, the cracks extend through gravels in the far field. Under different stress difference conditions, the right-wing cracks are directly facing large-size gravels and are in an "embedded" extension mode, which indicates that the gravel size and the intersection angle of hydraulic fractures and gravels have a certain influence on the extension mode. In addition, under different stress difference conditions, tensile microcracks are mainly generated, but a small number of shear microcracks are generated under higher stress difference (15MPa). Compared with the simulation results of low gravel strength conglomerate, it can be seen that the stress difference required for high gravel strength conglomerate to generate shear microcracks is larger.

[0084] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only high-strength gravel, within a preset gravel content range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be an attraction extension mode, a penetration extension mode, or an embedding extension mode, wherein the preset gravel content range is 25%-55%.

[0085] Specifically, Figure 7(a)-Figure 7(c) The crack extension law of high gravel strength conglomerate under three gravel content conditions is shown. The stress difference is set to 5MPa. Figure 7(a)-Figure 7(c) The gravel content is 25%, 40%, and 55% respectively, the gravel particle size is 2-6 mm, the gravel length-short axis ratio is 1.2-1.8, the fracturing fluid viscosity is 10 mPa·s, and the fracturing fluid injection rate is 10-4 m 2 / s. The results show that the greater the content of visible gravel, the lower the degree of crack curvature. At this time, the attraction of large-size gravel to the crack is reduced, and the extension through gravel is more significant. In addition, when the gravel content is 40%, the cracks formed are extremely asymmetric, while the cracks formed under low gravel content (25%) and high gravel content (55%) conditions are significantly more symmetrical. The asymmetric extension of the cracks is mainly caused by the embedding of the cracks in large-size gravel, which shows that the extension mode of the cracks encountering gravel is not only affected by the strength of the gravel, but also by factors such as the position, size and intersection angle of the gravel.

[0086] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only high-strength gravel, within a preset gravel particle size range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be a gravel extension mode, a through extension mode, or an embedded extension mode, wherein the preset gravel particle size range is 2 mm-10 mm.

[0087] Specifically, Figure 8(a)-Figure 8(c) The crack extension law of high-strength gravel conglomerate under three gravel particle size conditions is shown. The ground stress difference is set to 5MPa. Figure 8(a)-Figure 8(c) The gravel particle sizes are 2-6 mm, 4-8 mm, and 6-10 mm, respectively; the gravel content is 40%, the gravel length-short axis ratio is 1.2-1.8, the fracturing fluid viscosity is 10 mPa·s, and the fracturing fluid injection rate is 10-4 m 2 / s. The results show that under the condition of low gravel particle size (2-6 mm), gravel has a certain attraction to cracks, causing cracks to extend around gravel when encountering gravel, but the overall crack bending degree is small. When the gravel particle size reaches 4-8 mm and 6-10 mm, the attraction of large-size gravel to cracks is very obvious, resulting in a significant change in the crack trajectory and a greater degree of crack bending. The main extension modes of cracks encountering gravel are "penetrating gravel" and "embedding", which shows that large-size high-strength gravel has a significant effect on the local stress field, resulting in a greater degree of bending of the crack extension trajectory.

[0088] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only high-strength gravel, under the condition of low injection rate of fracturing fluid, within the preset stress difference range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be a gravel extension mode or a through extension mode, wherein the low injection rate of fracturing fluid is 1×10 -5 m 2 / s.

[0089] Specifically, Figure 9(a)-Figure 9(c) The fracture extension law of high gravel strength conglomerate under different fracturing fluid injection rates (fracturing displacement) and different stress difference conditions is shown. Figure 9(a)-Figure 9(c) The injection rate is 10 -5 m 2 / s, stress difference is 5MPa, 10MPa, 15MPa, gravel content is 40%, gravel particle size is 2-6mm, gravel length-short axis ratio is 1.2-1.8, fracturing fluid viscosity is 10mPa·s. The results show that with high injection rate (10 -4 m 2 / s) simulation results show that under low stress difference (5MPa) conditions, the lower the injection rate, the easier it is for the fracture to turn significantly after being attracted by the gravel, and the "gravel around" trend is more significant. Under high stress difference (15MPa) conditions, the fracture is straighter, and the right wing fracture has obvious "gravel penetration" phenomenon. The fracture as a whole tends to extend along the direction of the maximum principal stress. This is because at the far end of the fracture, the influence of the ground stress on the fracture extension is dominant. In addition, as the stress difference increases, the probability of shear microcracks increases.

[0090] In one embodiment, in step S103, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined by the following steps: when the dense sandy conglomerate contains only high-strength gravel, within a preset stress difference range and a preset fracturing fluid viscosity range, the trajectory extension mode of the hydraulic fracturing cracks encountering gravel is determined to be a passing extension mode or a bifurcated extension mode, wherein the preset fracturing fluid viscosity range is 3 mPa·s-50 mPa·s.

[0091] Specifically, Figure 10(a)-Figure 10(f) The crack extension law of high gravel strength sandy conglomerate under two fracturing fluid viscosities and three stress difference conditions is shown. Figure 10(a)-Figure 10(c) In the experiment, the viscosity of the fracturing fluid was 3 mPa·s, and the stress differences were 5 MPa, 10 MPa, and 15 MPa, respectively. Figure 10(d)-Figure 10(f) The viscosity of the fracturing fluid is 50 mPa·s, the stress difference is 5 MPa, 10 MPa, and 15 MPa, the gravel content is 40%, the gravel particle size is 2 to 6 mm, the gravel aspect ratio is 1.2 to 1.8, and the fracturing fluid injection rate is 10 -4 m 2 / s. The results show that the higher the viscosity of the fracturing fluid, the more obvious the trend of the "penetrating gravel" extension mode of the crack. When the viscosity reaches 50mPa·s, the right-wing crack directly penetrates the third gravel instead of being embedded in the first gravel. In addition, under low stress difference (5MPa) conditions, as the viscosity of the fracturing fluid increases, the cracks are significantly straighter, while under medium and high stress difference conditions (10MPa, 15MPa), the cracks are relatively straight under different fracturing fluid viscosities. In addition, as the viscosity of the fracturing fluid increases, the possibility of shear microcracks decreases. When the viscosity is 50mPa·s, no shear microcracks are generated under different stress difference conditions. In addition, bifurcated cracks may occur under high fracturing fluid viscosity and high stress difference conditions.

[0092] The present invention is based on the conglomerate hydraulic fracturing model, analyzes the influence of conglomerate reservoir geological factors (gravel strength, gravel content, gravel size, ground stress difference) and engineering factors (fracturing fluid viscosity, displacement) on the hydraulic fracture trajectory, and judges the six possible extension modes of hydraulic fractures encountering gravel, namely: penetration, arrest, embedding, turning, bifurcation and attraction. By understanding the main controlling factors and trajectory laws of conglomerate fracture extension, the change of conglomerate fracture trajectory can be revealed from a microscopic perspective, so as to achieve the purpose of optimizing construction parameters and controlling the optimal fracture morphology, and provide guidance for the design of conglomerate hydraulic fracturing engineering.

[0093] In one embodiment, a method for determining fracture trajectory of hydraulic fracturing in a tight conglomerate reservoir further includes: analyzing the main controlling factors and trajectory rules of conglomerate fracture extension, and providing feedback to modify construction parameters to control the target optimal fracture morphology.

[0094] There are a large number of gravel particles in the sandy conglomerate reservoir. The reservoir as a whole is characterized by diverse sedimentary types, complex spatial distribution, poor physical properties, and severe heterogeneity. The uneven distribution of gravel and the great difference in mechanical properties between gravel and matrix affect the trajectory of fracture extension. The fracture is prone to bend, which brings difficulties to hydraulic fracturing and sand addition. Therefore, it is very important to judge the trajectory of hydraulic fractures in the sandy conglomerate reservoir. The method of the present invention is based on the particle flow method, fully considering factors such as the size, shape, distribution and mechanical properties of gravel particles, and establishing a sandy conglomerate numerical model that is closer to the real reservoir. It simulates the evolution and distribution of fracture geometry during hydraulic fracturing, analyzes the influence of ground stress difference, gravel strength, gravel content, gravel particle size, gravel ratio, fracturing fluid injection rate and fracturing fluid viscosity on the fracture trajectory of sandy conglomerate fracturing, and reveals the changes in the fracture trajectory of sandy conglomerate from a microscopic perspective, providing a theoretical basis for guiding the optimization of sandy conglomerate fracturing construction parameters.

[0095] Fig.11 A screenshot of the two-dimensional display and parameter setting of the sweetness of the J72-9-P2 well according to an embodiment of the present invention is shown.

[0096] Anpeng 2HF Well is an evaluation well in Anpeng Township, Tongbai County, Henan Province, with a designed well depth of 5,000 meters. It is located in the Anpeng nose structure of the Biyang Sag. The deep strata in Anpeng have high oil and gas reserves (oil-bearing area of ​​5.34 km 2 , oil reserves 99.95×104t, natural gas reserves 6.74×108m 3), but the recovery rate is low (oil recovery rate is 10.53%, natural gas recovery rate is 6.74%), and the oil and gas production needs to be further released. The landing layer of Anpeng 2HF is the IX24 sublayer of the core 3 segment. The sand body thickness of this layer is 13-23m, the gas-bearing area is large, and the distribution is stable. It has a large exploration space. Through the drilled well Mi72, it is expected to encounter the Quaternary Pingyuan Formation, the Neogene Fenghuangzhen Formation, and the Paleogene Hetaoyuan Formation from top to bottom. The lithology of the target layer has certain changes in the direction of the wellbore trajectory. The target point A is mainly fine sandstone, and the target point B has a larger gravel size and is sandstone. Through the analysis and comparison of the above models, it can be seen that under the target reservoir conditions (stress difference <8MPa), the fracture expansion of the gravel rock at target point B is mainly around the gravel mode. The fracture has high tortuosity and high friction resistance, which reduces the sand carrying capacity of the fracturing fluid and easily causes sand falling out in the fracture, making it difficult to add sand. The on-site construction curve reflects this feature. The first stage of fracturing near target point B is obviously high in fracturing and difficult to add sand. The construction pressure is (70-85MPa) and the displacement is 7-13m 3 / min, the amount of liquid entering the ground is 2064m 3 , total sand volume 120.5m 3 , which fully demonstrates the adverse effects of gravel-around fractures in conglomerate reservoirs. In the design of this well, although the amount of sand for grinding was increased, the use of low displacement and high viscosity fracturing fluid was also conducive to the symmetrical extension of conglomerate fractures. At the same time, the use of high viscosity fracturing fluid can effectively increase the fracture width and reduce filtration. However, due to the geological conditions of the formation itself, such as small ground stress difference, high gravel content, small gravel particle size and low gravel strength, gravel-around fractures were formed, which increased the difficulty of construction.

[0097] There are a large number of gravel particles in the sandy conglomerate reservoir. The overall reservoir is characterized by diverse sedimentary types, complex spatial distribution, poor physical properties, and severe heterogeneity. The uneven distribution of gravel and the large differences in the mechanical properties of gravel and matrix affect the fracture extension trajectory, causing fracture bending and increased surface roughness, which brings difficulties to fracturing construction and increases the risk of sand plugging. Therefore, for sandy conglomerate reservoirs, the influence of gravel on the extension trajectory of hydraulic fractures is crucial.

[0098] The present invention first constructs a numerical description model of a sandstone reservoir based on the PFC method, wherein the key is to establish a gravel model, that is, to construct the gravel outline according to certain constraints, the particles within the outline are gravel particles, and the particles outside the outline are matrix particles. When randomly reconstructing the two-dimensional microstructure of the gravel, the shape of the gravel needs to be simplified. Irregular polygons are used to approximate gravels with more complex geometric shapes in reality, and the length of the major axis of the gravel is used to describe the size of the gravel. If the grading relationship of the gravel particle size cannot be given, when constructing a random structure model of sandstone, it is generally believed that the size of the gravel approximately satisfies the normal distribution, that is, the number of gravels with medium particle size is the largest, and the spatial position distribution of the gravel also has strong randomness. The gravel content can be represented by the ratio of the total area of ​​the gravel to the sample area.

[0099] The present invention establishes a fluid-solid coupling hydraulic fracturing model based on a sandy conglomerate reservoir model, applies confining pressure at the model boundary to simulate reservoir geostress, then pumps a fluid of a certain viscosity into the injection point at a certain fracturing fluid injection rate to simulate the hydraulic fracturing process, records the fracture geometry, bottom hole pressure, stress field, particle displacement field, and fluid distribution in the fracture at different times during the fracturing process, analyzes the influence of sandy conglomerate reservoir geological factors (gravel strength, gravel content, gravel size, geostress difference) and engineering factors (fracturing fluid viscosity, displacement) on the hydraulic fracture trajectory, and gives six possible extension modes of hydraulic fractures encountering gravel, namely: penetration, arrest, embedding, turning, bifurcation, and attraction, wherein the last three situations can be summarized as "gravel-around" extension.

[0100] The present invention optimizes construction parameters by understanding the main controlling factors and trajectory laws of conglomerate fracture extension, thereby achieving the purpose of forming the optimal fracture morphology and conductivity, reducing construction risks, and increasing transformation effects, providing guidance for the design of conglomerate hydraulic fracturing projects.

[0101] The method for determining the trajectory of hydraulic fracturing cracks in a dense sandy conglomerate reservoir provided by the present invention can also be used in conjunction with a computer-readable storage medium, on which a computer program is stored. The computer program is executed to run the method for determining the trajectory of hydraulic fracturing cracks in a dense sandy conglomerate reservoir.

[0102] A computer program can run computer instructions, which include computer program code. The computer program code may be in source code form, object code form, executable file, or some intermediate form.

[0103] Computer-readable storage media may include: any entity or device that can carry computer program code, recording media, USB flash drives, mobile hard disks, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0104] It should be noted that the content contained in computer-readable storage media can be appropriately increased or decreased based on the requirements of legislation and patent practices in the jurisdiction. For example, in some jurisdictions, based on legislation and patent practices, computer-readable storage media do not include electrical carrier signals and telecommunications signals.

[0105] According to another aspect of the present invention, a device for determining hydraulic fracturing fracture trajectories in a tight conglomerate reservoir is provided, which executes a method for determining hydraulic fracturing fracture trajectories in a tight conglomerate reservoir. The device comprises: a description model module, a fracturing model module, and a trajectory extension module.

[0106] The description model module is based on the particle flow method and takes into account the gravel characteristics of tight conglomerate to construct a conglomerate numerical description model for tight conglomerate reservoirs; the fracturing model module is used to establish a conglomerate hydraulic fracturing model based on the conglomerate numerical description model to simulate the fracturing progress at different times during the fracturing process; the trajectory extension module is based on the conglomerate hydraulic fracturing model and combines the factors affecting the hydraulic fracture trajectory to determine the trajectory extension mode of the hydraulic fracturing crack when encountering gravel.

[0107] In summary, the present invention provides a method for determining the fracture trajectory of hydraulic fracturing in a tight conglomerate reservoir, which has the following advantages over the prior art:

[0108] 1) Based on the particle flow method, the size, shape, distribution and mechanical properties of gravel particles are fully considered to establish a numerical description model of sandstone that is closer to the real reservoir;

[0109] 2) A conglomerate hydraulic fracturing model is established based on the conglomerate numerical description model, which can simulate the fracture geometry, bottom hole pressure, stress field, particle displacement field and fluid distribution in the fracture at different times during the fracturing process;

[0110] 3) Analyze the influence of sandstone reservoir geological factors (gravel strength, gravel content, gravel size, ground stress difference) and engineering factors (fracturing fluid viscosity, displacement) on the trajectory of hydraulic fractures, and determine the six possible extension modes of hydraulic fractures encountering gravel, namely: through extension mode, arrest extension mode, embedded extension mode, turning extension mode, bifurcation extension mode and attraction extension mode;

[0111] 4) Through the understanding of the main controlling factors and trajectory laws of conglomerate fracture extension, the changes in the trajectory of conglomerate fractures are revealed from a microscopic perspective, so as to optimize the construction parameters and control the optimal fracture morphology, providing guidance for the design of conglomerate hydraulic fracturing projects.

[0112] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0113] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0114] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral 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. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0115] Certain terms are used throughout this application document to indicate specific system components. As those skilled in the art will recognize, different names can usually be used to indicate the same components, so this application document is not intended to distinguish those components that are only different in name but not in function. In this application document, the terms "comprise", "include" and "have" are used in an open form, and therefore should be interpreted as meaning "including but not limited to...". In addition, the terms "substantially", "substantially" or "approximately" that may be used in this article relate to the tolerances of the corresponding terms accepted by the industry. The term "coupling" as may be used in this article includes direct coupling and indirect coupling via other components, elements, circuits, or modules, wherein for indirect coupling, the components, elements, circuits, or modules between them do not change the information of the signal but can adjust its current level, voltage level, and / or power level. Inferred coupling (for example, one of the elements is coupled to another element by inference) includes direct and indirect coupling between two elements in the same way as "coupling".

[0116] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0117] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0118] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir, characterized in that: The method comprises: Based on the particle flow method and considering the gravel characteristics of tight conglomerate, a numerical description model of conglomerate for tight conglomerate reservoir is constructed. Based on the sandstone numerical description model, a sandstone hydraulic fracturing model is established to simulate the fracturing progress at different times during the fracturing process; Based on the sandstone hydraulic fracturing model and combined with the factors affecting the hydraulic fracture trajectory, the trajectory extension mode of the hydraulic fracture encountering gravel is determined.

2. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir according to claim 1, characterized in that: The gravel characteristics include the size, shape, distribution and mechanical properties of gravel particles. The numerical description model of the sandstone reservoir is constructed by the following steps: According to the geometric size and number of particles of the dense sandy conglomerate sample, a rock matrix model containing rock matrix but not gravel is constructed; According to the size, shape and distribution characteristics of gravel particles, a gravel profile is generated on the basis of the rock matrix model to form a gravel particle cluster; Based on the mechanical properties of gravel particles, the mechanical parameter amplitudes of the rock matrix and the gravel particle clusters are calculated to obtain a numerical description model of the sandstone reservoir.

3. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir as claimed in claim 2, characterized in that: The gravel particle clusters are formed by the following steps: When randomly reconstructing the two-dimensional microstructure of gravel, the shape of the gravel is simplified, irregular polygons are used to replace gravels with complex geometric shapes, and the length of the long axis of the gravel is used to describe the particle size of the gravel. If the gradation relationship of gravel particle size is unknown, it is assumed that the particle size of gravel satisfies normal distribution and the spatial distribution of gravel satisfies random distribution; The gravel content is expressed by the ratio of the total gravel area of ​​the sample to the sample area.

4. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir according to any one of claims 1 to 3, characterized in that: The conglomerate hydraulic fracturing model is established by the following steps: By adopting fluid-solid coupling hydraulic fracture numerical simulation, confining pressure is applied to the model boundary of the sandstone numerical description model to simulate reservoir in-situ stress; Setting a fluid injection point in the sandstone numerical description model, and pumping a fluid of preset viscosity into the fluid injection point at a preset fracturing fluid injection rate to simulate a hydraulic fracturing process; The fracturing progress at different times during the simulated fracturing process is recorded, wherein the fracturing progress includes the geometric dimensions of the fracturing crack, bottom hole pressure, stress field, particle displacement field, and fluid distribution in the fracturing crack.

5. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir according to any one of claims 1 to 4, characterized in that: The hydraulic fracture trajectory influencing factors include: sandstone reservoir geological factors and engineering factors, wherein the sandstone reservoir geological factors include: gravel strength, gravel content, gravel particle size, and ground stress difference, and the engineering factors include: fracturing fluid viscosity and fracturing fluid injection rate.

6. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir as claimed in claim 5, characterized in that: The track extension mode includes: a through extension mode, a crack stop extension mode, an embedding extension mode, and a gravel-around extension mode, wherein the gravel-around extension mode includes: a turning extension mode, a bifurcated extension mode, and an attraction extension mode.

7. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir as claimed in claim 6, characterized in that: The trajectory extension mode of hydraulic fracturing cracks encountering gravel is determined by the following steps: When the dense sandy conglomerate contains only low-strength gravels, within the preset stress difference range, it is determined that the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is the through extension mode, wherein the gravel strength of the low-strength gravels is less than or equal to 9.5 Gpa, and the preset stress difference range is 5 MPa-15 MPa; When the dense sandy conglomerate contains only high-strength gravels, within the preset stress difference range, it is determined that the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is the gravel-circling extension mode and the embedded extension mode including the turning extension mode and the attraction extension mode, wherein the gravel strength of the high-strength gravels is greater than or equal to 16.2 GPa; When the dense sandy conglomerate contains only high-strength gravel, within the preset gravel content range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravel is judged to be the attraction extension mode, the penetration extension mode, and the embedding extension mode, wherein the preset gravel content range is 25%-55%; When the dense sandy conglomerate contains only high-strength gravels, within the preset gravel particle size range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravels is judged to be the gravel-around extension mode, the through extension mode, and the embedded extension mode, wherein the preset gravel particle size range is 2 mm-10 mm; When the dense sandy conglomerate contains only high-strength gravels, under the condition of low injection rate of the fracturing fluid, within the preset stress difference range, the trajectory extension mode of the hydraulic fracturing crack encountering gravels is judged to be the gravel extension mode and the through extension mode, wherein the low injection rate of the fracturing fluid is 1×10 -5 m 2 / s; When the dense sandy conglomerate contains only high-strength gravel, within the preset stress difference range and the preset fracturing fluid viscosity range, the trajectory extension mode of the hydraulic fracturing crack encountering the gravel is judged to be the passing extension mode and the bifurcation extension mode, wherein the preset fracturing fluid viscosity range is 3mPa·s-50mPa·s.

8. A method for determining the trajectory of hydraulic fracturing cracks in a tight conglomerate reservoir according to any one of claims 1 to 7, characterized in that: The method further comprises: analyzing the main controlling factors and trajectory rules of the extension of the gravel rock cracks, and providing feedback to modify the construction parameters so as to control the target optimal crack shape.

9. A storage medium, characterized in that: It contains a series of instructions for executing the method steps as claimed in any one of claims 1 to 8.

10. A device for determining the trajectory of hydraulic fracturing cracks in a dense sandy conglomerate reservoir, characterized in that: The method according to any one of claims 1 to 8 is performed, wherein the device comprises: The description model module is based on the particle flow method, taking into account the gravel characteristics of tight conglomerate, and constructing a conglomerate numerical description model for tight conglomerate reservoirs; A fracturing model module, which is used to establish a sandstone hydraulic fracturing model based on the sandstone numerical description model to simulate the fracturing progress at different times during the fracturing process; The trajectory extension module determines the trajectory extension mode of hydraulic fracturing cracks encountering gravel based on the sandstone hydraulic fracturing model and the factors affecting the hydraulic fracture trajectory.

Images