Straight well fiber strain-based fracture height and inclination interpretation method and system

Abstract

The application discloses a crack height and inclination interpretation method and system based on a straight well optical fiber strain, relates to the technical field of crack diagnosis and reservoir reconstruction, and comprises the following steps: a calculation model of the relationship between the axial displacement and the transverse displacement of a monitoring well optical fiber is constructed, and a plane strain analysis model is constructed; based on the plane strain analysis model, a curve graph of the axial displacement and the transverse displacement of the monitoring well optical fiber and a gradient curve graph thereof under different inclination conditions are drawn; the axial displacement of the optical fiber in the monitoring well is recorded in real time, the nearest time when the hydraulic fracturing crack extends to the nearest distance of the monitoring well is determined; and based on the nearest time and the axial displacement and the transverse displacement curve graph of the optical fiber and the gradient curve graph thereof, the crack height and the inclination change are analyzed in real time. The application effectively expands the further development of the reservoir reconstruction crack diagnosis technology and provides a new technology and a new method for the hydraulic fracturing crack parameter analysis.

Description

Technical Field

[0001] This invention relates to the field of fracture diagnosis and reservoir stimulation technology, and in particular to a method and system for interpreting fracture height and inclination based on fiber optic strain in vertical wells. Background Technology

[0002] The development of unconventional reservoirs has benefited from breakthroughs in three main areas: the "factory-style" operation mode of horizontal wells, advancements in horizontal well staged fracturing technology, and microseismic fracture monitoring technology. Currently, the application of horizontal well staged fracturing technology in my country is growing rapidly, becoming a powerful tool for increasing reserves and production in unconventional reservoirs such as shale gas, shale oil, and tight oil. A thorough understanding of the geometry and extension of hydraulic fracturing fractures in unconventional reservoir horizontal wells helps improve the effectiveness of fracturing operations, enhance well productivity, and increase oil and gas recovery rates. Operating companies need effective methods to determine the extent to which their hydraulic fracturing operations contribute to increasing well production and optimizing oil and gas field development. Therefore, whether for shale oil and gas or tight oil and gas fracturing, operating companies need to obtain information on the geometry, complexity, and orientation of horizontal well hydraulic fracturing fractures. Fracture monitoring and diagnosis are effective means of objectively evaluating the effectiveness of hydraulic fracturing, and the optimization and upgrading of key reservoir stimulation technologies require detailed fracture interpretation as support. However, the understanding of fracture propagation in unconventional reservoirs is unclear, especially the lack of mature technical means for monitoring and assessing fracture height in horizontal wells. This restricts the further development of reservoir stimulation technology and the optimization of horizontal well box positions, and requires research and development on methods for monitoring and assessing fracture height in horizontal wells. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for interpreting fracture height and inclination based on fiber optic strain in vertical wells, which effectively expands the further development of reservoir stimulation fracture diagnosis technology and provides new technologies and methods for hydraulic fracturing fracture parameter analysis.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] On the one hand, a method for interpreting fracture height and inclination based on fiber optic strain in vertical wells is provided, the method comprising the following steps:

[0006] A calculation model for the relationship between the axial and lateral displacements of the optical fiber in the monitoring well was constructed, and a plane strain analytical model was also constructed.

[0007] Based on the plane strain analytical model, curves of the axial and lateral displacements of the optical fiber in the monitoring well under different inclination conditions and their gradient curves were plotted.

[0008] The axial displacement of the optical fiber in the monitoring well is recorded in real time to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well to the nearest distance.

[0009] Based on the most recent moment and the optical fiber axial and lateral displacement curves and their gradient curves, the changes in crack height and inclination are analyzed in real time.

[0010] Furthermore, the calculation model for the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and the construction of the plane strain analytical model, include:

[0011] Calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz].

[0012] Based on the length of the deformed fiber micro-unit, the axial strain of the fiber within the fiber micro-unit [z, z+Δz] is calculated.

[0013] Based on the axial strain of the optical fiber, a calculation model for the relationship between the axial displacement and lateral displacement of the optical fiber in the monitoring well is constructed.

[0014] Based on the aforementioned calculation model, a plane strain analytical model is constructed.

[0015] Furthermore, the expression for the length of the deformed fiber micro-unit is:

[0016]

[0017] In the formula, L represents the length of the deformed fiber micro-unit, in meters; z represents the axial coordinate of the fiber, in meters; Δz represents the length of the micro-unit, in meters; u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0018] Furthermore, the expression for the axial strain of the optical fiber is:

[0019]

[0020] Taking the limit Δz→0 in formula (2), the relationship between the axial strain and transverse displacement of the optical fiber is obtained as follows:

[0021]

[0022] Transforming formula (3) yields the following formula for calculating the transverse displacement gradient based on the axial displacement of the optical fiber:

[0023]

[0024] In equations (2)-(4), ε represents the axial strain of the optical fiber as Δz→0, and is dimensionless; ε eThe axial strain of the optical fiber is dimensionless; L represents the length of the deformed fiber micro-element in meters; z represents the axial coordinate of the optical fiber in meters; Δz represents the length of the micro-element in meters; u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0025] Furthermore, the expression for the computational model is:

[0026]

[0027] In the formula: u x This represents lateral displacement, in meters (m); u z θ represents axial displacement in meters (m); P represents net pressure within the crack in MPa; v represents Poisson's ratio of the rock (dimensionless); E represents Young's modulus in MPa; r represents the distance between the fiber optic measuring point and the center of the crack in meters; r1 represents the distance between the fiber optic measuring point and the upper end of the crack in meters; r2 represents the distance between the fiber optic measuring point and the lower end of the crack in meters; θ represents the angle between the line containing r and the crack in rad; θ1 represents the angle between the line containing r1 and the crack in rad; θ2 represents the angle between the line containing r2 and the crack in rad.

[0028] Furthermore, the expression for the plane strain analytical model is:

[0029]

[0030] In the formula: This represents the axial displacement gradient and is dimensionless. Represents the lateral displacement gradient, dimensionless; u x This represents lateral displacement, in meters (m); u z Δz represents axial displacement, in meters (m); Δz represents the length of the micro-element, in meters; z represents the axial coordinate of the fiber, in meters; u x (z) represents the lateral displacement of the fiber when the axial coordinate is z, in meters; u z (z) represents the axial displacement of the fiber when the axial coordinate is z, in meters.

[0031] Furthermore, the real-time recording of the axial displacement of the optical fiber in the monitoring well, and the determination of the closest moment when the hydraulic fracturing fracture extends to the monitoring well at the closest distance, includes:

[0032] Real-time recording of the axial displacement of the optical fiber in the monitoring well, and calculation of the axial strain of the optical fiber;

[0033] Based on the axial strain of the optical fiber, a waterfall plot of the axial strain and a waterfall plot of the displacement of the optical fiber in the monitoring well are plotted.

[0034] Based on the fiber optic axial strain waterfall plot and displacement waterfall plot, the closest moment when the hydraulic fracturing fracture extends to the monitoring well is determined.

[0035] On the other hand, the present invention also provides a fracture height and inclination interpretation system based on fiber optic strain in vertical wells, the system comprising: a construction unit, a plotting unit, a determination unit, and an analysis unit; wherein,

[0036] The building blocks are used to construct a calculation model of the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and to construct an analytical model of plane strain.

[0037] The plotting unit is used to plot the axial and lateral displacement curves of the monitoring well fiber optic cable and their gradient curves under different inclination conditions based on the plane strain analytical model.

[0038] A determining unit is used to monitor the monitoring well and determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well at the closest distance.

[0039] The analysis unit is used to analyze the changes in crack height and inclination in real time based on the most recent moment and the optical fiber axial displacement and lateral displacement curves and their gradient curves.

[0040] Furthermore, the construction unit includes a first computing module, a second computing module, a first construction module, and a second construction module; wherein,

[0041] The first calculation module is used to calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz].

[0042] The second calculation module is used to calculate the axial strain of the optical fiber within the optical fiber micro-unit [z, z+Δz] based on the length of the deformed optical fiber micro-unit.

[0043] The first construction module is used to construct a calculation model of the relationship between the axial displacement and the lateral displacement of the optical fiber in the monitoring well based on the axial strain of the optical fiber.

[0044] The second building module is used to build a plane strain analytical model based on the calculation model.

[0045] Furthermore, the determining unit includes a third calculation module, a drawing module, and a determining module; wherein,

[0046] The third calculation module is used to record the axial displacement of the optical fiber in the monitoring well in real time and calculate the axial strain of the optical fiber.

[0047] The plotting module is used to plot the axial strain waterfall diagram and displacement waterfall diagram of the monitoring well fiber based on the axial strain of the fiber.

[0048] The determination module is used to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well, based on the fiber optic axial strain waterfall plot and displacement waterfall plot.

[0049] The technical effects and advantages of this invention are as follows:

[0050] This invention establishes an optical fiber strain evolution model during the propagation of hydraulic fracturing fractures. By fitting the relationship between changes in fracture height and inclination and optical fiber strain in adjacent vertical wells, it explains the changes in fracture height and inclination. This effectively utilizes the optical fiber strain signal from the vertical well to obtain fracture morphology parameters, providing an accurate basis for hydraulic fracturing fracture diagnosis and hydraulic fracturing process design.

[0051] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0052] Figure 1 This is a flowchart of a method for interpreting crack height and inclination based on fiber optic strain in a vertical well, according to the present invention.

[0053] Figure 2 This is a schematic diagram of the hydraulic fracturing fracture and the fiber optic monitoring well of the vertical well according to the present invention;

[0054] Figure 3 This is a schematic diagram illustrating the derivation of the relationship between the axial and lateral displacements of the vertical well fiber optic cable of the present invention.

[0055] Figure 4 This is a schematic diagram illustrating the calculation of fiber displacement caused by cracks with different inclination angles according to the present invention.

[0056] Figure 5 This is a graph of the axial displacement calculated using the plane strain model of the present invention.

[0057] Figure 6 This is a diagram of the transverse displacement curve calculated using the plane strain model of this invention.

[0058] Figure 7 This is a graph of the axial displacement gradient obtained from the plane strain model of the present invention.

[0059] Figure 8 This is a graph of the transverse displacement gradient obtained by calculating the plane strain model of the present invention.

[0060] Figure 9 This is a waterfall diagram of axial strain of the vertical well fiber optic cable of the present invention;

[0061] Figure 10This is a waterfall diagram of the axial displacement of the vertical well fiber optic cable according to the present invention;

[0062] Figure 11 This is a graph showing the axial displacement of the optical fiber in the monitoring well according to the present invention.

[0063] Figure 12 The real-time curves of crack height and inclination obtained for the explanation of this invention are shown. Detailed Implementation

[0064] 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.

[0065] The design concept of this invention includes: (1) constructing a calculation model of the relationship between the axial displacement and the transverse displacement of the optical fiber in the monitoring well (i.e., the vertical well) to determine the relationship between the axial displacement and the transverse displacement; (2) constructing a plane strain analytical model to calculate the distribution of the axial displacement and the transverse displacement of the optical fiber in the vertical well under different inclination conditions and its gradient distribution curve chart to interpret the monitoring data of the actual well; (3) vertical well distributed optical fiber strain fracturing monitoring, obtaining the real-time change waterfall diagram of optical fiber displacement and strain, determining the moment when the fracture extends to the closest point to the vertical well and related data; (4) real-time analysis of the changes in fracture height and inclination based on the changes in optical fiber strain and displacement distribution over time.

[0066] To this end, on the one hand, this invention discloses a method for interpreting crack height and inclination based on fiber optic strain in vertical wells. Figure 1 This is a flowchart of a method for interpreting crack height and inclination based on fiber optic strain in a vertical well, as described in this invention. Figure 1 As shown, the method includes the following steps:

[0067] S1. Construct a calculation model for the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and construct an analytical model for plane strain.

[0068] S2. Based on the plane strain analytical model, plot the curves of the axial displacement and lateral displacement of the optical fiber in the monitoring well under different inclination conditions, and their gradient curves.

[0069] S3. Record the axial displacement of the optical fiber in the monitoring well in real time to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well to the nearest distance;

[0070] S4. Based on the most recent moment and the optical fiber axial displacement and transverse displacement curves and their gradient curves, analyze the changes in crack height and inclination in real time.

[0071] Step S1 of the present invention specifically includes:

[0072] Calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz].

[0073] Based on the length of the deformed fiber micro-unit, the axial strain of the fiber within the fiber micro-unit [z, z+Δz] is calculated.

[0074] Based on the axial strain of the optical fiber, a calculation model for the relationship between the axial displacement and lateral displacement of the optical fiber in the monitoring well is constructed.

[0075] Based on the aforementioned calculation model, a plane strain analytical model is constructed.

[0076] Specifically, the expression for the length of the deformed fiber micro-unit is:

[0077]

[0078] In the formula, L represents the length of the deformed fiber micro-unit, in meters; z represents the axial coordinate of the fiber, in meters; Δz represents the length of the micro-unit, in meters; u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0079] Specifically, the expression for the axial strain of the optical fiber is:

[0080]

[0081] Taking the limit Δz→0 in formula (2), the relationship between the axial strain and transverse displacement of the optical fiber is obtained as follows:

[0082]

[0083] Transforming formula (3) yields the following formula for calculating the transverse displacement gradient based on the axial displacement of the optical fiber:

[0084]

[0085] In equations (2)-(4), ε represents the axial strain of the optical fiber as Δz→0, and is dimensionless; ε e The axial strain of the optical fiber is dimensionless; L represents the length of the deformed fiber micro-element in meters; z represents the axial coordinate of the optical fiber in meters; Δz represents the length of the micro-element in meters; u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0086] Specifically, the expression for the computational model is:

[0087]

[0088] In the formula: u x This represents lateral displacement, in meters (m); u z θ represents axial displacement in meters (m); P represents net pressure within the crack in MPa; v represents Poisson's ratio of the rock (dimensionless); E represents Young's modulus in MPa; r represents the distance between the fiber optic measuring point and the center of the crack in meters; r1 represents the distance between the fiber optic measuring point and the upper end of the crack in meters; r2 represents the distance between the fiber optic measuring point and the lower end of the crack in meters; θ represents the angle between the line containing r and the crack in rad; θ1 represents the angle between the line containing r1 and the crack in rad; θ2 represents the angle between the line containing r2 and the crack in rad.

[0089] Specifically, the expression for the plane strain analytical model is:

[0090]

[0091] In the formula: This represents the axial displacement gradient and is dimensionless. Represents the lateral displacement gradient, dimensionless; u x This represents lateral displacement, in meters (m); u z Δz represents axial displacement, in meters (m); Δz represents the length of the micro-element, in meters; z represents the axial coordinate of the fiber, in meters; u x (z) represents the lateral displacement of the fiber when the axial coordinate is z, in meters; u z (z) represents the axial displacement of the fiber when the axial coordinate is z, in meters.

[0092] Step S3 of the present invention specifically includes:

[0093] Real-time recording of the axial displacement of the optical fiber in the monitoring well, and calculation of the axial strain of the optical fiber;

[0094] Based on the axial strain of the optical fiber, a waterfall plot of the axial strain and a waterfall plot of the displacement of the optical fiber in the monitoring well are plotted.

[0095] Based on the fiber optic axial strain waterfall plot and displacement waterfall plot, the closest moment when the hydraulic fracturing fracture extends to the monitoring well is determined.

[0096] On the other hand, the present invention also discloses a fracture height and inclination interpretation system based on vertical well fiber optic strain, the system comprising:

[0097] Construction unit, drawing unit, determination unit, and analysis unit; among which,

[0098] The building blocks are used to construct a calculation model of the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and to construct an analytical model of plane strain.

[0099] The plotting unit is used to plot the axial and lateral displacement curves of the monitoring well fiber optic cable and their gradient curves under different inclination conditions based on the plane strain analytical model.

[0100] A determining unit is used to monitor the monitoring well and determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well at the closest distance.

[0101] The analysis unit is used to analyze the changes in crack height and inclination in real time based on the most recent moment and the optical fiber axial displacement and lateral displacement curves and their gradient curves.

[0102] Specifically, the construction unit includes a first computing module, a second computing module, a first construction module, and a second construction module; wherein,

[0103] The first calculation module is used to calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz].

[0104] The second calculation module is used to calculate the axial strain of the optical fiber within the optical fiber micro-unit [z, z+Δz] based on the length of the deformed optical fiber micro-unit.

[0105] The first construction module is used to construct a calculation model of the relationship between the axial displacement and the lateral displacement of the optical fiber in the monitoring well based on the axial strain of the optical fiber.

[0106] The second building module is used to build a plane strain analytical model based on the calculation model.

[0107] Specifically, the determining unit includes a third calculation module, a drawing module, and a determining module; wherein,

[0108] The third calculation module is used to record the axial displacement of the optical fiber in the monitoring well in real time and calculate the axial strain of the optical fiber.

[0109] The plotting module is used to plot the axial strain waterfall diagram and displacement waterfall diagram of the monitoring well fiber based on the axial strain of the fiber.

[0110] The determination module is used to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well, based on the fiber optic axial strain waterfall plot and displacement waterfall plot.

[0111] The method and system of the present invention will now be described in further detail with reference to specific embodiments.

[0112] Example:

[0113] In this embodiment, the distance S between the fiber optic monitoring vertical well and the hydraulically fractured fracture is 60m, and the net fluid pressure P inside the fracture is 1MPa. Basic parameters include: Young's modulus E of the rock is 30GPa, Poisson's ratio v is 0.2, reservoir thickness is 60m, and there are high-stress barriers above and below. Therefore, the fracture height will remain at 60m in the later stages of fracturing, and the monitoring range is 100m above and below the fracture center. Taking an injection time of 50min and a pump shutdown time of 10min as an example, fiber optic strain monitoring of the vertical well is performed throughout the entire process.

[0114] Step S1: Construct a calculation model for the relationship between the axial and lateral displacements of the monitoring well fiber optic cable, which is used to determine the relationship between the axial and lateral displacements.

[0115] Step S1 includes:

[0116] Step S11:

[0117] The lateral displacement of optical fibers in vertical wells can reflect information about crack height and inclination, while optical fibers can only undergo (monitor) axial deformation. Therefore, it is necessary to establish the relationship between the axial displacement and lateral displacement of optical fibers. Figure 2 This is a schematic diagram of the hydraulic fracturing fracture and the vertical well fiber optic monitoring well of the present invention, as shown below. Figure 2 As shown, when the hydraulic fracturing fracture and the optical fiber in the vertical well reach the closest distance S, the strain of the optical fiber can approximately satisfy the plane strain condition. Figure 3 This is a schematic diagram illustrating the derivation of the relationship between the axial and lateral displacements of the vertical well fiber optic cable of the present invention, as shown below. Figure 3 As shown, the axial strain of the optical fiber is mainly caused by the transverse displacement. Within the micro-element [z, z+Δz], the axial displacement of the optical fiber is caused by the transverse displacement. Therefore, the expression for the length of the deformed optical fiber micro-element is:

[0118]

[0119] In the formula, L represents the length of the deformed fiber micro-unit, in meters; z represents the axial coordinate of the fiber, in meters; Δz represents the length of the micro-unit (i.e., the spacing between fiber measuring points), in meters; u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0120] Step S12:

[0121] Based on the length of the deformed fiber micro-element, the axial strain of the fiber within the micro-element [z, z+Δz] is calculated, and its expression is as follows:

[0122]

[0123] In the formula, ε edenoted by axial strain of the optical fiber, which is dimensionless; L represents the length of the fiber micro-unit after deformation, in meters.

[0124] △z represents the length of the micro-element, in meters; u x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0125] Taking the limit Δz→0 in formula (2), the relationship between the axial strain and transverse displacement of the optical fiber is obtained as follows:

[0126]

[0127] ε represents the axial strain of the optical fiber as Δz→0, and is dimensionless; ε e denoted by z, representing the axial strain of the optical fiber, which is dimensionless; z represents the axial coordinate of the optical fiber, in meters (m); Δz represents the length of the micro-element, in meters (m); u x u represents the lateral displacement of the optical fiber, in meters (m). x (z) represents the lateral displacement of the optical fiber when the axial coordinate is z, and the unit is m.

[0128] Transforming formula (3) yields the following formula for calculating the transverse displacement gradient based on fiber optic axial strain:

[0129]

[0130] Step S13:

[0131] Equations (3) and (4) theoretically demonstrate that there is a correlation between the axial strain and the transverse displacement gradient of an optical fiber. Based on this, in actual monitoring, we can determine the transverse displacement of the optical fiber through its axial strain. To further illustrate this, we use the analytical solution of the displacement induced by hydraulic fracturing fractures for analysis.

[0132] Based on the analytical solution of plane strain crack elasticity, calculation formulas are established for the axial strain and peak location of cracks with different inclination angles generated in fiber optic monitoring vertical wells.

[0133] Figure 4 This is a schematic diagram illustrating the calculation of fiber displacement caused by cracks with different inclination angles according to the present invention, combined with... Figure 3 and Figure 4 The analytical formulas for the plane strain of the optical fiber's axial and lateral displacements are obtained as follows:

[0134]

[0135] In the formula: u x u represents the lateral displacement of the optical fiber, in meters (m). zθ represents the axial displacement of the optical fiber, in meters (m); P represents the net pressure inside the crack, in MPa; v represents the Poisson's ratio of the rock, dimensionless; E represents Young's modulus, in MPa; r represents the distance between the optical fiber measuring point and the center of the crack, in meters; r1 represents the distance between the optical fiber measuring point and the upper end of the crack, in meters; r2 represents the distance between the optical fiber measuring point and the lower end of the crack, in meters; θ represents the angle between the line containing r and the crack, in rad; θ1 represents the angle between the line containing r1 and the crack, in rad; θ2 represents the angle between the line containing r2 and the crack, in rad.

[0136] The theoretical solutions for the axial displacement gradient (i.e., axial strain) and the transverse displacement gradient (i.e., transverse strain) can be obtained through formula (5).

[0137] Step S2: Construct a plane strain analytical model to calculate the distribution of axial strain and lateral displacement of the fiber optic cable in a vertical well under different inclination conditions, as well as its gradient distribution curve, to interpret the monitoring data of the actual well.

[0138] Step S2 includes:

[0139] Step S21:

[0140] The axial strain distribution of the optical fiber under different fracture inclinations was calculated according to formula (5). In this embodiment, the distance s between the optical fiber monitoring well and the hydraulic fracturing fracture is 60m, and the net fluid pressure P inside the fracture is 1MPa. The axial and lateral displacement distributions of the optical fiber under different inclinations are calculated as follows: Figure 5 and Figure 6 As shown.

[0141] Figure 5 This is the axial displacement curve calculated using the plane strain model of the present invention. Figure 5 It can be seen that the axial displacement exhibits an antisymmetric distribution about the crack center, with the center of symmetry being the location of the crack center point. When the crack is vertical, the distance between the upper and lower peak positions is approximately equal to the crack height. Figure 6 This is a diagram of the transverse displacement curve calculated using the plane strain model of the present invention. Figure 6 It can be seen that when the inclination of the hydraulic fracturing fracture is 0 degrees, that is, when the fracture is a vertical fracture, the positions of the two peak values ​​of the lateral displacement are symmetrical, and the distance between the two peak points is approximately the fracture height. The peak positions of the axial displacement and the lateral displacement have good consistency, which is consistent with the results of the analytical derivation formula (4).

[0142] Since the derivative of formula (5) is relatively complex and the analytical expression after the derivative is relatively cumbersome, it is not convenient to apply. Since the hydraulic fracturing fracture will not come into contact with the fiber optic monitoring vertical well, the displacement and strain monitored by the fiber optic are continuous quantities. Therefore, the displacement gradient can be calculated by numerical differentiation.

[0143] The expressions for the axial displacement gradient and the lateral displacement gradient of the optical fiber are as follows:

[0144]

[0145] In the formula: This represents the axial displacement gradient and is dimensionless. Represents the lateral displacement gradient, dimensionless; u x This represents lateral displacement, in meters (m); u z Δz represents axial displacement in meters (m); Δz represents the length of the micro-element in meters; z represents the axial coordinate of the fiber in meters; u x (z) represents the lateral displacement of the fiber when the axial coordinate is z, in meters; u z (z) represents the axial displacement of the fiber when the axial coordinate is z, in meters.

[0146] Step S22:

[0147] Figure 7 This is a graph showing the axial displacement gradient obtained from the plane strain model of this invention. Figure 8 The transverse displacement gradient curve calculated by the plane strain model of this invention is shown in the figure. Based on the measured displacement peak value in the curve, combined with... Figure 7 and Figure 8 The curve characteristics can be used to determine the crack inclination. In this embodiment, the displacement peaks show a symmetrical distribution, so the inclination (relative to the vertical) is 0, which means that the hydraulic fracturing crack is a vertical crack.

[0148] Step S3: Vertical well distributed fiber optic strain fracturing monitoring, obtaining real-time fiber displacement and strain change waterfall plots, determining the moment when the fracture extends to the closest point to the vertical well and related data;

[0149] Step S3 includes:

[0150] Step S31:

[0151] The axial displacement of the optical fiber in the vertical well is recorded in real time during the fracturing process. Based on the calibrated length of the optical fiber in the monitoring well, the axial strain of the optical fiber is calculated through the axial displacement.

[0152] Step S32:

[0153] Based on the calculated axial strain of the fiber optic cable during the fracturing process, a cloud map of the fiber optic strain versus time within a range of 100–200 m above and below the perforation depth of the vertical well is plotted, i.e., a vertical well fiber optic (axial) strain waterfall plot. Figure 9 ; Plot a contour plot of the fiber axial displacement over time, i.e., a waterfall plot of the vertical fiber (axial) displacement, such as... Figure 10 .

[0154] Step S33:

[0155] Taking an injection time of 50 minutes and a pump shutdown time of 10 minutes as an example, fiber optic strain monitoring was conducted throughout the entire process in a vertical well. Basic parameters included: Young's modulus E of the rock was 30 GPa, Poisson's ratio v was 0.2, reservoir thickness was 60 m, and there were high-stress barriers above and below, so the fracture height would remain at 60 m in the later stages of fracturing. The distance S between the vertical fiber optic well and the hydraulic fracturing fracture was 60 m, and the monitoring range was 100 m above and below the fracture center. Figure 5 The axial strain waterfall diagram of the straight-well fiber optic cable of the present invention is shown below. Figure 9 As shown, it can be determined that the plane of the hydraulic fracturing fracture is closest to the fiber optic well, i.e., reaching the target depth. Figure 2 The closest moment of the nearest distance S is determined, and the fiber strain after this closest moment is analyzed to determine the upper and lower peak points and the peak value of the fiber strain. Figure 9 The position with a vertical coordinate of 0 is at the same depth as the crack center. From Figure 9 As can be seen, after 15 minutes of fracturing, a dark concentrated band of strain appeared in the strain monitored by the vertical well fiber optic cable, indicating that the fracture had reached its closest distance to the fiber optic cable. After this, the fiber optic strain can be approximated by the result of the plane strain model. Figure 10 This is a waterfall plot of the axial displacement of the optical fiber according to the present invention, as shown below. Figure 10 As shown, the closest point between the fracture and the vertical well can also be identified at approximately 15 minutes, but the clarity is lower than that of the previous method. Figure 9 This refers to the strain waterfall diagram.

[0156] Step S4: Analyze the changes in crack height and inclination in real time based on the changes in fiber strain and displacement distribution over time;

[0157] Step S4 includes:

[0158] Step S41:

[0159] Based on the obtained fiber strain data, a fiber axial displacement curve was plotted. Figure 11 This is a graph showing the axial displacement of the optical fiber in the monitoring well according to the present invention. Figure 11 As shown, by analyzing the positions of the upper and lower peaks, the crack height and inclination at different times can be determined;

[0160] Step S42:

[0161] Plot the curves showing the changes in crack height and inclination over time. Figure 12 The real-time curves of crack height and inclination obtained for the explanation of this invention are as follows: Figure 12 As shown, the crack height interpreted by the method of this embodiment is 65m, and the relative error with the actual crack height of 60m is 8%, which meets the engineering accuracy of hydraulic fracturing crack morphology interpretation; the crack inclination is 0 degrees, which is a vertical crack, consistent with the preset crack morphology.

[0162] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for interpreting crack height and inclination based on fiber optic strain in vertical wells, characterized in that, The method includes the following steps: A calculation model for the relationship between the axial and lateral displacements of the optical fiber in the monitoring well was constructed, and a plane strain analytical model was also constructed. Based on the plane strain analytical model, curves of the axial and lateral displacements of the optical fiber in the monitoring well under different inclination conditions and their gradient curves were plotted. The axial displacement of the optical fiber in the monitoring well is recorded in real time to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well to the nearest distance. Based on the most recent moment and the optical fiber axial and lateral displacement curves and their gradient curves, the changes in crack height and inclination are analyzed in real time. The aforementioned calculation model for the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and the construction of a plane strain analytical model, include: Calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz]. Based on the length of the deformed fiber micro-unit, the axial strain of the fiber within the fiber micro-unit [z, z+Δz] is calculated. Based on the axial strain of the optical fiber, a calculation model for the relationship between the axial displacement and lateral displacement of the optical fiber in the monitoring well is constructed. Based on the aforementioned calculation model, a plane strain analytical model is constructed; The expression for the length of the deformed fiber micro-unit is: ；（1） In the formula, L The value represents the length of the deformed fiber micro-unit in meters (m); z represents the axial coordinate of the fiber in meters (m); and Δz represents the length of the micro-unit in meters (m). u x This indicates the lateral displacement of the optical fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; The expression for the axial strain of the optical fiber is: ；（2） Taking the limit Δz→0 in formula (2), the relationship between the axial strain and transverse displacement of the optical fiber is obtained as follows: ；（3） Equation (3) is transformed into the following formula for calculating the transverse displacement gradient based on the axial displacement of the optical fiber: ；（4） In equations (2)-(4), ε ε represents the axial strain of the optical fiber as Δz→0, and is dimensionless; e This represents the axial strain of the optical fiber and is dimensionless. L The value represents the length of the deformed fiber micro-unit in meters (m); z represents the axial coordinate of the fiber in meters (m); and Δz represents the length of the micro-unit in meters (m). u x This indicates the lateral displacement of the optical fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; The expression for the computational model is: ；（5） In the formula: u x This represents lateral displacement, in meters (m). u z This represents axial displacement, in meters (m). P This represents the net pressure within the crack, expressed in MPa. v For the Poisson's ratio of the rock, it is dimensionless; E This refers to Young's modulus, expressed in MPa. r This represents the distance between the optical fiber measuring point and the center point of the crack, in meters. r 1 represents the distance between the optical fiber measuring point and the upper end of the crack, in meters; r 2 represents the distance between the optical fiber measuring point and the lower end of the crack, in meters; θ express r The angle between the line and the crack, in rad; θ 1 represents light r The angle between the line containing point 1 and the crack, in rad; θ 2 indicates r The angle between the line containing point 2 and the crack, in rad; The expression for the plane strain analytical model is: ；（6） In the formula: This represents the axial displacement gradient and is dimensionless. This represents the lateral displacement gradient and is dimensionless. u x This represents lateral displacement, in meters (m). u z Indicates axial displacement, in meters (m); Δ z The value represents the length of the micro-unit, in meters (m); z represents the axial coordinate of the fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; u z (z) The axial coordinate of the optical fiber is z The axial displacement of the optical fiber at that time, in meters.

2. The method for interpreting crack height and inclination based on fiber optic strain in a vertical well, as described in claim 1, is characterized in that... The real-time recording of the axial displacement of the optical fiber in the monitoring well, and the determination of the closest moment when the hydraulic fracturing fracture extends to the monitoring well at the nearest distance, includes: Real-time recording of the axial displacement of the optical fiber in the monitoring well, and calculation of the axial strain of the optical fiber; Based on the axial strain of the optical fiber, a waterfall plot of the axial strain and a waterfall plot of the displacement of the optical fiber in the monitoring well are plotted. Based on the fiber optic axial strain waterfall plot and displacement waterfall plot, the closest moment when the hydraulic fracturing fracture extends to the monitoring well is determined.

3. A fracture height and inclination interpretation system based on fiber optic strain in vertical wells, characterized in that, The system includes: a construction unit, a drawing unit, a determination unit, and an analysis unit; wherein, The building blocks are used to construct a calculation model of the relationship between the axial and lateral displacements of the optical fiber in the monitoring well, and to construct an analytical model of plane strain. The plotting unit is used to plot the axial and lateral displacement curves of the monitoring well fiber optic cable and their gradient curves under different inclination conditions based on the plane strain analytical model. A determining unit is used to monitor the monitoring well and determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well at the closest distance. The analysis unit is used to analyze the changes in crack height and inclination in real time based on the most recent moment and the optical fiber axial displacement and transverse displacement curves and their gradient curves. The construction unit includes a first computing module, a second computing module, a first construction module, and a second construction module; wherein, The first calculation module is used to calculate the length of the deformed fiber micro-unit based on the lateral displacement within the fiber micro-unit [z, z+Δz]. The second calculation module is used to calculate the axial strain of the optical fiber within the optical fiber micro-unit [z, z+Δz] based on the length of the deformed optical fiber micro-unit. The first construction module is used to construct a calculation model of the relationship between the axial displacement and the lateral displacement of the optical fiber in the monitoring well based on the axial strain of the optical fiber. The second construction module is used to construct a plane strain analytical model based on the calculation model; The expression for the length of the deformed fiber micro-unit is: ；（1） In the formula, L The value represents the length of the deformed fiber micro-unit in meters (m); z represents the axial coordinate of the fiber in meters (m); and Δz represents the length of the micro-unit in meters (m). u x This indicates the lateral displacement of the optical fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; The expression for the axial strain of the optical fiber is: ；（2） Taking the limit Δz→0 in formula (2), the relationship between the axial strain and transverse displacement of the optical fiber is obtained as follows: ；（3） Equation (3) is transformed into the following formula for calculating the transverse displacement gradient based on the axial displacement of the optical fiber: ；（4） In equations (2)-(4), ε ε represents the axial strain of the optical fiber as Δz→0, and is dimensionless; e This represents the axial strain of the optical fiber and is dimensionless. L The value represents the length of the deformed fiber micro-unit in meters (m); z represents the axial coordinate of the fiber in meters (m); and Δz represents the length of the micro-unit in meters (m). u x This indicates the lateral displacement of the optical fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; The expression for the computational model is: ；（5） In the formula: u x This represents lateral displacement, in meters (m). u z This represents axial displacement, in meters (m). P This represents the net pressure within the crack, expressed in MPa. v For the Poisson's ratio of the rock, it is dimensionless; E This refers to Young's modulus, expressed in MPa. r This represents the distance between the optical fiber measuring point and the center point of the crack, in meters. r 1 represents the distance between the optical fiber measuring point and the upper end of the crack, in meters; r 2 represents the distance between the optical fiber measuring point and the lower end of the crack, in meters; θ express r The angle between the line and the crack, in rad; θ 1 represents light r The angle between the line containing point 1 and the crack, in rad; θ 2 indicates r The angle between the line containing point 2 and the crack, in rad; The expression for the plane strain analytical model is: ；（6） In the formula: This represents the axial displacement gradient and is dimensionless. This represents the lateral displacement gradient and is dimensionless. u x This represents lateral displacement, in meters (m). u z Indicates axial displacement, in meters (m); Δ z The value represents the length of the micro-unit, in meters (m); z represents the axial coordinate of the fiber, in meters (m). u x (z) The axial coordinate of the optical fiber is z The lateral displacement of the optical fiber at that time, in meters; u z (z) The axial coordinate of the optical fiber is z The axial displacement of the optical fiber at that time, in meters.

4. The fracture height and inclination interpretation system based on fiber optic strain in a vertical well, as described in claim 3, is characterized in that... The determining unit includes a third calculation module, a drawing module, and a determining module; wherein... The third calculation module is used to record the axial displacement of the optical fiber in the monitoring well in real time and calculate the axial strain of the optical fiber. The plotting module is used to plot the axial strain waterfall diagram and displacement waterfall diagram of the monitoring well fiber based on the axial strain of the fiber. The determination module is used to determine the closest moment when the hydraulic fracturing fracture extends to the monitoring well, based on the fiber optic axial strain waterfall plot and displacement waterfall plot.

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