A method and system for measuring geometric parameters of hydraulic fractures

Abstract

The present invention discloses a method and system for measuring geometric parameters of hydraulic fractures, wherein the method for measuring geometric parameters of hydraulic fractures comprises the following steps: using a three-dimensional finite element method to establish a formation model containing hydraulic fractures, and longitudinally setting a multi-component induction logging coil system at a wellbore in the formation model containing hydraulic fractures to construct an induced electric field calculation model; calculating the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of hydraulic fractures; determining the coil system sensitive to the geometric parameters of hydraulic fractures; using the multi-component induction logging coil system to measure the geometric parameters of the hydraulic fractures to be measured, and obtaining the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fractures; and determining the size of the geometric parameters of the hydraulic fractures to be measured. The measurement results of the geometric parameters of the hydraulic fractures obtained by the present invention are of great significance to the design of the hydraulic fracture monitoring instrument and the calculation model of the fracture parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring geometric parameters of hydraulic fractures, and in particular to a method and a system for measuring geometric parameters of hydraulic fractures. Background Art

[0002] The exploration and development of global oil and gas resources are becoming more and more advanced. Conventional high-porosity, high-permeability integrated oil and gas reservoirs are gradually decreasing, and low-porosity, low-permeability oil and gas reservoirs are gradually being valued, such as tight oil, shale gas and other unconventional oil and gas resources. In order to improve the production efficiency of such reservoirs, hydraulic fracturing is one of the most effective and common methods. Through hydraulic fracturing, artificial fractures are created near the wellbore to improve the permeability of the reservoir, increase the oil leakage area of ​​the formation, and maximize the production capacity. Detecting and calculating the geometric parameters of hydraulic fractures is helpful for calculating the recoverable reserves of oil and gas reservoirs, and it is also helpful for determining the location of casing during the completion stage. It is very important to monitor the geometric parameters of hydraulic fractures using appropriate methods.

[0003] At present, the qualitative analysis and quantitative measurement methods for hydraulic fractures mainly include logging methods and inter-well microseismic methods. Traditional temperature logging, isotope logging, boron injection neutron lifetime logging and other methods have the disadvantages of limited construction time and poor accuracy in measuring hydraulic fractures. At the same time, nuclear logging methods such as isotope logging and boron injection neutron lifetime logging will cause certain pollution to the formation and are not suitable for promotion and application. Acoustic logging can calculate the height of hydraulic fractures and monitor the mode of hydraulic rock breaking. The advantage of this method is that it will not pollute the formation and is not affected by the formation pores, but the measurement accuracy and resolution depend on the wellbore environmental noise. At the same time, for closed fractures, it is difficult to accurately judge the pressure fractures formed in the dynamic process because their anisotropy values ​​are close to zero. Microseismic monitoring technology can be used to detect fractured oil and gas layers, but microseismic monitoring technology can only be used in the formation period of fractures, and the application effect is not ideal for fractures that have already formed. In addition, the velocity model of microseismic is difficult to obtain accurately, which affects the precise positioning of fractures.

[0004] Among many methods, electromagnetic induction logging is a non-destructive measurement method, and it is highly sensitive to the resistivity of formations and hydraulic fractures. In particular, when hydraulic fractures are filled with fluids with resistivity different from that of the surrounding formations, it will lead to anisotropy of the azimuthal resistivity around the well. The coil system of electromagnetic induction logging in different directions can realize the measurement of azimuthal resistivity around the well. In addition, it is suitable for detecting fractures at different stages. During detection, the wellbore environment can be oil-based mud, water-based mud or air, and other dynamic instruments can be well compatible with the same wellbore measurement environment. Therefore, as a supplement to seismic monitoring, it has become a research hotspot in recent years.

[0005] For small-sized fractures, the measurement frequency used when using electromagnetic induction logging is relatively high (>10kHy). In the prior art, conventional array induction logging (>10kHy) is used to study the logging response of secondary fractures during drilling, and the length and resistivity parameters of fractures around the wellbore are obtained; the sensitivity and measurability of electromagnetic induction methods in hydraulic fractures are studied using improved numerical pattern matching methods, and the application of this method in fracture networks is evaluated.

[0006] For large-scale fractures, low-frequency electromagnetic induction instruments (<10kHy) are currently commonly used when electromagnetic induction logging is used for measurement. In the prior art, there is a physical and numerical model based on electromagnetic technology to accurately detect fracture parameters, and inclined transmitting coil system and inclined shielding coil system instruments are proposed, and the relationship between the measurement signal and the fracture parameters is obtained; there is a discussion on the applicability of low-frequency resistivity measurement in horizontal wells in hydraulic fracture detection and measurement; there is a study on the low-frequency electromagnetic monitoring method of asymmetric fractures using numerical and physical models; there is a numerical simulation method to evaluate the feasibility of using low-frequency (<10kHy) electromagnetic induction method to monitor the length of vertical fractures. The above research is very helpful for the measurement of fracture parameters, but the coil systems used are all single axial or inclined coil systems with few combinations, so it is impossible to measure the integrity of fracture geometric parameters.

[0007] Multi-component electromagnetic induction logging not only has an axial coil system, but also a transverse coil system. Through the coil system composed of three mutually orthogonal transmitting coil systems and shielding coil systems, nine magnetic field intensities can be obtained. Through certain conversions, information such as induced electromotive force and formation resistivity can be obtained, which has great advantages in the integrity characterization of fracture parameters. There have been studies on the measurement of fracture length by the three components xx, yy, and zz of multi-component induction logging, and a method for measuring fracture length has been proposed and verified. However, the cross components of multi-component induction logging are not involved, and the source distance used is a single source distance. At the same time, the response characteristics of the width and height parameters of the fracture have not been investigated. Summary of the invention

[0008] The purpose of the present invention is to provide a method and system for measuring the geometric parameters of hydraulic fractures. Taking small-scale fractures as the research object, a systematic theoretical study is carried out on the method of measuring hydraulic fractures by using a multi-component induction logging coil system. A vertical formation model containing hydraulic fractures is established using a three-dimensional finite element method, and the relationship between the geometric parameters of the hydraulic fractures and the measurement signals measured by the coil systems in different receiving directions is analyzed. The coil systems that are sensitive to the geometric parameters of the hydraulic fractures and the applicable ranges of different sensitive coil systems in measuring the geometric parameters of the hydraulic fractures are determined.

[0009] The present invention provides a method for measuring the geometric parameters of a hydraulic fracture, comprising the following steps:

[0010] A three-dimensional finite element method is used to establish a pressure fracture formation model, and a multi-component induction logging coil system is vertically set at the wellbore in the pressure fracture formation model to construct an induced electric field calculation model;

[0011] By using the induced electric field calculation model, the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fracture are calculated, and the relationship between the geometric parameters of the fracture and the measurement signal values ​​measured by the coil systems with different receiving directions is determined;

[0012] Determine the coil system that is sensitive to the geometric parameters of the hydraulic fracture according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions;

[0013] According to the coil system that is sensitive to the geometric parameters of the hydraulic fracture, the geometric parameters of the hydraulic fracture to be measured are measured using a multi-component induction logging coil system, and the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture are obtained;

[0014] The size of the geometric parameters of the fracture to be measured is determined according to the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the fracture, and according to the relationship between the geometric parameters of the fracture and the measurement signal values ​​of the coil systems in different receiving directions.

[0015] Furthermore, the multi-component induction logging coil system includes a transmitting coil system, a shielding coil system, and a receiving coil system;

[0016] The transmitting coil system, the shielding coil system and the receiving coil system are all composed of three mutually perpendicular coils.

[0017] Further, the coil systems in different receiving directions in the multi-component induction logging coil system include xx coil system, xy coil system, xz coil system, yx coil system, yy coil system, yz coil system, zx coil system, zy coil system, and zz coil system;

[0018] The method of calculating the measurement signal values ​​of the coil systems in different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the hydraulic fracture includes:

[0019] Calculate the induced electromotive force of the coil system in different receiving directions when measuring the geometric parameters of the fracture;

[0020] The induced electromotive force of the coil system in one receiving direction when measuring the geometric parameters of the fracture is:

[0021] V=∫Edl (1)

[0022] Wherein, V is the induced electromotive force of the coil system when measuring the geometric parameters of the fracture;

[0023] l is the circumference of the coil system;

[0024] E is the electric field strength, which satisfies:

[0025]

[0026] n×E=0 (3)

[0027]

[0028] AE=B (5)

[0029] Where k0 is the wave number; ε r is the relative dielectric constant;

[0030] J s The current intensity applied to the coil system in different receiving directions;

[0031] μ0 and μ r are relative magnetic permeability and free space magnetic permeability respectively;

[0032] ω represents the current angular frequency; A is the total stiffness matrix; B is the applied condition;

[0033] V is the finite element solution area; is the curl operator; i is the imaginary unit; n is the normal vector.

[0034] Furthermore, the geometric parameters of the hydraulic fracture include the length, height and width of the hydraulic fracture;

[0035] The determination of the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​measured by the coil systems in different receiving directions includes:

[0036] The relationship between the length, height and width of the fracture and the induced electromotive force measured by the coil system in different receiving directions is determined respectively.

[0037] Furthermore, the coil system that is sensitive to the geometric parameters of the hydraulic fracture includes an xx coil system, an xz coil system, a yy coil system, a yz coil system, and a zz coil system.

[0038] Furthermore, the relationship between the length of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes:

[0039] The fitting relationships between the length of the fracture and the induced electromotive force of the coil system in different receiving directions during measurement are:

[0040]

[0041] Where Ex is the length of the fracture; EMF is the induced electromotive force of the coil system; A and B are constants.

[0042] Furthermore, the relationship between the height of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes:

[0043] When the coils in different receiving directions are used to measure the height of the fracture, the middle value in the distribution curve of the measured induced electromotive force is the position of the fracture interface;

[0044] When the xx coil system, the yy coil system, and the zz coil system measure the height of the fracture, the distribution curve of the induced electromotive force measured is symmetrically distributed.

[0045] Furthermore, the relationship between the width of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes:

[0046] When the xz coil system and the zz coil system measure the width of the fracture, as the width of the fracture gradually increases, the measured induced electromotive force decreases in a power-exponential law.

[0047] Furthermore, when the induced electric field calculation model includes a wellbore, the intensity of the induced electromotive force generated in the entire model area of ​​the induced electric field calculation model increases.

[0048] When the induced electric field calculation model includes formation resistivity, and when the source distance between the transmitting coil system and the shielding coil system is larger, the variation of the induced electromotive force measured by the coil systems in different receiving directions is larger.

[0049] The present invention provides a system for measuring geometric parameters of hydraulic fractures, comprising:

[0050] A computational model building module is used to establish a pressure fracture formation model using a three-dimensional finite element method, and to longitudinally set a multi-component induction logging coil system at the wellbore in the pressure fracture formation model to build an induced electric field computational model;

[0051] The data relationship establishment module is used to calculate the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fracture through the induction electric field calculation model, and determine the relationship between the geometric parameters of the fracture and the measurement signal values ​​measured by the coil systems with different receiving directions;

[0052] A measurement condition establishment module, used to determine a coil system that is sensitive to the geometric parameters of the hydraulic fracture according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions;

[0053] The measuring module is used to measure the geometric parameters of the hydraulic fracture to be measured by using a multi-component induction logging coil system according to the coil system that is sensitive to the geometric parameters of the hydraulic fracture, and obtain the measurement signal value of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture;

[0054] The measurement result determination module is used to determine the size of the geometric parameters of the pressure fracture to be measured according to the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the pressure fracture.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The present invention firstly establishes a common induced electric field calculation model of a formation containing vertical fractures based on the three-dimensional finite element method. Secondly, the geometric parameters of the fractures and the parameters of the multi-component induction logging coil system are changed, the relationship between the geometric parameters of the fractures and the measurement signal values ​​measured by the coil systems in different receiving directions in the multi-component induction logging system is investigated, and the coil system sensitive to the fracture geometric parameters is determined. On this basis, by establishing the relationship between the fracture geometric parameters and the measurement signal values ​​of the coil systems in different receiving directions, the applicable range of the fracture geometric parameters measured by the coil systems in different receiving directions is obtained, and the fracture geometric parameters are measured and analyzed according to the applicable range of each component to measure the fracture geometric parameters. Finally, the influence of the wellbore environment and the formation resistivity on the measurement signal value is studied. The results show that the multi-component induction logging method can calculate the three parameters of the fracture, and the method of selecting the combination of multi-source distance and multi-coil system is the key to realizing the integrity characterization of the fracture geometric parameters. The fracture geometric parameter measurement and analysis results obtained by the present invention are of great significance to the design of the fracture monitoring instrument and the calculation model of the fracture parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] 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:

[0058] Figure 1 It is a flowchart of a method for measuring geometric parameters of hydraulic fractures proposed by the present invention;

[0059] Figure 2 Schematic diagram of a multi-component induction logging coil system for a method of measuring geometric parameters of hydraulic fractures proposed in the present invention;

[0060] Figure 3 It is a schematic diagram of a formation model containing hydraulic fractures in a method for measuring geometric parameters of hydraulic fractures proposed in the present invention;

[0061] Figure 4A grid diagram of fractures and wellbores in a method for measuring geometric parameters of hydraulic fractures proposed by the present invention;

[0062] Figure 5 It is a position relationship diagram of a receiving coil system and grid division nodes of a method for measuring geometric parameters of hydraulic fractures proposed by the present invention;

[0063] Figure 6 It is the relationship between the length of the hydraulic fracture and the induced electromotive force EMF measured by the coil system in different receiving directions in the embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention;

[0064] Figure 7 It is the relationship between the height of the hydraulic fracture and the induced electromotive force EMF measured by the coil system in different receiving directions when the source distance is 0.6m in an embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention;

[0065] Figure 8 It is the relationship between the height of the hydraulic fracture and the induced electromotive force EMF measured by the coil system in different receiving directions when the source distance is 1.6m in the embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention;

[0066] Fig. 9 It is the relationship between the width of the hydraulic fracture and the induced electromotive force EMF measured by the coil system in different receiving directions in the embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention;

[0067] Fig.10 It is an equipotential surface distribution diagram of the electric field component Ez of the xz coil system plane when the transmitting coil system is x in an embodiment of the method for measuring the geometric parameters of a hydraulic fracture proposed by the present invention;

[0068] Fig.11 It is an equipotential surface distribution diagram of the electric field component Ez of the xy coil system plane when the transmitting coil system is x in the embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention;

[0069] Fig.12 It is the influence of mud on the induced electromotive force EMF measured by the coil system in different receiving directions when the source distance is 0.6m in an embodiment of the method for measuring the geometric parameters of hydraulic fractures proposed by the present invention;

[0070] Fig.13 The embodiment of the method for measuring the geometric parameters of hydraulic fractures proposed by the present invention is the influence of the mud in the wellbore on the induced electromotive force EMF measured by the coil system in different receiving directions when the source distance is 1.6m;

[0071] Fig.14It is the relationship between the formation-fracture resistivity contrast and the induced electromotive force EMF measured by the coil system in different receiving directions in an embodiment of the method for measuring the geometric parameters of the hydraulic fracture proposed by the present invention. DETAILED DESCRIPTION

[0072] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific implementation methods.

[0073] Example 1

[0074] like Figure 1 As shown, a method for measuring the geometric parameters of a hydraulic fracture comprises the following steps:

[0075] Step 1: Use the three-dimensional finite element method to establish a pressure fracture formation model, and vertically set a multi-component induction logging coil system at the wellbore in the pressure fracture formation model to construct an induced electric field calculation model.

[0076] Step 2: Calculate the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fractures through the induced electric field calculation model, and determine the relationship between the geometric parameters of the fractures and the measurement signal values ​​measured by the coil systems with different receiving directions.

[0077] Among them, the coil systems with different receiving directions in the multi-component induction logging coil system include xx coil system, xy coil system, xz coil system, yx coil system, yy coil system, yz coil system, zx coil system, zy coil system, and zz coil system.

[0078] The geometric parameters of the fracture include the length, height and width of the fracture.

[0079] (1) The relationship between the length of the fracture and the induced electromotive force measured by the coil system in different receiving directions, including:

[0080] The fitting relationship between the length of the fracture and the induced electromotive force of the coil system in different receiving directions during measurement is:

[0081]

[0082] Where Ex is the length of the fracture; EMF is the induced electromotive force of the coil system; A and B are constants

[0083] (2) When the coils in different receiving directions are used to measure the height of the fracture, the middle value of the distribution curve of the measured induced electromotive force is the position of the fracture interface;

[0084] When the height of the fracture is measured using the xx coil system, the yy coil system, and the zz coil system, the distribution curve of the measured induced electromotive force is a symmetrical distribution.

[0085] (3) When the width of the fracture is measured using the xz coil system and the zz coil system, as the width of the fracture gradually increases, the measured induced electromotive force decreases in a power law.

[0086] Step 3: According to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions, determine the coil system that is sensitive to the geometric parameters of the hydraulic fracture;

[0087] The coil systems that are sensitive to the geometric parameters of the fractures include the xx coil system, the xz coil system, the yy coil system, the yz coil system, and the zz coil system.

[0088] Step 4: Based on the coil system that is sensitive to the geometric parameters of the hydraulic fracture, the geometric parameters of the hydraulic fracture to be measured are measured using a multi-component induction logging coil system to obtain measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture;

[0089] Step 5: Determine the size of the geometric parameters of the fracture to be measured based on the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the fracture and the relationship between the geometric parameters of the fracture and the measurement signal values ​​of the coil systems in different receiving directions.

[0090] Example 2

[0091] The multi-component induction logging coil system includes a transmitting coil system T, a shielding coil system B, and a receiving coil system R, wherein the transmitting coil system T, the shielding coil system B, and the receiving coil system R are all composed of three mutually perpendicular coils, such as Figure 2 shown.

[0092] When the transmitting coil system is connected to an alternating current of a certain frequency, eddy currents will be generated in the stratum. The eddy currents will generate a secondary electric field at the receiving coil system and be recorded. The three shielding coil systems are used to eliminate the direct coupling signal. The three receiving coil systems are used to receive the induced electromotive force of the stratum, and finally obtain an induced electromotive force tensor EMF, as shown in the following formula (2). Through certain conversion, a conductivity tensor can be obtained as shown in the following formula (3), as follows:

[0093]

[0094]

[0095] Where i represents the direction of the transmitting coil system; j represents the direction of the receiving coil system;

[0096] V ijIt is the induced electromotive force after compensation of the transmitting coil system, the shielding coil system and the receiving coil system;

[0097] K ij is the instrument constant, expressed as the following tensor:

[0098]

[0099] Wherein L1 is the distance between the transmitting coil system and the shielding coil system, and L2 is the distance between the transmitting coil system and the receiving coil system.

[0100] Substituting formula (4) into formula (3) we can get the apparent conductivity tensor σ of anisotropic formation: a :

[0101]

[0102] The present invention does not consider the anisotropy of formation conductivity, so the formation resistivity in different directions in formula (4) is equal. At the same time, the instrument structure parameters of the present invention vary greatly. For the sake of convenience, the induced electromotive force is not calibrated, but the relationship between the fracture geometry parameters and the induced electromotive force is directly established.

[0103] Ignore the core rod, metal cover, solid coil system and other structures in the multi-component induction logging coil system and simplify it as follows: Figure 2 The coil system structure shown in the figure, in which the transmitting coil is replaced by a ring, an alternating current is applied to it, and the induced electromotive force generated in the entire model area is solved to obtain the induced electromotive force values ​​at different positions of the receiving coil. Figure 2 It can be seen that the structure of the multi-component induction logging coil system is asymmetric and cannot be simplified into a two-dimensional model for calculation. In addition, the geometric parameters of the hydraulic fractures required to be measured in the present invention vary greatly with the size of the formation model, which is a multi-scale problem and the model is relatively complex. Therefore, the finite element method with higher calculation accuracy is used for modeling.

[0104] Figure 3 (a) is a schematic diagram of the model established using the three-dimensional finite element method, including the formation, wellbore, instrument and vertical fracture. The top view of the model is shown in the figure Figure 3 As shown in (b), the hydraulic fracture forms two symmetrical wings with the wellbore. In fact, the hydraulic fracture is composed of many thin, independent fractures. The width of a single hydraulic fracture is below the millimeter level. For the convenience of research, their geological effects can be replaced by an equivalent fracture, and the resistivity of the equivalent fracture is the sum of the resistivities of each independent fracture.

[0105] like Figure 4This is a grid diagram of fractures and wells in a fractured formation model. The overall grid of the model is fine, and the grid size increases from the source center to the outside. In the process of grid division, the maximum and minimum grid sizes must be reasonably controlled to achieve the required accuracy of the calculation and effectively save the use of computer memory and reduce the calculation time. At the same time, the grid is encrypted at the transmitting coil system and the receiving coil system to ensure that the receiving coil system is on the grid division node, such as Figure 5 As shown in Figure 2, the boundary layer processing technology is used at the wellbore interface to reduce the energy loss of the electric field when it passes through the interface. The total mesh freedom of the model is about 2 million.

[0106] Example 3

[0107] Calculate the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the hydraulic fracture, including:

[0108] The induced electromotive force of the coil system in different receiving directions when measuring the geometric parameters of the hydraulic fracture is calculated respectively; the induced electromotive force of the coil system in one receiving direction when measuring the geometric parameters of the hydraulic fracture is:

[0109] V=∫Edl (6)

[0110] Wherein, V is the induced electromotive force of the coil system when measuring the geometric parameters of the fracture;

[0111] l is the circumference of the coil system; E is the electric field strength;

[0112] Apply current intensity J to the transmitting coil system x, y, and z at different directions respectively. s The current source, starting from the time-harmonic field Maxwell equations, it is easy to derive the electric field intensity in the formation medium to satisfy:

[0113]

[0114] The electric field boundary conditions on the cut-off surface of the finite element model are:

[0115] n×E=0 (8)

[0116] Using variational principle and functional analysis, the functional expression of the electric field E is obtained:

[0117]

[0118] AE=B (10)

[0119] Where k0 is the wave number; ε r is the relative dielectric constant;

[0120] J sThe current intensity applied to the coil system in different receiving directions;

[0121] μ0 and μ r are relative magnetic permeability and free space magnetic permeability respectively;

[0122] ω represents the current angular frequency; A is the total stiffness matrix; B is the applied condition;

[0123] V is the finite element solution area; is the curl operator; i is the imaginary unit; n is the normal vector;

[0124] The matrix equation in formula (10) is a large sparse matrix. In this paper, a stable biconjugate gradient solver (BiCGStab) is used to solve the equations. After obtaining the electric field intensity E, the line integral of the electric field intensity passing through the receiving coil system is performed to obtain the induced electromotive force of the receiving coil system in different directions.

[0125] Example 4

[0126] According to the above-constructed induced electric field calculation model, the radius of all coil systems simulated in this embodiment is 0.03m, and the measurement frequency is fixed at 62kHy. The hydraulic fractures studied in the present invention are small-sized hydraulic fractures, so the selection of high frequency can effectively avoid the influence of large-span fractures far away from the wellbore. In order to control the influence of mud resistivity in the wellbore on the measured voltage signal, the resistivity values ​​of the formation and the wellbore are set to the same value.

[0127] Therefore, the parameters in the induced electric field calculation model are set as follows:

[0128] The formation resistivity Rt is 100Ω·m and 1Ω·m respectively;

[0129] The resistivity of the fracture is 1000Ω·m (default oil-based mud intrusion fracture);

[0130] The coil-source distance is 1m.

[0131] The amplitude of the measurement signal value measured by the coil system in different receiving directions in the multi-component induction logging coil system is different. The larger the measurement signal, the easier it is to detect. On the contrary, when the signal is less than a certain value, the signal cannot be detected, or the signal-to-noise ratio cannot meet the use of fracture measurement. Table 1 is the calculation result, which can be obtained:

[0132] It can be seen that the amplitudes of the measured signals measured by the xx coil system, xz coil system, yy coil system, yz coil system, and zz coil system are relatively large, all greater than 0.1μV. The signals of other coil systems are relatively small, all at the nV level or lower, indicating that these coil systems are not sensitive to cracks. Therefore, the coil systems that are sensitive to crack geometric parameters include the xx coil system, xz coil system, yy coil system, yz coil system, and zz coil system.

[0133] Table 1 Measurement signal amplitude of different coil systems

[0134]

[0135] Example 5

[0136] Determine the relationship between the length of the fracture and the induced electromotive force measured by the coil system in different receiving directions, including:

[0137] The fracture length refers to the length of the fracture extending radially outward from the wellbore wall.

[0138] In this embodiment, the parameters of the hydraulic fractures and formations in the induced electric field calculation model are set as follows:

[0139] The resistivity of the hydraulic fracture is 1000Ω·m; the resistivity of the formation is 1Ω·m; the fracture height Ex is 10m; the fracture width is 0.0254m; the source distances between the transmitting coil system and the receiving coil system in different directions are 0.4m, 0.6m, 0.8m, 1m, 1.2m, 1.4m, 1.6m, 1.8m, and 2.0m respectively; the number of turns nt of the transmitting coil system and the number of turns nr of the receiving coil system are both 100 turns.

[0140] Figure 6 a to Figure 6 e represents the changes in the induced electromotive force measured by the coil systems in different receiving directions when the length of the medium-pressure crack changes, namely, the xx coil system, the xz coil system, the yy coil system, the yz coil system, and the zz coil system.

[0141] from Figure 6 It can be seen from a that when the source distance is 0.4m and 0.6m, the induced electromotive force gradually decreases with the change of the length of the fracture, and the length of the fracture is in a power exponential relationship with the induced electromotive force measured by the coil system in different receiving directions.

[0142] When the source distance is 0.8m, 1m, and 1.2m, the measured induced electromotive force shows a trend of first increasing and then decreasing as the length of the fracture increases.

[0143] When the source distance is 1.4 m or greater, the measured induced electromotive force increases first and then tends to be stable as the length of the fracture increases.

[0144] When the source distance is ≤0.6 m (referred to as short source distance) and ≥1.4 m (referred to as long source distance), the relationship between the length of the fracture and the measured induced electromotive force is fitted to obtain a power exponential relationship as shown in formula (1).

[0145] It can be seen that when the source distance between the transmitting coil system and the receiving coil system is ≤0.6 m, the length range of the measurable fracture is larger. When the length of the fracture is ≥1.6 m, the length of the fracture can also be calculated using formula (1).

[0146] When the source distance between the transmitting coil system and the receiving coil system is ≥1.4 m and when the length of the fracture is ≥1 m, the length of the fracture cannot be calculated using formula (1).

[0147] When the instrument in the multi-component induction logging coil system rotates a certain angle, the position of the coil system is converted through appropriate coordinate transformation and the fracture length is calculated.

[0148] like Figure 6 (b), for the xz coil system, when the source distance is ≤1.4m, as the length of the fracture increases, the induced electromotive force at the receiving coil system shows a power exponential change, and when the length of the fracture is greater than 1.2m, the induced electromotive force at the receiving coil system changes slightly. When the source distance is ≥1.6m, as the length of the fracture increases, the induced electromotive force at the receiving coil system first remains unchanged and then slowly decreases. Therefore, for the xz coil system, when using formula (1) to measure the length of the fracture, the instrument source distance in the multi-component induction logging coil system should be controlled within 1.4m as much as possible.

[0149] For the yy coil system and the yz coil system, as the length of the fracture increases, the induced electromotive force at the receiving coil system hardly changes. The reason is that the vertical fracture set in the induced electric field calculation model is on the x-axis, and when the transmitting coil system is in the y-direction, the induced eddy current plane formed is parallel to the vertical fracture surface, so the size of the eddy current is less affected by the fracture, and ultimately no induced electromotive force carrying fracture information is formed in the y-direction or z-direction of the receiving coil system.

[0150] For the zz coil system, under different source distances, as the length of the fracture increases, the induced electromotive force at the receiving coil system gradually decreases, also showing a power exponential law. When the source distance is small, the induced electromotive force at the receiving coil system changes greatly, while when the source distance is large, the induced electromotive force at the receiving coil system changes less. Therefore, when using formula (1) to measure the length of the fracture, it is more accurate to choose a short source distance.

[0151] Through the above analysis, it can be seen that as the length of the fracture increases, the measured voltage signal changes less and less. When the length of the fracture reaches a certain value, the measured voltage signal difference is small, and the measured voltage cannot be used to effectively evaluate the length of the fracture. The change in the voltage signal corresponding to the length data points A and B of two adjacent fractures is defined as the rate of change ROC, as shown in Formula 12. The point with the smaller value of the fracture length between the two data points is the maximum fracture length MaxEx that the instrument can detect.

[0152]

[0153] Table 2 lists the MaxEx corresponding to the xx coil system, the xz coil system and the zz coil system when the ROC is 5%, 10% and 20% respectively, and the interval between the length data points A and B of the two fractures is 0.2m.

[0154] It can be seen that for the same coil system, the higher the ROC, the lower the corresponding MaxEx, that is, the higher the instrument signal-to-noise ratio, the higher the detectable MaxEx.

[0155] In addition, compared with the xx coil system and the zz coil system, under the same source distance and ROC, the xz coil system can detect a larger MaxEx.

[0156] Table 2 Detectable MaxEx of different coil systems

[0157]

[0158] Example 6

[0159] Determine the relationship between the height of the fracture and the induced electromotive force measured by the coil system in different receiving directions, including:

[0160] The source distances of the transmitting coil system and the receiving coil system were selected as short source distance L=0.6m and long source distance L=1.6m respectively.

[0161] The parameters of the hydraulic fracture and formation in the model are selected as follows: the resistivity of the hydraulic fracture is 1000Ω·m, the resistivity of the surrounding rock is 1Ω·m, the length Ex of the hydraulic fracture is 2m, the width of the hydraulic fracture is 0.0254m, and the height H of the hydraulic fracture is selected as 0.5m, 1m, 1.5m, 2m, and 5m respectively. The instrument samples along the longitudinal depth of the hydraulic fracture with a sampling rate of 0.125m. The position of the hydraulic fracture in the z direction is at depth=0m, and sampling is carried out from depth=0.5m to depth=-5m.

[0162] Figure 7 The relationship between the induced electromotive force and the height of the fracture measured by the coil system in different receiving directions under short source distance can be seen:

[0163] The signal amplitude of the induced electromotive force measured by the zz coil system is the largest, and the signal amplitude of the induced electromotive force measured by the yz coil system is the smallest.

[0164] Under different fracturing models, when the instrument recording point enters and leaves the fracturing layer, the measurement response is different, and the obtained curve shape is also different. The greater the fracturing height, the wider the measured curve shape.

[0165] The induced electromotive force measured by all coil systems with different receiving directions forms the maximum and minimum values ​​of the signal on both sides of the top and bottom interfaces of the crack.

[0166] The curve distribution shape of the induced electromotive force obtained in the directions of xx coil system, yy coil system and zz coil system is symmetrical, while the curve shape in the directions of xz coil system and yz coil system is asymmetrical.

[0167] Figure 8 The relationship between the induced electromotive force measured by the coil system in different receiving directions and the height of the fracture when the source distance is 1.6m. It can be seen that compared with the source distance of 0.6m, when the source distance is 1.6m, the measurement signal values ​​of the induced electromotive force measured by the coil system in different receiving directions are significantly reduced. When the source distance is 1.6m, at different fracture heights, the curve distribution between the induced electromotive force measured by the coil system in different receiving directions and the height of the fracture is basically similar to that of the source distance of 0.6m. Therefore, the height of the fracture can be measured in combination with a short source distance, that is, a source distance of 0.6m.

[0168] From the above results, it can be seen that the curve distribution form between the induced electromotive force measured by the coil system in different receiving directions and the height of the fracture has a good correlation with the height of the fracture. The position corresponding to the middle value of the maximum and minimum values ​​of the curve distribution form between the induced electromotive force measured by the coil system in different receiving directions and the height of the fracture can be used to determine the position of the fracture interface. This method is called the half-amplitude method. This method is often used to divide the formation interface in resistivity logging. After determining the position of the upper and lower interfaces of the fracture, its height can be easily determined, and the difference in depth between the two is the height of the fracture. The model of the present invention is symmetric about depth=0. Therefore, after determining the position of a formation interface, the corresponding depth multiplied by 2 is the height of the fracture.

[0169] Table 3 lists the errors between the heights of the fractures determined by the xx coil system, the xz coil system, the yz coil system and the zz coil system and the heights of the actual fractures. It can be seen that the greater the height of the fracture, the more accurate the calculated height of the fracture. Since the longitudinal resolution of the short source distance coil system is better than that of the long source distance, the height of the fracture calculated by the short source distance coil system is closer to the true value. In addition, the calculation errors of the fracture height by the cross-component xz coil system and the yz coil system are smaller than those of the other two coil systems.

[0170] In general, the short source distance coil system is more suitable for calculating cracks with a height greater than 1m.

[0171] Table 3 Error analysis of crack height calculated by half amplitude method

[0172]

[0173] Example 7

[0174] Determine the relationship between the width of the fracture and the induced electromotive force measured by the coil system in different receiving directions, including:

[0175] The width of the hydraulic fracture is usually also called the opening degree. Generally speaking, the opening degree of the hydraulic fracture is in the order of millimeters, which often exceeds the resolution range of the logging instrument, making it difficult to measure and calculate the parameters. The multi-component sensing instrument can measure voltage signals in different directions. Theoretically, it has certain advantages in measuring the opening degree of the hydraulic fracture.

[0176] In the calculation model of the relationship between the opening of the hydraulic fracture and the induced electromotive force, the source distances were selected as L = 0.6m and L = 1.6m respectively. The parameters of the hydraulic fracture and formation in the model are selected as follows:

[0177] The resistivity of the fracture is 1000Ω·m;

[0178] The resistivity of the surrounding rock is 1Ω·m; the length of the hydraulic fracture Ex is 2m;

[0179] The width of the fracture varies from 2mm to 20mm;

[0180] The height H of the hydraulic fracture was selected as 10 m, and the instrument sampling point was located at depth = 0 m.

[0181] Fig. 9 The relationship between the width of the fracture and the induced electromotive force measured by the coil system in different receiving directions is shown in Figure 2.

[0182] (1) As the width of the fracture increases, the signal variation amplitude of the induced electromotive force measured by the long and short source distances in the xx coil system, the yy coil system, and the yz coil system is small, so these three components cannot be used to measure the width of the fracture.

[0183] (2) For the xz coil system and the zz coil system, as the width of the fracture increases, the signals of the induced electromotive force measured by the long and short source distance coil systems both show a decreasing trend, and show a power exponential decrease. At the same time, the signal strength of the induced electromotive force measured by the short source distance is not only greater than the signal strength of the induced electromotive force measured by the long source distance, but also has a larger signal variation within the same variation range of the fracture width. Therefore, the width of the fracture can be measured by the combination of the xz coil system and the zz coil system.

[0184] Analogously, the analysis method of the maximum fracture length that the instrument can detect is used to define the change in the voltage signal corresponding to the width data points A and B of two adjacent fractures as the rate of change ROC, and the point with the smaller fracture width value among the two data points is the maximum fracture width MaxW that the instrument can detect.

[0185] Table 4 lists the MaxW corresponding to the xx coil system and the zz coil system when the ROC is 5%, 10% and 20% respectively, and the interval between the width data points A and B of two adjacent hydraulic fractures is 0.002m. It can be seen that:

[0186] For the same coil system, the higher the ROC, the lower the corresponding MaxW, that is, the higher the signal-to-noise ratio of the instrument, the higher the detectable MaxW. In addition, under the same source distance and ROC, the xz coil system can detect a larger MaxEx.

[0187] Table 4 Detectable MaxW of different coil systems

[0188]

[0189] Example 8

[0190] The above analysis shows the relationship between the geometric parameters of the fracture and the induced electromotive force measured by the coil system in different receiving directions. However, in actual measurement, the voltage signal results of the induced electromotive force measured by the coil system in different receiving directions are often affected by other factors besides the structural parameters of the instrument itself, such as the actual wellbore size, mud resistivity, the resistivity of the fluid in the fracture and the resistivity of the formation, etc. Therefore, it is necessary to study the influence of these factors on the measured voltage.

[0191] When the induced electric field calculation model includes a wellbore, the intensity of the induced electromotive force generated in the entire model area of ​​the induced electric field calculation model increases.

[0192] When the induced electric field calculation model includes formation resistivity, and when the source distance between the transmitting coil system and the shielding coil system is larger, the variation of the induced electromotive force measured by the coil systems in different receiving directions is larger.

[0193] The specific implementation process is as follows:

[0194] The presence of mud in the wellbore has a certain influence on the measurement results of the geometric parameters of the fracture. Figure 2 The wellbore resistivity in the model shown is used to calculate the logging response curve of the tool with and without a wellbore using the above model.

[0195] In the model, the opening of the hydraulic fracture is 0.0254m, the height of the hydraulic fracture is 10m, the length of the hydraulic fracture is 2m, the formation resistivity is 1Ω·m, and the resistivity of the hydraulic fracture is 1000Ω·m.

[0196] Fig.10 It is the equipotential surface distribution diagram of the electric field component Ez in the xz coil system plane when the transmitting coil system is x.

[0197] in Fig.10 (a) does not include wellbore, Fig.10 (b) With wellbore. It can be seen that when the wellbore is considered in the model, the distribution and value of the induced electric field of the coil system are affected to a certain extent. In the model without wellbore, a negative electric field is generated near the coil system, which is completely different from the case of the model with wellbore.

[0198] Fig.11 is the equipotential surface distribution diagram of the electric field component Ez in the xy coil system plane when the ray coil system is x, where Fig.11 (a) does not include wellbore, Fig.11 (b) With wellbore. It can be seen that when the wellbore is included in the model, the electric field intensity in the wellbore is significantly higher than that without the wellbore.

[0199] In order to quantitatively study the influence of mud on the measurement signal, the logging response curves of different coil systems and different source distances were calculated, such as Fig.12 and Fig.13 shown.

[0200] For short-source-distance coil systems, the borehole has the following effects on the measurement signals of different coil systems:

[0201] xx coil system: The shape of the curve did not change, and the positive and negative values ​​of the measurement signal at the fracture did not change.

[0202] xz coil system: The positive and negative values ​​of the measurement signal at the fracture have changed. The presence of mud causes the absolute value of the measurement signal to increase. The measurement signal changes from symmetric to asymmetric when the instrument enters and leaves the fracture interface.

[0203] yy Coil system: The measurement signal change is small and can be ignored.

[0204] YZ coil system: The presence of mud causes the measurement signal to increase and the curve shape to change. The measurement signal of the instrument changes from symmetrical to asymmetrical when entering and leaving the fracture.

[0205] zz coil system: The presence of mud causes the measurement signal to decrease and the curve shape to change. The presence of mud has little effect on the calculation of fracture height, but has a certain effect on the calculation of fracture width and length.

[0206] Compared with the model without wellbore, the measurement signal changes of the coil system with a source distance of 1.6m are as follows:

[0207] xx Coil system: The positive and negative values ​​of the measurement signal at the fracture site have changed, and the measurement signal changes from symmetrical to asymmetrical when the instrument enters and leaves the fracture interface.

[0208] xz coil system: The positive and negative values ​​of the measurement signal at the fracture have changed, and the asymmetry of the measurement signal when the instrument enters and leaves the fracture interface has not changed.

[0209] yy Coil system: The measurement signal change is small and can be ignored.

[0210] yz coil system: Compared with the case without a wellbore, the instrument has more obvious corners when entering and leaving the fracture.

[0211] zz coil system: The presence of mud causes the measurement signal to increase, the curve shape does not change, and the measurement signal after the instrument passes through the fracture is the same as when there is no wellbore.

[0212] The formation resistivity, mud resistivity and proppant resistivity in the fracture jointly affect the amplitude of the measurement signal. Since multi-component induction logging is more commonly used in oil-based mud, the present invention only considers the influence of formation resistivity changes on the measurement signal.

[0213] In the model, Rt / Rmf varies from 0.001 to 10, the opening of the fracture is 1 in, the height of the fracture is 10 m, and the extension of the fracture is 2 m.

[0214] Fig.14 The relationship between the resistivity contrast ratio of the formation and the fracture and the induced electromotive force is shown in Figure 2. It can be seen that:

[0215] With the increase of resistivity contrast, the induced electromotive force of xx coil system, yx coil system and yz coil system all decreases, the induced electromotive force of xz coil system increases first and then decreases, and the induced electromotive force of zz coil system increases.

[0216] Relatively speaking, the influence of the stratum on the coil system with long source distance is less than that on the coil system with short source distance.

[0217] In addition, when Rt / Rmf is small, the induced electromotive force of the xx coil system, yy coil system, and yz coil system changes little, so when the background formation resistivity is low, the multi-component induction logging method is more effective in measuring the geometric parameters of the fracture. For high-resistance formations or xz coil system and zz coil system, in practice, in order to ensure that the geometric parameters of the fracture are accurately calculated using the above rules, the measurement formula parameters need to be calculated, corrected, and calibrated according to different formation contrasts to meet different formation environments.

[0218] Based on the results of three-dimensional numerical simulation of multi-component induction logging, the present invention proposes a method for measuring the geometric parameters of hydraulic fractures. Firstly, five sensitive coil systems with greater measurement signal strength are selected from the nine components, namely, the xx coil system, the xz coil system, the yy coil system, the yz coil system, and the zz coil system.

[0219] In the absence of a wellbore model, the relationship between the length, width and height of the fracture and the induced electromotive force signal of the multi-component induction logging was calculated using a three-dimensional finite element method. The results show that:

[0220] (1) Different components at different source distances have different sensitivities to fracturing, and combined measurement of fracturing parameters is required.

[0221] (2) Using the power exponential relationship between the length and width of the hydraulic fracture and the measured signal value, a measurement model for the length and width of the hydraulic fracture is established;

[0222] (3) A method for measuring the height of hydraulic fractures was established using the half-amplitude method.

[0223] (4) The xz coil system has more advantages in measuring the length and width of the hydraulic fracture. The cross components xz and yz have smaller calculation errors for the hydraulic fracture height than the other two coil systems. Therefore, the combination of different coil systems can realize the calculation of the geometric parameters of small-sized hydraulic fractures.

[0224] (5) The influencing factors of multi-component induction logging were analyzed. Compared with the influence of mud in the wellbore, the influence of formation resistivity is smaller.

[0225] Through the systematic research of the present invention, the following issues should be noted when using multi-component induction logging data to measure the geometric parameters of hydraulic fractures. The instrument uses the changing form of the curve rather than the specific measurement value to determine the fracture height. Therefore, when the fracture height is greater than the longitudinal resolution of the instrument, the fracture height is relatively easy to determine. In comparison, the calculation of the fracture width and length requires the use of electromotive force signals. In addition to the factors considered by the present invention, the influencing factors of measuring the electromotive force signal also include instrument eccentricity, wellbore irregularity (expansion or reduction), thin layers, well inclination angle, etc.

[0226] Example 9

[0227] The present invention provides a system for measuring geometric parameters of hydraulic fractures, comprising:

[0228] A computational model building module is used to establish a pressure fracture formation model using a three-dimensional finite element method, and to longitudinally set a multi-component induction logging coil system at the wellbore in the pressure fracture formation model to build an induced electric field computational model;

[0229] The data relationship establishment module is used to calculate the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fracture through the induction electric field calculation model, and determine the relationship between the geometric parameters of the fracture and the measurement signal values ​​measured by the coil systems with different receiving directions;

[0230] A measurement condition establishment module, used to determine a coil system that is sensitive to the geometric parameters of the hydraulic fracture according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions;

[0231] A measuring module is used to measure the geometric parameters of the hydraulic fracture to be measured using a multi-component induction logging coil system according to a coil system that is sensitive to the geometric parameters of the hydraulic fracture, and obtain measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture;

[0232] The measurement result determination module is used to determine the size of the geometric parameters of the hydraulic fracture to be measured according to the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture, and according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions.

[0233] The measurement result determination module is used to determine the size of the geometric parameters of the crack to be measured according to the induced electromotive force.

[0234] Finally, it should be noted that what is disclosed above is only a specific embodiment of the present invention, but the embodiment of the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for measuring geometric parameters of hydraulic fractures, characterized in that: The following steps are involved: A three-dimensional finite element method is used to establish a pressure fracture formation model, and a multi-component induction logging coil system is vertically set at the wellbore in the pressure fracture formation model to construct an induced electric field calculation model; By using the induced electric field calculation model, the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fracture are calculated, and the relationship between the geometric parameters of the fracture and the measurement signal values ​​measured by the coil systems with different receiving directions is determined; Determine the coil system that is sensitive to the geometric parameters of the hydraulic fracture according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions; According to the coil system that is sensitive to the geometric parameters of the hydraulic fracture, the geometric parameters of the hydraulic fracture to be measured are measured using a multi-component induction logging coil system, and the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture are obtained; Determine the size of the geometric parameter of the fracture to be measured according to the measurement signal value of each sensitive coil system when measuring the geometric parameter of the fracture, and according to the relationship between the geometric parameter of the fracture and the measurement signal value of the coil system in different receiving directions; The multi-component induction logging coil system includes a transmitting coil system, a shielding coil system, and a receiving coil system; The transmitting coil system, the shielding coil system and the receiving coil system are all composed of three mutually perpendicular coils; The coil systems in different receiving directions in the multi-component induction logging coil system include: xx coil system, xy coil system, xz coil system, yx coil system, yy coil system, yz coil system, zx coil system, zy coil system, and zz coil system; The method of calculating the measurement signal values ​​of the coil systems in different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the hydraulic fracture includes: Calculate the induced electromotive force of the coil system in different receiving directions when measuring the geometric parameters of the fracture; The induced electromotive force of the coil system in one receiving direction when measuring the geometric parameters of the fracture is: V=∫Edl (1) Wherein, V is the induced electromotive force of the coil system when measuring the geometric parameters of the fracture; l is the circumference of the coil system; E is the electric field strength, which satisfies: n×E=0 (3) AE=B (5) Where k0 is the wave number; ε r is the relative dielectric constant; J s The current intensity applied to the coil system in different receiving directions; μ0 and μ r are relative magnetic permeability and free space magnetic permeability respectively; ω represents the current angular frequency; A is the total stiffness matrix; B is the applied condition; V is the finite element solution area; is the curl operator; i is the imaginary unit; n is the normal vector.

2. A method for measuring geometric parameters of hydraulic fractures according to claim 1, characterized in that: The geometric parameters of the hydraulic fracture include the length, height and width of the hydraulic fracture; The determination of the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​measured by the coil systems in different receiving directions includes: The relationship between the length, height and width of the fracture and the induced electromotive force measured by the coil system in different receiving directions is determined respectively.

3. A method for measuring geometric parameters of hydraulic fractures according to claim 2, characterized in that: The coil system that is sensitive to the geometric parameters of the hydraulic fracture includes an xx coil system, an xz coil system, a yy coil system, a yz coil system, and a zz coil system.

4. A method for measuring geometric parameters of hydraulic fractures according to claim 3, characterized in that: The relationship between the length of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes: The fitting relationships between the length of the fracture and the induced electromotive force of the coil system in different receiving directions during measurement are: Where Ex is the length of the fracture; EMF is the induced electromotive force of the coil system; A and B are constants.

5. The method for measuring geometric parameters of hydraulic fractures according to claim 3, characterized in that: The relationship between the height of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes: When the coils in different receiving directions are used to measure the height of the fracture, the middle value in the distribution curve of the measured induced electromotive force is the position of the fracture interface; When the xx coil system, the yy coil system, and the zz coil system measure the height of the fracture, the distribution curve of the induced electromotive force measured is symmetrically distributed.

6. A method for measuring geometric parameters of hydraulic fractures according to claim 3, characterized in that: The relationship between the width of the fracture and the induced electromotive force measured by the coil system in different receiving directions includes: When the xz coil system and the zz coil system measure the width of the fracture, as the width of the fracture gradually increases, the measured induced electromotive force decreases in a power-exponential law.

7. The method for measuring geometric parameters of hydraulic fractures according to claim 1, characterized in that: When the induced electric field calculation model includes a wellbore, the intensity of the induced electromotive force generated in the entire model area of ​​the induced electric field calculation model increases; When the induced electric field calculation model includes formation resistivity, and when the source distance between the transmitting coil system and the shielding coil system is larger, the variation of the induced electromotive force measured by the coil systems in different receiving directions is larger.

8. A system for measuring geometric parameters of hydraulic fractures, characterized in that: include: A computational model building module is used to establish a pressure fracture formation model using a three-dimensional finite element method, and to longitudinally set a multi-component induction logging coil system at the wellbore in the pressure fracture formation model to build an induced electric field computational model; The data relationship establishment module is used to calculate the measurement signal values ​​of the coil systems with different receiving directions in the multi-component induction logging coil system when measuring the geometric parameters of the fracture through the induction electric field calculation model, and determine the relationship between the geometric parameters of the fracture and the measurement signal values ​​measured by the coil systems with different receiving directions; A measurement condition establishment module, used to determine a coil system that is sensitive to the geometric parameters of the hydraulic fracture according to the relationship between the geometric parameters of the hydraulic fracture and the measurement signal values ​​of the coil systems in different receiving directions; The measuring module is used to measure the geometric parameters of the hydraulic fracture to be measured by using a multi-component induction logging coil system according to the coil system that is sensitive to the geometric parameters of the hydraulic fracture, and obtain the measurement signal value of each sensitive coil system when measuring the geometric parameters of the hydraulic fracture; The measurement result determination module is used to determine the size of the geometric parameters of the pressure fracture to be measured according to the measurement signal values ​​of each sensitive coil system when measuring the geometric parameters of the pressure fracture, and according to the relationship between the geometric parameters of the pressure fracture and the measurement signal values ​​of the coil systems in different receiving directions; The multi-component induction logging coil system includes a transmitting coil system, a shielding coil system, and a receiving coil system; The transmitting coil system, the shielding coil system and the receiving coil system are all composed of three mutually perpendicular coils; The coil systems in different receiving directions in the multi-component induction logging coil system include: xx coil system, xy coil system, xz coil system, yx coil system, yy coil system, yz coil system, zx coil system, zy coil system, and zz coil system; The data relationship establishment module is specifically used for: Calculate the induced electromotive force of the coil system in different receiving directions when measuring the geometric parameters of the fracture; The induced electromotive force of the coil system in one receiving direction when measuring the geometric parameters of the fracture is: V=∫Edl (1) Wherein, V is the induced electromotive force of the coil system when measuring the geometric parameters of the fracture; l is the circumference of the coil system; E is the electric field strength, which satisfies: n×E=0 (3) AE=B (5) Where k0 is the wave number; ε r is the relative dielectric constant; J s The current intensity applied to the coil system in different receiving directions; μ0 and μ r are relative magnetic permeability and free space magnetic permeability respectively; ω represents the current angular frequency; A is the total stiffness matrix; B is the applied condition; V is the finite element solution area; is the curl operator; i is the imaginary unit; n is the normal vector.

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