A method for resistivity anisotropy correction of high angle deviated / horizontal array wells

Abstract

The application provides a large-inclination well / horizontal well array induction logging resistivity anisotropy correction method and relates to the field of geological exploration. The method comprises the following steps: modeling by adopting a three-dimensional finite difference method, performing array induction logging response simulation, and simulating the variation law of apparent resistivity under different inclination angles; establishing a resistivity correction chart according to the variation law of the apparent resistivity under different inclination angles obtained by simulation; if the anisotropy coefficient of the measured target well is known, a correction formula is obtained by chart fitting, and the resistivity is corrected through the correction formula; if the anisotropy coefficient of the measured target well is unknown, the anisotropy coefficient is calculated through a build-up section, a correction formula is obtained by chart fitting, and the resistivity is corrected through the correction formula. The method can effectively eliminate the resistivity'spike' phenomenon of the logging result, obtain a more approximate real formation resistivity value, and improve the accuracy of the reservoir evaluation of the large-inclination well and the horizontal well.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geological exploration, in particular to a well resistivity anisotropy correction method. BACKGROUND

[0002] With the continuous progress of oil and gas exploration, especially the wide application of high angle deviation wells / horizontal wells, it is of great significance for the exploration and development of unconventional oil and gas, which can maximize the optimization of oil and gas resource development and utilization. Array induction logging instrument uses a transmitting coil and multiple receiving coils, uses electromagnetic theory to theoretically calculate the obtained signals to complete the focusing synthesis of different detection depths and different longitudinal resolution effects.

[0003] Due to the angle between high angle deviation wells and horizontal wells and the formation, the influence of anisotropy of the formation is particularly prominent, so that the measured resistivity cannot intuitively reflect the real resistivity information of the formation, which causes certain difficulties for well logging interpretation and evaluation. Especially in the process of high angle deviation well / horizontal well drilling, affected by anisotropy and layer interface, the apparent resistivity value measured by the subarray with deep detection depth will have obvious fluctuation, causing the resistivity curve to present "spike" distribution. The resistivity spike distribution is caused by resistivity polarization effect or layer interface effect, which cannot reflect the original formation information, causes difficulties for well logging interpretation and evaluation, and affects the accuracy of reservoir evaluation. SUMMARY

[0004] The purpose of the present application is to provide a high angle deviation well / horizontal well array well resistivity anisotropy correction method, which first establishes a resistivity correction chart according to the simulated relationship between the deviation angle and the apparent resistivity, and then uses the chart to fit to obtain a correction formula for correcting the resistivity. The method can effectively eliminate the "spike" phenomenon of the logging result resistivity, obtain more approximate real formation resistivity value, and improve the accuracy of high angle deviation well and horizontal well reservoir evaluation.

[0005] To achieve the above purpose, the present application realizes the following technical scheme:

[0006] A high angle deviation well / horizontal well array induction logging resistivity anisotropy correction method, comprising the following steps:

[0007] Step S1: simulate the change of different subarray apparent resistivity of array induction logging with the deviation angle at different anisotropy coefficients through array induction logging response simulation;

[0008] Step S2: analyze the relationship between the apparent resistivity and the deviation angle at different detection depths of array induction logging, and establish a resistivity correction chart;

[0009] Step S3: use the chart to fit to obtain a correction formula, and correct the resistivity through the correction formula.

[0010] Further, the step S1 specifically comprises:

[0011] Based on Maxwell equations, using three-dimensional finite difference method, the transmitting source is equivalent to a magnetic dipole source, the receiving coil is equivalent to a receiving point, the response simulation of induction logging under complex formation conditions is converted into the problem of electromagnetic field generated by a magnetic dipole source in complex medium, and the response simulation of array induction logging is carried out.

[0012] Further, the apparent conductivity value of the induction logging composite coil system is obtained according to the induced electromotive force V in the receiving coil:

[0013] ;

[0014] The K is an instrument constant defined as

[0015]

[0016] In the above formula, A T A R is the area of the transmitting coil and the receiving coil; N T N R is the number of turns of the transmitting coil and the receiving coil; I T is the transmitting current; L is the coil spacing; sigma a is the conductivity value of the induction logging composite coil system; omega is the angular frequency; mu is the magnetic permeability;

[0017] The apparent resistivity is the reciprocal of the apparent conductivity.

[0018] Further, the induced electromotive force V in the receiving coil is obtained in the following manner:

[0019] According to Faraday's law of electromagnetic induction, by interpolating the adjacent magnetic field, the following magnetic field components of each receiving point are calculated using staggered grid:

[0020]

[0021] In the above formula, H x , H y , H z are the magnetic field components in the x direction, the y direction and the z direction respectively; E x , E y , E z are the electric field components in the x direction, the y direction and the z direction respectively; Delta x, Delta y, Delta z are the step lengths in the x direction, the y direction and the z direction respectively; i is the imaginary unit; omega is the angular frequency; mu is the magnetic permeability.

[0022] The induced electromotive force in the receiving coil is obtained by closed loop integration:

[0023]

[0024] In the above formula, E is the electric field intensity; H is the magnetic field intensity; t is time; H zz is the magnetic field intensity in the z direction; omega is the angular frequency; mu is the magnetic permeability; and S is the area.

[0025] Further, in the step S2, the variation law of the apparent resistivity at different hole inclinations comprises the relationship between each hole inclination and the corresponding apparent resistivity at different depths, and the different depths are 10 in, 20 in, 30 in, 60 in and 90 in respectively.

[0026] Further, the step S3 specifically comprises: judging whether the anisotropy coefficient of the measured target well is known; if the anisotropy coefficient of the measured target well is known, a correction formula is obtained by using a chart fitting, and the resistivity is corrected through the correction formula; if the anisotropy coefficient of the measured target well is unknown, the anisotropy coefficient is calculated through a build-up section, a correction formula is obtained by using a chart fitting, and the resistivity is corrected through the correction formula.

[0027] Further, according to the resistivity correction chart, the formation horizontal resistivity The correction formula is:

[0028]

[0029] In the formula, R is the apparent resistivity, and R0 is the formation horizontal resistivity. is the formation horizontal resistivity; is the hole inclination, and a, b and c are constant coefficients, which are obtained by fitting.

[0030] According to the formation horizontal resistivity The correction coefficient mu0 is calculated as:

[0031]

[0032] In the formula, R1 is the apparent resistivity when the hole inclination is 0°.

[0033] Further, in the step S3, the resistivity is corrected by using the following resistivity correction formula:

[0034]

[0035] In the formula, R2 is the apparent resistivity before correction, and R is the apparent resistivity after correction.

[0036] Compared with the prior art, the present application has the following beneficial effects:

[0037] I. For the compact formation, the rock structure is complex, and the heterogeneity is strong, the correction formula is fitted by the resistivity correction chart in S3 step, the resistivity correction formula is substituted, the resistivity is effectively corrected, the result is closer to the resistivity of the actual formation, especially in the drilling process of the high deviation well / horizontal well, after the resistivity correction, the "spike" of the resistivity is effectively reduced, the reality of the measurement of the formation resistivity is improved, and the accuracy of the reservoir evaluation is effectively improved.

[0038] II. The array induction logging has multiple detection depths, and multiple groups of formation resistivity information can be measured. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The flow chart of the correction method in the embodiment of the application is shown in the figure.

[0040] Figure 2 The coordinate graph of the apparent resistivity of each subarray with the known anisotropy coefficient when the horizontal resistivity is 1 ohm·m and the inclination angle is shown in the figure.

[0041] Figure 3 The coordinate graph of the apparent resistivity of each subarray with the known anisotropy coefficient when the horizontal resistivity is 100 ohm·m and the inclination angle is shown in the figure.

[0042] Figure 4 The apparent resistivity of each detection depth with the known anisotropy λ 2 =5 and the inclination angle is shown in the figure.

[0043] Figure 5 The apparent resistivity of each detection depth with the known anisotropy λ 2 =10 and the inclination angle is shown in the figure.

[0044] Figure 6 The fitting graph of the correction formula is shown in the figure.

[0045] Figure 7 The relationship graph of the correction coefficient and the inclination angle is shown in the figure.

[0046] Figure 8 The resistivity correction result map of the study area is shown in the figure.

[0047] Figure 9 The resistivity-frequency histogram is shown in the figure. DETAILED DESCRIPTION

[0048] The technical solutions of the application will be described clearly and completely in combination with the drawings. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the application.

[0049] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0050] As shown in Figure 1 : a large inclination well / horizontal well array induction logging resistivity anisotropy correction method, comprising the following steps:

[0051] Step S1: using three-dimensional finite difference method modeling, array induction logging response simulation, simulating the variation of apparent resistivity under different inclination angles;

[0052] Array induction logging response simulation is based on Maxwell equations; the transmitting source is equivalent to a magnetic dipole source, and the receiving coil is equivalent to a receiving point, so that the induction logging response simulation under complex formation conditions is converted into the electromagnetic field problem generated by the magnetic dipole source in the complex medium;

[0053] The apparent conductivity value at the receiving coil is obtained by the following method:

[0054] According to Faraday's law of electromagnetic induction, the magnetic field components at the receiving point are calculated by interpolating the adjacent magnetic fields and using staggered grids:

[0055] (2)

[0056] In the above formula, H x , H y , H z are the magnetic field components in the x, y and z directions respectively; E x , E y , E z are the electric field components in the x, y and z directions respectively; Δx, Δy, Δz are the step lengths in the x, y and z directions respectively; i is the imaginary unit; ω is the angular frequency; μ is the magnetic permeability.

[0057] The induced electromotive force in the receiving coil can be obtained by closed loop integration:

[0058] (3)

[0059] In the above formula, E is the electric field strength; H is the magnetic field strength; t is the time; H zz is the magnetic field strength in the z direction; ω is the angular frequency; μ is the magnetic permeability; S is the area.

[0060] Definition of instrument constant K:

[0061] (4)

[0062] In the above equation, A T A R is the area of the transmitter and receiver coils; N T N R is the number of turns of the transmitter and receiver coils; I T is the transmitter current; L is the coil spacing; σ a is the conductivity value of the induction logging composite coil system; ω is the angular frequency; μ is the magnetic permeability.

[0063] The apparent conductivity value of the induction logging composite coil system is obtained:

[0064] (5)

[0065] The apparent resistivity is the inverse of the apparent conductivity.

[0066] The magnitude of the inclination angle has an important influence on the array induction logging response. In anisotropic formations, the magnitude of the inclination angle will cause the logging response to be more complex. Figure 2 and Figure 3 The apparent resistivity of each sub-array is simulated as a function of the inclination angle for a known anisotropy coefficient when the horizontal resistivity is 1 Ω·m and 100 Ω·m, respectively. It is assumed that the anisotropy coefficient is 4 and the instrument frequency is 50 kHz. From Figure 1 It can be seen that the apparent resistivity increases with the increase of the inclination angle; compared with high-resistivity formations, the long sub-array cannot directly reflect the true resistivity information in low-resistivity formations due to the influence of the skin effect, and the low-resistivity formation is more seriously affected by anisotropy.

[0067] Step S2: Establish a resistivity correction chart according to the change law of the apparent resistivity obtained by simulation under different inclination angles;

[0068] Given the anisotropy coefficient, the change of the inclination angle and the apparent resistivity is studied, and a resistivity correction chart is established according to the different apparent resistivities of each detection depth (10 in, 20 in, 30 in, 60 in, 90 in) at different inclination angles. Figure 4 and Figure 5 are charts of the apparent resistivity of each detection depth as a function of the inclination angle for two different anisotropy coefficients. When the anisotropy coefficient is small, the apparent resistivity increases with the increase of the inclination angle but the change range is not large. When the anisotropy coefficient increases, the resistivity of the deeper detection depth abnormally increases, especially at high angles and low resistivity, the apparent resistivity fluctuates and rapidly increases.

[0069] Step S301: judging whether the anisotropy coefficient of the measured target well is known or not;

[0070] Step S302: when the anisotropy coefficient is known, the horizontal resistivity and the deviation angle can be fitted by using the above chart, and the corrected resistivity value can be calculated by the fitted formula. First, according to the resistivity correction chart, the correction formula is fitted:

[0071] (7)

[0072] wherein, is the horizontal resistivity of the formation, is the deviation angle; a, b, c are constant coefficients, which are obtained by fitting.

[0073] It can be seen that the R square is 0.99, and the fitting relationship is good. Figure 6

[0074] The correction coefficient μ0 is:

[0075] (8)

[0076] R1 is the apparent resistivity when the deviation angle is 0°.

[0077] It can be seen that with the increase of the deviation angle, the correction coefficient also gradually increases; when the deviation angle is small, the increasing trend of the correction coefficient is small. According to formulas 7 and 8, the corrected resistivity R is: Figure 7

[0078] (9) R2 is the apparent resistivity before correction.

[0079]

[0080] Step S303: if the anisotropy coefficient of the measured target well is unknown, the anisotropy coefficient is calculated through the build-up section, the correction formula is obtained by using the chart fitting, and the resistivity is corrected by the correction formula in S4.

[0081] Figure 8 is the resistivity correction result map of the study area. The third curve in the figure is the resistivity curve before correction, the fourth curve is the resistivity curve after correction, and the fifth curve is the comparison of the resistivity curve before and after correction at a single detection depth. Different color curves represent different detection depths, which are 10in, 20in, 30in, 60in and 90in respectively. After correction, the "spike" shape of the resistivity can be eliminated to a certain extent, so that the resistivity value is closer to the horizontal resistivity, which can reflect the true formation resistivity information. In order to further intuitively show the correction effect, the resistivity before and after correction and the straight well resistivity at the same horizon are compared, and the resistivity curves before and after correction are shown in the figure. Figure 9 ​​The frequency histogram shows that the resistivity values after correction are reduced to some extent and are closer to the resistivity values of the straight well.

[0082] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for correcting resistivity anisotropy in array induction logging of highly deviated / horizontal wells, characterized in that: Includes the following steps: Step S1: Simulate the change of apparent resistivity of different subarrays of array induction logging with different anisotropy coefficients as a function of well inclination angle through array induction logging response simulation. Step S2: Analyze the relationship between apparent resistivity and well inclination angle at different detection depths of array induction logging, and establish a resistivity correction chart; Step S3: Obtain the correction formula by fitting the chart, and correct the resistivity using the correction formula; Step S3 specifically includes: Determine whether the anisotropy coefficient of the target well is known; If the anisotropy coefficient of the target well is known, the correction formula is obtained by fitting the chart, and the resistivity is corrected by the correction formula. If the anisotropy coefficient of the target well is unknown, the anisotropy coefficient is calculated through the build-up section, and then the correction formula is obtained by fitting the chart. The resistivity is then corrected using the correction formula. The resistivity is corrected using the following formula: In the formula, θ is the well inclination angle; R2 is the resistivity before correction; R is the resistivity after correction; μ0 is the correction coefficient; The method for obtaining the correction coefficients in the correction formula is as follows: Based on the resistivity correction chart, fit the following... : in, is the well inclination angle; a, b, and c are constant coefficients obtained through fitting. according to The correction factor μ0 is calculated as follows: Where R1 is the apparent resistivity when the well inclination angle is 0°.

2. The correction method according to claim 1, characterized in that: Step S1 specifically includes: Based on Maxwell's equations, the three-dimensional finite difference method is used to treat the transmitting source as a magnetic dipole source and the receiving coil as a receiving point. The simulation of induction logging response under complex formation conditions is transformed into the electromagnetic field problem generated by the magnetic dipole source in the complex medium, and array induction logging response simulation is carried out.

3. The correction method according to claim 2, characterized in that: In step S1, the apparent resistivity is determined based on the apparent conductivity of the induction logging composite coil system and by testing the conductivity. Among them, the apparent conductivity value of the induction logging composite coil system The calculation formula is: K is a defined instrument constant: In the above formula, A T A R N represents the area of ​​the transmitting and receiving coils. T N R I represents the number of turns in the transmitting and receiving coils. T σ is the transmitting current; L is the coil pitch; σ is the transmitting current. a ω is the conductivity value of the induction logging composite coil system; μ is the angular frequency; μ is the magnetic permeability. Apparent resistivity is the reciprocal of test conductivity.

4. The correction method according to claim 3, characterized in that: The induced electromotive force V in the receiving coil is obtained in the following way: Based on Faraday's law of electromagnetic induction, the magnetic field components at each receiving point are calculated using an interlaced grid by interpolating the neighboring magnetic fields: In the above formula, H x H y H z These represent the magnetic field components in the x, y, and z directions, respectively; E x E y E z These are the electric field components in the x, y, and z directions, respectively. i ω is the imaginary unit; μ is the angular frequency; μ is the permeability. The induced electromotive force V in the receiving coil can be obtained by integrating from the closed coil: In the above formula, i H is the imaginary unit; t is time; H zz ω is the magnetic field strength in the z-direction; μ is the angular frequency; S is the permeability; and S is the area.

5. The correction method according to claim 1, characterized in that: In step S2, the variation law of apparent resistivity under different well inclination angles includes the relationship between each well inclination angle and its corresponding apparent resistivity at different depths, namely 10in, 20in, 30in, 60in, and 90in.

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