Method for correcting resistivity anisotropy of highly-deviated well / horizontal well array well

Abstract

The invention provides a highly-deviated well / horizontal well array induction logging resistivity anisotropy correction method, and relates to the field of geological exploration. The method comprises the following steps that a three-dimensional finite difference method is adopted for modeling, array induction logging response simulation is conducted, and apparent resistivity change rules under different hole drift angles are simulated; establishing a resistivity correction chart according to the change rule of the apparent resistivity under different hole drift angles obtained by simulation; if the anisotropy coefficient of the measured target well is known, a correction formula is obtained through 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 the deflecting section, then a correction formula is obtained through chart fitting, and the resistivity is corrected through the correction formula. The resistivity'spike 'phenomenon of a logging result can be effectively eliminated, a more approximate real formation resistivity value is obtained, and the accuracy of reservoir evaluation of a highly-deviated well and a horizontal well is improved.

Description

Technical Field

[0001] The invention relates to the technical field of geological exploration, and in particular to a method for correcting well resistivity anisotropy. Background Art

[0002] With the continuous progress of oil and gas exploration, especially the widespread application of high-angle wells / horizontal wells, the exploration and development of unconventional oil and gas has important significance, which can optimize the development and utilization of oil and gas resources to the maximum extent. The array induction logging instrument uses a transmitting coil and multiple sets of receiving coils, and uses electromagnetic theory to perform theoretical calculations on the obtained signals to achieve the effect of focusing synthesis of different detection depths and different vertical resolutions.

[0003] Since there is an angle between highly deviated wells and horizontal wells and the formation, the influence of formation anisotropy is particularly prominent, so that the measured resistivity cannot directly reflect the true resistivity information of the formation, causing certain difficulties in logging interpretation and evaluation. In particular, during the drilling of highly deviated wells / horizontal wells, affected by anisotropy and layer interfaces, the apparent resistivity values ​​measured by the sub-arrays with deeper detection depths will fluctuate significantly, causing the resistivity curve to present a "spike" distribution. The resistivity spike distribution is caused by the resistivity polarization effect or the influence of layer interfaces, and cannot reflect the original formation information, causing difficulties in logging interpretation and evaluation, and affecting the accuracy of reservoir evaluation. Summary of the invention

[0004] The purpose of the present invention is to provide a method for correcting resistivity anisotropy in a highly deviated well / horizontal well array. First, a resistivity correction chart is established according to the simulated relationship between the well inclination angle and the apparent resistivity, and then a correction formula is obtained by fitting the chart to correct the resistivity. The resistivity "spike" phenomenon in the logging result can be effectively eliminated, and a more approximate real formation resistivity value can be obtained, thereby improving the accuracy of reservoir evaluation in highly deviated wells and horizontal wells.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A method for correcting resistivity anisotropy of highly deviated well / horizontal well array induction logging, comprising the following steps:

[0007] Step S1: simulating the change of apparent resistivity of different sub-arrays of array induction logging with well inclination angle at different anisotropy coefficients through array induction logging response simulation;

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

[0009] Step S3: Obtain a correction formula by using plate fitting, and correct the resistivity by using the correction formula.

[0010] Further: the step S1 specifically includes:

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

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

[0013]

[0014] K is the instrument constant defined

[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 emission current; L is the coil distance; σ a is the conductivity value of the induction logging composite coil system; ω is the angular frequency; μ is the magnetic permeability;

[0017] Apparent resistivity is the reciprocal of test conductivity.

[0018] Further: The induced electromotive force V in the receiving coil is obtained by:

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

[0020]

[0021]

[0022]

[0023] 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 sizes in the x, y and z directions respectively; i is the imaginary unit; ω is the angular frequency; μ is the magnetic permeability.

[0024] By integrating the closed coil, we can get the induced electromotive force in the receiving coil:

[0025]

[0026] 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 intensity in the z direction; ω is the angular frequency; μ is the magnetic permeability; S is the area.

[0027] Further: in the step S2, the variation law of the apparent resistivity at different well inclination angles includes the relationship between each well inclination angle and its corresponding apparent resistivity at different depths, and the different depths are 10in, 20in, 30in, 60in, and 90in respectively.

[0028] Further: step S3 specifically includes: judging whether the anisotropy coefficient of the measured target well is known; if the anisotropy coefficient of the measured target well is known, obtaining a correction formula by using plate fitting, and correcting the resistivity by using the correction formula; if the anisotropy coefficient of the measured target well is unknown, calculating the anisotropy coefficient by the deflection section, and then obtaining a correction formula by using plate fitting, and correcting the resistivity by using the correction formula.

[0029] Further: According to the resistivity correction chart, the horizontal resistivity R of the formation is fitted. d Correction formula:

[0030]

[0031] In the formula, R d is the horizontal resistivity of the formation; θ is the well inclination angle, and a, b, c are constant coefficients obtained by fitting.

[0032] According to the horizontal resistivity R d Calculate the correction coefficient μ0 as:

[0033]

[0034] Among them, R1 is the apparent resistivity when the well inclination angle is 0°.

[0035] Further: in step S3, the resistivity is corrected using the following resistivity correction formula:

[0036]

[0037] Where R2 is the apparent resistivity before correction, and R is the apparent resistivity after correction.

[0038] Compared with the original technology, the present invention has the following beneficial effects:

[0039] 1. For dense formations, the rock structure is complex and the heterogeneity is strong. The present invention fits the correction formula through the resistivity correction chart in step S3 of right 1, and substitutes it into the resistivity correction formula to effectively correct the resistivity, so that the result is closer to the resistivity of the actual formation; especially in the drilling process of high-angle wells / horizontal wells, after resistivity correction, the "spike" shape of the resistivity is effectively reduced, the authenticity of the measurement of the formation resistivity is improved, and the accuracy of reservoir evaluation is effectively improved;

[0040] 2. Array induction logging has multiple detection depths and can measure multiple sets of formation resistivity information. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a flow chart of a correction method in an embodiment of the present invention;

[0042] Figure 2 is the coordinate diagram of the apparent resistivity of each subarray with the well inclination angle when the horizontal resistivity is 1Ω·m and the anisotropy coefficient is known;

[0043] Figure 3 It is the coordinate diagram of the apparent resistivity of each sub-array with the well inclination angle when the horizontal resistivity is 100Ω·m and the anisotropy coefficient is known;

[0044] Figure 4 is the anisotropy λ 2 =5, the graph showing the change of apparent resistivity at each detection depth with the well inclination angle;

[0045] Figure 5 is the anisotropy λ 2 =10, the graph showing the change of apparent resistivity at each detection depth with the well inclination angle;

[0046] Figure 6 It is the correction formula fitting diagram;

[0047] Figure 7 is the relationship diagram between the correction coefficient and the well inclination angle;

[0048] Figure 8 This is the resistivity correction result map of the study area;

[0049] Fig. 9 It is the resistivity-frequency histogram. DETAILED DESCRIPTION

[0050] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0052] like Figure 1 As shown: A method for correcting resistivity anisotropy of highly deviated well / horizontal well array induction logging, comprising the following steps:

[0053] Step S1: adopting three-dimensional finite difference method to model and simulate array induction logging response, and simulate the variation law of apparent resistivity at different well inclination angles;

[0054] The array induction logging response simulation is based on the Maxwell equations. The transmitting source is equivalent to a magnetic dipole source, and the receiving coil is equivalent to a receiving point. The induction logging response simulation under complex formation conditions is converted into an electromagnetic field problem generated by a magnetic dipole source in a complex medium.

[0055] The apparent conductivity value at the receiving coil is obtained as follows:

[0056] According to Faraday's law of electromagnetic induction, the magnetic field components at the receiving point are calculated by interpolating the neighboring magnetic fields using a staggered grid:

[0057]

[0058]

[0059]

[0060] 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 sizes in the x, y and z directions respectively; i is the imaginary unit; ω is the angular frequency; μ is the magnetic permeability.

[0061] By integrating the closed coil, we can get the induced electromotive force in the receiving coil:

[0062]

[0063] 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 intensity in the z direction; ω is the angular frequency; μ is the magnetic permeability; S is the area.

[0064] Define the instrument constant K:

[0065]

[0066] 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 emission current; L is the coil distance; σ a is the conductivity value of the induction logging composite coil system; ω is the angular frequency; μ is the magnetic permeability.

[0067] Calculate the apparent conductivity value of the induction logging composite coil system:

[0068]

[0069] Apparent resistivity is the reciprocal of test conductivity.

[0070] The size of the well inclination angle has an important influence on the array induction logging response. In anisotropic formations, the size of the well inclination angle will make the logging response more complicated. Figure 2 and Figure 3 The variation of apparent resistivity of each subarray with well inclination angle when the horizontal resistivity is 1Ω·m and 100Ω·m is simulated respectively. Assuming the anisotropy coefficient is 4 and the instrument frequency is 50kHz. Figure 1 It can be seen that the apparent resistivity increases with the increase of well inclination angle; compared with high-resistance formations, in low-resistance formations, due to the influence of skin effect, the long sub-array cannot directly reflect the true resistivity information, and low-resistance formations are more seriously affected by anisotropy.

[0071] Step S2: establishing a resistivity correction chart according to the variation law of apparent resistivity at different well inclination angles obtained by simulation;

[0072] Knowing the anisotropy coefficient, the changes in well inclination and apparent resistivity are studied, and a resistivity correction chart is established based on the differences in apparent resistivity at different detection depths (10in, 20in, 30in, 60in, 90in) at different well inclinations. Figure 4 and Figure 5The figure shows the change of apparent resistivity at each detection depth with the well inclination angle when the anisotropy coefficient is two different. When the anisotropy coefficient is small, as the well inclination angle increases, the apparent resistivity increases but the change range is not large. When the anisotropy coefficient increases, the resistivity increases abnormally at a deeper detection depth, especially at high angle and low resistance, the apparent resistivity fluctuates and increases rapidly.

[0073] Step S301: determining whether the anisotropy coefficient of the measured target well is known;

[0074] Step S302: When the anisotropy coefficient is known, the horizontal resistivity and the well inclination angle can be fitted using the above chart, and the corrected resistivity value can be calculated by the fitting formula. First, according to the resistivity correction chart, the correction formula is fitted:

[0075] R d =100+0.013*θ 2.03 (7)

[0076] Among them, R d is the horizontal resistivity of the formation; θ is the well inclination; a, b, c are constant coefficients obtained by fitting.

[0077] pass Figure 6 It can be seen that the R square is 0.99, and the fitting relationship is good.

[0078] The correction coefficient μ0 is:

[0079]

[0080] R1 is the apparent resistivity when the well inclination angle is 0°.

[0081] Depend on Figure 7 It can be seen that as the well inclination angle increases, the correction coefficient also gradually increases; when the well inclination angle is small, the increase trend of the correction coefficient is small. From equations 7 and 8, it can be seen that the corrected resistivity R is:

[0082]

[0083] R2 is the apparent resistivity before correction.

[0084] Step S303: If the anisotropy coefficient of the measured target well is unknown, the anisotropy coefficient is calculated through the deflection section, and then the correction formula is obtained by plate fitting, and the resistivity is corrected by the correction formula in S4.

[0085] Figure 8This is the resistivity correction result map of the study area. The third track in the figure is the resistivity curve before correction, the fourth track is the resistivity curve after correction, and the fifth track is the comparison of the resistivity curve of a single detection depth before and after correction. Curves of different colors 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, making the resistivity value closer to the horizontal resistivity and reflecting the true formation resistivity information. In order to further intuitively display the correction effect, the resistivity of the same layer before and after correction is compared with the vertical well resistivity. Fig. 9 It can be seen from the frequency histogram that the resistivity value after correction has decreased to a certain extent compared with that before correction, and is closer to the resistivity value of the vertical well.

[0086] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for correcting resistivity anisotropy in induction logging of highly deviated wells / horizontal well arrays, characterized by: The following steps are involved: Step S1: simulating the change of apparent resistivity of different sub-arrays of array induction logging with well inclination angle at different anisotropy coefficients through array induction logging response simulation; Step S2: Analyze the relationship between the apparent resistivity and the well inclination angle at different detection depths of array induction logging, and establish a resistivity correction chart; Step S3: Obtain a correction formula by using plate fitting, and correct the resistivity by using the correction formula.

2. The calibration method according to claim 1, characterized in that: The step S1 specifically includes: Based on Maxwell equations, the three-dimensional finite difference method is used to equate the transmitting source to a magnetic dipole source and the receiving coil to a receiving point. The induction logging response simulation under complex formation conditions is converted into the electromagnetic field problem generated by the magnetic dipole source in complex media, and the array induction logging response simulation is performed.

3. The calibration method according to claim 2, characterized in that: In step S1, the apparent resistivity is calculated based on the apparent conductivity of the induction logging composite coil system and the test conductivity: Among them, the apparent conductivity value σ of the induction logging composite coil system is a The calculation formula is: The K is the instrument constant defined as: 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 emission current; L is the coil distance; σ a is the conductivity value of the induction logging composite coil system; ω is the angular frequency; μ is the magnetic permeability; Apparent resistivity is the reciprocal of test conductivity.

4. The calibration method according to claim 3, characterized in that: The induced electromotive force V in the receiving coil is obtained as follows: According to Faraday's law of electromagnetic induction, the magnetic field components of each receiving point are calculated by interpolating the neighboring magnetic fields using a staggered grid: 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; i is the imaginary unit; ω is the angular frequency; μ is the magnetic permeability; By integrating the closed coil, we can get the induced electromotive force V in the receiving coil: In the above formula, i is the imaginary unit, H is the magnetic field intensity, t is the time, H zz is the magnetic field intensity in the z direction; ω is the angular frequency; μ is the magnetic permeability; S is the area.

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

6. The calibration method according to claim 1, characterized in that: Step S3 specifically includes: Determine whether the anisotropy coefficient of the measured target well is known; If the anisotropy coefficient of the measured target well is known, the correction formula is obtained by plate fitting, and the resistivity is corrected by the correction formula; If the anisotropy coefficient of the measured target well is unknown, the anisotropy coefficient is calculated through the deflection section, and then the correction formula is obtained by plate fitting, and the resistivity is corrected by the correction formula.

7. The calibration method according to claim 1, characterized in that: In step S3, the resistivity is corrected using the following correction formula: Where θ is the well inclination angle; R2 is the resistivity before correction; R is the resistivity after correction; μ0 is the correction coefficient.

8. The calibration method according to claim 7, characterized in that: The method for obtaining the correction coefficient of the correction formula in step S3 is: According to the resistivity correction chart, the horizontal resistivity R of the formation is fitted. d Fitting formula: R d =a+b*θ c Where θ is the well inclination angle; a, b, c are constant coefficients obtained by fitting; According to the horizontal resistivity R d Calculate the correction coefficient μ0 as: Among them, R1 is the apparent resistivity when the well inclination angle is 0°.

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