High-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging

Abstract

The application discloses a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging, which comprises the following steps: s1, establishing a high-resistivity formation electromagnetic wave resistivity logging method; s2, developing a magnetic dipole source electromagnetic field pseudo-analytical fast algorithm based on different borehole columnar layered formation models in the high-resistivity formation; s3, simulating and analyzing the problem of formation resistivity anomaly caused by the existence of the borehole; s4, selecting different borehole factor parameters under the high-resistivity formation condition, and determining the data range contained in the borehole correction database; s5, carrying out forward simulation and analysis on the borehole influencing factors such as mud resistivity, hole diameter, eccentricity and relative dielectric constant; s6, detailing the change rule of the response results of different influencing factors in the high-resistivity formation; and s7, combining the data obtained from the simulation results and establishing a borehole correction database, thereby forming the high-resistivity formation borehole correction method based on the high-frequency electromagnetic wave resistivity logging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil exploration and development, and belongs to the category of electrical logging methods, in particular to a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging. BACKGROUND

[0002] High-resistivity formation with oil-based mud is an important problem in current deep oil and gas exploration and development. Electromagnetic wave resistivity logging method can not only be applied to oil-based mud borehole environment, but also meet the demand of multi-frequency measurement. At present, the conventional induction and array induction instrument design can be effectively applied to medium and low resistivity formations, but it has poor sensitivity to high resistivity formations, so it is necessary to explore the feasibility of electromagnetic wave resistivity logging method in high resistivity formation. At the same time, due to different proportions of oil-based mud, the borehole resistivity is unknown, and borehole correction is an indispensable part of logging data processing, and the correction effect is related to the accuracy of reservoir identification. SUMMARY

[0003] The purpose of the present application is to provide a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

[0004] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0005] The high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging comprises the following steps:

[0006] s1. Establishing electromagnetic wave resistivity logging method for high-resistivity formation;

[0007] s2. Developing a pseudo-analytical fast algorithm for magnetic dipole source electromagnetic field based on different borehole columnar layered formation models in high-resistivity formation;

[0008] s3. Simulating and analyzing the problem of abnormal formation resistivity caused by the existence of borehole;

[0009] s4. Selecting different borehole factor parameters under high-resistivity formation conditions to determine the data range contained in the borehole correction database;

[0010] s5. Forward modeling and analysis of mud resistivity, hole diameter, eccentricity, relative dielectric constant and other borehole influencing factors;

[0011] s6. Detailing the change rule of the response results of different influencing factors in high-resistivity formation;

[0012] s7. Combining the data obtained from the simulation results and establishing a borehole correction database to form a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

[0013] In step s1, the frequency, coil structure and signal of the electromagnetic resistivity logging method are defined as:

[0014] The electromagnetic resistivity logging mainly characterizes the formation resistivity information by measuring the velocity and attenuation of the electromagnetic wave signal in the formation, wherein the influence of the complex dielectric constant is also considered, the dielectric constant is the ratio of the original applied electric field to the final medium electric field, is a physical quantity describing the polarization ability of the medium under the external electric field, and is related to the size of the frequency, when the frequency is higher, the dielectric constant contribution increases, and the dielectric constant difference between oil and water layers is obvious, which is very beneficial to the division of oil and water reservoirs.

[0015] Referring to the coil structure of the electromagnetic logging while drilling method, the instrument with a single transmitting coil and two receiving coils is expanded, it is assumed that the distance from the transmitting coil to the receiver is greater than the borehole diameter, for most cases, only the refracted wave has the greatest contribution at the receiving coil, for example, if the borehole resistivity R b is much smaller than the formation resistivity R t , then the reflected wave and the direct wave are more attenuated than the refracted wave, in this case, the refracted wave propagates parallel to the borehole axis; on the other hand, if R b >>R t , then the wavelength in the borehole will be much larger than the borehole diameter; thus, it can be concluded that the attenuation of the direct wave and the reflected wave is obviously greater than that of the refracted wave;

[0016] The borehole correction is independent of the borehole external parameters, which means that the correction of the invaded layer and the thin layer can be independent of the borehole correction; therefore, the influence of the invasion and the thin layer is not considered in the subsequent borehole correction; in addition, it should be noted that the influence of the borehole on the phase of the receiving coil is independent of the distance between the transmitting coil and the receiving coil, but the distance between the transmitting coil and the receiving coil should be greater than the diameter of the borehole.

[0017] In step s2, the steps of developing a pseudo-analytical fast algorithm for the electromagnetic field of a magnetic dipole source based on different wellbore columnar layered formation models in a high-resistivity formation are as follows:

[0018] Step s21, a pseudo-analytical solution fast calculation method for the electromagnetic field

[0019] For a magnetic dipole located at (p T , 0, 0), the field in the medium is expanded as the z component field in the cylindrical coordinate system:

[0020]

[0021] Step s22, the expression of the narrow-sense reflection / transmission coefficient is derived by matching the boundary conditions, that is:

[0022]

[0023]

[0024]

[0025]

[0026] In formula (2), represents the narrow sense reflection coefficient between two layers, represents the narrow sense transmission coefficient between two layers;

[0027] After the expansion and discussion of the narrow sense reflection / transmission coefficient, the expression of the standing wave and outward wave after the generalized reflection / transmission solution in the columnar layered medium is obtained, that is:

[0028]

[0029]

[0030] In step s5, the selection of different borehole factor parameters under the condition of high resistance formation is as follows:

[0031] Borehole mud conductivity R m , hole diameter a, instrument eccentricity E cc , and relative dielectric constant ε r , according to the actual situation of the formation: (1) considering that the mud is obtained by different oil-water ratio, it can be considered that the range of borehole mud resistivity is from fresh water mud to completely non-conductive pure oil mud, that is, R m = 1 Ω·m-100000 Ω·m; (2) the value range of the hole diameter is a = 0.05 m-0.22 m; (3) considering the size of the drill pipe and the size of the drill collar of the instrument, the instrument does not exist completely deviating from the center of the well shaft, that is, the eccentricity is selected as E cc = 0-0.8, wherein E cc = ρ Ecc / a, ρ Ecc is the distance of eccentricity; (4) considering the dielectric constant range of the formation and the mud, the value range of the relative dielectric constant is selected as ε r = 1-20; for the above parameters and their value ranges, the electromagnetic wave logging fast forward algorithm with borehole model is used to calculate different influence factor charts and establish a borehole correction database.

[0032] In step s7, the steps for establishing the borehole correction database are as follows:

[0033] Step s71, first calculate the phase difference and amplitude ratio under various formation and borehole conditions;

[0034] Step s72, according to the relationship between the phase difference, amplitude ratio and formation resistivity in the uniform formation medium, the measured response result is converted into apparent resistivity.

[0035] Beneficial effects: This invention systematically studies electromagnetic wave logging methods and wellbore correction methods for oil-based mud in high-resistivity formations. For different detection modes, it draws on the signal processing methods of induction logging and electromagnetic wave logging while drilling, calculates the electromagnetic resistivity logging response under different formation and wellbore conditions, and forms a wellbore correction chart and database. It proposes an electromagnetic resistivity logging method for high-resistivity formations and establishes a wellbore environment correction method for oil-based mud in high-resistivity formations, providing a theoretical basis and technical reference for the exploration and development of deep oil and gas, and high-resistivity shale oil and gas reservoirs. Attached Figure Description

[0036] Figure 1 This is a flowchart of the columnar layered multilayer medium response algorithm in this invention;

[0037] Figure 2 This is a schematic diagram illustrating the verification of the real part of the zz component of the magnetic field in the columnar layering procedure of this invention.

[0038] Figure 3 This is a schematic diagram illustrating the verification of the imaginary part of the zz component of the magnetic field in the columnar layering procedure of this invention.

[0039] Figure 4 This is a schematic diagram illustrating the variation of the principal component of the near-coil apparent resistivity with eccentricity in this invention.

[0040] Figure 5 This is a schematic diagram illustrating the variation of the principal component of the apparent resistivity of the far coil with eccentricity in this invention.

[0041] Figure 6 This is a diagram showing the correction coefficients of the near-coil at high frequencies in this invention;

[0042] Figure 7 This is a diagram showing the correction coefficients of the far coil at high frequencies in this invention.

[0043] Figure 8 This is a comparison diagram before and after the correction of mud resistivity in this invention. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0045] Combination Figure 1 As shown in the figure, this invention provides a method for extracting the response of a columnar layered multilayer medium in an electromagnetic wave logging system with a wellbore model, which includes the following steps:

[0046] s1. Establish the formation model of different borehole factors in high-resistivity formation, whose hole diameter is 0.1 m, mud resistivity in borehole is 1 Ω·m-100000 Ω·m, formation transverse resistivity is 1 Ω·m-10000 Ω·m, and relative dielectric constant is 1.

[0047] s2. Through the establishment of electromagnetic wave logging forward model containing borehole, the fast calculation formula of columnar layered medium model is obtained by using pseudo-analytical method.

[0048] S3. According to the selection of different borehole factor parameters under high-resistivity formation conditions, the data range contained in the borehole correction database is determined. The following important borehole factors are selected: borehole mud conductivity R m , hole diameter a, instrument eccentricity E cc , and relative dielectric constant ε r .

[0049] S4. Explore the problem of formation resistivity anomaly caused by the existence of borehole.

[0050] S5. Explore the change rule of logging response result value with formation transverse resistivity in high-frequency detection mode.

[0051] Using high-frequency measurement mode can ensure that the measured resistivity range covers the high-resistivity of formation. By determining the appropriate measurement frequency, source distance and coil distance, the phase difference and amplitude ratio curves can be kept monotonous, so as to ensure that the formation resistivity obtained by subsequent research and application of inversion method is a single value.

[0052] S6. Simulate and analyze the borehole factors such as mud resistivity, hole diameter, eccentricity, and relative dielectric constant.

[0053] The instrument is placed in the center; the formation is isotropic medium. Under the condition of high-resistivity formation oil-based mud, the three principal components of phase difference, amplitude ratio and apparent resistivity will be affected by mud resistivity, hole diameter and eccentricity.

[0054] S7. Detail the change rule of response result of different influencing factors in high-resistivity formation;

[0055] Considering that the lateral heterogeneity of formation properties changes slowly, if there is the result of the previous window, the result of the previous sliding window inversion can be used as the initial value of the current window, which has the advantages of fast convergence of cost function and high calculation efficiency.

[0056] S8. Combine the data obtained from simulation and establish borehole correction database to form the borehole correction method of electromagnetic wave logging in high-resistivity formation.

[0057] For mud resistivity Rm, hole diameter a, eccentricity Ecc, and relative dielectric constant ε rThe influence degree and logging response results are calculated respectively, and a wellbore correction database is established by using the method of correction chart.

[0058] The cylindrical layer medium pseudo-analytical solution of the magnetic dipole source in the step s2 is specifically:

[0059] Step s21, fast calculation method of electromagnetic field pseudo-analytical solution

[0060] For a magnetic dipole located at (ρ T ,0,0), the z-component field of the magnetic dipole in the medium can be expanded in the cylindrical coordinate system as:

[0061]

[0062] Step s22, first, the expression of the narrow-sense reflection / transmission coefficient is derived by matching the boundary conditions, that is:

[0063]

[0064]

[0065]

[0066]

[0067] In formula (2), represents the narrow-sense reflection coefficient between the two layers, represents the narrow-sense transmission coefficient between the two layers.

[0068] After the extension and discussion of the narrow-sense reflection / transmission coefficient, the expression of the standing wave and outward wave after the generalized reflection / transmission solution in the cylindrical layered medium is obtained, that is:

[0069]

[0070]

[0071] In step s6, the simulation and analysis method of the influence factors is specifically:

[0072] Step s61, based on the different sensitivities of the instrument responses to each parameter and the geological structure information given in step s1, the number of initial value selections of each to-be-inverted parameter is determined; the initial value selection method of each to-be-inverted parameter, refer to steps s6.2-s6.6.

[0073] Step s62, since the formation resistivity and the mud resistivity belong to the resistivity parameter, it is necessary to consider whether there is a mutual influence result, therefore, the anisotropy of the formation is also considered, and the resistivity anisotropy coefficient is set as λ=3, wherein σh is the formation transverse conductivity, σ v is the formation vertical conductivity.

[0074] Step s63, in the condition of high-resistivity formation oil-based mud, the three principal components of phase difference, amplitude ratio and apparent resistivity are firstly considered to be affected by mud resistivity, hole diameter and eccentricity.

[0075] Step s64, the principal components Ra,xx and Ra,yy are considered to be affected by formation transverse resistivity and formation anisotropy coefficient, but the principal component Ra,zz is not affected by formation anisotropy.

[0076] Step s65, the data obtained by simulation are combined and a wellbore correction database is established to form a high-resistivity formation electromagnetic wave logging wellbore correction method.

[0077] Step s66, the initial values selected in steps s62-s65 are freely combined.

[0078] As shown in Figure 2 and Figure 3 , the results calculated by the pseudo-analytical solution method are compared with the results calculated by the finite element numerical algorithm, and it can be seen from the figure that the curves and the scattered points are well matched to verify the effectiveness of the method.

[0079] In Figure 4 and Figure 5 , the -·- represents the case of mud resistivity 1 Ω·m, and the negative response value becomes smaller and smaller with the increase of eccentric distance, and it can be known that the influence is very large at low mud resistivity. Comparing the -·- in Figure 5 with the black solid line, the influence of high-resistivity mud resistivity on apparent resistivity is small, and the apparent resistivity value of the far coil is almost a straight line when the eccentricity changes, indicating that the result is less affected by the eccentricity, and the result can be closer to the true formation resistivity.

[0080] In Figure 6 and Figure 7 , the oil-based mud resistivity is 10000 Ω·m. The abscissa represents the size of the formation resistivity, and the ordinate represents the ratio of the corrected resistivity to the apparent resistivity.

[0081] In Figure 8In the wellbore before correction (the line in the figure), as the formation resistivity increases, the apparent resistivity value is smaller and smaller than the formation resistivity value, that is, away from the 45° test line. After correction (the line in the figure), when the formation resistivity is less than 1000 Ω·m, the corrected result is slightly larger than the 45° test line; when the formation resistivity is between 1000 Ω·m and 4000 Ω·m, the corrected result is basically coincident with the formation resistivity value; when the formation resistivity is greater than 4000 Ω·m, the corrected result has a slight error with the 45° line, but the error is less than 1%, and the correction effect is considered to be good.

[0082] Of course, the above description is only for the preferred embodiments of the present application, and the present application is not limited to the above-mentioned embodiments. It should be noted that any person skilled in the art can make all equivalent substitutions and obvious modifications under the teaching of the present application, and all the substitutions and modifications fall within the scope of the present application, and should be protected by the present application.

Claims

1. A borehole correction method for high-resistivity formations based on high-frequency electromagnetic resistivity logging, characterized in that, The method comprises the following steps: s1. establishing a high-resistivity formation electromagnetic wave resistivity logging method; s2. developing a pseudo-analytical fast algorithm for the electromagnetic field of a magnetic dipole source based on different borehole columnar layered formation models in high-resistivity formations; s3. simulating and analyzing the problem of formation resistivity anomalies caused by the presence of a borehole; s4. selecting different borehole factor parameters in high-resistivity formations to determine the data range contained in the borehole correction database; s5. forward modeling and analyzing the mud resistivity, hole diameter, eccentricity, and relative dielectric constant borehole influence factors; s6. detailing the change law of the response results of different influence factors in high-resistivity formations; s7. combining the data obtained from the simulation results and establishing a borehole correction database to form a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

2. The high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging according to claim 1, characterized in that, In the step s2, the step of developing a pseudo-analytical fast algorithm for the electromagnetic field of a magnetic dipole source based on different borehole columnar layered formation models in high-resistivity formations is specifically: Step s21, electromagnetic field pseudo-analytical solution fast calculation method For a magnetic dipole located at (p T , 0, 0), the field in the medium in the z-component field expansion in cylindrical coordinates is: Step s22, derive the expression of the narrow-sense reflection / transmission coefficient by matching the boundary conditions, that is: In equation (2), denotes the narrow-sense reflection coefficient between two layers, denotes the narrow-sense transmission coefficient between two layers; After the extension and discussion of the narrow-sense reflection / transmission coefficient, the expression of the standing wave and outward wave in the columnar layered medium after the generalized reflection / transmission solution is obtained, that is:

3. The high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging according to claim 1, characterized in that, In the step s5, the selection of borehole influence factor parameters in high-resistivity formations is specifically: wellbore mud conductivity R m , hole diameter a, instrument eccentricity E cc , and relative dielectric constant ε r , (1) the range of wellbore mud resistivity is from fresh water mud to completely non-conductive pure oil mud, i.e. R m = 1 Ω·m - 100000 Ω·m; (2) the range of hole diameter is a = 0.05 m - 0.22 m; (3) the eccentricity is selected as E cc = 0 - 0.8, where E cc = p Ecc / a, p Ecc is the eccentric distance; (4) the range of the relative dielectric constant is selected as ε r = 1 - 20.

4. The high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging according to claim 1, characterized in that, In the step s7, the step of establishing a borehole correction database is: Step s71, first calculate the phase difference and amplitude ratio under various formation and borehole conditions; Step s72, according to the relationship between the phase difference, amplitude ratio, and formation resistivity in a uniform formation medium, convert the actual measured response results into apparent resistivity.

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