CN116661008A - High-resistance stratum borehole correction method based on high-frequency electromagnetic wave resistivity logging - Google Patents

Abstract

The present invention discloses a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging, which includes steps: s1. Establishing an electromagnetic wave resistivity logging method for high-resistivity formations; s2. Based on different boreholes in high-resistivity formations Develop a pseudo-analytic fast algorithm for the magnetic dipole source electromagnetic field in the columnar layered formation model; s3. Simulate and analyze the problem of abnormal formation resistivity due to the existence of wellbore; s4. Selection of different wellbore factor parameters under high resistivity formation conditions , determined the data range included in the wellbore calibration database; s5. carried out forward modeling and analysis on the wellbore influencing factors such as mud resistivity, borehole diameter, eccentricity, and relative permittivity; s6. The change law of the response results of different influencing factors in the formation; s7. Combine the data obtained from the simulation results and establish a borehole correction database to form a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

Description

Hole correction method for high resistivity formation based on high frequency electromagnetic resistivity logging

technical field

The invention relates to the field of petroleum exploration and development, and belongs to the category of electrical logging methods, in particular to a high-resistance formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

Background technique

Oil-based mud high-resistivity formation is an important problem facing deep oil and gas exploration and development. The electromagnetic wave resistivity logging method can not only be applied in the oil-based mud borehole environment, but also meet the requirements of multi-frequency measurement. At present, the design of conventional induction and array induction tools can be effectively applied in low-to-medium resistivity formations, but they are less sensitive to high-resistivity formations. Therefore, it is necessary to explore the feasibility of electromagnetic wave resistivity logging method in high-resistivity formations. At the same time, if the wellbore resistivity is unknown due to different oil-based mud ratios, borehole correction is an indispensable part of logging data processing, and the correction effect is related to the accuracy of reservoir identification.

Contents of the invention

The purpose of the present invention is to propose a high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging.

In order to achieve the above object, the present invention adopts the following technical solutions:

A high-resistivity formation borehole correction method based on high-frequency electromagnetic resistivity logging includes the following steps:

s1. Establish an electromagnetic wave resistivity logging method for high-resistivity formations;

s2. Develop a pseudo-analytic fast algorithm for the magnetic dipole source electromagnetic field based on different wellbore-containing columnar layered formation models in high-resistivity formations;

s3. Simulate and analyze the problem of abnormal formation resistivity due to the existence of boreholes;

s4. The selection of different wellbore factor parameters under high-resistivity formation conditions determines the data range included in the wellbore calibration database;

s5. Forward modeling and analysis of wellbore influencing factors such as mud resistivity, borehole diameter, eccentricity, and relative permittivity;

s6. Describe in detail the changing law of the response results of different influencing factors in high-resistivity formations;

s7. Combine the data obtained from the simulation results and establish a borehole correction database to form a borehole correction method for high-resistivity formations based on high-frequency electromagnetic wave resistivity logging.

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

Electromagnetic wave resistivity logging mainly characterizes formation resistivity information by measuring the velocity and attenuation of electromagnetic wave signals in the formation, and the influence of complex permittivity is also taken into account. The permittivity is the ratio of the original applied electric field to the final medium electric field, which is The physical quantity describing the polarization ability of the medium under the external electric field is related to the frequency. When the frequency is high, the contribution of the dielectric constant increases, and the difference in the dielectric constant of the oil and water layers is obvious, which is very beneficial to the division of oil and water reservoirs;

Referring to the coil structure of the electromagnetic logging while drilling method, the instrument will be deployed with a single transmitting coil and two receiving coils. It is assumed that the distance from the transmitting coil to the receiver is greater than the diameter of the borehole. For most cases, only the refracted wave The contribution is greatest at the receiving coil, for example, if the borehole resistivity _Rb is much smaller than the formation resistivity _Rt , the reflected and direct waves are more attenuated than the refracted waves, which in this case are parallel to On the other hand, if R _b >>R _t , the wavelength in the borehole will be much larger than the borehole diameter; from this, we can conclude that the attenuation of the direct wave and the reflected wave is significantly greater than that of the refracted wave in conclusion;

Wellbore correction has nothing to do with the parameters outside the wellbore, which means that the correction of the invasion layer and thin layer can be carried out independently of the wellbore correction; therefore, the influence of invasion and thin layer will not be considered in the subsequent wellbore correction; secondly, it should be noted that The influence of the wellbore on the phase of the receiving coil has nothing to do with the distance between the transmitting coil and the receiving coil, but it must be ensured that the distance between the transmitting coil and the receiving coil is greater than the diameter of the wellbore.

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

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

For a magnetic dipole located at (ρ _T ,0,0), the field in the medium expands in cylindrical coordinates with the z-component field as:

Step s22, deriving the expression of the reflection/transmission coefficient in the narrow sense by matching the boundary conditions, namely:

In formula (2), Indicates the narrow reflection coefficient between two layers, /> Indicates the narrow-sense transmission coefficient between two layers;

After expanding and discussing the reflection/transmission coefficient in the narrow sense, the expressions of the standing wave and outward wave in the columnar layered medium after solving the generalized reflection/transmission coefficient are obtained, namely:

In step s5, the selection of different wellbore factor parameters under high-resistivity formation conditions is specifically as follows:

Wellbore mud conductivity R _m , borehole diameter a, tool eccentricity E _cc and relative permittivity ε _r , according to the actual situation of the formation: (1) Considering that the mud is obtained from different oil-water ratios, the wellbore mud can be regarded as The range of resistivity is from fresh water slurry to completely non-conductive pure oil mud, that is, R _m =1Ω·m-100000Ω·m; (2) The value range of well diameter is a=0.05m-0.22m; (3) Considering the drill pipe size and drill collar size of the tool, the tool does not completely deviate from the center of the well axis, that is, the eccentricity is selected as E _cc =0-0.8, where E _cc =ρ _Ecc /a, ρ _Ecc is the eccentric distance ; (4) Considering the range of the dielectric constant of the formation and mud, the value range of the relative dielectric constant is selected as ε _r =1-20; for the above parameters and their value range, the electromagnetic wave logging with the borehole model is used to quickly The forward calculation algorithm calculates the charts of different influencing factors and establishes the wellbore correction database.

In step s7, the steps of establishing the borehole correction database are as follows:

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

Step s72, according to the relationship between phase difference, amplitude ratio and formation resistivity in the homogeneous formation medium, the response result obtained by actual measurement is converted into apparent resistivity.

Beneficial effects: during the implementation of the present invention, the research on the electromagnetic wave logging method and borehole correction method for oil-based mud in high-resistivity formations is systematically carried out, and for different detection modes, the signal processing of induction logging and electromagnetic wave logging while drilling is used for reference In this way, the electromagnetic wave resistivity logging response of different formations and borehole conditions is calculated, the borehole correction chart and the borehole correction database are formed, an electromagnetic wave resistivity logging method for high resistivity formation is proposed, and a method for high resistivity formation is established The wellbore environment correction method of oil-based mud in resistive formations provides a theoretical basis and technical reference for oil exploration and development of deep oil and gas and shale oil and gas high resistivity reservoirs.

Description of drawings

Fig. 1 is the flow chart of columnar layered multilayer dielectric response algorithm among the present invention;

Fig. 2 is a schematic diagram of the real part of the magnetic field zz component verified by the columnar layering program in the present invention;

Fig. 3 is a schematic diagram of the imaginary part of the magnetic field zz component verified by the columnar layering program in the present invention;

Fig. 4 is the schematic diagram of the variation of the principal component of the proximal coil apparent resistivity with the eccentricity in the present invention;

Fig. 5 is a schematic diagram of the change of the main component of the apparent resistivity of the medium and long-distance coil with the eccentricity of the present invention;

Fig. 6 is the correction coefficient diagram of the near-coil under high frequency in the present invention;

Fig. 7 is the correction coefficient diagram of the far coil under the medium and high frequency of the present invention;

Fig. 8 is a comparison chart before and after the mud resistivity is corrected in the present invention.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

In combination with what is shown in Figure 1, the embodiment of the present invention provides a method for extracting the response algorithm of columnar layered multi-layer media with a borehole model electromagnetic wave logging, which includes the following steps:

s1 Establish the formation model of different wellbore influencing factors in the high-resistivity formation. The well diameter is 0.1m, the mud resistivity in the wellbore is 1Ω·m-100000Ω·m, and the lateral resistivity of the formation is 1Ω·m-10000Ω·m , with a relative permittivity of 1.

s2. By establishing a forward modeling model with borehole electromagnetic wave logging, and using a pseudo-analytic method, a fast calculation formula for a columnar layered medium model is obtained.

S3. According to the selection of different wellbore factor parameters under high-resistivity formation conditions, the data range included in the wellbore correction database is determined. The following important wellbore influencing factors are selected: wellbore mud conductivity R _m , borehole diameter a, tool eccentricity E _cc and relative permittivity ε _r .

S4. Explore the problem of formation resistivity anomalies due to the existence of boreholes.

S5. Explore the change law of the logging response result value with the lateral resistivity of the formation in the high-frequency detection mode.

The high-frequency measurement mode is used to ensure that the measured resistivity range covers high formation resistivity. By determining the appropriate measurement frequency, source distance, and coil distance, the phase difference and amplitude ratio curves can be kept monotonously changing, so as to ensure that the formation resistivity obtained by the inversion method in subsequent studies is a single value.

S6. Simulation and analysis of wellbore influencing factors such as mud resistivity, borehole diameter, eccentricity, and relative permittivity.

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

S7. Describe in detail the changing law of the response results of different influencing factors in the high resistivity formation;

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

S8. Combine the data obtained from the simulation results and establish a borehole correction database to form a borehole correction method for electromagnetic wave logging in high-resistivity formations.

For parameters such as mud resistivity Rm, borehole diameter a, eccentricity Ecc, and relative permittivity ε _r in the wellbore model, respectively calculate their influence degree and logging response results, and use the method of calibration chart to establish the well Eye Correction Database.

In the step s2, the pseudo-analytic solution of the columnar layer medium of the magnetic dipole source is specifically:

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

For a magnetic dipole located at (ρ _T ,0,0), its field in the medium can be expanded as:

Step s22, first derive the expression of the reflection/transmission coefficient in the narrow sense by matching the boundary conditions, namely:

In formula (2), Indicates the narrow reflection coefficient between two layers, /> Indicates the narrow-sense transmission coefficient between two layers.

After expanding and discussing the reflection/transmission coefficient in the narrow sense, the expressions of the standing wave and outward wave in the columnar layered medium after solving the generalized reflection/transmission coefficient are obtained, namely:

In step s6, the simulation and analysis methods of influencing factors are as follows:

Step s61, based on the sensitivity of the instrument response to each parameter and the geological structure information given in step s1, respectively determine the number of initial values of each parameter to be inverted; the selection method of the initial value of each parameter to be inverted, refer to step s6 .2-s6.6.

Step s62, since formation resistivity and mud resistivity both belong to the resistivity parameter, it is necessary to consider whether there is an interaction result, so the anisotropy of the formation is also considered, and the resistivity anisotropy coefficient is set to λ=3, in σ _h is the lateral conductivity of the formation, and σ _v is the vertical conductivity of the formation.

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

Step s64, consider the situation that the principal components Ra,xx and Ra,yy are also affected by the lateral resistivity of the formation and the anisotropy coefficient of the formation, but the principal component Ra,zz is not affected by the anisotropy of the formation.

Step s65, combining the data obtained from the simulation results and establishing a borehole correction database to form a borehole correction method for electromagnetic wave logging in high-resistivity formations.

Step s66, free combination of the initial values selected in steps s62-s65.

As shown in Fig. 2 and Fig. 3, the result calculated by the pseudo-analytical solution method is compared with the result calculated by the finite element numerical algorithm, as can be seen from the figure, the matching effect of the curve and the scatter point is good to verify the effectiveness of the method of the present invention .

In Fig. 4 and Fig. 5, -·- shows the case of mud resistivity 1Ω·m. As the eccentricity increases, the negative response value of Razz becomes smaller and smaller. It can be seen that it is affected at low mud resistivity Very big. Comparing -·- and the black solid line in Figure 5, the resistivity of the high-resistance mud has little effect on the apparent resistivity, and the apparent resistivity value of the far coil almost approaches a straight line when the eccentricity changes, indicating that the result is influenced by the eccentricity. The influence of the rate is small, and the result can be closer to the real formation resistivity.

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

In Fig. 8, before wellbore correction (-line in the figure), with the increase of formation resistivity, the value of apparent resistivity becomes smaller and smaller than the value of formation resistivity, that is, away from the 45° inspection line. After correction (-·-·line in the figure), when the formation resistivity is less than 1000Ω·m, the corrected result is slightly larger than the 45° inspection line; when the formation resistivity is 1000Ω·m-4000Ω·m, the correction The result after the correction basically coincides with the value of the formation resistivity; when the formation resistivity is greater than 4000Ω·m, the corrected result has a slight error with the 45° line, but the error is less than 1%, and the correction effect can be considered to be good.

Of course, the above descriptions are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments. It should be noted that all equivalent substitutions made by any person skilled in the art under the teaching of this specification , obvious deformation forms, all fall within the essential scope of this specification, and should be protected by the present invention.

Claims (4)

1. The high-resistivity formation borehole correction method based on high-frequency electromagnetic wave resistivity logging, is characterized in that, comprises the following steps: s1. Establish an electromagnetic wave resistivity logging method for high-resistivity formations; s2. Develop a pseudo-analytic fast algorithm for the magnetic dipole source electromagnetic field based on different wellbore-containing columnar layered formation models in high-resistivity formations; s3. Simulate and analyze the problem of abnormal formation resistivity due to the existence of boreholes; s4. Selection of different wellbore factor parameters under high-resistivity formation conditions, and determine the data range contained in the wellbore calibration database; s5. Carry out forward modeling and analysis on mud resistivity, borehole diameter, eccentricity, relative permittivity and borehole influence factors; s6. Describe in detail the changing law of the response results of different influencing factors in high-resistivity formations; s7. Combine the data obtained from the simulation results and establish a borehole correction database to form a borehole correction method for high-resistivity formations 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, based on different wellbore columnar layered formation models in the high-resistivity formation The steps of developing a pseudo-analytic fast algorithm for magnetic dipole source electromagnetic field are as follows: Step s21, fast calculation method of pseudo-analytical solution of electromagnetic field For a magnetic dipole located at (ρ _T ,0,0), the field in the medium expands in cylindrical coordinates with the z-component field as: Step s22, deriving the expression of the reflection/transmission coefficient in the narrow sense by matching the boundary conditions, namely: In formula (2), Indicates the narrow reflection coefficient between two layers, /> Indicates the narrow-sense transmission coefficient between two layers; After expanding and discussing the reflection/transmission coefficient in the narrow sense, the expressions of the standing wave and outward wave in the columnar layered medium after solving the generalized reflection/transmission coefficient are obtained, namely: 3. The high-resistivity formation borehole calibration method based on high-frequency electromagnetic wave resistivity logging according to claim 1, characterized in that, in the step s5, the selection of wellbore influencing factor parameters under high-resistivity formation conditions is specifically : Wellbore mud conductivity R _m , borehole diameter a, tool eccentricity E _cc and relative permittivity ε _r , (1) The range of wellbore mud resistivity is from fresh water mud to completely non-conductive pure oil mud, that is, R _m = 1Ω·m-100000Ω·m; (2) The value range of borehole diameter is a=0.05m-0.22m; (3) The choice of eccentricity is E _cc =0-0.8, where E _cc =ρ _Ecc / a, ρ _Ecc is the eccentric distance; (4) The value range of the relative permittivity 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, is characterized in that, in described step s7, the step of setting up 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 phase difference, amplitude ratio and formation resistivity in the homogeneous formation medium, the response result obtained by actual measurement is converted into apparent resistivity.