Oil-based mud micro-resistivity scanning imaging logging multi-parameter calculation method

Abstract

A kind of oil-based mud microresistivity scanning imaging logging multi-parameter calculation method, adopts the design mode of recessed electrode and button electrode combination, and sets recessed area on the surface of recessed electrode, does not limit the size of surface area of recessed electrode, in actual logging process, based on the acquisition data of recessed electrode and double-frequency measurement, realize the simultaneous calculation of five parameters of downhole formation resistivity, formation dielectric constant, mud cake thickness, mud resistivity and mud dielectric constant, the calculation method is simple, without complicated inversion calculation, and the capacitive coupling effect in high-resistance formation is considered, can be applied to low-resistance to high-resistance formation, expand the range of applicable downhole formation imaging conditions, can accurately serve for oil and gas logging exploration.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geophysical well logging technology, and particularly relates to a micro-resistivity scanning imaging logging method for oil-based mud, which is mainly based on a recessed electrode and a double-frequency measurement method to measure five parameters in a well, i.e., formation resistivity, formation dielectric constant, mud cake thickness, mud resistivity and mud dielectric constant, and the capacitive coupling effect in a high-resistivity formation is considered, and the formation resistivity can be calculated from low resistivity to high resistivity. BACKGROUND

[0002] Well logging, also known as geophysical well logging, is an important branch of applied geophysics, which uses physical parameters such as electrochemistry, electromagnetism, density, emission, etc. to study the properties of underground rocks and fluids to find oil and gas resources and other mineral resources, and has been widely applied in many fields such as oil and gas resources, metal mines, coal mines and hydrogeology.

[0003] In oil drilling, well logging must be performed when drilling to a certain formation depth, and the resistivity, conductivity, density, emission, etc. of the formation within a certain distance from the wellbore are measured by using logging instruments to determine important parameters such as formation porosity, oil and gas saturation, permeability, effective thickness, etc. This stage is commonly known as open hole logging. After the casing is run into the wellbore, the second logging is performed, and important parameters such as formation fluid flow rate, density, water holdup, temperature and pressure are measured by using testing instruments to monitor the fluid level of production wells or injection wells, which is commonly known as production logging or development logging.

[0004] Logging instruments refer to measuring devices and technologies used in oil exploration and development to detect various physical parameters in the underground environment in the wellbore, such as resistivity, density, natural potential, emission, temperature and pressure, etc. These physical data are processed to determine the performance parameters related to exploration and production.

[0005] In logging instruments, the micro-resistivity scanning imaging logging instrument uses a button electrode array on a plate to emit a current of a certain frequency to the formation. Due to the heterogeneity of the formation, the rock composition, structure and contained fluid contacted by the electrode are different, causing changes in the current in the formation. The changes in the current reflect the changes in the rock resistivity of the wellbore, and different resistivity values can be obtained by different color calibration, and the micro-resistivity imaging of the formation around the wellbore can be obtained, which provides rich geological information for logging interpretation.

[0006] During logging, mud is contained in the wellbore to play the role of lubrication, transmission, and keeping the pressure in the well stable. The mud often used is low-resistivity water-based mud, which is the earliest and most widely used. Another kind of mud is a dispersed system formed by taking oil (diesel oil or mineral oil) as the continuous phase, water or lipophilic solid (organic soil, oxidized asphalt, etc.) as the dispersed phase, and adding an appropriate amount of treating agent, lime, and weighting material. The main advantages of oil-based mud are that it can resist high temperature, has strong inhibition and salt and calcium pollution resistance, good lubricity, and can effectively reduce damage to oil and gas layers.

[0007] The current frequency used by the conventional micro-resistivity scanning imaging logging instrument suitable for water-based mud is low, the mud cake attached to the well wall has small resistivity, and the change of the measurement current can reflect the change of the resistivity of the formation around the well. Since the oil phase is the continuous phase, the resistivity of the oil-based mud is very high. When the mud cake is attached to the well wall, the resistivity of the mud cake is very high, which masks the change of the resistivity of the formation (especially low-resistivity formation). The conventional micro-resistivity scanning imaging logging instrument suitable for water-based mud is no longer applicable in oil-based mud.

[0008] At present, in order to carry out the micro-resistivity scanning imaging logging work in oil-based mud, the measures taken include developing conductive oil-based mud, four-terminal measurement method, capacitive coupling method, geophysical inversion method, etc. The patent with application number 201910294886.8 discloses an oil-based mud electrical imaging logging method based on a recessed electrode structure, which adopts a single measurement frequency, but does not consider the coupling of formation resistivity and formation dielectric constant, is suitable for relatively low resistivity formation, and only measures the formation resistivity, so the measurement result is single and is not convenient for subsequent formation interpretation and analysis. The article with the title "Oil-based mud electrical imaging logging four-parameter calculation method based on a pair of recessed electrodes in low resistivity formation" discloses an oil-based mud electrical imaging logging four-parameter calculation method based on a pair of recessed electrodes, which adopts a single frequency and obtains four parameters such as mud resistivity, mud dielectric constant, mud cake thickness and formation resistivity, thereby enriching the measurement data. However, this method also does not consider the coupling of formation resistivity and formation dielectric constant, and is only suitable for low resistivity formation, like the patent with application number 201910294886.8. The patent with application number 202011019657.4 is based on the patent with application number 201910294886.8 and identifies and judges wellbore cracks and holes, but also does not consider the coupling of formation resistivity and formation dielectric constant, and is only suitable for low resistivity formation. The patent with application number 201910124532.9 discloses a multi-frequency correction method based on oil-based mud environment micro-resistivity scanning imaging. This method is also used to obtain the formation resistivity in low resistivity formation, and needs a complex iterative calculation process. Through the above analysis, the existing methods have the disadvantages of high development cost, complicated data processing process, limited applicable formation conditions, inability to effectively separate mud cake / mud signal and formation signal, and influence of formation capacitive coupling effect. SUMMARY

[0009] In order to overcome the defects of the prior art, the purpose of the present application is to provide an oil-based mud micro-resistivity scanning imaging logging multi-parameter calculation method, which is based on the collected data of recessed electrodes and double-frequency measurement, realizes the simultaneous calculation of five parameters of downhole formation resistivity, formation dielectric constant, mud cake thickness, mud resistivity and mud dielectric constant, has a simple calculation method without complicated inversion calculation, considers the capacitive coupling effect in high resistivity formation, can be applied to low resistivity to high resistivity formation, expands the range of applicable downhole formation imaging conditions, and can accurately serve oil and gas logging exploration.

[0010] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0011] An oil-based mud micro-resistivity scanning imaging logging multi-parameter calculation method, comprising the following steps:

[0012] (1): The logging instrument 4 pushes the imaging pad 10 against the support arm 9, so that the imaging pad 10 is in close contact with the well wall of the wellbore 1;

[0013] The imaging pad 10 is a metal plate with surface inlaid insulation material, and two rows of recessed electrodes 11 and button electrodes 12 are distributed side by side at the middle position of the imaging pad 10, wherein a recessed area 13 exists between the surface of the recessed electrode 11 and the surface of the imaging pad 10, the surface of the button electrode 12 is consistent with the surface of the pad 10, and the length difference of the recessed area 13 is Δd; in order to facilitate the flow of oil-based mud in the recessed area 13, the surface area of the recessed electrode 11 is greater than that of the button electrode 12, and the number of the recessed electrode 11 is less than that of the button electrode 12;

[0014] A rectangular ring-shaped shielding electrode 14 is distributed around the array of the recessed electrode 11 and the button electrode 12, and A insulation material 15 exists between the recessed electrode 11 and the button electrode 12; the shielding electrode 14 and the imaging pad 10 are insulated from each other by B insulation material 16, and a pair of current return electrodes 17 are symmetrically distributed at both ends of the imaging pad 10, and the return electrode 17 and the main body of the imaging pad 10 are insulated from each other by C insulation material 18;

[0015] (2): The mud cake 3 with a thickness of d exists between the imaging pad 10 and the formation 2, the distance between the recessed electrode 11 and the well wall is d1, the distance between the button electrode 12 and the well wall is the thickness d of the mud cake, the thickness of the mud cake 3 opposite to the recessed electrode 11 and the button electrode 12 is the same, and d1-d=Δd is satisfied; the recessed electrode 11, the button electrode 12 and the shielding electrode 14 all emit current with two different frequencies at the same voltage U, and the two different frequencies are f1 and f2, and f1<f2; the current emitted by the recessed electrode 11 and the button electrode 12 is called measurement current 19, and the current emitted by the shielding electrode 14 is called shielding current 20; the measurement current 19 and the shielding current 20 pass through the mud cake 3 into the formation 2, and then pass through the mud cake 3 again to return to the return electrode 17;

[0016] (3): Calculating formation parameters according to the measurement data of the button electrode 12, specifically including:

[0017] Sub-step 3.1: Measuring the current of the button electrode 12 at frequencies f1 and f2 as I1 and I2 respectively, obtaining the measurement impedance according to the applied voltage U, and expressing the measurement impedance at the two frequencies based on the equivalent circuit model as

[0018]

[0019]

[0020] In formula (1) and (2), Z u1, Z u2 represents the measured impedance of the button electrode 12 under the condition of frequency f1, f2, r mu , C mu are the equivalent resistance and equivalent capacitance of the mud cake adjacent to the button electrode 12, respectively, r fu , C fu are the equivalent resistance and equivalent capacitance of the formation near the button electrode 12; Z mu , Z fu is the equivalent impedance of the mud cake and the equivalent impedance of the formation measured by the button electrode 12. j is the imaginary unit, and ω1, ω2 are the angular frequencies corresponding to the frequencies f1, f2, respectively, satisfying ω1 = 2πf1, ω2 = 2πf2.A u1 , B u1 are the real part and the imaginary part of the measured impedance of the button electrode 12 under the condition of frequency f1, respectively; A u2 , B u2 are the real part and the imaginary part of the measured impedance of the button electrode 12 under the condition of frequency f2, respectively;

[0021] Sub-step 3.2: in formula (1), (2), A u1 , B u1 , A u2 , B u2 are the data measured by the button electrode 12 on the imaging electrode plate under two frequencies f1, f2, which are known values; r mu , C mu , r fu , C fu , the parameter is introduced, where ε0 is the vacuum dielectric constant, and its value is approximately 8.854 × 10 -12 F / m, and formula (1), (2) are further rewritten as:

[0022]

[0023]

[0024]

[0025]

[0026] Sub-step 3.3: formula (3) ~ (6) are further arranged by using mathematical elimination method to obtain:

[0027]

[0028]

[0029] Formula (7), (8) constitute the parameters α mru , αfru The equation group is used to determine the size of mud and formation parameters according to the measured current I1, I2 and the change of the real part or imaginary part of the measured impedance under the condition of frequencies f1, f2. The matrix M shown in equation (9) is introduced, and the calculation flow scheme of the mud cake equivalent resistance, equivalent capacitance and the formation equivalent resistance, equivalent capacitance is formulated.

[0030]

[0031] The calculation flow scheme is specifically described as follows:

[0032] (a) The measured data of the button electrode 12 at two frequencies, including voltage, current, impedance, are prepared;

[0033] (b) According to the measured data of the button electrode 12, |det(M)| and The error limit parameters eps1, eps2 are set, and the condition shown in equation (10) is judged:

[0034]

[0035] If the condition shown in equation (10) is met, the mud cake equivalent resistance r mu and the equivalent capacitance C mu , the formation equivalent resistance r fu and the equivalent capacitance C fu are calculated according to the equation shown in equation (11), that is

[0036]

[0037] Otherwise, the value of α mru α fru , α mru + α fru is calculated according to the equation shown in equation (12), that is

[0038]

[0039] (c) After the value of α mru α fru , α mru + α fru is calculated, the value of and |I1| is calculated, where Re(I1), Re(I2) are respectively the real part of the measured current I1, I2 of the button electrode 12 under the condition of frequencies f1, f2, the error limit eps3 and the current limit I lim are set, and the condition shown in equation (13) is judged, that is

[0040]

[0041] If the condition shown in formula (13) is not met, the formation measured by the button electrode 12 is considered to be a low-resistance formation, and α is calculated according to the equation shown in formula (14): mru , α fru The value of

[0042]

[0043] Otherwise, the formation measured by the button electrode 12 is a high-resistance formation, and α is calculated according to the equation shown in formula (15): mru , α fru The value of

[0044]

[0045] (d) Calculate α mru , α fru After the value of the mud cake is calculated according to the equation shown in formula (16), the equivalent resistance r mu and equivalent capacitance C mu , equivalent formation resistance r fu and equivalent capacitance C fu ,Right now

[0046]

[0047] In the equation shown in formula (16), A u , B u are the real and imaginary parts of the measured impedance of the button electrode 12 corresponding to the angular frequency ω;

[0048] (e) Arrange data for subsequent parameter calculation;

[0049] (4): Under the conditions of two frequencies f1 and f2, the mud cake equivalent resistance r of the recessed electrode 11 is calculated by imitating the processing process of the measurement data of the button electrode 12 in step 3 using the measurement data of the recessed electrode 11. md , Mud cake equivalent capacitance C md , equivalent formation resistance r fd , formation equivalent capacitance C fd ;

[0050] At this point, under the two frequencies f1 and f2, the measurement data of the depression electrode 11 and the button electrode 12 were obtained, and the mud cake equivalent resistance and equivalent capacitance, formation equivalent resistance and equivalent capacitance of each were obtained, a total of 8 parameters;

[0051] (5): Combining the eight parameters obtained based on the measurement data of the depression electrode 11 and the button electrode 12, the five parameters of oil-based mud resistivity, oil-based mud dielectric constant (relative), mud cake thickness, formation resistivity and formation dielectric constant (relative) are solved. The specific description is:

[0052] 5.1, based on the foregoing process, the equivalent resistance and equivalent capacitance of the mud cake corresponding to the recessed electrode 11 and the button electrode 12 under the conditions of frequencies f1, f2, and the equivalent resistance and equivalent capacitance of the formation, that is,

[0053]

[0054] 5.2, the shape of the mud cake 3 between the recessed electrode 11 and the button electrode 12 and the formation 2 is equivalent to a small cylinder, and according to the resistance and capacitance calculation formula of the cylindrical medium, the equation shown in formula (18) can be obtained, that is,

[0055]

[0056] In the equation shown in formula (18), R m is the oil-based mud resistivity, ε mr is the mud dielectric constant, S d is the surface area of the recessed electrode 11, S u is the surface area of the button electrode 12, and θ is a proportional coefficient, which satisfies

[0057] 5.3, according to the equation shown in formula (18), the calculation results of the oil-based mud resistivity, the oil-based mud dielectric constant and the mud cake thickness are obtained, which are respectively denoted as R m * , ε mr * , d * , that is,

[0058]

[0059] In formula (19), δ1 and δ2 are proportional factors, which are used to adjust the proportion of the mud cake thickness value calculated according to the equivalent resistance and equivalent capacitance of the mud cake, and the two factors satisfy the relationship δ1+δ2=1;

[0060] 5.4, based on the equivalent resistance and equivalent capacitance of the formation of the recessed electrode 11 and the button electrode 12 shown in formula (17), the corresponding electrode coefficients K u , K d are introduced, and the calculation results of the formation resistivity and the formation dielectric constant can be obtained, which are respectively denoted as R t * , ε fr * , that is,

[0061]

[0062] In formula (20), δ3, δ4 are proportional factors of the calculation results of formation resistivity, respectively used for adjusting the proportion of the formation resistivity calculated according to the formation equivalent resistance of the recessed electrode 11 and the formation equivalent resistance of the button electrode 12, and the two factors satisfy but are not limited to the relationship δ3+δ4=1. δ5, δ6 are proportional factors of the calculation results of formation dielectric constant, respectively used for adjusting the proportion of the formation dielectric constant calculated according to the formation equivalent capacitance of the recessed electrode 11 and the formation equivalent capacitance of the button electrode 12, and the two factors satisfy but are not limited to the relationship δ5+δ6=1.

[0063] Advantages of the present application:

[0064] 1. Five parameters of oil-based mud resistivity, oil-based mud dielectric constant, mud cake thickness, formation resistivity and formation dielectric constant in low-resistance formation or high-resistance formation can be obtained simultaneously. The calculation process is simple, and there is a clear analytical expression for the calculation process of each parameter, without complex calculation process such as inversion iteration, and the calculation result can be directly used for formation imaging and evaluation.

[0065] 2. The recessed electrode and the button electrode are combined in the design, and the recessed area is arranged on the surface of the recessed electrode, without limiting the size of the surface area of the recessed electrode. In the actual logging process, this setting method is beneficial to the flow of oil-based mud on the surface of the electrode plate, the recessed electrode and the button electrode, so that the measurement data is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 It is the overall schematic diagram of the working implementation of the micro-resistivity scanning imaging logging in the present embodiment.

[0067] Figure 2 It is the combined schematic diagram of the front view and side view of the electrode plate of the oil-based micro-resistivity scanning logging instrument.

[0068] Figure 3 It is the schematic diagram of the change of the recessed electrode of the electrode plate of the oil-based micro-resistivity scanning logging instrument.

[0069] Figure 4 It is the schematic diagram of the working principle of the oil-based micro-resistivity scanning imaging logging instrument.

[0070] Figure 5 It is the equivalent circuit diagram of the oil-based micro-resistivity scanning imaging logging instrument.

[0071] Figure 6 It is the calculation process of the mud cake equivalent resistance, equivalent capacitance and formation equivalent resistance, equivalent capacitance.

[0072] Figure 7 It is the mud and formation multi-parameter calculation process.

[0073] Figure 8This is the result of five-parameter imaging of the low-resistivity inclined layer.

[0074] Figure 9 This is the result of five-parameter imaging of the high-resistance inclined layer. DETAILED DESCRIPTION

[0075] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0076] A multi-parameter calculation method for oil-based mud microresistivity scanning imaging logging includes the following steps:

[0077] (1): The present invention is actually used in well logging situations, such as Figure 1 shown. Figure 1 In the figure, a wellbore 1 passes through a formation 2 filled with oil-based mud. The formation 2 contains multiple layers of different reservoir types. Due to the pressure differential between the wellbore and the formation, a mud cake 3 of uneven thickness adheres to the wall of the wellbore 1. A logging instrument 4, in this case a microresistivity scanning imaging logging instrument, is suspended in the wellbore 1. The logging instrument 4 is connected to a derrick 6 on the surface via an armored cable 5. The other end of the armored cable 5 is connected to a winch 8 on a logging vehicle 7. The logging vehicle 7 is equipped with a conventional microcomputer control system to control the movement of the downhole logging instrument 4. The logging instrument 4 is connected to an imaging plate 10 via a support arm 9. During operation, the logging instrument 4 uses the support arm 9 to push against the imaging plate 10, ensuring close contact between the imaging plate 10 and the wall of the wellbore 1.

[0078] Figure 2 A schematic diagram of the front and side views of the imaging plate 10 is provided. The imaging plate 10 is a metal plate with an insulating material embedded in its surface. Two rows of recessed electrodes 11 and button electrodes 12, each numbering in number, are arranged side by side in the center of the imaging plate 10. A recessed region 13 exists between the surface of the recessed electrodes 11 and the surface of the imaging plate 10. The surface of the button electrodes 12 coincides with the surface of the plate 10, with a length difference of Δd between the recessed region 13 and the surface of the button electrodes 12. To facilitate the flow of oil-based mud in the recessed region 13, the surface area of ​​the recessed electrodes 11 is larger than that of the button electrodes 12. Figure 3 shown. Figure 3 The number of recessed electrodes 11 is smaller than the number of button electrodes 12. As shown in the first row of figures, there is one recessed electrode 11, which is a long strip-shaped electrode with a length equal to the length of the array of electrodes 12. However, the surface area of ​​recessed electrode 11 is larger than that of electrode 12. Moreover, the positions of recessed electrodes 11 and electrodes 12 on the electrode plate can be interchanged.

[0079] The rectangular ring-shaped shielding electrode 14 is distributed around the recessed electrode 11 and the array of button electrodes 12, and A insulating material 15 is present between the recessed electrode 11 and the button electrodes 12; the shielding electrode 14 and the imaging pole plate 10 are mutually insulated by B insulating material 16, and a pair of current return electrodes 17 are symmetrically distributed at both ends of the imaging pole plate 10, and the return electrodes 17 and the main body of the imaging pole plate 10 are mutually insulated by C insulating material 18.

[0080] (2) As shown in Figure 4 , the imaging pole plate 10 and the formation 2 contain a mud cake 3 with a thickness of d, the distance between the recessed electrode 11 and the well wall is d1, the distance between the button electrode 12 and the well wall is the thickness of the mud cake d, the thickness of the mud cake 3 opposite the recessed electrode 11 and the button electrode 12 is the same, and satisfies d1-d=Δd; the recessed electrode 11, the button electrode 12 and the shielding electrode 14 all emit current at the same voltage U, and the two different frequencies are f1 and f2, and f1<f2; the current emitted by the recessed electrode 11 and the button electrode 12 is called the measurement current 19, and the current emitted by the shielding electrode 14 is called the shielding current 20; the measurement current 19 and the shielding current 20 pass through the mud cake 3 into the formation 2, and then pass through the mud cake 3 again and return to the return electrode 17.

[0081] (3) Calculate the formation parameters according to the measurement data of the button electrode 12, which specifically includes:

[0082] Sub-step 3.1: Measure the current of the button electrode 12 at frequencies f1 and f2 as I1 and I2, respectively, and obtain the measurement impedance according to the applied voltage U, and express the measurement impedance at the two frequencies as Figure 5 based on the equivalent circuit model shown in

[0083]

[0084]

[0085] In formulas (1), (2) and Figure 5 , Z u1 , Z u2 represent the measurement impedance of the button electrode 12 at frequencies f1 and f2, r mu , C mu are the equivalent resistance and equivalent capacitance of the mud cake adjacent to the button electrode 12, r fu , C fu are the equivalent resistance and equivalent capacitance of the formation near the button electrode 12; Z mu , Z fuis the measured cake equivalent impedance and formation equivalent impedance by the button electrode 12. j is the imaginary unit, ω1, ω2 are the angular frequencies corresponding to the frequencies f1, f2, respectively, satisfying ω1 = 2πf1, ω2 = 2πf2. A u1 , B u1 are the measured impedance real part and imaginary part of the button electrode 12 at the frequency f1, respectively;A u2 , B u2 are the measured impedance real part and imaginary part of the button electrode 12 at the frequency f2, respectively;

[0086] Sub-step 3.2: in formula (1), (2), A u1 , B u1 , A u2 , B u2 is the data measured by the button electrode 12 on the imaging electrode plate at two frequencies f1, f2, which is a known value; r mu , C mu , r fu , C fu , so as to facilitate the acquisition of mud and formation parameter information. For this purpose, the parameter is introduced, where ε0 is the vacuum permittivity, and its value is approximately 8.854 × 10 -12 F / m, formula (1), (2) is further rewritten as:

[0087]

[0088]

[0089]

[0090]

[0091] Sub-step 3.3: formula (3) ~ (6) are further arranged by using mathematical elimination method to obtain:

[0092]

[0093]

[0094] Formula (7), (8) constitute an equation group about parameters α mru , α fru , the size of mud and formation parameters is determined according to the measured current I1, I2 and the change of the measured impedance real part or imaginary part under the condition of frequencies f1, f2, the matrix M shown in formula (9) is introduced, and the calculation flow scheme of cake equivalent resistance, equivalent capacitance and formation equivalent resistance, equivalent capacitance shown in formula (10) is formulated: Figure 6

[0095] ​

[0096] Figure 6 The calculation flow scheme is described in detail as follows:

[0097] (a) Prepare the measurement data of the button electrode 12 at two frequencies, including voltage, current, impedance;

[0098] (b) According to the measurement data of the button electrode 12, calculate |det(M)| and Set error limit parameters eps1, eps2, and judge according to the condition shown in equation (10):

[0099]

[0100] If the condition shown in equation (10) is met, calculate the mud cake equivalent resistance r mu and the equivalent capacitance C mu , the formation equivalent resistance r fu and the equivalent capacitance C fu , that is

[0101]

[0102] Otherwise, calculate the value of α mru α fru , α mru + α fru according to equation (12), that is

[0103]

[0104] (c) After calculating the value of α mru α fru , α mru + α fru , calculate the value of and |I1|, where Re(I1), Re(I2) are the real parts of the measured currents I1, I2 of the button electrode 12 at frequencies f1, f2, respectively, and set error limit eps3 and current limit I lim , judge according to the condition shown in equation (13), that is

[0105]

[0106] If the condition shown in equation (13) is not met, it is considered that the formation measured by the button electrode 12 is a low resistance formation, and the value of α mru , α fru is calculated according to equation (14), that is

[0107]

[0108] Otherwise, the formation measured by the button electrode 12 is a high-resistance formation, and the value of a is calculated according to the equation shown in equation (15) mru , the value of a fru

[0109]

[0110] (d) After the value of a mru , the value of a fru is calculated, the mud cake equivalent resistance r mu and the equivalent capacitance C mu are calculated according to the equation shown in equation (16) fu , the formation equivalent resistance r fu and the equivalent capacitance C u u

[0111]

[0112] In the equation shown in equation (16), A md , B md are the real part and the imaginary part of the measured impedance of the button electrode 12 corresponding to the angular frequency ω;

[0113] (e) The data is sorted for subsequent parameter calculation.

[0114] (4) Under the condition of two frequencies f1, f2, the measured data of the recessed electrode 11 is used to calculate the mud cake equivalent resistance r fd , the mud cake equivalent capacitance C fd , the formation equivalent resistance r md , and the formation equivalent capacitance C md of the recessed electrode 11 by imitating the process of handling the measured data of the button electrode 12 in step 3.

[0115] At this point, under the condition of two frequencies f1, f2, the measured data of the recessed electrode 11 and the button electrode 12 are obtained, and the mud cake equivalent resistance and the equivalent capacitance, the formation equivalent resistance and the equivalent capacitance of each are obtained, respectively, a total of 8 parameters.

[0116] (5) The 8 parameters obtained based on the measured data of the recessed electrode 11 and the button electrode 12 are combined to develop a scheme as shown in equation (17) to solve the oil-based mud resistivity, the oil-based mud dielectric constant (relative), the mud cake thickness, the formation resistivity, and the formation dielectric constant (relative) 5 parameters, which are specifically described as: Figure 7

[0117] 5.1, based on the foregoing process, the mud cake equivalent resistance and the equivalent capacitance corresponding to the recessed electrode 11 and the button electrode 12, the formation equivalent resistance and the equivalent capacitance under the condition of frequencies f1, f2 are prepared, that is

[0118]

[0119] 5.2, the shape of the mud cake 3 between the recessed electrode 11 and the button electrode 12 and the formation 2 is equivalent to a small cylinder, according to the resistance and capacitance calculation formula of the cylindrical medium, the equation shown in equation (18) can be obtained, that is

[0120]

[0121] In the equation shown in equation (18), R m is the oil-based mud resistivity, ε mr is the dielectric constant of the mud, S d is the surface area of the recessed electrode 11, S u is the surface area of the button electrode 12, and θ is a proportional coefficient, which satisfies

[0122] 5.3, according to the equation shown in equation (18), through mathematical derivation and calculation, the calculation results of the oil-based mud resistivity, the oil-based mud dielectric constant and the mud cake thickness are obtained, which are respectively denoted as R m * , ε mr * , d * , that is

[0123]

[0124] In equation (19), δ1 and δ2 are proportional factors, which are used to adjust the proportion of the mud cake thickness value calculated according to the equivalent resistance and equivalent capacitance of the mud cake. The two factors satisfy the relationship δ1+δ2=1.

[0125] 5.4, based on the formation equivalent resistance and equivalent capacitance of the recessed electrode 11 and the button electrode 12 shown in equation (17), the corresponding electrode coefficients K u , K d are introduced, so that the calculation results of the formation resistivity and the formation dielectric constant can be obtained, which are respectively denoted as R t * , ε fr * , that is:

[0126]

[0127] In formula (20), δ3 and δ4 are proportional factors of the calculation results of the formation resistivity, and are used for adjusting the proportion of the formation resistivity calculated according to the formation equivalent resistance of the recessed electrode 11 and the formation equivalent resistance of the button electrode 12, respectively, and the two factors satisfy but are not limited to the relationship δ3+δ4=1; δ5 and δ6 are proportional factors of the calculation results of the formation dielectric constant, and are used for adjusting the proportion of the formation dielectric constant calculated according to the formation equivalent capacitance of the recessed electrode 11 and the formation equivalent capacitance of the button electrode 12, respectively, and the two factors satisfy but are not limited to the relationship δ5+δ6=1.

[0128] The above is the measurement data of the recessed electrode 11 and the button electrode 12, and based on the equivalent circuit model, the oil-based mud resistivity, the oil-based mud dielectric constant, the mud cake thickness, the formation resistivity and the formation dielectric constant of five parameters in the low-resistance formation or the high-resistance formation can be obtained simultaneously through reasonable assumptions and mathematical calculations. The calculation process is simple, and each parameter has a clear analytical expression, without complex calculation process such as inversion iteration. The above calculation results can be used for formation imaging and evaluation.

[0129] Verification Case 1:

[0130] In order to verify and illustrate the main content of the present application, Figure 8 An example in the specific embodiment of the present application is given. The oil-based micro-resistivity scanning imaging logging instrument contains six electrode plates (which can also be set to other numbers), the formation model is a low-resistance inclined formation, and the step-shaped mud cake thickness setting mode is adopted. Using the measurement data of the recessed electrode and the button electrode, combined with the multi-parameter calculation method of the micro-resistivity scanning imaging logging instrument proposed in the present application, the calculation results of the mud resistivity, the mud dielectric constant, the mud cake thickness, the formation resistivity and the formation dielectric constant are obtained, so that imaging can be performed. Figure 8 In the figure, from left to right are depth channel, oil-based mud resistivity imaging, oil-based mud dielectric constant imaging, mud cake thickness imaging, formation resistivity imaging and formation dielectric constant imaging, dark color corresponds to low value, and bright color corresponds to high value. It can be seen that the formation resistivity image can clearly show the formation inclination and resistivity change. Similarly, the formation dielectric constant image can also clearly show the formation inclination and dielectric constant change. The mud cake thickness image can clearly show the step-shaped mud cake thickness change, and the formation interface inclination feature can also be shown in the image. Combined with the mud cake thickness image, the change of the oil-based mud resistivity and the oil-based mud dielectric constant can also be judged. It can be seen from the figure that the light and dark change trend of the oil-based mud resistivity image is consistent with that of the mud cake thickness image, and the light and dark change trend of the oil-based mud dielectric constant image is opposite to that of the mud cake thickness image, and combined with the three images, the change of the oil-based mud parameters can be analyzed.

[0131] Verification Case 2:

[0132] Figure 9 A second case of the embodiment of the present application is given. The formation model is a high-resistivity inclined formation, and the setting mode of the step change in mud cake thickness is also used. By using the measurement data of the recessed electrode and the button electrode, and combining the multi-parameter calculation method of the micro-resistivity scanning imaging logging proposed by the present application, the calculation results of the mud resistivity, the mud dielectric constant, the mud cake thickness, the formation resistivity and the formation dielectric constant are obtained, so that the imaging can be performed. The settings of each track in the figure are consistent with those in case 1. Figure 8 It can be seen that even in the high-resistivity formation, the imaging results can reflect the changes of the formation resistivity and the dielectric constant. Similarly, the mud cake thickness imaging reflects the step change in the mud cake thickness and can reflect the inclined characteristics of the formation interface. By comparing the oil-based mud resistivity image, the oil-based mud dielectric constant image and the mud cake thickness image, the changes of the oil-based mud parameters can also be analyzed.

[0133] In summary, the multi-parameter calculation method of the oil-based micro-resistivity scanning imaging logging based on the dual-frequency recessed electrode of the present application uses the dual-frequency measurement and the recessed electrode structure to realize the simultaneous calculation of the five parameters of the oil-based mud resistivity, the oil-based mud dielectric constant, the mud cake thickness, the formation resistivity and the formation dielectric constant. The calculation method is simple and does not require complicated inversion calculation. It can be applied to low-resistivity to high-resistivity formations, expands the range of applicable downhole conditions, and can accurately serve the oil and gas logging exploration.

Claims

1. A multi-parameter calculation method for oil-based mud microresistivity scanning imaging logging based on dual-frequency depression electrodes, characterized in that: The following steps are involved: Step 1: The logging instrument (4) uses the support arm (9) to push the imaging plate (10) so that the imaging plate (10) is in close contact with the wall of the wellbore (1); The imaging electrode plate (10) is a metal plate with an insulating material embedded on its surface. Two rows of recessed electrodes (11) and button electrodes (12) of unlimited number are arranged side by side in the middle of the imaging electrode plate (10). A recessed area (13) exists between the surface of the recessed electrode (11) and the surface of the imaging electrode plate (10). The surface of the button electrode (12) matches the surface of the imaging electrode plate (10). The length difference of the recessed area (13) is Δd. A rectangular ring-shaped shielding electrode (14) is distributed around the recessed electrode (11) and the button electrode (12) array, and an A insulating material (15) is present between the recessed electrode (11) and the button electrode (12); the shielding electrode (14) and the imaging plate (10) are insulated from each other by a B insulating material (16); a pair of current return electrodes (17) are symmetrically distributed at both ends of the imaging plate (10), and the return electrodes (17) and the main body of the imaging plate (10) are insulated from each other by a C insulating material (18); Step 2: A mud cake (3) with a thickness of d is contained between the imaging electrode (10) and the formation (2); the distance between the recessed electrode (11) and the well wall is d1; the distance between the button electrode (12) and the well wall is the mud cake thickness d; the thickness of the mud cake (3) facing the recessed electrode (11) and the button electrode (12) is the same, and satisfies d1-d=Δd; the recessed electrode (11), the button electrode (12) and the shielding electrode (14) all emit two currents of different frequencies at the same voltage U, the two different frequencies are f1 and f2, and f1<f2; the current emitted by the recessed electrode (11) and the button electrode (12) is called the measuring current (19), and the current emitted by the shielding electrode (14) is called the shielding current (20); the measuring current (19) and the shielding current (20) pass through the mud cake (3) into the formation (2), and then pass through the mud cake (3) and flow back to the return electrode (17); Step 3: Calculate formation parameters based on the button electrode (12) measurement data, specifically including: Sub-step 3.1: Measure the currents of the button electrode (12) at frequencies f1 and f2 as I1 and I2 respectively. According to the applied voltage U, the measured impedance is obtained. Based on the equivalent circuit model, the measured impedance at the two frequencies is expressed as In formula (1) and (2), Z u1 , Z u2 represents the measured impedance of the button electrode (12) at frequencies f1 and f2, r mu 、C mu are the mud cake equivalent resistance and mud cake equivalent capacitance of the mud cake adjacent to the button electrode (12), r fu 、C fu are the formation equivalent resistance and formation equivalent capacitance of the formation near the button electrode (12), respectively; j is an imaginary unit, ω1 and ω2 are the angular frequencies corresponding to the frequencies f1 and f2, respectively, satisfying ω1=2πf1, ω2=2πf2; A u1 、B u1 are respectively the real and imaginary parts of the measured impedance of the button electrode (12) at the frequency f1; A u2 、B u2 are respectively the real and imaginary parts of the measured impedance of the button electrode (12) at the frequency f2; Sub-step 3.2: In equations (1) and (2), A u1 、B u1 、A u2 、B u2 The data are measured by the button electrode (12) on the imaging plate at two frequencies f1 and f2, which are known values. The equations (1) and (2) are used to solve r mu 、C mu 、r fu 、C fu , introduce parameters Where ε0 is the dielectric constant of vacuum, and its value is approximately 8.854×10 -12 F / m, equations (1) and (2) are further rewritten as: Sub-step 3.3: Use mathematical elimination method to further sort out equations (3) to (6) to obtain: Equations (7) and (8) form the equations about parameter α mru , α fru The equation group is used to determine the size of the mud and formation parameters according to the changes of the measured currents I1, I2 and the real or imaginary part of the measured impedance under the conditions of frequencies f1 and f2. The matrix M shown in equation (9) is introduced to formulate the calculation process of the mud cake equivalent resistance, mud cake equivalent capacitance and formation equivalent resistance and formation equivalent capacitance: Step 4: Under the conditions of two frequencies f1 and f2, the mud cake equivalent resistance r of the concave electrode (11) is calculated by using the measurement data of the concave electrode (11) in the same way as the processing of the measurement data of the button electrode (12) in step (3). md , Mud cake equivalent capacitance C md , formation equivalent resistance r fd , formation equivalent capacitance C fd ; At this point, under the conditions of two frequencies f1 and f2, the measurement data of the recessed electrode (11) and the button electrode (12) are obtained, and the mud cake equivalent resistance and mud cake equivalent capacitance, the formation equivalent resistance and formation equivalent capacitance of each are obtained, a total of 8 parameters; Step 5: Combining the eight parameters obtained based on the measurement data of the depression electrode (11) and the button electrode (12), five parameters, namely, oil-based mud resistivity, oil-based mud dielectric constant, mud cake thickness, formation resistivity, and formation dielectric constant, are solved; The calculation process scheme for formulating the mud cake equivalent resistance, mud cake equivalent capacitance and formation equivalent resistance, formation equivalent capacitance is specifically described as follows: (a) preparing measurement data of the button electrode (12) at two frequencies, including voltage, current, and impedance; (b) Calculate |det(M)| and Set the error limit parameters eps1 and eps2, and make a judgment based on the conditions shown in formula (10): If the conditions shown in formula (10) are met, the equivalent resistance r of the mud cake can be calculated according to the equation shown in formula (11): mu And the mud cake equivalent capacitance C mu , formation equivalent resistance r fu and the formation equivalent capacitance C fu ,Right now Otherwise, calculate α according to the equation shown in formula (12) mru α fru , α mru +α fru The value of (c) Calculate α mru α fru , α mru +α fru After calculating the value of and |I1|, where Re(I1) and Re(I2) are the real parts of the measured currents I1 and I2 of the button electrode (12) under the conditions of frequencies f1 and f2, respectively. The error limit eps3 and the current limit I are set. lim , judge according to the conditions shown in formula (13), that is, If the condition shown in formula (13) is not met, the formation measured by the button electrode (12) is considered to be a low-resistance formation, and α is calculated according to the equation shown in formula (14): mru , α fru The value of Otherwise, the formation measured by the button electrode (12) is a high-resistance formation, and α is calculated according to the equation shown in formula (15): mru , α fru The value of (d) Calculate α mru , α fru After the value of the mud cake is calculated according to the equation shown in formula (16), the equivalent resistance r mu And the mud cake equivalent capacitance C mu , formation equivalent resistance r fu and the formation equivalent capacitance C fu ,Right now In the equation shown in formula (16), A u , B u are the real and imaginary parts of the measured impedance of the button electrode (12) corresponding to the angular frequency ω; (e) Organize the data for subsequent parameter calculation.

2. The multi-parameter calculation method for oil-based mud microresistivity scanning imaging logging based on dual-frequency depression electrode according to claim 1, characterized in that: The surface area of ​​the recessed electrode (11) is greater than the surface area of ​​the button electrode (12), and the number of the recessed electrodes (11) is less than the number of the button electrodes (12).

3. The multi-parameter calculation method for oil-based mud microresistivity scanning imaging logging based on dual-frequency depression electrode according to claim 1, characterized in that: The five parameters of oil-based mud resistivity, oil-based mud dielectric constant, mud cake thickness, formation resistivity and formation dielectric constant are specifically described as follows: 5.

1. Based on the above process, the mud cake equivalent resistance and mud cake equivalent capacitance, formation equivalent resistance and formation equivalent capacitance corresponding to the concave electrode (11) and the button electrode (12) under the conditions of frequencies f1 and f2 are prepared, that is, 5.

2. The shape of the mud cake (3) between the depression electrode (11), the button electrode (12) and the stratum (2) is equivalent to a small cylinder. According to the resistance and capacitance calculation formula of the cylindrical medium, the equation shown in equation (18) is obtained, that is, In the equation shown in formula (18), R m is the resistivity of oil-based mud, ε mr is the dielectric constant of mud, S d is the surface area of ​​the recessed electrode (11), S u is the surface area of ​​the button electrode (12), θ is the proportionality coefficient, and satisfies 5.

3. According to the equation shown in formula (18), the calculation results of oil-based mud resistivity, oil-based mud dielectric constant and mud cake thickness are obtained, which are denoted as R m * , ε mr * d * ,Right now In formula (19), δ1 and δ2 are the proportional factors of the mud cake thickness calculation results, which are used to adjust the proportion of the mud cake thickness values ​​calculated based on the mud cake equivalent resistance and mud cake equivalent capacitance. The proportional factors of the two mud cake thickness calculation results satisfy the relationship δ1+δ2=1; 5.

4. Based on the formation equivalent resistance and formation equivalent capacitance of the concave electrode (11) and the button electrode (12) shown in equation (17), the corresponding electrode coefficient K is introduced: d , K u , we can get the calculation results of formation resistivity and formation dielectric constant, which are respectively denoted as R t * , ε fr * ,Right now In formula (20), δ3 and δ4 are proportional factors of the formation resistivity calculation result, which are respectively used to adjust the proportion of the formation resistivity calculated based on the formation equivalent resistance of the button electrode (12) and the formation equivalent resistance of the recessed electrode (11), and the proportional factors of the two formation resistivity calculation results satisfy the relationship δ3+δ4=1; δ5 and δ6 are proportional factors of the formation dielectric constant calculation result, which are respectively used to adjust the proportion of the formation dielectric constant calculated based on the formation equivalent capacitance of the button electrode (12) and the formation equivalent capacitance of the recessed electrode (11), and the proportional factors of the two formation dielectric constant calculation results satisfy the relationship δ5+δ6=1.

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