High-precision well-ground electromagnetic inversion device and method

Abstract

The invention belongs to the technical field of geophysical oil-gas exploration, and particularly discloses a high-precision well-ground electromagnetic inversion device and method. The device comprises a data acquisition module, a data calculation module, a difference module, an inversion module and an analysis module. The method comprises the following steps: firstly, designing parameters and obtaining well-ground electromagnetic original data, then calculating normalized electric field component real part and imaginary part data of ground observation points, and then carrying out difference on the obtained data to obtain a difference electric field component real part and imaginary part of each ground observation point; then three-dimensional resistivity inversion is carried out to obtain a target interval three-dimensional resistivity data body; and finally, the target interval three-dimensional resistivity data body and induced polarization abnormity are combined to complete three-dimensional space distribution of the condition of oil gas contained in the excitation section in the well in the ground observation area. The method is used for exploration and development of oil and gas, the resistivity precision can be effectively improved, and a more reliable basis is provided for exploration and development of oil and gas reservoirs.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical oil and gas exploration, and particularly relates to a high-precision borehole-to-surface electromagnetic inversion device and method. Background Art

[0002] With the continuous deepening of oil and gas exploration and exploitation, deep and ultra-deep oil and gas targets have been included in the key exploration areas. In oil and gas exploration and exploitation, resistivity is an important basis for oil exploration. There are various methods for measuring resistivity. Among them, the borehole-to-surface electromagnetic method is a relatively common method. The borehole-to-surface electromagnetic method is an electromagnetic exploration method that supplies high-power alternating current to a finite-length wire in a borehole and receives electromagnetic responses on the ground. Compared with the surface electromagnetic method, the emission source is set in the borehole, making the response of the lower half-space more obvious and more conducive to the progress of exploration work. The borehole-to-surface electromagnetic technology can better identify the existence and distribution range of oil and gas reservoirs in deep and ultra-deep oil and gas exploration and development.

[0003] However, in the process of resistivity inversion using the borehole-to-surface electromagnetic method in deep and ultra-deep layers, since the deep and ultra-deep geological targets are far from the observation points, although the resistivity inversion resolution of the geological targets is higher than that of the surface artificial source electromagnetic method, it is still difficult to meet the requirements of the actual geological target resolution, and the obtained resistivity is still not accurate enough. Summary of the Invention

[0004] To solve the above deficiencies in the known technology, the present invention aims to provide a high-precision borehole-to-surface electromagnetic inversion device to improve the resistivity inversion resolution of geological targets and effectively identify the existence and distribution range of oil and gas reservoirs.

[0005] Another object of the present invention is to provide a high-precision borehole-to-surface electromagnetic inversion method. This method is implemented using the above high-precision borehole-to-surface electromagnetic inversion device, and this method can effectively improve the accuracy of resistivity and provide a more reliable basis for the exploration and development of oil and gas reservoirs.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] A high-precision borehole-to-surface electromagnetic inversion device includes a data acquisition module, a data calculation module, a difference module, an inversion module, and an analysis module;

[0008] The data acquisition module acquires the original borehole-to-surface electromagnetic data of different excitation signal periods in the target interval and outputs it to the data calculation module;

[0009] The data calculation module calculates the real and imaginary part data of the normalized horizontal radial electric field at each ground observation point when each excitation point is excited at each excitation signal period according to the received original borehole-to-surface electromagnetic data and outputs it to the difference module;

[0010] A differential module that calculates the real and imaginary part data of the normalized horizontal radial electric field at each ground observation point, obtains the real and imaginary parts of the differential horizontal radial electric field at each ground observation point in each excitation signal period, and outputs them to the inversion module;

[0011] An inversion module that performs three-dimensional resistivity inversion on the real and imaginary parts of the differential horizontal radial electric field to obtain a three-dimensional resistivity data volume of the target layer section, and outputs it to the analysis module;

[0012] An analysis module for jointly completing the three-dimensional spatial distribution of the oil and gas content in the well-excited section in the ground observation area by combining the three-dimensional resistivity data volume of the target layer section and the induced polarization anomaly of the target layer section.

[0013] The present invention also discloses a high-precision well-to-surface electromagnetic inversion method, and the method includes the following steps carried out in sequence:

[0014] S1. Design the well-excitation points, ground observation area, ground observation points, and excitation signal period in the target layer section according to the geological task, and use the data acquisition module to obtain the original well-to-surface electromagnetic data of different excitation signal periods in the target layer section;

[0015] S2. Read the original well-to-surface electromagnetic data, and use the data calculation module to calculate the real and imaginary part data of the normalized horizontal radial electric field at each ground observation point when each excitation point is excited in each excitation signal period;

[0016] S3. Perform data differentiation on the real and imaginary part data of the horizontal radial electric field using the differential module to obtain the real and imaginary parts of the differential horizontal radial electric field at each ground observation point when each excitation point is excited in each excitation signal period;

[0017] S4. According to the real and imaginary parts of the differential horizontal radial electric field, use the inversion module to perform three-dimensional resistivity inversion to obtain a three-dimensional resistivity data volume of the target layer section;

[0018] S5. Use the analysis module to complete the three-dimensional spatial distribution of the oil and gas content in the well-excited section in the ground observation area by combining the three-dimensional resistivity data volume of the target layer section and the induced polarization anomaly of the target layer section.

[0019] As a limitation, in step S1, the well-excitation points and ground observation points in the target layer section are determined according to the resolution in the geological task; after establishing a formation resistivity model of the work area based on the drilling well logging resistivity information, three-dimensional forward analysis is carried out to obtain the excitation signal period.

[0020] As a second limitation, the original well-to-surface electromagnetic data includes the coordinate positions of the excitation points, the coordinate positions of the ground observation points, the emission signal file of the well excitation, and the observation signal file of the ground observation.

[0021] As a further limitation, the calculation of the real and imaginary parts of the normalized horizontal radial electric field at all excitation points and ground observation points in each excitation signal period in step S2 includes:

[0022] a1) Read the in-well excitation current signal in the emission signal file and the horizontal radial electric field component signal in the observation signal file;

[0023] a2) Convert the in-well excitation current signal into real and imaginary part data in the complex domain through Fourier transform; after performing pole distance normalization on the horizontal radial electric field component signal observed at the ground observation point, then convert it into real and imaginary part data in the complex domain through Fourier transform;

[0024] a3) Perform current normalization on the electric field component in the complex domain to obtain the real and imaginary part data of the normalized horizontal radial electric field component in the complex domain;

[0025] The current normalization process is to divide the real and imaginary part data of the electric field collected at the ground observation point by the real and imaginary part data of the in-well excitation current respectively;

[0026] a4) Perform operations of removing outliers and filtering and denoising on the real and imaginary part data of the normalized horizontal radial electric field component to obtain the real and imaginary part data of the normalized horizontal radial electric field at each ground measurement point when each excitation point is excited in each excitation signal period.

[0027] As a further limitation, in step S3, the method for obtaining the real and imaginary parts of the differential horizontal radial electric field is:

[0028] If there are n excitation points, n > 2, when two excitation points with an interval of i, i ∈ [0, n - 2] excitation points are excited in each excitation signal period, the real and imaginary part data of the normalized horizontal radial electric field obtained from the ground observation points are subtracted respectively. Among them, when the excitation point near the bottom of the target interval is excited in the excitation signal period, the real and imaginary part data of the normalized horizontal radial electric field corresponding to each ground observation point are subtracted from the real and imaginary part data of the normalized horizontal radial electric field corresponding to the ground observation point when the excitation point near the top of the target interval is excited in the excitation signal period. A total of sets of approximate new excitation source excitation ground observation point data are obtained, that is, each ground observation point obtains sets of real and imaginary parts of the differential horizontal radial electric field in each excitation signal period.

[0029] As a third limitation, before performing step S4, it is necessary to perform three-dimensional inversion target layer grid encryption and dissection on the target interval according to the geological task. The grid density of the grid encryption and dissection is determined by the geological task resolution and is greater than or equal to the resolution of the geological task;

[0030] The target layer section of the encrypted dissection is greater than or equal to the ground observation area on the horizontal plane and extends beyond the plane where the uppermost excitation point is located and the plane where the lowermost excitation point is located in the vertical direction.

[0031] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention compared with the prior art are as follows:

[0032] (1) The device of the present invention conducts multiple excitations on the target layer section in the well, conducts multiple acquisitions at the ground observation points, and differentiates the multiple excitation electric field data through the differentiation module to obtain more accurate three-dimensional resistivity data, providing a more reliable basis for oil and gas exploration and development;

[0033] (2) The method of the present invention differentiates the multiple excitation electric field data collected at the ground observation points to eliminate the influence of the strata above the excitation points on the target layer. By encrypting the grid and dissecting the target body for the target layer section, high-precision three-dimensional inversion is completed using the three-dimensional resistivity inversion and the differentiated data volume, obtaining a high-precision resistivity data volume, and completing a more accurate three-dimensional oil and gas evaluation of the target layer using the resistivity data volume and other information.

[0034] In summary, the present invention can effectively improve the accuracy of resistivity and provide a more reliable basis for the exploration and development of oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Figure 1 It is the principle block diagram of Embodiment 1 of the present invention;

[0037] Figure 2 It is the schematic diagram of the ground observation network density of Embodiment 2 of the present invention;

[0038] Figure 3 It is the schematic diagram of the inversion target model and the ground observation points of Embodiment 2 of the present invention;

[0039] Figure 4 It is the plane schematic diagram of the resistivity after three-dimensional inversion of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] To better explain the present invention for easy understanding, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings through specific embodiments.

[0041] Embodiment 1 High-precision borehole-to-surface electromagnetic inversion device

[0042] As Figure 1 shown, this embodiment includes a data acquisition module, a data calculation module, a differentiation module, an inversion module, and an analysis module.

[0043] A data acquisition module, which acquires the original borehole-to-surface electromagnetic data of different excitation signal periods in the target interval and outputs them to the data calculation module.

[0044] A data calculation module, which calculates the real and imaginary part data of the normalized horizontal radial electric field at each surface observation point when each excitation point is excited in each excitation signal period according to the received original borehole-to-surface electromagnetic data, and outputs them to the difference module.

[0045] A difference module, which calculates the real and imaginary part data of the normalized horizontal radial electric field at each surface observation point to obtain the real and imaginary parts of the differential horizontal radial electric field at each surface observation point in each excitation signal period, and outputs them to the inversion module.

[0046] An inversion module, which performs three-dimensional resistivity inversion on the real and imaginary parts of the differential horizontal radial electric field to obtain a three-dimensional resistivity data volume of the target interval and outputs it to the analysis module;

[0047] An analysis module, which is used to jointly complete the three-dimensional spatial distribution of the oil and gas content in the well-excitation section in the ground observation area by combining the three-dimensional resistivity data volume of the target interval and the induced polarization anomaly of the target interval.

[0048] Example 2 High-precision borehole-to-surface electromagnetic inversion method

[0049] This example is implemented by using the high-precision electromagnetic inversion device in Example 1. This example includes the following steps carried out in sequence:

[0050] S1. Design the borehole excitation points, ground observation area, ground observation points and excitation signal periods in the target interval according to the geological task, and use the data acquisition module to obtain the original borehole-to-surface electromagnetic data of different excitation signal periods in the target interval;

[0051] S2. Read the original borehole-to-surface electromagnetic data, and use the data calculation module to calculate the real and imaginary part data of the normalized horizontal radial electric field at each surface observation point when each excitation point is excited in each excitation signal period respectively;

[0052] S3. Perform data difference on the real and imaginary part data of the horizontal radial electric field by using the difference module to obtain the real and imaginary parts of the differential horizontal radial electric field at each surface observation point when each excitation point is excited in each excitation signal period;

[0053] S4. According to the real and imaginary parts of the differential horizontal radial electric field, use the inversion module to perform three-dimensional resistivity inversion to obtain a three-dimensional resistivity data volume of the target interval;

[0054] S5. Use the analysis module to complete the three-dimensional spatial distribution of the oil and gas content in the well-excitation section in the ground observation area by combining the three-dimensional resistivity data volume of the target interval and the induced polarization anomaly of the target interval.

[0055] In this embodiment, a new drilling well is selected, and the target interval is 5990m to 6500m. The geological task in step S1 is to determine the oil and gas content within the range of 5990m to 6500m, including the excitation well, with a required horizontal resolution of 12.5m and a vertical resolution of 5m.

[0056] According to the geological task, the spacing between excitation points in the well is twice the vertical resolution, and the distance between ground observation points is twice the horizontal resolution. In this embodiment, the spacing between excitation points is 10m, with a total of 52 excitation points. The ground observation points are selected in an observation network of 25m×25m, and the observation area includes a range of 1100m×1700m including the excitation well. The total number of observation points is 45×69, that is, 3105; the excitation signal period is obtained through 3D forward modeling analysis after establishing the formation resistivity model of the work area based on the resistivity information of drilling well logging. Among them, the resistivity information of drilling well logging is known information collected before construction.

[0057] The borehole-to-surface electromagnetic raw data includes the coordinate positions of excitation points, the coordinate positions of ground observation points, the transmitted signal file excited in the well, and the observed signal file observed on the ground.

[0058] Table 1 shows the positions and corresponding numbers of the excitation points in the target interval of the well in this embodiment, and Table 2 shows the excitation signal period in this embodiment;

[0059] Table 1 Positions and corresponding numbers of the excitation points in the target interval of the well

[0060] Serial number Well depth Serial number Well depth Serial number Well depth Serial number Well depth AB01 6500 AB14 6370 AB27 6240 AB40 6110 AB02 6490 AB15 6360 AB28 6230 AB41 6100 AB03 6480 AB16 6350 AB29 6220 AB42 6090 AB04 6470 AB17 6340 AB30 6210 AB43 6080 AB05 6460 AB18 6330 AB31 6200 AB44 6070 AB06 6450 AB19 6320 AB32 6190 AB45 6060 AB07 6440 AB20 6310 AB33 6180 AB46 6050 AB08 6430 AB21 6300 AB34 6170 AB47 6040 AB09 6420 AB22 6290 AB35 6160 AB48 6030 AB10 6410 AB23 6280 AB36 6150 AB49 6020 AB11 6400 AB24 6270 AB37 6140 AB50 6010 AB12 6390 AB25 6260 AB38 6130 AB51 6000 AB13 6380 AB26 6250 AB39 6120 AB52 5990

[0061] Table 2 Excitation signal period

[0062] Serial number Excitation signal period Excitation signal frequency 1 0.32600 3.06748 2 0.40000 2.50000 3 0.46000 2.17391 4 0.51200 1.95313 5 0.68000 1.47059 6 0.82000 1.21951 7 1.02400 0.97656

[0063] Figure 2 The figure shows the schematic diagram of the survey network density of ground observation, where the small-diameter dots are ground observation points and the large-diameter dots are excitation wells.

[0064] In step S2 of this embodiment, the borehole-to-surface electromagnetic raw data is read, and the data calculation module is used to calculate the real and imaginary parts of the normalized horizontal radial electric field of 3105 ground observation points when 52 excitation points are excited in 7 excitation signal periods. The specific calculation process includes the following steps carried out in sequence:

[0065] a1) Read the excitation current signal in the well from the transmitted signal file and the horizontal radial electric field component signal in the observed signal file.

[0066] a2) Convert the current excitation signal in the well into real and imaginary part data in the complex domain through Fourier transform; after performing pole distance normalization on the horizontally radial electric field component signal observed at the ground observation point, then convert it into real and imaginary part data in the complex domain through Fourier transform;

[0067] a3) Perform current normalization on the complex domain of the electric field component to obtain the real and imaginary part data of the normalized horizontally radial electric field component in the complex domain; the current normalization process is to divide the real and imaginary part data of the electric field collected at the ground observation point by the real and imaginary part data of the current excited in the well respectively;

[0068] a4) Perform operations of removing outliers and filtering out noise on the real and imaginary part data of the normalized horizontally radial electric field component to obtain the real and imaginary part data of the normalized horizontally radial electric field at each ground measurement point when each excitation point is excited in each excitation signal period.

[0069] In this embodiment, the process of obtaining the real and imaginary parts of the differential horizontally radial electric field at each ground observation point in step S3 is as follows:

[0070] If there are n excitation points, when two excitation points with an interval of i, i ∈ [0, 50] excitation points are excited in each excitation signal period, the real and imaginary part data of the normalized horizontally radial electric field obtained from the ground observation point are subtracted respectively. Among them, when the excitation point near the bottom of the target interval is excited in the excitation signal period, the real and imaginary part data of the normalized horizontally radial electric field corresponding to each ground observation point are subtracted from the real and imaginary part data of the normalized horizontally radial electric field corresponding to the ground observation point when the excitation point near the top of the target interval is excited in the excitation signal period. A total of sets of approximate new excitation source excited ground observation point data are obtained, that is, each ground observation point obtains sets of real and imaginary parts of the differential horizontally radial electric field. In this embodiment, there are 52 sets of approximate new excitation source excited ground observation point data. In each excitation signal period, each ground observation point obtains 1326 sets of real and imaginary parts of the differential horizontally radial electric field.

[0071] In this embodiment, before step S4, the target layer section is subjected to three-dimensional inversion target layer grid encryption and dissection according to the geological task. The grid density of the grid encryption and dissection is determined by the geological task resolution and is greater than or equal to the geological task resolution. The grid density in this embodiment is 12.5 m × 12.5 m × 5 m, which is the same as the geological task resolution. The encrypted and dissected target layer section is greater than or equal to the ground observation area on the horizontal plane and greater than or equal to the plane where the uppermost excitation point is located and the plane where the lowermost excitation point is located in the vertical direction. When performing three-dimensional resistivity inversion, the influence of the casing must be considered. If there is three-dimensional seismic wave impedance data in the study area, the wave impedance data can be used. According to the relationship between the wave impedance and the conductivity, it is converted into conductivity to establish the initial model for inversion. If not, a homogeneous layered model can be used as the initial model for inversion.

[0072] Figure 3 The figure shows a plan view of the inversion target model and the ground observation points. The three black boxes represent three three-dimensional target bodies; Figure 4 The figure shows a plan view of the resistivity after three-dimensional inversion. The darker the color in the three squares in the figure, the greater the resistivity. After obtaining the three-dimensional resistivity data volume of the three-dimensional target body, the three-dimensional spatial distribution of the oil and gas content in the wellbore excitation section within the ground observation area is completed according to the induced polarization anomaly of the target layer section obtained by the existing technology.

Claims

1. A high-precision borehole-to-ground electromagnetic inversion device, characterized in that: It includes data acquisition module, data calculation module, difference module, inversion module and analysis module; The data acquisition module acquires the original electromagnetic data of the target layer at different excitation signal periods and outputs them to the data calculation module; The data calculation module calculates the real and imaginary data of the normalized horizontal radial electric field of each ground observation point when each excitation point is excited in each excitation signal cycle according to the received raw borehole-ground electromagnetic data, and outputs them to the differential module; The differential module calculates the normalized real and imaginary data of the horizontal radial electric field at each ground observation point, obtains the real and imaginary parts of the differential horizontal radial electric field at each ground observation point in each excitation signal cycle, and outputs them to the inversion module; The inversion module performs three-dimensional resistivity inversion on the real and imaginary parts of the differential horizontal radial electric field to obtain the three-dimensional resistivity data volume of the target layer segment, and outputs it to the analysis module; The analysis module is used to combine the three-dimensional resistivity data volume of the target layer and the induced polarization anomaly of the target layer to complete the three-dimensional spatial distribution of the oil and gas content in the induced section of the well in the ground observation area.

2. A high-precision borehole-to-earth electromagnetic inversion method, implemented by using the high-precision borehole-to-earth electromagnetic inversion device according to claim 1, characterized in that: The method comprises the following steps performed in sequence: S1. According to the geological task, the in-well excitation points, ground observation area, ground observation points and excitation signal period of the target layer are designed, and the raw electromagnetic data of the target layer with different excitation signal periods are obtained by using the data acquisition module; S2, reading the original electromagnetic data of the well and the ground, and using the data calculation module to respectively calculate the real and imaginary data of the normalized horizontal radial electric field of each ground observation point when each excitation point is excited in each excitation signal cycle; S3, using a differential module to perform data differentiation on the real and imaginary parts of the horizontal radial electric field, to obtain the real and imaginary parts of the differential horizontal radial electric field of each ground observation point when each excitation point is excited in each excitation signal cycle; S4, according to the real part and imaginary part of the differential horizontal radial electric field, using the inversion module to perform three-dimensional resistivity inversion to obtain the three-dimensional resistivity data volume of the target layer segment; S5. Using the analysis module, the three-dimensional spatial distribution of oil and gas content in the excited section of the well in the ground observation area is completed by combining the three-dimensional resistivity data body of the target layer and the excited polarization anomaly of the target layer.

3. The high-precision borehole-to-ground electromagnetic inversion method according to claim 2, characterized in that: In step S1, the in-well excitation points and ground observation points of the target layer are determined according to the resolution in the geological task; a formation resistivity model of the work area is established according to the drilling and logging resistivity information, and then a three-dimensional forward analysis is carried out to obtain the excitation signal period.

4. The high-precision borehole-to-ground electromagnetic inversion method according to claim 2 or 3, characterized in that: The raw well-ground electromagnetic data include the coordinate position of the excitation point, the coordinate position of the ground observation point, the emission signal file excited in the well and the observation signal file observed on the ground.

5. The high-precision borehole-to-ground electromagnetic inversion method according to claim 4, characterized in that: The step S2 of calculating the normalized real and imaginary data of the horizontal radial electric field at each ground observation point comprises the following steps performed in sequence: a1) reading the well excitation current signal in the transmission signal file and the horizontal radial electric field component signal in the observation signal file; a2) converting the excited current signal in the well into real data and imaginary data in the complex domain through Fourier transformation; performing pole-distance normalization processing on the horizontal radial electric field component signal observed at the ground observation point, and then converting it into real data and imaginary data in the complex domain through Fourier transformation; a3) performing current normalization processing on the complex domain of the electric field component to obtain normalized real and imaginary part data of the complex domain of the horizontal radial electric field component; The current normalization process is to divide the real and imaginary data of the electric field collected at the ground observation point by the real and imaginary data of the excited current in the well respectively; a4) performing flying spot removal and filtering and denoising operations on the normalized real and imaginary data of the horizontal radial electric field component to obtain the normalized real and imaginary data of the horizontal radial electric field at each ground measuring point when each excitation point is excited in each excitation signal cycle.

6. The high-precision borehole-to-ground electromagnetic inversion method according to claim 5, characterized in that: In step S3, the method for obtaining the real part and the imaginary part of the differential horizontal radial electric field is: If there are n excitation points, n>2, when two excitation points separated by interval i, i∈[0,n-2] are excited in each excitation signal cycle, the real and imaginary data of the normalized horizontal radial electric field obtained by the ground observation point are subtracted respectively. Among them, when the excitation point near the bottom of the target layer is excited in the excitation signal cycle, the real and imaginary data of the normalized horizontal radial electric field corresponding to each ground observation point are subtracted from the real and imaginary data of the normalized horizontal radial electric field corresponding to the excitation point near the top of the target layer when the excitation signal cycle is excited, and a total of A set of ground observation point data excited by the new excitation source is obtained, that is, each ground observation point obtains The real and imaginary parts of the differential horizontal radial electric field.

7. The high-precision borehole-to-ground electromagnetic inversion method according to any one of claims 2, 3, 5, and 6, characterized in that: Before executing step S4, the target layer segment needs to be divided into a three-dimensional inversion target layer grid according to the geological task. The grid density of the grid division is determined by the resolution of the geological task and is greater than or equal to the resolution of the geological task. The target layer segment of the dense subdivision is greater than or equal to the ground observation area in the horizontal plane, and exceeds the plane where the uppermost excitation point and the plane where the lowermost excitation point are located in the vertical direction.

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