CN111927443A - Logging system and method for measuring true resistivity of stratum based on electric field - Google Patents
Logging system and method for measuring true resistivity of stratum based on electric field Download PDFInfo
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Abstract
A logging system and method based on electric field measurement stratum true resistivity, the logging system includes measuring mechanism and gathering the analytical mechanism of the data in the pit; the collected data analysis mechanism comprises a ground mobile data collection mechanism and a data processing module; placing a shaft in a well log excavated to a measurement stratum, descending the underground measurement mechanism to the measurement stratum in the shaft, connecting a ground mobile data acquisition mechanism with the underground measurement mechanism through a cable, and arranging a cable hoisting device at a well mouth; the underground measuring mechanism consists of a measuring coil and an electric field measuring main control system. The invention is based on the detection and data processing technology under the conditions of full-space multi-frequency transmission and multi-point receiving measurement of the formation electric field, realizes the distribution of the electric field intensity measured along the well axis rapidly by obtaining mass electric field data, converts the electric field intensity distribution into a visual conductivity function, and realizes the rapid measurement of the resistivity of the true formation in different radial directions under the condition of high signal-to-noise ratio by carrying out self-adaptive processing on the visual conductivity function.
Description
Technical Field
The invention relates to a logging technology, in particular to a logging system and method for measuring true resistivity of a stratum based on an electric field.
Background
In the field of petroleum engineering, true formation resistivity is a very important electrical parameter in oilfield reservoir evaluation. At present, the resistivity logging instrument mainly uses a logging method of an electromagnetic wave induction logging geometric factor theory to measure the formation resistivity through a plurality of transmitting coils and receiving coils. In order to measure the medium resistivity of different radial directions and longitudinal directions of a stratum, in an array induction logging instrument AIT of an array induction logging instrument MIT and Schlumberger in China, based on an electromagnetic wave induction logging geometric factor theory, 1 group of short-to-long transmitting short joints and 8 groups of short joints are adopted for measuring the spacing between receiving coils, more radial direction and longitudinal direction repeated information exists between the receiving coils, real part signals and imaginary part signals are used simultaneously, data signal processing is complex, and the problems of inaccurate imaginary part measurement and the like are solved. In an HDIL (high density interconnect) of an array induction logging instrument of foreign Baker Atlas, based on the electromagnetic wave induction logging geometric factor theory, the distances among a receiving coil, a shielding coil and a transmitting coil of a detector are not integral multiples of the sampling distance, the working range of a measuring signal of a long-source-distance coil is small, a 10-in resistivity curve borehole with the shortest detection depth is seriously influenced during data processing, and the data processing is difficult.
The existing induction logging instrument adopts an electromagnetic wave induction logging geometric factor theory, can only process 5 resistivity curves with different depths, cannot accurately measure the formation radial resistivity at different position depths, has the defects of complex structures of a receiving circuit and an acquisition system and a calculation processing mode, high measurement cost and the like, and has poor practical application effect.
Disclosure of Invention
The invention aims to solve the problems that the processing of formation true resistivity measurement data is complex and the acquisition requirements of different radial depth information cannot be met in the prior art, and provides a logging system and a method for measuring formation true resistivity based on an electric field. And establishing a logging method of which the conductivity is a function of field point coordinates, eliminating the influences of the borehole environment and the layer thickness and providing true resistivity information of the stratum with different radial depths.
In order to achieve the purpose, the invention adopts the following technical scheme:
a logging system for measuring the true resistivity of a stratum based on an electric field comprises an underground measuring mechanism and a collected data analysis mechanism; the collected data analysis mechanism comprises a ground mobile data collection mechanism and a data processing module; placing a shaft in a well log excavated to a measurement stratum, descending the underground measurement mechanism to the measurement stratum in the shaft, connecting a ground mobile data acquisition mechanism with the underground measurement mechanism through a cable, and arranging a cable hoisting device at a well mouth; the underground measuring mechanism consists of a measuring coil and an electric field measuring main control system;
the measuring coil comprises a coil mandrel arranged in the glass fiber reinforced plastic outer tube, the coil mandrel is wound with the measuring coil consisting of a transmitting coil and a receiving coil through a coil framework, a coil pressure balancing device is arranged between the measuring coil and the glass fiber reinforced plastic outer tube, and the pressure balance between the coil and the inside and the outside of the glass fiber reinforced plastic in a high-temperature and high-pressure environment is realized through the coil pressure balancing device;
the electric field measurement main control system comprises a power supply module, a transmitting driving unit, a multi-channel preamplification unit, a main control unit and a data acquisition unit, wherein the transmitting driving unit transmits 5 current signals with different frequencies to a transmitting coil, receives electric field signals generated by the current signals passing through a measurement stratum through 8 groups of receiving coils, amplifies the received electric field signals through the multi-channel preamplification unit, and finally transmits the electric field signals to the main control unit through the data acquisition unit; the main control unit transmits the received electric field signal to the ground mobile data acquisition mechanism in real time through a telemetering communication circuit;
the ground mobile data acquisition mechanism is used for monitoring the acquired logging data in real time and controlling the adjustment of the scales and the logging positions at the same time; controlling the scales comprises completing scale file calling and scale calibration operation, and displaying an electric field logging curve in real time by loading a configuration file of a downhole measuring mechanism, a scale file and an upper logging or lower logging instruction during logging;
and the data processing module is used for processing the original electric field logging data of the ground mobile data acquisition mechanism in real time to obtain a final formation true resistivity logging curve.
The data processing module consists of a preprocessing apparent conductivity function module, a borehole correction module and a layer thickness processing and resolution unified processing module, and the preprocessing apparent conductivity function module carries out iterative processing on original electric field logging data, a scale coefficient and an apparent conductivity theoretical function to realize the conversion from an electric field signal to a stratum conductivity signal; the borehole correction module is used for correcting the borehole influence on the video conductivity data by using the borehole corrected borehole diameter and mud resistivity, including an auxiliary measured borehole diameter and mud curve or a fixed value input by a user; the layer thickness processing and resolution unified processing module is used for performing layer thickness correction processing on borehole correction output data, so that a logging system can measure formation resistivity information in different ranges, and through borehole environment influence correction and data processing, true resistivities of different radial directions of a formation are obtained, and finally a formation true resistivity logging curve required by a user is completed.
The coil core shaft is made of nonmagnetic metal materials, the coil pressure balancing device comprises a plurality of oil-filled filling sleeves which are sleeved on the coil core shaft through a cushion cover, a glass fiber reinforced plastic cushion ring is sleeved on the periphery of the end face of the coil core shaft connected with the cable, and the oil-filled filling sleeves are also separated from the end face of the coil framework and the end face of the glass fiber reinforced plastic cushion ring through the cushion cover; and a supporting filling sleeve is arranged between every two adjacent filling sleeves positioned between all the filling sleeves, and an O-shaped ring is arranged on the supporting filling sleeve.
The source distances of the 8 groups of receiving coils R1-R8 are 0.125m, 0.2m, 0.3m, 0.4m, 0.6m, 1.0m, 1.5m and 2.3m respectively, and all the coils are arranged on one side to form arrayed R1, R2, R3, R4, R5, R6, R7 and R8 receiving coils.
The electric field measurement main control system is designed based on a DSP and FPGA embedded architecture; the level conversion of the front-end multichannel conditioning signal is completed through a level conversion circuit, and the bipolar signal is adjusted to a unipolar signal suitable for AD acquisition; the automatic gain adjustment and amplification of signals of each channel are realized through a programmable gain amplification circuit, and the signal measurement dynamic range of the electric field logging instrument is ensured; the FPGA controls a plurality of channels of AD to finish signal acquisition, accumulating and denoising, storing the result in a double-port RAM arranged in the FPGA, informing a DSP to read data through interruption, finishing digital phase sensitive detection DSPD processing of 5 frequency signals of the plurality of channels, and forming 40 groups of real part data and 40 groups of imaginary part data; in a CAN communication period, the DSP completes the measurement of auxiliary parameters including the internal temperature and the working voltage of the measuring coil through the built-in AD, and the DSP completes data uploading through the built-in CAN through telemetering communication after data is framed.
The invention also provides a logging method for measuring the true resistivity of the stratum based on the electric field, which comprises the following steps:
301, inputting the formation electric field signal output by the electric field data calibration unit into a logging data temperature correction unit, and using a formula and a temperature correction database
Calculating electric field measurement signal corresponding to temperature by interval linear interpolation
Subtracting pair measurements generated by electronics and coil train due to formation temperature variationsInfluence of the Signal
Temperature correction is carried out on the 40 measured electric field signals to obtain 40 correction curves for eliminating temperature influence on electric field logging data;
wherein k isA(x) As a propagation coefficient of the full space equivalent, i.e. the apparent propagation coefficient, in which
iterative inversion processing is carried out on combined measurement electric field data to obtain sigmaa1(z) the conductivity equivalent in the space outside the borehole is the corrected conductivity σ for the boreholea1(z) wherein
By the formula:
wherein the lower interface of the target layer is h1Upper boundary surface is h2Let σ bea2(x) Is equal to sigmaa1(x) Obtaining 40 data curves and electric fields E for removing the borehole influence by the borehole correction processing unit1(x) The expression jointly uses a self-adaptive iterative inversion algorithm to calculate the corresponding radial field point position coordinate and the true formation resistivity;
When the scales are calibrated, the electric field data calibration unit accurately derives the measuring electric field E of the coil system according to the electric field logging theorycSelecting two stable scale points of air and water medium; wherein air is used as the low point EcLThe conductivity is 0S/m; pool as high point EcHCalculating the instrument response of the infinite uniform medium, wherein the diameter of the circular pool is more than 20m or the depth of the pool is more than 10 m;
the calibration method comprises the following steps:
step 201.1, measuring the electric field intensity E of the low-pointmLOr the instrument is suspended and lifted above 5 meters away from the ground by induced electromotive force, and the electric field intensity of the electric field instrument in the air or the induced electromotive force is measured;
step 201.2, measuring the high-point electric fieldStrength EmHOr the instrument is placed in the center of the water pool by inducing the electromotive force, and the electric field intensity of the electric field instrument at a high point is measured or the electromotive force is induced;
step 201.3, calibrating a formula E by using the high and low scalescH＝KEmH+ B and EcL＝KEmL+ B calculates the scale factor K, B to achieve the formation electric field signal calibrated for measurement.
Compared with the prior art, the invention has the following beneficial effects: the outer surface of the coil mandrel is wound with the glass fiber reinforced plastic to form the composite mandrel, a measuring coil consisting of a transmitting coil and a receiving coil is wound on the coil mandrel through a coil framework, and an integrated structure is formed by combining a coil pressure balancing device, so that the insulating, anti-deformation and pressure-bearing capacities of the electric field measuring coil are ensured. The electric field measurement main control system transmits 5 current signals with different frequencies of 1.0kHz, 2.5kHz, 5kHz, 10kHz and 20kHz, 8 groups of receiving coils receive the electric field signals generated by the current signals passing through a measurement stratum, low-noise amplification is carried out through the multi-channel preamplification unit, the data acquisition unit and the main control unit complete coil array signal acquisition, multi-frequency point digital phase-sensitive detection calculation and data packaging and then transmit the signals to the ground mobile data acquisition mechanism in real time through the telemetering communication circuit, and the ground mobile data acquisition mechanism is used for monitoring the acquired logging data in real time and controlling the calibration and the adjustment of the logging position. And the data processing module eliminates the influences of the borehole environment and the layer thickness through signal processing, and finally obtains the required true resistivity logging curve of the stratum. The invention is based on the detection and data processing technology under the condition of full-space multi-frequency emission and multi-point receiving measurement of a formation electric field, an electric field detector adopts a multi-array and wide frequency spectrum to collect underground massive electric field information, and high-precision electric field logging including the periphery of a well is realized; the method comprises the steps of obtaining mass electric field data, achieving distribution of electric field intensity measured along a well axis rapidly, converting the distribution of the electric field intensity into a visual conductivity function, and achieving rapid measurement of the resistivity of the true strata in different radial directions under the condition of high signal-to-noise ratio by performing self-adaptive processing on the visual conductivity function.
Drawings
FIG. 1 is a schematic diagram of a logging system according to the present invention;
FIG. 2 is a schematic view of an integrated structure of an electric field measuring coil;
FIG. 3 is a schematic diagram of the arrangement position of the electric field measuring coil;
FIG. 4 is a block diagram of an electric field measurement master control system according to the present invention;
FIG. 5 is a data processing flow diagram;
FIG. 6 is a graph of the electrical field as a function of conductivity;
FIG. 7 is a graph of electric field measurement radial probe response characteristics;
FIG. 8a is a graph of true conductivity versus apparent conductivity after treatment at a transmission frequency of 1 kHz;
FIG. 8b is a graph of true conductivity versus apparent conductivity after treatment at a transmission frequency of 2.5 kHz;
FIG. 8c is a graph of true conductivity versus apparent conductivity after treatment at a transmission frequency of 5 kHz;
FIG. 8d is a graph of true conductivity versus apparent conductivity after treatment at a transmission frequency of 10 kHz;
FIG. 8e is a graph of true conductivity versus apparent conductivity after treatment at a transmission frequency of 20 kHz;
FIG. 9 is a schematic diagram of a borehole calibration process for logging model data;
FIG. 10 is a diagram illustrating the results of well log data interpretation.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the present invention provides a logging system for measuring true resistivity of an earth formation by an electric field, which mainly comprises 7 links: the logging system for measuring the true resistivity of the stratum by the electric field mainly comprises an electric field logging instrument consisting of a measuring coil 1 and an electric field measuring main control system 2, and in a shaft 3 and the measured stratum 4, logging data measured by the electric field logging instrument are transmitted to a data processing module 7 for data processing of measured values by electric field logging measuring signals obtained by a ground moving data acquisition mechanism 6 through a cable hoisting device 5, so that logging of the true resistivity of the stratum by the electric field measuring instrument is completed.
The measuring coil 1 specifically comprises a coil mandrel 11, a coil framework 14, a transmitting coil, a receiving coil, a glass fiber reinforced plastic outer tube and a coil pressure balancing device, and an electric field measuring probe composed of a coil, mandrel and pressure balancing device integrated structure and a ceramic coil grooving process system is adopted, so that the insulating, anti-deformation and pressure-bearing capacities of the electric field measuring coil are ensured.
The electric field measurement main control system 2 is specifically composed of 5 module units including a power supply module, an emission driving unit, a multi-channel preamplification unit, a main control unit and a data acquisition unit. Mainly finishing transmitting 5 current signals with different frequencies to a transmitting coil, wherein the 5 frequencies are 1.0kHz, 2.5kHz, 5kHz, 10kHz and 20kHz respectively; the 8 groups of receiving coils receive electric field signals generated by transmitting signals through a stratum, the electric field signals are received through the multi-channel preamplification unit to be subjected to low-noise amplification, the electric field signals generated by the receiving coils are collected by the main control unit and the data collection unit, the coil array signal collection, the multi-frequency point digital phase-sensitive detection calculation and the data packing are completed, the electric field signals are uploaded to the ground through the telemetering communication circuit to be processed, and the measured stratum signals are obtained in real time.
The ground mobile data acquisition mechanism 6 is used for acquiring and monitoring the logging data of the electric field logging instrument in real time and controlling the scale and logging of the electric field logging instrument. The scale file calling is completed in the scale process, and the scale calibration operation is completed; and during logging, the electric field logging curve is displayed in real time by loading the instrument configuration file and the scale file and carrying out up-logging or down-logging.
The data processing module 7 is used for processing the original electric field logging data of the ground acquisition module in real time to obtain a final formation true resistivity logging curve. The preprocessing apparent conductivity function module carries out iterative processing on the original electric field data, the scale coefficient and the apparent conductivity theoretical function to realize the conversion from the electric field signal to the stratum conductivity signal; the borehole correction module uses the corrected borehole diameter and mud resistivity, which can be the borehole diameter and mud curve of auxiliary measurement or the fixed value input by the user, to correct the borehole influence on the apparent conductivity data. The layer thickness processing and resolution unified processing module is used for performing layer thickness correction processing on borehole correction output data, so that an electric field logging system can measure formation resistivity information in different ranges, different radial true resistivities of the formation are obtained through borehole environment influence correction and data processing, and finally a logging interpretation curve required by a user is completed.
The embodiment of the invention provides an integrated electric field measuring coil structure, as shown in fig. 2, the electric field instrument coil structure is composed of a coil mandrel, a ceramic coil, a glass fiber reinforced plastic outer tube and a pressure balance. The device comprises a glass fiber reinforced plastic backing ring 1, a cushion cover 2, a filling sleeve 1, a filling sleeve 2, a supporting filling sleeve, an O-shaped sealing ring (70mm multiplied by 3.1mm), a cushion cover 3, a filling sleeve 3, a coil framework, a regulating sheet, an SP cushion cover, a contact block assembly, a sealing gasket, a temperature cushion cover, a temperature probe seat and other parts, which are sequentially sleeved from the lower end of a mandrel according to a mechanical structure diagram 2 and are arranged in the mandrel. The electric field coil core shaft is made of special non-magnetic metal materials, glass fiber reinforced plastic is wound on the outer surface of the electric field coil core shaft to form a composite core shaft, and a group of transmitting coils and 8 groups of receiving coils are bonded into a whole according to designed size positions to form the electric field measuring coil detector. The diameter of the glass fiber reinforced plastic outer tube is 90mm, and the source distances from the R1 to the R8 of the 8 groups of receiving array main coils shown in FIG. 3 are respectively 0.125, 0.2, 0.3, 0.4, 0.6, 1.0, 1.5 and 2.3 m. All coils are arranged on one side, making up the receive arrays R1, R2, R3, R4, R5, R6, R7 and R8 receive coils.
As shown in fig. 4, an electric field measurement main control system according to an embodiment of the present invention uses an acquisition processing unit as a system control core to complete 5 types of frequency emission waveform control, level conversion, automatic gain control and calibration, auxiliary parameter measurement, multi-channel synchronous acquisition and processing, and system communication. Based on the embedded architecture design of the DSP and the FPGA, the system adopts the DSP with 32bit high speed and high performance and the FPGA as the main control element. The real-time performance of the high-speed FPGA is utilized to realize multi-channel synchronous acquisition and the flexibility and processing capacity of the high-performance DSP are utilized to realize signal processing. The main control acquisition processing unit has the working process that: the level conversion circuit completes the level conversion of the front-end multichannel conditioning signal and adjusts the bipolar signal to a unipolar signal suitable for AD acquisition; the programmable gain amplifying circuit realizes automatic gain adjustment and amplification of signals of each channel, and ensures the signal measurement dynamic range of the electric field logging instrument; the FPGA controls a plurality of channels of AD to finish signal acquisition, accumulating and denoising treatment is carried out, a result is stored in the internal RAM with two ports, a DSP is informed to read data through interruption, digital phase sensitive detection DSPD treatment of 5 frequency signals of a plurality of channels is finished, and 40 groups of real part data and 40 groups of imaginary part data are formed; in a CAN communication period, the DSP also needs to complete the measurement of auxiliary parameters such as the internal temperature and the working voltage of the measuring coil through the built-in AD, and the DSP completes data uploading through the built-in CAN through telemetering communication after data is framed.
The embodiment of the invention provides an electric field logging data processing method, which mainly comprises the following steps as shown in figure 5: the method comprises the steps of raw logging data 101, electric field logging data calibration 201, logging data temperature correction 301, apparent conductivity conversion processing 401, borehole correction processing 402, layer thickness correction processing 403, resolution unification processing 404 and radial inversion processing result output 405.
101, completing real-time acquisition of original electric field logging data through a ground mobile data acquisition mechanism 6, and simultaneously sending the logging data into an electric field logging data calibration unit 201;
comprises the following steps:
step 201.1, the measured electric field E of the coil system can be accurately derived according to the electric field logging theorycTwo stable scale points (air and water medium) are selected. Wherein air is used as the lower scale EcLThe conductivity was 0S/m.
Using large water pool as high point EcHThe diameter of the round pool is more than 20 meters, or the depth of the pool is more than 10 meters.
Calculating the instrument response (electric field intensity or induced electromotive force) of an infinite uniform medium by theory;
EcH＝KEmH+B (1)
EcL＝KEmL+B (2)
step 201.2, measuring the electric field intensity of the low-pointEmLOr the instrument is suspended and lifted above the ground by more than 5 meters by induced electromotive force, and the electric field intensity of the electric field instrument in the air is measured or the induced electromotive force is measured.
Step 201.3, measuring high-point electric field intensity EmHOr the instrument is placed in the center of the water pool by inducing the electromotive force, and the electric field intensity of the electric field instrument at a high point is measured or the electromotive force is induced.
Step 201.4, the scale factor K, B is calculated by using the formulas (1) and (2), and the measured formation electric field signal is calibrated.
301, inputting the formation electric field signal output by the electric field data calibration unit 201 into the logging data temperature correction unit 301, calculating the influence of the electric field measurement signal corresponding to the temperature generated by the electronic circuit and the coil system on the measurement signal due to the formation temperature change by using interval linear interpolation according to the measurement temperature probe data by using the temperature correction database
And (4) carrying out temperature correction on the 40 measured electric field signals by using a formula (3) to obtain 40 logging temperature correction data curves.
Wherein k isA(x) The propagation coefficient as the full space equivalent is the apparent propagation coefficient, where
Wherein sigmaA(x) The conductivity, which is a full-space equivalent, is the apparent conductivity.
The conductivity here is a function of the field point coordinates, at lower frequencies:
conversion of electric field distribution measured along the well axis into apparent conductivity σ by equation (4)A(x) The formula (2).
applied to a model of a borehole penetrating the formation, the borehole region being designated V0Radius of borehole being r0Conductivity of mud is σ0Using the algorithms of equations (6) - (9) to determine the apparent conductivity σ from the well axisA(x1) Apparent conductivity σ as a boreholeA(z) the equivalent conductivity of all formations other than the borehole is σa1(z) having:
in the formula:
wherein the content of the first and second substances,
σ can be found by performing iterative inversion processing from equation (6) and the measured electric field dataa1(z) the conductivity, which is spatially equivalent outside the borehole, is exactly σ for the borehole conductivitya1Apparent conductivity at (z).
Using equations (10) to (13):
in the formula:
in the formula (10), let σa2(x) Is equal to sigmaa1(x) And obtaining 40 data curves for removing the influence of the borehole by the borehole correction processing unit (402) and the formula (10) by using a self-adaptive iterative inversion algorithm to obtain the true conductivity of the stratum at different positions.
Fig. 6 shows the radial detection distribution range of the formation for different receiving positions of 8 sub-arrays of the invention, clearly showing that the 8 sub-arrays are reasonably distributed along the radial direction in different detection depth curves.
FIG. 7 is a graph of apparent conductivity function obtained after 5 different frequencies are processed by the apparent conductivity function in the formation, which clearly shows that the smooth relationship of the curves of the apparent conductivity function with different frequencies is reasonably distributed.
FIGS. 8a to 8e are graphs of real parts of relationships between given true conductivities of formations and apparent conductivities obtained after 5 different frequencies in 8 sub-arrays of the invention are processed by an apparent conductivity function in a mean formation. The instrument works at frequencies of 1kHz, 2.5kHz and 5kHz to measure the conductivity of 8 groups of receiving coils, and has good linear relation. The working range at the position with the longest distance of 2.3m is (0.001-100S/m), and the effective measuring range at the position with the longest distance of 2.3m is (0.001-50S/m) when the working frequency is 10 kHz; FIG. 8e shows that the effective measurement range of the 8 sub-arrays of the present invention is (0.001-10S/m) at the longest receiving distance of 2.3m with the working frequency of 20kHz, which effectively ensures the effective measurement range of the electric field logging to the stratum.
The embodiment of the invention provides a data processing result of an electric field logging instrument model, as shown in fig. 9, a borehole correction and data processing result graph is carried out on a multilayer underground model by using the data processing realized by the invention, and the data processing and thin layer layering capabilities of the electric field logging instrument on stratums with different contrast ratios are verified.
The embodiment of the invention provides a measured data processing result of an electric field logging instrument, as shown in fig. 10, a comparison graph of an X-well comprehensive data processing result and an array induction data processing result shows that the comparison result has a good consistency result, the curve relation of electric field logging processing in a permeable layer is reasonable, and the identification capability of the electric field logging instrument on the permeability of a reservoir and oil-containing water is reflected.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the technical solution of the present invention, and it should be understood by those skilled in the art that the technical solution can be modified and replaced by a plurality of simple modifications and replacements without departing from the spirit and principle of the present invention, and the modifications and replacements also fall within the protection scope covered by the claims.
Claims (7)
1. A logging system based on electric field measurement stratum true resistivity is characterized in that: the underground measurement device comprises an underground measurement mechanism and a collected data analysis mechanism; the collected data analysis mechanism comprises a ground mobile data collection mechanism (6) and a data processing module (7); placing a shaft (3) in a well log excavated to a measurement stratum (4), descending the underground measurement mechanism to the measurement stratum (4) in the shaft (3), connecting a ground mobile data acquisition mechanism (6) with the underground measurement mechanism through a cable, and arranging a cable hoisting device (5) at a well mouth; the underground measuring mechanism consists of a measuring coil (1) and an electric field measuring main control system (2);
the measuring coil (1) comprises a coil mandrel arranged in the glass fiber reinforced plastic outer tube, a measuring coil consisting of a transmitting coil and a receiving coil is wound on the coil mandrel through a coil framework, a coil pressure balancing device is arranged between the measuring coil and the glass fiber reinforced plastic outer tube, and the pressure balance between the coil and the inner and outer sides of the glass fiber reinforced plastic in a high-temperature and high-pressure environment is realized through the coil pressure balancing device;
the electric field measurement main control system (2) consists of a power supply module, a transmitting driving unit, a multi-channel preamplification unit, a main control unit and a data acquisition unit, wherein the transmitting driving unit transmits 5 current signals with different frequencies to a transmitting coil, receives electric field signals generated by the current signals through a measurement stratum (4) through 8 groups of receiving coils, amplifies the received electric field signals through the multi-channel preamplification unit, and finally transmits the electric field signals to the main control unit through the data acquisition unit; the main control unit transmits the received electric field signal to a ground mobile data acquisition mechanism (6) in real time through a telemetering communication circuit;
the ground mobile data acquisition mechanism (6) is used for monitoring the acquired logging data in real time and controlling the adjustment of the scales and the logging positions at the same time; controlling the scales comprises completing scale file calling and scale calibration operation, and displaying an electric field logging curve in real time by loading a configuration file of a downhole measuring mechanism, a scale file and an upper logging or lower logging instruction during logging;
and the data processing module (7) is used for processing the original electric field logging data of the ground mobile data acquisition mechanism (6) in real time to obtain a final true formation resistivity logging curve.
2. The electric field based logging system for measuring true resistivity of a formation as claimed in claim 1 wherein: the data processing module (7) consists of a preprocessing apparent conductivity function module, a borehole correction module and a layer thickness processing and resolution unified processing module, and the preprocessing apparent conductivity function module carries out iterative processing on original electric field logging data, a scale coefficient and an apparent conductivity theoretical function to realize the conversion from an electric field signal to a stratum conductivity signal; the borehole correction module is used for correcting the borehole influence on the video conductivity data by using the borehole corrected borehole diameter and mud resistivity, including an auxiliary measured borehole diameter and mud curve or a fixed value input by a user; the layer thickness processing and resolution unified processing module is used for performing layer thickness correction processing on borehole correction output data, so that a logging system can measure formation resistivity information in different ranges, and through borehole environment influence correction and data processing, true resistivities of different radial directions of a formation are obtained, and finally a formation true resistivity logging curve required by a user is completed.
3. The electric field based logging system for measuring true resistivity of a formation as claimed in claim 1 wherein:
the coil core shaft (11) is made of a non-magnetic metal material, the coil pressure balancing device comprises a plurality of oil-filled filling sleeves (13) which are sleeved on the coil core shaft (11) through a cushion cover (12), a glass fiber reinforced plastic cushion ring (17) is sleeved on the periphery of the end face, connected with a cable, of the coil core shaft (11), and the oil-filled filling sleeves (13) are also separated from the end face of the coil framework (14) and the end face of the glass fiber reinforced plastic cushion ring (17) through the cushion cover (12); a supporting filling sleeve (15) is arranged between every two adjacent filling sleeves (13) positioned between all the filling sleeves (13), and an O-shaped ring (16) is arranged on the supporting filling sleeve.
4. The electric field based logging system for measuring true resistivity of a formation as claimed in claim 1 wherein: the source distances of the 8 groups of receiving coils R1-R8 are respectively 0.125m, 0.2m, 0.3m, 0.4m, 0.6m, 1.0m, 1.5m and 2.3m, all the coils are arranged on one side, and arrayed R1, R2, R3, R4, R5, R6, R7 and R8 receiving coils are formed.
5. The electric field based logging system for measuring true resistivity of a formation as claimed in claim 1 wherein: the electric field measurement main control system (2) is designed based on a DSP and FPGA embedded architecture; the level conversion of the front-end multichannel conditioning signal is completed through a level conversion circuit, and the bipolar signal is adjusted to a unipolar signal suitable for AD acquisition; the automatic gain adjustment and amplification of signals of each channel are realized through a programmable gain amplification circuit, and the signal measurement dynamic range of the electric field logging instrument is ensured; the FPGA controls a plurality of channels of AD to finish signal acquisition, accumulating and denoising, storing the result in a double-port RAM arranged in the FPGA, informing a DSP to read data through interruption, finishing digital phase sensitive detection DSPD processing of 5 frequency signals of the plurality of channels, and forming 40 groups of real part data and 40 groups of imaginary part data; in a CAN communication period, the DSP completes the measurement of auxiliary parameters including the internal temperature and the working voltage of the measuring coil through the built-in AD, and the DSP completes data uploading through the built-in CAN through telemetering communication after data is framed.
6. A logging method for measuring the true resistivity of a stratum based on an electric field is characterized by comprising the following steps:
step 101, collecting electric field logging data in real time, and sending the logging data into an electric field logging data calibration unit;
step 201, an underground measuring mechanism measures and collects electric field data in real time, 40 real electric field signals of 5 different frequencies of a measuring and receiving coil system are obtained through a ground mobile data collecting mechanism (6) and are sent to an electric field data calibrating unit;
301, inputting the formation electric field signal output by the electric field data calibration unit into a logging data temperature correction unit, and using a formula and a temperature correction database
Calculating electric field measurement signal corresponding to temperature by interval linear interpolation
Subtracting the effect of electronics and coil system generation on the measurement signal due to formation temperature variations
Temperature correction is carried out on the 40 measured electric field signals to obtain 40 correction curves for eliminating temperature influence on electric field logging data;
step 401, inputting 40 data curves obtained by temperature correction into the apparent conductivity processing unit, combining with an electric field formula:
wherein k isA(x) As a propagation coefficient of the full space equivalent, i.e. the apparent propagation coefficient, in which
Step 402, inputting the 40 apparent conductivity data curves obtained by the apparent conductivity processing unit into the borehole correction processing unit, assuming the apparent conductivity σ of the well axisA(x1) Apparent conductivity σ as a boreholeA(z) the equivalent conductivity of all formations other than the borehole is σa1(z) well diameter r0Borehole mud conductivity is σ0By the formula:
iterative inversion processing is carried out on combined measurement electric field data to obtain sigmaa1(z) the conductivity equivalent in the space outside the borehole is the corrected conductivity σ for the boreholea1(z) wherein
Step 403, obtaining 40 data curves without borehole influence by the borehole correction processing unit, inputting the data curves into the layer thickness correction processing unit, wherein the conductivity of the target layer, i.e. the true conductivity, is σ (r), and the equivalent conductivity of all the strata except the target layer is σ (r)a2(x)；
By the formula:
wherein the lower interface of the target layerIs h1Upper boundary surface is h2Let σ bea2(x) Is equal to sigmaa1(x) Obtaining 40 data curves and electric fields E for removing the borehole influence by the borehole correction processing unit1(x) The expression jointly uses a self-adaptive iterative inversion algorithm to calculate the corresponding radial field point position coordinate and the true formation resistivity;
step 404, according to the curve passing of different field point coordinates of the layer thickness correction processing unit (403), establishing a resolution unified database h of 8 sub-arrays at 11 background conductivities sigma (0.001, 0.01, 0.02, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 and 2.0S/m)vfi(z) using the resolution formula σpvf(i+1)(z)＝hvfi(z)*σpvfi(z) wherein i is 1,2, …,4, σpvf(i+1)(z) is an objective function with uniform resolution; and (3) processing the curve after the resolution is processed uniformly by adopting a 5-parameter-based inversion algorithm to obtain the true formation resistivity Rt of 6 different position depths, namely completing the electric field logging process.
7. The method as claimed in claim 6, wherein the calibration unit accurately derives the measured electric field E of the coil system according to the electric field logging theory when calibrating the electric field datacSelecting two stable scale points of air and water medium; wherein air is used as the low point EcLThe conductivity is 0S/m; pool as high point EcHThe diameter of the circular pool is more than 20m or the depth of the pool is more than 10m, and the instrument response of the infinite uniform medium is calculated, wherein the calibration method comprises the following steps:
step 201.1, measuring the electric field intensity E of the low-pointmLOr the instrument is suspended and lifted above 5 meters away from the ground by induced electromotive force, and the electric field intensity of the electric field instrument in the air or the induced electromotive force is measured;
step 201.2, measuring high-point electric field intensity EmHOr the instrument is placed in the center of the water pool by inducing the electromotive force, and the electric field intensity of the electric field instrument at a high point is measured or the electromotive force is induced;
step 201.3, calibrating a formula E by using the high and low scalescH＝KEmH+ B and EcL＝KEmL+ B calculates the scale factor K, B to achieve the formation electric field signal calibrated for measurement.
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