Threaded borehole logging data positioning correction method based on correlation analysis

Abstract

The invention relates to the technical field of logging curve environment correction, and discloses a threaded borehole logging data positioning correction method based on correlation analysis, which comprises the following steps: extracting a logging curve influenced by a threaded borehole; according to the method, conversion from a time domain to a frequency domain is realized through wavelet transform, and a depth-frequency spectrum of a curve is obtained; identifying and extracting the characteristic parameters of the signal generated by the influence of the threaded borehole through a peak searching algorithm; filtering the original data based on the extracted characteristic parameters to obtain response curves of the threaded borehole in different logging methods; calculating the correlation of threaded borehole response curves of different logging methods, and positioning threaded borehole sections; and filtering the original data based on the threaded well section and the characteristic parameters of the signal generated by the threaded well influence to obtain a logging curve without the threaded well influence.

Description

Technical Field

[0001] The invention relates to the technical field of well logging curve environment correction, and in particular to a threaded wellbore logging data positioning correction method based on correlation analysis. Background Art

[0002] During the drilling operation, under the influence of geological factors, construction technology and other factors, threaded grooves may appear on the well wall of some sections of the well. In the same well, the grooves are of similar depth and evenly distributed, which is called the threaded wellbore phenomenon. On some logging curves, the response characteristics of the threaded wellbore are curves similar to chord waves and periodic oscillations. Affected by the threaded wellbore, some logging curves will have data distortion, which brings great difficulties to the logging interpretation work, and thus affects the accuracy of formation evaluation and oil and gas resource development.

[0003] To address the problem of distortion of logging curves caused by threaded wellbores, there are currently three methods: envelope correction, frequency domain filtering correction, and pre-casing and post-casing overlap correction. Among the three methods, the pre-casing and post-casing overlap correction method has a solid theoretical basis, but is difficult to be widely used due to construction conditions and data limitations; the envelope correction method is only applicable to curves with obvious fluctuations and vibrations; the frequency domain filtering correction can effectively remove the influence of threaded wellbores on the curve, but it may also eliminate the formation information recorded in the curve. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a threaded borehole logging data positioning correction method based on correlation analysis.

[0005] The present invention proposes a method for positioning and correcting threaded borehole logging data based on correlation analysis, comprising the following steps:

[0006] S1: Obtain several logging curves showing threaded borehole response characteristics;

[0007] S2: Perform continuous wavelet transform processing on each logging curve obtained in S1 to obtain the depth frequency spectrum corresponding to each curve;

[0008] S3: in the frequency spectra of each depth obtained in S2, identifying and extracting characteristic parameters of the signal generated by the threaded wellbore;

[0009] S4: Based on the characteristic parameters of the signal generated by the threaded wellbore obtained in S3, a filter is designed to filter each logging curve obtained in S1 to obtain the signal generated by the threaded wellbore in each curve;

[0010] S5: calculating the correlation of the signals generated by the threaded wellbore in each logging curve obtained in S4, setting a correlation threshold, and the well section with a correlation higher than the threshold is the well section affected by the threaded wellbore;

[0011] S6: Based on the characteristic parameters of the signal generated by the threaded wellbore obtained in S3 and the well section affected by the threaded wellbore obtained in S5, a filter is designed and a depth range for correction processing is input to obtain a logging curve that eliminates the influence of the threaded wellbore;

[0012] S7: Evaluate the correction quality. If the quality does not meet the standard, optimize the processing parameters and repeat S3 to S6. If the quality meets the standard, output the corrected logging curve to complete the correction process.

[0013] The present invention further provides that in S2, the step of obtaining the depth frequency spectrum is as follows: selecting an appropriate wavelet basis function, which should have frequency positioning capability and time-frequency local enhancement capability, taking the depth sampling interval equivalent to the time sampling interval, performing continuous wavelet transform on the logging curve obtained in S1, and obtaining the depth frequency spectrum of the logging curve.

[0014] The present invention further comprises the following steps in S3 for obtaining characteristic parameters of a signal generated by the influence of a threaded wellbore: the depth frequency spectrum obtained in S2 is subjected to median filtering over a depth range to achieve the effect of weakening the frequency characteristics of the non-threaded wellbore signal, and peak searching is performed at each frequency point and each depth point in turn to obtain the frequency characteristic parameters of the signal generated by the threaded wellbore.

[0015] The present invention further provides that in S4, the filter is a finite-length unit impulse response bandpass filter.

[0016] The present invention further comprises the following steps in S5: taking the signals generated by the threaded borehole in the two different logging curves obtained in S4, setting a suitable depth window length, calculating the correlation of the data in the window, moving the window and calculating the correlation of the data in the next window length, until the calculation of the data of the entire well section is completed. The correlation threshold is selected by statistical analysis.

[0017] The present invention further provides that in S6, the filter is a finite length unit impulse response band-stop or low-pass filter.

[0018] The present invention further provides that in S7, the degree to which the logging curve is affected by the threaded wellbore is quantified.

[0019] The present invention provides a threaded wellbore logging curve positioning correction method, comprising the following modules:

[0020] A data extraction module, used to obtain well logging curves;

[0021] The time-frequency domain conversion module is used to realize the conversion of the logging curve from the depth-amplitude domain to the depth-frequency domain, and obtain the depth frequency spectrum of the logging curve;

[0022] A characteristic parameter extraction module is used to weaken the frequency characteristics of non-threaded borehole signals in the depth frequency spectrum of the logging curve, and to identify and obtain the frequency characteristic parameters of the signals generated by the threaded borehole;

[0023] A correlation calculation module is used to calculate the correlation of signals generated by the threaded wellbore between different logging curves, obtain the correlation coefficient and select the threshold;

[0024] The FIR filter module is used to design a filter based on the frequency characteristic parameters of the signal generated by the threaded wellbore, select the filter working mode, and filter the logging curve;

[0025] The quality analysis module is used to analyze the correction quality of the curve, quantify the degree to which the curve is affected by the threaded wellbore, and obtain quality parameters;

[0026] A curve output module is used to output the corrected logging curve;

[0027] The data processing module is used to call other modules to realize the complete functions of the method.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1; The present invention proposes a threaded borehole logging data positioning correction method based on correlation analysis, which can automatically identify the signal generated by the threaded borehole in the logging curve and extract its frequency response characteristics.

[0030] 2. Based on the frequency characteristics, four finite-length unit impulse response filters can be automatically designed and applied to corresponding scenarios.

[0031] 3. It can automatically locate and record the well section with threaded borehole phenomenon; it can filter the logging curve affected by the thread to eliminate the influence of the threaded borehole in the logging curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A threaded wellbore logging curve correction processing flow chart of a threaded wellbore logging data positioning correction method based on correlation analysis proposed by the present invention;

[0033] Figure 2 The depth frequency spectra of two logging curves of a threaded borehole logging data positioning correction method based on correlation analysis proposed by the present invention;

[0034] Figure 3 A statistical diagram of correlation coefficients of signals generated by different well sections affected by threaded wellbore in a threaded wellbore logging data positioning correction method based on correlation analysis proposed by the present invention;

[0035] Figure 4 A comparison chart of correction results of different well sections of a threaded borehole logging data positioning correction method based on correlation analysis proposed by the present invention using existing correction technology and the positioning correction method proposed by the present invention;

[0036] Figure 5 This is a display diagram of the correction results of the positioning correction method of threaded wellbore logging data based on correlation analysis proposed by the present invention in four types of logging curves. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0038] This paper proposes a threaded borehole logging curve positioning correction method based on correlation analysis, which can achieve the function of obtaining the characteristic parameters of the signal generated by the threaded borehole, automatically locating the well section affected by the threaded borehole, and combining the band-stop filter for filtering processing to eliminate the influence of the threaded borehole and retain the correction effect of the formation information. The processing flow of the invention is shown in Figure 1 .

[0039] Example

[0040] Step 1: Select two curves that are severely affected by the threaded wellbore and have obvious repeated oscillation phenomenon. In this example, the wellbore CAL curve and the compensated acoustic time difference DT curve are selected;

[0041] Step 2: Perform continuous wavelet transform on the wellbore CAL curve and the compensated acoustic time difference DT curve obtained in step 1 to obtain the depth frequency spectrum, such as Figure 2 As shown;

[0042] Step 3: Set a median filter window and perform median filtering on the depth range of the depth frequency spectrum to achieve the effect of weakening the frequency characteristics of the non-threaded borehole signal. Perform peak search at each frequency point and each depth point to obtain the frequency characteristic parameters of the signal generated by the threaded borehole;

[0043] Step 4: Based on the frequency characteristic parameters of the signal generated by the threaded wellbore obtained in step 3, a FIR bandpass filter is designed to extract the signals generated by the threaded wellbore in the wellbore CAL curve and the compensated acoustic time difference DT curve respectively;

[0044] Step 5: Set a correlation calculation depth window, move the window along the depth axis, calculate the correlation of the wellbore CAL curve and the compensated acoustic time difference DT curve in the window in turn, record the correlation coefficient, count the correlation coefficients of different well sections and select the threshold, such as Figure 4As shown, the correlation threshold selected in this processing is 0.7;

[0045] Step 6: The well section with correlation above the threshold is regarded as the threaded well section, and the well section with correlation below the threshold is regarded as the non-threaded well section. Based on the frequency characteristic parameters of the signal generated by the threaded well obtained in step 3, a FIR band-stop filter is designed, and filtering is performed on the threaded well section to obtain the corrected compensated acoustic time difference DT curve;

[0046] Step 7: Evaluate the calibration quality. If the calibration quality does not meet the standard, return to step 3 or step 5, manually set the median filter parameters, correlation calculation parameters and thresholds until the calibration quality meets the standard. If the calibration quality meets the standard, output the calibrated curve.

[0047] Using the above technical steps, the threaded borehole effect in the logging curve can be effectively removed, such as Figure 4 (c)

[0048] Using the above technical steps, the part of the well logging curve that records the formation information can be effectively retained, such as Figure 4 (a) Figure 4 (b)

[0049] Using the above technical steps, various logging curves seriously affected by threaded boreholes can be corrected, while eliminating the influence of threaded boreholes and retaining valid data recording formation information, such as Figure 5 shown.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for positioning and correcting threaded borehole logging data, characterized in that: The following steps are involved: S1: Obtain several logging curves showing threaded borehole response characteristics; S2: Perform continuous wavelet transform processing on each logging curve obtained in S1 to obtain the depth frequency spectrum corresponding to each curve; S3: in the frequency spectra of each depth obtained in S2, identifying and extracting characteristic parameters of the signal generated by the threaded wellbore; S4: Based on the characteristic parameters of the signal generated by the threaded wellbore obtained in S3, a filter is designed to filter each logging curve obtained in S1 to obtain the signal generated by the threaded wellbore in each curve; S5: calculating the correlation of the signals generated by the threaded wellbore in each logging curve obtained in S4, setting a correlation threshold, and the well section with a correlation higher than the threshold is the well section affected by the threaded wellbore; S6: Based on the characteristic parameters of the signal generated by the threaded wellbore obtained in S3 and the well section affected by the threaded wellbore obtained in S5, a filter is designed and a depth range for correction processing is input to obtain a logging curve that eliminates the influence of the threaded wellbore; S7: Evaluate the correction quality. If the quality does not meet the standard, optimize the processing parameters and repeat S1 to S6. If the quality meets the standard, output the corrected logging curve to complete the correction process.

2. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S2, the steps for obtaining the depth frequency spectrum are as follows: select an appropriate wavelet basis function, which should have frequency positioning capability and time-frequency local enhancement capability, use the depth sampling interval equivalent to the time sampling interval, perform continuous wavelet transform on the logging curve obtained in S1, and obtain the depth frequency spectrum of the logging curve.

3. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S3, the steps for obtaining characteristic parameters of the signal generated by the threaded wellbore are as follows: the depth frequency spectrum obtained in S2 is subjected to median filtering over a depth range to achieve the effect of weakening the frequency characteristics of the non-threaded wellbore signal, and peak searching is performed at each frequency point and each depth point in turn to obtain the frequency characteristic parameters of the signal generated by the threaded wellbore.

4. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S4, the filter is a finite-length unit impulse response bandpass filter.

5. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S5, the steps of calculating the correlation and setting the correlation threshold are as follows: taking the signals generated by the threaded borehole in the two different logging curves obtained in S4, setting a suitable depth window length, calculating the correlation of the data in the window, moving the window and calculating the correlation of the data in the next window length, until the calculation of the data of the entire well section is completed. The correlation threshold is selected by statistical analysis.

6. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S6, the filter is a finite-length unit impulse response band-stop or low-pass filter.

7. The threaded borehole logging data positioning correction method according to claim 1, characterized in that: In S7, the degree to which the logging curve is affected by the threaded wellbore is quantified.

8. A threaded borehole logging data positioning and correction system, characterized in that: Includes the following modules: A data extraction module, used to obtain well logging curves; The time-frequency domain conversion module is used to realize the conversion of the logging curve from the depth-amplitude domain to the depth-frequency domain, and obtain the depth frequency spectrum of the logging curve; A characteristic parameter extraction module is used to weaken the frequency characteristics of non-threaded borehole signals in the depth frequency spectrum of the logging curve, and to identify and obtain the frequency characteristic parameters of the signals generated by the threaded borehole; A correlation calculation module is used to calculate the correlation of signals generated by the threaded wellbore between different logging curves, obtain the correlation coefficient and select the threshold; The FIR filter module is used to design a filter based on the frequency characteristic parameters of the signal generated by the threaded wellbore, select the filter working mode, and filter the logging curve; The quality analysis module is used to analyze the correction quality of the curve, quantify the degree to which the curve is affected by the threaded wellbore, and obtain quality parameters; A curve output module is used to output the corrected logging curve; The data processing module is used to call other modules to realize the complete functions of the method.

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