High pressure adjusting device and method in underground X-ray density measurement

Abstract

The invention provides a high pressure adjusting device and method in underground X-ray density measurement. The device comprises a detector; the detector is connected with the X-ray source through a channel, and a filter is installed at the connecting position of the detector and the channel. The outer side of the detector is surrounded by a shielding body; photons reach the detector through the filter, and the filter filters low-energy photons and transmits a high-energy part of an initial spectrum to the detector. The method comprises the following steps: step 1, setting shielding body thickness of a channel and energy spectrums of different high voltages; 2, determining the relation between different high voltages and the normalized difference value; 3, determining the relationship between different high voltages and counting; and step 4, correcting different high voltages and counting to complete high voltage adjustment. According to the method, the change of the high pressure of the underground X-ray generator can be effectively monitored, the accuracy of the counting rate of the X-ray density logging is ensured, and the method has important significance on the calculation precision of the X-ray density logging.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield logging, and in particular to a device and method for regulating high pressure in downhole X-ray density measurement. Background Art

[0002] Lithology density logging is an important method to measure formation density and photoelectric absorption cross-section index. 137 Cs lithology density logging and X-ray source lithology density logging, 137 Cs lithology density logging uses the chemical element cesium, which is naturally radioactive. Although the X-rays in X-ray source lithology density logging are also radioactive, they can be controlled by turning the power on and off to minimize the harm to the human body. The output of high voltage may be unstable, and the fluctuations it produces will change the energy spectrum of the emitted photons. The measured count rate may introduce additional uncertainties, so it is necessary to improve the accuracy of density measurement by adjusting the output. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a medium and high pressure regulating device and method for underground X-ray density measurement, which has a reasonable design, overcomes the shortcomings of the prior art and has good effects.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A medium- and high-pressure regulating device for underground X-ray density measurement, comprising a detector;

[0006] The detector is connected to the X-ray source by a channel, and a filter is installed at the connection position between the detector and the channel; the outer side of the detector is surrounded by a shielding body;

[0007] The photons reach the detector through a filter, which filters out the low-energy photons and passes the high-energy portion of the initial spectrum to the detector.

[0008] Preferably, the filter is a tungsten filter.

[0009] A method for adjusting medium and high pressure in underground X-ray density measurement, comprising the following steps:

[0010] Step 1, setting the shield thickness of the channel and the energy spectrum of different high voltages;

[0011] Step 2, determining the relationship between different high pressures and the normalized difference;

[0012] Step 3, determining the relationship between different high voltages and counts;

[0013] Step 4, calibrate different high voltages and counts to complete high voltage regulation.

[0014] Preferably, in step 1, the X-ray detection system is simulated using Monte Carlo simulation, the detector receives the X-rays filtered by the filter, and the energy spectrum of the detector at different high voltages is obtained.

[0015] Furthermore, in step 1, the filter is made of a high-density material, the high-density material is tungsten, lead or tungsten-nickel-iron alloy, and the thickness ranges from 3 to 10 mm.

[0016] Preferably, in step 1, the thickness of the shielding body is in the range of 20-40 mm.

[0017] Preferably, in step 2, the high energy peak in the energy spectrum of different high pressures is divided into two windows, wherein the count of the left window is LW and the count of the right window is RW;

[0018] X-ray high pressure is defined as G by normalized difference, and G is expressed as:

[0019]

[0020] Determine the relationship between different high pressures and G factors; the relationship is obtained by fitting:

[0021] G=aU+b

[0022] Among them, a and b are coefficients, and U is the high voltage generated by the X-ray generator.

[0023] Preferably, in step 3, the instrument is simulated under different high pressure conditions by using Monte Carlo simulation; the ratio K of the counting rate under different high pressures to the counting rate under high pressure used when the instrument is working normally is obtained. U , K U It is expressed as:

[0024]

[0025] Among them, W U is the counting rate at different high voltages, and W0 is the counting rate under high voltage used when the instrument is working normally.

[0026] Preferably, in step 4, different high voltage G and count rate ratio K are established U The relationship between high voltage and count rate ratio K U The relationship between and G is used to correct the count rate.

[0027] Furthermore, different high voltage G and count rate ratio K U The formula is:

[0028]

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] The present invention provides a method for regulating high voltage in downhole X-ray density measurement. In the downhole application process, the high voltage of the X-ray generator of the logging tool is controlled according to the normalized difference between multiple windows of the high-energy peak value of the spectral data obtained by the monitoring detector, so that the X-ray source is stable, thereby obtaining higher density and photoelectric factor measurement accuracy. The present invention solves the counting error caused by the fluctuation of downhole X-ray high voltage and greatly improves the accuracy of X-ray density logging. The present invention can effectively monitor the change of the high voltage of the downhole X-ray generator and ensure the accuracy of the X-ray density logging count rate, which is of great significance to the calculation accuracy of X-ray density logging. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a device for high voltage regulation in X-ray density measurement.

[0032] Figure 2 It is a schematic diagram of the energy spectrum of different high-voltage monitoring detectors.

[0033] Figure 3 Yes Figure 2 Schematic diagram of separating the high-energy peak data into multiple windows.

[0034] Figure 4 is a schematic diagram of the dependence of the shape factor G on the energy at the end point of the X-ray system generator.

[0035] Figure 5 It is the relationship between different high pressure count ratios and high pressure in X-ray density logging tools.

[0036] Figure 6 It is a schematic diagram of artificially changing the high voltage of the X-ray generator.

[0037] Figure 7 This is a schematic diagram of measuring the change in detector count rate due to high voltage.

[0038] Figure 8 is the count rate after the detector is calibrated.

[0039] Fig. 9 is the relative error of the count rate after correction.

[0040] In the attached drawings: 1 is a channel; 2 is a filter; 3 is a detector; and 4 is a shielding body. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0042] The present invention provides a method for adjusting medium and high pressure in underground X-ray density measurement, which specifically comprises the following steps:

[0043] 1: Obtain the thickness of the shield 4 of channel 1 and the energy spectra of different high voltages;

[0044] Specifically, the X-ray detection system is simulated using Monte Carlo simulation, the monitoring detector 3 receives the X-rays filtered by the filter 2, and the energy spectrum of the monitoring detector is obtained;

[0045] 2: Determine the relationship between different high pressures and normalized differences;

[0046] Specifically, the high energy peaks of the energy spectra of different high pressures are divided into two windows, where the count of the left window is LW and the count of the right window is RW;

[0047] X-ray high pressure can be defined as G using the normalized difference, which can be expressed as:

[0048]

[0049] Determine the relationship between U and G factors at different high pressures; the relationship can be obtained by fitting:

[0050] G=aU+b

[0051] Among them, a and b are coefficients, respectively, and U is the high voltage generated by the X-ray generator;

[0052] 3: Determine the relationship between different high voltages and counts;

[0053] Specifically: Monte Carlo simulation is used to simulate the instrument under different high pressure conditions; the ratio of the counting rate under different high pressures to the counting rate under high pressure used when the instrument is working normally is obtained, and the ratio can be expressed by K U express:

[0054]

[0055] Among them, W U is the counting rate at different high voltages, and W0 is the counting rate under high voltage used when the instrument is working normally.

[0056] 4: Calibrate different high voltages and counts;

[0057] Specific: Establish different high voltage and K U The relationship between high pressure and K U The relationship between and G is used to correct the count rate.

[0058] The present invention provides a medium- and high-pressure regulating device for underground X-ray density measurement, comprising a detector 3 .

[0059] The monitoring detector crystal is surrounded by an inner shield, which may be made of a heavy material. In addition, a heavy metal filter (such as a tungsten filter) can be placed in the direct channel of the inner shield, which provides a path between the X-ray source and the monitoring detector. Therefore, photons can reach the monitoring detector only after passing through the heavy metal filter. The filter can filter low-energy photons, passing only the high-energy part of the initial spectrum to the monitoring detector, and a low-energy peak and a high-energy peak can be seen in the X-ray spectrum data. The position of the high-energy peak depends on the energy of the electron beam, and the low-energy peak is caused by the mutual excitation of some photons passing through the filter with the material of the filter (such as tungsten) resulting in fluorescence emission.

[0060] The peak position in the X-ray energy spectrum is not easy to determine. In addition, the count rate depends not only on the endpoint energy of the X-ray source, but also on the beam current. Therefore, it may be difficult to define the X-ray source high voltage using the peak position and the count rate at the peak. However, by dividing the high-energy peak into multiple windows, a form factor that is sensitive to the endpoint energy can be calculated. The counts in the left window to the left of the high-energy peak are referred to as LW here, and the counts in the right window are referred to as RW here. The X-ray source high voltage can be defined by the form factor (G) of the normalized difference, which is quite sensitive to the endpoint energy and of the X-ray source.

[0061] Example

[0062] X-ray density measurement in high voltage regulation Figure 1 As shown. The device is measured inside the X-ray density logging instrument. The monitoring detector is surrounded by a lead shield 4. The monitoring detector is connected to the X-ray source using channel 1. Filter 2 is located at the connection between the monitoring detector and channel 1. Therefore, photons can only pass through filter 2 to reach monitoring detector 3. Filter 2 will filter low-energy photons and then pass the high-energy part of the initial spectrum to monitoring detector 3. The result is as shown in Figure 2 shown.

[0063] In this embodiment, the filter 2 is made of a tungsten filter. The filter 2 can also be made of other high-density materials, such as heavy metals such as tungsten, lead, and tungsten-nickel-iron alloy.

[0064] On this basis, the normalized differences of multiple windows of high-energy peaks were determined, e.g. Figure 3 As shown, the subsequent output of the X-ray generator is monitored based on the normalized difference. The present invention can effectively monitor the change of the high voltage of the downhole X-ray generator, ensure the accuracy of the X-ray density logging count rate, and has important significance for the calculation accuracy of the X-ray density logging.

[0065] A medium- and high-pressure regulating device and method for underground X-ray density measurement, specifically comprising the following steps:

[0066] Step 1: Obtain the shielding thickness of the channel and the energy spectrum of different high voltages;

[0067] Specifically, the X-ray detection system is simulated using Monte Carlo simulation, the monitoring detector receives the X-rays filtered by tungsten, and the energy spectrum of the monitoring detector is obtained; in this embodiment, the thickness of the filter 3 is 3-10 mm, and the thickness of the shielding body 4 ranges from 20-40 mm.

[0068] Step 2: Determine the relationship between different high pressures and the normalized difference;

[0069] Specifically, the high energy peaks of the energy spectra of different high pressures are divided into two windows, where the count of the left window is LW and the count of the right window is RW;

[0070] X-ray high pressure can be defined as G using the normalized difference, which can be expressed as:

[0071]

[0072] Determine the relationship between different high pressures and G factors; the relationship can be obtained by fitting:

[0073] G=aU+b

[0074] Among them, a and b are coefficients respectively; U is the high voltage generated by the X-ray generator.

[0075] Step 3: Determine the relationship between different high voltages and counts; specifically: use Monte Carlo simulation to simulate the instrument under different high voltages; calculate the ratio of the count rate under different high voltages to the count rate under the high voltage used when the instrument is working normally, and the ratio can be expressed as K U express:

[0076]

[0077] Among them, W U is the counting rate at different high voltages, and W0 is the counting rate under high voltage used when the instrument is working normally.

[0078] Step 4: Calibrate different high voltages and counts;

[0079] Specific: Establish different high voltage and K U The relationship between high pressure and K U The relationship between and G is used to correct the counting rate. U The relationship formula is:

[0080]

[0081] The basic principle of the present invention is described below:

[0082] The monitoring detector crystal is surrounded by an inner shield, which may be made of a heavy material. In addition, a heavy metal filter (such as a tungsten filter) can be placed in the direct channel of the inner shield, which provides a path between the X-ray source and the monitoring detector. Therefore, photons can reach the monitoring detector only after passing through the heavy metal filter. The filter can filter low-energy photons, passing only the high-energy part of the initial spectrum to the monitoring detector, and a low-energy peak and a high-energy peak can be seen in the X-ray spectrum data. The position of the high-energy peak depends on the energy of the electron beam, and the low-energy peak is caused by the mutual excitation of some photons passing through the filter with the material of the filter (such as tungsten) resulting in fluorescence emission.

[0083] The peak position in the X-ray energy spectrum is difficult to determine. In addition, the count rate depends not only on the endpoint energy of the X-ray source, but also on the beam current. Therefore, it may be difficult to define the X-ray source high voltage using the peak position and the count rate at the peak. However, by dividing the high-energy peak into multiple windows, the form factor that is sensitive to the endpoint energy can be calculated. The counts in the left window to the left of the high-energy peak are referred to as LW here, and the counts in the right window are referred to as RW here. The X-ray source high voltage can be defined by the form factor (G) of the normalized difference, which is quite sensitive to the endpoint energy and of the X-ray source. The invention is further explained below through specific application examples:

[0084] Based on the above theoretical relationship, Monte Carlo simulation is used to simulate the response of different high-pressure X-rays in the formation. Figure 7 The method of the present invention is used to calibrate the counting rate of different high voltages. The corrected results and errors are shown in Figure 8 , Fig. 9 As shown. Figure 8 , Fig. 9 It can be seen that the present invention can well correct the change in count rate caused by high pressure fluctuation. Therefore, through the analysis of the above specific embodiments, it is shown that the present invention has a high accuracy in monitoring the count rate of X-ray density logging.

[0085] Of course, the above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A medium and high pressure regulating device for underground X-ray density measurement, characterized in that: including a detector (3); The detector (3) is connected to the X-ray source via a channel (1), and a filter (2) is installed at the connection position between the detector (3) and the channel (1); the outer side of the detector (3) is surrounded by a shielding body (4); The photons pass through the filter (2) and reach the detector (3), which will filter out the low-energy photons and pass the high-energy part of the initial spectrum to the detector (3).

2. The medium and high pressure regulating device for underground X-ray density measurement according to claim 1, characterized in that: The filter (2) is a tungsten filter.

3. A method for regulating medium and high pressure in underground X-ray density measurement, characterized in that: The following steps are included: Step 1, setting the thickness of the shielding body (4) of the channel (1) and the energy spectra of different high voltages; Step 2, determining the relationship between different high pressures and the normalized difference; Step 3, determining the relationship between different high voltages and counts; Step 4, calibrate different high voltages and counts to complete high voltage regulation.

4. A method for adjusting medium and high pressure in underground X-ray density measurement according to claim 3, characterized in that: In step 1, the X-ray detection system is simulated using Monte Carlo simulation, the detector (3) receives the X-rays filtered by the filter (2), and the energy spectrum of the detector (3) at different high voltages is obtained.

5. A method for adjusting medium and high pressure in underground X-ray density measurement according to claim 4, characterized in that: In step 1, the filter (2) is made of a high-density material, which is tungsten, lead or tungsten-nickel-iron alloy, and has a thickness ranging from 3 to 10 mm.

6. The method for adjusting medium and high pressure in underground X-ray density measurement according to claim 3, characterized in that: In step 1, the thickness of the shielding body (4) is in the range of 20-40 mm.

7. A method for adjusting medium and high pressure in underground X-ray density measurement according to claim 3, characterized in that: In step 2, the high energy peaks in the energy spectra of different high pressures are divided into two windows, where the count of the left window is LW and the count of the right window is RW; X-ray high pressure is defined as G by normalized difference, and G is expressed as: Determine the relationship between different high pressures and G factors; The relationship is obtained by fitting: G=aU+b Among them, a and b are coefficients respectively; U is the high voltage generated by the X-ray generator.

8. The method for adjusting medium and high pressure in underground X-ray density measurement according to claim 3, characterized in that: In step 3, the instrument is simulated under different high pressure conditions using Monte Carlo simulation; the ratio K of the counting rate under different high pressures to the counting rate under the high pressure used when the instrument is working normally is obtained. U , K U It is expressed as: Among them, W U is the counting rate at different high voltages, and W0 is the counting rate under high voltage used when the instrument is working normally.

9. The method for adjusting medium and high pressure in underground X-ray density measurement according to claim 3, characterized in that: In step 4, establish different high voltage G and count rate ratio K U The relationship between high voltage and count rate ratio K U The relationship between and G is used to correct the count rate.

10. A method for adjusting medium and high pressure in underground X-ray density measurement according to claim 8, characterized in that: Different high voltage G and count rate ratio K U The formula is:

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