A high-pressure regulating device and method for downhole X-ray density measurement

Abstract

This invention provides a high-pressure adjustment device and method for downhole X-ray density measurement. The device includes a detector; a channel connects the detector and an X-ray source, and a filter is installed at the connection point between the detector and the channel; a shield surrounds the detector; photons pass through the filter to reach the detector, where the filter filters out low-energy photons and transmits the high-energy portion of the initial spectrum to the detector. The method includes the following steps: Step 1, setting the shield thickness of the channel and the energy spectrum of different high pressures; Step 2, determining the relationship between different high pressures and the normalized difference; Step 3, determining the relationship between different high pressures and the count; Step 4, correcting the different high pressures and the count to complete the high-pressure adjustment. This invention can effectively monitor changes in the high pressure of the downhole X-ray generator, ensuring the accuracy of the X-ray density logging count rate, which is of great significance to the accuracy of X-ray density logging calculations.

Description

Technical Field

[0001] This invention belongs to the field of oilfield logging technology, specifically to a device and method for high-pressure adjustment in downhole X-ray density measurement. Background Technology

[0002] Lithology density logging is an important method for measuring formation density and photoelectric absorption cross section index. Lithology density logging includes... 137 Cs lithological density logging and X-ray source lithological density logging, 137 Cs lithology density logging uses the chemical element cesium, which is naturally radioactive. While X-rays from X-ray source lithology density logging are also radioactive, they can be controlled by switching the power on and off, minimizing harm to humans. High-pressure output can be unstable, and fluctuations can alter the energy spectrum of emitted photons, potentially introducing additional uncertainty into the measured count rate. Therefore, adjusting the output is necessary to improve the accuracy of density measurements. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a high-pressure adjustment device and method for downhole X-ray density measurement. The device is rationally designed, overcomes the shortcomings of the prior art, and has good performance.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A high-pressure regulating device for downhole X-ray density measurement, including a detector;

[0006] The detector is connected to the X-ray source via a channel, and a filter is installed at the connection point between the detector and the channel; the detector is surrounded by a shield.

[0007] Photons pass through a filter to reach the detector. The filter filters out 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 high-pressure adjustment in downhole X-ray density measurement includes the following steps.

[0010] Step 1: Set the shielding thickness of the channel and the energy spectrum for different high voltages;

[0011] Step 2: Determine the relationship between different high voltages and the normalized difference;

[0012] Step 3: Determine the relationship between different high voltages and counting;

[0013] Step 4: Correct the different high voltages and counters to complete the 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 is obtained at different high voltages.

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

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

[0017] Preferably, in step 2, the high-energy peaks in the energy spectrum of different high pressures are divided into two windows, where the count in the left window is LW and the count in the right window is RW.

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

[0019]

[0020] The relationship between different high pressures and the G factor was determined; this relationship was obtained through fitting:

[0021] G = aU + b

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

[0023] Preferably, in step 3, Monte Carlo simulation is used to simulate the instrument under different high-pressure conditions; the ratio K of the count rate under different high pressures to the count rate under the high pressure used when the instrument is operating normally is calculated. U K U Represented as:

[0024]

[0025] Among them, W U The count rates are for different high voltages, where W0 is the high voltage used when the instrument is operating normally.

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

[0027] Furthermore, the ratio of different high voltages G to count rates K U The formula is:

[0028]

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

[0030] This invention provides a high-pressure adjustment method for downhole X-ray density measurement. During downhole applications, the high pressure of the X-ray generator in the logging tool is controlled based on the normalized difference between multiple windows of high-energy peak values ​​obtained from the spectral data monitored by the detector. This stabilizes the X-ray source, thereby achieving higher accuracy in density and photoelectric factor measurements. This invention solves the counting error caused by downhole X-ray high-pressure fluctuations, significantly improving the accuracy of X-ray density logging. This invention can effectively monitor changes in the high pressure of the downhole X-ray generator, ensuring the accuracy of the X-ray density logging count rate, which is of great significance for the accuracy of X-ray density logging calculations. Attached Figure Description

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

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

[0033] Figure 3 It is Figure 2 A schematic diagram showing the high-energy peak data separated into multiple windows.

[0034] Figure 4 This is a schematic diagram showing the dependence of the form factor G on the energy at the X-ray system generator endpoint.

[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 This is a schematic diagram showing the artificial alteration of the high voltage in an X-ray generator.

[0037] Figure 7 This is a schematic diagram showing how the detector's count rate changes under high voltage.

[0038] Figure 8 It is the count rate after the monitoring detector has been calibrated.

[0039] Figure 9 It is the relative error of the corrected count rate.

[0040] In the attached diagram: 1 is the channel; 2 is the filter; 3 is the detector; 4 is the shield. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0042] This invention provides a high-pressure adjustment method for downhole X-ray density measurement, specifically including the following steps:

[0043] 1: Determine the thickness of the shield 4 of channel 1 and the energy spectrum at different high voltages;

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

[0045] 2: Determine the relationship between different high voltages and the normalized difference;

[0046] Specifically, the high-energy peaks of the energy spectrum at different high pressures are divided into two windows, with the count in the left window being LW and the count in the right window being RW.

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

[0048]

[0049] The relationship between the U and G factors under different high pressures can be determined; this relationship can be obtained through fitting.

[0050] G = aU + b

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

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

[0053] Specifically: Monte Carlo simulation is used to simulate the instrument under different high-pressure conditions; the ratio of the count rate under different high-pressure conditions to the count rate under the high-pressure condition when the instrument is operating normally is calculated, and this ratio can be represented by K. U express:

[0054]

[0055] Among them, W U The count rates are for different high voltages, where W0 is the high voltage used when the instrument is operating normally.

[0056] 4: Calibrate for different high voltages and counting methods;

[0057] Specifically: Establish different high voltages and K U The relationship between high pressure and K; U The relationship between G and the count rate is used to correct for the count rate.

[0058] The present invention discloses a high-pressure adjustment device for downhole X-ray density measurement, comprising a detector 3.

[0059] The monitoring detector crystal is surrounded by an internal shield, which may be made of a heavy material. Furthermore, a heavy metal filter (e.g., a tungsten filter) can be placed in the direct channel of the internal shield, providing a path between the X-ray source and the monitoring detector. Therefore, photons can only reach the monitoring detector after passing through the heavy metal filter. The filter filters out low-energy photons, delivering only the high-energy portion of the initial spectrum to the monitoring detector, resulting in a low-energy peak and a high-energy peak visible in the X-ray spectral data. The position of the high-energy peak depends on the energy of the electron beam, while the low-energy peak is caused by fluorescence emission resulting from the mutual excitation of some photons passing through the filter with the filter material (e.g., tungsten).

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

[0061] Example

[0062] High voltage adjustment in X-ray density measurement, such as Figure 1 As shown in the diagram, this device measures inside an X-ray density logging instrument. The monitoring detector is surrounded by a lead shield 4, and a channel 1 connects the monitoring detector to the X-ray source. A filter 2 is located at the connection point between the monitoring detector and channel 1. Therefore, photons can only reach the monitoring detector 3 through filter 2. Filter 2 filters out low-energy photons and then transmits the high-energy portion of the initial spectrum to the monitoring detector 3, as shown in the diagram. Figure 2 As shown.

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

[0064] Based on this, multiple window-normalized differences for high-energy peak values ​​were determined, such as... Figure 3 As shown, the subsequent output of the X-ray generator is monitored based on this normalized difference. This invention can effectively monitor changes in the high pressure of the downhole X-ray generator, ensuring the accuracy of the X-ray density logging count rate, which is of great significance to the accuracy of X-ray density logging calculations.

[0065] A high-pressure adjustment device and method for downhole X-ray density measurement, specifically including the following steps:

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

[0067] Specifically, the X-ray detection system is simulated using Monte Carlo simulation, and the energy spectrum of the detector is obtained by monitoring the X-rays received by the detector after tungsten filtering. In this embodiment, the thickness of filter 3 is 3-10mm, and the thickness of shield 4 is 20-40mm.

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

[0069] Specifically, the high-energy peaks of the energy spectrum at different high pressures are divided into two windows, with the count in the left window being LW and the count in the right window being RW.

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

[0071]

[0072] The relationship between different high pressures and the G factor can be determined; this relationship can be obtained through fitting:

[0073] G = aU + b

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

[0075] Step 3: Determine the relationship between different high voltages and counting; specifically: use Monte Carlo simulation to simulate the instrument under different high voltage conditions; calculate the ratio of the counting rate under different high voltages to the counting rate under the high voltage used when the instrument is operating normally. This ratio can be represented by K. U express:

[0076]

[0077] Among them, W U The count rates are for different high voltages, where W0 is the high voltage used when the instrument is operating normally.

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

[0079] Specifically: Establish different high voltages and K U The relationship between high pressure and K; U The relationship between G and K is used to correct the count rate. Ultimately, different high voltages and K... U The formula relating them is:

[0080]

[0081] The basic principles of this invention are explained below:

[0082] The monitoring detector crystal is surrounded by an internal shield, which may be made of a heavy material. Furthermore, a heavy metal filter (e.g., a tungsten filter) can be placed in the direct channel of the internal shield, providing a path between the X-ray source and the monitoring detector. Therefore, photons can only reach the monitoring detector after passing through the heavy metal filter. The filter filters out low-energy photons, delivering only the high-energy portion of the initial spectrum to the monitoring detector, resulting in a low-energy peak and a high-energy peak visible in the X-ray spectral data. The position of the high-energy peak depends on the energy of the electron beam, while the low-energy peak is caused by fluorescence emission resulting from the mutual excitation of some photons passing through the filter with the filter material (e.g., tungsten).

[0083] The peak position in the X-ray energy spectrum is difficult to determine. Furthermore, 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 high voltage of an X-ray source using only the peak position and the count rate below the peak. However, by dividing the high-energy peak into multiple windows, a form factor sensitive to the endpoint energy can be calculated. The count in the left window to the left of the high-energy peak is referred to here as LW, and the count in the right window is referred to here as RW. The high voltage of the X-ray source can be defined using the normalized difference form factor (G), which is quite sensitive to the endpoint energy of the X-ray source. The invention is further illustrated below with specific application examples:

[0084] Based on the above theoretical relationships, Monte Carlo simulations were used to model the response of different high-pressure X-rays in the formation, as follows: Figure 7 As shown. The method of this invention is used to correct the count rate for different high voltages. The corrected results and errors are shown below. Figure 8 , Figure 9 As shown. According to Figure 8 , Figure 9 As can be seen, this invention can effectively correct for changes in the count rate caused by high-pressure fluctuations. Therefore, the analysis of the above specific embodiments demonstrates that this invention has a high accuracy rate for monitoring the count rate in X-ray density logging.

[0085] Of course, the above specific embodiments further illustrate the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments 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 within the scope of protection of the present invention.

Claims

1. A method for high voltage regulation in downhole X-ray density measurements, characterized by, The method adopts a high-voltage adjusting device in downhole X-ray density measurement, comprising a detector (3); The detector (3) is connected with an X-ray source through a channel (1), and a filter (2) is installed at the connecting position of the detector (3) and the channel (1); and a shielding body (4) surrounds the outside of the detector (3); Photons reach the detector (3) through the filter (2), and the filter (2) filters low-energy photons and transmits high-energy parts of the initial spectrum to the detector (3); The method Comprises the following steps, Step 1, setting the thickness of the shielding body (4) of the channel (1) and the energy spectrum of different high pressures; Step 2, determining the relationship between different high pressures and normalized difference values; Step 3, determine the relationship between different high voltage and count; use Monte Carlo simulation to simulate the instrument under different high voltage; calculate the count rate under different high voltage and the count rate ratio K of the instrument under normal working condition and the high voltage used U , K U is expressed as: Among them, W U The count rates are for different high voltages, where W0 is the count rate at the high voltage used when the instrument is working normally. Step 4, correct the different high pressure and count, complete the high pressure adjustment; the G factor of different high pressure and the count rate ratio K U The formula is: 。 2. The method for high voltage regulation in downhole X-ray density measurement according to claim 1, characterized in that, The filter (2) is a tungsten filter.

3. The method of claim 1, wherein, In step 1, the X-ray detection system is simulated by Monte Carlo simulation, the detector (3) receives the filtered X-rays of the filter (2), and the energy spectrum of the detector (3) under different high pressures is obtained.

4. The method of claim 3, wherein the high voltage is regulated by a feedback loop. In step 1, the filter (2) is made of high-density material, and the high-density material is tungsten, lead or tungsten-nickel-iron alloy, and the thickness range is 3-10mm.

5. The method of claim 1, wherein, In step 1, the thickness of the shielding body (4) is 20-40mm.

6. The method of claim 1, wherein, In step 2, the high-energy peak in the energy spectrum of different high pressures is divided into two windows, and the count of the left window is LW and the count of the right window is RW; The X-ray high voltage is defined as the normalized difference value G, and G is expressed as: Determine the relationship between different high pressures and G factor; The relationship is obtained by fitting as follows: Wherein, a and b are coefficients; U is the high voltage generated by the X-ray generator.

7. The method of claim 1, wherein, In step 4, the relationship between the G-factor and the count rate ratio K at different high pressures is established; the count rate is corrected according to the relationship between the G-factor and the count rate ratio K. U In step 4, the relationship between the G-factor and the count rate ratio K at different high pressures is established; the count rate is corrected according to the relationship between the G-factor and the count rate ratio K. U In step 4, the relationship between the G-factor and the count rate ratio K at different high pressures is

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