Method for determining formation bulk density using a pulsed neutron gamma density logging tool

Abstract

The application discloses a method for determining formation bulk density by using a pulsed neutron gamma density logging instrument, and comprises the following steps: placing the pulsed neutron gamma density logging instrument in a calibration well to run, establishing a standard response formula between the response result of the logging instrument and the formation bulk density, then placing the logging instrument in two secondary calibration cylinders with different bulk densities respectively, and calibrating and transmitting values of the two secondary calibration cylinders; using the two secondary calibration cylinders to perform primary calibration and verification of the logging instrument; using a calibrator to perform pre-measurement calibration response of the verified logging instrument before logging, then placing the logging instrument in an unknown well to perform measurement, after the measurement is completed, using the calibrator to perform post-measurement calibration response of the logging instrument again, comparing the pre-measurement calibration response value with the post-measurement calibration response value, and thus the formation bulk density in the unknown well is determined. The method effectively ensures the reliability of the test result through primary calibration, secondary calibration and tertiary calibration.

Description

Technical Field

[0001] This invention belongs to the field of pulsed neutron source logging technology in oil and gas exploration, and relates to a method for determining formation volume density using a pulsed neutron gamma density logging tool. Background Technology

[0002] Pulsed neutron gamma density logging works by detecting inelastic gamma rays generated by fast neutrons. These rays interact with electrons in the formation via a series of interactions (primarily Compton scattering) before reaching a gamma detector and being recorded. The recorded gamma rays are then used to calculate the formation electron density, which in turn is used to calculate the formation volume density. This technique effectively avoids the radioactive threats associated with using radioactive isotope sources in formation logging.

[0003] Before conducting logging operations, pulsed neutron gamma density logging tools require calibration in a model well with known physical parameters. This calibration process involves calculating the conversion coefficient between the instrument's response and the engineering quantity. Existing logging methods only calibrate the instrument in a standard well group before directly testing it in the well. However, over long-term use, pulsed neutron gamma density logging tools experience issues such as instrument wear and changes in the stability of electronic components. Furthermore, the performance of electronic components varies among multiple instruments produced in batches. Existing testing methods cannot guarantee the testing stability of individual instruments, the reliability of test results, or the consistency between instruments in a batch. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for determining formation volume density using a pulsed neutron gamma density logging instrument, thereby effectively solving the problems of stability in long-term use of pulsed neutron gamma density logging instruments and consistency of test results among batches of instruments.

[0005] This invention is achieved through the following technical solution:

[0006] A method for determining formation volume density using a pulsed neutron gamma density logging tool includes the following steps:

[0007] S1: The pulsed neutron gamma density logging tool is operated in several standard wells with different lithologies and densities in a full-space calibration process. A standard response formula is established between the response result of the pulsed neutron gamma density logging tool and the formation volume density. Then, the pulsed neutron gamma density logging tool is placed in secondary calibration cylinders M1 and M2 respectively. Based on the standard response formula, the secondary calibration cylinders M1 and M2 are calibrated and their volume densities are obtained. The volume densities of the secondary calibration cylinders M1 and M2 are different.

[0008] S2: Use the secondary scale cylinder M1 to perform main calibration on the logging tool to obtain the calibration factor of the logging tool; then place the logging tool in the secondary scale cylinder M2 for measurement, and combine the calibration factor to complete the calibration of the logging tool;

[0009] S3: Before logging using a pulsed neutron gamma density logging tool, use a calibrator to perform a pre-logging response on the calibrated logging tool. Then, place the logging tool in the unknown well for testing. After the test is completed, use the calibrator again to perform a post-logging response on the logging tool. Compare the pre-logging response value with the post-logging response value to determine the formation volume density in the unknown well.

[0010] Preferably, the standard response formula in step S1 is as follows:

[0011]

[0012] Where, f1(lnR) n )=a1(lnR n ) 3 +a2(lnR n ) 2 +a3(lnR n )+a4

[0013] f2(lnR n )=b1(lnR n ) 2 +b2(lnR n )+b3

[0014] In the formula, ρ b is the formation volume density of the full-space calibrated well; a1, a2, a3, a4, b1, b2, b3 and A are the fitting coefficients;

[0015] ln R γ1 is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the first gamma window;

[0016] ln R γ2 is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the second gamma window;

[0017] lnR n This is the natural logarithm of the ratio of thermal neutron count rates.

[0018] Preferably, the process of obtaining the inelastic scattering gamma count rate ratio of the first gamma window and the inelastic scattering gamma count rate ratio of the second gamma window is as follows:

[0019]

[0020] In the formula, R γ1 The ratio of the inelastic scattering gamma count rate of the first gamma window;

[0021] N1 is the count rate of the first gamma energy window of the first pure gamma non-elastic spectrum data;

[0022] N2 is the count rate of the first gamma energy window of the second pure gamma non-elastic spectrum data;

[0023]

[0024] In the formula, R γ2 The ratio of the inelastic scattering gamma count rate of the second gamma window;

[0025] M1 is the count rate of the second gamma energy window of the first pure gamma non-elastic spectrum data;

[0026] M2 is the count rate of the second gamma energy window of the second pure gamma non-elastic spectrum data;

[0027] The process of obtaining the thermal neutron count rate ratio is as follows:

[0028]

[0029] In the formula, R n This is the ratio of thermal neutron count rates;

[0030] Q1 represents the first thermal neutron count rate data;

[0031] Q2 represents the second thermal neutron count rate data.

[0032] Preferably, the process of acquiring the first pure gamma non-ballistic spectrum data and the second pure gamma non-ballistic spectrum data is as follows:

[0033]

[0034]

[0035] In the formula, N1 represents the first pure gamma non-elastic spectrum data. This is the first gamma mixture spectrum data. This is the first gamma capture spectrum data;

[0036] N2 represents the second pure gamma non-elastic spectrum data. This is the second gamma mixture spectrum data. For the second gamma capture spectrum data;

[0037] α is a preset coefficient.

[0038] Preferably, in step S2, the calibration factor includes calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio; the processes for obtaining the calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are as follows:

[0039]

[0040] In the formula, K1 is the scale factor for the ratio of inelastic scattering gamma count rate of the first gamma window;

[0041] K2 is the scale factor for the ratio of inelastic scattering gamma count rate of the second gamma window;

[0042] K3 is the scale factor for the thermal neutron count rate ratio;

[0043] ln R M1γ1 ln R M1γ2 and ln R M1n The natural logarithm values ​​of the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are obtained during the calibration transfer in the secondary scale cylinder M1 in step S1.

[0044] as well as The natural logarithm values ​​are the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio, obtained during the main calibration in the secondary calibration cylinder M1 in step S2.

[0045] Preferably, K1, K2, and K3 are all greater than 0.95 and less than 1.05.

[0046] Preferably, the calibration process of the logging tool in step S2 specifically involves: performing measurements in the secondary graduated cylinder M2 to obtain... and And the calibration density value of the secondary graduated cylinder M2 is obtained.

[0047]

[0048] In the formula, as well as To perform measurements in the secondary graduated cylinder M2, the ratio of inelastic scattered gamma count rate of the first gamma window, the ratio of inelastic scattered gamma count rate of the second gamma window, and the ratio of thermal neutron count rate were obtained.

[0049] The calibration density value of the secondary graduated cylinder M2 The volume density ρ of the secondary graduated cylinder M2 obtained in step S1 M2b If a comparison is made, In ρ M2b ±0.015g / cm 3 Within the specified range, the logging instrument is calibrated.

[0050] Preferably, in step S3, the results of the pre-measurement and post-measurement calibrations are compared to determine the formation volume density in the unknown well, specifically as follows:

[0051]

[0052] In the formula, The ratio of the inelastic scattering gamma count rate of the first gamma window of the post-measurement calibration response;

[0053] The ratio of the inelastic scattering gamma count rate of the first gamma window of the pre-measurement calibration response;

[0054] The ratio of the inelastic scattering gamma count rate of the second gamma window in the post-measurement calibration response;

[0055] The ratio of the inelastic scattering gamma count rate of the second gamma window in the pre-measurement calibration response;

[0056] The ratio of thermal neutron count rates in the post-measurement calibration response;

[0057] The ratio of thermal neutron count rates in the pre-measurement calibration response;

[0058] If δ1, δ2, and δ3 are all greater than 0.95 and less than 1.05, then the determination of the formation volume density in the unknown well is complete.

[0059] Preferably, the density range of the full-space graduated well is 1.68 g / cm³. 3 ~2.92g / cm 3 .

[0060] Preferably, the full-space graduated well includes any one of the following formations: concrete formation, limestone formation, sandstone formation, and dolomite formation.

[0061] Compared with the prior art, the present invention has the following beneficial technical effects:

[0062] A method for determining formation volumetric density using a pulsed neutron gamma density logging tool involves first running the tool in a fully calibrated well to establish a standard response formula between the tool's response and the formation volumetric density of a standard well. Then, calibration values ​​are transferred using secondary calibration cylinders with different volumetric densities for subsequent secondary calibration, thus completing the first-level calibration. Further, the calibrated secondary calibration cylinder M1 is used for the main calibration of the logging tool, and a calibrated secondary calibration cylinder M2 is used for measurement verification, thus completing the second-level calibration. This effectively ensures the stability of the logging tool after long-term use or storage, or the consistency among multiple instruments from the same batch. Finally, before and after testing unknown wells, the logging tool is recalibrated using a calibrator, completing the third-level calibration. The third-level calibration is used to determine the logging tool's operating status, effectively ensuring the reliability of the test results.

[0063] Furthermore, K1, K2, and K3 are all greater than 0.95 and less than 1.05, effectively ensuring the stability of a single instrument or the consistency of multiple instruments in the same batch.

[0064] Furthermore, if In ρ M2b ±0.015g / cm 3 Within the specified range, the logging tool is calibrated, effectively ensuring its stability during long-term use.

[0065] Furthermore, if δ1, δ2, and δ3 are all greater than 0.95 and less than 1.05, the formation volume density in the unknown well is determined, effectively ensuring the reliability of the test results. Attached Figure Description

[0066] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a schematic diagram of the process for determining formation volume density using a pulsed neutron gamma density logging tool in this invention.

[0068] Figure 2 This is a schematic diagram of the structure of a pulsed neutron gamma density logging instrument according to the present invention;

[0069] Figure 3A schematic diagram of the full-space first-stage density standard calibration well (vertical) structure of the pulsed neutron gamma density logging tool provided in Embodiment 2 of the present invention: (A) top view, (B) axial cross-sectional view;

[0070] Figure 4 A schematic diagram of the full-space two-stage density calibration cylinder (horizontal type) structure of the pulsed neutron gamma density logging instrument provided in Embodiment 2 of the present invention: (A) axial cross-sectional view, (B) top view;

[0071] Figure 5 The gamma mixed spectrum data (total gamma spectrum), gamma capture spectrum data (captured gamma spectrum), and inelastic gamma spectrum data (inelastic gamma spectrum) obtained by the gamma detector in the pulsed neutron gamma density logging calibration method provided in Embodiment 2 of the present invention, as well as the energy window division;

[0072] Figure 6 This is a schematic diagram of the data processing device in the pulsed neutron gamma density logging tool provided in Embodiment 2 of the present invention.

[0073] Among them: 1. Pulsed neutron gamma density logging tool probe, 5. Data processing equipment, 100. Housing, 101. Pulsed neutron generator, 102. Shielding body, 103. First thermal neutron detector, 104. First gamma detector, 105. Second thermal neutron detector, 106. Second gamma detector, 201. Standard wellbore, 202. Standard well formation rock block, 301. Second-level graduated cylinder wellbore, 302. Second-level graduated cylinder formation rock block, 501. Processor, 502. Bus, 503. Memory. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0075] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0076] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0077] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0078] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0079] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0080] The present invention will now be described in further detail with reference to the accompanying drawings:

[0081] Example 1

[0082] like Figure 1 As shown, a method for determining formation volume density using a pulsed neutron gamma density logging tool includes the following steps:

[0083] S1: The pulsed neutron gamma density logging instrument is operated in several standard wells with different lithologies and densities in a full-space calibration process. A standard response formula is established between the response result of the pulsed neutron gamma density logging instrument and the formation volume density of the standard wells. Then, the pulsed neutron gamma density logging instrument is placed in secondary calibration cylinders M1 and M2 respectively. Based on the standard response formula, the secondary calibration cylinders M1 and M2 are calibrated and their volume densities are obtained. The volume densities of the secondary calibration cylinders M1 and M2 are different. In this invention, the calibration well is preferably a full-space calibration well because the detector of the pulsed neutron gamma density logging instrument is not wrapped with a tungsten shield, and the instrument's gamma response is affected by both formation neutron transport and gamma transport. This means that formation density measurement is no longer affected by a single factor. Existing half-space lithology density standard calibration well groups, calibration methods, and equipment cannot meet the calibration requirements of the pulsed neutron gamma density logging instrument. The density range of this full-space calibrated well is 1.68 g / cm³. 3 ~2.92g / cm 3 The calibration well includes any one of the following formations: concrete, limestone, sandstone, and dolomite.

[0084] The specific process of establishing the standard response formula in this step is as follows:

[0085] S101: Acquire the first gamma mixed spectrum data, the first gamma capture spectrum data, the second gamma mixed spectrum data, the second gamma capture spectrum data, the first thermal neutron count rate data, and the second thermal neutron count rate data;

[0086] S102: Obtain the first pure gamma non-bullet spectrum data through the first gamma mixed spectrum data and the first gamma capture spectrum data; obtain the second pure gamma non-bullet spectrum data through the second gamma mixed spectrum data and the second gamma capture spectrum data, specifically:

[0087]

[0088]

[0089] In the formula, This is the first pure gamma non-elastic spectrum data. This is the first gamma mixture spectrum data. This is the first gamma capture spectrum data;

[0090] This is the second pure gamma non-elastic spectrum data. This is the second gamma mixture spectrum data. For the second gamma capture spectrum data;

[0091] α is a preset coefficient.

[0092] S103: Obtain the ratio of inelastic scattering gamma count rate of the first gamma window and the ratio of inelastic scattering gamma count rate of the second gamma window using the first pure gamma inelastic spectrum data and the second pure gamma inelastic spectrum data; obtain the ratio of thermal neutron count rate using the first thermal neutron count rate data and the second thermal neutron count rate data;

[0093] The process of obtaining the inelastic scattering gamma count rate ratio of the first gamma window and the inelastic scattering gamma count rate ratio of the second gamma window in this step is as follows:

[0094] S1031: A first gamma energy window and a second gamma energy window are set on both the first and second pure gamma inelastic spectrum data. The energy range of the first gamma density energy window is different from that of the second gamma density energy window. Positron annihilation indicates that when high-energy incident gamma rays pass through the formation, an energy peak related to the pair effect is formed at 0.511 MeV in the gamma spectrum. To exclude the influence of the pair effect on neutron gamma density measurement, this characteristic peak should be excluded from the selected gamma energy window range. Therefore, the lower limit energy of the two gamma ray energy windows should be set to be greater than 0.511 MeV. Meanwhile, to reduce the statistical fluctuation error of gamma counting, the energy ranges of the two gamma energy windows can partially overlap.

[0095] S1032: Obtain the ratio of the inelastic scattering gamma count rate of the first gamma window using the count rate of the first gamma inelastic spectrum data and the first gamma window of the second pure gamma inelastic spectrum data.

[0096] The ratio of the inelastic scattering gamma count rate of the second gamma window is obtained by using the count rate of the second gamma window of the first pure gamma inelastic spectrum data and the second pure gamma inelastic spectrum data.

[0097] Specifically:

[0098]

[0099] In the formula, R γ1 The ratio of the inelastic scattering gamma count rate of the first gamma window;

[0100] N1 is the count rate of the first gamma energy window of the first pure gamma non-elastic spectrum data;

[0101] N2 is the count rate of the first gamma energy window of the second pure gamma non-elastic spectrum data;

[0102]

[0103] In the formula, R γ2 The ratio of the inelastic scattering gamma count rate of the second gamma window;

[0104] M1 is the count rate of the second gamma energy window of the first pure gamma non-elastic spectrum data;

[0105] M2 is the count rate of the second gamma energy window of the second pure gamma non-elastographic data.

[0106] Furthermore, the process for obtaining the thermal neutron count rate ratio is as follows:

[0107]

[0108] In the formula, R n This is the ratio of thermal neutron count rates;

[0109] Q1 represents the first thermal neutron count rate data;

[0110] Q2 represents the second thermal neutron count rate data.

[0111] S104: By using the ratio of inelastic scattered gamma count rates in the first gamma window, the ratio of inelastic scattered gamma count rates in the second gamma window, the ratio of thermal neutron count rates, and the formation bulk density of the standard well, the fitting coefficients are obtained, and the final standard response formula is as follows:

[0112]

[0113] Where, f1(lnR) n )=a1(lnR n ) 3 +a2(lnR n ) 2 +a3(lnR n )+a4

[0114] f2(lnR n )=b1(lnR n ) 2 +b2(lnR n )+b3

[0115] In the formula, ρ b is the formation volume density of the standard well; a1, a2, a3, a4, b1, b2, b3 and A are the fitting coefficients;

[0116] ln R γ1 is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the first gamma window;

[0117] ln R γ2 is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the second gamma window;

[0118] lnR n This is the natural logarithm of the ratio of thermal neutron count rates.

[0119] Among them, the secondary scale cylinders M1 and M2 can be the secondary scale cylinders in the existing technology, that is, the secondary scale cylinders used in chemical source lithology density instruments.

[0120] S2: Use the secondary calibration cylinder M1 to perform main calibration on the logging tool to obtain the calibration factor of the logging tool; then place the logging tool in the secondary calibration cylinder M2 for measurement, and combine the calibration factor to complete the calibration of the logging tool; this step can effectively eliminate the influence of probe wear, radioactive source decay and differences between instruments in the same batch on the logging results.

[0121] The calibration factors in this step include the calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio. The processes for obtaining the calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are as follows:

[0122]

[0123] In the formula, K1 is the scale factor for the ratio of inelastic scattering gamma count rate of the first gamma window;

[0124] K2 is the scale factor for the ratio of inelastic scattering gamma count rate of the second gamma window;

[0125] K3 is the scale factor for the thermal neutron count rate ratio;

[0126] ln R M1γ1 ln R M1γ2 and ln R M1n The natural logarithm values ​​of the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are obtained during the calibration transfer in the secondary scale cylinder M1 in step S1.

[0127] as well as The natural logarithm values ​​are the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio, obtained during the main calibration in the secondary calibration cylinder M1 in step S2.

[0128] In a preferred embodiment of the present invention, K1, K2, and K3 are all greater than 0.95 and less than 1.05.

[0129] The specific calibration process for the logging tool in this step is as follows: Measurements are taken in the secondary graduated cylinder M2 to obtain... and And the calibration density value of the secondary graduated cylinder M2 is obtained.

[0130]

[0131] In the formula, as well as To perform measurements in the secondary graduated cylinder M2, the ratio of inelastic scattered gamma count rate of the first gamma window, the ratio of inelastic scattered gamma count rate of the second gamma window, and the ratio of thermal neutron count rate were obtained.

[0132] The calibration density value of the secondary graduated cylinder M2 The volume density ρ of the secondary graduated cylinder M2 obtained in step S1 M2b If a comparison is made, In ρ M2b ±0.015g / cm 3 If the logging tool is within the specified range, the calibration is complete; otherwise, the logging tool's condition is unstable and may malfunction, requiring maintenance.

[0133] S3: Before logging using the pulsed neutron gamma density logging tool, the calibrated logging tool is pre-calibrated using the calibrator XXX. The logging tool is then placed in the unknown well for testing. After the test, the logging tool is again calibrated using the calibrator, and the pre-calibration response value is compared with the post-calibration response value to determine the formation volume density in the unknown well. This comparison of the pre-calibration response value and the post-calibration response value effectively monitors the working status of the pulsed neutron gamma density instrument, ensuring the effectiveness of the logging.

[0134] This step compares the results of the pre-measurement and post-measurement calibrations to determine the formation volume density in the unknown well. Specifically:

[0135]

[0136] In the formula, The ratio of the inelastic scattering gamma count rate of the first gamma window of the post-measurement calibration response;

[0137] The ratio of the inelastic scattering gamma count rate of the first gamma window of the pre-measurement calibration response;

[0138] The ratio of the inelastic scattering gamma count rate of the second gamma window in the post-measurement calibration response;

[0139] The ratio of the inelastic scattering gamma count rate of the second gamma window in the pre-measurement calibration response;

[0140] The ratio of thermal neutron count rates in the post-measurement calibration response;

[0141] The ratio of thermal neutron count rates in the pre-measurement calibration response;

[0142] If δ1, δ2, and δ3 are all greater than 0.95 and less than 1.05, the formation volume density in the unknown well is determined. If δ1, δ2, and δ3 are not within this range, the logging tool is unstable and may malfunction, requiring maintenance.

[0143] The calibrator used is a portable calibrator. The difference between the portable calibrator used in the prior art is that the portable calibrator used in this invention does not have a radiation source. Because the pulsed neutron gamma density logging tool itself has a built-in signal source, the portable calibrator used in the existing compensated neutron porosity instrument can be used. In addition, in terms of size, it needs to be matched and set according to the pulsed neutron gamma density logging tool of this invention.

[0144] Furthermore, the aforementioned first gamma mixture spectrum data, first gamma capture spectrum data, second gamma mixture spectrum data, second gamma capture spectrum data, first thermal neutron count rate data, and second thermal neutron count rate data were obtained using a pulsed neutron gamma density logging tool. For example... Figure 2As shown, this pulsed neutron-gamma density logging tool includes a probe 1, a housing 100 on the probe 1, and a pulsed neutron generator 101, a first thermal neutron detector 103, a first gamma detector 104, a second thermal neutron detector 105, a second gamma detector 106, and a data processing device 5 mounted on the housing 100. The pulsed neutron generator 101, the first thermal neutron detector 103, the first gamma detector 104, the second thermal neutron detector 105, the second gamma detector 106, and the data processing device 5 are arranged sequentially at intervals along the length of the housing 100. The first thermal neutron detector 103, the first gamma detector 104, the second thermal neutron detector 105, and the second gamma detector 106 are connected to the data processing device 5. The first gamma mixed spectrum data and the first gamma capture spectrum data are obtained through the first gamma detector 104; the second gamma mixed spectrum data and the second gamma capture spectrum data are obtained through the second gamma detector 106; the first thermal neutron count rate data and the second thermal neutron count rate data are obtained through the first thermal neutron detector 103 and the second thermal neutron detector 105, respectively. The first gamma detector 104 and the second gamma detector 106 can be high-energy gamma ray detection efficiency lanthanum bromide crystals, and the first and second thermal neutron detectors can be He-3 counting tubes. The pulsed neutron generator 101 is shielded from the first thermal neutron detector 103 by a shield 102. Furthermore, the second thermal neutron detector 105 consists of three neutron detectors arranged side-by-side, increasing the count rate of the far-field neutron detector. The first thermal neutron detector 103 and the first gamma detector 104 are relatively close to the pulsed neutron generator 101, so they can be referred to as near-thermal neutron detectors and near-gamma detectors, respectively. Similarly, the second thermal neutron detector 105 and the second gamma detector 106 are relatively far from the pulsed neutron generator 101, so they can be referred to as far-thermal neutron detectors and far-gamma detectors, respectively.

[0145] The logging tool's first thermal neutron detector 103 and second thermal neutron detector 105 record the thermal neutron count rate after deceleration in the formation and return to the instrument; the logging tool's first gamma detector 104 and second gamma detector 106 record the inelastic gamma-ray energy spectrum generated by secondary gamma sources in the formation and transported to the instrument. The ratio of thermal neutron count rates is related to the formation neutron deceleration length and can be used to characterize neutron transport.

[0146] The near-gamma and far-gamma detectors of the logging tool are mainly used to detect inelastic gamma rays generated when fast neutrons produced by a pulsed neutron generator enter the formation and undergo inelastic collisions with nearby atomic nuclei. The volumetric density is calculated by setting two gamma energy windows based on the energy spectra of the inelastic gamma rays recorded by the near-gamma and far-gamma detectors. To reduce the statistical error of the gamma count rate within each energy window, the energy ranges included in the two energy windows can partially overlap.

[0147] Example 2

[0148] This embodiment further illustrates the present invention.

[0149] A method for determining formation volume density using a pulsed neutron gamma density logging tool includes:

[0150] Step S1: Select several standard well conditions with different lithologies and densities.

[0151] like Figure 3 As shown, the standard well is a vertical full-space calibration well, which includes a vertical standard wellbore 201 and a vertical standard well formation rock block 202. In this embodiment, the standard well conditions include: a) the formation water and well fluid are fresh water; b) the well diameter is 200 mm (8 in); c) the ambient temperature is normal (25°C); d) the ambient pressure is 0.1 MPa; e) there is no mud cake on the well wall.

[0152] In this embodiment, the calibration well group is vertical, including wells with a density range of 1.68 g / cm³. 3 ~2.92g / cm 3 Density standard calibration wells for the entire space of concrete, limestone, sandstone and dolomite strata.

[0153] Step S2: The pulsed neutron gamma density logging instrument of the present invention is placed at the effective measurement points of the calibrated well group to obtain near-gamma mixed spectrum data (i.e., first gamma mixed spectrum data), far-gamma mixed spectrum data (i.e., second gamma mixed spectrum data), near-gamma capture spectrum data (i.e., first gamma capture spectrum data), far-gamma capture spectrum data (i.e., second gamma capture spectrum data), near-thermal neutron count rate data (i.e., first thermal neutron count rate data), and far-thermal neutron count rate data (i.e., second thermal neutron count rate data).

[0154] In this embodiment, the specific steps include: a) placing the pulsed neutron-gamma density instrument at the effective measurement point of a standard well and preheating it for 30 minutes; b) turning on the pulsed neutron generator via ground software control and measuring the standard well for 180-300 seconds to obtain near-gamma mixed spectrum data, far-gamma mixed spectrum data, near-gamma capture spectrum data, far-gamma capture spectrum data, near-thermal neutron count rate data, and far-thermal neutron count rate data; c) turning off the pulsed neutron generator via software control, waiting for 30 minutes, and then moving the pulsed neutron-gamma density logging instrument to the effective measurement point of the next standard well to continue the measurement.

[0155] In this embodiment, the total gamma spectrum and capture spectrum are determined by the near-gamma detector and the far-gamma detector of the pulsed neutron gamma density logging tool, and the thermal neutron count is determined by the near-thermal neutron detector and the far-thermal neutron detector of the pulsed neutron gamma density logging tool.

[0156] Step S3: By reducing the hydrogen peak, the capture spectrum in the gamma mixed spectrum is proportionally subtracted to obtain the pure gamma inelastic spectrum.

[0157] In this embodiment, the hydrogen reduction peak formula is:

[0158] N Ine =N Tot -α·N Cap

[0159] Where: N Ine It is a pure gamma non-bullet spectrum; N Tot The spectrum is a pure gamma mixture; N Cap This is the gamma capture spectrum; α is a preset coefficient, which can be determined by the characteristic capture energy peak of hydrogen at 2.23 MeV.

[0160] Step S4: Divide the inelastic gamma spectral data into energy windows with determined density in the logging process, and determine the gamma energy window count rate in each calibration well.

[0161] like Figure 5 As shown, in this embodiment, the gamma energy window should include two gamma density energy windows W1 and W2 with different energy ranges. To reduce the statistical error of the gamma count rate within the energy window, the energy ranges included in the two energy windows can partially overlap.

[0162] Step S5 involves fitting the near-gamma window count rate, far-gamma window count rate, near- and far-thermal neutron count rates obtained from the calibration well group measurements with the formation density, determining the fitting coefficients, and determining the standard response formula, specifically as follows:

[0163]

[0164] in,

[0165] f1(lnR n )=a1(lnR n ) 3 +a2(lnR n ) 2 +a3(lnR n )+a4

[0166] f2(lnR n )=b1(lnR n ) 2 +b2(lnR n )+b3

[0167] Where: ρ b R is the formation volume density; γ1 R represents the ratio of inelastic scattering gamma count rates in the first energy window W1 (near-pure gamma inelastic data / far-pure gamma inelastic data); γ2 R represents the ratio of inelastic scattering gamma count rates in the second energy window W2 (near-pure gamma inelastic data / far-pure gamma inelastic data); n denoted as the thermal neutron count ratio (near-field thermal neutron count rate / far-field thermal neutron count rate); a1, a2, a3, a4, b1, b2, b3, and A are coefficients determined by calibrating the well group response using standard wells, i.e., fitting coefficients.

[0168] In this embodiment, the Marquardt iterative algorithm is used to determine the fitting coefficients.

[0169] Step S6: According to the standard response formula, perform density calibration and value transfer on two secondary graduated cylinders M1 and M2 with different volumetric densities;

[0170] like Figure 4 As shown, the secondary graduated cylinder preferably has a fully horizontal structure, including a secondary graduated cylinder borehole 301 and a secondary graduated cylinder formation rock block 302. In this embodiment, the secondary graduated cylinder is horizontal, and during calibration and value transmission, the borehole of the graduated cylinder is filled with air, 1.5m above the ground.

[0171] In this embodiment, the secondary graduated cylinders M1 and M2 are two rock or metal blocks with different densities in the entire space.

[0172] Step S7: Before logging with the pulsed neutron gamma density instrument, use the secondary calibration cylinder M1 (a standard module calibrated by the primary calibration well group) to perform the main calibration and establish the relationship between the instrument response and the formation volume density.

[0173] In this embodiment, the main calibration is generally performed after the pulsed neutron gamma density instrument is delivered from the factory and before field logging;

[0174] The main scale can check the instrument's performance, allowing the instrument to be calibrated to its factory condition before logging, reducing the impact of instrument wear, especially probe wear, changes in detector sensitivity caused by various factors during use, and pulse neutron generator lifespan on logging.

[0175] Step S8: Measurement and verification are performed in another secondary scale cylinder M2. The density value is obtained through the above relationship and compared with the nominal density value of the scale. This is an important step in verifying the main scale.

[0176] Step S8: Pre- and post-measurement calibration, monitor the working status of the neutron pulse neutron gamma density instrument, and ensure the effectiveness of the pulse neutron gamma density instrument logging.

[0177] In this embodiment, the pre- and post-measurement gamma background calibration is a gamma background measurement performed before and after the instrument is run into the well. During the measurement process, the instrument is required to turn off the pulsed neutron generator and move away from the radiation source to prevent the radiation source from affecting the instrument's background measurement.

[0178] As described above, the pulsed neutron gamma density logging instrument acquires the first gamma mixture spectrum data, the first gamma capture spectrum data, the second gamma mixture spectrum data, the second gamma capture spectrum data, the first thermal neutron count rate data, and the second thermal neutron count rate data using a first-stage calibrated well group. Based on these data and the formation volume density of a standard well, a controllable source neutron gamma density calculation response formula is derived. Density calibration and value transfer are performed on two second-stage calibrated cylinders M1 and M2 with different volume densities according to the response formula. A second-stage calibration is used before logging with the pulsed neutron gamma density instrument. The main calibration is performed using calibration cylinder M1 (a standard module calibrated through the primary calibration well group) to establish the relationship between instrument response and formation volume density, eliminating the influence of probe wear, radioactive source decay, and differences between instruments in the same batch on logging. Measurement and verification are performed in another secondary calibration cylinder M2. The density value is obtained through the above relationship and compared with the nominal density value of the calibrator to verify the correctness of the main calibration. Pre- and post-measurement calibration is performed to monitor the working status of the neutron pulse neutron gamma density instrument and ensure the effectiveness of the pulse neutron gamma density instrument logging.

[0179] As described above, the calibration process involves selecting several standard wells with different lithologies and densities within a primary calibration well group; placing the pulsed neutron gamma density instrument at effective measurement points within the calibration well group to obtain gamma mixed spectrum data, gamma capture spectrum data, and thermal neutron count rate data; subtracting the capture spectrum from the gamma mixed spectrum by reducing the hydrogen peak to obtain the pure gamma inelastic spectrum; dividing the inelastic gamma spectrum data according to the density window defined in well logging engineering to determine the gamma energy window count rate in each calibration well; fitting the far- and near-field gamma energy window count rates and far- and near-field thermal neutron count rates obtained from the calibration well group measurements with the formation density to determine the fitting coefficients; and inputting the fitting coefficients into the well logging program to complete the instrument calibration. This invention provides a calibration method and data processing equipment for pulsed neutron gamma density logging instruments.

[0180] An embodiment of the present invention also provides a structure for a data processing device, such as... Figure 6 As shown, the data processing device 5 includes a processor 501 and a memory 503. The processor 501 executes computer execution instructions stored in the memory to implement the various steps performed by the data processing device in the above embodiment. The memory 503 stores computer execution instructions.

[0181] The processor described above can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. A general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The memory may include high-speed RAM, and may also include non-volatile memory (NVM), such as at least one disk drive, and may also be a USB flash drive, external hard drive, read-only memory, disk, or optical disc, etc. Memory 503 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, disk, or optical disc. The storage medium can be any available medium accessible to general-purpose or special-purpose computers.

[0182] The memory 503 can be either standalone or integrated with the processor 501. One exemplary memory is coupled to the processor, enabling the processor to read information from and write information to the memory. Alternatively, the memory can be an integral part of the processor. The processor and memory can reside in application-specific integrated circuits (ASICs). Of course, the processor and memory can also exist as discrete components in an electronic device or host device.

[0183] When the memory 503 is configured independently, the data processing device also includes a bus 502 for connecting the processor 501 and the memory 503. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of illustration, the buses shown in the accompanying drawings are not limited to a single bus or a single type of bus.

[0184] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 determining formation volume density using a pulsed neutron gamma density logging tool, characterized in that, Includes the following steps: S1: The pulsed neutron gamma density logging tool is operated in several standard wells with different lithologies and densities in a full-space calibration system. A standard response formula is established between the response result of the pulsed neutron gamma density logging tool and the formation volume density. Then, the pulsed neutron gamma density logging tool is placed in secondary calibration cylinders M1 and M2 respectively. Based on the standard response formula, the secondary calibration cylinders M1 and M2 are calibrated and their volume densities are obtained. The volume densities of the secondary calibration cylinders M1 and M2 are different. S2: Use the secondary scale cylinder M1 to perform main calibration on the logging tool to obtain the calibration factor of the logging tool; then place the logging tool in the secondary scale cylinder M2 for measurement, and combine the calibration factor to complete the calibration of the logging tool; S3: Before logging using a pulsed neutron gamma density logging tool, use a calibrator to perform a pre-logging response on the calibrated logging tool. Then, place the logging tool in the unknown well for testing. After the test is completed, use the calibrator again to perform a post-logging response on the logging tool. Compare the pre-logging response value with the post-logging response value to determine the formation volume density in the unknown well.

2. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 1, characterized in that, The standard response formula in step S1 is as follows: in, In the formula, The formation volume density of the full-space calibrated well; 、 、 、 、 、 、 and These are the fitting coefficients; is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the first gamma window; is the natural logarithm of the ratio of the inelastic scattering gamma count rate of the second gamma window; This is the natural logarithm of the ratio of thermal neutron count rates.

3. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 2, characterized in that, The specific process for obtaining the inelastic scattering gamma count rate ratio of the first gamma window and the inelastic scattering gamma count rate ratio of the second gamma window is as follows: In the formula, The ratio of the inelastic scattering gamma count rate of the first gamma window; The count rate of the first gamma energy window for the first pure gamma non-elastic spectrum data; The count rate of the first gamma energy window for the second pure gamma non-elastic spectrum data; In the formula, The ratio of the inelastic scattering gamma count rate of the second gamma window; The count rate of the second gamma energy window for the first pure gamma non-elastic spectrum data; The count rate of the second gamma energy window for the second pure gamma non-elastic spectrum data; The process of obtaining the thermal neutron count rate ratio is as follows: In the formula, This is the ratio of thermal neutron count rates; This is the first thermal neutron count rate data; This is the data for the second thermal neutron count rate.

4. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 3, characterized in that, The specific process for obtaining the first pure gamma non-spectral data and the second pure gamma non-spectral data is as follows: In the formula, This is the first pure gamma non-elastic spectrum data. This is the first gamma mixture spectrum data. This is the first gamma capture spectrum data; This is the second pure gamma non-elastic spectrum data. This is the second gamma mixture spectrum data. For the second gamma capture spectrum data; These are preset coefficients.

5. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 1, characterized in that, In step S2, the calibration factor includes calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio. The processes for obtaining the calibration factors for the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are as follows: ； ； ； In the formula, is the scale factor for the ratio of inelastic scattering gamma count rate of the first gamma window; is the scale factor for the ratio of inelastic scattering gamma count rate of the second gamma window; This is the scale factor for the thermal neutron count rate ratio; , as well as The natural logarithm values ​​of the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio are obtained during the calibration transfer in the secondary scale cylinder M1 in step S1. , as well as The natural logarithm values ​​are the inelastic scattering gamma count rate ratio of the first gamma window, the inelastic scattering gamma count rate ratio of the second gamma window, and the thermal neutron count rate ratio, obtained during the main calibration in the secondary calibration cylinder M1 in step S2.

6. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 5, characterized in that, The , , All are greater than 0.95 and less than 1.

05.

7. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 5, characterized in that, The specific calibration process of the logging tool in step S2 is as follows: Measurements are performed in the secondary graduated cylinder M2 to obtain... , and And obtain the calibration density value of the secondary graduated cylinder M2. : = = In the formula, , as well as To perform measurements in the secondary graduated cylinder M2, the ratio of inelastic scattered gamma count rate of the first gamma window, the ratio of inelastic scattered gamma count rate of the second gamma window, and the ratio of thermal neutron count rate were obtained. The calibration density value of the secondary graduated cylinder M2 The volume density of the secondary graduated cylinder M2 obtained in step S1 If a comparison is made, exist g / cm 3 Within the specified range, the logging instrument is calibrated.

8. The method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 1, characterized in that, In step S3, the results of the pre-measurement and post-measurement calibrations are compared to determine the formation volume density in the unknown well. Specifically: ； ； ； In the formula, The ratio of the inelastic scattering gamma count rate of the first gamma window of the post-measurement calibration response; The ratio of the inelastic scattering gamma count rate of the first gamma window of the pre-measurement calibration response; The ratio of the inelastic scattering gamma count rate of the second gamma window in the post-measurement calibration response; The ratio of the inelastic scattering gamma count rate of the second gamma window in the pre-measurement calibration response; The ratio of thermal neutron count rates in the post-measurement calibration response; The ratio of thermal neutron count rates in the pre-measurement calibration response; like , as well as If all values ​​are greater than 0.95 and less than 1.05, then the determination of the formation volume density in the unknown well is complete.

9. A method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 1, characterized in that, The density range of the full-space calibrated well is 1.68 g / cm³. 3 ~2.92g / cm 3 .

10. A method for determining formation volume density using a pulsed neutron gamma density logging tool according to claim 1, characterized in that, The full-space calibration well includes any one of the following formations: concrete formation, limestone formation, sandstone formation, and dolomite formation.

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