CN116794749A - Density correction method for gamma-gamma density logging - Google Patents

Density correction method for gamma-gamma density logging Download PDF

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CN116794749A
CN116794749A CN202310906987.2A CN202310906987A CN116794749A CN 116794749 A CN116794749 A CN 116794749A CN 202310906987 A CN202310906987 A CN 202310906987A CN 116794749 A CN116794749 A CN 116794749A
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density
ngr
ggnr
ggfr
detector
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焦仓文
乔宝强
赵丹
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Beijing Research Institute of Uranium Geology
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Beijing Research Institute of Uranium Geology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V13/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/04—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging
    • G01V5/08—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays
    • G01V5/12—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity specially adapted for well-logging using primary nuclear radiation sources or X-rays using gamma or X-ray sources

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  • High Energy & Nuclear Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Measurement Of Radiation (AREA)

Abstract

The application relates to the technical field of gamma-gamma density logging, in particular to a density correction method of gamma-gamma density logging, which comprises the following steps: obtaining count rate ratio R of long-source detector GGFR and natural gamma detector NGR by using model well GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR The method comprises the steps of carrying out a first treatment on the surface of the Acquiring a density scale coefficient of the density logging instrument; logging by adopting the density logging instrument, and obtaining the counting rates N of the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR NGR 、N GGFR And N GGNR The method comprises the steps of carrying out a first treatment on the surface of the According to the acquired count rate N NGR 、N GGFR 、N GGNR And count rate ratio R GGFR/NGR 、R GGNR/NGR Calculating and obtaining the net count rate of the long source detector GGFR and the short source detector GGNR, and finishing the correction of the count rate of the density parameter calculation; according to density scale factor and net meterThe number rate calculates the formation density. The application can effectively correct the density and meet the requirement of density logging on the precision.

Description

Density correction method for gamma-gamma density logging
Technical Field
The application relates to the technical field of gamma-gamma density logging, in particular to a density correction method of gamma-gamma density logging.
Background
Density is one of the necessary parameters of conventional geophysical well logging, gamma-gamma density well logging is a well logging method that determines the density of a formation from the compton effect produced by gamma rays interacting with a substance. Density logging based on the gamma-gamma scattering principle is not alternative in identifying formation lithology, obtaining formation wave impedance and formation porosity applications based on ore density and sonic velocity.
In sandstone uranium mine exploration, a density logging curve has obvious difference on mudstone and sandstone strata, and generally sandstone has a reduced density value and reduced permeability along with the increase of the content of the mudstone. Therefore, the ore-bearing aquifer of the in-situ leaching sandstone type uranium ores is determined, the lithology and the permeability of the ore-bearing aquifer provide basic physical parameter information for in-situ leaching mining, and density logging is not carried out.
However, gamma rays of radioactive strata are an interference to density logging, which can cause distortion of density curves, affect correct identification of lithology, even divide permeable lithology into impermeable rock formations, and seriously affect selection of subsequent leaching mining processes.
Disclosure of Invention
In order to solve the above problems, the embodiment of the application provides a density correction method for gamma-gamma density logging, which can effectively correct density and meet the requirement of density logging on precision.
For this purpose, the following technical scheme is adopted in the embodiment of the application:
a density correction method of gamma-gamma density logging is applied to a density logging instrument, wherein the density logging instrument comprises a natural gamma detector NGR, a long source detector GGFR and a short source detector GGNR; the density correction method includes: obtaining count rate ratio R of long-source detector GGFR and natural gamma detector NGR by using model well GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR The method comprises the steps of carrying out a first treatment on the surface of the The model well is a rock sample with known density and nominal content, which is obtained through testing, and the response difference of the long source detector GGFR and the short source detector GGNR relative to the natural gamma detector NGR to the natural gamma rays of the model well is obtained through the ratio of the counting rate; acquiring density scale system of density logging instrumentA number; the density scale coefficient is calibration data of the density logging instrument determined according to a standard density sample; logging by adopting the density logging instrument, and obtaining the counting rates N of the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR NGR 、N GGFR And N GGNR The method comprises the steps of carrying out a first treatment on the surface of the Taking the count rate N of the natural gamma detector NGR NGR Respectively multiplied by the ratio R of the count rates GGFR/NGR And R is GGNR/NGR Acquiring a count rate N of natural gamma rays of a radioactive formation downhole to a long source detector GGFR and a short source detector GGNR GGFR 、N GGNR Then at the count rate N of the long-source detector GGFR GGFR And count rate N of short source detector GGNR GGNR Respectively subtracting the interference values corresponding to the two detectors, and calculating and obtaining the net count rate N of the long source detector GGFR and the short source detector GGNR GGFR cleaner And N GGNR cleaner Completing the correction of the counting rate for calculating the density parameters; the formation density is calculated from the density scale factor and the net count rate.
As an implementation manner, the model well is selected from any one of a saturated logging model or a field check model.
As an implementation manner, the method uses model wells to obtain the count rate ratio R of the long-source detector GGFR to the natural gamma detector NGR GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR Comprising: obtaining nominal content of N model wells, wherein N is more than or equal to 2; acquiring count rates N of natural gamma detector NGR, long-source detector GGFR and short-source detector GGNR in N model wells NGR ’、N GGFR ' and N GGNR 'A'; based on nominal content of N model wells and N count rates N NGR ’、N GGFR ' and N GGNR ' obtaining a linear fitting curve of the counting rate and the nominal content of the model well; obtaining corresponding count rate ratio R according to the ratio of slopes of linear fitting curves of the natural gamma detector NGR, the long-source detector GGFR and the short-source detector GGNR GGFR/NGR R is R GGNR/NGR 。
As a can be implementedIn the present embodiment, the nominal content of the model well is 0.2-5167×10 -6 g/g。
As one implementation, the following formula is used to obtain the net count rates N of the long source detector GGFR and the short source detector GGNR GGFR cleaner And N GGNR cleaner And (3) finishing correction of the calculation counting rate of the density parameter solution:
N GGFR cleaner ＝N GGFR -N NGR ×R GGFR/NGR
N GGNR cleaner ＝N GGNR -N NGR ×R GGNR/NGR 。
As an implementation manner, the acquiring the density scale factor of the density logging instrument includes: acquiring an aluminum module and an organic glass module with known density as a scale module; adopting cesium source as radioactive source of density logging instrument; sequentially mounting an aluminum module and an organic glass module on a probe of a density logging instrument, and starting the density logging instrument to enable a cesium source to emit rays to a scale module; recording a count rate reading of the logging instrument and a known density value of a scale module, and drawing a relation curve between the count rate reading and the density according to the recorded count rate reading and the module density; fitting and analyzing the relation curve to obtain ln N=Aρ b +B, and obtaining density scale coefficients A and B of the density logging tool, wherein ρ b Density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the B-intercept, is constant.
As an implementation, the calculating the formation density according to the density scale factor and the net count rate includes:
the formation density was calculated using the following formula:
ρ b ＝(1/A)ln N-B/A
wherein: ρ b -formation density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the B-intercept, is constant.
As one possible embodiment, the cesium source is 200mm apart from the short source detector GGNR; the distance between the cesium sources and the long source detector GGFR is 350m; the cesium source is spaced 2500mm from the natural gamma detector NGR.
As one implementation, the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR all use sodium iodide crystals with diameters and lengths of 30mm and 80mm, 23mm and 40mm, 13mm and 10mm respectively, and energy thresholds of 130keV.
As one implementation, the short source detector GGNR is built in with a tantalum silver plate.
The embodiment of the application utilizes the ratio (R) of the counting rate of the natural gamma detector to the counting rate of the long and short source detectors GGFR/NGR ，R GGNR/NGR ) And correcting the counting rate of the long and short source detectors, namely subtracting the influence of the natural gamma rays of the radioactive stratum on the density measurement by using the counting rate ratio to finish the correction of the density parameters, and then calculating the density value by using the density scale coefficient to reduce the distortion of the density curve. The density correction method provided by the embodiment of the application is an effective density correction method, and meets the requirement of density logging on precision.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present application, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
The various regions, shapes and relative sizes, positional relationships between them shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
Like elements are denoted by like reference numerals throughout the various figures. For clarity, various parts in the drawings are not drawn to scale, and certain features may be exaggerated or omitted to more clearly illustrate and explain the present application.
FIG. 1 is a schematic diagram of a density logging tool according to an embodiment of the present application;
FIG. 2 is a flow chart of a density correction method according to an embodiment of the present application;
FIG. 3 is a linear fit curve of count rate versus model nominal content obtained by the natural gamma detector NGR, the long-range detector GGFR, and the short-range detector GGNR of the MD604-2005 density three-sided logging tool on 4 saturated logging models, respectively;
FIG. 4 is a schematic diagram of a field verification model provided in an embodiment of the present application;
FIG. 5 is a schematic illustration of borehole 1-2-16Z logging density correction;
fig. 6 is a schematic diagram of correction of the density curve of the drilled hole SYG-1 bare Kong Cejing.
Detailed Description
The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.
In the description of the present specification, reference to the terms "one embodiment," "some embodiments," "exemplary," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Formation density is a very useful and characteristic parameter for formation evaluation, is an important basis for ascertaining a regional formation sequence and classifying mineral formations, and plays an important role in formation classification. Gamma-gamma density logging has very important significance in the work of sandstone-type uranium mining investigation, and is an indispensable logging method. The main purpose of gamma-gamma density logging is to identify formation lithology, and to obtain formation wave impedance and porosity from ore density and sonic logging.
However, radioactivity in a sandstone uranium mineralization area can greatly interfere density measurement data, so that stratum division and lithology recognition are affected, and stratum lithology judgment is greatly affected. If the ore layer contains an impermeable stratum such as a calcareous layer and mudstone, the impermeable layer is calculated after being removed in the well logging interpretation and resource quantity evaluation, and if the interlayer cannot be finely and accurately divided, the well logging interpretation result and the resource quantity evaluation are influenced. Therefore, it is necessary to correct the disturbance of the density logging value of the ore layer due to radioactivity contained in the ore layer to obtain more accurate density data, and more accurately divide the stratum and estimate the sandstone-type uranium ore resource amount.
In order to eliminate the interference of natural gamma rays on density measurement, a plurality of methods are proposed by workers of traditional density logging, for example, two well logging measurements are carried out by using a density three-side logging instrument, namely, one well logging with a hanging source and one well logging without a hanging source, and when the density is calculated, the influence of natural radiation counting on the density measurement is deducted by using the difference value of the counting rate of a detector, so that the method is an effective method, but the working efficiency is relatively low. Workers also propose to subtract the effect of natural gamma on the count rate of long-source detectors using empirical coefficient fitting, but the universality of this approach has certain limitations.
In order to solve the problem that strong radioactive ores in the stratum interfere with density logging data, the embodiment of the application applies a density correction method of gamma-gamma density logging in the process of measuring the stratum density by a density logging instrument, and the method utilizes the counting rate of a natural gamma detector and long and short source detectorsRatio of count rate (R GGFR/NGR ，R GGNR/NGR ) And correcting the counting rate of the long and short source detectors by using the coefficients, and then calculating the density value by using the density scale coefficients.
Before describing the density correction method in detail, the structure of the density logging instrument provided by the embodiment of the application needs to be described. Referring to fig. 1, the density logging tool is a density three-sided (i.e., offset density) logging tool, comprising a sidewall contact device 1, a probe 2 (also referred to as a sled), an electrical circuit (not shown), and a gamma-ray detector. The gamma ray detector includes a short source detector GGNR, a long source detector GGFR and a natural gamma detector NGR.
Wherein a radiation source, a short source detector GGNR and a long source detector GGFR are sequentially mounted on the probe 2. The natural gamma detector NGR is installed at the head end of the density logging instrument. In addition, the sidewall contact device 1 one end is installed on the lateral wall of the density logging instrument, and the other end can be abutted on the well wall when logging, so that the density logging instrument can also be abutted on the well wall. And the distance between the end of the leaning device 1, which is clung to the well wall, and the radioactive source is 369mm.
The interaction between gamma rays and substances is in three forms, namely 1, photoelectric absorption; 2. compton scattering; 3. electron pair effect. Illustratively, the radiation source of the density logging instrument is selected 137 A source of Cs. Because in this embodiment, the density logging tool is selected to be 137 The Cs source, which emits gamma rays having an energy of 0.662MeV, eliminates the possibility of electron pair formation and, if the threshold of the detector is properly selected, also minimizes the effect of photoelectric absorption so that the detector records only those gamma rays that undergo one or more compton scattering with the formation. Illustratively, in this embodiment, the natural gamma detector NGR, the long source detector GGFR, and the short source detector GGNR all employ sodium iodide crystals having diameters and lengths of 30mm and 80mm, 23mm and 40mm, 13mm and 10mm, respectively, and energy thresholds of 130keV. In order to reduce the influence of photoelectric effect caused by low-energy gamma rays, a short source detector GGNR is internally provided with a tantalum silver sheet, and low-energy scattering gamma rays are filtered.
For selected 137 Cs radioactive source and measured energy thresholdFor a typical formation consisting of medium atomic number atoms, compton dominates the interaction of photons with the formation when the attenuation coefficient of the formation is proportional to the electron density of the formation, which in turn is proportional to the bulk density, the mass attenuation coefficient mu for most minerals and most formations m Is substantially constant, which is the basis for density logging.
When logging, the probe is first put into the well, and under the action of the sidewall contact device, the probe is abutted against the well wall, the radiation source emits gamma photons to the stratum through the emission window, after the gamma photons are scattered and absorbed by the stratum, one or more times of Compton scattering gamma photons generated between part of gamma photons and the stratum are received by two gamma ray detector (short source detector GGNR and long source detector GGFR) crystals at different distances from the radiation source to generate photoelectric effects, and electric signals are generated and amplified and screened by a circuit to be recorded. The radiation source and the gamma ray detector are separated by a shielding material such that photons received by the detector are gamma photons scattered by the formation. The density of the stratum is different, the scattering and absorption capacity of gamma photons are different, the detector records different readings, and the density value of the stratum can be determined according to the readings of the detector after the calibration of the density correction method in the embodiment of the application.
It is worth mentioning that the detection sensitivity a of the density logging instrument to the stratum satisfies the following formula:
A＝-u m ·d
wherein d is the source distance; mu (mu) m The mass absorption coefficient of the formation, which is theoretically the sum of the 3 absorption coefficients of the photoelectric effect, the Compton effect and the electron pair effect. Due to the adoption of 137 Cs source gamma ray energy is 662keV and almost completely Compton effect with stratum substances, so mu m Approximately equal to the compton absorption coefficient. From the above equation, the larger the source distance d, the higher the density tool sensitivity A, and the greater the depth of detection. However, too large a source distance d may decrease the count rate and increase the statistical error.
The distance between the gamma ray detector and the radiation source is called the source distance. In this embodiment, the short source detector GGNR is 200mm from the cesium source. The long source detector GGFR has a source distance of 350m from the cesium source. The natural gamma detector NGR is 2500mm from the cesium source.
In addition, in actual logging, mud cake is inevitably entrained between the probe and the stratum due to factors such as irregular well wall, pushing and the like, and the density value (called apparent density) measured by the instrument is related to not only the stratum density but also the thickness, density and average atomic number of the mud cake. Therefore, the long source detector GGFR and the short source detector GGNR arranged in the probe can realize the calculation of the stratum density by adopting a double source distance compensation method. In particular, when a mudcake is present, the influence of the mudcake on the long source detector is different from the short source detector. The thickness, density and average atomic number of the mud cake can be estimated by comparing the gamma radiation intensity difference measured by the long source detector and the short source detector and according to the known absorption relation of the mud cake property and gamma radiation, and the calculated mud cake parameters are utilized to compensate the GGFR measured value of the long source detector, so that a more accurate stratum density value is obtained.
In the absence of mud cake, two detectors of different source distances were used to measure their count rate versus formation density:
ln N＝Aρ b +B
i.e.
ρ b ＝(1/A)ln N-B/A
Wherein: ρ b -formation density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the B-intercept, is constant.
For long source detector GGFR: ρ GGFR ＝(1/A GGFR )lnN GGFR -B GGFR /A GGFR ；
For short source detector GGNR: ρ GGNR ＝(1/A GGNR )lnN GGNR -B GGNR /A GGNR 。
Let ρ be GGFR ＝ρ GGNR Then:
lnN GGFR ＝(A GGFR /A GGNR )lnN GGNR -(A GGFR /A GGNR )B GGNR +B GGFR 。
that is, lnN GGFR And lnN GGNR Is a linear relationship with a slope of A GGFR /A GGNR We refer to this line as the ridge line, which is at an angle α=arctg (a GGFR /A GGNR ) Called the spine angle, due to A GGFR /A GGNR Only the source distance is related, so that the spine angle is unchanged after the geometrical parameters of the instrument are set, and each point on the spine line corresponds to a density value.
As described above, the natural radioactive gamma rays of the formation may be received by the long source detector GGFR, causing the measured density values to deviate from the true values. Thus, in this embodiment, a natural gamma detector NGR is mounted on the density three-sided logging tool to measure the natural radioactivity of the formation for depth alignment and formation contrast. The natural gamma detector NGR is located at the top of the logging tool, while the long source detector GGFR and the short source detector GGNR for density parameter measurement are located at the bottom of the density three-side logging tool, and the natural gamma detector NGR is considered to be substantially unaffected by the active radioactive source (cesium source) because the source distance of the natural gamma detector NGR from the cesium source is 2500mm. Therefore, when the actual borehole is used for logging, the counting rate ratio (R) of the natural gamma detector and the long and short source detector can be utilized GGFR/NGR ,R GGNR/NGR ) The counting rate of the long and short source detectors for density calculation is subtracted proportionally so as to reduce the influence of natural gamma rays.
The density correction method of gamma-gamma density logging according to the embodiment of the present application is described in detail below with reference to the accompanying drawings.
Referring to fig. 2, a density correction method for gamma-gamma density logging according to an embodiment of the present application includes the following steps:
s201, obtaining a count rate ratio R of a long-source detector GGFR and a natural gamma detector NGR by using a model well GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR 。
It is understood that the count rate refers to the number of rays or particles received by the detector per unit of time, which is typically measured in terms of the number of rays or particles received per second.
The model well is a rock sample with known density and nominal content obtained by testing, and the response difference of the long source detector GGFR and the short source detector GGNR to the natural gamma rays of the model well is obtained by the ratio of the counting rate. The model well is illustratively selected from any one of a saturated logging model or a field check model. It is assumed here that the count rate of each detector is considered to be proportional to the radioactivity intensity of the formation. That is, the scaling factor of the count rate ratio may be obtained on standard model wells, such as saturated logging models, or may be obtained using non-standard model wells, such as field check models.
In one implementation, the count rate ratio R of the long source detector GGFR to the natural gamma detector NGR is obtained using model wells GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR Comprising the following steps: obtaining nominal content of N model wells, wherein N is more than or equal to 2; acquiring count rates N of natural gamma detector NGR, long-source detector GGFR and short-source detector GGNR in N model wells NGR ’、N GGFR ' and N GGNR 'A'; based on nominal content of N model wells and N count rates N NGR ’、N GGFR ' and N GGNR ' obtaining a linear fitting curve (energy scale linearization treatment) of the counting rate and the nominal content of the model well; obtaining corresponding count rate ratio R according to the ratio of slopes of linear fitting curves of the natural gamma detector NGR, the long-source detector GGFR and the short-source detector GGNR GGFR/NGR R is R GGNR/NGR 。
Illustratively, a count rate scaling factor is obtained using a saturated logging model. Specifically, to obtain the ratio of the count rates of the long source detector GGFR, the short source detector GGNR and the natural gamma detector NGR more accurately, a saturated logging model (UF-0.03-I, UF-0.1-I, UF-0.2-I, UF-0.5-I) of the national defense scientific and technological industrial radioactive metering station (1313) is used for data acquisition by using an MD604 density three-side logging instrument, and dead time (refer to the capacity of the detector to recover after receiving one ray or particle and prepare to receive the next ray or particle) is corrected and energy scale linearized (Table 1).
TABLE 1MD604 Density three-side tool Natural gamma Detector NGR, long Source Detector GGFR, short Source Detector GGNR dead time and count Rate ratio
It will be appreciated that the saturation logging models (UF-0.03-I, UF-0.1-I, UF-0.2-I, UF-0.5-I) described above differ only in the nominal content of uranium. Specifically, referring to fig. 3, fig. 3 is a linear fitting curve of count rate and model nominal content obtained on the 4 saturated logging models respectively for a natural gamma detector NGR, a long-source distance detector GGFR, and a short-source distance detector GGNR of the MD604-2005 density three-side logging instrument, and obtaining corresponding R according to the ratio of their slopes GGFR/NGR R is R GGNR/NGR Ratio of the two.
Illustratively, the detector count rate ratio is obtained using a field check model. Specifically, as long as the number of model wells is ensured to be enough, for example, N is more than 3, the R can be obtained by using a site check model developed by a nuclear industry aerial survey remote sensing center metering station GGFR/NGR R is R GGNR/NGR Ratio of the two. Fig. 4 is a schematic view of the structure of the field check model. Referring to FIG. 4, the field check model includes handles and feet that facilitate the carrying and placement of the field check model on the logging site by personnel; referring to the top view on the right side of fig. 4, the model well with a cylindrical middle part is checked on site.
Illustratively, the field check model provided in this embodiment has 6. Table 2 is a list of the main element and impurity element contents of the 6 kinds of check models.
Table 2 in-situ check model element content table
Note that: the result of the value a is only provided for reference (provided by the nuclear industry aerial survey remote sensing center).
As can be seen from the above, the nominal content of the model well in the embodiment of the application is 0.2-5167×10, whether it is a field check model or a saturated logging model -6 g/g, such that the density correction method of this embodiment has the ability to perform density correction over a wider range of formation radioactivity intensities.
S202, acquiring a density scale coefficient of the density logging instrument.
The density scale factor is calibration data for the density tool determined from the standard density samples. Specifically, an aluminum module and an organic glass module with known density are obtained as a scale module;
cesium sources (US 14CS001184 and US14CS 001224) are used as the radiation source for the density logging tool;
sequentially mounting an aluminum module and an organic glass module on a probe of a density logging instrument, and starting the density logging instrument to enable a cesium source to emit rays to a scale module;
recording a count rate reading of the logging instrument and a known density value of a scale module, and drawing a relation curve between the count rate reading and the density according to the recorded count rate reading and the module density;
fitting and analyzing the relation curve to obtain ln N=Aρ b +B, and obtaining density scale coefficients A and B of the density logging tool, wherein ρ b Density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the B-intercept, is constant.
That is, in this embodiment, the MD604 tool was calibrated for density parameters using cesium sources (US 14CS001184 and US14CS 001224) using aluminum modules and plexiglass modules, and the sensitivity, spine angle, and results are shown in table 3.
TABLE 3 MD604 Density Scale results
S203, logging by adopting the density logging instrument, and obtaining the count rates N of the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR NGR 、N GGFR And N GGNR 。
S204, according to the acquired counting rate N NGR 、N GGFR 、N GGNR And count rate ratio R GGFR/NGR 、R GGNR/NGR And calculating the net count rate of the long source detector GGFR and the short source detector GGNR, and finishing the correction of the count rate of the density parameter calculation.
Illustratively, the count rate N of the natural gamma detector NGR is taken NGR Respectively multiplied by the ratio R of the count rates GGFR/NGR And R is GGNR/NGR Acquiring a count rate N of natural gamma rays of a radioactive formation downhole to a long source detector GGFR and a short source detector GGNR GGFR 、N GGNR Then at the count rate N of the long-source detector GGFR GGFR And count rate N of short source detector GGNR GGNR Respectively subtracting the interference values corresponding to the two detectors, and calculating and obtaining the net count rate N of the long source detector GGFR and the short source detector GGNR GGFR cleaner And N GGNR cleaner And (5) finishing correction of the calculation count rate of the density parameter calculation.
Specifically, the correction of the calculation rate for the density parameter solution is completed by adopting the following formula:
N GGFR cleaner ＝N GGFR -N NGR ×R GGFR/NGR
N GGNR cleaner ＝N GGNR -N NGR ×R GGNR/NGR 。
S205, calculating the stratum density according to the density scale coefficient and the net count rate.
The formation density was calculated using the following formula:
ρ b ＝(1/A)ln N-B/A
wherein: ρ b -formation density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-LingSensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the B-intercept, is constant.
It should be noted that, the short source detector GGNR in the compensated density logging instrument is mainly used to correct the influence of the mud cake because the detection depth is shallow relative to the detection depth of the long source detector GGFR. In the well test procedure below, both with the field check model and the bare Kong Cejing, the density calculation and correction process is based on long source detector counts.
The density correction method in the embodiments of the present application is then experimentally compared to the count rate direct deduction method of two down hole measurements in conventional density correction practices, using an on-site verification model, for example. For convenience of description, the density correction method provided by the embodiment of the application is hereinafter referred to as a count rate ratio method.
The nominal uranium content of the verification model UH-0.03-II is 396X 10 -6 g/g. Using 4 MD604 tools, respectively: 1) Counting rate direct deduction method (namely subtracting the long and short source counting rate when the cesium source is not used from the long and short source counting rate when the cesium source is hung, which is equivalent to twice well logging, one time of source hanging logging and one time of non-source hanging logging); 2) Detector count rate ratio method (R GGFR/NGR ) The influence of low density calculation results caused by the change of the count of long and short sources caused by gamma rays of the ore deposit is corrected, and the results are shown in Table 4.
TABLE 4 check model (UH-0.03-II) Density correction results
As can be seen from Table 4, the measured density before correction was significantly lower, and the average value was 1.84g/cm 3 The counting rate deduction method of the two well logging is simulated to obtain the density average value of 2.01g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The density average value is 2.00g/cm obtained by the counting rate ratio deduction method (equivalent to one well logging) 3 . For the UH-0.03-II model, the density correction result is ideal, and especially the count rate direct deduction method is equivalent to the count rate ratio deduction method. Since there is no siteChecking the nominal value of the model, taking the measurement mean value as a reference value, wherein the error is +/-0.03 g/cm 3 Within a range of (2).
The model was checked for UH-0.5-II (its nominal uranium content of 5 167X 10) -6 g/g), using the count rate of the long-source detector, using the count rate deduction method and the count rate ratio method (R GGFR/NGR ) The density value of the field check model is calculated, and the counting rate ratio deduction method is closer to the actual (1.12 g/cm before correction) 3 The count rate deduction method was 2.54g/cm 3 And the counting rate ratio method is 2.05g/cm 3 ) The counting rate ratio method provided by the embodiment of the application has the capability of carrying out density correction in a wider range of formation radioactivity intensity.
Next, the density logger and the density correction method provided by the embodiment of the application are adopted to perform the comparison of the bare Kong Cejing well logging test and the well logging test. Note that the bare Kong Cejing (Open Hole Logging) refers to a logging method that performs data acquisition and recording by lowering a density logging tool into the borehole during drilling, before completion operations are performed. Well logging (Cased Hole Logging) refers to a method of logging through casing (logging) that has been completed after completion operations have been performed.
In FIGS. 5 and 6, GR represents quantitative gamma logging, expressed as the rate of irradiation (nC/(kg.h)), unless otherwise specified; n (N) NGR 、N GGFR 、N GGNR The count rates of the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR in the MD604 logging instrument are respectively shown, and the parameters before Den-correction and after Den-correction respectively show the density values before and after density correction by using the density correction method in the embodiment of the application.
FIG. 5 is a schematic diagram of borehole 1-2-16Z logging density correction. Referring to fig. 5,1-2-16Z well bore: gamma-gamma density logging is used for determining the position of a filter in a well and the thickness of fine gravel and coarse gravel, and the position of the filter is used for throwing the coarse gravel according to the well forming process requirement; the filter is filled with fine gravel at a position above and below the filter, and the density of the fine gravel is relatively lower than that of the coarse gravel. From the log in FIG. 5, it can be seen that the short source detector GGNR count rate is substantially independent of formation placementThe effect of the gamma rays is based on the count rate of the long source detector. The two curves on the far right side in FIG. 5 are the density log before and after density correction, the Den-corrected log is essentially a reflection of the mineral seam process structure compared to the Den-corrected log because the density log has a limited depth of detection, the corrected density values are essentially coarse particles (depth interval 390.0-396.15 m, density average 1.767 g/cm) 3 ) The density of the fine particles (the depth interval is 386.60-389.75 m, and 396.15-399.40 m, the average density is about 2.017 g/cm) 3 ). The quantitative gamma logging can reach up to 700 nC/(kg.h) in the mine section. The density correction is ideal by using the counting rate GGFR of the long-source detector.
Fig. 6 is a schematic diagram of correction of the density curve of the drilled hole SYG-1 bare Kong Cejing. Referring to FIG. 6, SYG-1 borehole, bare Kong Cejing, at 295.0-310.0 m depth, the long and short source detector count rates change, truly reflecting the change in formation density around the wellbore. And in the depth sections of 405.36-406.35 m and 423.80-426.34 m, the depth sections are just positioned at the position of the ore deposit, so that obvious interference is caused to the counting rate of the long-source detector. Accordingly, the contrast before and after density correction is obvious, and Den-before-correction density measurement values are lower, so that the inference of formation lithology is directly influenced. After density correction, the average density of the depth section of 405.36-406.35 m is 2.289g/cm 3 2.279g/cm from the upper stratum mean 3 Approaching; and the average density value of the depth segment of 423.80-426.34 m after correction is 2.363g/cm 3 With an upper formation density average of 2.331g/cm 3 Also close, should belong to the same lithology (coarse sandstone).
The borehole example validation results demonstrate that at 1 500 nC/(kg.h) density correction of the radioactive formation (FIG. 6), satisfactory results can be achieved using the count rate ratio method for density correction using the long source detector GGFR count rate. For the hard rock radioactive stratum, the influence of mud cakes does not exist, and it can be inferred that the density correction method provided by the embodiment of the application is also applicable.
In view of the above, the embodiment of the application discloses a density correction method for gamma-gamma density logging, which is an effective correction method for the problem of low formation volume density obtained by the gamma-gamma density logging method caused by natural gamma rays of a formation. Compared with the direct deduction method of obtaining the count rate of each detector after two well trips, the density correction method is effective in the larger natural gamma radiation intensity range of the stratum, and only one well trip is needed, so that the occupied drilling time is reduced. It should be noted that, the density correction method provided by the embodiment of the application is not limited to using the MD604 logging instrument, and as long as the density logging instrument has a natural gamma detector, the influence of natural gamma radioactivity on density measurement can be subtracted by adopting the detector count rate ratio deduction method provided by the application.
Finally, the above embodiments are only used to illustrate the technical solution of the present application. It will be appreciated by those skilled in the art that, although the application has been described in detail with reference to the foregoing embodiments, various modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof. Such modifications and substitutions do not depart from the spirit and scope of the corresponding technical solutions in the various embodiments of the application.

Claims (10)

1. A density correction method of gamma-gamma density logging is applied to a density logging instrument, wherein the density logging instrument comprises a natural gamma detector NGR, a long source detector GGFR and a short source detector GGNR;
the density correction method is characterized by comprising the following steps:
obtaining count rate ratio R of long-source detector GGFR and natural gamma detector NGR by using model well GGFR/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR The method comprises the steps of carrying out a first treatment on the surface of the The model well is a rock sample with known density and nominal content, which is obtained through testing, and the response difference of the long source detector GGFR and the short source detector GGNR relative to the natural gamma detector NGR to the natural gamma rays of the model well is obtained through the ratio of the counting rate;
acquiring a density scale coefficient of the density logging instrument; the density scale coefficient is calibration data of the density logging instrument determined according to a standard density sample;
logging by adopting the density logging instrument, and obtaining the counting rates N of the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR NGR 、N GGFR And N GGNR ；
Taking the count rate N of the natural gamma detector NGR NGR Respectively multiplied by the ratio R of the count rates GGFR/NGR And R is GGNR/NGR Acquiring a count rate N of natural gamma rays of a radioactive formation downhole to a long source detector GGFR and a short source detector GGNR GGFR 、N GGNR Then at the count rate N of the long-source detector GGFR GGFR And count rate N of short source detector GGNR GGNR Respectively subtracting the interference values corresponding to the two detectors, and calculating and obtaining the net count rate N of the long source detector GGFR and the short source detector GGNR GGFR cleaner And N GGNR cleaner Completing the correction of the counting rate for calculating the density parameters;
the formation density is calculated from the density scale factor and the net count rate.
2. The density correction method according to claim 1, wherein the model well is selected from any one of a saturated logging model or a field check model.
3. The method of density correction according to claim 1, wherein the model well is used to obtain a count rate ratio R of the long source detector GGFR to the natural gamma detector NGR GGFK/NGR Count rate ratio R of short source detector GGNR to natural gamma detector NGR GGNR/NGR Comprising:
obtaining nominal content of N model wells, wherein N is more than or equal to 2;
acquiring count rates N of natural gamma detector NGR, long-source detector GGFR and short-source detector GGNR in N model wells NGR ’、N GGFR ' and N GGNR ’；
Based on nominal content of N model wells and N count rates N NGR ’、N GGFR ' and N GGNR ' obtaining a linear fitting curve of the counting rate and the nominal content of the model well;
obtaining corresponding count rate ratio R according to the ratio of slopes of linear fitting curves of the natural gamma detector NGR, the long-source detector GGFR and the short-source detector GGNR GGFR/NGR R is R GGNR/NGR 。
4. A density correction method according to claim 3, characterized in that the nominal content of the model well is between 0.2 and 5167 x 10 -6 g/g。
5. The method of density correction according to any one of claims 1 to 4, characterized in that the net count rate NG of the long source detector GGFR and the short source detector GGNR is obtained using the following formula GFR cleaner And N GGNR cleaner And (3) finishing correction of the calculation counting rate of the density parameter solution:
N GGFR cleaner ＝N GGF R-N NGR ×R GGFR/NGR
N GGNR cleaner ＝N GGNR -N NGR ×R GGNR/NGR 。
6. The method of any one of claims 1-4, wherein the obtaining a density scale factor of a density tool comprises:
acquiring an aluminum module and an organic glass module with known density as a scale module;
adopting cesium source as radioactive source of density logging instrument;
sequentially mounting an aluminum module and an organic glass module on a probe of a density logging instrument, and starting the density logging instrument to enable a cesium source to emit rays to a scale module;
recording a count rate reading of the logging instrument and a known density value of a scale module, and drawing a relation curve between the count rate reading and the density according to the recorded count rate reading and the module density;
fitting and analyzing the relation curve to obtain lnN=Aρ b +B, and obtaining density scale coefficients A and B of the density logging instrument,wherein ρ is b Density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the The B-intercept is constant.
7. The density correction method as set forth in claim 1, wherein said calculating formation density from the density scale factor and the net count rate includes:
the formation density was calculated using the following formula:
ρ b ＝(1/A)ln N-B/A
wherein: ρ b -formation density in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the N-detector count rate in s -1 The method comprises the steps of carrying out a first treatment on the surface of the A-sensitivity coefficient in s -1 /(g/cm 3 ) The method comprises the steps of carrying out a first treatment on the surface of the The B intercept is constant.
8. The density correction method as claimed in claim 6, wherein the cesium source is 200mm apart from the short source detector GGNR; the distance between the cesium sources and the long source detector GGFR is 350m; the cesium source is spaced 2500mm from the natural gamma detector NGR.
9. The method according to any one of claims 1 to 4, wherein the natural gamma detector NGR, the long source detector GGFR and the short source detector GGNR are all sodium iodide crystals having diameters and lengths of 30mm and 80mm, 23mm and 40mm, 13mm and 10mm, respectively, and energy thresholds of 130kev.
10. The density correction method as claimed in claim 9, wherein said short source detector GGNR incorporates tantalum silver flakes.
CN202310906987.2A 2023-07-21 2023-07-21 Density correction method for gamma-gamma density logging Pending CN116794749A (en)

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