While-drilling high-precision density logging inversion method based on multi-energy window

Abstract

The invention discloses a while-drilling high-precision density logging inversion method based on a multi-energy window, and the method comprises the following steps: S1, measuring an energy spectrum through gamma rays in the measurement process of a scale well in different stratum densities and stratum lithology factors, determining an energy window range and a first counting rate, obtaining an initial function relation between the first counting rate in the scale well and the stratum density and the stratum lithology index; s2, through actually measuring a first counting rate of gamma rays in different stratum densities, gaps, stratum lithology indexes, slurry densities and slurry lithology indexes, carrying out multi-energy window cooperative solving of a multi-dimensional overdetermined nonlinear equation set, and obtaining a final function relational expression; and S3, on the basis that the forward modeling result is accurate, setting an initial value, solving a multi-dimensional overdetermined nonlinear equation set for the final function relation, and performing inversion verification to determine the correctness of the final function relation. And the measurement precision of the formation density and the lithologic index of the while-drilling lithologic density logging is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield logging, and in particular relates to a high-precision density logging while drilling inversion method based on a multi-energy window. Background Art

[0002] The azimuth density logging while drilling method provides density imaging data in 16 azimuths of 360° around the well, providing formation density and lithology data for real-time formation evaluation and geological guidance, and using more precise inversion methods to accurately evaluate the formation, which has important practical significance for guiding reservoir development.

[0003] The current azimuthal density logging method while drilling often uses two gamma detectors, near and far, for formation evaluation. In terms of data processing methods, the near and far apparent density values ​​measured by the two detectors are used to eliminate the influence of mud cake in the borehole or the gap between the instrument and the wellbore wall through the "ridge rib diagram" correction, so as to evaluate the formation parameters. However, a high-energy density window and a low-energy lithology window are set for the energy spectrum, and one energy window is used to measure the density, and the ratio of the two energy windows is used to measure the lithology index. Therefore, there is a certain correlation between the measurement of the formation lithology and density, and the instrument is the response relationship of the scale when there is no gap with the wellbore. When there is a gap, the energy spectrum or energy window count measured by each detector of the instrument is a comprehensive response of the gap and the five parameters of the formation, mud density, and lithology index, which leads to a large error in this method. Schlumberger used a multivariate regression method to solve the fitting empirical formula between multiple parameters and energy window counts, but the fitting inversion result is not accurate enough and this method has certain limitations.

[0004] Therefore, this patent proposes a new multi-parameter inversion and initial value setting method for density logging while drilling. Each energy window count is the comprehensive contribution of five parameters. A more accurate response relationship formula is used to make up for the lack of accuracy of multi-detector density logging instruments in inversion, and accurate formation parameters are obtained, thereby effectively improving the inversion accuracy of azimuthal density logging while drilling. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a high-precision density logging inversion method while drilling based on a multi-energy window, which solves the problem of insufficient inversion accuracy of multi-detector density logging instruments used in the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a high-precision density logging inversion method while drilling based on a multi-energy window, comprising the following steps:

[0007] S1. During the measurement of calibration wells with different formation densities and formation lithology factors, gamma rays are used to measure the energy spectrum, determine the energy window range and the first count rate, and then obtain the initial functional relationship between the first count rate in the calibration well and the formation density and formation lithology index;

[0008] S2, by measuring the first count rate of gamma rays in different formation densities, gaps, formation lithology indices, mud densities, and mud lithology indices, multi-energy windows are used to collaboratively solve the multi-dimensional overdetermined nonlinear equations to obtain the final functional relationship;

[0009] S3. On the basis of accurate forward modeling results, set initial values ​​and solve the multi-dimensional overdetermined nonlinear equations for the final functional relationship, and perform inversion verification to determine the correctness of the final functional relationship.

[0010] Further: S1 comprises the following sub-steps:

[0011] S11, determining corresponding instruments and geological conditions according to the structure of the azimuth density logging while drilling instrument, wherein the instrument includes a drill collar and a detector, and the geological conditions include a borehole size and a formation size;

[0012] S12, conduct azimuth density logging while drilling, and measure the energy spectrum of different formation densities and different formation lithology factors in the calibration well;

[0013] S13, based on the Compton effect and the photoelectric effect, the energy spectrum that can reflect the different response relationships of gamma rays to lithology and density is divided into different energy windows, and the first counting rate of different formation densities and different formation lithology indexes in the calibration well is obtained;

[0014] S14, performing a multi-energy window collaborative solution on the first count rate, the formation density and the formation lithology index, and obtaining an initial functional relationship between the first count rate, the formation density and the formation lithology index in the calibration well;

[0015] S15. Invert the initial functional relationship.

[0016] Further: in said S14, the expression of the initial functional relation f1 is specifically:

[0017] f1=a1+a2ρ+a3ρ 2 +a4L

[0018] Wherein, ρ is the formation density, L is the lithology factor of the formation, a1 is the first constant, a2 is the second constant, a3 is the third constant, and a4 is the fourth constant.

[0019] Further: S2 comprises the following sub-steps:

[0020] S21, obtaining a second count rate of gamma rays at different formation densities, gaps, formation lithology indexes, mud densities, and mud lithology indexes by measuring with a while-drilling azimuth density logging instrument according to the divided energy windows;

[0021] S22. According to the second counting rate, the relationship terms with the mud density, mud lithology index and clearance are added to the initial functional relationship, and the multi-dimensional overdetermined nonlinear equations are solved by multi-energy windows to obtain the final functional relationship.

[0022] Further: in said S22, the expression of the final functional relationship f2 is specifically:

[0023] f2=a1+a2ρ+a3ρ 2 +a4L+a5(ρ-ρ m )t+a6(ρ-ρ m ) 2 t+a7(LL m )t

[0024] In the formula, ρ m is the mud density, L m is the mud lithology factor, t is the size of the gap, a5 is the fifth constant, a6 is the sixth constant, and a7 is the seventh constant.

[0025] Further: S3 includes the following sub-steps:

[0026] S31. Set the initial value of the formation density, specifically:

[0027] Set the initial value of formation density. The initial value of formation density is obtained by fitting the functional relationship between the near-far density difference and the mudcake effect correction value. The mudcake effect correction value is the difference between the true formation density and the far density.

[0028] S32. Set the initial value of the lithology factor of the formation, specifically:

[0029] Based on the first count rate of different formation densities and different formation lithology indexes in the calibration well, the count ratio of high and low energy windows is obtained, and the initial value of the formation lithology factor is obtained by fitting the relationship;

[0030] S33, using the ultrasonic gap to set the initial value of the gap size;

[0031] S34, setting initial values ​​of mud density and mud lithology factor according to drilling mud parameters;

[0032] S35, setting a cost function, verifying the inversion method, setting the cost function as a quality control factor for the measurement, iterating the calculation until the inversion effect is optimal, and determining the correctness of the final functional relationship.

[0033] Further: In S35, the expression of the cost function C(ε) is specifically:

[0034] C(ε)=C1+C2

[0035] Where C1 is the measurement reconstruction error term, which is used to measure the difference between the actual measurement value and the theoretical response F(ε), and C2 is the stability parameter of the control result deviating from the formation, which is used to prevent large gaps;

[0036]

[0037] Where W i is the actual measured value, F i (ε) is the theoretical response value, is the forward modeling error, is measurement error or statistical noise;

[0038]

[0039] In the formula, is the average value of the parameter vector, ε is a variable in the iterative process of the inversion algorithm, is the average value of the difference between the parameter vector and the parameters obtained by the inversion iteration.

[0040] The beneficial effects of the present invention are:

[0041] (1) The present invention provides a high-precision density logging inversion method while drilling based on a multi-energy window, which can improve the data accuracy and imaging resolution of the azimuthal lithologic density logging while drilling, effectively improve the measurement accuracy of the formation density and lithologic index of the lithologic density logging while drilling, reduce the influence of the wellbore environment, and overcome the shortcomings of the ridge-rib image processing technology.

[0042] (2) The present invention adopts a new density and lithology factor measurement method, uses the energy spectrum of the near detector and the high energy part of the far detector to deduce the formation density and lithology factor, and realizes density calculation by collaboratively solving a multi-dimensional overdetermined nonlinear equation group. When performing inversion, the initial value is set to ensure the global optimality of the solution, which can help obtain real and accurate formation parameters and has high accuracy in inversion applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The present invention is a flow chart of a high-precision density logging inversion method while drilling based on a multi-energy window.

[0044] Figure 2 This is the first way to divide the energy window for gamma-ray density measurement.

[0045] Figure 3 The second method of dividing the energy window for gamma-ray density measurement.

[0046] Figure 4 This is an imaging comparison diagram of the original data and the data after inversion processing using the LM method. DETAILED DESCRIPTION

[0047] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0048] like Figure 1 As shown, in one embodiment of the present invention, a high-precision density logging inversion method while drilling based on a multi-energy window includes the following steps:

[0049] S1. During the measurement of calibration wells with different formation densities and formation lithology factors, gamma rays are used to measure the energy spectrum, determine the energy window range and the first count rate, and then obtain the initial functional relationship between the first count rate in the calibration well and the formation density and formation lithology index;

[0050] S2, by measuring the first count rate of gamma rays in different formation densities, gaps, formation lithology indices, mud densities, and mud lithology indices, multi-energy windows are used to collaboratively solve the multi-dimensional overdetermined nonlinear equations to obtain the final functional relationship;

[0051] S3. On the basis of accurate forward modeling results, set initial values ​​and solve the multi-dimensional overdetermined nonlinear equations for the final functional relationship, and perform inversion verification to determine the correctness of the final functional relationship.

[0052] The S1 comprises the following sub-steps:

[0053] S11, determining corresponding instruments and geological conditions according to the structure of the azimuth density logging while drilling instrument, wherein the instrument includes a drill collar and a detector, and the geological conditions include a borehole size and a formation size;

[0054] In this embodiment, the detector includes a near detector and a far detector.

[0055] S12, conduct azimuth density logging while drilling, and measure the energy spectrum of different formation densities and different formation lithology factors in the calibration well;

[0056] S13, based on the Compton effect and the photoelectric effect, the energy spectrum that can reflect the different response relationships of gamma rays to lithology and density is divided into different energy windows, and the first counting rate of different formation densities and different formation lithology indexes in the calibration well is obtained;

[0057] In this embodiment, the energy window is Figures 2-3 As shown, taking the energy spectrum of 42 to 502 keV being divided into four energy windows as an example, the energy window of 42 to 124 keV is sensitive to lithology, the energy window of 124 to 502 keV is sensitive to density, and each energy window can obtain a first counting rate.

[0058] S14, performing a multi-energy window collaborative solution on the first count rate, the formation density and the formation lithology index, and obtaining an initial functional relationship between the first count rate, the formation density and the formation lithology index in the calibration well;

[0059] S15. Invert the initial functional relationship to ensure the correctness of the initial functional relationship.

[0060] In S14, the initial functional relationship f1 is specifically expressed as:

[0061] f1=a1+a2ρ+a3ρ 2 +a4L

[0062] Wherein, ρ is the formation density, L is the lithology factor of the formation, a1 is the first constant, a2 is the second constant, a3 is the third constant, and a4 is the fourth constant.

[0063] The S2 comprises the following sub-steps:

[0064] S21, obtaining a second count rate of gamma rays at different formation densities, gaps, formation lithology indexes, mud densities, and mud lithology indexes by measuring with a while-drilling azimuth density logging instrument according to the divided energy windows;

[0065] S22. According to the second counting rate, the relationship terms with the mud density, mud lithology index and clearance are added to the initial functional relationship, and the multi-dimensional overdetermined nonlinear equations are solved by multi-energy windows to obtain the final functional relationship.

[0066] In S22, the expression of the final functional relationship f2 is specifically:

[0067] f2=a1+a2ρ+a3ρ 2 +a4L+a5(ρ-ρ m )t+a6(ρ-ρ m ) 2 t+a7(LL m )t

[0068] In the formula, ρ m is the mud density, L m is the mud lithology factor, t is the size of the gap, a5 is the fifth constant, a6 is the sixth constant, and a7 is the seventh constant.

[0069] The S3 comprises the following sub-steps:

[0070] S31. Set the initial value of the formation density, specifically:

[0071] Set the initial value of formation density. The initial value of formation density is obtained by fitting the functional relationship between the near-far density difference and the mudcake effect correction value. The mudcake effect correction value is the difference between the true formation density and the far density.

[0072] S32. Set the initial value of the lithology factor of the formation, specifically:

[0073] Based on the first count rate of different formation densities and different formation lithology indexes in the calibration well, the count ratio of high and low energy windows is obtained, and the initial value of the formation lithology factor is obtained by fitting the relationship;

[0074] S33, using the ultrasonic gap to set the initial value of the gap size;

[0075] S34, setting initial values ​​of mud density and mud lithology factor according to drilling mud parameters;

[0076] S35, setting a cost function, verifying the inversion method, setting the cost function as a quality control factor for the measurement, iterating the calculation until the inversion effect is optimal, and determining the correctness of the final functional relationship.

[0077] In S35, the expression of the cost function C(ε) is specifically:

[0078] C(ε)=C1+C2

[0079] Where C1 is the measurement reconstruction error term, which is used to measure the difference between the actual measurement value and the theoretical response F(ε), and C2 is the stability parameter of the control result deviating from the formation, which is used to prevent large gaps;

[0080]

[0081] Where W i is the actual measured value, F i (ε) is the theoretical response value, is the forward modeling error, is measurement error or statistical noise;

[0082]

[0083] In the formula, is the average value of the parameter vector, ε is a variable in the iterative process of the inversion algorithm, is the average value of the difference between the parameter vector and the parameters obtained by the inversion iteration.

[0084] The basic principle of the present invention is to realize the inversion and initial value setting method of high-precision density logging while drilling based on multiple energy windows. First, the principle of azimuthal lithologic density logging while drilling is analyzed, and the instrument is placed in a calibration well for actual measurement. According to the energy window division method of gamma-ray density measurement, a method of collaboratively solving multidimensional equations with multiple energy windows is adopted to obtain the functional relationship between the count rate in the calibration well and the formation density and formation lithologic factors. Then, on the basis of the obtained functional relationship in the calibration well, the response relationship of the formation gap is added, and the method of collaboratively solving multidimensional equations with multiple energy windows is also adopted to obtain the final functional relationship. Then, the final functional relationship is inverted and verified, the initial value is set, and the calculation parameters in the formula are adjusted to make the inversion data closer to the true value. Finally, the original data is compared with the data for inversion verification, and the actual application effect is checked and analyzed.

[0085] like Figure 4 As shown, it is an imaging comparison diagram of the original data and the data after inversion processing by the LM method. It can be seen from the figure that the inversion effect of the LM inversion method is better and the accuracy is higher. Not only that, the density logging curve processed by the LM inversion method has a certain consistency between the five parameter data formations and the actual formation parameter values, but there will be a certain error. Most of the inversion values ​​are the same as the true value or the error is within the measurement accuracy. The high-precision density logging method based on multi-energy windows improves the accuracy of the data, achieves high resolution, and ultimately achieves high precision. It can be seen that the method of the present invention can effectively realize high-precision density logging and meet engineering requirements. It can be used in oil and gas drilling and logging operations and has a wide range of application scenarios.

[0086] The beneficial effects of the present invention are as follows: the present invention provides a high-precision density logging inversion method while drilling based on a multi-energy window, which can improve the data accuracy and imaging resolution of the azimuthal lithologic density logging while drilling, effectively improve the measurement accuracy of the formation density and lithologic index of the lithologic density logging while drilling, reduce the influence of the wellbore environment, and overcome the shortcomings of the ridge-rib image processing technology.

[0087] The present invention adopts a new density and lithology factor measurement method, uses the energy spectrum of the near detector and the high energy part of the far detector to deduce the formation density and lithology factor, and realizes density calculation by collaboratively solving a multi-dimensional overdetermined nonlinear equation group. When performing inversion, the initial value is set to ensure the global optimality of the solution, which can help obtain real and accurate formation parameters and has high accuracy in inversion applications.

[0088] In the description of the present invention, it is necessary to understand that the orientation or positional relationship indicated by the terms "center", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "radial", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", and "third" are used only for descriptive purposes, and cannot be understood as indicating or implying the relative importance or the number of implicitly specified technical features. Therefore, the features defined by "first", "second", and "third" may explicitly or implicitly include one or more of the features.

Claims

1. A high-precision density logging inversion method while drilling based on a multi-energy window, characterized in that: The following steps are involved: S1. During the measurement of calibration wells with different formation densities and formation lithology factors, gamma rays are used to measure the energy spectrum, determine the energy window range and the first count rate, and then obtain the initial functional relationship between the first count rate in the calibration well and the formation density and formation lithology index; S2, by measuring the first count rate of gamma rays in different formation densities, gaps, formation lithology indices, mud densities, and mud lithology indices, multi-energy windows are used to collaboratively solve the multi-dimensional overdetermined nonlinear equations to obtain the final functional relationship; S3. On the basis of accurate forward modeling results, set initial values ​​and solve the multi-dimensional overdetermined nonlinear equations for the final functional relationship, and perform inversion verification to determine the correctness of the final functional relationship.

2. The multi-energy window-based high-precision density logging while drilling inversion method according to claim 1, characterized in that: The S1 comprises the following sub-steps: S11, determining corresponding instruments and geological conditions according to the structure of the azimuth density logging while drilling instrument, wherein the instrument includes a drill collar and a detector, and the geological conditions include a borehole size and a formation size; S12, conduct azimuth density logging while drilling, and measure the energy spectrum of different formation densities and different formation lithology factors in the calibration well; S13, based on the Compton effect and the photoelectric effect, the energy spectrum that can reflect the different response relationships of gamma rays to lithology and density is divided into different energy windows, and the first counting rate of different formation densities and different formation lithology indexes in the calibration well is obtained; S14, performing a multi-energy window collaborative solution on the first count rate, the formation density and the formation lithology index, and obtaining an initial functional relationship between the first count rate, the formation density and the formation lithology index in the calibration well; S15. Invert the initial functional relationship.

3. The multi-energy window-based high-precision density logging while drilling inversion method according to claim 2 is characterized in that: In S14, the initial functional relationship f1 is specifically expressed as: f1=a1+a2ρ+a3ρ 2 +a4L Wherein, ρ is the formation density, L is the lithology factor of the formation, a1 is the first constant, a2 is the second constant, a3 is the third constant, and a4 is the fourth constant.

4. The high-precision density logging inversion method while drilling based on multi-energy windows according to claim 3 is characterized in that: The S2 comprises the following sub-steps: S21, obtaining a second count rate of gamma rays at different formation densities, gaps, formation lithology indexes, mud densities, and mud lithology indexes by measuring with a while-drilling azimuth density logging instrument according to the divided energy windows; S22. According to the second counting rate, the relationship terms with the mud density, mud lithology index and clearance are added to the initial functional relationship, and the multi-dimensional overdetermined nonlinear equations are solved by multi-energy windows to obtain the final functional relationship.

5. The multi-energy window-based high-precision density logging while drilling inversion method according to claim 4, characterized in that: In S22, the expression of the final functional relationship f2 is specifically: f2=a1+a2ρ+a3ρ 2 +a4L+a5(p-p m )t+a6(p-p m ) 2 t+a7(LL m )t In the formula, ρ m is the mud density, L m is the mud lithology factor, t is the size of the gap, a5 is the fifth constant, a6 is the sixth constant, and a7 is the seventh constant.

6. The multi-energy window based high-precision density logging while drilling inversion method according to claim 1, characterized in that: The S3 comprises the following sub-steps: S31. Set the initial value of the formation density, specifically: Set the initial value of formation density. The initial value of formation density is obtained by fitting the functional relationship between the near-far density difference and the mudcake effect correction value. The mudcake effect correction value is the difference between the true formation density and the far density. S32. Set the initial value of the lithology factor of the formation, specifically: Based on the first count rate of different formation densities and different formation lithology indexes in the calibration well, the count ratio of high and low energy windows is obtained, and the initial value of the formation lithology factor is obtained by fitting the relationship; S33, using the ultrasonic gap to set the initial value of the gap size; S34, setting initial values ​​of mud density and mud lithology factor according to drilling mud parameters; S35, setting a cost function, verifying the inversion method, setting the cost function as a quality control factor for the measurement, iterating the calculation until the inversion effect is optimal, and determining the correctness of the final functional relationship.

7. The multi-energy window-based high-precision density logging while drilling inversion method according to claim 6, characterized in that: In S35, the expression of the cost function C(ε) is specifically: C(ε)=C1+C2 Where C1 is the measurement reconstruction error term, which is used to measure the difference between the actual measurement value and the theoretical response F(ε), and C2 is the stability parameter of the control result deviating from the formation, which is used to prevent large gaps; Where W i is the actual measured value, F i (ε) is the theoretical response value, is the forward modeling error, is measurement error or statistical noise; In the formula, is the average value of the parameter vector, ε is a variable in the iterative process of the inversion algorithm, is the average value of the difference between the parameter vector and the parameters obtained by the inversion iteration.

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