A method for drilling while high-precision density logging inversion based on multi-energy window

Abstract

The application discloses a method for drilling high-precision density logging inversion based on a multi-energy window, which comprises the following steps: S1, in the measurement process of the calibration well in different stratum densities and stratum lithology factors, gamma ray measurement energy spectrum is used to determine the energy window range and the first count rate, and then an initial function relationship between the first count rate in the calibration well and the stratum density and the stratum lithology index is obtained; S2, the first count rate of the measured gamma ray in different stratum densities, gaps, stratum lithology indexes, mud densities and mud lithology indexes is used to solve a multi-dimensional over-determined nonlinear equation set in a multi-energy window, and a final function relationship is obtained; and S3, on the basis of the accurate forward result, an initial value is set, the final function relationship is used to solve the multi-dimensional over-determined nonlinear equation set, and inversion verification is carried out to determine the correctness of the final function relationship. The method effectively improves the measurement precision of the stratum density and the lithology index of the drilling lithology density logging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oilfield logging, and particularly relates to a high-precision density logging inversion method while drilling based on multiple energy windows. BACKGROUND

[0002] The method of azimuthal density logging while drilling provides 16 azimuthal density imaging data of 360 degrees around the well, and provides formation density and lithology data for real-time evaluation of the formation and geosteering, etc. A more accurate inversion method is used to accurately evaluate the formation, which has important practical significance for guiding the development of the reservoir.

[0003] The current method of azimuthal density logging while drilling often uses two near and far gamma detectors to evaluate the formation. In the data processing method, the near and far apparent density values measured by the two detectors are used to eliminate the influence of the mud cake in the wellbore or the gap between the instrument and the well wall through "ridge rib graph" correction, so as to evaluate the formation parameters. However, one high-energy density window and one 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, so there is a certain correlation between the measurement of the formation lithology and the density. The instrument is calibrated in the case that there is no gap between the wellbore and the instrument, and the response relationship is calibrated. 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 five parameters of the gap, the formation, the mud density and the lithology index. This leads to a large error of the method. Schlumberger Company once used a multiple regression method to solve the fitting empirical formula between multiple parameters and energy window counts, but the precision of the fitting inversion result was insufficient and the method had certain limitations.

[0004] Therefore, the present patent proposes a new multi-parameter inversion and initial value setting method for density logging while drilling. Each energy window count is a comprehensive contribution of five parameters, and a more accurate response relationship formula is used to make up for the insufficient precision of the multi-detector density logging instrument in the inversion aspect, so as to obtain accurate formation parameters, thereby effectively improving the inversion precision of the azimuthal density logging while drilling. SUMMARY

[0005] In view of the above deficiencies in the prior art, the present application provides a high-precision density logging inversion method while drilling based on multiple energy windows, which solves the problem of insufficient precision of the multi-detector density logging instrument in the inversion aspect in the prior art.

[0006] In order to achieve the above-mentioned application purposes, the technical scheme adopted by the present application is as follows: a high-precision density logging inversion method while drilling based on multiple energy windows, comprising the following steps:

[0007] S1, using gamma-ray measurement spectrum in the measurement process of the calibration well in different formation density, formation lithology factor, determining the energy window range and the first count rate, and then obtaining the initial function relationship between the first count rate in the calibration well and the formation density and the formation lithology index;

[0008] S2, by measuring the first count rate of gamma rays in different formation density, gap, formation lithology index, mud density, mud lithology index, solving the multi-dimensional over-determined nonlinear equation set in multiple energy windows, and obtaining the final function relationship;

[0009] S3, on the basis of accurate forward result, setting initial value and solving multi-dimensional over-determined nonlinear equation set of final function relationship, carrying out inversion verification to determine the correctness of final function relationship.

[0010] Further, the S1 comprises the following steps:

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

[0012] S12, carrying out while-drilling process measurement of azimuthal density logging, measuring the energy spectrum of the measuring instrument in different formation density and different formation lithology factors in the calibration well;

[0013] S13, based on Compton effect and photoelectric effect, dividing the energy spectrum which can reflect the different response relationship of gamma rays to lithology and density into different energy windows, and obtaining the first count rate of different formation density and different formation lithology index in the calibration well;

[0014] S14, solving the first count rate and the formation density and the formation lithology index in multiple energy windows, and obtaining the initial function relationship between the first count rate in the calibration well and the formation density and the formation lithology index;

[0015] S15, inverting the initial function relationship.

[0016] Further, in the S14, the expression of the initial function relationship f1 is specifically:

[0017] f1=a1+a2ρ+a3ρ 2 +a4L

[0018] In the formula, 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, the S2 comprises the following steps:

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

[0021] S22, adding the relationship terms of the mud density, the mud lithology index and the gap to the initial function relationship on the basis of the second count rate, and solving the multi-dimensional over-determined nonlinear equation set in a multi-energy window to obtain a final function relationship.

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

[0023] f2=a1+a2ρ+a3ρ 2 +a4L+a5(ρ-ρ m )t+a6(ρ-ρ m ) 2 t+a7(L-L 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, the S3 includes the following steps:

[0026] S31, setting an initial value of the formation density, specifically:

[0027] Setting the initial value of the formation density. By fitting the function relationship of the near-far density difference and the mud cake influence correction value, the mud cake influence correction value is the difference relationship between the formation true density and the far density, the initial value of the formation density is obtained;

[0028] S32, setting an 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 the high and low energy windows is obtained, and the initial value of the lithology factor of the formation is obtained by fitting the relationship;

[0030] S33, setting the initial value of the size of the gap by using the ultrasonic gap;

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

[0032] S35, setting a cost function, verifying the inversion method, setting the cost function as a quality control factor of the measurement, and iteratively calculating until the inversion effect is optimal to determine the correctness of the final function relationship.

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

[0034] C(ε) = C1 + C2

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

[0036]

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

[0038]

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

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

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

[0042] (2) The present application 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 derive the formation density and lithology factor, and realizes density calculation by cooperatively solving a multi-dimensional over-determined nonlinear equation set. Initial value setting is performed during inversion to ensure the global optimality of the solution, which can help obtain real and accurate formation parameters, and has high accuracy in inversion application. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a flowchart of a while-drilling high-precision density logging inversion method based on a multi-energy window of the present application.

[0044] Figure 2 is a gamma ray density measurement energy window division mode one.

[0045] Figure 3 is a gamma ray density measurement energy window division mode two.

[0046] Figure 4 The imaging contrast chart of the original data and the data after the L-M method inversion processing. DETAILED DESCRIPTION

[0047] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims, all the inventions utilizing the concept of the present application are within the scope of protection.

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

[0049] S1, in the measurement process of the calibration well in different formation densities and formation lithology factors, the gamma ray measurement spectrum is used to determine the energy window range and the first count rate, and then the initial functional relationship between the first count rate and the formation density and the formation lithology index in the calibration well is obtained;

[0050] S2, by measuring the first count rate of the gamma ray in different formation densities, gaps, formation lithology indexes, mud densities and mud lithology indexes, a multi-energy window is used to solve a multi-dimensional overdetermined nonlinear equation set to obtain the final functional relationship;

[0051] S3, on the basis of the accurate forward result, the initial value is set and the multi-dimensional overdetermined nonlinear equation set is solved to verify the final functional relationship and determine the correctness of the final functional relationship.

[0052] The S1 comprises the following steps:

[0053] S11, according to the structure of the drilling azimuthal density logging instrument, the corresponding instrument and geological conditions are determined, 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, the drilling process of the azimuthal density logging is measured, and the energy spectrum of the measuring instrument in the calibration well in different formation densities and different formation lithology factors is measured;

[0056] S13, based on the Compton effect and the photoelectric effect, the energy spectrum reflecting the different response relationship of the gamma ray to the lithology and the density is divided into different energy windows, and the first count rate of the calibration well in different formation densities and different formation lithology indexes is obtained;

[0057] ​In the embodiment, the energy window is as shown in the figure to divide the energy spectrum 42 to 502 keV into four energy windows, for 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 a first count rate can be obtained for each energy window. Figures 2-3

[0058] S14, the first count rate, the formation density and the formation lithology index are solved in the multi-energy window to obtain an initial function relationship between the first count rate, the formation density and the formation lithology index in the calibration well.

[0059] S15, the initial function relationship is inverted to ensure the correctness of the initial function relationship.

[0060] In the S14, the expression of the initial function relationship f1 is specifically:

[0061] f1=a1+a2ρ+a3ρ 2 +a4L

[0062] In the formula, 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 includes the following steps:

[0064] S21, the second count rate of the gamma ray in different formation density, gap, formation lithology index, mud density, mud lithology index is measured by the while-drilling azimuthal density logging instrument according to the divided energy window;

[0065] S22, the relationship term of the mud density, the mud lithology index and the gap is added to the initial function relationship according to the second count rate, and the multi-energy window is solved to obtain the final function relationship.

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

[0067] f2=a1+a2ρ+a3ρ 2 +a4L+a5(ρ-ρ m )t+a6(ρ-ρ m ) 2 t+a7(L-L 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 includes the following steps:​

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

[0071] The initial value of the formation density is set. By fitting the function relationship of the near-far density difference and the mud cake influence correction value, the mud cake influence correction value is the difference between the true formation density and the far density, the initial value of the formation density is obtained;

[0072] S32, setting 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 high and low energy window count ratio is obtained, and the relationship formula fitting is carried out to obtain the initial value of the lithology factor of the formation;

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

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

[0076] S35, setting the cost function, verifying the inversion method, setting the cost function as the quality control factor of measurement, iterative calculation to the optimal inversion effect, and determining the correctness of the final function relationship.

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

[0078] C(ε)=C1+C2

[0079] In the formula, 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 for preventing large gap.

[0080]

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

[0082]

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

[0084] The basic principle of the present application is based on the implementation of the while-drilling high-precision density logging inversion and initial value setting method of the multi-energy window. First, the principle of the while-drilling azimuthal lithology density logging is analyzed, the instrument is placed in a calibration well for actual measurement, and a multi-energy window is used to solve a multi-dimensional equation to obtain the functional relationship between the count rate in the calibration well and the formation density and the formation lithology factor according to the energy window division method of the gamma ray density measurement. Then, based on the obtained functional relationship in the calibration well, the response relationship of the formation gap is added, and a multi-energy window is also used to solve a multi-dimensional equation 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, so that the inversion data is closer to the true value. Finally, the original data and the data after inversion verification are compared, and the actual application effect is viewed and analyzed.

[0085] As shown in Figure 4 The imaging comparison chart of the original data and the data after L-M method inversion processing. As can be seen from the figure, the inversion effect of the L-M inversion method is good, and the precision is high. Moreover, after the L-M inversion method processing, the density logging curve, the five parameter data formation and the true formation parameter value have certain consistency, but there will be certain error, most of the inversion values are the same as the true values or the error is within the measurement accuracy. The high-precision density logging method based on the multi-energy window improves the accuracy of the data, realizes high resolution, and finally realizes high precision. Therefore, it can be known that the method of the present application can effectively realize high-precision density logging and meet the requirements of engineering, and can be used in oil and gas drilling and logging operation, and has a wide application scene.

[0086] The present application has the advantages that: the present application provides a while-drilling high-precision density logging inversion method based on a multi-energy window, which can improve the data accuracy and imaging resolution of the while-drilling azimuthal lithology density logging, effectively improve the measurement accuracy of the formation density and the lithology index of the while-drilling lithology density logging, reduce the influence of the wellbore environment, and overcome the shortcomings of the ridge rib processing technology.

[0087] The present application 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 derive the formation density and the lithology factor, and realizes density calculation by solving a multi-dimensional over-determined nonlinear equation group. The initial value is set during inversion to ensure the global optimality of the solution, which can help to obtain real and accurate formation parameters, and has high accuracy in inversion application.

[0088] In the description of the application, it needs to be understood that the terms "center", "thickness", "upper", "lower", "horizontal", "top", "bottom", "inner", "outer", "radial" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implying the number of technical features indicated. Therefore, the features defined by "first", "second", "third" can explicitly or implicitly include one or more of the features.

Claims

1. A high-precision density logging inversion method based on multi-window drilling, characterized in that, Includes the following steps: S1. During the measurement process 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 and formation density and formation lithology index in the calibration well. S1 includes the following steps: S11. Based on the structure of the drilling azimuth density logging instrument, determine the corresponding instrument and geological conditions. The instrument includes drill collars and detectors, and the geological conditions include wellbore size and formation size. S12. Conduct azimuth density logging during the drilling process and measure the energy spectrum of different formation densities and different formation lithology factors in the calibrated well. S13. Based on the Compton effect and 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 to obtain the first count rate of different formation densities and different formation lithology indices in the calibration well. S14. Perform multi-window collaborative solution on the first count rate, formation density, and formation lithology index to obtain the initial functional relationship between the first count rate, formation density, and formation lithology index in the calibration well; S15. Inverse the initial functional relationship; S2. By measuring the first count rate of gamma rays in different formation densities, gaps, formation lithology indices, mud density, and mud lithology indices, a multi-window collaborative solution of multidimensional overdetermined nonlinear equations is performed to obtain the final functional relationship. S3. Based on the accuracy of the forward modeling results, set initial values ​​and solve the multidimensional overdetermined nonlinear equations for the final functional relationship, and perform inversion verification to determine the correctness of the final functional relationship.

2. The high-precision density logging inversion method based on multi-window drilling according to claim 1, characterized in that, In S14, the initial functional relationship is... f The specific expression for 1 is: In the formula, For the density of the formation, L Lithological factors of strata a 1 is the first constant. a 2 is the second constant. a 3 is the third constant. a 4 is the fourth constant.

3. The high-precision density logging inversion method based on multi-window drilling according to claim 2, characterized in that, S2 includes the following steps: S21. Based on the defined energy windows, the second count rate of gamma rays was obtained by measuring the azimuth density logging instrument during drilling for different formation densities, gaps, formation lithology indices, mud densities, and mud lithology indices. S22. Based on the second count rate, add the relationship terms with mud density, mud lithology index and interstitial space to the initial functional relationship, and perform multi-window collaborative solution of multidimensional overdetermined nonlinear equations to obtain the final functional relationship.

4. The high-precision density logging inversion method based on multi-window drilling according to claim 3, characterized in that, In S22, the final functional relationship is... f The expression for 2 is as follows: In the formula, For mud density, L m Mud lithology factor, t The size of the gap, a 5 is the fifth constant. a 6 is the sixth constant. a 7 is the seventh constant.

5. The high-precision density logging inversion method based on multi-window drilling according to claim 1, characterized in that, S3 includes the following steps: S31. Set the initial value for the formation density, specifically as follows: The initial value of the formation density is set, and the initial value of the formation density is obtained by fitting the functional relationship between the near and far density difference and the mud cake influence correction value. The mud cake influence correction value is the relationship between the formation true density and the far density. S32. Set the initial values ​​for the lithology factors of the formation, specifically as follows: Based on the first count rate of different formation densities and different formation lithology indices 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. Use the ultrasonic gap to set the initial value of the gap size; S34. Set the initial values ​​of mud density and mud lithology factor according to drilling mud parameters; S35. Set a cost function, verify the inversion method, set the cost function as the quality control factor of the measurement, iterate the calculation until the inversion effect is optimal, and determine the correctness of the final functional relationship.

6. The high-precision density logging inversion method based on multi-window drilling according to claim 5, characterized in that, In S35, the cost function C ( The specific expression for ) is: In the formula, C 1 represents the measurement reconstruction error term, used to compare the actual measured value with the theoretical response. F ( ), C 2 is a stability parameter used to control deviations from the formation, and is used to prevent large gaps; In the formula, These are actual measured values. F i ( () represents the theoretical response value. Forward modeling error, This could be measurement error or statistical noise. In the formula, The average value of the parameter vector. This is a variable in the iterative process of the inversion algorithm. This is the average of the differences between the parameter vector and the parameters obtained from the inversion iteration.

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