CN117908142A - Method and system for preprocessing through-casing resistivity logging data - Google Patents
Method and system for preprocessing through-casing resistivity logging data Download PDFInfo
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Abstract
The invention relates to a preprocessing method and a preprocessing system for logging data of resistivity of a through-casing, belonging to the technical field of oil-gas field development, wherein the method comprises the following steps: reading the original data, and extracting the depth of the oil well and the resistivity of the through-casing; processing the resistivity of the casing passing through each depth point by utilizing a box graph to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point; removing abnormal values of the resistivity of the sleeve passing through the sleeve according to the upper limit value and the lower limit value, and processing normal values of the resistivity of the sleeve passing through the sleeve at the same depth point to generate single data of the resistivity of the sleeve passing through the sleeve; single data of the over-casing resistivity is interpolated into data of equal depth intervals using Akima interpolation. The method adopted by the invention does not change the probability of data detection, and the number of the marks on the abnormal value is more reasonable, so that the method is suitable for screening larger data and smaller data.
Description
Technical Field
The invention belongs to the technical field of oil and gas field development, and particularly relates to a method and a system for preprocessing logging data of through-casing resistivity.
Background
The monitoring of the saturation of the residual oil in the middle and later stages of the development of the oil field has important significance for the production increase and the production stabilization and the water control of the oil field. The resistivity logging through the casing opens up a new prospect for effectively and accurately calculating the saturation after casing under proper conditions, and the interpretation technology is simple and the method is mature. Because almost all open hole wells use resistivity to calculate the water saturation of the original stratum, the current oil saturation level can be estimated very directly by only comparing the original resistivity logging curve with the casing resistivity logging curve, and the method is widely applied to oil fields at home and abroad. The logging instrument for resistivity of the through-casing is different from the common logging instrument in design and measurement mode in that the logging instrument for resistivity of the formation is used for measuring reliable data by detecting weak current signals leaked from the casing into the formation. Thus, the raw through-casing resistivity log is also significantly different from the common log. Compared with conventional logging data, the resistivity logging data of the casing passing through the casing has the following characteristics:
(1) The measured values are discrete. The through casing resistivity logging instrument is performed in a point measurement mode, and the instrument is used for static measurement at each measurement point in the casing well, because the noise signal introduced by the instrument in the traveling process is far greater than the stratum signal to be detected. The nature of the spot measurement determines that the measurement is discrete in depth.
(2) One measurement point has a plurality of measurements and may also contain abnormal measurements. Multiple measurement methods are widely used in repeatable observation systems in order to reduce errors. The logging instrument with resistivity through casing has more than 3 measurements in the objective interval, but the number of repeated measurements is limited by many aspects, especially the protection aspect of the instrument. The logging instrument with the through-casing resistivity operates in a high-temperature and high-pressure environment in the well, and the one-time down-hole measurement time of the instrument is not suitable to be too long, so that the instrument is not damaged or the service life of the instrument is shortened. Thus, the number of repeated measurements is typically no more than 10. Thus, formation resistivity data measured at the same depth are irregular, have a fluctuation, and are mixed with one or a plurality of larger or smaller outliers, which are called abnormal measured values.
(3) The depth interval between the measurement points is not equal. To save measurement time, the depth interval for through-casing resistivity logging is typically 0.5m, which can be reduced to 0.3m at thin intervals of interest, and relatively large, such as 1m, between measurement points at non-intervals of interest. This results in the measurement data of a well being of unequal depth intervals throughout. Whereas conventional log data is digitized with a depth interval of typically 0.125m.
In view of the above characteristics, the resistivity measurement data of the casing passing through the casing needs to be preprocessed to form single-value and equidistant data, so that the data is convenient for subsequent processing and is matched with other logging data for application.
At present, the common methods for screening the resistivity measurement values of the casing pipe are mainly a Lagrange criterion screening method and the interpolation method is mainly Lagrange interpolation, cubic spline interpolation and linear interpolation methods. The glabros criterion detects one outlier at a time. The outlier is deleted from the dataset and the test is iterated until no outlier is detected. Multiple iterations will change the probability of detection and the test should not be used for six or less sample sizes (n > 6) because it often marks most points as outliers.
At present, the interpolation methods of the common casing resistivity include global polynomial interpolation methods and cubic spline interpolation methods proposed by Newton, lagrangian, hermite and the like, but the methods are easy to generate morphological swinging phenomenon and have large calculated amount. The linear interpolation curve formed by the interpolation method is a broken line and has no smoothness.
In order to solve the above problems, a method and a system for preprocessing the logging data of the resistivity of the through-casing are needed to be designed, abnormal measured values are removed, and the data with equal depth intervals and encryption are formed by interpolation.
Disclosure of Invention
In view of the above problems, the present invention provides a method for preprocessing logging data of resistivity of a casing, the method comprising:
Reading the original data, and extracting the depth of the oil well and the resistivity of the through-casing;
Processing the resistivity of the casing passing through each depth point by utilizing a box graph to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
Removing abnormal values of the resistivity of the sleeve passing through the sleeve according to the upper limit value and the lower limit value, and processing normal values of the resistivity of the sleeve passing through the sleeve at the same depth point to generate single data of the resistivity of the sleeve passing through the sleeve;
single data of the over-casing resistivity is interpolated into data of equal depth intervals using Akima interpolation.
Preferably, the processing of the casing resistivity at each depth point using the box graph comprises the steps of:
Sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
extracting a median, a lower quartile Q1 and an upper quartile Q3 from the over-casing resistivity sequence;
and calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing.
Preferably, the median is the middle most number or the average of the middle two numbers in the over-casing resistivity sequence;
The lower quartile Q1 is a number (1+n)/4 after the resistivity sequence of the sleeve is equally divided into four parts;
the upper quartile Q3 is a number of (1+n) x 3/4 after the sleeve resistivity sequence is equally divided into four parts;
where n represents the number of through-casing resistivity data points measured at a certain depth.
Preferably, the calculation method of the upper limit value includes:
calculating q3+1.5IQR to obtain an upper limit contrast value, wherein the quartile range iqr=q3-Q1;
and comparing the upper limit comparison value with the maximum value in the over-casing resistivity sequence, and taking the smaller value as the upper limit value.
Preferably, the calculating method of the lower limit value includes:
Calculating Q1-1.5IQR to obtain a lower limit comparison value, wherein the quartile range IQR=Q3-Q1;
and comparing the lower limit contrast value with the minimum value in the over-casing resistivity sequence, and taking the larger value as the lower limit value.
Preferably, the abnormal value is a value of the through-casing resistivity below a lower limit value and above an upper limit value;
the normal value is a value of the filter sleeve resistivity which is equal to or more than a lower limit value and equal to or less than an upper limit value.
Preferably, the method for generating single data of the resistivity of the casing pipe comprises the following steps:
an arithmetic average of all normal values of the through-casing resistivity at the same depth point is obtained, and the arithmetic average is used as single data of the through-casing resistivity at the depth point.
Preferably, interpolating single data of the over-casing resistivity into data of equal depth intervals using Akima interpolation comprises the steps of:
establishing a curve fitted by a cubic polynomial between every two single data, wherein the curve ensures that the first derivative is continuous;
All n single data were constructed as non-equidistant sample points (x i,yi) (i=0, 1, …, n-1), where x i represents the i-th depth, y i represents the composite casing resistivity single data corresponding to the depth, x 0<x1<…<xn-1; if satisfied at 2 endpoints on subinterval [ x k,xk+1 ] (k=0, 1,2, …, n-2):
Then a unique cubic polynomial can be determined in any 2 adjacent subintervals:
f(x)＝a0+a1(x-xk)+a2(x-xk)2+a3(x-xk)3,
A function approximation at the interpolation point x (x e x k,xk+1) in the subinterval is calculated from the cubic polynomial.
The invention also provides a through casing resistivity logging data preprocessing system, which comprises:
The information extraction module is used for extracting the depth of the oil well and the resistivity of the casing pipe;
The information processing module is used for processing the resistivity of the casing passing through each depth point to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
The data generation module is used for eliminating abnormal values of the resistivity of the sleeve and processing normal values of the resistivity of the sleeve at the same depth point to generate single data of the resistivity of the sleeve;
and the data processing module is used for interpolating the resistivity of the casing pipe into data with equal depth intervals.
Preferably, the information processing module is configured to process the resistivity of the casing passing through each depth point, and includes:
the information processing module is used for sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
extracting a median, a lower quartile Q1 and an upper quartile Q3 from the over-casing resistivity sequence;
and calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing.
Preferably, the median is the middle most number or the average of the middle two numbers in the over-casing resistivity sequence;
The lower quartile Q1 is a number (1+n)/4 after the resistivity sequence of the sleeve is equally divided into four parts;
the upper quartile Q3 is a number of (1+n) x 3/4 after the sleeve resistivity sequence is equally divided into four parts;
where n represents the number of through-casing resistivity data points measured at a certain depth.
Preferably, the upper limit value is a value that is smaller than the maximum value of the over-casing resistivity sequence;
the upper limit contrast value is equal to q3+1.5IQR, where the quartile range iqr=q3-Q1.
Preferably, the lower limit value is a value with a lower limit contrast value that is larger than a minimum value of the resistivity sequence of the casing pipe;
The lower limit comparison value is equal to Q1-1.5IQR, where the quartile range iqr=q3-Q1.
Preferably, the abnormal value is a value of the through-casing resistivity below a lower limit value and above an upper limit value;
the normal value is a value of the filter sleeve resistivity which is equal to or more than a lower limit value and equal to or less than an upper limit value.
Preferably, the data generation module is configured to generate single data of the resistivity of the casing, including:
The data generation module is used for calculating the arithmetic average value of all normal values of the casing resistivity at the same depth point, and taking the arithmetic average value as single data of the casing resistivity at the depth point.
The invention has the following beneficial effects:
(1) Firstly, the invention utilizes the box graph to process the over-sleeve resistivity, and the upper limit value and the lower limit value formed by processing are used for screening the data of the over-sleeve resistivity, so that single data of the over-sleeve resistivity is formed. Secondly, the single data of the resistivity of the sleeve is interpolated into the data with equal depth intervals by adopting an Akima interpolation method, and because the Akima interpolation only uses fewer local data points, the interpolation curve is not easy to swing, the curve is more similar to the original data form, and compared with the linear interpolation, the smoothness of the curve is ensured, and the interpolation method has better effect on the data than the Lagrange interpolation, the cubic spline interpolation and the linear interpolation method;
(2) The invention utilizes the box graph to process the resistivity of the casing pipe to obtain reasonable data of the resistivity of the casing pipe, does not need to presume that the data obeys a specific distribution form in advance, does not have any restriction requirement on the data, and only truly and intuitively represents the original appearance of the data shape; on the other hand, the box graph judging standard of the abnormal value is based on quartiles and quartiles, the quartiles have certain resistance, and part of data can be arbitrarily far without greatly disturbing the quartiles, so the abnormal value cannot influence the standard, and the box graph recognizing result is relatively objective. It can be seen that the box plot has certain advantages in identifying outliers.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 shows a flow chart of a method of preprocessing through-casing resistivity logging data in an embodiment of the invention;
FIG. 2 shows a graph of the information contained in the dbf file of the resistivity of the over-casing in an embodiment of the invention;
FIG. 3 is a schematic diagram showing detection of outliers in a bin map according to an embodiment of the present invention;
FIG. 4 is a schematic diagram showing outlier screening and synthesis according to an embodiment of the present invention;
FIG. 5 is a schematic diagram showing interpolation method in comparison with the embodiment of the present invention;
FIG. 6 is a diagram showing the results of a specific process in an embodiment of the present invention;
FIG. 7 shows a flow chart of a through-casing resistivity logging data preprocessing system in an embodiment of the invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the invention provides a preprocessing method for logging data of resistivity of a through casing, which is characterized in that the method comprises the following steps:
Reading the original data, and extracting the depth of the oil well and the resistivity of the through-casing; in this embodiment, in order to ensure the quality of the logging data, multiple measurements are often performed at the same depth, i.e. the same depth contains multiple measurement points, and the raw data is stored in the dbf file, and the reading of the dbf database file is needed to be implemented by utilizing dbfread libraries based on the Python programming language, as shown in fig. 2, where GL represents the depth and R represents the resistivity measurement of the casing.
Processing the resistivity of the casing passing through each depth point by utilizing a box graph to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
Removing abnormal values of the resistivity of the sleeve according to the upper limit value and the lower limit value, and processing normal values of the resistivity of the sleeve at the same depth point to generate single data of the resistivity of the sleeve;
single data of the over-casing resistivity is interpolated into data of equal depth intervals using Akima interpolation.
As shown in fig. 3, the processing of the through-casing resistivity at each depth point using a box graph includes the steps of:
Sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
Extracting a median, a lower quartile Q1 and an upper quartile Q3 from the through-casing resistivity sequence; wherein, the median is the middle number or the average value of the middle two numbers in the resistivity sequence of the casing; the lower quartile Q1 is the number of (1+n)/4 after the average division of the resistivity sequence of the sleeve is divided into four parts; the upper quartile Q3 is the number of (1+n) x 3/4 after the average division of the resistivity sequence of the sleeve is divided into four parts; wherein n represents the number of through-casing resistivity data points measured at a certain depth;
calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing; the calculation method of the upper limit value comprises the following steps: calculating q3+1.5IQR to obtain an upper limit contrast value, wherein the quartile range iqr=q3-Q1; comparing the upper limit contrast value with the maximum value in the over-casing resistivity sequence, and taking the smaller value as the upper limit value; the calculation method of the lower limit value comprises the following steps: calculating Q1-1.5IQR to obtain a lower limit comparison value, wherein the quartile range IQR=Q3-Q1; and comparing the lower limit contrast value with the minimum value in the over-casing resistivity sequence, and taking the larger value as the lower limit value.
The abnormal value is a value of the through-casing resistivity below the lower limit value and above the upper limit value; the normal value is a value of the filter sleeve resistivity which is equal to or higher than the lower limit value and equal to or lower than the upper limit value.
The method for generating the single data of the resistivity of the casing pipe comprises the following steps:
Calculating the arithmetic average value of all normal values of the resistivity of the casing passing through the same depth point; in the embodiment, the resistivity normal measured value at the same depth point after the abnormal value is removed is R 1′,R2′,…,Rk', and K is more than or equal to 2 and less than or equal to N. The arithmetic mean is taken here as the measurement optimum at this depth point, i.e. the resistivity R 0 at this depth point is taken as:
The arithmetic average value is taken as single data of the through-casing resistivity at the depth point, and particularly as shown in fig. 4, a first vertical column from left to right is a box-type graph of original measurement data and calculated quartile limits of the through-casing resistivity RLAC, a second vertical column is a box-type graph of corresponding measurement data, wherein a solid origin is an outlier, and a third vertical column is the arithmetic average value of measurement values after the outlier is removed, namely the synthesized final through-casing resistivity data. The data outside the box (e.g., xx25, xx30, etc.) represents depth.
Interpolation of single data of over-casing resistivity into data of equal depth intervals using Akima interpolation comprises the steps of:
Establishing a curve fitted by a cubic polynomial between every two single data, wherein the curve ensures that the first derivative is continuous;
All n single data are constructed as non-equidistant sample points (x i,yi) (i=0, 1, …, n-1), where xi represents the i-th depth, yi represents the synthesized casing resistivity single data corresponding to the depth, x 0<x1<…<xn-1; if satisfied at 2 endpoints on subinterval [ x k,xk+1 ] (k=0, 1,2, …, n-2):
Then a unique cubic polynomial can be determined in any 2 adjacent subintervals:
f(x)＝a0+a1(x-xk)+a2(x-xk)2+a3(x-xk)3,
the function approximation at the interpolation point x (x e x k,xk+1) in the subinterval is calculated from the cubic polynomial.
As shown in fig. 5, according to the characteristic that the resistivity data changes with the depth, the linear interpolation, cubic spline interpolation and Akima interpolation methods respectively interpolate the resistivity data of the casing pipe into equal-depth interval data with a sampling interval of 0.125m, and analyze the interpolation result. The graph is a linear interpolation graph, a cubic spline interpolation graph and an Akima interpolation graph in sequence from left to right. As can be seen from the graph, the linear interpolation method has poor curve smoothness; when the sampling interval is larger, the curve swinging property is larger and the application effect is poorer; the Akima interpolation only uses fewer local data points, so that the curve is not easy to swing, the original data form is more similar, and the smoothness of the curve is ensured compared with the linear interpolation. Data outside the box (e.g., xx90, xx00, etc.) represents depth.
As shown in FIG. 6, the measurement of the resistivity of the casing is performed after the completion of the well, so as to verify the accuracy of the logging result of the resistivity of the casing, wherein the drawing comprises an original point measurement data diagram of the resistivity of the casing, a data diagram after screening the resistivity of the casing, a comparison diagram of the resistivity of the casing and the deep resistivity of the casing after original treatment, a deep channel, a comparison diagram of the resistivity of the casing and the deep resistivity of the casing treated by the technical scheme of the invention and a stratum analysis diagram in sequence from left to right. In the original processed casing resistivity and deep resistivity comparison chart and the casing resistivity and deep resistivity comparison chart processed by the technical scheme of the invention, the solid origin represents data of casing resistivity RLAC, and the dotted line represents data of deep resistivity RD. As can be seen from the figure, the treatment effect is better by utilizing the technical scheme of the invention.
As shown in fig. 7, the present invention further proposes a logging data preprocessing system for resistivity logging through casing, which is characterized in that the system includes:
The information extraction module is used for extracting the depth of the oil well and the resistivity of the casing pipe;
The information processing module is used for processing the resistivity of the casing passing through each depth point to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
The data generation module is used for eliminating abnormal values of the resistivity of the sleeve and processing normal values of the resistivity of the sleeve at the same depth point to generate single data of the resistivity of the sleeve;
and the data processing module is used for interpolating the resistivity of the casing pipe into data with equal depth intervals.
The information processing module is used for processing the resistivity of the casing passing through each depth point, and comprises the following steps:
the information processing module is used for sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
Extracting a median, a lower quartile Q1 and an upper quartile Q3 from the through-casing resistivity sequence; wherein, the median is the middle number or the average value of the middle two numbers in the resistivity sequence of the casing; the lower quartile Q1 is the number of (1+n)/4 after the average division of the resistivity sequence of the sleeve is divided into four parts; the upper quartile Q3 is the number of (1+n) x 3/4 after the average division of the resistivity sequence of the sleeve is divided into four parts; wherein n represents the number of through-casing resistivity data points measured at a certain depth;
Calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing; the upper limit value is a value of which the upper limit contrast value is smaller than the maximum value of the resistivity sequence of the casing pipe; the upper limit contrast value is equal to q3+1.5IQR, where the interquartile range iqr=q3-Q1; the lower limit value is a value with a larger lower limit contrast value than the minimum value of the resistivity sequence of the casing pipe; the lower limit contrast value is equal to Q1-1.5IQR, where the quartile range iqr=q3-Q1.
The abnormal value is a value of the through-casing resistivity below the lower limit value and above the upper limit value; the normal value is a value of the filter sleeve resistivity which is equal to or higher than the lower limit value and equal to or lower than the upper limit value. The data generation module is used for generating single data of the resistivity of the casing, and comprises the following steps: the data generation module is used for calculating the arithmetic average value of all normal values of the casing resistivity at the same depth point, and taking the arithmetic average value as single data of the casing resistivity at the depth point.
Those of ordinary skill in the art will appreciate that: although the invention has been described in detail with reference to the foregoing embodiments, it is to be understood that 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 technical solutions of the embodiments of the present invention.
Claims (15)
1. A method for preprocessing through casing resistivity logging data, the method comprising:
Reading the original data, and extracting the depth of the oil well and the resistivity of the through-casing;
Processing the resistivity of the casing passing through each depth point by utilizing a box graph to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
Removing abnormal values of the resistivity of the sleeve passing through the sleeve according to the upper limit value and the lower limit value, and processing normal values of the resistivity of the sleeve passing through the sleeve at the same depth point to generate single data of the resistivity of the sleeve passing through the sleeve;
single data of the over-casing resistivity is interpolated into data of equal depth intervals using Akima interpolation.
2. A method of pre-processing resistivity logging data over casing as claimed in claim 1,
Processing the resistivity of the casing passing through each depth point by using a box graph comprises the following steps:
Sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
extracting a median, a lower quartile Q1 and an upper quartile Q3 from the over-casing resistivity sequence;
and calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing.
3. A method of pre-processing resistivity logging data over casing as claimed in claim 2,
The median is the middle number or the average value of the middle two numbers in the casing resistivity sequence;
The lower quartile Q1 is a number (1+n)/4 after the resistivity sequence of the sleeve is equally divided into four parts;
the upper quartile Q3 is a number of (1+n) x 3/4 after the sleeve resistivity sequence is equally divided into four parts;
where n represents the number of through-casing resistivity data points measured at a certain depth.
4. A method of preprocessing through casing resistivity logging data as claimed in claim 3,
The calculation method of the upper limit value comprises the following steps:
calculating q3+1.5IQR to obtain an upper limit contrast value, wherein the quartile range iqr=q3-Q1;
and comparing the upper limit comparison value with the maximum value in the over-casing resistivity sequence, and taking the smaller value as the upper limit value.
5. A method of preprocessing through casing resistivity logging data as claimed in claim 3,
The calculation method of the lower limit value comprises the following steps:
Calculating Q1-1.5IQR to obtain a lower limit comparison value, wherein the quartile range IQR=Q3-Q1;
and comparing the lower limit contrast value with the minimum value in the over-casing resistivity sequence, and taking the larger value as the lower limit value.
6. A method of pre-processing resistivity logging data over casing as claimed in claim 1,
The abnormal value is a value of the through-casing resistivity below a lower limit value and above an upper limit value;
the normal value is a value of the filter sleeve resistivity which is equal to or more than a lower limit value and equal to or less than an upper limit value.
7. A method of pre-processing resistivity logging data over casing as claimed in claim 1,
The method for generating the single data of the resistivity of the casing pipe comprises the following steps:
an arithmetic average of all normal values of the through-casing resistivity at the same depth point is obtained, and the arithmetic average is used as single data of the through-casing resistivity at the depth point.
8. A method of pre-processing resistivity logging data over casing as claimed in claim 1,
Interpolation of single data of over-casing resistivity into data of equal depth intervals using Akima interpolation comprises the steps of:
establishing a curve fitted by a cubic polynomial between every two single data, wherein the curve ensures that the first derivative is continuous;
All n single data are constructed as non-equidistant sample points (x i,yi) (i=0, 1, …, n-1), where xi represents the i-th depth, yi represents the synthesized casing resistivity single data corresponding to the depth, x 0<x1<…<xn-1; if satisfied at 2 endpoints on subinterval [ x k,xk+1 ] (k=0, 1,2, …, n-2):
Then a unique cubic polynomial can be determined in any 2 adjacent subintervals:
f(x)＝a0+a1(x-xk)+a2(x-xk)2+a3(x-xk)3,
A function approximation at the interpolation point x (x e x k,xk+1) in the subinterval is calculated from the cubic polynomial.
9. A through casing resistivity logging data preprocessing system, the system comprising:
The information extraction module is used for extracting the depth of the oil well and the resistivity of the casing pipe;
The information processing module is used for processing the resistivity of the casing passing through each depth point to obtain an upper limit value and a lower limit value of reasonable data of the resistivity of the casing passing through the corresponding depth point;
The data generation module is used for eliminating abnormal values of the resistivity of the sleeve and processing normal values of the resistivity of the sleeve at the same depth point to generate single data of the resistivity of the sleeve;
and the data processing module is used for interpolating the resistivity of the casing pipe into data with equal depth intervals.
10. A through casing resistivity logging data preprocessing system as claimed in claim 9, wherein,
The information processing module is used for processing the resistivity of the casing passing through each depth point, and comprises the following steps:
the information processing module is used for sequencing the resistivity of the casing pipe from large to small to obtain a resistivity sequence of the casing pipe;
extracting a median, a lower quartile Q1 and an upper quartile Q3 from the over-casing resistivity sequence;
and calculating the upper limit value and the lower limit value of reasonable data of the resistivity of the casing.
11. A through casing resistivity logging data preprocessing system as claimed in claim 10, wherein,
The median is the middle number or the average value of the middle two numbers in the casing resistivity sequence;
The lower quartile Q1 is a number (1+n)/4 after the resistivity sequence of the sleeve is equally divided into four parts;
the upper quartile Q3 is a number of (1+n) x 3/4 after the sleeve resistivity sequence is equally divided into four parts;
where n represents the number of through-casing resistivity data points measured at a certain depth.
12. A through casing resistivity logging data preprocessing system as claimed in claim 11, wherein,
The upper limit value is a value of which the upper limit contrast value is smaller than the maximum value of the resistivity sequence of the casing pipe;
the upper limit contrast value is equal to q3+1.5IQR, where the quartile range iqr=q3-Q1.
13. A through casing resistivity logging data preprocessing system as claimed in claim 11, wherein,
The lower limit value is a value with a larger lower limit contrast value than the minimum value of the resistivity sequence of the casing pipe;
The lower limit comparison value is equal to Q1-1.5IQR, where the quartile range iqr=q3-Q1.
14. A through casing resistivity logging data preprocessing system as claimed in claim 9, wherein,
The abnormal value is a value of the through-casing resistivity below a lower limit value and above an upper limit value;
the normal value is a value of the filter sleeve resistivity which is equal to or more than a lower limit value and equal to or less than an upper limit value.
15. A through casing resistivity logging data preprocessing system as claimed in claim 9, wherein,
The data generation module is used for generating single data of the resistivity of the casing, and comprises the following steps:
The data generation module is used for calculating the arithmetic average value of all normal values of the casing resistivity at the same depth point, and taking the arithmetic average value as single data of the casing resistivity at the depth point.
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