CN115718326A - High-resolution resistivity extraction method based on micro-resistivity imaging - Google Patents
High-resolution resistivity extraction method based on micro-resistivity imaging Download PDFInfo
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Abstract
The invention relates to the technical field of logging evaluation of unconventional oil and gas reservoir strata, in particular to a high-resolution resistivity extraction method based on micro-resistivity imaging, which comprises the steps of carrying out histogram statistics on electrical imaging data according to depths, wherein the electrical imaging data meet the condition that both skewness coefficients and kurtosis coefficients are less than 1; the electrical imaging data is scaled into a resistivity image from the conductivity according to an electrical imaging sampling interval point-to-point scaling method; obtaining P35, P50 and P65; the average value of P35, P50 and P65 was taken as the value of the high-resolution resistivity. The method mainly makes full use of the extremely high longitudinal resolution of the electrical imaging data, extracts a high-resolution resistivity by adopting a mathematical statistics method, improves the resolution capability of the thin layer of the reservoir to be the same as the electrical imaging data, and can accurately identify the thin layer with the thickness of more than 0.5cm, thereby further accurately counting the effective thickness.
Description
Technical Field
The invention relates to the technical field of logging evaluation of unconventional oil and gas reservoir strata, in particular to a high-resolution resistivity extraction method based on micro-resistivity imaging.
Background
With the depth of oil exploration, exploration targets gradually turn to unconventional oil and gas reservoirs, reservoirs such as compact oil and shale oil have the characteristics of strong non-mean property and thin interbed development, the monolayer thickness of the reservoir with the thin interbed characteristic is generally smaller than the longitudinal resolution of a conventional logging instrument, and the longitudinal resolution of a main flow instrument is 30cm to 60cm, so that the error between the calculated oil saturation and the analyzed oil saturation is large, the effective thickness of the reservoir cannot be divided, the effective thickness of the reservoir is a key parameter for evaluating the reservoir, and the accurate statistics of the effective thickness of the reservoir is one of important tasks for evaluating the logging and calculating the reserves.
The method for extracting high-resolution resistivity by utilizing electrical imaging data only comprises a piecewise linear scaling method adopted by Schlumberger, can meet the identification of a thin layer with the thickness of more than 20cm, but has poor resolution capability on the thin layer with the thickness of less than 20cm, and mainly depends on two defects of the method, wherein the first method is that the piecewise linear method is adopted when the electrical imaging data is scaled, so that the longitudinal resolution is artificially reduced, and the synthesized resistivity longitudinal resolution is lower than the resolution of the electrical imaging data; secondly, the method adopts shallow resistivity scales, and the shallow resistivity is easily influenced by the shaft environment in the acquisition process, so that the accuracy of the extracted high-resolution resistivity is influenced.
Disclosure of Invention
The invention provides a high-resolution resistivity extraction method based on micro-resistivity imaging, overcomes the defects of the prior art, and can effectively solve the problem that the existing logging evaluation technology has poor resolution capability on a thin layer with the thickness of less than 20 cm. The invention can extract a high-resolution resistivity which can represent the real resistivity of the stratum.
The technical scheme of the invention is realized by the following measures: a high-resolution resistivity extraction method based on micro-resistivity imaging comprises the following steps:
the method comprises the following steps: selecting electric imaging data subjected to acceleration correction, bad electrode removal and polar plate series connection, and carrying out histogram statistics on the electric imaging data according to depth, wherein the electric imaging data need to meet the condition that skewness coefficient and kurtosis coefficient are both smaller than 1, so that the distribution of the resistivity approximately obeys normal distribution, the method is suitable for extracting high-resolution resistivity by the method provided by the invention, and if the skewness coefficient and the kurtosis coefficient are both larger than 1, the accuracy of the extracted high-resolution resistivity by the method is uncertain;
step two: the electrical imaging data is scaled into a resistivity image from the conductivity according to an electrical imaging sampling interval point-to-point scaling method;
step three: according to the positive-too distribution characteristic of the resistivity at each depth point, if the measured resistivity of a certain button at a certain depth is X, X is a continuous random variable with the value larger than 0, F (X) is a distribution function of X,
F(x)＝P{X≤x} (0＜x＜∞) (1)
if the density function is f (x), then
The resistivity values of the arbitrary distribution probability are obtained by the bisection method, the dividing line method or the tangent method, wherein P35, P50 and P65 are obtained, and the resistivity values of the P35, P50 and P65 with the cumulative probabilities of 35%, 50% and 65% are obtained, that is, the P35, P50 and P65 are obtained respectively
The corresponding resistivity x value;
step four: calculating a value which can most represent the resistivity of the depth point by adopting a high probability average thought, wherein the value is a high resolution resistivity value, calculating the average value of P35, P50 and P65, and synthesizing the high resolution resistivity;
HIGH＝(P35+P50+P65)/3 (3)
where HIGH is HIGH resolution resistivity.
The following is further optimization or/and improvement of the technical scheme of the invention:
in the second step, the electrical imaging data is scaled into a resistivity image from the conductivity according to a point-to-point scaling method of the depth electrical imaging sampling interval, the deep resistivity is selected from the scale resistivity, and the scaling formula is as follows:
wherein R is i For the resistivity value of each button electrode after passing through the deep resistivity scale,n is the number of buttons of the electrical imaging instrument, ri is the measured conductivity value of each button, R LLD Is the deep resistivity value of a conventional log.
Compared with the conventional electric imaging scale which adopts the shallow resistance scale, the method adopts the deep resistivity to scale, and aims to ensure that the resistivity after the scale is close to the real resistivity of the stratum to the maximum extent.
The method mainly makes full use of the extremely high longitudinal resolution of the electrical imaging data, extracts a high-resolution resistivity by adopting a mathematical statistics method, improves the resolution capability of the thin layer of the reservoir to be as high as the electrical imaging data, and can accurately identify the thin layer with the thickness of more than 0.5cm, thereby further accurately counting the effective thickness.
Drawings
FIG. 1 is a flow chart of the method for extracting high-resolution resistivity based on micro-resistivity according to the invention.
FIG. 2 is a schematic diagram of the present invention for extracting high resolution resistivity.
Fig. 3 is a graph of histogram statistics for electrical imaging of the JI222 well FMI according to the method of the present invention.
FIG. 4 is a graph comparing the longitudinal resolution of the JI222 well with the high resolution curves extracted by the method of the present invention and by the method of Schlumberger.
In fig. 3, the first pass is the depth pass, the second pass is the electrical imaging plot, the third pass is the histogram, the fourth pass is the skewness coefficient, and the fifth pass is the kurtosis coefficient.
In fig. 4, the first trace is a depth trace, the second trace is an electrical imaging graph, the third trace is a high-resolution resistivity curve extracted by the method provided by the present invention, and the fourth trace is a high-resolution resistivity curve extracted by a schlumberger linear scale method.
Detailed Description
The present invention is not limited by the following examples, and specific embodiments may be determined according to the technical solutions and practical situations of the present invention.
The invention is further described below with reference to examples:
example 1: as shown in the attached figure 1, the high-resolution resistivity extraction method based on micro-resistivity imaging comprises the following steps:
step 101: selecting electrical imaging data after acceleration correction, bad electrode removal and polar plate series connection, and carrying out histogram statistics on the electrical imaging data according to the depth, wherein the electrical imaging data need to meet the condition that both skewness coefficient and kurtosis coefficient are less than 1;
step 102: the electrical conductivity imaging data is scaled into a resistivity image according to an electrical imaging sampling interval point-to-point scaling method;
step 103: obtaining P35, P50 and P65 by adopting a bisection method, a secant method or a tangent method;
step 104: the average of P35, P50 and P65 was calculated to synthesize high resolution resistivity.
Example 2: the high-resolution resistivity extraction method based on micro-resistivity imaging comprises the following steps:
1) The FMI electrical imaging data of the JI222 well after acceleration correction, bad electrode removal and polar plate series connection is selected, the window length of 0.5m and the step length of 0.2m are selected, histogram statistics is carried out on the electrical imaging data according to the depth, and as can be seen from the graph 3, the electrical imaging skewness coefficient and the kurtosis coefficient of the well are both smaller than 1, which indicates that the distribution of the resistivity can be considered to be approximately normal distribution, and the method is suitable for the method provided by the invention;
2) The method comprises the following steps of (1) according to a point-to-point calibration method of a depth electrical imaging sampling interval, calibrating electrical conductivity of electrical imaging data into a resistivity image, selecting deep resistivity from the calibrated resistivity, and adopting a calibration formula as follows:
3) Obtaining P35, P50 and P65, wherein the P50 and P65 are respectively the resistivity values when the cumulative probability is 35%, 50% and 65%I.e. P35, P50, P65 are each
The corresponding resistivity x value, fig. 2;
4) Calculating a value which can represent the resistivity of the depth point most by adopting a high probability average idea, wherein the value is a high-resolution resistivity value, calculating the average value of P35, P50 and P65, and synthesizing the high-resolution resistivity;
HIGH＝(P35+P50+P65)/3 (3)
as shown in fig. 4, the high-resolution resistivity curve extracted by the method described in embodiment 2 has a very high longitudinal resolution, and the resolution capability for a thin layer is significantly higher than that of the existing schlumberger linear scaling method, and can reach 0.5cm.
The technical characteristics form an embodiment of the invention, which has strong adaptability and implementation effect, and unnecessary technical characteristics can be increased or decreased according to actual needs to meet the requirements of different situations. Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (2)
1. A high resolution resistivity extraction method based on micro-resistivity imaging is characterized by comprising the following steps:
the method comprises the following steps: selecting electrical imaging data after acceleration correction, bad electrode removal and polar plate series connection, and carrying out histogram statistics on the electrical imaging data according to the depth, wherein the electrical imaging data need to meet the condition that both skewness coefficients and kurtosis coefficients are less than 1;
step two: the electrical imaging data is scaled into a resistivity image from the conductivity according to an electrical imaging sampling interval point-to-point scaling method;
step three: if the measured resistivity of a certain button at a certain depth is X, X is a continuous random variable with the value larger than 0, F (X) is a distribution function of X,
F(x)＝P{X≤x}(0＜x＜∞) (1)
if the density function is f (x), then
P35, P50 and P65 are resistivity values at an integrated probability of 35%, 50% and 65%, respectively, that is, P35, P50 and P65 are values at an integrated probability of 35%, 50% and 65%, respectively
The corresponding resistivity x value;
step four: calculating the average value of P35, P50 and P65, and synthesizing high-resolution resistivity;
HIGH＝(P35+P50+P65)/3 (3)
where HIGH is HIGH resolution resistivity.
2. The method for extracting high-resolution resistivity based on micro-resistivity imaging according to claim 1, wherein in the second step, the electrical imaging data is scaled from the conductivity to the resistivity image according to a point-to-point scaling method of depth electrical imaging sampling intervals, the deep resistivity is selected from the scale resistivity, and the scaling formula is as follows:
wherein R is i For the resistivity value of each button electrode after passing through the deep resistivity scale, n is the number of buttons of the electrical imaging instrument, ri is the measured conductivity value of each button, R LLD Is the deep resistivity value of a conventional log.
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