阅读说明：本技术 一种基于微地震的地应力方位预测方法 (Earth stress azimuth prediction method based on microseism ) 是由 崔二龙 唐慧莹 常程 张德良 张景 张烈辉 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种基于微地震的地应力方位预测方法,包括以下步骤：S1：获取目标井的微地震数据和井轨迹数据；S2：将所述微地震数据按照所述目标井压裂的段数进行分样；S3：对每一压裂段的微地震数据进行聚类分析,获得每一压裂段中人工裂缝的微地震数据；S4：分别对每一压裂段人工裂缝的微地震数据进行拟合,获得各压裂段拟合曲线的截距和斜率；S5：计算各压裂段所述斜率的反正切值,得到各压裂段所述人工裂缝的角度,各压裂段人工裂缝的角度即为各压裂段最大水平主应力的方位。本发明能够更准确的获得人工裂缝的方位,从而更准确地预测地层的水平应力方位,为储层压裂改造提供技术支持。(The invention discloses a microseism-based ground stress azimuth prediction method, which comprises the following steps of: s1: acquiring micro-seismic data and well trajectory data of a target well; s2: sampling the microseism data according to the fractured sections of the target well; s3: performing clustering analysis on the micro-seismic data of each fracturing section to obtain the micro-seismic data of the artificial cracks in each fracturing section; s4: fitting the microseism data of each fracturing section artificial crack to obtain the intercept and the slope of a fitting curve of each fracturing section; s5: and calculating the arctangent value of the slope of each fracturing section to obtain the angle of the artificial crack of each fracturing section, wherein the angle of the artificial crack of each fracturing section is the direction of the maximum horizontal main stress of each fracturing section. The method can more accurately obtain the azimuth of the artificial fracture, thereby more accurately predicting the horizontal stress azimuth of the stratum and providing technical support for reservoir fracturing modification.)

1. A method for predicting the geostress azimuth based on microseism is characterized by comprising the following steps:

s1: acquiring micro-seismic data and well trajectory data of a target well;

s2: sampling the microseism data according to the fractured sections of the target well;

s3: performing clustering analysis on the micro-seismic data of each fracturing section to obtain the micro-seismic data of the artificial cracks in each fracturing section;

s4: fitting the microseism data of each fracturing section artificial crack to obtain the intercept and the slope of a fitting curve of each fracturing section;

s5: and calculating the arctangent value of the slope of each fracturing section to obtain the angle of the artificial crack of each fracturing section, wherein the angle of the artificial crack of each fracturing section is the direction of the maximum horizontal main stress of each fracturing section.

2. The microseismic-based geostress orientation prediction method of claim 1 wherein in step S1 the microseismic data includes the time, location, and magnitude of the microseismic event.

3. The microseism-based ground stress azimuth prediction method according to claim 1, wherein in step S3, the clustering analysis is performed by using a DBSCAN clustering algorithm.

4. The microseism-based ground stress azimuth prediction method according to claim 3, wherein the step S3 specifically comprises the following sub-steps:

s31: presetting a neighborhood distance threshold value eps of a certain sample of the DBSCAN clustering algorithm and a threshold value min _ samples of the number of samples in a neighborhood with a certain sample distance as eps;

s32: inputting microseism data of a certain fracturing section into the DBSCAN clustering algorithm as basic data;

s33: inputting preset eps and min _ samples to the DBSCAN clustering algorithm, and performing clustering class division on the input micro-seismic data;

s34: calculating the distance from the central point of each divided category to the center of the fracturing section selected in the step S32, wherein the category with the minimum distance is the artificial fracture;

s35: judging whether the division of the artificial cracks is correct or not;

if not, adjusting the values of eps and min _ samples, and repeating the steps S31-S35;

if the fracture is correct, another fracture section is selected, and the steps S32-S35 are repeated until all the fracture sections are separated from the natural fracture and the artificial fracture.

5. The microseism-based ground stress azimuth prediction method according to claim 4, wherein in step S35, whether the artificial fracture is correctly divided is judged by the following criteria: and (4) taking lg logarithm as the seismic level of the micro-seismic data of the divided artificial fracture category, and if 80-100% of the seismic levels of the micro-seismic points are less than 1, determining that the artificial fracture is divided correctly.

6. The microseismic-based geostress orientation prediction method of claim 1 wherein in step S4, the microseismic data of each fracture section artificial fracture is fitted using a least squares method.

7. The microseismic-based geostress orientation prediction method of claims 1-6 wherein the predictor further comprises the steps of:

s6: deleting abnormal values in all the maximum horizontal principal stress orientation values;

s7: and for the rest maximum horizontal principal stress azimuth values, obtaining the maximum horizontal principal stress distribution condition of the target well through an interpolation algorithm.

8. The microseism-based ground stress azimuth prediction method according to claim 7, wherein if a plurality of target wells exist in the target area, after obtaining the maximum horizontal principal stress distribution of each target well, the prediction method further comprises the following steps:

s8: and obtaining the maximum horizontal principal stress distribution condition of the target area through an interpolation algorithm.

Technical Field

The invention relates to the technical field of oil and gas reservoir exploitation, in particular to a micro-seismic-based ground stress azimuth prediction method.

Background

Shale and other low-porosity and low-permeability reservoirs can obtain commercial capacity only through large-scale fracturing modification, the ground stress is an important factor for fracturing modification, and how to obtain the ground stress parameter is a problem to be solved urgently. The currently common ground stress azimuth measuring method comprises indoor experimental measurement, microseism data fitting and the like. The indoor experimental determination is limited by the number of samples, only the stress azimuth corresponding to a few spatial points can be obtained, and meanwhile, the deviation between the core determination condition and the original formation condition is easy to occur due to the fact that the core is taken out from the underground and then is measured on the ground. By the spatial distribution position of the microseismic event, the stress azimuth of the formation can be roughly estimated according to the principle that the main fracture is perpendicular to the maximum horizontal main stress. But the method directly fits the microseismic event, cannot separate the artificial fracture from the natural fracture, and easily leads to the wrong estimation of the ground stress azimuth.

Disclosure of Invention

Aiming at the problems, the invention aims to provide a microseism-based ground stress azimuth prediction method, which automatically separates the microseism data points corresponding to the artificial cracks and the natural cracks through a clustering algorithm, and then performs fitting of the maximum horizontal main stress by using the microseism data points corresponding to the artificial cracks, thereby more accurately judging the ground stress azimuth.

The technical scheme of the invention is as follows:

a method for predicting a geostress azimuth based on microseisms comprises the following steps:

s1: acquiring micro-seismic data and well trajectory data of a target well;

s2: sampling the microseism data according to the fractured sections of the target well;

s3: performing clustering analysis on the micro-seismic data of each fracturing section to obtain the micro-seismic data of the artificial cracks in each fracturing section;

s4: fitting the microseism data of each fracturing section artificial crack to obtain the intercept and the slope of a fitting curve of each fracturing section;

s5: and calculating the arctangent value of the slope of each fracturing section to obtain the angle of the artificial crack of each fracturing section, wherein the angle of the artificial crack of each fracturing section is the direction of the maximum horizontal main stress of each fracturing section.

Preferably, in step S1, the micro-seismic data includes the time, location, and magnitude of the occurrence of the micro-seismic event.

Preferably, in step S3, the clustering analysis is performed by using a DBSCAN clustering algorithm.

Preferably, step S3 specifically includes the following sub-steps:

s31: presetting a neighborhood distance threshold value eps of a certain sample of the DBSCAN clustering algorithm and a threshold value min _ samples of the number of samples in a neighborhood with a certain sample distance as eps;

s32: inputting microseism data of a certain fracturing section into the DBSCAN clustering algorithm as basic data;

s33: inputting preset eps and min _ samples to the DBSCAN clustering algorithm, and performing clustering class division on the input micro-seismic data;

s34: calculating the distance from the central point of each divided category to the center of the fracturing section selected in the step S32, wherein the category with the minimum distance is the artificial fracture;

s35: judging whether the division of the artificial cracks is correct or not;

if not, adjusting the values of eps and min _ samples, and repeating the steps S31-S35;

if the fracture is correct, another fracture section is selected, and the steps S32-S35 are repeated until all the fracture sections are separated from the natural fracture and the artificial fracture.

Preferably, in step S35, it is determined whether the artificial fracture is correctly divided by the following criteria: and (4) taking lg logarithm as the seismic level of the micro-seismic data of the divided artificial fracture category, and if 80-100% of the seismic levels of the micro-seismic points are less than 1, determining that the artificial fracture is divided correctly.

Preferably, in step S4, the micro-seismic data of the artificial fracture of each fracture section is fitted by using a least square method.

Preferably, the predictor further comprises the steps of: s6: deleting abnormal values in all the maximum horizontal principal stress orientation values; s7: and for the rest maximum horizontal principal stress azimuth values, obtaining the maximum horizontal principal stress distribution condition of the target well through an interpolation algorithm.

Preferably, if there are a plurality of target wells in the target area, after obtaining the maximum horizontal principal stress distribution condition of each target well, the predicting method further includes the following steps: s8: and obtaining the maximum horizontal principal stress distribution condition of the target area through an interpolation algorithm.

The invention has the beneficial effects that:

the method can separate the artificial fracture and the natural fracture in the microseism event of each fracturing section; the prediction of the ground stress azimuth can be carried out by utilizing the distinguished artificial crack micro-seismic points, and the prediction is compared with the data of an actual well site, so that the result is more accurate, and the process is more intelligent and faster.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic diagram of an embodiment of a determination result of an artificial fracture for a X1 well;

FIG. 2 is a graph illustrating magnitude results for data points in a well X1 according to an exemplary embodiment;

FIG. 3 is a schematic diagram illustrating the numeric results of input parameters for each fracturing stage of an X1 well according to an embodiment;

FIG. 4 is a schematic illustration of the prediction of fracture angles for different methods of an embodiment X1 well;

FIG. 5 is a graph illustrating the results of an embodiment X1 well stress distribution.

Detailed Description

The invention is further illustrated with reference to the following figures and examples. It should be noted that, in the present application, the embodiments and the technical features of the embodiments may be combined with each other without conflict. It is noted that, unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The use of the terms "comprising" or "including" and the like in the present disclosure is intended to mean that the elements or items listed before the term cover the elements or items listed after the term and their equivalents, but not to exclude other elements or items.

The invention provides a microseism-based ground stress azimuth prediction method, which comprises the following steps of:

s1: micro-seismic data and well trajectory data for a target well are acquired, the micro-seismic data including time, location, and magnitude of occurrence of a micro-seismic event.

S2: and carrying out sample division on the micro seismic data according to the fractured sections of the target well.

S3: and performing cluster analysis on the micro-seismic data of each fracturing section to obtain the micro-seismic data of the artificial cracks in each fracturing section.

In a specific embodiment, the clustering analysis is performed on the microseismic data of each fracture section by using a DBSCAN clustering algorithm. The DBSCAN clustering algorithm is a density-based clustering algorithm, which generally assumes that classes can be determined by how closely the samples are distributed. The main principle is as follows: samples of the same category are closely connected, namely samples of the same category must exist in a short distance around any sample of the category; by dividing closely connected samples into one class, a cluster class is obtained; and dividing all closely connected samples into different categories to obtain a final clustering category result.

Performing the clustering analysis on the microseism data of each fracture section by adopting a DBSCAN clustering algorithm, and specifically comprising the following substeps:

s31: presetting a neighborhood distance threshold value eps of a certain sample of the DBSCAN clustering algorithm and a threshold value min _ samples of the number of samples in a neighborhood with a certain sample distance as eps;

s32: inputting microseism data of a certain fracturing section into the DBSCAN clustering algorithm as basic data;

s33: inputting preset eps and min _ samples to the DBSCAN clustering algorithm, and performing clustering class division on the input micro-seismic data;

s34: calculating the distance from the central point of each divided category to the center of the fracturing section selected in the step S32, wherein the category with the minimum distance is the artificial fracture;

s35: judging whether the division of the artificial cracks is correct or not;

if not, adjusting the values of eps and min _ samples, and repeating the steps S31-S35;

if the fracture is correct, another fracture section is selected, and the steps S32-S35 are repeated until all the fracture sections are separated from the natural fracture and the artificial fracture.

In a specific embodiment, in step S35, it is determined whether the artificial fracture is correctly divided according to the following criteria: and (4) taking lg logarithm as the seismic level of the micro-seismic data of the divided artificial fracture category, and if 80-100% of the seismic levels of the micro-seismic points are less than 1, determining that the artificial fracture is divided correctly. It should be noted that 80% -100% is the preferred threshold range of the present invention, and the user can set it by himself according to the precision requirement, for example, the values of 85%, 90%, 95% are used. The precision requirement is not high, and the equivalent value of 60 percent and 70 percent can also be adopted.

In a specific embodiment, the idea of adjusting the values of eps and min _ samples is as follows: firstly, increasing parameters, if the number of data points of the micro seismic data obtained after the parameters are increased is less than that before after the log of lg is taken, the parameters need to be decreased, and if the number of data points of the micro seismic data obtained after the parameters are increased is more than that before the data points of the micro seismic data obtained after the log of lg is taken and is less than 1, but the data points do not reach the threshold value of 80-100%, the parameters are continuously increased; and vice versa.

It should be noted that the DBSCAN clustering algorithm used in the foregoing embodiment is only a preferred clustering algorithm of the present invention, and when performing cluster analysis on the microseismic data of each fracture zone, other clustering algorithms in the prior art, such as a Kmeans algorithm, an agglomerative clustering algorithm, and the like, may also be used in the present invention.

S4: and respectively fitting the microseism data of the artificial cracks of each fracturing section to obtain the intercept and the slope of the fitting curve of each fracturing section.

In a specific embodiment, the microseismic data of the artificial fracture of each fracture section is fitted by a least squares method. The main idea of the least squares method is to minimize the sum of the squared errors (also called residuals) of the true and predicted values by determining unknown parameters. The method is the prior art, and the specific steps are not described herein again.

S5: and calculating the arctangent value of the slope of each fracturing section to obtain the angle of the artificial crack of each fracturing section, wherein the angle of the artificial crack of each fracturing section is the direction of the maximum horizontal main stress of each fracturing section.

In a specific embodiment, the predictor further comprises the steps of:

s6: outliers in all maximum horizontal principal stress orientation values are deleted.

Optionally, the outlier is a stress bearing value where the stress bearing prediction is too different (more than 15% of the mean) from the adjacent fracture stage. It should be noted that 15% is a preferred threshold of the present embodiment, and the user may set other thresholds, for example, 5%, 10%, 20%, etc., according to the accuracy requirement.

S7: and for the rest maximum horizontal principal stress azimuth values, obtaining the maximum horizontal principal stress distribution condition of the target well through an interpolation algorithm.

In a specific embodiment, the target well is in a target area, and there are multiple target wells in the target area, and after obtaining the maximum horizontal principal stress distribution of each target well, the predicting method further includes the following steps: s8: and obtaining the maximum horizontal principal stress distribution condition of the target area through an interpolation algorithm.

In a specific embodiment, an X1 well of a certain target area is used as a target well, and the method for predicting the geostress azimuth of the well based on the microseism performs the geostress azimuth prediction of the well, and specifically comprises the following steps:

s1: microseismic data and well trajectory data were obtained for the X1 wells, and the results are shown in tables 1 and 2, respectively:

TABLE 1 microseismic fraction data for X1 wells

TABLE 2 well trajectory part data for X1 well

It should be noted that the microseismic data and well trajectory data of the X1 well are more, and table 1 and table 2 are only partial data thereof.

S2: and sampling the micro seismic data according to the number of the fractured sections of the target well, and respectively storing the micro seismic data of each section in different text files according to formats, so that the micro seismic data are convenient to read.

S3: and performing cluster analysis on the microseism data of each fracturing section by adopting a DBSCAN clustering algorithm to obtain the microseism data of the artificial fractures in each fracturing section, and drawing the classification result and the well track on a coordinate system to facilitate observation.

It should be noted that, in this embodiment, the microseism data is clustered by using two clustering algorithms, namely a Kmeans algorithm and an agglomeration clustering algorithm, and the artificial cracks are judged by using an artificial judgment method, and the judgment results of the four methods are shown in fig. 1. As can be seen from FIG. 1, the artificial crack judgment result of the clustering algorithm of the invention is more accurate than the judgment result of the artificial judgment method in the prior art, and the optimal clustering result of the DBSCAN clustering algorithm of the invention is more accurate in the other three different clustering algorithms.

It should be noted that, in this embodiment, the threshold value for whether the clustering is correctly performed is 90%, and the data point pairs of the natural fracture magnitude of the artificial fracture are shown in fig. 2.

It should be noted that, in this embodiment, the input parameter min _ samples of the DBSCAN clustering algorithm is 50 to 100, and the range of eps is 1 to 5, so as to complete clustering. The min _ samples and eps values of each fracture section are shown in fig. 3.

S4: and respectively carrying out linear fitting on the microseism data of the artificial cracks of each fracturing section by using a least square method to obtain the intercept and the slope of a fitting curve of each fracturing section.

S5: and calculating the arctangent value of the slope of each fracturing section to obtain the angle of the artificial crack of each fracturing section, wherein the angle of the artificial crack of each fracturing section is the direction of the maximum horizontal main stress of each fracturing section.

The results of the prediction of the orientation of the geostress by the four methods are shown in table 3 and fig. 4:

TABLE 3X 1 well different method prediction ground stress azimuth results

As can be seen from table 3 and fig. 4, the artificially determined ground stress orientation has a large difference from the judgment of the clustering method, and the artificial cracks and the natural cracks are not distinguished by the artificial judgment, so that the predicted ground stress orientation is not accurate enough, the artificial cracks and the natural cracks can be distinguished by the clustering method, the judgment of the ground stress orientation is more accurate, and in addition, different clustering methods are adopted, so that the orientation value result difference is small.

S6: rejecting stress orientation values S1 and S21 for which the stress orientation prediction differs too much from the neighbors;

s7: and (3) obtaining the maximum horizontal main stress distribution condition in the single well area through an interpolation algorithm for the stress orientations of the rest full well fracturing sections, wherein the result is shown in fig. 5.

It should be noted that, if there are multiple fracturing wells with microseismic monitoring data in the target area, the spatial distribution of the maximum horizontal principal stress of the target area can be obtained through sequential gaussian or other interpolation algorithms.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.