阅读说明：本技术 基于剪切破裂共轭准则的叠后裂缝储层表征方法 (Post-stack fracture reservoir characterization method based on shear fracture conjugation criterion ) 是由 何文渊 孙平 于 2020-10-23 设计创作，主要内容包括：本发明公开了基于剪切破裂共轭准则的叠后裂缝储层表征方法,方法包括：首先,通断层保护滤波增强现有断层信息,保留现有构造特征,不损害断层信息的前提下进行,之后针对断层保护滤波的数据体进行脊线加强的相干增强,在张量方向场的约束下进行蚁群追踪,最后进行基于剪切破裂共轭准则的张量方向场叠后裂缝模拟,实现裂缝储层定量表征。本发明方法综合制定了从背景噪声去除到叠后数据增强处理最后进行裂缝模拟的全流程裂缝储层表征方法,充分利用了裂缝是基于剪切破裂共轭准则的这一特征,将单一的叠后裂缝模拟手段进行多层次处理,丰富裂缝细节,增加识别准确率,为油气勘探领域的裂缝性储层钻探提供了有利的技术保障。(The invention discloses a method for representing a post-stack fracture reservoir based on a shear fracture conjugation criterion, which comprises the following steps: firstly, on-off layer protection filtering enhances the existing fault information, retains the existing structural characteristics, and is carried out on the premise of not damaging the fault information, then ridge line enhanced coherence enhancement is carried out on a fault protection filtering data body, ant colony tracking is carried out under the constraint of a tensor direction field, and finally tensor direction field post-stack fracture simulation based on a shear fracture conjugation criterion is carried out, so that quantitative characterization of a fracture reservoir is realized. The method comprehensively formulates a full-flow fracture reservoir characterization method from background noise removal to post-stack data enhancement processing and finally performs fracture simulation, fully utilizes the characteristic that the fracture is based on a shear fracture conjugation criterion, performs multi-level processing on a single post-stack fracture simulation means, enriches fracture details, increases identification accuracy, and provides favorable technical support for drilling of fractured reservoirs in the field of oil and gas exploration.)

1. The method for characterizing the post-stack fracture reservoir based on the shear fracture conjugation criterion is characterized by comprising the following steps of:

step one, by identifying fault target characteristics of a target data volume, analyzing similar characteristic attributes of a variation trend direction/tendency along a seismic axis to obtain a result fault protection data volume;

step two, aiming at the result fault protection data body in the step one, carrying out ridge line fracture enhancement processing, and obtaining a fracture enhancement result data body by searching occurrence mutation characteristics along the earthquake axis inclination direction;

step three, identifying tiny fractures on the fracture enhancement result data volume in the step two according to an ant colony seed point tracking method;

and step four, according to the microscopic 'conjugate' linear characteristics of the micro fracture and the statistical rule of the distribution of the micro fracture, further strengthening the smaller fracture characteristics of the results obtained in the step three, extracting the difference characteristics/enhancing the common characteristics according to the functional requirements, and predicting the X-type fracture reservoir stratum according to the shear fracture conjugation criterion.

2. The method for characterizing a post-stack fracture reservoir based on the shear fracture conjugation criterion in claim 1, wherein the step one of obtaining an achievement fault protection data volume process specifically comprises; by analyzing the occurrence, tendency and trend of different earthquake homodromous axes of the target position line and the trace line position, the existing structural characteristics and trend are kept, and the fracture characteristics are prevented from being fuzzified by filtering, so that a result fault protection data body which is free of noise background and keeps the original earthquake occurrence and structural characteristics is obtained.

3. The method for characterizing a post-stack fracture reservoir based on the shear fracture conjugation rule in claim 1, wherein the performing of the crest line fracture enhancement processing procedure on the achievement fault protection data volume in the first step in the second step comprises:

s201, estimating the direction of the ridge line based on the growth of the seed region, wherein the process is shown as the following formula:

in which RB denotes the region in the direction of the ridge to be calculated, RB_AdjA four/eight-channel region representing the region; thetaRepresenting the direction angle of the sine wave modeling fitting in the search area; f represents the frequency of sine wave modeling in the search area; a represents the amplitude values of all sampling points in the search area; w represents a gaussian fit function within the region for weighting the amplitudes within the smoothed region to reduce the noise level within the region; when the two regions are continuous, O_fA value of 1, a non-connection value of 0;

s202, carrying out coherent enhancement processing on the ridge line by a nonlinear ridge line enhancement method, wherein the process is shown as the following formula:

wherein rho is a coherence enhancing factor (0-1); AA 'and BB' represent the principal direction of the fault at the i, j position and the normal direction thereof, respectively; g (n)_AA'-k) represents a gaussian function centered around the kth CDP point in the AA' direction; delta C_kijRepresenting the gradient of the coherence value of the point at the k-th CDP point and the ij position; delta C_BB'Represents the coherence gradient in the BB' direction; c_ijIs the value of the coherent attribute at the CDP location for lane number i, lane number j.

4. The method for characterizing a post-stack fractured reservoir based on the shear fracture conjugation rule of claim 1, wherein the step four is to perform extraction of difference features/enhancement of common features according to functional requirements, and the step of performing the X-type fractured reservoir prediction process according to the shear fracture conjugation rule specifically comprises the following sub-steps:

s401, calculating a weight kernel function k in each direction in a neighborhood based on a tensor field of a target simulation point, and using an optimized clustering method to weight and fit fracture attribute values in the main direction of the simulation point, wherein the fracture attribute values are shown as follows:

in the formula p_iRepresenting the position of the ith point in the data window; p is a radical of₀Representing a window center position; h is_pRepresenting a kernel function K_pThe variance of (a); d_m(M_i,M₀) Representing the distance between the point i of the directional model m and the central point; h is_mRepresents the variance of the orientation model m; k_m(M_i,M₀) Representing a kernel function value at the position of the i point of the model m;

s402, establishing a tensor gradient direction sum, and performing seed point path fitting as shown in the following formula:

STGO in the formula_(i,j)Representing the sum of the directional gradient tensors of the i, j points within the window w; g_w(m, n) represents the directional tensor gradient at m, n points within the window w; a gradient filtered using a gaussian kernel function;representing the gradient of i, j points in a window w, wherein the gradient is obtained by calculation after the smoothing of a Gaussian kernel function so as to reduce the noise influence; t represents a judgment threshold value of the gradient, the absolute value is larger than the value and is taken as an effective direction, the absolute value is smaller than the value, and no statistics is added to the direction;

s403, synthesizing the sum of gradient directions of orthogonal tensors, which is shown as the following formula:

ISTGO_h(i,j)＝STGO_ru(i,j)+STGO_rd(i,j)

ISTGO_v(i,j)＝STGO_ld(i,j)+STGO_rd(i,j)

S_I＝max{|ISTGO₁|…|ISTGO_i|…|ISTGO₈|}

in the formula, ru represents the upper right direction, ru represents the lower right direction, and the upper right direction and the lower right direction can be combined into a gradient mark ISTGO in the horizontal direction_h(ii) a ld represents the upper right direction, rd represents the lower right direction, and the upper right and the lower right can synthesize the gradient identification ISTGO in the vertical direction_v；S_IMarking a main direction mark; ISTGO_iIdentifying the gradient of the synthesized orthogonal tensor in the ith direction, and taking the direction with the maximum gradient as a main direction;

s404, judging the gradient direction of the tensor, and counting the relative crack density and the main crack development azimuth in the unit radius R based on the crack simulation result.

Technical Field

The invention relates to the technical field of oil and gas exploration, in particular to a method for representing a post-stack fracture reservoir based on a shear fracture conjugation criterion.

Background

In recent years, unconventional reservoirs such as shale gas and compact oil and gas reservoirs are more and more emphasized in oil and gas exploration at home and abroad, wherein fractures are decisive factors influencing the yield of the reservoirs, and the fractured reservoirs of the oil and gas fields in China have high potential and high demand and are important places for increasing storage and production. However, the prediction and description of the fractured reservoir are difficult and low in precision compared with the conventional reservoir, and are the main target of the attack and the customs of each large oil and gas field for a long time. Currently, there are two main types of commonly used fracture reservoir characterization methods: the method comprises the steps of post-stack fracture detection, pre-stack fracture detection based on post-stack fracture attributes and pre-stack fracture detection, and pre-stack wide azimuth gather based on the pre-stack wide azimuth gather, wherein pre-stack wide azimuth data required by a pre-stack fracture detection technology is difficult to acquire, high in cost and low in calculation efficiency, so that a post-stack fracture reservoir characterization method is more common.

The conventional post-stack crack prediction method is mainly based on 2 types:

the first type: based on the geometrical attributes of coherence, curvature, frequency division and the like of the post-stack seismic attributes, the method has the advantages of simple and quick operation process, high efficiency, good prediction effect on large-scale fracture and crack, high accuracy and wide application range when used in the initial exploration stage. However, for the fine exploration and development block, the method has low prediction precision, can only carry out qualitative description, cannot carry out quantitative prediction and cannot meet the standard of fine reservoir prediction;

the second type: the improved post-stack attribute prediction method based on ant tracking is an improvement of a first method, seed points are set on the basis of post-stack attributes such as coherence and curvature, point-to-point tracking is carried out through an ant tracking algorithm, and quantitative distribution data of cracks are obtained.

In conclusion, the traditional characterization methods for the post-stack fracture reservoirs have high uncertainty, cannot accurately identify the fracture reservoirs, and cannot provide effective technical support for fine reservoir prediction.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for characterizing a post-stack fracture reservoir based on a shear fracture conjugation criterion. In actual work, small fault and crack information is often polluted by noise, firstly, on-off layer protection filtering enhances the existing fault information, the existing structural features are reserved, the fault information is not damaged, then, ridge line enhanced coherence enhancement is carried out on a data body of fault protection filtering, ant colony tracking is carried out under the constraint of a tensor direction field, and finally, tensor direction field post-stack crack simulation based on a shear fracture conjugation criterion is carried out to realize quantitative characterization of a crack reservoir.

The purpose of the invention is realized by the following technical scheme:

the method for representing the post-stack fracture reservoir based on the shear fracture conjugation criterion comprises the following specific steps:

step 1, analyzing similar characteristic attributes of a variation trend direction/tendency along a seismic axis by identifying fault target characteristics of a target data volume; the existing structural characteristics are reserved, fault information is not damaged, and calculation errors caused by stratum attitude are effectively reduced, so that the effect of removing background noise is achieved.

Step 2, aiming at the result fault protection data body in the step 1, fracture enhancement processing is carried out, and shape mutation characteristics along the inclination direction of the seismic axis are searched; on the basis of identifying the trend of the fault layer, similar differences under different backgrounds are enhanced, so that the characteristics of the fault layer on the attributes are more continuous, and the definition of the attributes on fault layer depicting is improved.

And 3, identifying the tiny fracture on the data body of the fracture enhancement result strengthened by the ridge line in the step 2 according to the ant colony seed point tracking method.

And 4, according to the linear characteristics of micro fracture (crack) microcosmic 'conjugation' and the statistical rule of the banding distribution of the linear characteristics, further strengthening the smaller crack characteristics (difference) of the result obtained in the step 3, namely strengthening according to the data characteristic direction, wherein the target characteristics are linear continuous change response changing along a plane, adaptively counting the target 'direction continuity' and 'difference', extracting/enhancing the common characteristics of the difference characteristics according to the functional requirements, and predicting the X-type crack reservoir stratum according to the shear fracture conjugation criterion.

The invention has the beneficial effects that: the method comprehensively formulates a full-flow fracture reservoir characterization method from background noise removal to post-stack data enhancement processing and finally performs fracture simulation, fully utilizes the characteristic that the fracture is based on a shear fracture conjugation criterion, performs multi-level processing on a single post-stack fracture simulation means, enriches fracture details, increases identification accuracy, and provides favorable technical support for drilling of fractured reservoirs in the field of oil and gas exploration.

Drawings

FIG. 1 is a flow chart of the method of the present invention.

FIG. 2 is a diagram of the results of fault protection using a post-stack seismic data volume in accordance with an embodiment of the present invention.

FIG. 3 is a graph showing the results of fracture enhancement using the ridge line enhancement method according to an embodiment of the present invention.

Fig. 4 is a data result diagram of ant colony algorithm tracking performed on a fault and crack enhanced data volume according to an embodiment of the invention.

FIG. 5 is a graph of natural fractures and models based on shear fracture conjugation criteria according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating principal direction fracture property simulation performed according to an embodiment of the present invention

FIG. 7 is a path diagram of seed point fitting according to an embodiment of the present invention.

Figure 8 is a graph of the gradient direction and outcome of a synthetic tensor performed by an embodiment of the present invention.

FIG. 9 is a diagram of the final results of a conjugate fracture simulation performed by an embodiment of the present invention.

FIG. 10 is a fracture density and orientation map for a conjugate fracture simulation performed in accordance with an embodiment of the present invention.

Detailed Description

In order to more clearly understand the technical features, objects, and effects of the present invention, embodiments of the present invention will now be described with reference to the accompanying drawings.

In this embodiment, as shown in fig. 1, the method for characterizing a post-stack fracture reservoir based on the shear fracture conjugation criterion includes the following steps:

step 1, analyzing similar characteristic attributes of a variation trend direction/tendency along a seismic axis by identifying fault target characteristics of a target data volume; the existing structural characteristics are reserved, fault information is not damaged, and calculation errors caused by stratum attitude are effectively reduced, so that the effect of removing background noise is achieved.

Step 2, aiming at the result fault protection data body in the step 1, fracture enhancement processing is carried out, and shape mutation characteristics along the inclination direction of the seismic axis are searched; on the basis of identifying the trend of the fault layer, similar differences under different backgrounds are enhanced, so that the characteristics of the fault layer on the attributes are more continuous, and the definition of the attributes on fault layer depicting is improved.

And 3, identifying the tiny fracture on the data body of the fracture enhancement result strengthened by the ridge line in the step 2 according to the ant colony seed point tracking method.

And 4, according to the linear characteristics of micro fracture (crack) microcosmic 'conjugation' and the statistical rule of the banding distribution of the linear characteristics, further strengthening the smaller crack characteristics (difference) of the result obtained in the step 3, namely strengthening according to the data characteristic direction, wherein the target characteristics are linear continuous change response changing along a plane, adaptively counting the target 'direction continuity' and 'difference', extracting/enhancing the common characteristics of the difference characteristics according to the functional requirements, and predicting the X-type crack reservoir stratum according to the shear fracture conjugation criterion.

The post-stack fracture identification process based on the shear fracture conjugation criterion is as follows:

1. fault protected filtering

High signal-to-noise ratio, high resolution and high fidelity are basic principles of seismic data processing, but when three highs are pursued, more false images are inevitably generated in an original post-stack data body due to factors such as noise background, and noise pollution of the type can bring great interference to post-stack crack prediction, so the influence brought by noise is firstly removed in the post-stack crack prediction.

The invention adopts a filtering method based on fault protection (earthquake occurrence driving constraint), and the existing structural characteristics and trends are kept and the fracture characteristics are prevented from being fuzzified by filtering by analyzing the occurrence, the tendency, the trend and other factors of different earthquake homodromous axes of a target position line and a trace line position, so that a post-stack processing data body which removes a noise background and keeps the original earthquake occurrence and the structural characteristics, namely a fault protection result, is obtained as shown in figure 2.

2. Ridgeline coherence enhancement

The micro fracture response may be difficult to identify in the post-stack seismic data volume, and needs to be promoted by a corresponding fracture enhancement means, resulting in an enhanced fracture display result fig. 3. Firstly, on the basis of a data volume with noise background removed, estimating the data volume by ridge line direction based on the growth of a seed region:

in which RB denotes the region in the direction of the ridge to be calculated, RB_AdjA four/eight-channel region representing the region; theta represents a direction angle of the search area which is fitted by sine wave modeling; f represents the frequency of sine wave modeling in the search area; a represents the amplitude values of all sampling points in the search area; w represents a gaussian fit function within the region for weighting the amplitudes within the smoothed region to reduce the noise level within the region. When the two regions are continuous, O_fThe value is 1 and the non-connection value is 0.

Carrying out coherence enhancement processing on the ridge line by a nonlinear ridge line enhancement method:

wherein rho is a coherence enhancing factor (0-1); AA 'and BB' represent the principal direction of the fault at the i, j position and the normal direction thereof, respectively; g (n)_AA'-k) represents a gaussian function centered around the kth CDP point in the AA' direction; delta C_kijRepresenting the gradient of the coherence value of the point at the k-th CDP point and the ij position; delta C_BB'Represents the coherence gradient in the BB' direction; c_ijIs the value of the coherent attribute at the CDP location for lane number i, lane number j.

3. Ant colony fracture tracking

The ant tracking technology is a technology for further enhancing fracture information and suppressing other information through partially processed post-stack coherent data, and can simulate a dynamic crawling track of an ant colony in the nature when searching for food, various seed points are placed into a processed coherent data body for crack search, and a crack plane after ant colony tracking is obtained as shown in fig. 4, wherein selection and judgment of the seed points require manual work to give explained or confirmed existing crack characteristics to a system.

4. Conjugate fracture simulation

The structural stress field change rate of the crack region is stronger than that of the non-crack region, and the crack region is easy to form a vertical, horizontal and shear high-bias stress field of the region, such a stress environment has a strong destructive effect on surrounding rock bodies, and an unstable abnormal region (namely a butterfly-shaped destructive region) is generated, namely X-shaped conjugate shear fracture, as shown in a part a of the attached drawing in fig. 5. The stress environment determines the fracture size and strength of X-type shear fracture, and the method is based on the fracture X-type shear fracture conjugation criterion to establish a fracture simulation model, as shown in part b in figure 5, and predicts the spreading characteristics of a fracture type reservoir.

Firstly, based on the tensor field of the target simulation point, the weight kernel function k in each direction in the neighborhood is calculated, and the fracture attribute value in the main direction of the simulation point is subjected to weighted fitting by using an optimized clustering method, and the process is shown in fig. 6.

In the formula p_iRepresenting the position of the ith point in the data window; p is a radical of₀Representing a window center position; h is_pRepresenting a kernel function K_pThe variance of (a); d_m(M_i,M₀) Representing the distance between the point i of the directional model m and the central point; h is_mRepresents the variance of the orientation model m; k_m(M_i,M₀) Representing the kernel function value at the i-point location of model m.

Second, the tensor gradient direction sum is established, and the seed point path fitting is carried out, and the process is shown in fig. 7.

STGO in the formula_(i,j)Representing the sum of the directional gradient tensors of the i, j points within the window w; g_w(m, n) represents the directional tensor gradient at m, n points within the window w; a gradient filtered using a gaussian kernel function;representing the gradient of i, j points in a window w, wherein the gradient is obtained by calculation after the smoothing of a Gaussian kernel function so as to reduce the noise influence; t represents a judgment threshold value of the gradient, the absolute value is larger than the value and is taken as an effective direction, and the direction is not added with statistics.

Third, the process of synthesizing the orthogonal tensor gradient direction sums is shown in fig. 8.

ISTGO_h(i,j)＝STGO_ru(i,j)+STGO_rd(i,j)

ISTGO_v(i,j)＝STGO_ld(i,j)+STGO_rd(i,j) (6)

In the formula, ru represents the upper right direction, ru represents the lower right direction, and the upper right direction and the lower right direction can be combined into a gradient mark ISTGO in the horizontal direction_h(ii) a ld represents the upper right direction, rd represents the lower right direction, and the upper right and the lower right can synthesize the gradient identification ISTGO in the vertical direction_v。

S_I＝max{|ISTGO₁|…|ISTGO_i|…|ISTGO₈|} (7)

In the formula S_IMarking a main direction mark; ISTGO_iA resultant orthogonal tensor gradient in the ith direction is identified. The direction in which the gradient is greatest is taken as the principal direction.

Finally, the tensor gradient direction is judged, and a crack simulation result is obtained, as shown in fig. 9. The relative crack density and the main crack development azimuth within the unit radius R are counted based on the crack simulation result data, and the result is shown in FIG. 10. The method considers the stress field direction and the rock fracture criterion comprehensive effect, adopts the vector ant colony tracking algorithm to accord with the geological rule, and has strong noise immunity and high result reliability.

The statistical formula of the crack density is as follows:

the statistical formula of the main orientation of the crack is as follows:

wherein R represents a data window with radius R; n is a radical of_fRepresenting the number of points representing the fracture attributes counted within the data window; max (N)_f) Representing the maximum value in the crack attribute values of the R radius statistics of the whole region of the crack attribute;indicating the azimuth at the ith valid azimuth within the current radius R; l is_iRepresenting the effective extension length of the current crack at the ith effective azimuth; coh (hydrogen sulfide)_iRepresenting the coherence value of the ith point in the active orientation of the current fracture extension.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.