Methods, apparatuses, and storage media for predicting small-scale directional fractures in shale reservoirs

Abstract

The application discloses a method, equipment and storage medium for predicting small-scale directional cracks of a shale reservoir, and the method comprises the following steps: S1, acquiring seismic attributes in a work area by using post-stack seismic data; S2, observing the extracted seismic attribute profile in S1, selecting a time window thickness, and respectively extracting the plane of the seismic attribute; S3, determining single-attribute directional cracks according to the plane attribute extracted in S2; S4, analyzing the distribution trend of the plane directional cracks; and S5, determining small-scale directional crack information of the shale reservoir. The method can effectively comprehensively utilize information in aspects of the seismic, logging and drilling, quickly determine information such as the extension direction, length and reliability of the directional cracks of the shale reservoir, and determine the plane distribution of the small-scale directional cracks of the shale reservoir, thereby providing a basis for shale gas horizontal well testing layer selection, segmentation, fracturing design, pressure channeling prevention and the like.

Description

Technical Field

[0001] This invention relates to the field of geophysical technology, and in particular to a method, apparatus, and storage medium for predicting small-scale directional fractures in shale reservoirs. Background Technology

[0002] Shale gas is produced from shale reservoirs. Shale reservoirs with development and production value generally have characteristics such as a large thickness of high-quality shale, moderate burial depth, wide distribution, and good gas content. The main method for shale gas development currently involves drilling horizontal wells into target shale reservoirs and then using staged hydraulic fracturing to break up the shale reservoir and release the shale gas.

[0003] Due to long-term geological tectonic activity, shale reservoirs develop various faults and fractures. These range from large-scale faults with displacements of tens or even hundreds of meters to small-scale fractures with displacements of meters or even none. Some small-scale fractures develop in a network pattern, while others develop directionally along a certain direction.

[0004] The deployment of horizontal wells generally avoids major faults. During fracturing, the development of network fractures helps to break up shale reservoirs. However, the development of directional fractures causes stress to be released along the direction of fracture extension during fracturing, preventing the shale reservoir from being fully transformed and broken up, thus affecting the fracturing effect. Therefore, predicting and identifying small-scale directional fractures is crucial for fracturing design and construction.

[0005] Predicting small-scale fractures has always been a challenge in geophysical forecasting. Seismic waves propagate through the strata at an average speed of 4,000-6,000 meters per second with a frequency of 20-40 Hz. When passing through fractures, although the fractures do have some influence on the propagation of seismic waves, this influence is very weak and it is difficult to see the anomaly directly on the final seismic profile. Summary of the Invention

[0006] The small-scale directional cracks described in this invention are directional cracks with a crack displacement on the order of meters.

[0007] The purpose of this invention is to overcome the problem in the prior art that it is difficult to directly detect anomalies in small-scale directional fractures of shale reservoirs on seismic profiles, and to provide a method, equipment and storage medium for predicting small-scale directional fractures of shale reservoirs.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for predicting small-scale directional fractures in shale reservoirs includes the following steps:

[0010] S1. Calculate and obtain seismic attributes within the work area using post-stack seismic data;

[0011] S2. Observe the seismic attribute profile extracted in S1, select the time window thickness, and perform planar extraction of seismic attributes respectively;

[0012] S3. Based on the planar attributes extracted in S2, determine the single-attribute directional cracks;

[0013] S4. Conduct a planar directional crack distribution trend analysis;

[0014] S5. Determine information on small-scale directional fractures in shale reservoirs.

[0015] The method for predicting small-scale directional fractures in shale reservoirs, as described in this invention, uses post-stack seismic data to extract seismic attributes that reflect fracture information. Planar extraction is performed on these seismic attributes, and abnormally high values ​​of the planar attributes reflect the distribution of vertical or high-angle fractures. Single-attribute directional fracture determination allows for more accurate identification of parameters for fractures with clear directions and a certain extension length. Combined with relevant information from seismic, logging, and drilling data, the method can quickly determine the extension direction, length, and reliability of directional fractures in shale reservoirs, thus identifying the planar distribution of directional fractures in shale reservoirs. This provides a basis for shale gas horizontal well testing, layer selection and segmentation, fracturing design, and fracturing channeling prevention.

[0016] Preferably, the seismic attributes in S1 include seismic ant body attributes and seismic curvature attributes.

[0017] The preferred extraction methods are seismic ant body attributes and seismic curvature attributes. Seismic ant body attributes can extract information on subtle faulting of seismic wave groups or weak changes in reflected energy directly caused by directional fracture zones in the strata. Seismic curvature attributes can reflect the possibility of directional fractures parallel to the fold direction due to strata folding. Both can reflect the possible development of directional fractures directly or indirectly.

[0018] Preferably, the time window thickness in S2 should include the ant body anomaly and curvature anomaly of the target shale reservoir.

[0019] Preferably, the thickness of the time window in S2 is not less than 20 meters.

[0020] Preferably, the planar extraction method for seismic attributes in S2 is to extract them by averaging the attributes of sample points from top to bottom within the time window thickness.

[0021] With this setup, the selected time window can include the ant body anomaly and curvature anomaly of the main target shale reservoir, and the time window thickness is not less than 20 meters. This allows the focus to be on the target shale reservoir, so that the attribute results can reflect small-scale fractures as much as possible. The extraction is performed by averaging the attributes of the sample points from top to bottom within the time window thickness. This strengthens vertically distributed anomalies within the time window, while weakening tilted or locally vertically distributed anomalies, making the identified fractures more accurate.

[0022] Preferably, the determination of single-attribute directional cracks in S3 includes:

[0023] For directional fracture identification based on ant body attributes, linear continuous ant attribute anomalies with an outlier intensity greater than 50% of the maximum outlier intensity in the horizontal well platform area and an extension length exceeding 100 meters are identified as possible directional fractures, and their length and orientation information are measured.

[0024] For the determination of directional fractures based on curvature attributes, linear continuous curvature attribute anomalies with an outlier intensity greater than 30% of the maximum outlier intensity in the horizontal well platform area and an extension length exceeding 200 meters are identified as possible directional fractures, and their length and orientation information are measured.

[0025] By using single-attribute directional crack identification, the parameters of cracks with a clear direction and a certain extension length can be determined more accurately.

[0026] Preferably, the analysis step in S4 is as follows:

[0027] S41. Based on the location of anomalies related to fracture development shown during the horizontal well drilling and fracturing process in the work area, analyze the main trend of directional fracture distribution in the area;

[0028] S42. Based on the main strike of the faults already interpreted in the work area, infer the possible main directions of directional fractures in the area;

[0029] S43. Based on the small faults with a displacement of less than 5 meters encountered in the horizontal wells within the work area, the abnormal drilling conditions of horizontal wells related to fracture development, and the planar location distribution of abnormalities that occurred in the fractured horizontal wells during the fracturing process, combined with the interpreted fault strikes within the work area, the possible directions of directional fractures within the work area are inferred, and the direction of directional fractures within the work area is determined.

[0030] Based on the interpreted main strike of faults within the work area, combined with relevant information from seismic, logging, and drilling data, the main direction of directional fractures within the work area can be predicted relatively accurately.

[0031] Preferably, the method for determining the directional crack information in S5 is as follows: select the directional cracks that are basically consistent with the main direction of the directional cracks determined in S4 from the directional cracks determined by the ant body attributes and curvature attributes, and use them as the directional cracks for comprehensive prediction, and extract the information of the predicted directional cracks.

[0032] A prediction device includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor to enable the at least one processor to perform a method for predicting small-scale directional fractures in shale reservoirs provided by the present invention.

[0033] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a method for predicting small-scale directional fractures in shale reservoirs provided by the present invention.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. The method for predicting small-scale directional fractures in shale reservoirs as described in this invention uses post-stack seismic data to extract seismic attributes that reflect fracture information. Planar extraction is performed on these seismic attributes, and abnormally high values ​​of the planar attributes can reflect the distribution of vertical or high-angle fractures. Single-attribute directional fracture determination allows for more accurate identification of parameters for fractures with clear directions and a certain extension length. Combined with relevant information from seismic, logging, and drilling data, the extension direction, length, and reliability of directional fractures in shale reservoirs can be quickly determined, thus identifying the planar distribution of directional fractures in shale reservoirs. This provides a basis for shale gas horizontal well testing, layer selection and segmentation, fracturing design, and fracturing channeling prevention.

[0036] 2. The preferred extraction of seismic ant body attributes and seismic curvature attributes is as follows: seismic ant body attributes can extract information on subtle faulting of seismic wave groups or weak changes in reflected energy directly caused by directional fracture zones in the strata; seismic curvature attributes can reflect the possibility of directional fractures parallel to the fold direction due to strata folding. Both can reflect the possible development of directional fractures directly or indirectly.

[0037] 3. The selected time window can include the anomalies of the ant bodies and curvature of the main target shale reservoir, and the thickness of the time window is not less than 20 meters. It can focus on the target shale reservoir and make the attribute results reflect small-scale fractures as much as possible. The extraction is carried out by averaging the attributes of the sample points from top to bottom within the time window thickness. This makes vertically distributed anomalies in the time window stronger, while tilted or only locally existing anomalies in the vertical direction are weakened, making the fracture identification more accurate. Attached Figure Description

[0038] Figure 1 A flowchart of the method for predicting small-scale directional fractures in shale reservoirs provided by the present invention;

[0039] Figure 2 A map showing the directional fracture identification of ant body attributes associated with the A-1HF horizontal well;

[0040] Figure 3 The directional small-scale cracks are finally determined by the directional crack prediction method of the present invention. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0042] Example 1

[0043] like Figure 1 As shown, a method for predicting small-scale directional fractures in shale reservoirs includes the following steps:

[0044] S1. Calculate and obtain seismic attributes within the work area using post-stack seismic data, wherein the seismic attributes include seismic ant body attributes and seismic curvature attributes;

[0045] First, a suitable combination of seismic attributes is determined. Two attributes, seismic ant volume and seismic curvature, are selected for combination. The seismic ant volume attribute can extract information on subtle fault movements or weak changes in reflected energy of seismic wave groups directly caused by directional fracture zones in the strata. The seismic curvature attribute reflects the possibility of directional fractures parallel to the fold trend caused by strata folding. Both reflect potential directional fractures directly or indirectly. Three-dimensional data volumes of seismic ant volume and seismic curvature attributes are calculated using post-stack seismic data volumes. During the calculation process, appropriate calculation parameters are selected based on the intensity of fault or fracture development in the area. For example, if the fracture development intensity in the area is low, smaller calculation elements can be used to ensure that the calculated attribute results reflect small-scale fractures as much as possible.

[0046] S2. Observe the seismic attribute profile extracted in S1, select the time window thickness, and perform planar extraction of seismic attributes respectively;

[0047] By observing and calculating the seismic anomaly and curvature attributes profiles, and selecting an appropriate time window thickness, planar extraction of the two attributes is performed. The time window thickness should include the anomaly and curvature anomalies of the main target shale reservoir, with a corresponding thickness of not less than 20 meters. Extraction is performed by averaging the attributes of sample points from top to bottom within the time window thickness. This strengthens vertically distributed anomalies within the time window, while weakening obliquely distributed or locally vertically existing anomalies. By averaging the anomaly and curvature attributes within the 3D data time window, planar anomaly and planar curvature attributes are obtained. High anomaly values ​​in these attributes reflect the possible distribution of vertical fractures or high-angle fractures.

[0048] S3. Based on the planar attributes extracted in S2, determine single-attribute directional cracks. The determination of single-attribute directional cracks includes:

[0049] S31. Determining directional fractures based on ant body attributes: On the extracted planar ant attributes, linear continuous ant attribute anomalies with an outlier intensity greater than 50% of the maximum outlier intensity in the horizontal well platform area and an extension length exceeding 100 meters are identified as possible directional fractures, and their length, orientation, and other information are measured.

[0050] like Figure 2 As shown in the figure, in this embodiment, taking a certain A platform-1HF horizontal well as an example, fracture identification is performed using ant body attributes, and the identification results are shown in Table 1.

[0051] Table 1. Ant body attribute identification directional fracture parameters related to Well A-1HF.

[0052]

[0053] from Figure 2 It can be seen that crack No. 4 coincides with the small section confirmed by actual drilling. The fault displacement of this actual drilling is only 1 meter, which to some extent can corroborate that the ant body properties can identify small-scale cracks on the meter scale.

[0054] S32. Determining directional fractures based on curvature attributes: Based on the extracted planar curvature attributes, linear continuous curvature attribute anomalies with an outlier intensity greater than 30% of the maximum outlier intensity in the horizontal well platform area and an extension length exceeding 200 meters are identified as possible directional fractures, and their length, orientation, and other information are measured.

[0055] S4. Conduct a planar directional crack distribution trend analysis;

[0056] S4 includes the following steps:

[0057] S41. Based on the location of anomalies related to fracture development shown during the horizontal well drilling and fracturing process in the work area, analyze the main trend of directional fracture distribution in the area;

[0058] S42. Based on the main strike of the faults already interpreted in the work area, infer the possible main directions of directional fractures in the area;

[0059] S43. Based on the abnormal drilling conditions of horizontal wells in the work area, such as extremely small faults with a displacement of less than 5 meters, leakage, pressure anomalies, and total hydrocarbon anomalies related to fracture development, as well as the planar location distribution of abnormalities such as casing deformation or pressure channeling in fractured horizontal wells during the fracturing process, and combined with the main orientation of the faults already interpreted in the work area, the possible main directions of directional fractures in the work area are inferred, and the main directions of directional fractures in the work area are determined.

[0060] The main direction of the fracture is generally parallel or perpendicular to the strike of the identifiable fault, and parallel to the direction of hydraulic channeling during fracturing. Drilling anomalies, fracturing casing deformation anomalies, and the plane location of the actual drilled minimal fault can be basically distributed in a straight line in this direction.

[0061] S5. Select fractures from the directional fractures determined by the ant body attributes and curvature attributes that are basically consistent with the main direction of the directional fractures determined in S4. These are used as the directional fractures for comprehensive prediction. Information such as the direction, length, and reliability of fractures with high probability and potential to affect fracturing within the area is determined. If a directional fracture has been verified by actual drilling, its reliability is high; if a directional fracture is reflected in both the ant body attributes and curvature attributes, it is a fracture with relatively high reliability; the rest are fractures with moderate reliability. This achieves the reliability classification of directional fractures. The predicted directional fractures are numbered, and their direction, length, and classification are statistically analyzed to obtain the final prediction results.

[0062] like Figure 3 As shown in Table 2, by superimposing the ant-body attributes and curvature attributes, and based on the horizontal well drilling anomalies encountered in the work area, such as extremely small faults with a displacement of less than 5 meters, leakage related to fracture development, pressure anomalies, and total hydrocarbon anomalies, as well as the planar location distribution of anomalies such as casing deformation in fractured horizontal wells during fracturing, and the direction of pressure channeling during fracturing, combined with the main strike of the interpreted faults in the work area, a total of 10 small-scale directional fractures at the meter level were identified. Among them, one fracture with high reliability, known as fracture No. 2, has been confirmed by actual drilling of a horizontal well on platform A; two fractures with relatively high reliability, which are fractures that show abnormalities after superimposing the ant-body attributes and curvature attributes; and seven fractures with average reliability.

[0063] Table 2A: Information on Small-Scale Directional Cracks Predicted Comprehensively in Platform Area

[0064]

[0065] Example 2

[0066] This embodiment provides a prediction device, including at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enable the at least one processor to perform a method for predicting small-scale directional fractures in shale reservoirs as described in Embodiment 1.

[0067] Example 3

[0068] This embodiment provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a method for predicting small-scale directional fractures in shale reservoirs as described in Embodiment 1.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting small-scale directional fractures in shale reservoirs, characterized in that, Includes the following steps: S1. Calculate and obtain seismic attributes within the work area using post-stack seismic data; The earthquake attributes include earthquake ant body attributes and earthquake curvature attributes; S2. Observe the seismic attribute profile extracted in S1, select the time window thickness, and perform planar extraction of seismic attributes respectively; The time window thickness includes the anticline anomaly and curvature anomaly of the target shale reservoir; The thickness of the time window shall not be less than 20 meters; The planar extraction method for seismic attributes is as follows: the attributes of the sample points are averaged from top to bottom within the time window thickness. S3. Based on the planar attributes extracted in S2, determine the single-attribute directional cracks; Single-attribute directional crack determination includes: Determining directional fractures based on ant body attributes: On the extracted planar ant attributes, linear continuous ant attribute anomalies with an outlier intensity greater than 50% of the maximum outlier intensity in the horizontal well platform area and an extension length exceeding 100 meters are identified as possible directional fractures, and their length and orientation information are measured. Determining directional fractures based on curvature attributes: Based on the extracted planar curvature attributes, straight continuous curvature attribute anomalies with an intensity greater than 30% of the maximum anomaly intensity in the horizontal well platform area and an extension length exceeding 200 meters are identified as possible directional fractures, and their length and orientation information are measured. S4. Conduct a planar directional crack distribution trend analysis; S5. Determine information on small-scale directional fractures in shale reservoirs.

2. The method for predicting small-scale directional fractures in shale reservoirs according to claim 1, characterized in that, In step S1, a three-dimensional data volume of seismic ant body attributes and seismic curvature attributes is calculated using the post-stack seismic data volume.

3. The method for predicting small-scale directional fractures in shale reservoirs according to claim 1, characterized in that, The analysis steps in S4 are as follows: S41. Based on the location of anomalies related to fracture development shown during the horizontal well drilling and fracturing process in the work area, analyze the distribution trend of directional fractures in the area; S42. Based on the main strike of the faults already interpreted in the work area, infer the possible directions of directional fractures in the area; S43. Based on the small faults with a displacement of less than 5 meters encountered by horizontal wells in the work area, the abnormal drilling conditions of horizontal wells related to fracture development, and the planar location distribution of abnormalities that occurred in fractured horizontal wells during the fracturing process, combined with the interpreted fault strikes in the work area, the possible directions of directional fractures in the work area are inferred, and the direction of directional fractures in the work area is determined.

4. The method for predicting small-scale directional fractures in shale reservoirs according to claim 3, characterized in that, Horizontal well drilling anomalies associated with fracture development include lost circulation.

5. The method for predicting small-scale directional fractures in shale reservoirs according to claim 3, characterized in that, Horizontal well drilling anomalies associated with fracture development include pressure anomalies.

6. The method for predicting small-scale directional fractures in shale reservoirs according to claim 3, characterized in that, Horizontal well drilling anomalies associated with fracture development include total hydrocarbon anomalies.

7. The method for predicting small-scale directional fractures in shale reservoirs according to claim 3, characterized in that, Abnormalities that occur during the fracturing process of a fractured horizontal well include: deformation or cross-flow of the horizontal well casing.

8. A method for predicting small-scale directional fractures in shale reservoirs according to any one of claims 1-7, characterized in that, The method for determining the directional crack information in S5 is as follows: select the directional cracks that are basically consistent with the directional cracks determined in S4 from the directional cracks determined by the ant body attributes and curvature attributes, and use them as the directional cracks for comprehensive prediction, and extract the information of the predicted directional cracks.

9. A prediction device, characterized in that, It includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enable the at least one processor to perform the directional crack prediction method according to any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of a method for predicting small-scale directional fractures in shale reservoirs as described in any one of claims 1-8.

Images