Shale reservoir fracture prediction method and fracture description and description tool

Abstract

The invention provides a shale reservoir fracture prediction method and a fracture depicting and describing tool, and the method comprises the steps: carrying out the decomposition of post-stack seismic data based on a multi-level multi-azimuth method, and obtaining N different levels of seismic decomposition data; performing spectral analysis and directivity optimization on the seismic decomposition data of each level, selecting the seismic decomposition data of the level x with the first high-frequency information rank and the seismic decomposition data of at least one level with more original effective seismic information, and performing superposition and combination to obtain high-resolution seismic data; and carrying out ant body attribute calculation based on a variance body, obtaining ant body seismic attributes, carrying out plane slice extraction of a target horizon, and obtaining a crack prediction result. According to the method, the recombination rate of the fracture prediction result and actual drilling fault and well leakage can reach 60% or above, and the shale reservoir fracture prediction precision is remarkably improved; the method has important guiding significance on actual exploration, development and production.

Description

Technical Field

[0001] The present invention relates to the field of exploration geophysics and oil and gas development technology, in particular to the field of shale reservoir fracture characterization and description, and specifically to a shale reservoir fracture prediction method and a fracture characterization and description tool. Background Art

[0002] Fractures not only store oil and gas, but also are important channels for oil and gas migration, which has a significant impact on the oil and gas production capacity of the reservoir. If the spatial distribution of fractures can be accurately predicted, it will be important for studying fracture oil and gas reservoirs, improving the success rate of exploration, and improving development efficiency. Especially for shale reservoirs with self-generating and self-storing properties, fracture development plays an important role in hydrocarbon gas storage, horizontal and vertical migration, and shale oil and gas development. Therefore, the prediction of fracture spatial distribution is a key factor in shale gas preservation and development deployment.

[0003] At present, the prediction of shale reservoir fractures has just started, mainly drawing on the fracture prediction methods of carbonate rock, clastic rock and other reservoirs. The indirect methods of fracture prediction can be roughly divided into three types: geological method, well logging method and seismic method. The geological method is the most direct and simple means, which can make quantitative predictions, but it cannot meet the high-precision requirements of oil and gas field development, and it cannot be widely used in reservoir prediction; the well logging method has an abnormal response to fractures and can make qualitative judgments, but it is seriously affected by the environment, has frequent multi-solutions, and is not easy to produce and use in large quantities; the seismic method can be observed continuously in the vertical and horizontal directions, and its cost is relatively low, and it has a significant effect on reservoir fracture prediction. The main method used in reservoir prediction is the seismic method. The seismic method is divided into pre-stack fracture prediction technology and post-stack fracture prediction technology. The pre-stack fracture prediction technology has high cost and is mainly used to identify high-angle fracture development areas. It has high requirements for seismic data and is affected by high coverage times, uniform distribution, and wide azimuth. The most widely used method for fracture prediction in shale reservoirs is the post-stack fracture prediction technology of the seismic method. This technology mainly uses seismic attributes such as coherence volume attributes, curvature attributes, variance volume attributes, ant volume attributes, variance ant volume attributes, etc. to predict the fracture development area.

[0004] The main basis for judging fracture prediction by post-stack seismic attributes is the discontinuity characteristics of the post-stack seismic data event axis, which reflects the seismic response characteristics of the fracture development site. However, due to the resolution of seismic data, seismic attributes are usually difficult to accurately identify medium- and small-scale fractures. At the same time, the type of seismic attributes and the related parameter settings of each attribute have a great impact on the fracture prediction results. In summary, the current prediction methods of post-stack seismic attributes mainly have problems such as low accuracy, high multi-solution, and limited prediction reliability. In actual production, the results of fracture prediction by seismic attributes are difficult to form a good match with the actual fractures and faults encountered in drilling.

[0005] Therefore, developing a shale reservoir fracture prediction method with high accuracy and high prediction reliability has important guiding significance for actual exploration, development and production. Summary of the invention

[0006] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a tool for characterizing and describing shale reservoir fractures; another purpose of the present invention is to improve the reliability of shale reservoir fracture prediction.

[0007] In order to achieve the above object, the present invention provides a shale reservoir fracture prediction method, comprising the following steps:

[0008] Based on the multi-level and multi-directional method, the post-stack seismic data are decomposed to obtain N different levels of seismic decomposition data;

[0009] Performing spectrum analysis and directional optimization on each level of earthquake decomposition data, selecting the level x earthquake decomposition data with the most high-frequency information and at least one level of earthquake decomposition data with more original earthquake effective information;

[0010] Superimposing and combining the level x and the at least one level seismic decomposition data to obtain high-resolution seismic data;

[0011] Perform ant body attribute calculation based on variance body on high-resolution seismic data to obtain ant body seismic attributes;

[0012] The plane slice extraction of the target layer is performed on the seismic attributes of the ant body to obtain the fracture prediction results.

[0013] Optionally, the fracture prediction result is a stratigraphic plane slice.

[0014] Optionally, the method further includes the steps of: using actual drilling faults and well leakage information to constrain the variance body-based ant body attribute calculation, and by continuously adjusting the ant body attribute parameters, making the consistency rate between the stratigraphic plane slices and the actual drilling faults and well leakage greater than a preset value, thereby obtaining a shale reservoir fracture prediction result.

[0015] Optionally, the method further comprises: before constraining, collecting the information of lost circulation and fault encountered in the horizontal well of the target layer and projecting it onto the plane slice of the layer.

[0016] Optionally, the method further comprises the step of: evaluating the post-stack seismic data before the step of decomposing the post-stack seismic data, and pre-processing the post-stack seismic data if the evaluation is poor.

[0017] Optionally, the evaluation includes determining a signal-to-noise ratio, and the preprocessing includes at least one of denoising, flattening, and amplitude equalization.

[0018] Optionally, N=7, the level x is level 1, and the at least one level is level 2.

[0019] Optionally, retaining more original earthquake valid information means: retaining the most original earthquake valid information, or retaining the first most and the second most original earthquake valid information.

[0020] Optionally, the preset value is greater than 50%.

[0021] Another aspect of the present invention provides a computer device, comprising: at least one processor, and a memory storing program instructions, wherein the program instructions are configured to be executed by the at least one processor.

[0022] Optionally, the program instructions include instructions for executing the above method.

[0023] Another aspect of the present invention provides a computer-readable storage medium having computer program instructions stored thereon, wherein the computer program instructions implement the above method when executed by a processor.

[0024] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0025] (1) The accuracy of fracture prediction based on post-stack seismic attributes in shale reservoirs has been significantly improved.

[0026] (2) The signal-to-noise ratio of seismic data with poor signal-to-noise ratio can be improved and fracture prediction can be performed.

[0027] (3) The composite rate of shale reservoir fracture prediction results and actual drilling faults and well leakage has increased significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects and / or features of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0029] Figure 1 A flow chart of a shale reservoir fracture prediction method in Example Embodiment 1 is shown.

[0030] Figure 2 The seismic profile of the “multi-level and multi-azimuth” decomposition of the seismic data in Example 1 is shown.

[0031] Figure 3 The stratigraphic plane slice diagram of the conventional method for predicting fractures in the study area in Example 1 is shown.

[0032] Figure 4A plane slice diagram of the fracture layer predicted by the method of the present invention in the study area in Example 1 is shown.

[0033] Figure 5 The diagram shows the coincidence rate of fractures predicted by the method of the present invention and the drilling leakage and faults in the study area in Example 1.

[0034] Fig. 6A The figure shows the matching situation between the fracture prediction profile of the conventional method and the actual drilling leakage point.

[0035] Figure 6B The diagram shows the matching of the fracture prediction profile of the method of the present invention and the actual drilling leakage point. DETAILED DESCRIPTION

[0036] Hereinafter, the present invention will be described in detail in conjunction with exemplary embodiments and drawings, but the following embodiments are only used to help understand the technology of the present invention and shall not be used as a further limitation on the protection scope of the present invention.

[0037] Exemplary Embodiment 1

[0038] This exemplary embodiment provides a shale reservoir fracture prediction method, the operation process of the method is as follows: Figure 1 As shown, the following steps may be included:

[0039] S01: Decompose the post-stack seismic data based on a multi-level and multi-directional method to obtain N different levels of seismic decomposition data.

[0040] In this embodiment, before the step of decomposing the post-stack seismic data, the post-stack seismic data is evaluated. In the case where the quality evaluation of the post-stack seismic data fails, that is, the resolution of the post-stack seismic data of the target shale reservoir is low (such as the main frequency of the earthquake is lower than 20Hz, such as 19Hz, 15Hz, 10Hz, etc.) and / or the signal-to-noise ratio is low. The higher the signal-to-noise ratio, the better the seismic data, which is generally above 10:1. If it is lower than 10:1, the seismic data needs to be reprocessed, i.e., preprocessed. The preprocessing is to start from the pre-stack data set, perform denoising, flattening and amplitude equalization on the pre-stack data set, and extract the 10° to 28° pre-stack data set with a high seismic signal-to-noise ratio and relatively preserved amplitude as the post-stack original seismic data for subsequent processing.

[0041] S02: Perform spectrum analysis and directional optimization on each level of earthquake decomposition data, and select the level x earthquake decomposition data with the most high-frequency information and at least one level of earthquake decomposition data that retains more original earthquake effective information.

[0042] In this embodiment, the core of the "multi-level multi-directional" data decomposition method is to decompose the seismic signal in the frequency domain into multi-level data of different levels, different directions, and containing different geological information, and extract the directional information of the geological body in the different levels of information in combination with the hierarchical filter processing. Different levels of information correspond to different resolutions and levels, and then select the level data with better resolution for reorganization processing, so as to achieve the effect of significantly improving the resolution of seismic data. The hierarchical filter can highlight the directional characteristics of fractures and cracks in seismic data, and at the same time has the effect of improving filtering accuracy and reducing the amount of calculation. The function expression of the hierarchical filter is as follows:

[0043]

[0044] Where: f θ (x,y) refers to the function of the hierarchical filter in the θ direction;

[0045] k j (θ) refers to the interpolation function in the θ direction;

[0046] refers to the basis function in the θ direction;

[0047] θ refers to the rotation angle;

[0048] j refers to the number of basis filters.

[0049] The specific processing process of the hierarchical filter is to take each seismic data as input, perform convolution operation on the input seismic data with a set of three base filters in different directions, then multiply the seismic data after direction filtering by the corresponding interpolation function, and then add up the parts to get the final filtered data.

[0050] The pre-stack gathers of 10° to 28° with high seismic signal-to-noise ratio and relatively preserved amplitude are decomposed based on "multi-level and multi-directional" data, for example, seismic data of 7 different levels can be obtained. Then a spectrum analysis is performed on it. The purpose of the spectrum analysis in the present invention is to verify the effectiveness of each level, and other levels may be selected in other application examples. The main frequency of the seismic data from level 1 to level 7 decreases successively, and the seismic profile of level 2 is very similar to the post-stack result data, and the detailed information of the seismic data is highlighted, and the discontinuity characteristics of the original data phase axis are partially enhanced. For example, the seismic decomposition data of level 1 with the most high-frequency information and level 2 with the most original seismic effective information are selected as subsequent analysis and processing data.

[0051] S03: Superimpose and combine the level x and the at least one level seismic decomposition data to obtain high-resolution seismic data.

[0052] In this embodiment, retaining more original earthquake effective information means: retaining the most original earthquake effective information, or retaining the first most and the second most original earthquake effective information. For example, data of different levels can be selected for superposition and combination, such as superposition and combination of level 1, level 2 and level 3, superposition and combination of level 1 and level 2, or superposition and combination of level 2 and level 3.

[0053] The basis for selecting seismic decomposition data is mainly to select a level with the most high-frequency information to improve data resolution, and then select 1-2 levels close to the original seismic data for reconstruction. The reconstructed data retains the main effective information of the original data while improving the resolution. In this embodiment, the seismic decomposition data of levels 1 and 2 are selected for data superposition to obtain high-frequency seismic reconstruction data of level 1+2. The seismic reconstruction data of level 1+2 and the original seismic data are compared in profile. The seismic reconstruction data of level 1+2 retains the morphology of the event axis of the original seismic data, and the resolution is significantly improved. Therefore, the seismic reconstruction data of level 1+2 is used as the high-resolution post-stack seismic data for the following fracture prediction operation.

[0054] S04: Calculate ant volume attributes based on variance volume on high-resolution seismic data to obtain ant volume seismic attributes.

[0055] The present invention uses the variance ant volume fusion attribute technology. This technology first needs to smooth the high-resolution 1+2 seismic reconstruction data to eliminate the discontinuity of the phase axis caused by the formation tilt and noise, and highlight the characteristics of faults and cracks. Next, it is necessary to obtain the structural interpretation seismic variance value σ 2 , the formula is as follows:

[0056]

[0057] Where: i refers to the number of seismic traces, which is a real number;

[0058] j refers to the variance calculation time;

[0059] I refers to the number of horizons and fault traces selected when calculating variance;

[0060] L refers to the time window length under variance calculation time;

[0061] w refers to the triangular weighting function of the earthquake variance volume, and its interval range is [0, 1];

[0062] x refers to the average amplitude value during the variance calculation time.

[0063] According to the above formula, the seismic variance value of structural interpretation can be obtained. The ant volume tracking technology is used on the seismic variance volume data. The advantage of the ant volume tracking technology is that the seismic variance value anomaly can be converted into a fault boundary whose longitudinal extension matches the medium-small secondary cracks.

[0064] S05: Extract the plane slice of the target layer based on the seismic attributes of the ant body to obtain the fracture prediction result.

[0065] After the variance ant volume fusion attribute technology is completed, it is necessary to perform a plane slice operation on the variance ant volume fusion attribute data volume of the target layer. Since the use of the ant volume technology not only identifies the fault fracture information, but also may enhance the noise. Therefore, it is necessary to make a preliminary evaluation of the quality of the target layer fracture prediction on the plane slice map.

[0066] During the drilling process of shale gas wells, well leakage events are often related to faults and natural fractures. The information of medium-small faults encountered in actual drilling directly proves the existence of medium-small fractures in the formation. Therefore, in order to accurately predict the fractures of the target layer in this work area, it is necessary to collect the drilling reports of the drilling group in this work area, find out the information of well leakage and faults encountered in actual drilling, so as to verify the actual effect of fracture prediction. In order to verify the information more accurately, the horizontal well can also be calibrated for well seismic calibration, and further verification can be done on the seismic profile. The fracture prediction results are updated by continuously adjusting the variance ant body attribute parameters to better match the actual drilling faults and well leakage information; finally, the ant body attribute parameters with the best fracture prediction effect for the target layer in this work area are selected, and the fracture distribution with a good matching relationship between the fracture density of the shale target layer and the actual drilling fractures and faults is obtained. When the consistency rate of the fracture prediction results with the actual drilling faults and well leakage reaches more than 60%, the fracture prediction results are relatively reliable.

[0067] Exemplary Embodiment 2

[0068] This exemplary embodiment provides a computer device, comprising: at least one processor, and a memory storing program instructions, wherein the program instructions are configured to be executed by the at least one processor, and the program instructions include instructions for executing the shale reservoir fracture prediction method described in exemplary embodiment 1.

[0069] Exemplary Embodiment 3

[0070] This exemplary embodiment provides a computer-readable storage medium having computer program instructions stored thereon. When the computer program instructions are executed by a processor, the method for predicting shale reservoir fractures in the exemplary embodiment 1 described above is implemented.

[0071] In order to better understand the above exemplary embodiment 1 of the present invention, it is further described below with reference to specific examples.

[0072] Example 1

[0073] In the study area, the method of exemplary implementation 1 is used to perform data decomposition and theoretical frequency conversion on the original seismic data to obtain information of seven different levels. The seismic profile is as follows: Figure 2 As shown, from Figure 2 It can be seen that level 1 has a higher main frequency, greatly improves the resolution, and highlights the small-scale details of the seismic data. Level 2 retains the main information of the original seismic data while improving the resolution. Level 3 has limited improvement in profile, and levels 4-7 have low resolution. Therefore, levels 3-7 are discarded in the analysis, and only the better levels 1 and 2 are retained for data reorganization. After reorganization, the preferred level of the high frequency spectrum is obtained, and the variance ant volume fusion attribute technology is used to perform the fracture prediction layer plane slice diagram, such as Figure 4 As shown, the plane slice diagram of the fracture layer predicted by the method of the present invention in the study area; Figure 3 This is a plane slice diagram of the fracture prediction layer in the study area using the conventional method, that is, a plane slice diagram of the fracture prediction layer using the variance ant volume fusion attribute technology directly using the original post-stack seismic data. Figure 4 It can be clearly seen that the crack prediction results of the method of the present invention are more dense. The crack density predicted by the method of the present invention has been significantly improved.

[0074] Fig. 6A The matching between the fracture prediction profile of the conventional method and the actual drilling leakage point is shown. The predicted fracture position on the profile does not match the leakage point position. Figure 6B The matching of the fracture prediction profile of the method of the present invention and the actual drilling leakage point is shown. The fracture prediction results are more dense and the predicted fracture positions match the well leakage point positions. The profile conformity rate based on the method of the present invention is much higher than that of the conventional method. The conventional method has a conformity rate of about 48%, while the conformity rate of the updated method of the present invention can reach 72.3%, which is about 25% higher than that of the conventional method, and the fracture density has a significant increase. It proves that the fracture content of the shale reservoir fracture prediction method based on data decomposition theory of the present invention is richer.

[0075] The method of the present invention significantly improves the accuracy of crack prediction in the work area. The key is to verify the constraints of the plane slice map predicted by the variance ant body fusion attribute technology using the leakage and fault information in the actual drilling. By continuously modifying the variance ant body fusion attribute parameters, the compliance rate of crack prediction can be greater than 70%. Figure 5 The plane crack prediction results of the method of the present invention are shown. Each point of the well trajectory above represents the location of the well leakage and fault encountered during drilling. The crack prediction results on the plane have a high consistency with the actual well leakage and fault location, indicating that the method is effective. Fig. 6A and Figure 6B Comparison of the cross-sectional diagrams of the conventional crack prediction method and the method of the present invention shows that the method of the present invention is superior to the conventional method.

[0076] Although the present invention has been described above by combining with exemplary embodiments, it will be apparent to those skilled in the art that various modifications and changes may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the claims.

Claims

1. A shale reservoir fracture prediction method, characterized in that: The prediction method comprises the following steps: Based on the multi-level and multi-directional method, the post-stack seismic data are decomposed to obtain N different levels of seismic decomposition data; Performing spectrum analysis and directional optimization on each level of earthquake decomposition data, selecting the level x earthquake decomposition data with the most high-frequency information and at least one level of earthquake decomposition data with more original earthquake effective information; Superimposing and combining the level x and the at least one level seismic decomposition data to obtain high-resolution seismic data; Perform ant body attribute calculation based on variance body on high-resolution seismic data to obtain ant body seismic attributes; The plane slice extraction of the target layer is performed on the seismic attributes of the ant body to obtain the fracture prediction results.

2. The shale reservoir fracture prediction method according to claim 1, characterized in that: The fracture prediction result is a layer plane slice; The method also includes the steps of: using the actual drilling fault and well leakage information to constrain the variance body-based ant body attribute calculation, and by continuously adjusting the ant body attribute parameters, making the coincidence rate between the stratigraphic plane slice and the actual drilling fault and well leakage greater than a preset value, thereby obtaining a shale reservoir fracture prediction result.

3. The shale reservoir fracture prediction method according to claim 1, characterized in that: The method further comprises: before constraining, collecting the information of lost circulation and fault encountered in the horizontal well of the target layer and projecting them onto the plane slice of the layer.

4. The shale reservoir fracture prediction method according to claim 1, characterized in that: The method further comprises the step of: evaluating the post-stack seismic data before the step of decomposing the post-stack seismic data, and pre-processing the post-stack seismic data if the evaluation is poor.

5. The shale reservoir fracture prediction method according to claim 4, characterized in that: The evaluation includes determining the signal-to-noise ratio, and the preprocessing includes at least one of denoising, flattening and amplitude equalization.

6. The shale reservoir fracture prediction method according to claim 1, characterized in that: The N=7, the order x is order 1, and the at least one order is order 2.

7. The shale reservoir fracture prediction method according to claim 1, characterized in that: The retaining of more original earthquake valid information means: retaining the most original earthquake valid information, or retaining the first most and the second most original earthquake valid information.

8. The shale reservoir fracture prediction method according to claim 1, characterized in that: The preset value is above 50%.

9. A computer device, characterized in that: include: At least one processor and a memory storing program instructions, wherein the program instructions are configured to be executed by the at least one processor, and the program instructions include instructions for executing the method according to any one of claims 1-8.

10. A computer-readable storage medium having computer program instructions stored thereon, characterized in that: When the computer program instructions are executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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