A method for identifying the boundary of a draped anticline

Abstract

This invention relates to a method for identifying the boundary of anticlines, belonging to the field of oil and gas field exploration and development technology. First, seismic data is acquired, and spectral analysis is performed on the seismic data. The phase of the seismic data is rotated, and the rotated data is interpreted using relative isochronous stratigraphic layers. The interpreted seismic top layer is flattened, and the flattened seismic data is used to determine stratigraphic slices. Based on the amplitude attributes and lateral differences of the stratigraphic slices, the planar morphology of the anticline is identified. This method saves the cost of high-resolution seismic processing and solves the problem of increased uncertainty in imaging results caused by high resolution.

Description

Technical Field

[0001] This invention relates to a method for identifying the boundary of anticlines, belonging to the field of oil and gas field exploration and development technology. Background Art

[0002] With the acceleration of exploration and development and the deepening understanding of oil and gas accumulation, the detailed analysis of gas reservoirs using 3D seismic data is one of the important means to improve drilling success rates. Through the study of draped anticlines, we can identify these anticlines. A draped anticline is a local uplift formed by the deposition of relatively new strata on a basement paleo-uplift, which, through subsequent tectonic movements, becomes a local uplift high point, developing at the basin edge. For example, in the northern edge of a certain basin, numerous small draped anticlines with areas ranging from 0.5 to 2 km² have developed. The contact surface between the bottom of the anticline and the basement is an unconformity, serving as the main channel for oil and gas migration and adjustment, gradually accumulating into reservoirs at the top of the anticline. Therefore, accurately identifying and characterizing the boundaries of draped anticlines, and how to accurately identify their boundaries using 3D seismic technology, through verification and summarization in production practice and technological improvements, will enable the identification and precise characterization of small anticlines, providing corresponding technical support for gas reservoir understanding and well location deployment.

[0003] Currently, in structural interpretation and reservoir prediction, pre-stack time migration amplitude-preserving seismic data is used, with dominant seismic frequencies generally between 20-25 Hz. This results in low seismic resolution and limited identification accuracy. Improving resolution and delineating anticline boundaries would be costly and time-consuming, and the imaging results would have significant uncertainties, thus hindering timely application in production.

[0004] Existing technologies mainly utilize forward modeling to analyze trap amplitude and variable velocity layer maps to improve the accuracy of post-construction two-dimensional structural maps, but do not utilize changes in relevant seismic attributes to identify anticline boundaries. Patent document CN113805227A discloses a method for identifying pinch-out lines of concealed strata. This method is based on utilizing the instantaneous frequency attributes of a large time window, using changes in seismic frequency magnitude to identify the location of pinch-out lines in strata, but it lacks specific descriptions for identifying small-scale anticlines. Summary of the Invention

[0005] The purpose of this invention is to provide a method for identifying draped anticline boundaries, in order to solve the problems of low accuracy in low-resolution identification of anticline boundaries, and high cost and uncertain imaging effect caused by high-resolution identification.

[0006] To achieve the above objectives, the present invention includes:

[0007] The present invention provides a method for identifying the boundary of an anticline, comprising the following steps:

[0008] 1) Acquire seismic data, perform spectral analysis on the seismic data to determine the dominant frequency and bandwidth range of the seismic data, and determine the initial range within the target area based on the dominant frequency and bandwidth range of the seismic data;

[0009] 2) Determine the phase type of the seismic data. Based on the phase type of the seismic data, forward modeling, and drilling calibration analysis results, determine the phase rotation angle and rotate the seismic data according to the angle.

[0010] 3) Determine the relative isochronous surface based on the phase-rotated seismic data, and interpret the seismic horizon within the initial range based on the relative isochronous surface. The relative isochronous surface is a surface at the top of the seismic strata that has a continuous seismic wave group, stable sedimentation, and clear geological meaning.

[0011] 4) Flatten the interpreted top seismic horizon to obtain the top flattened seismic data volume. Based on the sampling interval of the top flattened data volume and the seismic data, determine the stratigraphic slice interval and obtain the amplitude attributes of multiple stratigraphic slices.

[0012] 5) Compare the amplitude attribute values ​​of multiple formation slices with the known well drilling characteristics within the initial range, select the optimal formation slice attribute, and overlay the optimal formation slice attribute value with the structural map of the location of the slice to select the area where the contour lines are closed as the boundary range of the anticline.

[0013] Beneficial Effects: The anticline boundary identification method of this invention, based on geological understanding and seismic data spectral analysis, utilizes existing seismic data, performs phase angle rotation, and determines the relative isochronous surface with anticlines based on the phase-rotated seismic data. It then performs detailed interpretation of the seismic data with anticlines, obtains stratigraphic slices based on the interpreted data, and identifies the planar morphology of the anticlines based on the differences in stratigraphic slice attributes and amplitude attributes, thereby determining the anticline boundary range. This method maximizes the potential of seismic data, saves on the cost of high-resolution seismic processing, and solves the problem of increased uncertainty in imaging effects caused by high resolution. Delineating the boundary range of small anticlines based on the magnitude and lateral differences of seismic attribute values ​​can provide a basis for gas reservoir identification and well location deployment.

[0014] Furthermore, the optimal formation slice attribute selection step is as follows: based on the amplitude attributes corresponding to the drilling characteristics of existing wells within the initial range, the multiple formation slice attributes in step 4) are compared one by one, and the formation slice attribute with the highest conformity rate with the amplitude attributes corresponding to the drilling characteristics of existing wells is selected.

[0015] Furthermore, in step 5), when overlaying the optimal stratigraphic slice attributes with the structural map of the slice's location, the color code value of the optimal stratigraphic slice attributes needs to be adjusted to match the structural map. Figure 1 The corresponding color mark value.

[0016] Beneficial effect: When overlaying the optimal stratigraphic slice attributes with the structural map, it is necessary to adjust the color scale values ​​of the optimal stratigraphic slice attributes and the structural map. Figure 1 Using consistent color swatches makes it easier to obtain areas where contour lines close, and these areas can be used as the boundaries of anticlines.

[0017] Furthermore, in step 1), the seismic data is loaded into the seismic interpretation work area, and the analysis window includes the entire target layer's top and bottom phase axes to obtain a spectral analysis diagram.

[0018] Furthermore, the flattening of the top seismic horizon was accomplished using seismic translation software.

[0019] Furthermore, the spectral analysis plot uses energy representation on the vertical axis. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method for identifying the boundary of an anticline in an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of seismic data extracted in an embodiment of the method of the present invention;

[0022] Figure 3 This is a spectral analysis diagram of seismic data in an embodiment of the method of the present invention;

[0023] Figure 4 This is a phase-rotation seismic comparison diagram from an embodiment of the method of the present invention;

[0024] Figure 5 This is a schematic diagram of the anticline engraving effect in an embodiment of the method of the present invention. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] Example of a method for identifying the boundary of an draped anticline:

[0027] like Figure 1 The method for identifying the boundary of an anticline, as shown, acquires existing seismic data, performs phase angle rotation, and determines the relative isochronous surface with an anticline based on the phase-rotated seismic data. The seismic data with anticline is then finely interpreted, and stratigraphic slices are obtained based on the interpreted data. The planar morphology of the anticline is identified based on the stratigraphic slice attributes and lateral differences, thereby determining the anticline boundary range. The specific implementation is as follows:

[0028] This example uses a well area on the northern edge of a basin as an example, with an application area of ​​1000 km². 2The area has full 3D seismic coverage, but source rocks are underdeveloped. There are 170 drilled wells in the area, with over 120 encountering the basement. Influenced by the Archean basement uplift, the overlying strata directly drape over the basement uplift, resulting in numerous small, draped anticlines ranging in size from 0.5 to 2 km². 2 between.

[0029] 1) Acquire seismic data, perform spectral analysis on the seismic data, and determine the dominant frequency and bandwidth range of the seismic data based on the spectral analysis diagram.

[0030] Seismic data for the region is acquired, loaded into the seismic interpretation work area, and spectral analysis is performed to analyze the spectral characteristics of the target stratigraphic segment. The resolution of the strata within the target area is determined by the dominant frequency and bandwidth of the seismic data. This resolution allows for the identification of the initial extent of the anticline, and based on this initial extent, the boundary extent of the anticline can be further determined. For example... Figure 2 As shown, seismic data is loaded into the seismic interpretation work area. The analysis window includes the entire target layer's top and bottom phase axes. The spectral analysis plot uses vertical axis energy representation and displays it in decibels. Figure 3 As shown, spectral analysis can identify stratigraphic absolute resolution (less than λ / 4), with small overlying anticlines ranging in size from 0.5 to 2 km². 2 In this embodiment, the dominant seismic frequency is 20Hz, and the vertical absolute resolution of the identifiable strata is 50m.

[0031] 2) Determine the phase type of the seismic data. Based on the phase type of the seismic data, forward modeling, and drilling calibration analysis results, determine the phase rotation angle.

[0032] Specifically, to improve the stratigraphic resolution of seismic data, this embodiment commonly uses a -90-degree phase volume. The seismic data volume is rotated by a -90-degree phase volume so that the main lobe of the reflected wave corresponds to the center of the thin layer, thereby overcoming the shortcomings of zero-phase waves. Simultaneously, the polarity of the seismic profile is made to have lithological interface significance, such as... Figure 4 As shown, comparing the original seismic profile with the seismic profile after a -90-degree phase rotation, the stratigraphic resolution of the seismic profile after the -90-degree phase rotation is significantly improved, and the lithological boundaries are clearer. Therefore, a -90-degree phase rotation of the seismic data volume improves the stratigraphic resolution of the seismic data, makes the lithological boundaries clearer, and makes the boundary between the anticline boundary and the basement interpretation clearer. According to forward modeling analysis, compared with a 90-degree phase rotation, the -90-degree phase rotation has weaker wavelet sidelobes and makes thin layers easier to identify. Therefore, without changing the original seismic data characteristics, the -90-degree phase rotation enables the correspondence between the reservoir interface and the phase of the reflection wave group, further enriching the geological information reflected by the seismic wave group and improving the vertical identification capability.

[0033] 3) Based on the phase-rotated seismic data, determine the relative isochronous surface and interpret the seismic horizon based on the relative isochronous surface.

[0034] In this embodiment, the relative isochronous surface is defined as: a surface with continuous seismic wave groups, relatively stable sedimentation, and clear geological significance, determined from the top of the seismic data volume after a 90-degree phase rotation. For example, the seismic wave group T at the top and bottom interface of the Lower Shihezi Formation in the study area. 9f 、T 9d Relatively continuous, geologically significant geological interfaces can serve as relative isochronous surfaces for earthquakes in the region. Based on this, fine-grained seismic stratigraphic interpretation is conducted. Interpreted stratigraphic layers are examined, and adjacent layers with indistinct reflection characteristics are supplemented with interpretations based on the principles of equal thickness or following certain variation patterns, thus achieving stratigraphic isochronism. To effectively characterize small anticlines, the minimum seismic interpretation interval in this embodiment is 2×2, locally densified to 1×1.

[0035] 4) Flatten the interpreted top seismic horizon to obtain the top-flattened seismic data volume.

[0036] After the stratigraphic layers are thoroughly interpreted and interpolated to 1×1, the top seismic horizons are flattened. This can be accomplished using relatively mature commercial seismic interpretation software, such as Landmark and Jason, to obtain a flattened seismic data volume.

[0037] 5) Based on the top flattened data volume and the sampling interval of the seismic data, the stratigraphic slice interval is determined, and the amplitude attributes of multiple stratigraphic slices are obtained.

[0038] Specifically, based on the seismic data sampling interval of 1ms stratigraphic slice interval, the seismic attributes of the stratigraphic slices are directly obtained from the -90 degree seismic data volume.

[0039] 6) Based on the amplitude attribute values ​​of the formation slices and the lateral differences (i.e., the amplitude differences between different formation slice attributes), the amplitude attribute values ​​of multiple formation slices are compared with the known well drilling characteristics within the initial range. The optimal formation slice attribute is selected, and the optimal formation slice attribute value is superimposed with the structural map of the location of the slice. The area where the contour lines are closed is selected as the boundary range of the anticline.

[0040] Based on the amplitude attributes corresponding to the drilling characteristics of existing wells within the initial range, the multiple formation slice attributes in step 5) are compared one by one, and the formation slice attribute with the highest consistency rate with the amplitude attributes corresponding to the drilling characteristics of existing wells is selected as the optimal attribute map.

[0041] The optimal slice plane attributes (optimal attribute map) are adjusted using color scales. Based on forward modeling and theoretical models, the anticline boundary is made to have a positive relative amplitude. Next, considering existing well drilling characteristics, the color scale value range is adjusted to ensure the color scale values ​​of the optimal slice plane attributes are consistent with those of the structural map. Finally, as... Figure 5As shown, the layer values ​​are extracted from the location of the slice, and the structural map is overlaid with the slice attributes at intervals of 1-2 meters. The area closed by contour lines (iso-depth lines) is used as the identification range of the draped anticline.

[0042] After a -90-degree phase rotation, different locations can be cut laterally through stratigraphic slicing, thus creating lateral differences. For example, seismic wave peaks are positive amplitude values, and color codes can be adjusted to be more prominent, such as red or black.

[0043] This embodiment uses layer-by-layer slices made on a conventional seismic profile. The color code value represents the amplitude attribute. After the top seismic horizon is flattened after interpretation, the slices are cut exactly at the wave crest according to the determined stratigraphic slice interval, with positive amplitude values ​​representing the anticline boundary.

[0044] Among them, the known well drilling characteristics refer to the actual formation encountered by existing wells. For example, in this area, the normal formations are the Shanxi and Taiyuan Formations. If both are missing, or only the Shanxi Formation remains, and the formation thickness is less than 5 meters, and the current structure is still a micro-structure, it is determined that the well location is a draped anticline.

Claims

1. A method for identifying the boundary of a draped anticline, characterized in that, Includes the following steps: 1) Acquire seismic data, perform spectral analysis on the seismic data to determine the dominant frequency and bandwidth range of the seismic data, and determine the initial range within the target area based on the dominant frequency and bandwidth range of the seismic data; 2) Determine the phase type of the seismic data. Based on the phase type of the seismic data, forward modeling, and drilling calibration analysis results, determine the phase rotation angle and rotate the seismic data according to the angle. 3) Determine the relative isochronous surface based on the phase-rotated seismic data, and interpret the seismic horizon within the initial range based on the relative isochronous surface. The relative isochronous surface is a surface at the top of the seismic strata that has a continuous seismic wave group, stable sedimentation, and clear geological meaning. 4) Flatten the interpreted top seismic horizon to obtain the top flattened seismic data volume. Based on the sampling interval of the top flattened data volume and the seismic data, determine the stratigraphic slice interval and obtain the amplitude attributes of multiple stratigraphic slices. 5) Compare the amplitude attribute values ​​of multiple formation slices with the known well drilling characteristics within the initial range, select the optimal formation slice attribute, and overlay the optimal formation slice attribute value with the structural map of the location of the slice to select the area where the contour lines are closed as the boundary range of the anticline.

2. The method for identifying the boundary of an embankment according to claim 1, characterized in that, The optimal formation slice attribute selection steps are as follows: based on the amplitude attributes corresponding to the drilling characteristics of existing wells within the initial range, compare the multiple formation slice attributes in step 4) one by one, and select the formation slice attribute with the highest conformity rate with the amplitude attributes corresponding to the drilling characteristics of existing wells.

3. The method for identifying the boundary of an embankment according to claim 2, characterized in that, In step 5), when the optimal stratigraphic slice attribute is overlaid with the structural map of the location of the slice, the color code value of the optimal stratigraphic slice attribute needs to be adjusted to the same color code value as the structural map.

4. The method for identifying the boundary of an embankment according to claim 1, characterized in that, In step 1), the seismic data is loaded into the seismic interpretation work area, and the analysis window includes the entire target layer's top and bottom phase axes to obtain a spectral analysis diagram.

5. The method for identifying the boundary of an embankment according to claim 1 or 2, characterized in that, The flattening of the top seismic horizon was accomplished using seismic translation software.

6. The method for identifying the boundary of an embankment according to claim 4, characterized in that, The spectral analysis plot uses energy as the vertical axis representation.

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