Fracture block oil reservoir large fault footwall earthquake time section structure illusion identification method

Abstract

The invention discloses a fault block oil reservoir large fault footwall seismic time section structure illusion identification method. The method comprises the following steps that (1) a fault distribution rule is clarified by a coherent slice; (2) carrying out horizon calibration and low-speed layer bottom surface whole-area tracking interpretation; (3) large fault section interpretation; (4) forward modeling of large fault models in different forms and identification of illustrations in different types; the method is suitable for the technical field of seismic data structure artifact recognition, more actual geological conditions are considered, different types of false structures are simulated, the forming conditions and characteristics of different structure artifacts are clarified, judgment of true and false structures in structure interpretation is effectively guided, and the method has the advantages of being high in practicability and easy to popularize. And the method for recovering the false structure by utilizing low-speed zone bottom surface seismic interpretation horizon trend control is simple and efficient, and finally, real structural morphological characteristics can be displayed.

Description

Technical Field

[0001] The present invention belongs to the technical field of seismic data structural illusion recognition, and specifically relates to a method for recognizing the structural illusion of a seismic time section in the hanging wall of a large fault in a fault-block reservoir. Background Technique

[0002] In fault-block reservoirs, large faults control hydrocarbon accumulation, and small faults complicate the reservoir and control oil and water. Through fine structural interpretation of fault-block reservoirs, new potential areas can often be discovered. In the later stage of development, newly interpreted small fault blocks and small highs are important positions for remaining oil potential tapping. With the continuous deepening of development, it is found that some small fault blocks and small highs have large differences from actual wells, which are false structures and cause great economic losses. Due to the complexity of underground lithology and structure, large lateral velocity variations in strata, and the limitations of seismic data processing methods, structural illusions will appear on seismic time sections. Zhou Huawei elaborated in detail on the structural illusions caused by misjudgment of imaging signals, insufficient illumination, and wave velocity model errors; Li Suhua analyzed through forward modeling the influence of abnormal bodies with different lithology combinations on the underlying seismic reflection axis and proposed that impedance differences would cause structural illusions in the underlying strata; Deng Guocheng used forward modeling technology to identify collapse columns in coal seams; Huang Cheng identified illusions of undulating strata and fault-like illusions through forward modeling; Li Qingzhen, Wang Yanhui, Li Cao, etc. verified through forward models that due to the loss of low-velocity layers by large faults, false structures appear in the hanging wall of large faults and proposed to verify fault illusions through dense well networks; Chen Haiqing proposed to solve the problem of structural illusions through prestack depth migration and variable velocity mapping; Zhang Zaijin eliminated the structural illusions caused by faults through prestack depth migration using the velocity model established by grid tomography velocity modeling technology under well control and structural constraint conditions.

[0003] Chinese invention patent CN113589367A discloses a method for correcting the structural trend near a large fault based on area conservation, including: Step 1, based on geological and drilling, logging, well logging and other data, establish a stratigraphic structure model on both sides of the large fault, and clarify the main area of structural distortion near the large fault through seismic model forward modeling; Step 2, analyze the imaging mechanism of false structures based on the geometric propagation principle of seismic waves, and clarify that the strata on both sides of the fault are significantly different, and the velocity distortion of the strata on both sides of the fault plane is the main reason for the structural trend error; Step 3, based on the seismic velocity imaging mechanism and the area conservation theorem of the actual geological structure section, establish the relationship between the time-domain structural section and the actual structural section, and determine the method for correcting the structural trend.

[0004] Chinese Invention Patent CN112415580A A method for eliminating the mutation interface of the velocity model and a prestack depth migration processing method, including: creating a buffer area within a preset buffer distance around the mutation interface of the depth-domain layer velocity model; constructing multiple smooth paths from the first boundary to the second boundary of the buffer area in a preset direction; determining the velocity smoothing values of each sample point on each smooth path according to the velocity values of the sample points at both ends of each smooth path and the preset initial velocity gradient value; using the velocity smoothing values of each sample point on each smooth path as the velocity values of each sample point, so that the velocity values of the sample points on the same smooth path increase or decrease in sequence, so as to eliminate the mutation interface of the depth-domain layer velocity model. The present invention eliminates the mutation interface of the depth-domain layer velocity model, thereby eliminating imaging artifacts and even false faults, and improving the accuracy of the depth-domain layer velocity model.

[0005] Chinese Invention Patent CN113534243B discloses a passive-source Marchenko imaging method and system. The present invention relates to a passive-source Marchenko imaging method and system, belonging to the field of seismic exploration imaging. First, the cross-correlation method is used to perform seismic interference processing on the collected passive-source seismic data to obtain the virtual-source seismic data at each geophone position; then, noise reduction processing and preprocessing of direct wave removal and wavelet deconvolution are performed to obtain the reflection Green's function response; the Marchenko method is used to perform multiple wave elimination processing on the reflection Green's function response to obtain the reflection Green's function response after wave elimination; forward modeling is performed on an inaccurate velocity model to obtain the direct wave response; the reflection Green's function response after wave elimination and the direct wave response are used as inputs to reconstruct the up-going Green's function and the down-going Green's function, and the reflection coefficient is calculated; the imaging result is obtained after arrangement. There is no need to input an accurate velocity model, and false structures will not be caused by multiple waves, effectively improving the imaging effect.

[0006] Chinese Invention Patent CN110967745A discloses a depth-domain velocity modeling method for igneous rocks, including: obtaining the initial velocity field and logging stratification data of igneous rocks; inversely calculating the background velocity field based on the initial velocity field and logging stratification data; based on the background velocity field, improving the resolution and performing network tomography inversion iteration to obtain the initial igneous rock depth-domain velocity model; adding well-seismic error and structural error to the objective function of the initial igneous rock depth-domain velocity model to obtain the final igneous rock depth-domain velocity model.

[0007] Chinese invention patent CN114265111A discloses a method for interpreting true and false faults caused by gypsum-salt rock, including: tracking and interpreting the top and bottom of the gypsum-salt body to obtain the distribution law of the gypsum-salt body; establishing a geological model of the gypsum-salt body according to the distribution law of the gypsum-salt body; based on the geological model of the gypsum-salt body, obtaining the first seismic reflection characteristics corresponding to different distribution laws of the gypsum-salt body and the second seismic reflection characteristics corresponding to the faults caused by the gypsum-salt sliding through forward modeling research; establishing a criterion for judging true and false faults according to the forward modeling results; carrying out fault detection on the seismic data volume, identifying and extracting all parts where the seismic reflection isochrones are dislocated; forming a preliminary fault body according to the parts where the seismic reflection isochrones are dislocated; based on the preliminary fault body, statistically calculating the throw on the seismic reflection profile for the stratigraphic dislocation characteristics on both sides of the fault; excluding the false faults in the preliminary fault body according to the criterion for judging true and false faults and the throw to obtain the fault distribution.

[0008] Regarding the problem of structural illusions, researchers have also done a lot of work. Currently, there are mainly two methods to solve such problems. One is to improve from the processing method, establish a suitable velocity model and use prestack depth migration to fundamentally eliminate illusions. The other is to identify false structures through forward modeling of the actual geological model and controlled by a dense well pattern. The former requires a large investment in eliminating false structures from the aspect of seismic processing and is also difficult, and it is difficult to achieve by conventional operations. The latter requires less investment and is easier to achieve.

[0009] Many researchers have verified through seismic forward modeling that when a large fault cuts off the low-velocity zone, upward bulges or dislocations of isochrones will form in the strata near the footwall of the large fault on the time seismic profile. However, the conditions for the generation of different types of false structures are not fully demonstrated, and the characteristics of false structures are not well described. It is difficult to distinguish true and false structures without the control of a dense well pattern. Through years of three-dimensional seismic structure research, it is found that not all footwalls of large faults that cut off the low-velocity layer will show false structures. For the same large fault, false structures may appear at some planar positions and not at others, and the types of false structures are also different. Some are false faults and some are false highs. Small faults and small highs near large faults are often the main targets for remaining oil potential tapping. Therefore, it is particularly important to distinguish these true and false structures. Without the control of a dense well pattern, it is impossible to effectively distinguish true and false structures near large faults using the current seismic profile structural illusion identification method. Summary of the Invention

[0010] The purpose of the present invention is to overcome the defects of the prior art and provide a method for identifying structural illusions on the seismic time profile of the footwall of a large fault in a fault-block oil reservoir.

[0011] To achieve the above purpose, the present invention adopts the following technical solutions:

[0012] A method for identifying structural illusions on the seismic time profile of the footwall of a large fault in a fault-block oil reservoir includes the following steps:

[0013] (1) Coherent slice clear tomography distribution law;

[0014] (2) Horizon calibration and full - area tracking interpretation of the bottom surface of the low - velocity layer;

[0015] (3) Large - fault profile interpretation;

[0016] (4) Forward modeling of large - fault models with different morphologies and identification of different types of artifacts;

[0017] (5) Tectonic artifact correction.

[0018] Preferably, in the step (1), it specifically includes: extracting coherent attributes from seismic data, browsing the coherent slices within 400 ms above and below the research interval, and clarifying the distribution law of large faults.

[0019] Preferably, in the step (2), horizon calibration specifically includes: comparing and analyzing the wells on both sides of the large fault, finding the low - velocity layer from the acoustic curve, reading the formation velocities from the low - velocity layer to each layer above and below the research interval in the well; performing fine horizon calibration to determine the seismic profile positions of the low - velocity layer and the target interval.

[0020] Preferably, in the step (2), full - area tracking interpretation is performed on the bottom surface of the low - velocity layer and the large fault.

[0021] Preferably, in the step (3), it specifically includes: performing fine profile interpretation of the fault through the seismic profile along the strike of the large fault, depicting the fault surface morphology of the large faults from the low - velocity layer to the research interval, calculating the morphological change range of the large fault, the formation dip angle of the low - velocity bottom surface, and the docking thickness of the high - velocity layer and the low - velocity layer on both sides of the fault.

[0022] Preferably, the morphological change range of the large fault is the dip - angle change range of the large fault.

[0023] Preferably, in the step (4), the large - fault models with different morphologies specifically include: establishing a geological model based on the fault dip - angle change with the formation velocities of each stratum, the morphology of the large fault, the docking thickness of the high - velocity layer and the low - velocity layer on both sides of the fault, and the formation dip angle.

[0024] Preferably, in the step (4), the identification of different types of artifacts specifically includes: the seismic reflection characteristics of each stratum when the low - velocity layer is lost by large faults with different dip angles.

[0025] Preferably, in the step (4), the forward - modeling results specifically include:

[0026] 1) When no false structure is generated, the method process ends;

[0027] 2) When a false structural high is generated, analyze its characteristics and determine its location. When a false fault is generated, analyze its characteristics and establish a discriminant criterion for the false fault, and identify the false structure on the seismic section based on the forward modeling results.

[0028] Preferably, in the step (5), it specifically includes: referring to the trend of the seismic interpretation horizon at the bottom of the low-velocity layer, performing restoration and correction on the seismic event axes at the false fault and the high of the false structure, and compiling the final structure map.

[0029] Preferably, in the step (5), the trend of the seismic interpretation horizon at the bottom of the low-velocity layer is the formation dip angle at the bottom of the low-velocity layer.

[0030] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0031] 1. In the present invention, based on the three-dimensional seismic fine interpretation of the bottom surface of the low-velocity layer and large faults, combined with the forward modeling model established with drilling and logging data, the data used is more abundant.

[0032] 2. In the present invention, the forward modeling model takes into account the changes in fault dip angle, formation dip angle, and formation docking thickness, and the established model is more in line with the sedimentary characteristics of the actual block, and the forward modeling simulation results are more real and reliable.

[0033] 3. In the present invention, more actual geological conditions are considered, different types of false structures are simulated, the conditions and characteristics for the formation of different structural illusions are clarified, effectively guiding the discrimination of true and false structures in structural interpretation, and the method of using the trend of the seismic interpretation horizon at the bottom of the low-velocity zone to control the restoration of false structures is simple and efficient, and finally the true structural morphological characteristics can be displayed.

[0034] 4. In the present invention, it can effectively guide structural interpreters to quickly identify different types of structural illusions in the hanging wall of large faults and quickly and accurately restore the illusions, with a simple process and convenient operation.

[0035] 5. In the present invention, it provides accurate basic guidance for the potential tapping of remaining oil in fault-block reservoirs, has a guiding role in the later development of such reservoirs, has a broad promotion and application prospect, and remarkable economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the flow chart of the present invention;

[0037] Figure 2 is the calibration, horizon and fault interpretation section of the large fault low-velocity layer in the embodiment of the present invention;

[0038] Figure 3 is the forward modeling model and simulation result display diagram of the hanging wall of the large fault with a dip angle of 60 degrees in the embodiment of the present invention;

[0039] Figure 4 This is a forward model of the footwall of a large fault with a dip angle of 75 degrees and a display diagram of simulation results in an embodiment of the present invention;

[0040] Figure 5 This is a forward model of the footwall of a large fault with a dip angle of 85 degrees and a display diagram of simulation results in an embodiment of the present invention;

[0041] Figure 6 A schematic diagram of a seismic section for identifying a pseudo-fault at the footwall of a large fault based on forward modeling results in an embodiment of the present invention;

[0042] Figure 7 A schematic diagram of a seismic profile for identifying a pseudo-anticline at the foot of a large fault based on forward modeling results in an embodiment of the present invention;

[0043] Figure 8 A schematic diagram of an earthquake profile for restoring a pseudo-fault according to the bottom trend of a low-velocity layer in an embodiment of the present invention;

[0044] Figure 9 A schematic diagram of a seismic profile for restoring a false anticline based on the bottom trend of a low-velocity layer in an embodiment of the present invention;

[0045] Figure 10 It is the calibration of the low-velocity layer of the large fault, the horizon and the fault interpretation section in the embodiment of the present invention;

[0046] Figure 11 This is a diagram showing the forward model of a fault with a steep top and a gentle bottom and the simulation results in an embodiment of the present invention;

[0047] Figure 12 Schematic diagram of a seismic profile for identifying a pseudo-fault at the footwall of a large fault based on forward modeling results in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following is combined with Figures 1-12 , further illustrating a specific implementation of a method for identifying structural artifacts in a seismic time section of a large fault footwall in a fault-block reservoir of the present invention. The method for identifying structural artifacts in a seismic time section of a large fault footwall in a fault-block reservoir of the present invention is not limited to the description of the following embodiments.

[0049] Embodiment 1:

[0050] A method for identifying structural artifacts in seismic time sections of the footwall of a large fault in a fault-block reservoir, such as Figure 1 As shown, the following steps are included:

[0051] (1) Coherent slices clarify the fault distribution pattern;

[0052] (2) Stratum calibration and full-area tracking interpretation of the bottom of the low-velocity layer;

[0053] (3) Interpretation of large fault sections;

[0054] (4) Forward modeling of large fault models in different forms and identification of different types of artifacts;

[0055] (5) Correction of structural artifacts.

[0056] Furthermore, in step (1), it specifically includes: extracting coherent attributes from seismic data, browsing coherent slices within 400 ms above and below the research interval, and clarifying the distribution law of large faults.

[0057] Furthermore, in step (2), the horizon calibration specifically includes: comparing and analyzing the wells on both sides of the large fault, finding the low-velocity layer from the acoustic curve, and reading the formation velocities from the low-velocity layer to each horizon above and below the research interval; performing fine horizon calibration to determine the seismic section positions of the low-velocity layer and the target interval.

[0058] Furthermore, in step (2), the whole area is traced and interpreted for the bottom surface of the low-velocity layer and the large fault.

[0059] Furthermore, in step (3), it specifically includes: performing fine section interpretation of the fault on the seismic section along the strike of the large fault, depicting the fault plane morphology of the large faults from the low-velocity layer to the research interval, calculating the morphological change range of the large fault, the formation dip angle of the low-velocity bottom surface, and the docking thickness of the high-velocity and low-velocity layers on both sides of the fault.

[0060] Furthermore, the morphological change range of the large fault is the dip angle change range of the large fault.

[0061] Furthermore, in step (4), the large fault models in different forms specifically include: establishing a geological model based on the fault dip angle change according to the velocities of each formation, the morphology of the large fault, the docking thickness of the high-velocity and low-velocity layers on both sides of the fault, and the formation dip angle.

[0062] Furthermore, in step (4), the identification of different types of artifacts specifically includes: the seismic reflection characteristics of each formation when the low-velocity layer is lost due to large faults with different dip angles.

[0063] Furthermore, in step (4), the forward modeling results specifically include:

[0064] 1) When no false structure is generated, the method process ends;

[0065] 2) When a false structural high is generated, analyze its characteristics and determine its generation position. When a false fault is generated, analyze its characteristics and establish a discriminant criterion for the false fault, and identify the false structure on the seismic section based on the forward modeling results.

[0066] Furthermore, in step (5), it specifically includes: referring to the trend of the seismic interpretation horizon of the low-velocity layer bottom surface, restoring and correcting the seismic event axes at the false fault and the false structural high, and compiling the final structure map.

[0067] Further, in step (5), the trend of the seismic interpretation horizon at the bottom of the low-velocity layer is the formation dip angle at the bottom of the low-velocity layer.

[0068] Example 2:

[0069] A method for identifying the structural illusion of a seismic time section in the hanging wall of a large fault in a fault-block reservoir. Taking Block L11 in the eastern part of Shinan Oilfield in the western section of the central uplift belt of Dongying Sag as an example, the main oil-bearing series of this block are the 7th and 8th sand groups of Shahejie Formation. It is a semi-closed fault block blocked by the north boundary fault and the southern fault, and internally complicated by low-order faults. The small faults inside play an important controlling role in the distribution of oil and water. At present, the delineation of low-order faults does not meet the requirements of fine tapping potential during the extra-high water cut period, resulting in contradictions in geological development in the later stage. It is necessary to carry out fine structural research to identify faults and structures. During the structural interpretation process, it is found that there are serious well-seismic contradictions in this block. One is that the time-depth difference of adjacent wells is large when using the same one, and the other is that there are obvious faults on the seismic section but no breakpoints on the wells. By comparing multiple actual drilled wells with multiple sets of seismic data, it is found that there is a velocity trap in the seismic data of this block within a certain distance from the hanging wall of the north boundary fault, and the seismic axis is upturned, resulting in a structural illusion, which directly affects the understanding of the real structural form by structural interpreters. Therefore, it is urgent to carry out the identification of structural illusions, identify the structure, and clarify the distribution law of remaining oil.

[0070] In Example 2, the method for identifying the structural illusion on the seismic time section in the hanging wall of the large fault described in the present invention is used for identifying the structural illusion, and the steps are as follows:

[0071] (21) Extract the coherence attribute of the seismic data of the target interval, and browse the coherence slices within 400 MS above and below the 7th and 8th sand groups of Shahejie Formation to clarify the planar distribution law of the large fault;

[0072] (22) As Figure 2 shown, compare and analyze the wells on both sides of the large fault, find the low-velocity layer from the acoustic curve, and read the formation velocities of each layer above and below the research interval from the wells; and conduct fine horizon calibration on the seismic section to determine the seismic section positions of the low-velocity layer and the target interval, and then conduct full-area tracking and interpretation on the bottom surface of the low-velocity layer and the large fault;

[0073] (23) Conduct fine interpretation on the large fault for the seismic section passing through the strike of the large fault, analyze the morphological changes (dip angle changes) of the large fault, calculate the formation dip angle at the bottom of the low-velocity layer, and observe the formation docking situation on both sides of the fault; in Example 2, the dip angle of the large fault is between 55° and 85°, the formation dip angle at the bottom of the low-velocity layer is 9°, the low-velocity layer is faulted out by the fault, and the docking thickness of the high-velocity formation and the low-velocity layer on both sides of the fault is 160 m;

[0074] (24) Based on the fault morphology, the docking thickness of high-speed and low-speed formations, and the formation dip angle in step (23), and referring to the formation velocity read in the well in step (22), a forward modeling of faults with different dip angles is established; Model 1 is a large fault model with a dip angle of 60 degrees. The forward modeling result shows that a false structural high point (false anticline) appears in the hanging wall of the large fault. Its characteristics are: it appears in the area clamped by the bottom surface of the low-speed zone and the large fault, the seismic event axis warps upward and then bends downward, and the axis of the false anticline intersects with the bottom surface of the low-speed layer and the large fault at one point (as Figure 3 shown); Model 2 is a large fault model with a dip angle of 75 degrees. The forward modeling result shows that a false fault appears in the hanging wall of the large fault. Its characteristics are: the fault is nearly vertical, and the false fault intersects with the bottom surface of the low-speed layer and the large fault at one point (as Figure 4 shown); Model 3 is a large fault model with a dip angle of 85 degrees. The forward modeling result shows that a false fault appears in the hanging wall of the large fault. Its characteristics are: nearly vertical, intersects with the large fault, and is very close to the large fault. The steeper the large fault, the more inseparable the false fault is from the large fault (as Figure 5 shown); And referring to the forward modeling results of Model 1 to Model 3, the structural illusions in Example 2 are identified (as Figures 6-7 shown);

[0075] (25) Referring to the trend of the seismic interpretation horizon at the bottom surface of the low-speed layer (the formation dip angle at the bottom surface of the low-speed layer), the trend of the seismic event axis that generates false faults and false anticlines on the top surfaces of the 7th and 8th sand groups in the study interval is restored and corrected (as Figure 9 shown).

[0076] By adopting the above technical solutions:

[0077] The method of the present invention is based on the full-region tracking and interpretation of the bottom surface of the low-speed layer and large faults. Referring to the formation velocity of the actual block, the formation dip angle at the bottom surface of the low-speed layer, and the docking thickness of the high-speed and low-speed layers, a geological model of faults with different dip angles is established, and the types, positions, and characteristics of false structures are forward modeled and simulated. In the implementation block, the method for identifying structural illusions in the present invention is used to finely interpret the top surfaces of the 7th and 8th sand groups in the Sha-2 formation, identifying a false anticline and 6 false faults in the middle of the hanging wall of the large fault at the northern boundary. Finally, the structure of the whole region is determined, the distribution law of remaining oil is clarified, providing a reliable geological basis for the adjustment of the later development well pattern and the tapping of remaining oil.

[0078] Example 3:

[0079] A method for identifying structural artifacts in the seismic time section of the footwall of a large fault in a fault-block reservoir. Taking the G89-F142 block in the middle of the Jinjia-Zhenglizhuang-Fanjia nose-like structural belt in the Boxing Sag as an example, the oil-bearing formation of this block is the pure upper part. Due to the influence of two tectonic movements in the Shahejie and Kongdian periods, faults are relatively developed. This block is a beach-bar sand deposit and belongs to a low-permeability reservoir. In the later stage, it is developed by fracturing and water injection. The distribution law of the fault system has a significant impact on the later development effect. Therefore, it is necessary to carry out fine structural interpretation to clarify the faults. During the structural interpretation process, it is found that there is strike-slip in some faults in some places, and vertical faults appear in some parts of the footwall of the large fault on the north boundary. There is a large difference when adjacent wells are calibrated with the same velocity. There may be structural artifacts in some parts of the footwall of the large fault. Therefore, it is urgent to carry out the identification of structural artifacts and clarify the fault system.

[0080] Example 3 uses the method for identifying structural artifacts on the seismic time section of the footwall of the large fault described in the present invention to identify structural artifacts. The steps are as follows:

[0081] (21) Extract the coherence attribute of the seismic data of the target interval, and browse the coherence slices within 1000 MS near the target interval to clarify the planar distribution law of the large fault;

[0082] (22) Conduct a comparative analysis of the wells on both the hanging wall and the footwall of the large fault. Find the low-velocity layer from the acoustic curve, and read the formation velocities of each layer above and below the research interval from the well; and conduct fine horizon calibration on the seismic section to determine the seismic section positions of the low-velocity layer and the target interval. Then, conduct a full-area tracing and interpretation of the bottom surface of the low-velocity layer and the large fault (as Figure 10 shown);

[0083] (23) Conduct a fine interpretation of the large fault on the seismic section passing through the strike of the large fault, analyze the morphological changes (dip angle changes) of the large fault, calculate the formation dip angle of the bottom surface of the low-velocity layer, and observe the docking thickness of the formations on both sides of the fault; in Example 3, the large fault is steep at the top and gentle at the bottom. The fault near the low-velocity layer is 85 degrees, and the fault in the target interval is about 75 degrees. The bottom surface of the low-velocity layer dips northward (dip angle 7 degrees). The low-velocity layer is faulted out by the fault, and the docking thickness of the high-velocity formations on both sides of the fault and the low-velocity layer is 150 meters;

[0084] (24) Based on the fault morphology, the docking thickness of the high- and low-velocity formations, and the formation dip angle in step (23), and referring to the formation velocities read from the well in step (22), establish a fault model that is steep at the top and gentle at the bottom; the forward modeling result shows that a false fault appears in the footwall of the large fault. Its characteristics are: nearly vertical, intersecting with the large fault, very close to the large fault, and the false fault is more inseparable from the large fault at the steeper part of the large fault (as Figure 11 shown); and identify the false structure in Example 3 with reference to the forward modeling result of the model;

[0085] (25) Refer to the trend of the seismic interpretation horizon at the bottom of the low-velocity layer (formation dip angle at the bottom of the low-velocity layer), and perform restoration and correction on the seismic event trend of the false fault generated on the pure upper surface of the research interval (as Figure 12 shown).

[0086] By adopting the above technical solution:

[0087] In Example 3 of the method of the present invention, false faults on the hanging wall of large faults are identified, and the identification results are in good agreement with the drilling, and finally the faults and structures in Example 3 are determined.

[0088] In summary, the specific implementation process of the present invention is as follows:

[0089] In the present invention, first, extract the coherence attribute of the seismic data of the target interval to clarify the distribution law of large faults; then analyze the logging curves in the work area, find the low-velocity layer in the upper part of the target interval, and read the formation velocities of each layer above and below the low-velocity layer and the research interval. Determine the seismic profile positions of the low-velocity layer and the target horizon through horizon calibration, and perform full-area tracking and interpretation on the bottom surface of the low-velocity layer and large faults; then perform fine interpretation of the faults on the seismic profiles passing through the strike of large faults, depict the fault surface morphology of the large faults from the low-velocity layer to the research interval, and calculate the range of morphological changes (dip angle changes) of large faults, the formation dip angle at the bottom of the low-velocity layer, and the docking thickness of the high-velocity layer and the low-velocity layer on both sides of the fault; based on the formation velocities, formation dip angles, and formation docking thicknesses read from the well, establish a geological model based on the dip angle change of the fault for forward modeling, and clarify the types of false structures, specific locations, characteristics, etc. through forward modeling; finally, identify the structural false appearances from the seismic profiles according to the characteristics of the forward-modeled structural false appearances, and restore the false structures under the control of the trend of the seismic interpretation horizon at the bottom of the low-velocity layer, and finally determine the structures in the whole area.

[0090] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs, characterized in that, it includes the following steps: (1) Coherent slices to clarify the distribution law of faults; (2) Horizon calibration and full-area tracking and interpretation of the bottom surface of the low-velocity layer; (3) Profile interpretation of large faults; (4) Forward modeling of large fault models with different morphologies and identification of different types of artifacts; (5) Correction of structural artifacts.

2. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (1), specifically including: extracting coherent attributes from seismic data, browsing the coherent slices within 400 ms above and below the study interval to clarify the distribution law of large faults.

3. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (2), the horizon calibration specifically includes: comparing and analyzing the wells on both sides of the large fault, finding the low-velocity layer from the acoustic curve, reading the formation velocities from the low-velocity layer to each horizon above and below the study interval; performing fine horizon calibration to determine the seismic profile positions of the low-velocity layer and the target interval.

4. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (2), full-area tracking and interpretation of the bottom surface of the low-velocity layer and the large fault are carried out.

5. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (3), specifically including: performing fine profile interpretation of the fault through the seismic profile along the strike of the large fault, depicting the fault surface morphology of the large fault from the low-velocity layer to the study interval, and calculating the morphological change range of the large fault, the formation dip angle of the low-velocity bottom surface, and the docking thickness of the high-velocity layer and the low-velocity layer on both sides of the fault.

6. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 5, characterized in that: the morphological change range of the large fault is the dip angle change range of the large fault.

7. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (4), the large fault models with different morphologies specifically include: establishing a geological model based on the fault dip angle change with the formation velocities of each layer, the morphology of the large fault, the docking thickness of the high-velocity layer and the low-velocity layer on both sides of the fault, and the formation dip angle.

8. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (4), the identification of different types of artifacts specifically includes: the seismic reflection characteristics of each layer when the low-velocity layer is faulted out by large faults with different dip angles.

9. A method for identifying structural artifacts in seismic time sections of the footwall of large faults in fault-block reservoirs according to claim 1, characterized in that, in the step (4), the forward modeling results specifically include: 1) When no false structure is generated, the method process ends; 2) When a false structural high is generated, analyze its characteristics and determine its generation location. When a false fault is generated, analyze its characteristics and establish a discriminant criterion for the false fault, and identify the false structure on the seismic section based on the forward modeling results.

10. A method for identifying structural artifacts on a seismic time section of the hanging wall of a major fault in a fault-block oil reservoir according to claim 1, wherein, in the step (5), it specifically includes: referring to the trend of the seismic interpretation horizon at the bottom of the low-velocity layer, restoring and correcting the seismic event axes at the false fault and the false structural high, and compiling the final structure map.

11. A method for identifying structural artifacts on a seismic time section of the hanging wall of a major fault in a fault-block oil reservoir according to claim 10, wherein, in the step (5), the trend of the seismic interpretation horizon at the bottom of the low-velocity layer is the formation dip angle at the bottom of the low-velocity layer.

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