A method for spatial amplitude compensation of seismic data from an unevenly eroded formation

Abstract

The application provides a seismic spatial amplitude compensation method for unevenly denuded strata, relates to the field of oil and gas geophysical exploration, and combines geological understanding with seismic data analysis to determine the rationality of amplitude compensation based on data analysis under the guidance of geology. Then, the seismic data is divided into three parts, i.e. background trend signal, reservoir signal and noise signal, the reservoir signal and the noise signal are subjected to pulse interference, the background trend signal is obtained through median filtering, the amplitude compensation factor is further obtained, and the seismic signal is subjected to spatial amplitude compensation. Finally, the compensated data is reasonably judged again in combination with geological understanding and well production conditions. The method mainly based on stacked data has good applicability and generalization, and high feasibility.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geophysical exploration, specifically to a method for compensating for seismic spatial amplitude in unevenly eroded strata. Background Technology

[0002] In oil exploration and development, unconformities formed by sedimentary hiatuses due to tectonic uplift or stratigraphic erosion often serve as important oil and gas migration channels. Long-term weathering and leaching below these unconformities can also form karst fracture-vuggy reservoirs, which, after being filled with oil and gas, easily develop into large-scale buried hill oil and gas reservoirs. These fracture-vuggy reservoirs are mainly composed of caves, faults, and fractures of varying scales, exhibiting extremely strong lateral heterogeneity. Accurate seismic identification of these reservoirs is a crucial task in oil and gas geophysical exploration.

[0003] For buried hill type oil and gas reservoirs, uneven erosion of the underlying strata beneath the unconformity surface, coupled with differences in the amount of erosion and variations in structural morphology, often results in significant differences in the burial depth of karst fracture-cavity reservoirs within the same stratum laterally. On seismic profiles, the varying thickness of the overlying strata leads to different energy absorption and attenuation of seismic signals, causing reservoirs of the same size to produce different seismic responses. If effective spatial amplitude compensation for these seismic energy differences cannot be performed on the target stratum, it becomes impossible to accurately determine the reservoir size using techniques such as seismic inversion and attribute description, thus affecting oilfield reserve prediction.

[0004] In seismic processing, amplitude compensation techniques primarily address seismic wave absorption and attenuation caused by loose surface media such as undulating surfaces and complex sand dunes. A commonly used method is to investigate the near-surface quality factor Q value to describe the overall effect of this absorption and attenuation, but this approach cannot effectively compensate for the amplitude of deep target layers. Other processing techniques, such as spherical geometric diffusion compensation and surface uniformity amplitude compensation, either primarily target near-surface differences or provide overall compensation on the shot domain CMP gather, failing to provide targeted compensation for strata below the unconformity. Regarding amplitude compensation for the lateral heterogeneity of target layers, Gu Xiaodi of CNPC proposed an amplitude compensation method under strong wave impedance interfaces, mainly used to suppress seismic wave absorption and attenuation in coal seams. This method uses the amplitude of seismic traces without coal seam amplitude anomalies as a reference standard, determining a reasonable compensation factor by comparing the amplitude difference between the attenuated seismic traces and the standard seismic traces. This method has been effectively applied in the Junggar Basin. However, this method is not suitable for amplitude compensation in unevenly eroded formations. This is because, firstly, the erosion of buried hill oil and gas reservoirs is mostly integral, making it impossible to establish a unified normal amplitude seismic trace reference standard in the three-dimensional seismic zone. Secondly, the erosion amount in unevenly eroded formations is spatially gradual, and its influence on underlying strata differs from that of coal seams. Huang Weihua proposed a well-controlled pre-stack Q-compensation technique based on VSP (Very Low-Speed ​​Logging). While this method can achieve accurate amplitude energy compensation, its drawbacks are also significant: it relies excessively on VSP logging, cannot be implemented in areas without VSP logging, and cannot achieve lateral spatial amplitude compensation of target layers beyond logging.

[0005] In summary, there is currently no effective technology for compensating for seismic spatial amplitude in unevenly eroded strata. Summary of the Invention

[0006] Current technologies for amplitude compensation in unevenly eroded formations mostly provide overall energy compensation, failing to account for amplitude differences in the target layer caused by lateral absorption and attenuation variations in the overlying strata. They rely on well logging data such as VSP to calculate compensation amounts, which is ineffective in areas without well logging or between wells. This invention primarily addresses the inconsistency in lateral spatial amplitude of the target layer caused by differences in overlying strata thickness due to varying erosion amounts. By performing amplitude energy analysis on the original seismic data, a compensation factor for planar lateral spatial variation is determined. Based on this factor, spatial amplitude compensation is performed to obtain seismic data with relatively consistent amplitude energy in the target layer. Reservoir identification and sculpting below the unconformity surface based on the compensated seismic data yields more scientifically sound reservoir volume characterization and reserve calculations. Furthermore, this invention uses post-stack seismic data as input, requiring less computation compared to pre-stack gather processing. Conventional workstations can meet the computational needs, making it highly operable for seismic interpreters. Multiple calculations and adjustments can be made based on geological understanding or single-well production data to achieve accurate reservoir characterization and reserve calculation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a method for earthquake spatial amplitude compensation, comprising the following steps:

[0009] (1) Energy trend analysis of earthquake data: Analyze the energy trend of earthquake data to determine whether amplitude energy compensation is necessary;

[0010] (2) Calculation of compensation factor for eroded strata:

[0011] Assuming the original input seismic signal consists of three parts: background trend signal Sd(x,y,t), reservoir signal Sr(x,y,t), and noise signal Sn(x,y,t), then the seismic signal S0(x,y,t) is expressed as:

[0012] S0(x,y,t)=Sd(x,y,t)+Sr(x,y,t)+Sn(x,y,t) (b);

[0013] The compensation factor Qd(x,y,t) is calculated based on the seismic signal S0(x,y,t);

[0014] (3) Spatial amplitude compensation:

[0015] S(x,y,t)=S0(x,y,t)*Qd(x,y,t) (e)

[0016] Where S(x,y,t) is the seismic signal after spatial amplitude compensation, and Qd(x,y,t) is the compensation factor.

[0017] Furthermore, the earthquake spatial amplitude compensation method further includes step (4): compensation quality control.

[0018] Furthermore, the compensation quality control includes: calculating the root mean square amplitude energy plane distribution within the time window T(x,y)min for the compensated seismic signal S(x,y,t), analyzing whether it still has the same trend as the thickness of the tectonic erosion, and repeating steps (1)-(3) if so.

[0019] Further, the energy trend analysis of the seismic data in step (1) specifically includes: assuming the distribution variable of the erosion thickness in the plane is represented by D(x,y), where x and y are represented by geodetic coordinates, and the current residual thickness variable of the eroded strata is represented by T(x,y), taking the unconformity at the top of the eroded strata as the top interface, and the minimum residual thickness T(x,y)min as the unified time window, the root mean square amplitude plane map is extracted. Assuming the root mean square amplitude energy plane distribution function is E(x,y), by comparing its similar trend characteristics with the erosion thickness plane distribution, it is represented by the following function:

[0020] E(x,y)=kE*D(x,y)+ER(x,y)+EN(x,y) (a)

[0021] Where kE is the similarity coefficient of the root mean square amplitude per unit area, ER(x,y) is the plane characteristic of the root mean square amplitude of the reservoir seismic signal, and EN(x,y) is the root mean square amplitude of the seismic noise.

[0022] The above indicates that seismic waves are affected by uneven erosion of the strata during propagation, and amplitude energy compensation is required.

[0023] Further, the calculation of the compensation factor Qd(x,y,t) in step (3) includes the following steps: performing median filtering on the original seismic signal S0(x,y,t) at two levels, treating both the noise signal and the reservoir signal as impulse noise, selecting a smaller filtering window in the first level to eliminate the noise signal Sn(x,y,t), and selecting a larger filtering window in the second level to eliminate the reservoir signal Sr(x,y,t). Then, according to formula (b), the background trend signal Sd(x,y,t) is obtained at this time. Sd(x,y,t) is normalized to Sd'(x,y,t), and its reciprocal is taken as the compensation factor Qd(x,y,t).

[0024] Qd(x,y,t)=1 / Sd'(x,y,t) (d).

[0025] Furthermore, the calculation of Sd'(x, y, t) is specifically as follows:

[0026] Sd'(x,y,t)=Sd(x,y,t) / [Sd(x,y,t)max-Sd(x,y,t)min] (c).

[0027] Furthermore, the smaller filtering window mentioned in step (2) is two seismic grids.

[0028] Furthermore, the larger filtering window mentioned in step (2) is 5-7 seismic grids.

[0029] Furthermore, if there is production data from multiple single wells within the work area, the reservoir is characterized by reservoir inversion and attribute extraction of the compensated seismic signal. A threshold value is set to calculate the volume of the single-crystal reservoir, and the relationship between single-well production capacity, output and reservoir volume is analyzed to further review the effect of amplitude compensation.

[0030] Furthermore, the seismic spatial amplitude compensation method of the present invention can be applied to oil and gas geophysical exploration.

[0031] In some specific embodiments, the seismic spatial amplitude compensation method of the present invention includes the following steps:

[0032] (1) Energy trend analysis of seismic data. Generally speaking, sedimentary discontinuities and erosion caused by strata uplift are controlled by paleotectonic features and have a certain trend in the plane. Assuming that the distribution function of erosion thickness in the plane is D(x,y), and the current residual thickness of the eroded strata is T(x,y), taking the unconformity at the top of the eroded strata as the top interface, and taking the minimum residual thickness T(x,y)min as the unified time window, the root mean square amplitude plane map is extracted. Assuming that the root mean square amplitude energy plane distribution function is E(x,y), by comparing it with the plane distribution of erosion thickness, it has similar trend characteristics and can be represented by the following function:

[0033] E(x,y)=kE*D(x,y)+ER(x,y)+EN(x,y) (a)

[0034] Where kE is the similarity coefficient of the root mean square amplitude per unit area, ER(x,y) is the plane characteristic of the root mean square amplitude of the reservoir seismic signal, and EN(x,y) is the root mean square amplitude of the seismic noise.

[0035] This demonstrates that seismic waves are affected by uneven erosion of the strata during propagation, necessitating amplitude energy compensation.

[0036] (2) Calculation of compensation factor for eroded strata

[0037] Median filtering is applied to the raw seismic data. This is a nonlinear signal processing technique based on the Tongji Theory of Ranking, which effectively suppresses noise. When filtering digital signals, a computational space window is first defined, and all samples within the window are sorted. The median of the sorted samples is then taken as the output. The value of a point in the seismic signal sequence is replaced by the median of all points in the neighboring spatial window, making it approximate the trend change and eliminating impulse noise. Similar to formula (a) above, we assume that the original input seismic signal consists of three parts: the background trend signal Sd(x,y,t), the reservoir signal Sr(x,y,t), and the noise signal Sn(x,y,t). Then, the seismic signal S0(x,y,t) can be expressed as:

[0038] S0(x,y,t)=Sd(x,y,t)+Sr(x,y,t)+Sn(x,y,t) (b)

[0039] The original seismic signal S0(x,y,t) is subjected to median filtering at two levels. Both the noise signal and the reservoir signal are treated as impulse noise. The first level selects a small filtering window (about 2 seismic grids, which can be adjusted appropriately according to the actual effect) to eliminate the noise signal Sn(x,y,t). The second level selects a larger filtering window (about 5-7 seismic grids, which can be adjusted according to the effect) to eliminate the reservoir signal Sr(x,y,t). Then, according to formula (b), the background trend signal Sd(x,y,t) can be obtained. Sd(x,y,t) is normalized to Sd'(x,y,t) and its reciprocal is taken as the compensation factor Qd(x,y,t).

[0040] Sd'(x,y,t)=Sd(x,y,t) / [Sd(x,y,t)max-Sd(x,y,t)min] (c)

[0041] Qd(x,y,t)=1 / Sd'(x,y,t) (d)

[0042] Where Sd'(x, y, t) is the normalized Sd(x, y, t). The significance of normalization is to establish data consistency and facilitate processing.

[0043] (3) Spatial amplitude compensation

[0044] When compensating for seismic data, the signal of the original input data is multiplied by a compensation factor, i.e.:

[0045] S(x,y,t)=S0(x,y,t)*Qd(x,y,t) (e)

[0046] S(x,y,t) represents the spatially amplitude-compensated seismic signal. This compensation not only addresses the background trend term of the original seismic data but also compensates for reservoir signals and noise signals, ensuring amplitude energy balance across the entire compensation space. Noise signals are also altered, requiring further denoising and interpretative processing for subsequent reservoir prediction. If VSP logging in the study area yields the Q-value of the eroded formation at that well point, it can be used as the spatial amplitude compensation calibration for that point; otherwise, it does not affect the next step of the work.

[0047] (4) Compensation Quality Control

[0048] After spatial amplitude compensation, the compensated data needs to be reviewed to ensure that the energy imbalance caused by uneven erosion has been eliminated and meets the requirements for seismic reservoir prediction. The root mean square amplitude energy plane distribution within the time window T(x,y)min is calculated for the compensated seismic signal S(x,y,t), and it is analyzed whether it still exhibits the same trend as the tectonic erosion thickness. If so, the above steps are repeated. If spatial amplitude compensation for unevenly eroded strata has been completed, then...

[0049] If there are multiple single-well production data in the work area, the reservoir can be characterized by reservoir inversion and attribute extraction after compensation. A threshold value can be set to calculate the volume of a single-crystal reservoir and analyze the relationship between single-well production capacity, output and reservoir volume to further review the effect of amplitude compensation.

[0050] The technical effects achieved by this invention are:

[0051] (1) The amplitude compensation factor is based on the analysis of the stratigraphic amplitude energy of the original seismic data and takes into account the spatial variation of the erosion surface. It is a product of the combination of geophysical data analysis and geological law understanding. It is not a purely mathematical calculation and has good scientificity and rationality.

[0052] (2) The input data is post-stack earthquakes, and the data volume is relatively small. In actual work, it can be calculated and adjusted multiple times to meet the production needs of geological targets. Both earthquake processing personnel and interpreters can calculate and run it on their daily work computers.

[0053] (3) The spatial amplitude compensation method does not depend on well logging. The accuracy of the calculation can be further improved by well logging calibration. If there is no well logging, it will not affect the overall calculation. Multiple compensations can be carried out by joint analysis with the later reservoir characterization to improve the amplitude compensation accuracy. Attached Figure Description

[0054] Figure 1 A flowchart for earthquake spatial amplitude compensation method for unevenly eroded strata;

[0055] Figure 2The target layer root mean square amplitude plane plot of the original seismic data;

[0056] Figure 3 For seismic impedance inversion plan view and fracture-cavity reservoir collective carving;

[0057] Figure 4 This is the impedance plane diagram of the filtered background trend signal;

[0058] Figure 5 A three-dimensional comparison of the collective signal of the fracture-cavity reservoir before and after amplitude compensation is shown, where a: oblique view before amplitude compensation; b: top view before amplitude compensation; c: oblique view after amplitude compensation; d: top view after amplitude compensation. Detailed Implementation

[0059] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0060] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention.

[0061] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0062] Example 1

[0063] To illustrate the technical structure and function of this invention, the following section uses the TT 3D seismic study area of ​​a buried hill oil and gas field in the Tarim Basin as an example to further elaborate on the seismic spatial amplitude compensation technology for unevenly eroded strata studied in this paper:

[0064] The reservoirs of this oil and gas field are mainly carbonate karst fracture-vuggy reservoirs below the unconformity of buried hills. On the seismic profile, they mainly show beaded reflection characteristics. There are obvious north-south differences in the degree of erosion of the strata below the unconformity. The northeastern part of the TT three-dimensional area has the largest erosion, while the western and southwestern parts have the smallest erosion.

[0065] (1) According to the method flow Figure 1As shown, firstly, based on the geological understanding of stratigraphic erosion, an energy trend analysis of the target layer is performed on the original seismic data, and a root mean square amplitude attribute plane map of the strata below the unconformity is extracted. Figure 2 The figure clearly shows a significant consistency between attribute distribution and erosion intensity. Generally, the northeastern region exhibits the strongest amplitude energy, while the western and southwestern regions show the weakest energy, with the strong erosion line as the boundary. The unified threshold value sculpting of karst fissure-cavity reservoirs using this seismic data also reveals similar regional differences. The seismic signal for the entire region consists of the background trend signal Sdd(x,y,t), the reservoir signal Srr(x,y,t), and the noise signal Snn(x,y,t). Therefore, the seismic signal S0(x,y,t) can be expressed as:

[0066] S0(x,y,t)=Sdd(x,y,t)+Srr(x,y,t)+Snn(x,y,t)

[0067] (2) Calculation of compensation factor for eroded strata. The seismic signal in the TT work area also consists of three parts: stratum trend signal, fracture-cavity reservoir signal, and noise signal. For ease of explanation, impedance inversion is performed on the seismic data, and the impedance plane distribution within a certain time window is extracted along the unconformity surface, as shown below. Figure 3 As shown, the 3D sculpting of the beaded cavity reservoir within this time window appears as low-impedance anomalies in the background. Median filtering with different filtering windows was applied twice to the seismic data of the TT 3D work area. The first filtering used a window with seismic grid 2 to eliminate noise, and the second filtering used a window with seismic grid 5 to filter the beaded reservoir. After the two filtering processes, a relatively smooth trend signal Sdd(x, y, t) was formed. Extracting the impedance plane plot from the trend signal clearly shows that noise and reservoir signals have been eliminated. Figure 4 The compensation factor data body is obtained by normalizing the trend signal and taking its reciprocal. The maximum value of the trend signal in the entire region is 600, and the minimum value is 50. After normalization, Sdd'(x,y,t) = Sdd(x,y,t) / 550. The compensation factor data body Qdd(x,y,t) = 1 / Sdd'(x,y,t)

[0068] (3) Spatial amplitude compensation is performed on the original earthquake based on the compensation factor data volume, and amplitude energy compensation is achieved by multiplying the two. Since there is no Q-value calibration for VSP and other logging results in this area, the data volume after compensation factor calculation is temporarily used as the compensation result data volume.

[0069] (4) The above-mentioned compensation results data were reviewed for effectiveness. Based on the well-seismic calibration results of the study area, a three-dimensional sculpting of the fracture-cavity reservoirs in the entire area was performed on the seismic data before and after compensation. See Figure 5As shown, the original data shows that the distribution of fracture-vuggy reservoirs is concentrated in the northeastern part of the study area, which is severely affected by the absorption and attenuation of unevenly eroded strata. However, the overall distribution of the compensated fracture-vuggy reservoirs is more reasonable and can meet production needs.

[0070] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for earthquake spatial amplitude compensation, characterized in that: Includes the following steps: (1) Energy trend analysis of earthquake data: Analyze the energy trend of earthquake data to determine whether amplitude energy compensation is necessary; (2) Calculation of compensation factor for eroded strata: Assume the original input seismic signal consists of three parts: background trend signal, background trend signal, and background trend signal. , storage collective signal and noise signals Then the earthquake signal Represented as: （b）； According to earthquake signals The compensation factor was calculated. ; (3) Spatial amplitude compensation: (e) in, This is the seismic signal after spatial amplitude compensation. As a compensation factor; The energy trend analysis of the seismic data in step (1) specifically includes: assuming that the distribution variable of the erosion thickness in the plane is... In this representation, x and y are the plane geodetic coordinates, and the current residual thickness of the eroded strata is expressed as... This indicates that the top unconformity of the eroded strata is taken as the top interface, and the minimum residual thickness of the strata is taken as the boundary. To unify the time window, the root mean square amplitude plane plot is extracted, assuming the root mean square amplitude energy plane distribution function is... By comparing its similar trend characteristics with the planar distribution of erosion thickness, it can be represented by the following function: （a） in, It is the similarity coefficient of the root mean square amplitude per unit area. It is the plane characteristic of the root mean square amplitude of reservoir seismic signals. It is the root mean square amplitude of the earthquake noise; The spatial amplitude compensation factor mentioned in step (3) The calculation includes the following steps: for seismic signals Perform two levels of median filtering to treat both the noise signal and the stored collective signal as impulse noise. The first level uses a smaller filtering window to eliminate the noise signal. The second level selects a larger filtering window to eliminate the stored collective signal. The background trend signal is obtained according to formula b. ,right Normalize to Sd'(x, y, t), and then take its reciprocal as the compensation factor. ; （d）。 2. The seismic spatial amplitude compensation method according to claim 1, characterized in that: It also includes step (4): compensatory quality control.

3. The earthquake spatial amplitude compensation method according to claim 2, characterized in that: The compensation quality control includes: processing the seismic signal after spatial amplitude compensation. calculate The plane distribution of root mean square amplitude energy within the time window is analyzed to determine whether it still has the same trend as the thickness of tectonic erosion. If so, steps (1)-(3) are repeated.

4. The seismic spatial amplitude compensation method according to claim 1, characterized in that: The calculation of Sd'(x, y, t) is as follows: （c）。 5. The seismic spatial amplitude compensation method according to claim 1, characterized in that: The smaller filtering window mentioned in step (2) is two seismic grids.

6. The seismic spatial amplitude compensation method according to claim 1, characterized in that: The larger filtering window mentioned in step (2) is 5-7 seismic grids.

7. The earthquake spatial amplitude compensation method according to claim 1, characterized in that: If there are multiple single-well production data in the work area, the seismic signal after spatial amplitude compensation is used to characterize the reservoir through reservoir inversion and attribute extraction. A threshold value is set to calculate the volume of the single-crystal reservoir, and the relationship between single-well production capacity, output and reservoir volume is analyzed to further review the effect of amplitude compensation.

8. The application of the seismic spatial amplitude compensation method as described in any one of claims 1-7 in oil and gas geophysical exploration.

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