CN117148437A - Thin reservoir earthquake quantitative calibration and top surface structure accurate mapping method - Google Patents
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Abstract
The invention provides a thin reservoir earthquake quantitative calibration and top surface structure accurate mapping method, which comprises the following steps: step 1: forward modeling the characteristic that the seismic reflection phase changes along with the thickness, namely forward modeling the seismic reflection of a thin reservoir, and analyzing the characteristic that the phase changes of the top-bottom interference of the thin reservoir; step 2: mathematically deriving a relationship of the seismic reflection phase with the thickness variation, i.e., mathematically deriving a quantitative relationship of the thickness of the thin reservoir with the seismic reflection phase variation; step 3: the position of the thin reservoir is calibrated quantitatively, and the structure is formed into a graph, namely, the spatial position of the thin reservoir is calibrated based on the quantitative relation between the thickness of the thin reservoir and the phase change, so that the accurate formation of the top surface structure is realized. The quantitative relationship between the thin Chu Cenghou degrees and the seismic reflection phase is found by the quantitative calibration and the accurate imaging method of the top surface structure of the thin reservoir, the spatial position of the thin reservoir can be calibrated quantitatively, and the accurate imaging of the top surface structure is realized.
Description
Technical Field
The invention relates to the technical field of seismic data interpretation of geophysical exploration, in particular to a method for quantitative calibration of earthquake of a thin reservoir and accurate mapping of a top surface structure.
Background
The reservoir deposited in eastern land of China has fast transverse change and small thickness, and the fine reservoir seismic description is important, so that the method is a high-efficiency oil and gas exploration and development foundation. The thickness of the reservoir layer of land-phase sedimentary is generally less than 1/4 of the seismic wavelength, belonging to thin reservoirs. The seismic reflection waves at the top and bottom surfaces of the thin reservoir have interference phenomenon, and attribute parameters such as the phase and the amplitude of the seismic reflection are related to thickness variation. The current research shows that the amplitude and the thickness of the thin reservoir layer are in positive correlation, the quantitative relation between the phase and the thickness of the thin reservoir layer is not clear, so that the reservoir layer cannot be accurately calibrated, and the description precision is low.
Researchers have made various attempts to address the problem of thin reservoir seismic descriptions. Li Qingzhong (1993) proposes that the tracking of sand must be performed with wave impedance profiles or integral seismic traces in roads that are strike a high precision survey. The cloud research group (2003) applies the tuning action of the amplitude to detect geological targets with the stratum thickness smaller than 1/4 wavelength, and the research of the limit problem of the seismic resolution of (2004) provides the problems of identifying and distinguishing the thin layer. Wang Pengfei (2012) model forward analysis of the seismic response characteristics of the spring light block thin reservoir qualitatively analyzes the phenomenon that the top-bottom interface of the thin reservoir deviates from the peak (valley), and improves the frequency of seismic data and the horizon calibration accuracy. Li Guofa, wang Yajing, etc. (2014) illustrate the interference characteristics of thin interbed seismic slices, and propose that reservoirs can be detected within the composite view period, zero points are in the middle of the reservoir, amplitude properties are positively correlated with reservoir thickness, and reservoir thickness can be predicted. The methods play a certain role in improving the recognition precision of the thin interbed, but do not describe the method correspondingly in terms of how to accurately calibrate the reservoir and accurately describe the top surface structure of the reservoir.
In application number: in the chinese patent application CN201611079816.3, a method for constructing a graph for developing a later complex block-breaking speed change is related to: step 1, obtaining the layer speed of a single well through seismic interpretation horizon and geological stratification; step 2, extracting the along-layer seismic attribute capable of reflecting lithology change, and superposing the attribute map with the equal T0 map; step 3, encrypting speed points of non-well and well distribution uneven areas based on the principle that the stratum speeds at the same lithology and the same time are consistent; step 4, interpolation is carried out on the single-well layer speed by taking the seismic interpretation horizon as a trend surface and the fault boundary as an interpolation boundary, and a two-dimensional layer speed field is established; and 5, multiplying the generated two-dimensional layer speed grid with an equal T0 grid to perform time-depth conversion, and obtaining a final structural diagram. The method provides accurate basic guidance for the research and development of the well pattern recombination of the residual oil distribution rule of the complex broken block fine oil reservoir description, has guidance effect on the later development of the oil reservoir, and has wide popularization and application prospect and remarkable economic and social benefits.
In application number: in the Chinese patent application of CN201610966691.X, a calibration method for improving the interpretation precision of a fault structure earthquake belongs to the field of petroleum and natural gas rolling development, wherein a selected single well in each fault structure is selected in the fault structure to be used as a well synthesis record, the earthquake time depth relation in each fault where the selected single well is positioned is determined, and the corresponding relation between the drilling stratum and the earthquake of all wells in each fault is established by utilizing the time depth relation between the drilling stratum of the selected single well in each fault and the corresponding fault earthquake phase; for single wells with different fracture stages, the fracture stage boundary fault depth of the single well drilling is taken as the boundary, the depth relation data of the corresponding stages are extracted according to the fracture stage positions of each stage of the well body, the depth relation of the single well with more than two fracture stages during the drilling is established, and the interpretation precision of the fracture stage structure earthquake is improved.
In application number: in the chinese patent application CN200710061369.3, a three-dimensional earthquake optimal time window river channel sand reservoir prediction and evaluation technology is related. Technical field: and (5) predicting and evaluating the three-dimensional seismic reservoir. Technical problems: the traditional method has insufficient river channel prediction resolution. The technical scheme is as follows: three-dimensional visual scanning is carried out at intervals of 1-2ms along the layer, an optimal time window is determined according to the range of the target river channel display, corresponding sub-bodies are cut, window attribute perspective scanning such as root mean square amplitude, wave impedance and the like is carried out, automatic tracking is carried out, top and bottom surface images are extracted, time equal thickness images are calculated and converted into sand equal thickness images, top surface structure images are converted into time depth images, and reservoir physical property evaluation is reconstructed through curves, so that prediction and evaluation of river channel sand plane morphology, longitudinal thickness and reservoir physical property are realized. The method can effectively suppress interference by using an optimal time window, is suitable for various data volumes, can effectively forecast and evaluate thin river single sand bodies with the thickness far smaller than 1/4 wavelength under the condition of frequent interbedding of sandstone, comprises river single sand bodies which do not correspond to wave crests or wave troughs, and has good application effect in petroleum exploration and development.
The prior art is greatly different from the method, the technical problem which is needed to be solved by the user cannot be solved, and therefore, the method for quantitative calibration of the earthquake of the thin reservoir and accurate imaging of the top surface structure is invented.
Disclosure of Invention
The invention aims to provide a thin reservoir seismic quantitative calibration and top surface structure accurate mapping method for researching the relation of the phase of thin reservoir seismic reflection along with thickness change and forming quantitative calibration of the top surface position of a reservoir and accurate description of the top surface structure.
The aim of the invention can be achieved by the following technical measures: the method for accurately mapping the thin reservoir earthquake quantitative calibration and the top surface structure comprises the following steps:
step 1: forward modeling the characteristic that the seismic reflection phase changes along with the thickness, namely forward modeling the seismic reflection of a thin reservoir, and analyzing the characteristic that the phase changes of the top-bottom interference of the thin reservoir;
step 2: mathematically deriving a relationship of the seismic reflection phase with the thickness variation, i.e., mathematically deriving a quantitative relationship of the thickness of the thin reservoir with the seismic reflection phase variation;
step 3: the position of the thin reservoir is calibrated quantitatively, and the structure is formed into a graph, namely, the spatial position of the thin reservoir is calibrated based on the quantitative relation between the thickness of the thin reservoir and the phase change, so that the accurate formation of the top surface structure is realized.
The aim of the invention can be achieved by the following technical measures:
in the step 1, forward modeling is performed to simulate the characteristic that the seismic reflection phase changes along with the thickness, and the thin reservoir is a reservoir with the thickness less than lambda/4 seismic wavelength; and analyzing the relation between the phase of the seismic reflection wave of the thin reservoir and the thickness h of the reservoir, wherein the peak of the phase gradually deviates upwards from the top surface of the reflection layer along with the thickness reduction, which is called phase shift, and the phase shift quantity and the thickness are in a linear negative correlation relation.
In the step 2, the relation of the variation of the seismic reflection phase W (t) along with the thickness h is deduced mathematically, the relation of the thickness and the phase shift quantity can be quantitatively represented by obtaining the phase characteristics of the two points of which the thickness is approximately 0 and lambda/4 according to the linear negative correlation of the phase shift quantity and the thickness.
In step 2, when the relation of the seismic reflection phase W (t) along with the thickness h is mathematically deduced, under a certain condition of surrounding rock, the top-interface seismic reflection of the thin reservoir is denoted as sin (ωt), and the bottom-interface seismic reflection of the thin reservoir is denoted as:
sin(ωt+φ)，φ＝4πh/λ，
wherein ω is frequency, φ is the seismic wavelength when traveling in two passes;
phase: w (t) =sin (ωt) -sin (ωt+Φ) =2cos (ωt+Φ/2) sin (- Φ/2).
In step 2, at a thickness h=λ/4, W (t) =2cos (ωt+pi/2) sin (-pi/2) =2sin (ωt), the seismic reflection phase is consistent with the top-interface seismic reflection of the thin reservoir.
In step 2, when the thickness h tends to 0, a function limit that the phi tends to 0 is calculated according to the relation between the thickness h and phi, wherein W (t) =2cos (ωt+phi/2) sin (-phi/2) =2cos (ωt) · (-phi/2) = - Φcos (ωt) =Φsin (ωt-pi/2); the phase difference between the seismic reflection phase and the top interface seismic reflection phase of the thin reservoir is pi/2, namely the phase shift is pi/2; in the time domain, the phase shift amount is T/4, and T is the period of the seismic wave.
In the step 3, the thin reservoir is quantitatively calibrated, the phase shift amount and the thickness are in a linear negative correlation, the phase shift amount of which the thickness is towards 0 is-pi/2, and the time phase shift amount is-T/4; the phase shift amount with the thickness equal to lambda/4 is 0, and the phase shift amount is T/4 (1-4 h/lambda); therefore, the position of the seismic calibration thin reservoir is the peak position to be shifted downwards by T/4 (1-4 h/lambda), and the quantitative calibration of the top surface of the thin reservoir is realized.
In step 3, a description of the structure of the top surface of the thin reservoir is performed, the peak of the seismic phase is tracked, the proportional relation between the amplitude a and the thickness h is utilized to calculate the thickness h=ka, k as a constant, the phase shift T/4 (1-4 h/λ) is further calculated, and the time value of the top surface of the thin reservoir is the time value of the peak plus the phase shift, i.e. t+t/4 (1-4 h/λ), so that an accurate structure diagram of the top surface of the thin reservoir is realized.
The method for quantitative calibration of earthquake of thin reservoir and accurate imaging of top surface structure comprises the following steps: forward modeling the phase change characteristics of the thin reservoir (less than 1/4 wavelength) seismic reflection; mathematical deduction of quantitative relation between thickness of thin reservoir and seismic reflection phase change is realized, and mathematical expression of phase shift quantity is realized; and calibrating the space position of the thin reservoir based on the thickness of the thin reservoir and the phase shift amount of the phase change, so as to realize accurate graph formation of the top surface structure.
The invention defines the interference characteristics of the seismic waves at the top and bottom of the thin reservoir from the physical mechanism, discovers the quantitative relation between the thin Chu Cenghou degrees and the seismic reflection phase, and solves the problem that the top surface of the reservoir deviates from the peak in the calibration of the thin Chu Cengge seismic record. The quantitative relation characterization of the thickness of the thin reservoir layer and the seismic reflection phase change, namely the mathematical expression of the phase shift quantity, is realized. And accurately calibrating the spatial position of the thin reservoir by using the thickness of the thin reservoir and the phase shift quantity of the seismic reflection phase, thereby realizing accurate mapping of the top surface structure of the thin reservoir.
Compared with the traditional method, on the basis of researching the relation between the thickness and the amplitude of the thin reservoir, the relation between the thickness and the waveform is increased, the physical phenomenon that the wave crest deviates from the top surface of the reservoir and is seismic wave interference is correct is clarified, and the problem of horizon calibration which puzzles the seismic description of the thin reservoir is solved; the thickness of the thin reservoir and the phase shift quantity of the seismic reflection phase change are quantitatively represented, so that accurate graph formation of the top surface structure of the thin reservoir can be realized, and the problem of inaccurate description of the top surface structure of the thin reservoir is solved.
Drawings
FIG. 1 is a flow chart of one embodiment of a thin reservoir seismic quantitative calibration and top surface construction accurate mapping method of the present invention;
FIG. 2 is a diagram of a wedge model seismic wave equation forward modeling thin reservoir phase change signature in accordance with an embodiment of the present invention;
FIG. 3 is a schematic representation of thin reservoir quantitative calibration of a seismic section of a CD zone in accordance with an embodiment of the invention;
FIG. 4 is a schematic diagram of a CB45 well Ngs IV 1 sand seismic reflection phase peak configuration in accordance with an embodiment of the invention;
FIG. 5 is a diagram of the thickness of a CB45 well Ngs IV 1 sand in an embodiment of the invention;
FIG. 6 is a schematic diagram of the top surface of a CB45 well Ngs IV 1 sand body according to an embodiment of the invention.
FIG. 7 is a schematic diagram of thin reservoir quantitative calibration of a CB27 well seismic profile in accordance with one embodiment of the present invention;
FIG. 8 is a diagram of the thickness of a CB27 well Ngs III 1 sand in an embodiment of the invention;
FIG. 9 is a schematic diagram of a CB27 well Ngs III 1 sand seismic reflection phase peak configuration (conventional method) according to an embodiment of the invention;
FIG. 10 is a schematic diagram of the top surface of a CB27 well Ngs III 1 sand body according to an embodiment of the present invention.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, 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 belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular forms also are intended to include the plural forms unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, and/or combinations thereof.
Aiming at the defects of the existing method, the invention provides a method for quantitative calibration of earthquake of a thin reservoir and accurate mapping of a top surface structure. The invention forward simulates the phase change characteristics of the seismic reflection of a thin reservoir (less than 1/4 wavelength); mathematically deriving a quantitative relationship of the thickness of the thin reservoir to the seismic reflection phase variation; based on the change relation between the thin Chu Cenghou degrees and the phase, the spatial position of the thin reservoir is quantitatively calibrated, and the accurate graph formation of the top surface structure is realized.
The following are several specific examples of the application of the present invention.
Example 1
In an embodiment 1 to which the present invention is applied, as shown in fig. 1, fig. 1 is a flowchart of a method for seismic quantitative calibration and accurate mapping of a top surface structure of a thin reservoir according to the present invention. The method for accurately mapping the seismic quantitative calibration and the top surface structure of the thin reservoir comprises the following steps:
step 1: forward modeling of the characteristics of the seismic reflection phase as a function of thickness: forward modeling seismic reflection of a thin reservoir (less than 1/4 wavelength) and analyzing phase change characteristics of top-bottom interference of the thin reservoir;
and the forward modeling simulates the characteristic that the seismic reflection phase changes with thickness. The thin reservoir is a reservoir with a thickness less than lambda/4 of the seismic wavelength; and analyzing the relation between the phase of the seismic reflection wave of the thin reservoir and the reservoir thickness (h), wherein the peak of the phase gradually deviates upwards from the top surface of the reflection layer along with the thickness reduction, which is called phase shift, and the phase shift quantity and the thickness are in a linear negative correlation relation.
Step 2: mathematical deduction of the relation of the seismic reflection phase to the thickness: mathematically deriving a quantitative relationship of the thickness of the thin reservoir to the seismic reflection phase variation;
the mathematical derivation of the seismic reflection phase W (t) as a function of thickness h. According to the linear negative correlation between the phase shift and the thickness, the phase characteristics of the two points of which the thickness is approximately 0 and lambda/4 are obtained, and the relation between the thickness and the phase shift can be quantitatively represented.
The mathematical derivation of the seismic reflection phase W (t) as a function of thickness h. Under certain conditions of surrounding rock, the top interface seismic reflection of the thin reservoir is denoted as sin (ωt), the bottom interface seismic reflection of the thin reservoir is denoted as sin (ωt+φ), φ=4πh/λ, where ω is frequency, φ is the seismic wavelength when traveling in two passes. The phase W (t) =sin (ωt) -sin (ωt+Φ) =2 cos (ωt+Φ/2) sin (- Φ/2). At thickness h=λ/4, W (t) =2cos (ωt+pi/2) sin (-pi/2) =2sin (ωt) is readily available, and the seismic reflection phase coincides with the top-interface seismic reflection of thin reservoirs. When the thickness h tends to 0, a function limit of phi tends to 0 is calculated according to the relation between the thickness h and phi, wherein W (t) =2 cos (ωt+phi/2) sin (-phi/2) =2 cos (ωt) · (-phi/2) = - Φcos (ωt) =Φsin (ωt-pi/2). The phase of the seismic reflection is pi/2 different from the phase of the seismic reflection at the top interface of the thin reservoir, i.e. the phase shift is pi/2. In the time domain, the phase shift amount is T/4, and T is the period of the seismic wave.
Step 3: quantitatively calibrating the position of the thin reservoir and constructing a graph: based on the quantitative relation between the thickness of the thin reservoir layer and the phase change, the spatial position of the thin reservoir layer is calibrated, and the accurate graph formation of the top surface structure is realized.
Thin reservoir locations are quantitatively calibrated. The phase shift amount and the thickness are in a linear negative correlation, the phase shift amount of which the thickness is towards 0 is-pi/2, and the time phase shift amount is-T/4; the phase shift amount equal to lambda/4 is 0, and the phase shift amount is T/4 (1-4 h/lambda). Therefore, the position of the seismic calibration thin reservoir is the peak position to be shifted downwards by T/4 (1-4 h/lambda), and the quantitative calibration of the top surface of the thin reservoir is realized.
Thin reservoir topside configuration description. Tracking the peak of the seismic phase, and calculating the thickness h=ka and k as constants by utilizing the proportional relation between the amplitude A and the thickness h, and further calculating the phase shift amount T/4 (1-4 h/lambda), wherein the time value of the top surface of the thin reservoir layer is the time value T of the peak plus the phase shift amount, namely t+T/4 (1-4 h/lambda), so that the accurate construction diagram of the top surface of the thin reservoir layer is realized.
Example 2
In a specific embodiment 2 of the present invention, a specific technical solution is described by taking a quantitative calibration of the earthquake of a thin reservoir in a CD area and an accurate graph of the top surface structure as an example.
In step 1, forward modeling simulates a thickness-dependent characteristic of the seismic reflection phase. The main problem faced by the thin reservoir seismic method description is that the seismic wavelength is far greater than the reservoir thickness, and the phenomenon of seismic reflection wave interference of the top and bottom of the thin reservoir occurs. The interference phenomenon of the thin reservoir can cause the change of the properties such as amplitude, phase and the like, and particularly the phase change directly affects the calibration and accurate description of the reservoir. To intuitively describe the phase change of the thin reservoir seismic reflection wave, a wedge-shaped seismic model is designed, and the forward modeling simulates the seismic phase characteristics changing along with the thickness of the thin reservoir. FIG. 2 is a plot of the phase change characteristics of a wedge model seismic wave equation forward modeling thin reservoir, with the dark portion being the wedge model (thickness 0- λ/4), on which is the reflection phase resulting from the wave equation forward modeling, and the upper curve of the plot is the maximum amplitude extracted along the peak. Forward results indicate that the amplitude is positively correlated with reservoir thickness. The peak of the phase gradually deviates upward from the top surface of the reflective layer as the thickness decreases, known as phase shift. When the thickness is equal to lambda/4, the phase shift amount is minimum, the peak of the reflection phase coincides with the top surface of the reflection layer, when the thickness is close to 0, the peak of the reflection phase deviates the top surface of the reflection layer to the maximum, and the thickness is in a linear negative correlation relationship.
In step 2, the relationship of the seismic reflection phase W (t) as a function of thickness h is mathematically derived. According to the linear negative correlation between the phase shift and the thickness, if the phase characteristics of the two points of which the thickness is approximately 0 and lambda/4 are obtained, the relation between the thickness and the phase shift can be quantitatively represented.
Under certain conditions of surrounding rock, the top interface seismic reflection of the thin reservoir is denoted as sin (ωt), the bottom interface seismic reflection of the thin reservoir is denoted as sin (ωt+φ), φ=4πh/λ, where ω is frequency, φ is the seismic wavelength when traveling in two passes. The seismic reflection phase W (t) =sin (ωt) -sin (ωt+Φ) =2cos (ωt+Φ/2) sin (- Φ/2).
When the thickness h=λ/4, W (t) =2cos (ωt+pi/2) sin (-pi/2) =2sin (ωt) is easily obtained. This indicates that the seismic reflection phase is consistent with the top interface seismic reflection of the thin reservoir.
When the thickness h tends to 0, a function limit of phi tends to 0 is calculated according to the relation between the thickness h and phi, wherein W (t) =2 cos (ωt+phi/2) sin (-phi/2) =2 cos (ωt) · (-phi/2) = - Φcos (ωt) =Φsin (ωt-pi/2). The phase of the seismic reflection is pi/2 different from the phase of the seismic reflection at the top interface of the thin reservoir, i.e. the phase shift is pi/2. In the time domain, the phase shift amount is T/4, and T is the period of the seismic wave.
According to mathematical deduction, the seismic reflection phase W (T) is in a negative correlation with the change of the thickness h (0-lambda/4), when the thickness h tends to 0, the phase shift amount is T/4, and when the thickness h is equal to lambda/4, the phase shift amount is 0.
In step 3, thin reservoir locations are quantitatively calibrated and configured as a map. And (3) conclusion from the step (2) that the phase shift amount and the thickness are in a linear negative correlation relationship, the phase shift amount of which the thickness is towards 0 is T/4, the phase shift amount of which the thickness is equal to lambda/4 is 0, and the phase shift amount of the seismic reflection of the thin reservoir is deduced to be T/4 (1-4 h/lambda). Therefore, the position of the seismic calibration thin reservoir is the peak position to be shifted downwards by T/4 (1-4 h/lambda), and the quantitative calibration of the top surface of the thin reservoir is realized. FIG. 3 is a thin reservoir quantitative calibration of a seismic section of the CD area. The thickness of the oil layer of the North-Qihe 45 well is 8 m, the top surface burial depth is 1281 m, the layer speed is 2670 m/s, the main frequency is 38 Hz, the wavelength lambda is 70 m, and the period T is 26 ms. From the phase shift T/4 (1-4 h/lambda), the phase shift is calculated to be 3.5 milliseconds, i.e., the reservoir top surface position is 3.5 milliseconds below the seismic peak. The quantitative calibration technology solves the problem that the top surface of the reservoir layer is not at the peak in the thin reservoir layer calibration in theory, and quantitatively calibrates the position of the top surface.
Thin reservoir topside configuration description. Li Guofa, wang Yajing, etc. (2014) thin interbed seismic slice interpretation, suggest that reservoirs can be detected within each composite view period, and that the amplitude attribute is positively correlated with reservoir thickness. Therefore, the peak of the seismic phase is tracked, a seismic reflection phase peak structure map can be formed (fig. 4), and the thickness h=ka, k is obtained as a constant (fig. 5) by using the proportional relation between the amplitude a and the thickness h. The phase shift T/4 (1-4 h/lambda) is further calculated, and the time value of the top surface of the thin reservoir is the time value of the peak plus the phase shift, i.e., t+T/4 (1-4 h/lambda), so that an accurate construction of the top surface of the thin reservoir is achieved (FIG. 6). As can be seen from fig. 4, the sand body runs north-west, the construction has features of south-to-north, the buried depth at the well point 1273 meters, 8 meters from the actual top surface of the reservoir; as can be seen from fig. 5, the sand body runs north and west, the thickness is thinned along the center of the river channel to two sides, and the thickness at the well point is 8 meters; as can be seen from FIG. 6, after the sand body is truly constructed into a graph, the structural characteristics change obviously, the axial north is constructed, the burial depth at the well point is 1281 m, which is the same as the actual top surface of the reservoir, the structural characteristics of the sand body top surface can be truly reflected, and the horizontal well can be better subjected to geological evaluation and design.
Example 3
In embodiment 2 of the present invention, the seismic quantitative calibration and top surface construction of a thin reservoir in the CB27 well region of the CD oilfield body are taken as an example. The well has four wells, CB27A-3, CB27A-5, and CB27A-6, and the target layer of the embodiment is the upper III 1 sand body of the building. In step 1, the four wells are respectively calibrated by synthetic seismic records, and the top surface of the calibrated reservoir is moved downwards relative to the wave crest, which is consistent with the forward conclusion of fig. 2, so that the calibration accuracy is proved. The phase shift amounts of CB27, CB27A-3, CB27A-5, CB27A-6 read after seismic calibration are 2.7 milliseconds, 3 milliseconds, 5.1 milliseconds and 4.5 milliseconds, respectively. FIG. 7 is a composite record of the calibration results for CB27, CB27A-3, CB27A-6, it being seen that the calibrated reservoir top surface is below the peak. In step 2, the phase shift of the top surface of the four-well reservoir is calculated by using a thin reservoir phase shift formula T/4 (1-4 h/lambda). The CB27 well zone reservoir has a layer velocity of 2700 m/s, a dominant frequency of 35 Hz, a wavelength λ of 77 m, and a period T of 28.6 milliseconds. CB27 reservoir thickness was 12m and the calculated phase shift was 2.69 milliseconds from the phase shift equation T/4 (1-4 h/λ). The reservoir thicknesses of the other three wells CB27A-3, CB27A-5 and CB27A-6 are 11 meters, 5.5 meters and 7.5 meters, respectively, and the calculated phase shift amounts are 3.06 milliseconds, 5.11 milliseconds and 4.55 milliseconds, respectively. The phase shift amount calculated by the method is matched with the actual calibration result as the phase shift amount error of the calibration reading is respectively 0.01 millisecond, 0.06 millisecond, 0.01 millisecond and 0.05 millisecond.
In step 2, the positive correlation between the amplitude a and the thickness h is used to find the thickness h=ka, k as a constant (fig. 8), the thicknesses of the target layers of the four wells CB27, CB27A-3, CB27A-5 and CB27A-6 calculated are respectively 12.1 meters, 10.7 meters, 5.4 meters and 7.5 meters, and the thicknesses of the reservoirs of the four wells are respectively 12 meters, 11 meters, 5.5 meters and 7.5 meters, and the calculated thicknesses are equivalent to the actual thicknesses. The peaks of the seismic phases are tracked, a structural diagram of the peaks of the seismic reflection phases is drawn by a traditional method (figure 9), the depths of the top surfaces of the four wells CB27, CB27A-3, CB27A-5 and CB27A-6 in figure 9 are 1397 meters, 1402.5 meters, 1376 meters and 1386.5 meters, and the depths of the top surfaces of the wells are 1401 meters, 1407 meters, 1383 meters and 1393.5 meters, and errors of 4 meters, 4.5 meters, 7 meters and 7 meters exist between the two. From the conclusion of the step 3, it is known that the time value of the top surface of the thin reservoir is the time value of the peak plus the phase shift, i.e., t+t/4 (1-4 h/λ), so that an accurate construction diagram of the top surface of the thin reservoir is realized (fig. 10), the depths of the top surface construction diagrams of the four wells in fig. 10 are 1401.1 meters, 1407.2 meters, 1383.1 meters and 1393.5 meters, respectively, and the errors of the actual drilling depths are 0.1 meters, 0.2 meters, 0.1 meters and 0 meters, respectively, which are consistent with the actual drilling depths (table 1). In fig. 9, the layer sand body of the land 27 well is a relatively uniform and gentle monoclinic structure inclined from west to east. With the proprietary method, the western section of the fig. 10 construction becomes steeper and the middle section is a flatter construction after time shift and reservoir thickness correction. The structure of FIG. 10 is matched with drilling data, can accurately reflect the structural characteristics of the top surface of a reservoir, and can further guide oil reservoir evaluation and horizontal well design.
TABLE 1 CB27 well Ngs III 1 depth at well points of sand body seismic reflection phase peak structure map and drilling actual depth comparison table
| Well name | Depth of top surface (m) | Depth of bottom surface (m) | Traditional method (m) | Patent method (m) |
| cb27 | 1401 | 1413 | 1397 | 1401.1 |
| cb27a-3 | 1407 | 1418 | 1402.5 | 1407.2 |
| cb27a-5 | 1383 | 1388.5 | 1376 | 1383.1 |
| cb27a-6 | 1393.5 | 1401 | 1386.5 | 1393.5 |
According to the method, the phase characteristics of the seismic reflection of the thin reservoir layer along with the thickness change are analyzed through forward modeling, the peak of the phase is definitely deviated from the top surface of the reservoir layer upwards gradually along with the thickness reduction, and the phase shift quantity and the thickness are in a linear negative correlation relation; mathematically deriving a quantitative relationship between the thickness h of the thin reservoir and the variation of the seismic reflection phase W (T), the thickness being from lambda/4 to 0, the amount of phase shift being from 0 to T/4; the position of the seismic calibration thin reservoir is the peak position shifted downwards by T/4 (1-4 h/lambda), so that the quantitative calibration of the top surface of the thin reservoir is realized; and calculating the thickness by utilizing the proportional relation between the amplitude A and the thickness h, and obtaining the accurate position of the top surface of the reservoir by adding the time value of the wave crest and the phase shift amount, thereby realizing the accurate construction diagram of the top surface of the thin reservoir.
Finally, it should be noted that: the foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but although the present invention has been described in detail with reference to the foregoing embodiment, it will be apparent to those skilled in the art that modifications may be made to the technical solution described in the foregoing embodiment, or equivalents may be substituted for some of the technical features thereof. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Other than the technical features described in the specification, all are known to those skilled in the art.
Claims (8)
1. The method for accurately mapping the thin reservoir earthquake quantitative calibration and the top surface structure is characterized by comprising the following steps:
step 1: forward modeling the characteristic that the seismic reflection phase changes along with the thickness, namely forward modeling the seismic reflection of a thin reservoir, and analyzing the characteristic that the phase changes of the top-bottom interference of the thin reservoir;
step 2: mathematically deriving a relationship of the seismic reflection phase with the thickness variation, i.e., mathematically deriving a quantitative relationship of the thickness of the thin reservoir with the seismic reflection phase variation;
step 3: the position of the thin reservoir is calibrated quantitatively, and the structure is formed into a graph, namely, the spatial position of the thin reservoir is calibrated based on the quantitative relation between the thickness of the thin reservoir and the phase change, so that the accurate formation of the top surface structure is realized.
2. The method for accurately mapping the thin reservoir seismic quantitative calibration and the top surface structure according to claim 1, wherein in the step 1, forward modeling is performed on the characteristic that the seismic reflection phase changes along with the thickness, and the thin reservoir is a reservoir with the thickness less than lambda/4 seismic wavelength; and analyzing the relation between the phase of the seismic reflection wave of the thin reservoir and the thickness h of the reservoir, wherein the peak of the phase gradually deviates upwards from the top surface of the reflection layer along with the thickness reduction, which is called phase shift, and the phase shift quantity and the thickness are in a linear negative correlation relation.
3. The method for quantitative calibration and accurate mapping of a top surface structure of a thin reservoir seismic reflection according to claim 1, wherein in the step 2, the relation of the thickness and the phase shift amount can be quantitatively represented by mathematically deducing the relation of the seismic reflection phase W (t) with the thickness h, and obtaining the phase characteristics of the two points that the thickness tends to 0 and lambda/4 according to the linear negative correlation of the phase shift amount and the thickness.
4. The method for accurately mapping seismic quantitative calibration and top surface construction of thin reservoirs according to claim 3, wherein in the step 2, when the relation of the seismic reflection phase W (t) with the thickness h is mathematically deduced, under the condition that the surrounding rock is certain, the top-interface seismic reflection of the thin reservoirs is denoted as sin (ωt), and the bottom-interface seismic reflection of the thin reservoirs is denoted as:
sin(ωt+φ)，φ＝4πh/λ，
wherein ω is frequency, φ is the seismic wavelength when traveling in two passes;
phase: w (t) =sin (ωt) -sin (ωt+Φ) =2cos (ωt+Φ/2) sin (- Φ/2).
5. The method for quantitative calibration and accurate mapping of a top surface structure of a thin reservoir according to claim 4, wherein in step 2, when the thickness h=λ/4, W (t) =2 cos (ωt+pi/2) sin (-pi/2) =2 sin (ωt), the seismic reflection phase is consistent with the top surface seismic reflection of the thin reservoir.
6. The method for accurately mapping seismic quantitative calibration and top surface construction of a thin reservoir according to claim 5, wherein in step 2, when the thickness h tends to 0, a function limit of phi tends to 0 is calculated according to the relation between the thickness h and phi, wherein W (t) =2cos (ωt+phi/2) sin (-phi/2) =2cos (ωt) · (-phi/2) = - Φcos (ωt) =Φsin (ωt-pi/2); the phase difference between the seismic reflection phase and the top interface seismic reflection phase of the thin reservoir is pi/2, namely the phase shift is pi/2; in the time domain, the phase shift amount is T/4, and T is the period of the seismic wave.
7. The method for quantitatively calibrating the earthquake of the thin reservoir and accurately mapping the top surface structure according to claim 1, wherein in the step 3, the position of the thin reservoir is quantitatively calibrated, the phase shift amount and the thickness are in a linear negative correlation, the phase shift amount of which the thickness is approximately 0 is-pi/2, and the time phase shift amount is-T/4; the phase shift amount with the thickness equal to lambda/4 is 0, and the phase shift amount is T/4 (1-4 h/lambda); therefore, the position of the seismic calibration thin reservoir is the peak position to be shifted downwards by T/4 (1-4 h/lambda), and the quantitative calibration of the top surface of the thin reservoir is realized.
8. The method for accurately mapping the thin reservoir seismic quantitative calibration and the top surface structure according to claim 7, wherein in the step 3, the thin reservoir top surface structure description is performed, the peak of the seismic phase is tracked, the proportional relation between the amplitude a and the thickness h is utilized to obtain the thickness h=ka, k as a constant, the phase shift T/4 (1-4 h/λ) is further obtained, the time value of the thin reservoir top surface is the time value of the peak plus the phase shift, namely t+t/4 (1-4 h/λ), and therefore the accurate mapping of the thin reservoir top surface is realized.
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