A low-frequency model establishment method based on seismic geologic information constraint

Abstract

The application belongs to the technical field of seismic exploration, and discloses a low-frequency model establishing method based on seismic geological information constraint, which comprises the following steps: S1, a first low-frequency model is established by a compaction trend correction method; a second low-frequency model is established by a seismic attribute constraint method; S2, a low-frequency component in the first low-frequency model is extracted as a very low-frequency background trend, and a frequency component higher than the very low-frequency in the second low-frequency model is extracted as a medium-high frequency theme part; S3, the very low-frequency background trend and the medium-high frequency theme part in step S2 are fused in a frequency domain, and a low-frequency model based on seismic geological information constraint is obtained. The low-frequency model established by the application is more in line with the real change rule of the underground formation, and can better solve the problem of low-frequency model establishment of a region with large vertical structural height difference and fast lateral facies change. The application is suitable for a region with the geological characteristics of large vertical structural height difference and fast lateral facies change.

Description

Technical Field

[0001] This invention belongs to the field of seismic exploration technology, specifically a method for establishing a low-frequency model based on seismic geological information constraints. Background Technology

[0002] Seismic inversion technology is one of the important means to characterize reservoir features and distribution range in oil and gas exploration and development. Its results are controlled by multiple factors, including seismic data wavelets, low-frequency models, frequency band range, and inversion methods. Deterministic inversion, essentially based on seismic traces, is widely recognized as one of the most reliable inversion methods. Due to limitations in field seismic data acquisition conditions, signals below 10 Hz in conventional seismic data are suppressed, resulting in the loss of low-frequency information. However, the seismic data used in seismic inversion must be full-bandwidth; therefore, external supplementation of the missing low-frequency information is necessary during deterministic inversion. Since low-frequency models can reduce wavelet sidelobe effects and enhance the spatial identification ability of geological bodies, establishing a reasonable low-frequency model is crucial for improving inversion accuracy.

[0003] Conventional low-frequency model establishment methods mainly utilize mathematical methods such as distance weighting, global or local kriging to interpolate and extrapolate logging curves to obtain low-frequency models. This method is limited by the number of wells, planar distribution, and interpolation algorithms. The established low-frequency models suffer from severe well-circling phenomenon, do not conform to geological change patterns, and have significant uncertainties in the results. Summary of the Invention

[0004] The purpose of this invention is to provide a method for establishing a low-frequency model based on seismic geological information constraints, providing a stable and reliable phase control model for thin reservoir prediction through geostatistical inversion, and providing favorable technical support for the exploration and development of Jurassic thin sandstone oil and gas reservoirs.

[0005] To achieve the above objectives, the present invention employs the following technical methods: A method for establishing a low-frequency model based on seismic geological information constraints includes the following steps: S1. Establish the first low-frequency model using the compaction trend correction method; establish the second low-frequency model using the seismic attribute constraint method; S2. Extract the low-frequency components from the first low-frequency model as the very low-frequency background trend, and extract the frequency components higher than the very low frequency from the second low-frequency model as the mid-to-high frequency theme components; S3. The very low frequency background trend and the medium and high frequency theme parts in step S2 are fused in the frequency domain to obtain the low frequency model based on seismic geological information constraints.

[0006] As a limitation: the specific method for establishing the first low-frequency model using the compaction trend correction method in step S1 is as follows: the compaction trend relationship of the impedance is obtained by fitting the longitudinal wave impedance of the mudstone of the entire well section of the calibrated well with time intersection; the impedance volume with compaction trend background and the compaction trend curve at the well point are calculated according to the compaction trend relationship of the impedance; the compaction trend curve at the well point is obtained by subtracting the compaction trend curve at the well point from the actual longitudinal wave impedance curve above the well; the decompaction trend curve above the well is used to establish the decompaction trend volume through inter-well interpolation; the compaction trend volume and the decompaction trend volume are added together to obtain the first low-frequency model.

[0007] As a further limitation: the specific method for establishing the second low-frequency model using the seismic attribute constraint method in step S1 is as follows: comprehensively analyze well logging facies, core facies, and seismic facies, and establish sample sets of three sedimentary microfacies categories for drilled wells: tributary channels, channel-bay, and tributary bay; extract amplitude, frequency, waveform clustering, and instantaneous attributes from the sample wells in the sample sets of the three sedimentary microfacies categories; select relevant attributes that match the drilled wells by comparing and analyzing the amplitude, frequency, waveform clustering, and instantaneous attributes of the sample wells with those of the drilled wells; obtain the comprehensive seismic attributes that match the sample wells and micro-paleogeography to the highest degree by conducting sample-supervised surface attribute pattern recognition; and establish the second low-frequency model using the well-to-well interpolation method under the constraint of the comprehensive seismic attributes.

[0008] The beneficial effects achieved by this invention, due to the adoption of the above-described solution, compared with the prior art, are as follows: (1) The present invention provides a method for establishing a low-frequency model based on seismic geological information constraints. The first low-frequency model established by the compaction trend correction method can effectively eliminate the influence of large structural elevation differences. (2) The present invention provides a method for establishing a low-frequency model based on seismic geological information constraints. By carrying out sample-supervised surface attribute pattern recognition, the comprehensive seismic attribute with the highest matching degree with sample wells and micro-paleomorphology is obtained, which greatly improves the accuracy of using a single attribute to reflect the characteristics of sedimentary facies zone changes and provides a high-precision constraint attribute for seismic attribute constraint modeling. (3) The present invention provides a method for establishing a low-frequency model based on seismic geological information constraints. The first low-frequency model is established by the compaction trend correction method and the second low-frequency model is established by the seismic attribute constraint method. The frequency components are reasonably selected and frequency domain fusion is performed. The resulting low-frequency model trend is more consistent with the real change law of underground strata. It can better solve the problem of establishing a low-frequency model with large vertical structural height difference and rapid horizontal facies zone change.

[0009] This invention is applicable to areas with geological characteristics of large vertical structural elevation differences and rapid changes in facies zones in the lateral direction. Attached Figure Description

[0010] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0011] Figure 1 This is a flowchart of an embodiment of the present invention; Figure 2 This is a flowchart illustrating the process of establishing a first low-frequency model using the compaction trend correction method according to an embodiment of the present invention. Figure 3 This is a flowchart illustrating the process of establishing a second low-frequency model using the seismic attribute constraint method in an embodiment of the present invention. Figure 4 This is an impedance profile of the first low-frequency model established by the compaction trend correction method in this embodiment of the invention. Figure 5 This is the impedance profile of the second low-frequency model established by the seismic attribute constraint method in this embodiment of the invention. Figure 6 This is an impedance profile of a low-frequency model constrained by seismic geological information in an embodiment of the present invention. Figure 7 A comparison diagram of the low-frequency deterministic inversion results supplemented to the conventional well interpolation impedance model and the low-frequency deterministic inversion results supplemented to the low-frequency model based on seismic geological information constraints according to the embodiment of the present invention. Detailed Implementation

[0012] The present invention will be further described below with reference to the embodiments. However, those skilled in the art should understand that the present invention is not limited to the following embodiments. Any improvements and equivalent changes made based on the specific embodiments of the present invention are within the scope of protection of the claims of the present invention.

[0013] Example: A method for establishing a low-frequency model based on seismic geological information constraints A method for establishing a low-frequency model based on seismic geological information constraints, the flowchart of which is as follows: Figure 1 As shown, it includes the following steps: S1. The first low-frequency model is established using the compaction trend correction method. The impedance profile of the first low-frequency model is shown below. Figure 4 As shown; a second low-frequency model is established using the seismic attribute constraint method, and the impedance profile of the second low-frequency model is shown below. Figure 5 As shown; S2. Extract the 0-3Hz frequency components from the first low-frequency model as the very low-frequency background trend, and extract the frequency components above 3Hz from the second low-frequency model as the mid-to-high frequency theme part. S3. The very low frequency background trend and the mid-to-high frequency theme components from step S2 are fused in the frequency domain to obtain the low-frequency model constrained by seismic geological information. The impedance profile of the low-frequency model is shown below. Figure 6 As shown.

[0014] The flowchart for establishing the first low-frequency model using the compaction trend correction method in step S1 is as follows: Figure 2 As shown, the specific method is as follows: The compaction trend relationship of the impedance is obtained by fitting the longitudinal wave impedance of the mudstone in the entire well section of the calibrated well with time cross-plotting: y = ax + b, where y represents impedance, x represents time, and a and b are constants; Based on the compaction trend relationship of the impedance, the impedance body with compaction trend background and the compaction trend curve at the well point are calculated; The compaction trend curve at the well point is obtained by subtracting the compaction trend curve at the well point from the actual longitudinal wave impedance curve above the well; The decompaction trend body is established by inter-well interpolation of the decompaction trend curve above the well; The first low-frequency model is obtained by adding the compaction trend body and the decompaction trend body.

[0015] The flowchart for establishing the second low-frequency model using the seismic attribute constraint method in step S1 is as follows: Figure 3 As shown, the specific method is as follows: A comprehensive analysis of well logging facies, core facies, and seismic facies is conducted to establish three sedimentary microfacies sample sets for drilled wells: tributary channels, channel-bay, and tributary bay. Amplitude, frequency, waveform clustering, and instantaneous attributes of the sample wells in these sample sets are extracted. By comparing the amplitude, frequency, waveform clustering, and instantaneous attributes of the sample wells with those of drilled wells, the following attributes are selected: spectral clustering, sum of autocorrelation, second derivative of envelope, median filtered reflection intensity, root mean square amplitude, and 9Hz single-frequency amplitude. Supervised surface attribute pattern recognition is performed to obtain the comprehensive seismic attributes that best match the sample wells and paleogeomorphology. Under the constraint of the comprehensive seismic attributes, a second low-frequency model is established using inter-well interpolation.

[0016] The study area in this embodiment is the Putaogou-Pubei area, located in the western arcuate zone of the Taipei Depression in the Turpan-Hami Basin. The target layer, the Jurassic Qiketai Formation, is buried at a depth of 3000-3800m. The bottom boundary of the Qiketai Formation exhibits a "western convex, eastern concave" structural feature, with a maximum elevation difference of 800 meters. The P-wave impedance of mudstone in the same stratum increases significantly with depth at different burial depths. The target stratum is a braided river delta front subfacies deposit with rapid facies zoning. A comparison is shown between the planar plot of the low-frequency deterministic inversion result supplemented by the conventional well interpolation impedance model and the planar plot of the low-frequency deterministic inversion result supplemented by the low-frequency model based on seismic geological information constraints in this embodiment of the invention. Figure 7 As shown in the figure, the low-frequency model established in this embodiment can effectively eliminate the influence of large vertical structural elevation differences and rapid changes in facies zones in the lateral direction, improve the consistency between the planar variation trend of the deterministic inversion results and geological understanding, make the inversion results more reliable, and increase the drilling consistency rate from 65% to 75%.

Claims

1. A method for establishing a low-frequency model based on seismic geological information constraints, characterized in that, Includes the following steps: S1. Establish a first low-frequency model using the compaction trend correction method; establish a second low-frequency model using the seismic attribute constraint method; the first low-frequency model and the second low-frequency model are established independently during the modeling process; S2. Extract the low-frequency components from the first low-frequency model as the very low-frequency background trend, and extract the frequency components higher than the very low frequency from the second low-frequency model as the mid-to-high frequency theme part; the low-frequency components are 0-3Hz, and the very low-frequency components are 3Hz. S3. The very low frequency background trend and the medium and high frequency theme parts in step S2 are fused in the frequency domain to obtain the low frequency model based on seismic geological information constraints. The specific method for establishing the first low-frequency model in step S1 using the compaction trend correction method is as follows: the longitudinal wave impedance of the mudstone in the entire well section of the calibrated well is fitted with time intersection to obtain the compaction trend relationship of the impedance; the impedance body with compaction trend background and the compaction trend curve at the well point are calculated based on the compaction trend relationship of the impedance. The decompaction trend curve at the well point is obtained by subtracting the actual longitudinal wave impedance curve at the well point from the actual longitudinal wave impedance curve at the well point; the decompaction trend body is established by inter-well interpolation of the decompaction trend curve at the well point; the first low-frequency model is obtained by adding the compaction trend body and the decompaction trend body.

2. The method for establishing a low-frequency model based on seismic geological information constraints according to claim 1, characterized in that, The specific method for establishing the second low-frequency model using the seismic attribute constraint method in step S1 is as follows: comprehensively analyze well logging facies, core facies, and seismic facies, and establish sample sets of three types of sedimentary microfacies for the drilled wells: tributary channels, channel-bay, and tributary bay; extract amplitude, frequency, waveform clustering, and instantaneous attributes of the sample wells in the sample sets of the three types of sedimentary microfacies; and select the relevant attributes that match the drilled wells by comparing and analyzing the amplitude, frequency, waveform clustering, and instantaneous attributes of the sample wells with those of the drilled wells. By conducting sample-supervised surface attribute pattern recognition, the comprehensive seismic attribute with the highest matching degree with the sample wells and micro-paleomorphology is obtained; under the constraint of the comprehensive seismic attribute, the inter-well interpolation method is used to establish a second low-frequency model.

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