A reservoir fluid identification method based on post-stack seismic

Abstract

The present invention belongs to the technical field of oilfield development, and specifically relates to a method for identifying reservoir fluid based on post-stack seismic. The method comprises the following steps: through fine calibration of well seismic data, reservoir inversion description is carried out to explain the spatial distribution range of river channel sand bodies; spectral decomposition of post-stack seismic data is performed to obtain data of different seismic frequencies; frequency fitting is performed in the time-frequency domain; the plane distribution of attenuation gradients is extracted along the layer; and the oil and gas distribution range inside the reservoir is predicted. The method of the present invention can effectively predict the oil content of river phase sand bodies, qualitatively predict the plane distribution range of oil-bearing sand bodies, provide a basis for the deployment of shallow river phase marginal sand body wells, and is conducive to the efficient development of such oil reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield development, and in particular relates to a reservoir fluid identification method based on post-stack seismic. Background Art

[0002] The shallow oil and gas reservoirs in Shengli offshore oilfield are channel sand bodies of Guantao Formation, which are scattered in the plane, mostly potato-shaped or strip-shaped. The oil layer is single in the vertical direction, mostly 1-2 layers, and the single layer thickness is thin, mostly 3-5m. The relationship of the internal superposition of sand bodies is not easy to identify. Multiple sets of sand bodies have a single reflection axis in seismic. At the same time, the reservoir fluid is complex, and different sand bodies have different oil-water interfaces, making it difficult to identify the oil content of the reservoir.

[0003] Chinese invention patent CN107966731B discloses a method for identifying the overlapping areas of river facies sand bodies based on seismic waveform structural attributes, and the method steps are as follows: Step 1: Prepare data, prepare geological data, seismic data and logging data; Step 2: Select the target layer of a period time window, and extract the waveform structural attributes of integral, statistical and differential categories; Step 3: Identify the thicker sand body distribution area through the integral attribute, and find the thicker sand body distribution area; Step 4: Identify the overlapping areas of sand bodies by means of statistical attributes. If there are overlapping sand bodies in the thick sand body area, some lines or ties will appear in the thick sand body area on the kurtosis, coefficient of variation and skewness attribute slices, and these lines and ties are mostly reflected in the overlapping areas of sand bodies; Step 5: Verify and identify the overlapping areas of sand bodies again based on the differential attributes, and verify and identify the lines or ties formed by the overlapping of river sand bodies again through the composite envelope difference, half-time curvature difference and peak-to-valley kurtosis difference attribute slices, and perform joint analysis with the statistical attribute slices to determine the overlapping areas of the river channels. This method proposes seismic waveform structural attributes, has a clear calculation formula, and is easy to implement. It proposes to extract seismic waveform structural attributes in one cycle, with a fast calculation speed. Each seismic waveform structural attribute extracted in one cycle has a very obvious advantage in predicting and identifying the superimposed area of ​​river phase reservoir sand bodies by using the waveform structural attributes extracted in one cycle.

[0004] Chinese invention patent CN105093303B discloses a seismic interpretation method for fine characterization of discontinuous boundaries of fluvial sand bodies, which includes the following steps: 1) According to the positive rhythmic sedimentary characteristics of fluvial sand bodies, combined with the requirements of subsequent attribute analysis for attribute extraction time window, the sand body envelope method is used to interpret the structure of the sand body unit; 2) Ant tracking attributes and curvature attributes are extracted for the target reservoir segment; 3) Amplitude plane attributes, curvature plane attributes and ant tracking plane attributes are extracted with the top and bottom of the interpreted sand body envelope as the time window; 4) The curvature plane attributes and ant tracking plane attributes of the seismic profile are taken for comparative analysis to determine the discontinuous boundaries of the sand bodies; 5) Amplitude-type attributes are deduced by longitudinal slicing to assist in determining the discontinuous boundaries caused by the longitudinal superposition of sand bodies and to divide the sand body depositional periods; 6) The judgment result of the discontinuous boundary plane obtained in step 4) and the conclusion of the longitudinal sand body period division obtained in step 5) are used to jointly assist in the establishment of sedimentary facies recognition.

[0005] For this type of reservoir well deployment, the accuracy of reservoir prediction description is particularly important, especially the prediction of sand body fluid properties. However, there is no method for identifying reservoir fluids using post-stack seismic. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for identifying reservoir fluids based on post-stack seismic. By clarifying the seismic spectrum characteristics of different fluids in marginal sand body reservoirs, the present invention can effectively predict the oil content of marginal sand bodies and provide a basis for the deployment of shallow river phase marginal sand body wells.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a reservoir fluid identification method based on post-stack seismic, which comprises the following steps:

[0009] Step 1. Carry out reservoir inversion description through fine calibration of well seismic data to explain the spatial distribution range of river channel sand bodies;

[0010] Step 2. Perform spectral decomposition on the post-stack earthquakes to obtain data of different earthquake frequencies;

[0011] Step 3. Perform frequency fitting in the time-frequency domain;

[0012] Step 4. Extract the attenuation gradient plane distribution along the layer;

[0013] Step 5. Predict the oil and gas distribution range inside the reservoir.

[0014] Furthermore, the method also includes identifying the target reservoir type and selecting a shallow fluvial sandstone reservoir.

[0015] Furthermore, in step 1, the reservoir inversion description includes: fine synthetic record calibration, determining the logging-seismic time-depth relationship, conducting reservoir seismic response characteristic analysis, determining the seismic characteristics of sandstone reservoirs, performing logging-constrained inversion, and quantitatively describing the spatial distribution range of the reservoir.

[0016] Furthermore, in step 2, the seismic spectrum decomposition includes: using the spectrum decomposition technology of S transform to obtain a frequency domain time-frequency four-dimensional data volume.

[0017] Furthermore, in step 3, according to the spatial distribution of the sand body determined by reservoir inversion, the seismic spectrum of the strata overlying the sand body, the seismic spectrum of the sand body interior, and the seismic spectrum of the strata underlying the sand body are extracted respectively.

[0018] Furthermore, according to the thickness and spatial position of the sand body predicted by reservoir inversion, the corresponding seismic time window is selected to perform seismic spectrum of the overlying strata, internal strata, and underlying strata of the sand body, and frequency attenuation fitting is performed in the time-frequency domain.

[0019] Furthermore, in step 4, based on the frequency attenuation data calculated in step 3, the attenuation gradients of the seismic spectrum inside the reservoir and the seismic spectrum of the overlying strata are calculated respectively, and the attenuation gradient of the seismic spectrum of the underlying strata of the sand body relative to the seismic spectrum inside the reservoir is extracted, and the planar distribution of the attenuation gradient is extracted along the layer.

[0020] Furthermore, in step 5, according to the reservoir plane attenuation gradient obtained in step 4, the completed drilling test data is analyzed to determine the attenuation gradient range of different fluids, and according to the determined fluid attenuation threshold value, the plane distribution of the oil-bearing sand body is qualitatively described.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The method of the present invention is applicable to shallow fluvial sandstone reservoirs, can effectively predict the oil content of fluvial sand bodies, and qualitatively predict the plane distribution range of oil-bearing sand bodies, providing a basis for the deployment of shallow fluvial marginal sand body wells, and is conducive to the efficient development of such oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 This is a flow chart of a method for identifying reservoir fluid based on post-stack seismic according to a specific embodiment of the present invention;

[0025] Figure 2 It is a seismic spectrum analysis diagram of the overlying, internal and underlying strata of the sand body according to a specific embodiment of the present invention;

[0026] Figure 3 A comparison diagram of the frequency attenuation profile and the actual drilling logging according to a specific embodiment of the present invention;

[0027] Figure 4 This is a fluid plane distribution diagram predicted by the method described in a specific embodiment of the present invention, wherein the dotted line represents the oil distribution. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0030] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0031] Example 1

[0032] like Figure 1 As shown, the post-stack seismic reservoir fluid identification method comprises the following steps:

[0033] Step 1. Through fine calibration of well seismic data, reservoir inversion description is carried out to explain the spatial distribution range of the channel sand body; reservoir inversion description includes: fine synthetic record calibration, determination of the time-depth relationship of well logging seismic data, analysis of reservoir seismic response characteristics, determination of the seismic characteristics of sandstone reservoirs, logging constrained inversion, and quantitative description of the spatial distribution range of the reservoir.

[0034] Step 2. Perform spectral decomposition on the post-stack seismic data to obtain data of different seismic frequencies: Seismic spectrum decomposition includes: using the spectrum decomposition technology of S transform to obtain a frequency domain time-frequency four-dimensional data volume.

[0035] Step 3. Perform frequency fitting in the time-frequency domain:

[0036] According to the spatial distribution of sand bodies determined by reservoir inversion, the seismic spectra of the strata overlying the sand bodies, the seismic spectra of the interior of the sand bodies, and the seismic spectra of the strata underlying the sand bodies are extracted respectively; according to the thickness and spatial position of the sand bodies predicted by reservoir inversion, the corresponding seismic time window is selected to perform seismic spectra of the strata overlying, internal, and underlying the sand bodies, and frequency attenuation fitting is performed in the time-frequency domain.

[0037] Step 4. According to the frequency attenuation data calculated in step 3, respectively calculate the attenuation gradients of the seismic spectrum inside the reservoir and the seismic spectrum of the overlying strata, the attenuation gradient of the seismic spectrum of the underlying strata of the sand body relative to the seismic spectrum inside the reservoir, and extract the planar distribution of the attenuation gradient along the layer;

[0038] Step 5. According to the reservoir plane attenuation gradient obtained in step 4, analyze the completed drilling test data, determine the attenuation gradient range of different fluids, and qualitatively describe the plane distribution of the oil-bearing sand body according to the determined fluid attenuation threshold value.

[0039] Example 2

[0040] The reservoir fluid identification method based on post-stack seismic data described in Example 1 was applied to Block 18 of Chengbei in a certain oil reservoir.

[0041] The seismic spectrum of the overlying, internal and underlying strata of the oil reservoir sand body is as follows: Figure 2 As shown; the comparison between the frequency attenuation profile and the actual drilling logging is shown in Figure 3 The qualitative description of the plane distribution of the obtained oil-bearing sand body is as follows Figure 4 On this basis, 4 development wells were deployed, including 3 horizontal wells, with an average daily oil production of 49 tons and a new annual production capacity of 45,000 tons, which brought huge economic benefits.

[0042] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A reservoir fluid identification method based on post-stack seismic, characterized in that: The following steps are involved: Step 1. Carry out reservoir inversion description through fine calibration of well seismic data to explain the spatial distribution range of river channel sand bodies; Step 2. Perform spectral decomposition on the post-stack earthquakes to obtain data of different earthquake frequencies; Step 3. Perform frequency fitting in the time-frequency domain; Step 4. Extract the attenuation gradient plane distribution along the layer; Step 5. Predict the oil and gas distribution range inside the reservoir; The method further includes identifying the target reservoir type and selecting a shallow fluvial facies sandstone reservoir; In step 1, reservoir inversion description includes: fine synthetic record calibration, determination of logging-seismic time-depth relationship, reservoir seismic response characteristic analysis, determination of sandstone reservoir seismic characteristics, logging-constrained inversion, and quantitative description of reservoir spatial distribution range; In step 2, the seismic spectrum decomposition includes: using the spectrum decomposition technology of S transform to obtain a frequency domain time-frequency four-dimensional data volume; In step 3, according to the spatial distribution of the sand body determined by reservoir inversion, the seismic spectrum of the strata overlying the sand body, the seismic spectrum of the sand body interior, and the seismic spectrum of the strata underlying the sand body are extracted respectively; According to the sand body thickness and spatial position predicted by reservoir inversion, the corresponding seismic time window is selected to perform seismic spectrum analysis on the overlying, internal and underlying strata of the sand body, and frequency attenuation fitting is performed in the time-frequency domain; In step 4, according to the frequency attenuation data calculated in step 3, the attenuation gradients of the seismic spectrum inside the reservoir and the seismic spectrum of the overlying strata are calculated respectively, and the attenuation gradient of the seismic spectrum of the underlying strata of the sand body relative to the seismic spectrum inside the reservoir is extracted along the layer. In step 5, according to the reservoir plane attenuation gradient obtained in step 4, the completed drilling test data is analyzed to determine the attenuation gradient range of different fluids, and according to the determined fluid attenuation threshold value, the plane distribution of the oil-bearing sand body is qualitatively described.

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