Accurate delineation method of sand-mud transition zone in uranium reservoir based on 3D seismic velocity inversion

Abstract

The present invention relates to a method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion, comprising the steps of positioning and calibrating the uranium reservoir based on well seismic data, implementing structural interpretation of the target layer and constructing an initial inversion model, implementing high-resolution velocity inversion to obtain a velocity body and quality control, filtering the velocity body to obtain a low-frequency velocity body, maximizing the dominant velocity value of the ore-bearing sand-mud transition zone, obtaining a body characterizing the sand-mud transition zone attribute, and delineating the sand-mud transition zone. This method achieves a three-dimensional depiction of the sand-mud transition zone in full three-dimensional space; it can analyze the spatial configuration relationship between the ore body and the sand-mud transition zone, thereby facilitating the summary of the corresponding mineralization laws and mineralization-controlling factors; the sand-mud transition zone finally delineated is of great significance for the comprehensive analysis of the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone, and provides strong technical support for enriching the overall mineralization theory of sandstone-type uranium deposits and establishing prospecting models.

Description

Technical Field

[0001] The present invention belongs to the technical field of sandstone-type uranium mine exploration, and specifically relates to a new method for three-dimensional stereoscopic characterization of the sand-mud transition zone of a uranium reservoir based on a three-dimensional seismic velocity inversion method, and particularly relates to a method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion. Background Art

[0002] Typically, stable interlayers develop at both the top and bottom of uranium reservoirs, forming a "mud-sand-mud" structure. The interlayers are typically mudstone, silty mudstone, or argillaceous siltstone. Stable interlayers facilitate the long-term, stable migration of uranium- and oxygen-bearing fluids within the sandstone, contributing to the continued mineralization process. Therefore, sandstone-type uranium deposits are mostly formed in the sand-mud transition zone of the target reservoir.

[0003] Studies have found that sandstone-type uranium deposits are often found in sand bodies with interlayer structures such as "mud-sand-mud", especially in the sand-mud transition zone in the reservoir. The prior art discloses a uranium mineralization geological feature and regional mineralization law in the northeastern part of the Ordos Basin, and concludes that uranium mineralization in this area is mostly distributed in the sand body thickness thinning zone and the sand body edge phase change area. This is mainly due to the change in the sedimentary environment in the area, which has slowed down the water flow rate and increased the mud content here. Moreover, with the increase of organic matter, uranium ore is easy to precipitate and enrich into mineralization here. In summary, it can be concluded that the sand-mud transition zone in the sandstone-type uranium reservoir with a "mud-sand-mud" structure is one of the favorable areas for sandstone-type uranium mineralization. Therefore, how to achieve a three-dimensional depiction of the sand-mud transition zone in the uranium reservoir and accurately delineate it will provide important reference and practical significance for the prospecting of sandstone-type uranium deposits.

[0004] Currently, there is limited research on the precise delineation of the sand-mud transition zone in uranium reservoirs. The main methods include core sampling, tomographic logging, logging curve analysis, wave impedance analysis, and interval velocity calculation. Regarding core sampling, in 2016, Zhang Pingping published a technique for inverting sensitive factors for mid- to deep-layer reservoirs based on core testing. This technique combines core testing results with logging data from wells already drilled in the target area, using mudstone as the base value to calculate the percentage difference in sand and mud between different intervals. In 2023, Yuan Yuxuan published a method for establishing a high-precision sequence stratigraphic framework in marine fine-grained sedimentary rocks using high-resolution sequence stratigraphy. The method uses detailed core descriptions and high-precision thin-section analysis to determine the reservoir's lithofacies type and sand-mudstone content. Regarding tomographic logging, in 2023, Liu Liling published an inversion method using a joint iterative reconstruction method based on first arrival information from multiple wells. This method uses high-resolution geological images and allows direct observation of the rock composition around the wellbore wall, thereby providing a better understanding of the sand-mudstone content of the underground reservoir. Regarding well logging analysis, in 2015, Qu Lu published a method for lithologic identification and classification by analyzing the logging response characteristics of different lithologies in different boreholes, thereby indirectly assisting in the identification of sand-mud transition zones within reservoirs. In 2016, Dong Zhen published a method for establishing a favorable logging identification model using quantitative simulation of favorable lithologic combinations. This method analyzes the sand and mud content of reservoirs by analyzing the characteristics of favorable lithologic combinations, rationally classifying lithologic types based on well logging data from the work area, and quantitatively simulating lithologic combination logging. Regarding wave impedance analysis, in 2017, Peng Jun published a method for deriving lithologic impedance from a mathematical transformation of longitudinal and shear wave impedances. This method not only effectively identifies sand and mud, providing a valuable reference for reservoir prediction, but also allows for the effective differentiation of overlapping sand bodies. In 2020, Li Ziwei published preliminary research results on the differences in wave impedance between ore-bearing sand bodies and surrounding rocks in sandstone-type uranium deposits. The method successfully distinguished the ore-bearing sand bodies from the surrounding rocks by combining the elastic parameters of the ore-bearing sand bodies and surrounding rocks with differences in wave impedance parameters. Regarding the layer velocity calculation method, Qin Fengrong disclosed a method in 1995 to calculate the sand and mudstone content using the corrected layer velocity. The sand and mudstone content in the reservoir was calculated based on the difference in sand and mudstone velocities on the velocity spectrum after detailed interpretation.

[0005] The five methods described above study the sand-mud transition zone in uranium reservoirs from different perspectives. However, core sampling is costly, complex, and lacks representativeness when sampling is limited. Tomographic logging is expensive, making it prohibitive for widespread practical application. Well logging lithology analysis relies heavily on well logging data from the work area, which can lead to a "one-dimensional" view when the work area is relatively small. Wave impedance analysis, limited by the inherent bandwidth of seismic data, results in low resolution impedance inversion, making it inadequate for detailed characterization of the sand-mud transition zone. Inter-layer velocity calculation methods primarily utilize well interpolation to generate velocity spectra, placing high demands on the quality and quantity of well logging data. Furthermore, the analysis results can be subject to errors in work areas with complex lithologies and frequent tectonic movement. Furthermore, all five methods described above focus on the differentiation and content of sand and mud rocks, providing only a partial view of the sand-mud transition zone and failing to accurately delineate the sand-mud transition zone in the full three-dimensional space of uranium reservoirs. This is obviously very unfavorable for comprehensively analyzing the mineralization mechanism and distribution pattern of sandstone-type uranium deposits in the sand-mud transition zone and participating in subsequent mineral exploration work.

[0006] Therefore, it is urgent to develop a method for accurately delineating the sand-mud transition zone of uranium reservoirs based on three-dimensional seismic velocity inversion, so that it can perform three-dimensional characterization of the sand-mud transition zone, analyze the spatial configuration relationship between the ore body and the sand-mud transition zone, and then analyze the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone, and ultimately provide strong technical support for enriching the overall mineralization theory of sandstone-type uranium deposits and establishing prospecting models. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for accurately delineating the sand-mud transition zone of uranium reservoirs based on three-dimensional seismic velocity inversion. High-resolution three-dimensional seismic, drilling and logging data are combined with high-resolution reservoir velocity inversion methods to conduct in-depth research on the sand-mud transition zone of uranium reservoirs, so as to solve the problem of three-dimensional characterization of the sand-mud transition zone, analyze the spatial configuration relationship between the ore body and the sand-mud transition zone, and then analyze the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion comprises the following steps:

[0010] a. Read in 3D seismic, drilling and logging data and comprehensively evaluate the data quality;

[0011] b. Accurately locate the target interval of the uranium reservoir and perform fine well-seismic calibration;

[0012] c. Conduct detailed structural interpretation of the target uranium reservoir interval and construct an initial velocity inversion model;

[0013] d. Perform high-resolution 3D seismic velocity inversion on the target uranium reservoir interval to obtain velocity volumes and conduct quality control;

[0014] e. Perform high-pass filtering on the high-resolution inverted velocity body to obtain a low-frequency velocity body;

[0015] f. Maximize the dominant velocity value of the sand-mud transition zone on the low-frequency velocity body to obtain the final sand-mud transition zone attribute body;

[0016] g. Based on the attribute body of the sand-mud transition zone and the lithologic data and mineral-bearing information of the work area, the three-dimensional attribute body is used to accurately delineate the sand-mud transition zone.

[0017] Furthermore, in step a, the drilling and logging data mainly include natural gamma ray logging curves, lithologic curves and acoustic time difference logging curves, which are used to accurately locate the target layer of the uranium reservoir and construct a velocity inversion model; high-resolution three-dimensional seismic data can finely depict the stratigraphic structure information of the target mining area and accurately locate the spatial position and range of the uranium reservoir layer in the target mining area.

[0018] Furthermore, in step b, the range of the target layer section of the uranium reservoir is achieved by selecting the high-value area of ​​the natural gamma curve in the uranium reservoir, and the fine well-seismic calibration is completed by making a seismic synthetic record through the acoustic time difference logging curve and comparing it with the wellside seismic trace, utilizing the correlation between the synthetic seismic record and the wellside seismic trace, and adjusting the time-depth correspondence and the wavelet morphology.

[0019] Furthermore, in step c, the fine structural interpretation is based on the fine well-seismic calibration in step b. First, the well profile and the backbone profile are compared. Secondly, the structural interpretation scheme is determined, and then fine layer tracking and fault interpretation are performed again to complete the structural interpretation work. Finally, based on the structural interpretation results, the initial velocity inversion model is established through the method of inter-well interpolation combined with low-pass filtering.

[0020] Furthermore, in step d, high-resolution velocity inversion is performed on the target layer of the uranium reservoir to obtain a reliable velocity body. By comparing the seismic profile and the extracted plane attributes, it is analyzed whether the inversion result trend of the initial velocity inversion model is consistent with that of the high-resolution inversion velocity body. Secondly, the velocity curves of the well bypass and the well logging are extracted from the inverted high-resolution velocity body to calculate the coincidence rate between the two. Finally, the accuracy of the high-resolution inversion velocity body profile and the well logging parameters is evaluated to complete the quality control work.

[0021] Furthermore, in step e, low-frequency information is removed by high-pass filtering, which can effectively improve the problem of different compaction effects on velocity due to large differences in target layer depths, thereby being more conducive to uranium reservoir prediction.

[0022] Furthermore, in step f, the calculation formula is as follows:

[0023]

[0024] V ijk is the velocity value of any point in the three-dimensional space of the uranium reservoir target layer in the low-frequency velocity body, V is the median value of the dominant velocity value of the ore-bearing sand-mud transition zone in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, max-ijk is the maximum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, V min-ijk The minimum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, and the data body A of the maximum value of the preferred velocity value in the sand-mud transition zone after maximizing the merit value sm This is the final desired body that can characterize the properties of the sand-mud transition zone.

[0025] Furthermore, in step g, the correlation between the sand-mud transition zone, mineral-bearing information and the sand-mud transition zone attribute body in the well lithology is statistically analyzed, thereby determining the threshold value that can represent the sand-mud transition zone in the three-dimensional sand-mud transition zone attribute body, thereby accurately delineating the sand-mud transition zone in the three-dimensional attribute body.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This study addresses the problems of previous methods, such as complex operation, low resolution, and susceptibility to well data, resulting in a "one-hole view." By comprehensively utilizing high-resolution 3D seismic, drilling, and logging data in conjunction with high-resolution reservoir velocity inversion methods, we conduct in-depth research on the sand-mud transition zone in uranium reservoirs. This method, based on 3D seismic velocity inversion, proposes a precise delineation method for the sand-mud transition zone in uranium reservoirs. This method offers the following advantages:

[0028] 1. Because there is a solid physical basis between seismic wave velocity and seismic data, the method of the present invention has a better theoretical basis and reliability compared with previous methods based on resistivity inversion or gamma inversion;

[0029] 2. Compared with the traditional well-connected profiling method based on well data analysis, the method of the present invention ultimately accurately delineates the sand-mud transition zone based on 3D seismic velocity inversion data. Therefore, it can truly achieve 3D stereoscopic depiction of the sand-mud transition zone in full 3D space.

[0030] 3. The three-dimensional spatial distribution range of the sand-mud transition zone obtained by the method of the present invention is helpful for analyzing the spatial configuration relationship between the ore body and the sand-mud transition zone, and further helps to summarize the corresponding mineralization laws and ore-controlling factors;

[0031] 4. The present invention obtains the final sand-mud transition zone attribute body by maximizing the dominant velocity value of the ore-bearing sand-mud transition zone on the inverted velocity body through detailed statistical results of seismic velocity in the ore-bearing well section. Therefore, the sand-mud transition zone attribute body has important significance for pointing to favorable ore-prospecting areas.

[0032] 5. The three-dimensional attribute body of the sand-mud transition zone accurately delineated by the present invention is of great significance for the comprehensive analysis of the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone, and can provide strong technical support for the enrichment of the overall mineralization theory of sandstone-type uranium deposits and the establishment of prospecting models. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a flowchart of the overall implementation of the method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to the present invention;

[0035] Figure 2 Schematic diagram of a detailed implementation process of a specific embodiment of the method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to the present invention;

[0036] Figure 3 This is an example effect analysis diagram: Among them, Figure 3 a is the three-dimensional horizon interpretation result of the target layer of the uranium reservoir; Figure 3 b is the well-connected section of the target horizon of the uranium reservoir; Figure 3 c is the superposition of the high-resolution inversion velocity body and the mine; Figure 3 d is the high-resolution inversion velocity body well section; Figure 3 e is the well-connected section of the sand-mud transition zone attribute body; Figure 3 f is the overlapping plane of the demarcated sand-mud transition zone and the mine. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0038] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of the present invention, the terms "first", "second", etc. are used only to distinguish the description and should not be understood as indicating or implying relative importance.

[0039] The present invention provides a method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion, comprising the following steps: positioning and calibrating the uranium reservoir based on well seismic data, performing structural interpretation on the target layer and constructing an initial inversion model, performing high-resolution velocity inversion to obtain a velocity body and perform quality control, filtering the velocity body to obtain a low-frequency-removed velocity body, maximizing the dominant velocity value of the ore-bearing sand-mud transition zone, obtaining a body characterizing the properties of the sand-mud transition zone, and delineating the sand-mud transition zone.

[0040] like Figure 1 As shown, the method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion of the present invention includes the following steps:

[0041] a. Import 3D seismic, drilling, and logging data and comprehensively evaluate their quality. Drilling and logging data primarily include natural gamma ray logs, lithologic curves, and sonic transit time logs, which are primarily used to accurately locate target uranium reservoir intervals and build velocity inversion models. High-resolution 3D seismic data can precisely characterize the stratigraphic structure of the target mining area and accurately locate the spatial location and extent of the uranium reservoir intervals in the target mining area.

[0042] b. Accurately locate the target uranium reservoir interval and perform fine borehole seismic calibration. The target uranium reservoir interval is determined by selecting the high-value area of ​​the natural gamma ray curve in the uranium reservoir. Fine borehole seismic calibration is achieved by creating synthetic seismic records from acoustic time-difference logging curves and comparing them with seismic traces near the well. The correlation between the synthetic seismic records and seismic traces near the well is utilized, and the time-depth correspondence and wavelet morphology are adjusted.

[0043] c. Conduct a detailed structural interpretation of the target uranium reservoir interval and construct an initial velocity inversion model. This detailed structural interpretation is based on the detailed well-seismic calibration in step b. First, compare the well profile with the backbone profile. Next, determine the structural interpretation plan. Then, perform detailed horizon tracing and fault interpretation to complete the structural interpretation. Finally, based on the structural interpretation results, establish an initial velocity inversion model using interwell interpolation combined with low-pass filtering.

[0044] d. Perform high-resolution 3D seismic velocity inversion on the target uranium reservoir interval to obtain a velocity volume and conduct quality control. This involves: performing high-resolution velocity inversion on the target uranium reservoir interval to obtain a reliable velocity volume. By comparing seismic profiles and extracted plane attributes, the consistency between the initial velocity inversion model and the inversion results of the high-resolution inversion velocity volume is analyzed. Next, velocity curves from well bypasses and well logging are extracted from the inverted high-resolution velocity volume to calculate the consistency between the two. Finally, the accuracy of the high-resolution inversion velocity volume profile and well logging parameters is evaluated to complete the quality control work.

[0045] e. Perform high-pass filtering on the high-resolution inversion velocity volume to obtain a low-frequency velocity volume. Removing low-frequency information through high-pass filtering can effectively improve the problem of velocity compaction effect differences caused by large differences in target layer depths, thereby making it more conducive to uranium reservoir prediction;

[0046] f. Maximize the preferred velocity value of the sand-mud transition zone for the low-frequency velocity body to obtain the final sand-mud transition zone attribute body. The calculation formula is as follows:

[0047]

[0048] V ijk is the velocity value of any point in the three-dimensional space of the uranium reservoir target layer in the low-frequency velocity body, V is the median value of the dominant velocity value of the ore-bearing sand-mud transition zone in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, max-ijk is the maximum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, V min-ijk The minimum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, and the data body A of the maximum value of the preferred velocity value in the sand-mud transition zone after maximizing the merit value sm This is the final desired body that can characterize the properties of the sand-mud transition zone.

[0049] g. Based on the sand-mud transition zone attribute body and the on-site lithologic data and mineral-bearing information of the work area, the three-dimensional attribute body is accurately delineated. Among them: the correlation between the sand-mud transition zone and mineral-bearing information in the on-site lithology and the sand-mud transition zone attribute body is statistically analyzed. In this way, the threshold value that can represent the sand-mud transition zone in the three-dimensional sand-mud transition zone attribute body is determined, so as to accurately delineate the sand-mud transition zone in the three-dimensional attribute body.

[0050] The present invention realizes the three-dimensional depiction of the sand-mud transition zone in full three-dimensional space; it can analyze the spatial configuration relationship between the ore body and the sand-mud transition zone, which is helpful to summarize the corresponding mineralization laws and ore-controlling factors; the sand-mud transition zone finally delineated is of great significance for the comprehensive analysis of the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone, and provides strong technical support for enriching the overall mineralization theory of sandstone-type uranium deposits and establishing prospecting models.

[0051] Example 1

[0052] A method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion comprises the following steps:

[0053] a. As attached Figure 2 As shown in a, the basic data such as logging, drilling, and 3D seismic are read in, among which: the logging data are natural gamma curves, lithology curves and acoustic time difference curves. The former is used to locate the spatial position and range of the target layer where the sandstone type uranium deposit is located. Analysis of the drilling and logging data shows that the lithology in the mine-bearing section can be divided into sandstone, mudstone and sand-mud transition lithology. Among them, most of the high-value areas of the natural gamma curve correspond to the sand-mud transition lithology. The latter is used for fine well-seismic calibration, establishing the temporal and spatial correspondence between seismic and well data, and the calibration of the acoustic time difference curve. The velocity curve in the well is calculated using the formula (Δt is the acoustic time difference); secondly, high-resolution 3D seismic data can accurately depict the stratigraphic structure information of the target mining area and accurately locate the spatial position and range of the uranium reservoir layer in the target mining area;

[0054] b. As attached Figure 2 As shown in Figure b, the precise positioning and fine borehole seismic calibration of the target interval of the uranium reservoir are achieved. The scope of the target interval of the uranium reservoir is achieved by selecting the high-value area of ​​the natural gamma curve. The fine borehole seismic calibration is achieved by first calibrating the target interval position in a large section and then finely calibrating it within the target interval. This is mainly achieved by creating seismic synthetic records using acoustic time difference logging curves and comparing them with seismic traces near the well. The correlation between the synthetic seismic records and the seismic traces near the well is utilized, and the time-depth correspondence and wavelet morphology are adjusted.

[0055] c. As attached Figure 2 Figure c shows a detailed 3D seismic structural interpretation of the target uranium reservoir interval. This structural interpretation is based on the detailed well-seismic calibration in step b. First, the well profile and the backbone profile are compared. Then, the structural interpretation scheme is determined. Then, detailed horizon tracing and fault interpretation are performed. Then, an initial model for velocity inversion is constructed based on the detailed structural interpretation results of the mineralized horizons. Analysis of the schematic diagram shows that: horizon interpretation is carried out sequentially along each survey line, fault interpretation is achieved by combining the coherent attributes of the seismic data, and the initial velocity inversion model is established through interwell interpolation combined with low-pass filtering.

[0056] d. As attached Figure 2As shown in d, based on step c, high-resolution velocity inversion is performed on the target uranium reservoir segment. The following steps are performed: A reliable velocity body is obtained by performing high-resolution velocity inversion on the target uranium reservoir segment. The initial velocity inversion model is analyzed to determine whether the inversion trend of the high-resolution inversion velocity body is consistent with that of the inversion result of the high-resolution inversion velocity body by comparing seismic profiles and extracted plane attributes. Secondly, the velocity curves of the well bypass and well logging are extracted from the inverted high-resolution velocity body to calculate the coincidence rate between the two (the coincidence rate for the work area in this case reached over 80%). Finally, the accuracy of the high-resolution inversion velocity body profile and the well logging parameters is evaluated to complete the quality control work. The schematic diagram shows that the high-value area of ​​the natural gamma ray curve on the well in the target uranium reservoir segment corresponds to the sand-mud transition zone, and also corresponds to the median velocity area of ​​the entire target segment in the high-resolution velocity body.

[0057] e. As attached Figure 2 As shown in Figure e, the high-resolution inversion velocity body is subjected to high-pass filtering to obtain a low-frequency velocity body. Removing low-frequency information by high-pass filtering can effectively improve the problem of different compaction effects on velocity caused by large differences in target layer depths, thereby being more conducive to uranium reservoir prediction. Analysis of the schematic diagram shows that the velocity body after removing low frequencies can more intuitively display the positional relationship between the mineralization site and the sand-mud transition zone.

[0058] f. As attached Figure 2 As shown in Figure 5, the ultimate sand-mud transition zone attribute body is obtained by maximizing the advantageous velocity value of the sand-mud transition zone on the low-frequency velocity body. The calculation formula is as follows:

[0059]

[0060] V ijk is the velocity value of any point in the three-dimensional space of the uranium reservoir target layer in the low-frequency velocity body, V is the median value of the dominant velocity value of the ore-bearing sand-mud transition zone in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, max-ijk is the maximum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, V min-ijk The minimum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, and the data body A of the maximum value of the preferred velocity value in the sand-mud transition zone after maximizing the merit value sm This is the ultimate attribute volume that characterizes the sand-mud transition zone. Analysis of the schematic diagram shows that the sand-mud transition zone attribute volume, after maximizing the preferred velocity value of the sand-mud transition zone, can accurately delineate the sand-mud transition zone of the uranium reservoir and effectively and finely depict the spatial relationship between the ore-bearing well and the sand-mud transition zone. In other words, the ore-bearing portion of the well is mostly located in the sand-mud transition zone attribute volume's merit zone of the target uranium reservoir formation.

[0061] g、As attached Figure 2As shown in Figure g, the sand-mud transition zone is precisely delineated in the three-dimensional attribute volume based on the sand-mud transition zone attribute volume combined with the wellbore lithologic data and mineralization information of the work area. The correlation between the sand-mud transition zone, mineralization information, and the sand-mud transition zone attribute volume in the wellbore lithology is statistically analyzed to determine the threshold value that represents the sand-mud transition zone in the three-dimensional sand-mud transition zone attribute volume, thereby accurately delineating the sand-mud transition zone in the three-dimensional attribute volume. The analysis of the schematic diagram shows that the red area is the delineated sand-mud transition zone. The darker the red, the better the mineralization of the sand-mud transition zone. Mineralized wells are marked in yellow, while those without are marked in black. The vast majority of mineralized wells are located in the red area, i.e., the delineated sand-mud transition zone. This shows that this method can not only accurately delineate the sand-mud transition zone, but also effectively serve the prediction of uranium reservoirs and the deployment of exploration wells.

[0062] Figure 3 Given Figure 2 Analysis of some core results from the specific implementation process in the study area reveals the following phenomena and conclusions:

[0063] 1. Figure 3 a is the basic spatial structure of several core strata in the target uranium reservoir section. The strata dip to the northwest and strike northwest-southeast. The stratigraphic undulations of the target section are gentle, and there is inheritance between the several core strata, which is conducive to the formation of ore-bearing sand bodies with interbedded structures such as "mud-sand-mud" required for sandstone-type uranium mineralization.

[0064] 2. Figure 3 b is the well-connected section of the target uranium reservoir. Analysis of this figure clearly shows that the high values ​​of the natural gamma curve on the well correspond to the sand-mud transition zone in the lithology curve on the well. This phenomenon and law fully demonstrate that the sand-mud transition zone has a good indicative effect on the distribution of sandstone-type uranium deposits.

[0065] 3. Figure 3 cd are the superposition of the high-resolution inversion velocity body and the mine, and the high-resolution inversion velocity body and well section, respectively. Analysis of this figure shows that the velocity value of the mudstone in the target layer of the uranium reservoir is small, ranging from 2992 to 3200 m / s, and the velocity value of the sandstone is large, ranging from 3480 to 3632 m / s. The sand-mud transition zone is in the velocity value range of 3200 to 3480 m / s in the target layer of the uranium reservoir, and most of the uranium mineralization is located in this area.

[0066] 4. Figure 3e is the sand-mud transition zone attribute body connected to the well profile. It can be seen that the yellow part of the lithologic curve on the well is sandstone, the black part is mudstone, the blue part is the sand-mud transition zone, and the blue curve beside the well is the natural gamma curve. Analysis of the relationship between the sand-mud transition zone attribute body and the natural gamma curve and lithologic curve of the ore-bearing well shows that the high-value area of ​​the natural gamma curve on the ore-bearing well is the ore-bearing part, which corresponds to the sand-mud transition zone area on the lithologic curve. At the same time, the high-value part of the attribute body merit, i.e., the red area, corresponds to the sand-mud transition zone attribute body profile. It can be concluded that the sand-mud transition zone attribute body has a good correspondence with the mineralization part in the uranium reservoir in terms of spatial position, so that it is possible to better find the favorable mineralization area of ​​sandstone-type uranium deposits.

[0067] 5. Figure 3 f is the superimposed plane of the delineated sand-mud transition zone and the wells. Analysis of the relationship between the delineated sand-mud transition zone and the wells on the superimposed plane shows that wells containing wells are marked in yellow, while wells without wells are marked in black. Most wells containing wells are located in the delineated sand-mud transition zone, or red areas. The darker the red, the better the mineralization correlation of the sand-mud transition zone. Most wells without wells are located in the non-sand-mud transition zone, or blue areas. This shows that the delineated sand-mud transition zone attributes can provide a good indicator of the distribution of sandstone-type uranium deposits, thereby better predicting uranium reservoirs and serving the deployment of exploration wells. This is of great significance for studying the mechanism of sandstone-type uranium mineralization and determining the direction of prospecting.

[0068] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion, characterized in that: The following steps are involved: a. Read in 3D seismic, drilling and logging data and comprehensively evaluate the data quality; b. Accurately locate the target interval of the uranium reservoir and perform fine well-seismic calibration; c. Conduct detailed structural interpretation of the target uranium reservoir interval and construct an initial velocity inversion model; d. Perform high-resolution 3D seismic velocity inversion on the target uranium reservoir interval to obtain velocity volumes and conduct quality control; e. Perform high-pass filtering on the high-resolution inverted velocity body to obtain a low-frequency velocity body; f. Maximize the preferred velocity value of the sand-mud transition zone for the low-frequency velocity body to obtain the final sand-mud transition zone attribute body; the calculation formula is as follows: V ijk is the velocity value of any point in the three-dimensional space of the uranium reservoir target layer in the low-frequency velocity body, V is the median value of the dominant velocity value of the ore-bearing sand-mud transition zone in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, max-ijk is the maximum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, V min-ijk The minimum velocity value in the three-dimensional space of the target layer of the uranium reservoir after removing the low-frequency velocity body, and the data body A of the maximum value of the preferred velocity value in the sand-mud transition zone after maximizing the merit value sm This is the final desired body that can characterize the properties of the sand-mud transition zone; g. Based on the sand-mud transition zone attribute body and the on-site lithologic data and mineral-bearing information of the work area, the three-dimensional attribute body is accurately delineated. The correlation between the sand-mud transition zone and mineral-bearing information in the on-site lithology and the sand-mud transition zone attribute body is statistically analyzed to determine the threshold value that can represent the sand-mud transition zone in the three-dimensional sand-mud transition zone attribute body, thereby accurately delineating the sand-mud transition zone in the three-dimensional attribute body.

2. The method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: In step a, the drilling and logging data mainly include natural gamma ray logging curves, lithologic curves and acoustic time difference logging curves, which are used to accurately locate the target uranium reservoir segment and build a velocity inversion model; high-resolution three-dimensional seismic data can finely depict the stratigraphic structure information of the target mining area and accurately locate the spatial position and range of the uranium reservoir segment in the target mining area.

3. The method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: In step b, the range of the target layer of the uranium reservoir is achieved by selecting the high-value area of ​​the natural gamma curve in the uranium reservoir. The fine well-seismic calibration is completed by making a seismic synthetic record through the acoustic time difference logging curve and comparing it with the wellside seismic trace. The correlation between the synthetic seismic record and the wellside seismic trace is utilized, and the time-depth correspondence and the wavelet morphology are adjusted at the same time.

4. The method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: Step c, fine structural interpretation, is based on the fine well-seismic calibration in step b. First, the well profile and the backbone profile are compared. Secondly, the structural interpretation scheme is determined, and then fine horizon tracking and fault interpretation are performed again to complete the structural interpretation work. Finally, based on the structural interpretation results, the initial velocity inversion model is established through interwell interpolation combined with low-pass filtering.

5. The method for accurately delineating the sand-mud transition zone in a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: In step d, high-resolution velocity inversion is performed on the target layer of the uranium reservoir to obtain a reliable velocity body. By comparing the seismic profile and the extracted plane attributes, the trend of the inversion results of the initial velocity inversion model and the high-resolution inversion velocity body is analyzed to see whether they are consistent. Secondly, the velocity curves of the well bypass and the well logging are extracted from the inverted high-resolution velocity body to calculate the consistency rate between the two. Finally, the accuracy of the high-resolution inversion velocity body profile and the well logging parameters is evaluated to complete the quality control work.

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