Uranium reservoir sand-mud transition zone accurate delineation method based on three-dimensional seismic velocity inversion

Abstract

The invention relates to a precise delineation method for a uranium reservoir sand-mud transition zone based on three-dimensional seismic velocity inversion. Comprising the following steps: positioning and calibrating a uranium reservoir based on well-seismic data; carrying out structural interpretation on a target interval and constructing an inversion initial model; carrying out high-resolution velocity inversion to obtain a velocity body and carrying out quality control; filtering the velocity body to obtain a low-frequency-removed velocity body; and obtaining an attribute body representing the sand-mud transition zone, and realizing delineation of the sand-mud transition zone. According to the method, the three-dimensional depiction of the sand-mud transition zone in the full three-dimensional space is realized; the spatial configuration relationship between the ore body and the sand-mud transition zone can be analyzed, so that corresponding mineralization rules and ore control elements can be summarized; the finally delineated sand-mud transition zone has important significance for comprehensively analyzing the mineralization mechanism and the distribution rule of the sandstone-type uranium deposit in the aspect of the sand-mud transition zone, and provides powerful technical support for enriching the integral mineralization theory of the sandstone-type uranium deposit and establishing a prospecting model.

Description

Technical Field

[0001] The invention belongs to the technical field of sandstone-type uranium ore exploration, and specifically relates to a new method for three-dimensionally depicting 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] Usually, stable interlayers are developed at the top and bottom of uranium reservoirs, forming a "mud-sand-mud" structure. The lithology of the interlayers is usually mudstone, silty mudstone or muddy siltstone, etc. Stable interlayers are conducive to the long-term and stable migration of uranium-containing and oxygen-containing fluids in the sand body, which is conducive to the continuous mineralization. Therefore, most sandstone-type uranium deposits are formed in the sand-mud transition zone of the target reservoir.

[0003] Research has 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 it is concluded that uranium mineralization in this area is mostly distributed in the thinning zone of the sand body thickness and the phase change area at the edge of the sand body. This is mainly due to the change in the sedimentary environment in the area, which slows down the water flow rate and increases the accumulation of mud content here. In addition, 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 stereoscopic 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] At present, there are few studies on the precise delineation of the sand-mud transition zone in uranium reservoirs, mainly including core sampling method, tomography logging method, logging curve method, wave impedance analysis method and layer velocity calculation method. Regarding the core sampling method, in 2016, Zhang Pingping disclosed a medium-deep reservoir sensitivity factor inversion technology based on core testing, combining the core test results with the logging data analysis of the wells drilled in the target area, and using mudstone as the base value to calculate the sand-mud difference percentage in different layers. In 2023, Yuan Yuxuan disclosed a method for establishing a high-precision sequence stratigraphic framework in marine fine-grained sedimentary rocks using high-resolution sequence stratigraphy methods, in which the lithofacies type and sand-mudstone content of the reservoir were obtained through detailed core description and high-precision thin section analysis. Regarding the tomography logging method, in 2023, Liu Liling disclosed a joint iterative reconstruction method inversion based on multiple inter-well first arrival information, through high-resolution geological images and direct observation of the rock composition around the well wall, so as to better understand the sand-mudstone content of the underground reservoir. Regarding the logging curve analysis method, in 2015, Qu Lu disclosed a method for lithology identification and division by analyzing the logging response characteristics of different lithologies in different boreholes, thereby indirectly helping to find the sand-mud transition zone in the reservoir. In 2016, Dong Zhen disclosed a method of using quantitative simulation of favorable lithology combinations to establish a favorable lithology combination logging identification mode. The sand and mud content analysis of the reservoir was achieved by analyzing the characteristics of favorable lithology combinations, reasonable lithology division of logging data in the work area, and quantitative simulation of lithology combination logging. Regarding the wave impedance analysis method, in 2017, Peng Jun disclosed a method for obtaining lithology impedance by certain mathematical transformation of longitudinal wave impedance and transverse wave impedance. It can not only effectively identify sand and mudstone and provide a good reference for reservoir prediction, but also the lithology impedance can better distinguish the superposition relationship between sand bodies. In 2020, Li Ziwei disclosed the preliminary research results on the difference in wave impedance between ore-bearing sand bodies and surrounding rocks in sandstone-type uranium deposits. The ore-bearing sand bodies and surrounding rocks were successfully distinguished by combining the elastic parameters of the ore-bearing sand bodies and surrounding rocks with the difference in wave impedance parameters. Regarding the layer velocity calculation method, in 1995 Qin Fengrong disclosed a method for calculating the sand and mudstone content using the corrected layer velocity, and calculated the sand and mudstone content in the reservoir based on the difference in sand and mudstone velocities on the velocity spectrum after detailed interpretation.

[0005] The above five methods study the sand-mud transition zone of uranium reservoirs from different angles. However, the core sampling method is costly, complicated to operate, and lacks representativeness when sampling is small. The tomographic logging method is expensive and is not conducive to widespread practical application. The logging lithology analysis method relies heavily on the logging data of the work area, and it is easy to have the problem of "one-hole view" when there are few wells in the work area. The wave impedance analysis method is limited by the inherent bandwidth of seismic waves, and the resolution of wave impedance inversion is low, which cannot meet the needs of fine characterization of the sand-mud transition zone. The layer velocity calculation method itself is mostly based on the velocity spectrum made by the well interpolation method, which has high requirements on the quality and quantity of logging data, and there are certain errors in the analysis results in the work area with complex lithology and frequent tectonic movements. In addition, the above five methods are all about studying the distinction and content of sand and mudstone, which can only reflect the situation of the sand-mud transition zone from the side, and cannot accurately delineate the sand-mud transition zone of the uranium reservoir in full three-dimensional space. This is obviously very unfavorable for comprehensive analysis of the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone and for participation in subsequent prospecting work.

[0006] Therefore, it is urgently necessary to develop a method for accurately delineating the sand-mud transition zone of uranium reservoirs based on three-dimensional seismic velocity inversion, so that the sand-mud transition zone can be portrayed in three dimensions, the spatial configuration relationship between the ore body and the sand-mud transition zone can be analyzed, and then the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone can be analyzed, ultimately providing 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, and to use high-resolution three-dimensional seismic, drilling and logging data combined with a high-resolution reservoir velocity inversion method 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 further analyze the mineralization mechanism and distribution law of sandstone-type uranium deposits in the sand-mud transition zone.

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

[0009] A method for accurately delineating the sand-mud transition zone of 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 layer of the uranium reservoir and perform fine well seismic calibration;

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

[0013] d. Carry out high-resolution 3D seismic velocity inversion on the target layer of uranium reservoir to obtain velocity volume and conduct quality control;

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

[0015] f. The low-frequency velocity body is processed to maximize the dominant velocity value of the sand-mud transition zone 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 lithological data and mineral-bearing information of the work area, the three-dimensional attribute body is accurately delineated for the sand-mud transition zone.

[0017] Furthermore, in step a, the drilling and logging data are mainly natural gamma logging curves, lithology curves and sonic time difference logging curves, which are used to accurately locate the target layer segment of the uranium reservoir and build a velocity inversion model; high-resolution three-dimensional seismic data can finely characterize the stratigraphic structure information of the target mining area and accurately locate the spatial position and range of the uranium reservoir layer segment 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 seismic trace near the well, using the correlation between the synthetic seismic record and the seismic trace near the well, and adjusting the time-depth correspondence and the wavelet morphology.

[0019] Furthermore, 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 plan is determined, and then fine layer tracking and fault interpretation are carried out again to complete the structural interpretation work. Finally, based on the structural interpretation results, the initial velocity inversion model is established by 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 model of the velocity inversion is consistent with that of the high-resolution inversion velocity body. Secondly, the velocity curves of the well bypass and the logging are extracted from the inverted high-resolution velocity body to calculate the coincidence rate between the two. Finally, the accuracy is evaluated from the high-resolution inversion velocity body profile and the well logging parameters 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 differences in velocity compaction effects caused by 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 target layer of the uranium reservoir in the low-frequency velocity body, V is the median value of the dominant velocity value of the transition zone of ore-bearing sand and mud in the three-dimensional space of the target layer of the uranium reservoir without the low-frequency velocity body. max-ijk is the maximum velocity in the three-dimensional space of the target layer of the uranium reservoir without 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 optimal value sm This is the ultimate 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] In view of the problems of complicated operation, low resolution and "one-hole view" easily affected by well data in previous methods, the present invention comprehensively utilizes high-resolution 3D seismic, drilling and logging data combined with high-resolution reservoir velocity inversion method to conduct in-depth research on the sand-mud transition zone of uranium reservoirs, and proposes a method for accurately delineating the sand-mud transition zone of uranium reservoirs based on 3D seismic velocity inversion. This method has 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 the previous methods based on resistivity inversion or gamma inversion;

[0029] 2. Compared with the traditional well-connected profile method based on well data analysis, the method of the present invention ultimately accurately delineates the sand-mud transition zone based on the three-dimensional seismic velocity inversion data volume, so it can truly realize the three-dimensional stereoscopic depiction of the sand-mud transition zone in the full three-dimensional 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 inversion 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 directional significance for the favorable area of ​​ore prospecting.

[0032] 5. The three-dimensional attribute body of the sand-mud transition zone finally and 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 drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 It is an overall implementation flow chart of 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;

[0035] Figure 2 It is a schematic diagram of a detailed explanation of the implementation process of a specific embodiment of 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;

[0036] Figure 3 It 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 stratum of the uranium reservoir; Figure 3 c is the superposition of the high-resolution inversion velocity body and the mine shaft; 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 in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

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

[0039] The present invention provides a method for accurately delineating a sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion, comprising the following steps: positioning and calibrating a uranium reservoir based on well seismic data, implementing structural interpretation on a target layer segment and building 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 a ore-bearing sand-mud transition zone, obtaining a body characterizing an attribute 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 comprises the following steps:

[0041] a. Read in 3D seismic, drilling and logging data and comprehensively evaluate the data quality. Drilling and logging data mainly include natural gamma logging curves, lithology curves and acoustic time difference logging curves, which are mainly used for accurate positioning of target uranium reservoir segments and building velocity inversion models. 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 segments in the target mining area.

[0042] b. Accurately locate the target layer of the uranium reservoir and finely calibrate the well seismic, where: 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, and finely calibrate the well seismic by making a synthetic seismic record from the acoustic time difference logging curve and comparing it with the seismic trace near the well, using the correlation between the synthetic seismic record and the seismic trace near the well, and adjusting the time-depth correspondence and the wavelet morphology;

[0043] c. Carry out fine structural interpretation of the target layer of the uranium reservoir and construct an initial velocity inversion model, wherein: the fine structural interpretation is based on the fine well seismic calibration in step b, firstly, the well section and the backbone section are compared, then the structural interpretation scheme is determined, and then fine layer tracking and fault interpretation are carried out again to complete the structural interpretation work, and finally, based on the structural interpretation results, the initial velocity inversion model is established by the method of inter-well interpolation combined with low-pass filtering;

[0044] d. Carry out high-resolution three-dimensional seismic velocity inversion on the target layer of the uranium reservoir to obtain the velocity body and conduct quality control, including: Carry out high-resolution velocity inversion on the target layer of the uranium reservoir to obtain a reliable velocity body, and analyze whether the inversion result trend of the initial model of velocity inversion is consistent with that of the high-resolution inversion velocity body by comparing the seismic profile and the extracted plane attributes. Secondly, extract the velocity curve of the well bypass and the well logging from the inverted high-resolution velocity body to calculate the coincidence rate between the two. Finally, perform accuracy evaluation on the high-resolution inversion velocity body profile and the well logging parameters to complete the quality control work;

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

[0046] f. The ultimate attribute body of the sand-mud transition zone is obtained by maximizing the dominant velocity value of the sand-mud transition zone for the low-frequency velocity 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 target layer of the uranium reservoir in the low-frequency velocity body, V is the median value of the dominant velocity value of the transition zone of ore-bearing sand and mud in the three-dimensional space of the target layer of the uranium reservoir without the low-frequency velocity body. max-ijk is the maximum velocity in the three-dimensional space of the target layer of the uranium reservoir without 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 desired body that can characterize the properties of the sand-mud transition zone.

[0049] g. Based on the sand-mud transition zone attribute body combined with the well lithology data and mineral-bearing information of the work area, the three-dimensional attribute body is accurately delineated of the sand-mud transition zone, including: statistically analyzing the correlation between the sand-mud transition zone and mineral-bearing information in the well lithology and the sand-mud transition zone attribute body, 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.

[0050] The present invention realizes the stereoscopic 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 of 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 includes natural gamma curve, lithology curve and acoustic time difference curve. The former is used to locate the spatial position and range of the target layer where the sandstone type uranium ore is located. Analysis of drilling and logging data shows that the lithology in the ore-bearing section can be divided into sandstone, mudstone and sand-mud transition lithology. 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, to establish the time-space correspondence between seismic and well data, and to calibrate the acoustic time difference curve. The velocity curve in the well is obtained by converting the formula (Δt is the acoustic time difference); secondly, high-resolution three-dimensional 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 section in the target mining area;

[0054] b. As attached Figure 2 As shown in b, the precise positioning and fine well seismic calibration of the target layer section of the uranium reservoir, where: the scope of the target layer section of the uranium reservoir is achieved by selecting the high-value area of ​​the natural gamma curve, and the fine well seismic calibration is to first calibrate the target layer section position in a large section, and then finely calibrate within the target layer section, mainly through the acoustic time difference logging curve to make a synthetic seismic record and compare it with the seismic trace beside the well, using the correlation between the synthetic seismic record and the seismic trace beside the well, and adjusting the time-depth correspondence and the wavelet shape to complete it;

[0055] c. As attached Figure 2 As shown in Figure c, the fine three-dimensional seismic structural interpretation of the target layer of the uranium reservoir is based on the fine well-seismic calibration in step b. First, the well section and the backbone section are compared, then the structural interpretation scheme is determined, and then fine layer tracking and fault interpretation are carried out again. Then, the initial model of velocity inversion is constructed based on the fine structural interpretation results of the ore-bearing layer. Analysis of the schematic diagram shows that: the layer interpretation is implemented one by one, the fault interpretation is realized by combining the coherent attributes of the seismic data, and the initial model of velocity inversion is established by inter-well interpolation combined with the low-pass filtering method;

[0056] d. As attached Figure 2As shown in step d, based on step c, high-resolution velocity inversion is performed on the target layer of the uranium reservoir, wherein: a reliable velocity body is obtained by performing high-resolution velocity inversion on the target layer of the uranium reservoir, and the trend of the inversion results of the initial model of the velocity inversion is analyzed to see if it is consistent with that of the high-resolution inversion velocity body by comparing the seismic profile and the extracted plane attributes. 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 (the coincidence rate of the two in the work area of ​​this case is more than 80%). Finally, the accuracy is evaluated from the high-resolution inversion velocity body profile and the well logging parameters to complete the quality control work. From the analysis of the schematic diagram, it can be seen that the high-value area of ​​the natural gamma curve on the well in the target layer of the uranium reservoir corresponds to the sand-mud transition zone, and also corresponds to the velocity median area of ​​the overall target layer 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 the low-frequency velocity body. Removing low-frequency information through high-pass filtering can effectively improve the problem of different compaction effects on velocity due to large differences in target layer depths, which is more conducive to uranium reservoir prediction. Analysis of the schematic diagram shows that the velocity body after removing the low frequency 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 Fig. 5, the dominant velocity value of the sand-mud transition zone is maximized for the low-frequency velocity body to obtain the final attribute body of the sand-mud transition zone. The calculation formula is as follows:

[0059]

[0060] V ijk is the velocity value of any point in the three-dimensional space of the target layer of the uranium reservoir in the low-frequency velocity body, V is the median value of the dominant velocity value of the transition zone of ore-bearing sand and mud in the three-dimensional space of the target layer of the uranium reservoir without the low-frequency velocity body. max-ijk is the maximum velocity in the three-dimensional space of the target layer of the uranium reservoir without 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 optimal value sm This is the final desired attribute body that can characterize the sand-mud transition zone. From the analysis of the schematic diagram, it can be seen that the attribute body of the sand-mud transition zone 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 can effectively and finely depict the spatial position relationship between the ore-bearing well and the sand-mud transition zone, that is, most of the ore-bearing part of the ore-bearing well is located in the sand-mud transition zone attribute body merit area of ​​the target stratum of the uranium reservoir.

[0061] g. As attached Figure 2As shown in Figure g, the sand-mud transition zone is accurately delineated based on the sand-mud transition zone attribute body combined with the well lithology data and mineral information of the work area. The correlation between the sand-mud transition zone, mineral information and the sand-mud transition zone attribute body in the well lithology 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, so as to accurately delineate the sand-mud transition zone of the three-dimensional attribute body. From the analysis of the schematic diagram, it can be seen 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. The marking color of the wells containing minerals is yellow, and the marking color of the wells without minerals is black. Most of the wells containing minerals are located in the red area, that is, the delineated sand-mud transition zone, which 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 The following are some of the core results of the specific implementation process in the study area. Analysis of them can lead to the following phenomena and conclusions:

[0063] 1. Figure 3 a is the basic spatial structural form of several core strata in the target layer section of the uranium reservoir. The strata dip to the northwest and strike northwest-southeast. The stratigraphic fluctuations of the target layer section are relatively gentle and there is inheritance between several core strata, which is conducive to the formation of ore-bearing sand bodies with interlayer 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 layer of the uranium reservoir. By analyzing this figure, it can be clearly found that the place with high values ​​of the natural gamma curve on the well corresponds to the sand-mud transition zone in the lithology curve on the well. This phenomenon and law fully illustrate 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 high-resolution inversion velocity body and mine well, and the high-resolution inversion velocity body and well section, respectively. By analyzing the figure, it can be intuitively found that the velocity value of mudstone in the target layer of uranium reservoir is small, ranging from 2992 to 3200 m / s, and the velocity value of sandstone is large, ranging from 3480 to 3632 m / s. The sand-mud transition zone is in the 3200-3480 m / s area of ​​the velocity value range of the target layer of uranium reservoir, and most of the uranium mineralization parts are located in this area.

[0066] 4. Figure 3e is the sand-mud transition zone attribute body connected to the well section. It can be seen that the yellow part of the lithology 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 lithology 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 lithology 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 section. 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 better to find the favorable area for sandstone-type uranium mineralization;

[0067] 5. Figure 3 f is the superimposed plane of the delineated sand-mud transition zone and the mine. By analyzing the relationship between the delineated sand-mud transition zone and the mine on the superimposed plane, it can be seen that the marking color of the mine-bearing well is yellow, and the marking color of the mine-free well is black. Most of the mine-bearing wells are located in the delineated sand-mud transition zone, i.e., the red area. The deeper the red, the better the mineralization correlation of the sand-mud transition zone. Most of the mine-free wells are located in the non-sand-mud transition zone, i.e., the blue area. This shows that the delineated sand-mud transition zone attribute body can have a good indication effect on the distribution of sandstone-type uranium deposits, thereby better realizing the prediction of uranium reservoirs and serving the deployment of exploration wells, which 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 used. 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 more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and 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 of 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 layer of the uranium reservoir and perform fine well seismic calibration; c. Conduct detailed structural interpretation of the target uranium reservoir segment and construct an initial velocity inversion model; d. Carry out high-resolution 3D seismic velocity inversion on the target layer of uranium reservoir to obtain velocity volume and conduct quality control; e. Perform high-pass filtering on the high-resolution inversion velocity body to obtain a low-frequency velocity body; f. The low-frequency velocity body is processed to maximize the dominant velocity value of the sand-mud transition zone to obtain the final sand-mud transition zone attribute body; g. Based on the attribute body of the sand-mud transition zone and the lithological data and mineral-bearing information of the work area, the three-dimensional attribute body is accurately delineated for the sand-mud transition zone.

2. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: Step a: The drilling and logging data mainly include natural gamma logging curves, lithology curves and acoustic time difference logging curves, which are used to accurately locate the target layer of the uranium reservoir 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 layer in the target mining area.

3. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized in that: Step b, the scope 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 seismic synthetic records through the acoustic time difference logging curve and comparing them with the seismic traces near the well, using the correlation between the synthetic seismic records and the seismic traces near the well, and adjusting the time-depth correspondence and the wavelet morphology.

4. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized in that: 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 plan is determined, and then fine layer tracking and fault interpretation are carried out again to complete the structural interpretation work. Finally, based on the structural interpretation results, the initial velocity inversion model is established by inter-well interpolation combined with low-pass filtering.

5. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: 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 model of the velocity inversion is consistent with that of the high-resolution inversion velocity body. Secondly, the velocity curves of the well bypass and the logging are extracted from the inverted high-resolution velocity body to calculate the coincidence rate between the two. Finally, the accuracy is evaluated from the high-resolution inversion velocity body profile and the well logging parameters to complete the quality control work.

6. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized by: Step e, removing low-frequency information by high-pass filtering, can effectively improve the problem of differences in velocity compaction effects caused by large differences in target layer depths, thus being more conducive to uranium reservoir prediction.

7. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized in that: Step f, the calculation formula is as follows: V ijk is the velocity value of any point in the three-dimensional space of the target layer of the uranium reservoir in the low-frequency velocity body, V is the median value of the dominant velocity value of the transition zone of ore-bearing sand and mud in the three-dimensional space of the target layer of the uranium reservoir without the low-frequency velocity body. max-ijk is the maximum velocity in the three-dimensional space of the target layer of the uranium reservoir without 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 desired body that can characterize the properties of the sand-mud transition zone.

8. The method for accurately delineating the sand-mud transition zone of a uranium reservoir based on three-dimensional seismic velocity inversion according to claim 1 is characterized in that: Step g, statistically analyzing the correlation between the sand-mud transition zone, mineral-bearing information and the sand-mud transition zone attribute body in the well lithology, 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.

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