Paleocurrent analysis method based on paleochannel configuration and seismic geomorphology analysis

Abstract

The application discloses a paleocurrent direction analysis method based on an ancient river channel configuration and seismic geomorphology analysis, and belongs to the technical field of oil and natural gas exploration and development. The method comprises the following steps: obtaining well logging data, recording well data and core data of a region to be measured; analyzing the paleocurrent direction of the region to be measured according to the obtained well logging data, recording well data and core data; analyzing seismic attribute characteristics of the region to be measured according to three-dimensional seismic data; analyzing the number of water channels, the width of the water channels and the internal structure characteristics of the ancient river channel according to the aforementioned characteristics; comprehensively judging the paleocurrent direction; and verifying and supplementing each other to eliminate the defects of multiple solutions possibly existing in a single research method, and to solve the problems of low accuracy of the paleocurrent direction judgment of a small block which is only provided with three-dimensional seismic data and lacks outcrop area, well logging and core data.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, specifically relating to a paleocurrent direction analysis method based on paleochannel configuration and seismic geomorphology analysis. Background Technology

[0002] Currently, commonly used paleocurrent direction analysis methods can be broadly categorized into two types: microscopic methods for determining the direction of water flow at a specific location and macroscopic methods for determining the direction of water flow over a large area. Microscopic methods mainly include typical sedimentary structures, the directional arrangement of gravel and elongated fossils, stratigraphic dip logging and imaging logging, and magnetic susceptibility anisotropy. Macroscopic methods include heavy mineral analysis, rock composition analysis, variations in the percentage content of sandstone and conglomerate, the distribution of sedimentary facies and sedimentary systems, variations in stratigraphic thickness, seismic stratigraphy, and paleontological studies. However, all of these methods have certain limitations when used in different geological contexts.

[0003] Microscopic methods can visually and accurately determine paleocurrent direction through specific bedding or stratification structures, such as the dip direction of forelandite layers in trough-like cross-bedding parallel to the paleocurrent direction, the dip of forelandite layers in platy cross-bedding, and the dip of steeply dipped surfaces in asymmetric ripple marks. Furthermore, the imbricate directional arrangement of gravels and elongated fossils can also reflect paleocurrent direction; for example, in sedimentary environments such as rivers and gravity channels, the long axis represents the paleocurrent direction, while in coastal and lacustrine environments, the long axis is perpendicular to the paleocurrent direction. However, these methods are not suitable for study blocks without outcrops or with severe outcrop coverage. Dip logging and imaging logging, even in the absence of outcrops and core samples, can determine paleocurrent direction by observing the varying degrees of display of typical flow-indicating sedimentary structures on dip vector maps and imaging logging images. While their accuracy has improved significantly, they are heavily dependent on logging data. Magnetic susceptibility anisotropy is a method that uses the anisotropy of internal magnetic susceptibility controlled by the original sedimentary structure to reverse the original structure at the time, and then uses this to reconstruct the paleocurrent direction. It can not only determine the paleocurrent direction with a single well, but is also not affected by factors such as the original topography and structure. However, it has strict requirements for sample selection and is not suitable for research blocks without outcrops or with scarce core data.

[0004] While macroscopic methods offer broad coverage, they lack precision and often require core samples, outcrops, and other data, making them time-consuming and unsuitable for detailed studies of small blocks. Seismic stratigraphy, on the other hand, is only applicable in study areas with complete seismic data and well-developed preseismic reflections. It can infer paleocurrent directions based on preseismic reflection structures, but its applicability is limited to study areas lacking outcrop data or with underdeveloped preseismic structures.

[0005] In summary, for small blocks with missing outcrop areas, scarce well logging and core data, and only available 3D seismic data, there is an urgent need for a highly accurate paleocurrent direction analysis method that conforms to actual geological conditions and is widely applicable. Summary of the Invention

[0006] To address the issues of missing outcrop areas, scarce well logging and core data, and low accuracy in determining paleocurrent direction for small blocks with only 3D seismic data, this invention proposes a paleocurrent direction analysis method based on paleochannel configuration and seismic geomorphology analysis. This method is highly accurate, conforms to actual geological conditions, and is widely applicable.

[0007] The objective of this invention is achieved through the following technical solution: A paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis includes the following steps: S1. Obtain core data of the study area, and then combine it with well logging data of the study area to classify the sedimentary lithofacies types of the study area, clarify the lithofacies assemblage types, and analyze the depositional genesis and environment of the ancient waterway; S2. Obtain three-dimensional seismic data of the study area, analyze the seismic attribute characteristics of the study area, and combine with step S1 to finely characterize the planar geometry and internal structure of the ancient waterway; S3. Analyze the ancient waterways that were finely depicted in step S2 to obtain the direction in which the number of waterways increases. The direction in which the number of waterways increases is the ancient flow direction of the waterways obtained in this step. S4. By statistically analyzing the width of the ancient waterway in different directions as finely depicted in step S2, and by statistically comparing the sampled widths in different directions, the variation pattern of the ancient waterway width is clarified, and the trend direction of the river channel from wide to narrow is obtained. The trend direction of the river channel from wide to narrow is the ancient flow direction of the river channel obtained in this step. S5. Based on steps S1 and S2, clarify the truncation and downflow convergence relationship in the development process of the ancient waterway, and then determine the upstream direction of the ancient river channel by the characteristics of the truncation and convergence relationship, that is, determine the ancient water flow direction in this step. S6. Combining steps S3-S5, determine the ancient flow direction.

[0008] Furthermore, in step S1, the core data includes information on the material composition, lithology, grain size, color, bioturbation, sedimentary structure, and layer thickness of the cores from the study area.

[0009] Furthermore, in step S1, the method for determining the lithofacies assemblage type is as follows: based on sediment grain size, combined with sedimentary structures and material composition, the sedimentary lithofacies types in the study area are divided, and then the lithofacies assemblage type is determined by combining the different vertical superposition relationships of lithofacies.

[0010] Furthermore, in step S1, the method for analyzing the depositional environment of ancient waterways is as follows: different lithofacies assemblage types are analyzed, and the depositional environment of ancient waterways is analyzed through color, erosion, contained debris, and structure.

[0011] Furthermore, in step S2, PaleoScan software is used to interpret the acquired three-dimensional seismic data, establish a sequence stratigraphic framework, analyze the seismic attribute characteristics of the study area, and use synthetic vertical seismic profile records to correct the seismic data. Seismic sedimentology research methods are used to perform stratigraphic slice analysis, bedding plane attribute extraction, and inter-layer attribute extraction analysis to finely characterize the planar geometry and internal structure of the ancient waterway.

[0012] Furthermore, in step S3, the method for obtaining the direction of increase in the number of river channels is as follows: based on the detailed depiction of the planar geometry of the ancient waterway in step S2, the distribution direction of the ancient waterway is obtained, the number of river channels perpendicular to the direction of the ancient waterway is counted, and based on the characteristic that the number of river channels will continuously increase and several tributaries will develop from the main stream during the development and evolution of the river, the ancient flow direction of the river channel is obtained.

[0013] Furthermore, in step S4, the method for clarifying the variation law of ancient waterway width is as follows: when the study area is the downstream of the river, based on the characteristic that the width of the river gradually narrows from the upstream direction to the downstream direction, the sampling intervals of the horizontal and vertical directions are fixed to eliminate the interference of human selection. Then, the waterway width in different directions of the ancient waterway is statistically compared, and the sampling width in different directions is statistically compared to obtain the trend direction of the river channel from wide to narrow, i.e., the ancient flow direction.

[0014] Furthermore, in step S5, the method for determining the ancient water flow direction is as follows: in the depicted seismic plane map, select a seismic plane map with a clear internal structure of the ancient waterway, and based on the lateral migration characteristics indicated by the internal structure of the ancient waterway, clarify the truncation and downflow convergence relationship in the development process of the ancient waterway, and then determine the upstream direction of the ancient river channel by the characteristics of the truncation and convergence relationship, thereby determining the ancient water flow direction.

[0015] Furthermore, the method for obtaining truncation and downflow convergence is as follows: In the development and evolution of rivers, the river channel continuously migrates and lateralizes, forming various sedimentary microfacies types. From these sediments, it is possible to obtain the characteristics of truncation in the upstream direction of the point dam, which transforms into downflow convergence characteristics in the downstream direction of the river, so as to determine the direction of paleocurrent.

[0016] Furthermore, the sedimentary microfacies types include point bar deposits, reverse point bar deposits, meandering zone deposits, and abandoned channel deposits.

[0017] The beneficial effects of this technical solution are as follows: 1. This scheme can be used to conduct detailed paleocurrent analysis in small blocks with missing outcrop areas, scarce well logging and core data, but available 3D seismic data and well-developed river channels.

[0018] 2. Compared with the commonly used seismic stratigraphy method for determining paleocurrent direction, the technical solution disclosed in this invention can be used to determine the paleocurrent direction of small blocks in areas where pre-earthquake sedimentary reflection is underdeveloped, and can be combined with river channel development to further refine the paleocurrent direction determination.

[0019] 3. This invention proposes a new research direction for the study of ancient flow directions.

[0020] 4. In this invention, the paleocurrent direction indicated by the changes in the number of river channels, the changes in the width of the river channels, and the internal structure of the river channels is combined and mutually verified and supplemented to eliminate the defects of multiple solutions that may exist in a single research method. Attached Figure Description

[0021] Figure 1 This is a flowchart of the paleocurrent analysis method of the present invention.

[0022] Figure 2 This is a diagram of sedimentary rock facies types.

[0023] Figure 3 This is a diagram of a composite waterway-filled sedimentary rock facies.

[0024] Figure 4 This is a diagram illustrating an isolated river channel-filled sedimentary rock facies.

[0025] Figure 5 This is a diagram illustrating the sedimentary rock facies assemblage of a crevasse fan.

[0026] Figure 6 This is a diagram of the overflow sedimentary rock facies assemblage.

[0027] Figure 7 This is a diagram of sedimentary rock facies assemblage in a floodplain.

[0028] Figure 8 This is a diagram illustrating the sedimentary rock facies assemblage in an underwater river channel.

[0029] Figure 9 This is a diagram of the sedimentary rock facies assemblage of the estuary.

[0030] Figure 10 This is a diagram of a composite sedimentary rock facies of river channel and estuary bar.

[0031] Figure 11 This is a planar distribution diagram of the RMS amplitude properties of different sand groups.

[0032] Figure 12 These are cross-sectional distribution diagrams of different sand groups.

[0033] Figure 13This is a map showing the distribution characteristics of the number of channels in different sand groups.

[0034] Figure 14 This is a diagram showing the characteristics of channel width variation in different sand groups.

[0035] Figure 15 This is a diagram showing the truncation and undercurrent convergence relationship during the development of the ancient waterway in the middle of the 14th sandstone group.

[0036] Figure 16 It represents the truncation and subsurface convergence relationship during the development of the paleochannel in the western part of the central section of the 16th sandstone group.

[0037] Figure 17 This is a diagram showing the truncation and undercurrent convergence relationship during the development of the ancient waterway in the northeastern part of the 16th sandstone group. Detailed Implementation

[0038] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Example: This embodiment uses paleocurrent analysis of a certain area in the Sichuan Basin as an example to further illustrate the specific solution of the invention. (Refer to...) Figure 1 .

[0040] Step 1: Analyze the comprehensive data from drilling cores, logging, and well logging to identify lithofacies and lithofacies assemblages. Combine the correlation between vertical lithofacies assemblages and sedimentary dynamics and sedimentary environment to clarify the genesis and environment of ancient waterways.

[0041] The specific steps include: (1) Identify the lithofacies type.

[0042] By observing the composition, lithology, grain size, color, bioturbation, sedimentary structures, and layer thickness of the core material, combined with well logging and well logging data, and based on sediment grain size, combined with sedimentary structures and material composition, the sedimentary facies types of the study area were classified. The lithology of the study area is mainly sandstone, siltstone, and mudstone, with conglomerate locally developed. The main bedding types are massive bedding, trough cross-bedding, platy cross-bedding, parallel bedding, post-accretionary bedding, normal sequence bedding, reverse sequence bedding, wavy cross-bedding, and horizontal bedding. Based on the above data, the lithofacies of the study area can be divided into 15 types: massive conglomerate (Sc), parallel bedding sandstone (Ps), tabular cross-bedding sandstone (Ts), trough cross-bedding sandstone (Cs), post-sedimentary bedding sandstone (Bs), graded sandstone (Ns), inverse graded sandstone (Is), massive sandstone (Ss), rippled cross-bedding siltstone (Rsi), horizontal bedding siltstone (Hsi), mélangeous facies (Cd), dark gray mudstone (Dm), purplish-red mudstone (Pm), dark gray mudstone (Gm), and variegated mudstone (Mm). (Reference) Figure 2 , Figure 2 In the middle: A-massive conglomerate facies; B-parallel bedding sandstone facies; C-platy cross-bedding sandstone facies; D-trough cross-bedding sandstone facies; E-post-accretive cross-bedding sandstone facies; F-order-grained sandstone facies; G-inverse-order-grained sandstone facies; H-massive sandstone facies; I-sand-ribbed cross-bedding siltstone facies; J-horizontal bedding siltstone facies; K-malignant accretionary facies; L-grayish-black mudstone facies; M-grayish-green and purplish-red mudstone facies; N-variegated mudstone facies.

[0043] (2) Identify the lithofacies assemblage type.

[0044] Based on the different vertical superposition relationships of lithofacies, a total of eight lithofacies assemblages were established. These are: composite channel-filling sedimentary lithofacies assemblage (FA1), isolated channel-filling sedimentary lithofacies assemblage (FA2), crevasse fan sedimentary lithofacies assemblage (FA3), overflow bank sedimentary lithofacies assemblage (FA4), floodplain sedimentary lithofacies assemblage (FA5), underwater channel sedimentary lithofacies assemblage (FA6), mouth bar sedimentary lithofacies assemblage (FA7), and channel-mouth bar composite sedimentary lithofacies assemblage (FA8).

[0045] The composite channel-filling sedimentary facies assemblage mainly consists of massive conglomerate facies, trough-shaped cross-bedding sandstone facies, and parallel-bedding sandstone facies. (Refer to...) Figure 3 .

[0046] The isolated channel-filling sedimentary facies assemblage is mainly composed of trough-shaped cross-bedding sandstone facies and tabular cross-bedding sandstone facies, reference Figure 4 .

[0047] The crevasse facies assemblage of sedimentary rocks mainly consists of trough-shaped cross-bedding sandstone facies, parallel-bedding sandstone facies, graded sandstone facies, mixed sedimentary facies, and rippled cross-bedding siltstone facies. (Reference) Figure 5 .

[0048] The overflow sedimentary facies assemblage mainly consists of cross-bedding siltstone facies, horizontally bedding siltstone facies, mixed sedimentary facies, and purplish-red mudstone facies. (Reference) Figure 6 ; The sedimentary rock facies assemblage of the floodplain mainly consists of purplish-red mudstone facies, variegated mudstone facies, and grayish-green mudstone facies. (Reference) Figure 7 ; The underwater channel sedimentary facies assemblage mainly consists of massive conglomerate facies, parallel-bedding sandstone facies, trough-shaped cross-bedding sandstone facies, and post-sedimentary bedding sandstone facies. (Reference) Figure 8 ; The sedimentary facies assemblage of the estuary bar mainly consists of cross-bedding siltstone facies, horizontally bedding siltstone facies, massive sandstone facies, inversely graded sandstone facies, and parallel-bedding sandstone facies. (Reference) Figure 9 ; The aforementioned channel-estuary bar composite sedimentary facies assemblage mainly consists of grayish-green mudstone facies, trough-shaped cross-bedding sandstone facies, inverse graded sandstone facies, and parallel bedding sandstone facies. (Reference) Figure 10 .

[0049] (3) Clarify the depositional environment of ancient waterways.

[0050] In FA1, the widespread development of erosion interfaces indicates extensive erosion and relatively strong hydrodynamic conditions, characteristic of a river channel complex. The rounded red mudstone gravel suggests that the river eroded the adjacent floodplain. Compared to FA1, FA2 exhibits relatively weaker erosive power. The presence of red clay clasts, carbonaceous debris, and mica indicates a longer transport distance of sediments within the channel. The alternation of sandstone layers with variegated mudstone facies is characteristic of the central or distal floodplain, suggesting that FA2 may be a branch channel of FA1 or an abandoned channel. FA3, similar to FA1, exhibits extensive erosion and relatively strong hydrodynamics, also characteristic of a river channel complex, but its stratigraphic thickness and overall composition are less than in FA1. The development of trough-shaped cross-bedding sandstone facies and mixed sedimentary facies reflects crevasse fan depositional characteristics. Furthermore, the facies transition from trough-shaped cross-bedding sandstone facies to rippled cross-bedding siltstone facies indicates a rapid decrease in water depth, also reflecting crevasse fan depositional characteristics.

[0051] FA4, dominated by interbedded pink sandstone, siltstone, and purplish-red mudstone, reflects a floodplain environment. The absence of erosion surfaces indicates it was not subjected to flooding. Carbonate nodules in the purplish-red mudstone facies indicate the exposure of the floodplain. Sand ripple bedding and horizontal bedding suggest weak hydrodynamics during deposition, while strong bioturbation indicates shallow-water conditions during deposition. FA5, with its relatively thick mudstone, indicates a stable hydrodynamic environment. The interbedded gray-green mudstone and variegated mudstone facies may indicate frequent inundation and exposure processes. Root traces in carbonate nodules, gypsum nodules, and the variegated and purplish-red mudstone facies indicate paleosol development, providing evidence of long-term exposure of floodplain sediments.

[0052] The facies superposition pattern of FA6 is similar to that of FA1, representing a composite channel-infill sedimentary body. FA6 deposits also belong to channel deposits. However, the common retained mud and gravel deposits are green or dark gray, indicating an anoxic underwater environment. The close proximity of sandstone layers to grayish-green mudstone facies further confirms this as an underwater channel deposit. FA7 exhibits a distinct reverse gradation, a typical characteristic of estuary bar deposits. Well-developed sand ripple bedding and bioturbation suggest a shallow water depth. The grayish-green siltstone and mudstone further indicate an anoxic underwater environment. FA8's lower reverse gradation is similar to FA7, representing an estuary bar deposit, while its upper normal gradation is similar to FA6, representing an underwater channel deposit. Vertical superposition of estuary bars and channel deposits is common at the shallow-water delta front. Estuary bar deposits at the underwater channel front are easily eroded by subsequent distributary channels, leading to the formation of a composite channel and estuary bar sedimentary body at the shallow-water delta front. Therefore, FA8 is used as one of the criteria for identifying shallow-water deltas.

[0053] In summary, FA1-FA3 are fluvial channel deposits, FA4-FA5 are fluvial non-channel deposits, and FA6-FA8 are shallow-water delta front deposits. The overall sedimentary environment of the paleochannels in the study area is a fluvial-deltaic depositional environment.

[0054] Step Two: Stratigraphic interpretation was carried out on the three-dimensional seismic data of the study area. Using seismic sedimentology research methods, various analyses were conducted, including stratigraphic slice analysis, bedding layer attribute extraction, and inter-layer attribute extraction, to finely characterize the planar geometry and internal structure of the ancient waterway.

[0055] The 3D seismic body used in this study covers an area of ​​8130 km². 2 The frequency range of the 3D seismic data is 11-77 Hz, with a dominant frequency of approximately 35 Hz and a vertical resolution of approximately 12.5 m. PaleoScan software was used to interpret the stratigraphy of the 3D seismic data, establish a sequence stratigraphic framework, analyze seismic properties, and correct the seismic data using synthetic vertical seismic profile records to identify channel deposits.

[0056] (1) Depict the planar geometric shape of the ancient waterway.

[0057] Seismic stratigraphic analysis primarily focused on the 23rd sand group. Through analysis of its root mean square (RMS) amplitude properties, the planar distribution patterns of paleochannels in the study area were summarized. Taking the 3rd sand group as an example, the planar distribution pattern of sediments in the study area was further analyzed, such as... Figure 11 As shown.

[0058] The second sand group corresponds to the early stage of J2s1. See [link / reference] Figure 11 Part A of the X region is dominated by shallow-water delta front deposits. High-amplitude banded sandstones are mainly distributed in the western part of the X region, exhibiting a distinct tortuous shape, corresponding to underwater channel deposits, with the channel width gradually decreasing from southwest to northeast. Sheet-like weak-amplitude reflection zones are commonly found in front of the channel, possibly representing mouth bar deposits. Sheet-like weak-amplitude reflection zones are also present in the western part of the Y region.

[0059] The J2s2 early stage, corresponding to the 6th sand group, mainly consists of shallow-water delta front deposits. See [link to relevant documentation]. Figure 11 In the central B section, tortuous high-amplitude underwater channel deposits and sheet-like low-amplitude mouth bar deposits are also common. Compared with the second sand group, the distribution area of ​​shallow-water delta front deposits in the western part of regions X and Y is significantly reduced in the sixth sand group. A new set of shallow-water delta front deposits developed in the eastern part of region Y, occupying most of the study area. Strong-amplitude tortuous seismic reflections are more common in the eastern part of region Y, and the width of the channels gradually decreases from northeast to southwest.

[0060] The 15th sand group corresponding to the middle J2s2 period is mainly composed of fluvial fan deposits. See [link to relevant documentation]. Figure 11 In section C, against a background of sheet-like, weak-amplitude reflections, the RMS amplitude properties of the 15th sand group exhibit tortuous characteristics at different scales. Compared to the 2nd and 6th sand groups, the banded reflections show strong tortuosity. From region Y to region X, the width of the tortuous seismic reflections gradually decreases from northeast to southwest. These wide tortuous seismic reflections represent channel-infill complexes, while the narrow tortuous seismic reflections may be isolated channel-infill deposits or channels in breach distributary deposits. The sheet-like, weak-amplitude reflections surrounding the tortuous banded reflections indicate breach fan or overflow deposits. The overall distribution pattern further suggests fluvial fan deposition.

[0061] (2) Depict the internal structure of the ancient waterway.

[0062] Two seismic profiles were plotted on the 3D seismic data, with the distribution of seismic profiles corresponding to the planar distribution. The internal configuration of the paleochannels was then located and marked on the seismic profiles. (Reference) Figure 12 , Figure 12Part A shows the bright spot reflections in a cross-section perpendicular to the sediment transport direction, indicating channel distribution; Part B shows the migration of the sedimentation center in a cross-section parallel to the sediment transport direction; Part C shows the positions of different sections in A and B. The channel distribution in a cross-section perpendicular to the sediment transport direction from northwest to southeast is shown as bright spot reflections. Figure 12 Sections A and C. Bright spot reflections are most common in J2s22 and J2s23, with a relatively large width in J2s23. Bright spot reflections are rare in J2s1, J2s21, and J2s24. Figure 12 Part A. In the upper part of J2s1, bidirectional imbricate progradational reflections were identified, indicating shallow-water delta front sedimentation in a northwest to southeast direction. This distribution pattern corresponds to... Figure 12 The planar distribution shown in section B.

[0063] A cross-section parallel to the direction of sediment transport, running from southwest to northeast, shows the migration of the sedimentary center. (See...) Figure 12 Sections B and C. Bidirectional progradational reflections were identified in J2s1, J2s21, and J2s22, indicating sediment deposition from both southwest and northeast directions, further suggesting the existence of two source channels. Furthermore, strong amplitude reflections were most common in J2s23, corresponding to… Figure 12 The bright spot reflection of J2s23 in part A.

[0064] Step 3: Based on the aforementioned distribution direction of ancient waterways, count the number of waterways perpendicular to the ancient waterway direction to clarify the variation pattern of the number of ancient waterways in different directions.

[0065] During the development and evolution of rivers, the number of channels continuously increases, evolving from a few main streams into numerous tributaries. Therefore, changes in the number of channels can be used to roughly determine the direction of ancient water flow. RMS amplitude attribute analysis was used to obtain the channel distribution of 23 sandstone groups in the study area, and the number of channels perpendicular to the ancient waterway direction was statistically analyzed. The statistical data were plotted into a histogram, and the histogram was used to further clarify the changing patterns of the number of channels in different directions. Taking three sandstone groups as examples, this study further illustrates how changes in the number of ancient waterways reflect the direction of ancient water flow.

[0066] refer to Figure 13 , Figure 13 These are distribution characteristics of the number of channels in different sand groups. Among them: A shows that the number of channels in region Y increases from northeast to southwest in the second sand group, while it increases from southwest to northeast in region X; B shows that the number of channels in region Y increases from northeast to southwest in the sixth sand group, while it increases from southwest to northeast in region X; C shows that the number of channels in region Y and region X both show an increasing trend from northeast to southwest in the fifteenth sand group.

[0067] As can be seen from the above, the number of channels in the second and sixth sandstone groups increases from northeast to southwest in region Y, while the opposite is true in region X (see [link to relevant documentation]). Figure 13 Therefore, in the second and sixth sand groups, the paleocurrent in region Y was from northeast to southwest, while in region X it was from southwest to northeast. In the 15th sand group, the number of channels in both regions X and Y increases from northeast to southwest (see reference). Figure 13 Therefore, the paleocurrent direction of the 15th sand group was generally from northeast to southwest.

[0068] Step 4: Based on the distribution direction of the ancient waterways, the width of the ancient waterways in different directions is statistically analyzed. The sampling intervals in the horizontal and vertical directions are fixed to eliminate interference from human selection. The sampling widths in different directions are statistically compared to clarify the variation pattern of the ancient waterway width.

[0069] The paleochannels in the study area are downstream channels of a river, characterized by a gradual narrowing of channel width from upstream to downstream. Therefore, RMS amplitude analysis can be used to obtain detailed channel width variations for each sand group in different regions, thus enabling analysis of paleocurrent direction. Channel widths for different sand groups were statistically analyzed, and the data were plotted into histograms to clarify the width variation patterns in different directions. Using three sand bodies as examples, the paleocurrent direction was further determined, with reference to... Figure 14 , Figure 14 The diagram shows the characteristics of channel width variation in different sand groups. In A, the channel width in region Y decreases from northeast to southwest in sand group 2, while in region X it decreases from southwest to northeast. In B, the channel width in region Y decreases from northeast to southwest in sand group 6, while in region X it decreases from southwest to northeast. In C, the channel width in region X and region X both show a decreasing trend from northeast to southwest in sand group 15.

[0070] As mentioned above, the channel width of both the second and sixth sand groups decreases from northeast to southwest in region Y, while the opposite is true in region X (see [reference]). Figure 14 Therefore, the paleocurrent direction of the second and sixth sand groups in region Y was northeast to southwest, while the paleocurrent direction in region X was southwest to northeast. In the 15th sand group, the channel width in regions X and Y gradually decreases from northeast to southwest (see [reference]). Figure 14 Therefore, the paleocurrent direction of the 15th sand group was generally from northeast to southwest.

[0071] Step 5: Select seismic plane attributes with clear internal structure of ancient waterways, and clarify the truncation and undercurrent convergence relationship in the development process of ancient waterways based on the lateral migration characteristics indicated by the internal structure of ancient waterways.

[0072] During the development and evolution of rivers, the river channel continuously migrates and accumulates laterally, forming various sedimentary microfacies such as point bar deposits, anti-point bar deposits, meander zone deposits, and abandoned channel deposits. From these deposits, it can be found that the deposits upstream of the point bar exhibit truncation characteristics, while those downstream of the river transform into downflow convergence characteristics. Therefore, these characteristics can be used to determine the direction of ancient water flow.

[0073] In the seismic plane properties of the 23 sand groups depicted in the second step, we search for sand group plane maps with clear internal structures and obvious lateral migration characteristics, and identify and clarify the truncation and undercurrent convergence relationships in the development process of ancient waterways.

[0074] Taking the 14th and 16th sand groups as examples, the paleocurrent direction was further determined. A series of distinct lateral channel deposits can be found in the central part of the seismic plan of the 14th sand group. These were identified, and their truncation and downflow convergence relationships were characterized. The truncation relationship in the figure is located in the northeast, transitioning to downflow convergence towards the southwest. Furthermore, the channel is continuous and runs through the study area, indicating that the upstream direction of the paleochannel throughout the study area is northeast. Figure 15 Therefore, during the 14th stage of river channel development, the study area exhibited a unidirectional paleocurrent, flowing from northeast to southwest.

[0075] In the west-central part of the seismic plan of the 16th sandstone group, a significant lateral thickening of the channel sediments can be observed, indicating that the channel underwent multiple stages of evolution. The truncation and downflow convergence relationships within these sediments were identified and characterized. The truncation relationship in the figure is located in the southwest, transitioning to downflow convergence towards the northeast, indicating that the upstream direction of the ancient waterway in the west-central part is southwest. Figure 16 Lateral sediments identified in the northeastern part of the study area indicate that the ancient waterway flowed northeastward. (See...) Figure 17 Therefore, during the 16th stage of river channel development, bidirectional paleocurrents were observed in the study area. The paleocurrent direction was southwest to northeast in the southwest of the study area, and northeast to southwest in the northeast of the study area.

[0076] Step 6: By combining the variation patterns of the number of ancient waterways in different directions in Step 3, the variation patterns of width in Step 4, and the truncation and undercurrent convergence relationship indicated by the internal structure in Step 5, the direction of the ancient water flow is determined.

[0077] The variation in the number of ancient waterways reveals that, among the 23 sandstone formations in the study area, formations 1, 2, 3, 5, 6, 8, 9, 11, 16, and 19 exhibited bidirectional paleocurrents, flowing southwest to northeast in region X and northeast to southwest in region Y. Formations 4, 7, 10, 12, 13, 14, 15, 17, 18, 20, 21, 22, and 23 showed unidirectional paleocurrents, flowing northeast to southwest in both regions X and Y. The variation in the width of the ancient waterways indicates that formations 2, 4, 5, 6, 7, 8, 9, 13, 16, 19, and 20 exhibited bidirectional paleocurrents, while formations 1, 3, 10, 11, 12, 14, 15, 17, 18, 21, 22, and 23 exhibited unidirectional paleocurrents.

[0078] Combining the patterns observed in both studies with the truncation and overcurrent convergence relationships within the paleochannels, it is concluded that during the development of sandstone formations 1-9, 16, and 19, the paleochannels in the study area were primarily bidirectional, flowing from the southwest and northeast towards the central part of the area, respectively. From formation 10 onwards, the paleochannel flow changed from bidirectional to unidirectional, flowing from northeast to southwest throughout the entire study area. However, during the development of sandstone formations 16 and 19, small-scale tectonic movements may have caused a change in the paleochannel direction, transforming it from unidirectional to bidirectional.

[0079] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis, characterized in that, Includes the following steps: S1. Obtain core data of the study area, and then combine it with well logging data of the study area to classify the sedimentary lithofacies types of the study area, clarify the lithofacies assemblage types, and analyze the depositional genesis and environment of the ancient waterway; S2. Obtain three-dimensional seismic data of the study area, analyze the seismic attribute characteristics of the study area, and combine with step S1 to finely characterize the planar geometry and internal structure of the ancient waterway; S3. Analyze the ancient waterways that were finely depicted in step S2 to obtain the direction in which the number of waterways increases; S4. By statistically analyzing the width of the ancient waterway in different directions as finely depicted in step S2, and by statistically comparing the sampled widths in different directions, the variation pattern of the ancient waterway width is clarified, and the trend direction of the river channel narrowing is obtained. S5. Based on steps S1 and S2, clarify the truncation and downflow convergence relationship in the development process of the ancient waterway, and then determine the upstream direction of the ancient river channel through the characteristics of the truncation and convergence relationship. The method for obtaining truncation and downflow convergence is as follows: During the development and evolution of rivers, the river channel continuously migrates and lateralizes, forming various sedimentary microfacies types. From these sediments, it is possible to obtain the characteristics of truncation in the upstream direction of the point dam, which transforms into downflow convergence characteristics in the downstream direction of the river, so as to determine the direction of paleocurrent. S6. Combining steps S3-S5, determine the ancient flow direction.

2. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that: In step S1, the core data includes information on the material composition, lithology, grain size, color, bioturbation, sedimentary structure, and layer thickness of the cores from the study area.

3. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 2, characterized in that, In step S1, the method for determining the lithofacies assemblage type is as follows: based on sediment grain size, combined with sedimentary structures and material composition, the sedimentary lithofacies types in the study area are divided, and then the lithofacies assemblage type is determined by combining the different vertical superposition relationships of lithofacies.

4. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 2, characterized in that, In step S1, the method for analyzing the depositional environment of ancient waterways is as follows: different lithofacies assemblage types are analyzed, and the depositional environment of ancient waterways is analyzed by color, erosion, contained debris, and structure.

5. The paleocurrent direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that: In step S2, PaleoScan software is used to interpret the acquired three-dimensional seismic data, establish a sequence stratigraphic framework, analyze the seismic attribute characteristics of the study area, and use synthetic vertical seismic profile records to correct the seismic data. Seismic sedimentology research methods are used to perform stratigraphic slice analysis, bedding plane attribute extraction, and inter-layer attribute extraction analysis to finely characterize the planar geometry and internal structure of the ancient waterway.

6. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that, In step S3, the method for obtaining the direction of increase in the number of river channels is as follows: based on the detailed depiction of the planar geometry of the ancient waterway in step S2, the distribution direction of the ancient waterway is obtained. The number of river channels perpendicular to the direction of the ancient waterway is counted. Based on the characteristic that the number of river channels will continuously increase and several tributaries will develop from the main stream during the development and evolution of the river, the ancient flow direction of the river channel is obtained.

7. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that, In step S4, the method for clarifying the variation law of ancient waterway width is as follows: when the study area is the downstream of the river, based on the characteristic that the width of the river gradually narrows from the upstream direction to the downstream direction, the sampling intervals of the horizontal and vertical directions are fixed to eliminate the interference of human selection. Then, the waterway width in different directions of the ancient waterway is statistically compared, and the sampling width in different directions is statistically compared to obtain the trend direction of the river channel from wide to narrow, i.e., the ancient flow direction.

8. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that, In step S5, the method for determining the direction of ancient water flow is as follows: on the depicted seismic plane map, select a seismic plane map with a clear internal structure of the ancient waterway, and based on the lateral migration characteristics indicated by the internal structure of the ancient waterway, clarify the truncation and downflow convergence relationship in the development process of the ancient waterway, and then determine the upstream direction of the ancient river channel by the characteristics of the truncation and convergence relationship, thereby determining the direction of ancient water flow.

9. The paleoflow direction analysis method based on paleochannel configuration and seismic geomorphology analysis according to claim 1, characterized in that: The sedimentary microfacies types include point bar deposits, reverse point bar deposits, meandering zone deposits, and abandoned channel deposits.

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