Method for predicting paleocurrent direction of braided river based on linear fractal theory

Abstract

The invention discloses a method for predicting the paleo-water flow direction of a braided river based on a linear fractal theory. The method comprises the following steps: S1, collecting well drilling data of a known unit, and drawing a plane layout diagram of the paleo-water flow direction of the known unit braided river; s2, coarsening the known unit plaid river paleocurrent direction plane distribution diagram to obtain a known unit coarsening model; s3, coarsening the model of a known unit, and solving linear fractal parameters according to known paleocurrent nodes; s4, utilizing a linear calculation formula to predict the palaeowater flow direction of the unknown unit to distinguish the river, and drawing a distribution diagram; and S5, according to actual geology, perfecting the plane distribution map of the paleocurrent direction of the unknown unit, and completing prediction of the paleocurrent direction of the braided river. According to the method for predicting the paleo-water flow direction of the braided river based on the linear fractal theory, the paleo-water flow direction is predicted through the mathematical theory, the accuracy of predicting the paleo-water flow direction of the braided river in a non-exploration mature area is improved, and the problem that prediction cannot be conducted due to lack of data in the non-mature exploration area is solved.

Description

Technical Field

[0001] This invention belongs to the field of natural gas exploration and development technology, specifically involving a method for predicting the direction of ancient flow in braided rivers based on linear fractal theory. Background Technology

[0002] In the field of oil and gas geological exploration technology, the analysis and determination of ancient flow direction of braided rivers is one of the important means to analyze the sedimentary environment and sedimentary system of the study block. The ancient flow direction of braided rivers determines the main source direction and diffusion direction of sediments in a certain period, which is related to the distribution pattern of sand bodies and the spread of sedimentary systems. It is of great significance for predicting the distribution range of favorable reservoirs, optimizing injection and production schemes, and improving recovery rate.

[0003] Currently, commonly used methods for analyzing the paleocurrent direction of braided rivers can be broadly categorized into two types: microscopic methods for determining the flow direction at a specific location and macroscopic methods for determining the flow direction over a large area. Microscopic methods mainly include the directional arrangement of typical sedimentary structures, 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, sedimentary facies and sedimentary system distribution, stratigraphic thickness variations, seismic stratigraphy, and paleontological studies.

[0004] However, the above methods have certain limitations when used in different geological contexts. Microscopic methods can directly and accurately determine the direction of ancient water flow through specific bedding or layer structures, such as the dip direction of pre-accumulated fine layers in trough-like cross-bedding parallel to the direction of ancient water flow, the dip of pre-accumulated fine layers in platy cross-bedding, and the dip of steeply dipped surfaces in asymmetric ripple marks [Jin Xueying 2018]. Furthermore, the imbricate directional arrangement of gravels and elongated fossils can also reflect the direction of ancient water flow; for example, in sedimentary environments such as rivers and gravity channels, the long axis represents the direction of ancient water flow, while in coastal and lacustrine environments, the long axis is perpendicular to the direction of ancient water flow [Li Xiangdong 2020, Du Yuansheng 2018, Liang Liping 2012]. However, these methods are not suitable for study blocks without outcrops or with severe outcrop cover. Dip logging and imaging logging can determine the direction of ancient water flow by displaying typical flow direction-indicating sedimentary structures to varying degrees on dip vector maps and imaging logging images, even when outcrops and core samples are missing in the field [Liu Bei 2022; Fu Jianwei 2021; Chinese invention patent "Dip logging data correction, model establishment and paleoflow direction determination method and device" filed on September 19, 2022, application number 202211134748.1 and Chinese invention patent "A method for determining paleoflow direction using electrical imaging logging" filed on May 16, 2018, application number 201810465781.X]. While their accuracy has improved significantly, they are still heavily limited by the availability of logging data. Magnetic susceptibility anisotropy can be used to determine the direction of paleocurrent using single-well data and is not affected by factors such as original topography and structure [Zhang Dongmeng 2023, Li Yanjie 2022, Zou Ning 2017]. However, it has strict requirements for sample selection and is not suitable for research blocks without outcrops or with scarce core data.

[0005] While macroscopic methods offer broad coverage, they lack precision and often require core samples and outcrop data, making them time-consuming and unsuitable for detailed studies of small blocks. Seismic stratigraphy, on the other hand, requires complete seismic data and well-developed preseismic reflections in the study area. The Chinese invention patent "A Method for Paleocurrent Direction Analysis Based on Paleochannel Configuration and Seismic Geomorphology Analysis" (application date: 2022-09-22, application number 202211154709.8) is not highly applicable to study areas lacking outcrop data or with underdeveloped preseismic structures.

[0006] To address the issues of missing outcrop areas, scarcity of well logging and core data, and low accuracy in determining paleoflow direction in small blocks with 3D seismic data, it is urgent to develop a new method for predicting the paleoflow direction of braided rivers. Summary of the Invention

[0007] The purpose of this invention is to provide a method for predicting the paleocurrent direction of braided rivers based on linear fractal theory. By using mathematical theory to predict the paleocurrent direction, the accuracy of paleocurrent direction prediction for braided rivers in non-mature exploration areas is improved, and the problem of being unable to predict paleocurrent direction in non-mature exploration areas due to lack of data is solved.

[0008] The technical solution adopted in this invention is a method for predicting the paleocurrent direction of braided rivers based on linear fractal theory. The specific steps are as follows:

[0009] S1. Collect drilling data of known units and draw a planar distribution map of the ancient water flow direction of braided rivers in known units based on the drilling data;

[0010] S2. Coarsen the planar distribution map of the ancient flow direction of the braided river in the known unit to obtain the coarsened model of the known unit;

[0011] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0012] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit, and draw a distribution map of the paleocurrent direction of the unknown unit.

[0013] S5. Modify and improve the ancient water flow direction distribution map of the unknown unit based on the actual geological conditions to be predicted, and complete the prediction of the ancient water flow direction of the braided river.

[0014] The invention is further characterized by:

[0015] The drilling data in S1 includes the well location coordinates of the study area, the sand body thickness of the study layer, and the sand body distribution map.

[0016] Specifically, Geomap 3.6, an industrial mapping software, was used in S1 to draw a planar distribution map of the ancient flow direction of the braided river.

[0017] In S2, after coarsening the planar distribution map of the ancient flow direction of the braided river in the known unit, the main, regular, and reliable branches are retained, while the uncertain parts are removed.

[0018] The specific operation method of S3 is as follows:

[0019] Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas.

[0020] xB1=xA1+L / v1*cosα (1)

[0021] yB2=yA1+L / v1*sinα (2)

[0022] xB2=xA2+L / v1*cos(α+γ) (3)

[0023] yB2=yA2+L / v1*sin(α-γ)(4)

[0024] xC2=xB2+L / v2*cos(α+β) (5)

[0025] yC2=yB2+L / v2*sin(α-β) (6)

[0026] xD2==xB2+L / v3*cos(α+γ) (7)

[0027] yD2=yA2+L / v3*sin(α-γ) (8)

[0028] The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions.

[0029] The specific method for S4 is as follows: using the values ​​of the linear fractal parameters α, β, γ, v1, v2, v3, and L obtained from S3, and the linear calculation formula, the paleocurrent direction joints of the unknown unit are calculated. Based on the calculation of the paleocurrent joints of the unknown unit, the linear calculation formula is as follows:

[0030] x n+1 =k*x n +e (9)

[0031] y n+1 =g*x n +f (10)

[0032] Then, the distribution map of the ancient water flow direction of the unknown unit was drawn using the industrial mapping software Geomap 3.6.

[0033] The specific method of S5 is as follows: using the unknown paleowater flow direction plane distribution map drawn by S4, modifying and improving the drawn paleowater flow direction plane distribution map in combination with the geological background, deploying well locations, and completing the prediction of the paleowater flow direction of the braided river.

[0034] The beneficial effects of this invention are:

[0035] (1) This invention is a method for predicting the paleoflow direction of braided rivers based on linear fractal theory. It has the characteristics of linear fractal mathematical model in the comprehensive analysis of the paleoflow direction of braided rivers in known units in mature exploration areas. It innovatively establishes a method for predicting the paleoflow direction of braided rivers in unknown units (immature exploration areas) using linear fractal mathematical model. This invention applies the method of predicting the paleoflow direction of braided rivers based on linear fractal theory to geological oil and gas field exploration. It is easy to operate, quantitative, and fills the gap in immature exploration areas where prediction is not possible due to limited data. It provides geological basis for the optimal well location deployment and the search for favorable natural gas enrichment areas in exploration and development blocks.

[0036] (2) The prediction method of this invention is based on the development characteristics of braided river paleocurrents. It can make relatively accurate predictions of the planar distribution of braided river paleocurrents with low exploration levels by using the linear fractal principle. It has strong practicality, reliability and operability. Attached Figure Description

[0037] Figure 1 This is a paleocurrent direction distribution map of a known stratigraphic unit in a certain region of a basin in Embodiment 1 of the prediction method of the present invention;

[0038] Figure 2 This is a model diagram of the paleocurrent direction of a known unit in a certain stratigraphic layer of a certain region in a basin, as shown in Embodiment 1 of the prediction method of the present invention.

[0039] Figure 3 This is a paleocurrent direction distribution map of a known unit and a predicted unit in a certain stratigraphic layer of a certain region in a basin, as shown in Embodiment 1 of the prediction method of the present invention. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0041] The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory includes the following specific steps:

[0042] S1. Collect drilling data of known units (exploration mature areas) and draw a planar distribution map of the ancient flow direction of braided rivers in the known units based on the drilling data;

[0043] The drilling data includes the well location coordinates of the study area, the sand body thickness of the study strata, and the sand body distribution map.

[0044] Specifically, Geomap 3.6, an industrial mapping software, was used to draw a planar distribution map of the ancient flow direction of the braided river.

[0045] S2. Coarsening the planar distribution map of the ancient flow direction of the braided river in the known unit (exploration mature area) is called modeling. The main, regular and reliable branches are retained, and the uncertain parts are removed to obtain the coarsened model of the known unit.

[0046] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0047] The specific operating method is as follows:

[0048] Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas.

[0049] xB1=xA1+L / v1 *cosα (1)

[0050] yB2=yA1+L / v1 *sinα (2)

[0051] xB2=xA2+L / v1 *cos(α+γ) (3)

[0052] yB2=yA2+L / v1 *sin(α-γ) (4)

[0053] xC2=xB2+L / v2 *cos(α+β) (5)

[0054] yC2=yB2+L / v2 *sin(α-β) (6)

[0055] xD2==xB2+L / v3 *cos(α+γ) (7)

[0056] yD2=yA2+L / v3 *sin(α-γ) (8)

[0057] The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions.

[0058] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit (unexplored immature area) and draw the distribution map of the paleocurrent direction of the unknown unit.

[0059] The specific method is as follows: using the values ​​of the linear fractal parameters α, β, γ, v1, v2, v3, and L obtained from S3 and the linear calculation formula, the paleocurrent direction joints of the unknown unit are calculated. Based on the calculation of the paleocurrent joints of the unknown unit, the linear calculation formula is as follows:

[0060] x n+1 =k*x n +e (9)

[0061] y n+1 =g*x n +f (10)

[0062] Then, the distribution map of the ancient water flow direction of the unknown unit was drawn using the industrial mapping software Geomap 3.6.

[0063] S5. Based on the actual geological conditions to be predicted, modify and improve the ancient water flow direction distribution map of the unknown unit (exploration immature area) to complete the prediction of the ancient water flow direction of the braided river.

[0064] The specific method is as follows: using the unknown paleowater flow direction planar distribution map drawn by S4, and combining it with the geological background, the drawn paleowater flow direction planar distribution map is modified and improved, well locations are deployed, and the prediction of the paleowater flow direction of the braided river is completed.

[0065] This invention predicts the paleocurrent direction of braided rivers based on linear fractal theory. This technique enables accurate prediction of the paleocurrent direction of braided rivers. Although braided rivers exhibit complex geomorphological features with crisscrossing valleys, from a modern mathematical perspective, they possess significant fractal characteristics at both macro and micro scales—"their constituent parts are similar to the whole in some way." Based on this characteristic, this patent innovatively utilizes mathematical theory to predict paleocurrent direction, improving the accuracy of paleocurrent direction prediction in braided rivers in non-mature exploration areas. It solves the problem of unpredictable paleocurrent direction prediction in non-mature exploration areas due to a lack of data. The method is simple, low-cost, and easy to promote, possessing strong market competitiveness. It provides a favorable basis for further predicting sand body distribution and also provides geological evidence for the selection of exploration and development blocks, well location deployment, and the search for favorable natural gas enrichment areas.

[0066] This patent studies the linear fractal nature of the paleocurrent direction of braided rivers from the same source and water system. Specifically, viewed from a fractal perspective, the paleocurrent direction of braided rivers exhibits a self-similar, multi-level, dendritic branching structure. This manifests as secondary paleocurrent directions obliquely intersecting with the primary paleocurrent direction, continuously subdividing into more secondary paleocurrents. The differences between paleocurrents and secondary paleocurrents lie only in their approximate positions and scales. The next level of branching can be seen as the result of translation, rotation, expansion, and contraction of the previous level's branching structure.

[0067] Example 1

[0068] A specific study section within a certain basin consists of braided river deposits of the same provenance and drainage system. The paleocurrents and secondary paleocurrents differ only in location and scale. The subsequent bifurcation structure can be viewed as the result of translation, rotation, and expansion / contraction of the preceding paleocurrent, exhibiting linear fractal characteristics. Therefore, this patented technique can be used to predict the overall planar distribution of braided river paleocurrents in immature exploration areas of unknown units by analyzing the planar distribution of braided river paleocurrent directions in known units of mature exploration areas.

[0069] The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory includes the following specific steps:

[0070] S1. Collect drilling data from known units (exploration mature areas), and draw a planar distribution map of the ancient flow direction of braided rivers in the known units based on the drilling data, such as... Figure 1 As shown;

[0071] The drilling data includes the well location coordinates of the study area, the sand body thickness of the study strata, and the sand body distribution map.

[0072] Specifically, Geomap 3.6, an industrial mapping software, was used to draw a planar distribution map of the ancient flow direction of the braided river.

[0073] S2. The planar distribution map of the braided river paleocurrent direction in the known unit (exploration mature area) is coarsened, i.e., modeled. The main, regular, and reliable branches are retained, while uncertain parts are removed, resulting in a coarsened model of the known unit, such as... Figure 1 As shown;

[0074] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0075] The specific operating method is as follows:

[0076] Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas.

[0077] xB1=xA1+L / v1 *cosα (1)

[0078] yB2=yA1+L / v1 *sinα (2)

[0079] xB2=xA2+L / v1 *cos(α+γ) (3)

[0080] yB2=yA2+L / v1 *sin(α-γ) (4)

[0081] xC2=xB2+L / v2 *cos(α+β) (5)

[0082] yC2=yB2+L / v2 *sin(α-β) (6)

[0083] xD2==xB2+L / v3 *cos(α+γ) (7)

[0084] yD2=yA2+L / v3 *sin(α-γ) (8)

[0085] The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions, and their specific values ​​are shown in Table 1.

[0086] Table 1 Fractal Parameters of Prediction Unit

[0087] Prediction Unit α(。) β(。) γ(。) V1 V2 v3 L(km) 1 105 38 37 3.5 3.1 2.9 6.2 2 121 32 34 2.6 2.0 1.9 4.5

[0088] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit (unexplored immature area) and draw the distribution map of the paleocurrent direction of the unknown unit.

[0089] The specific method is as follows: using the values ​​of the linear fractal parameters α, β, γ, v1, v2, v3, and L obtained from S3 and the linear calculation formula, the paleocurrent direction joints of the unknown unit are calculated. Based on the calculation of the paleocurrent joints of the unknown unit, the linear calculation formula is as follows:

[0090] x n+1 =k*x n +e (9)

[0091] y n+1 =g*x n +f (10)

[0092] Then, the distribution map of the ancient water flow direction of the unknown unit was drawn using the industrial mapping software Geomap 3.6, such as... Figure 3 As shown.

[0093] S5. Based on the actual geological conditions to be predicted, modify and improve the planar distribution map of the ancient water flow direction of the unknown unit (the exploration immature area) to complete the prediction of the ancient water flow direction of the braided river.

[0094] The specific method is as follows: using the unknown paleowater flow direction planar distribution map drawn by S4, and combining it with the geological background, the drawn paleowater flow direction planar distribution map is modified and improved, well locations are deployed, and the prediction of the paleowater flow direction of the braided river is completed.

[0095] Example 2

[0096] The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory includes the following specific steps:

[0097] S1. Collect drilling data of known units and draw a planar distribution map of the ancient water flow direction of braided rivers in known units based on the drilling data;

[0098] The drilling data includes the well location coordinates of the study area, the sand body thickness of the study strata, and the sand body distribution map.

[0099] Specifically, Geomap 3.6, an industrial mapping software, was used to draw a planar distribution map of the ancient flow direction of the braided river.

[0100] S2. Coarsening the planar distribution map of the ancient flow direction of the braided river in the known unit, i.e. modeling, retaining the main, regular, and reliable branches, and removing the uncertain parts, to obtain the coarsened model of the known unit.

[0101] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0102] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit, and draw a distribution map of the paleocurrent direction of the unknown unit.

[0103] S5. Based on the actual geological conditions to be predicted, modify and improve the planar distribution map of the ancient water flow direction of the unknown unit to complete the prediction of the ancient water flow direction of the braided river.

[0104] Example 3

[0105] The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory includes the following specific steps:

[0106] S1. Collect drilling data of known units and draw a planar distribution map of the ancient water flow direction of braided rivers in known units based on the drilling data;

[0107] S2. Coarsening the planar distribution map of the ancient flow direction of the braided river in the known unit, i.e. modeling, retaining the main, regular, and reliable branches, and removing the uncertain parts, to obtain the coarsened model of the known unit.

[0108] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0109] The specific operating method is as follows:

[0110] Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas.

[0111] xB1=xA1+L / v1 *cosα (1)

[0112] yB2=yA1+L / v1 *sinα (2)

[0113] xB2=xA2+L / v1 *cos(α+γ) (3)

[0114] yB2=yA2+L / v1 *sin(α-γ) (4)

[0115] xC2=xB2+L / v2 *cos(α+β) (5)

[0116] yC2=yB2+L / v2 *sin(α-β) (6)

[0117] xD2==xB2+L / v3 *cos(α+γ) (7)

[0118] yD2=yA2+L / v3 *sin(α-γ) (8)

[0119] The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions.

[0120] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit, and draw a distribution map of the paleocurrent direction of the unknown unit.

[0121] S5. Based on the actual geological conditions to be predicted, modify and improve the planar distribution map of the ancient water flow direction of the unknown unit to complete the prediction of the ancient water flow direction of the braided river.

[0122] The specific method is as follows: using the unknown paleowater flow direction planar distribution map drawn by S4, and combining it with the geological background, the drawn paleowater flow direction planar distribution map is modified and improved, well locations are deployed, and the prediction of the paleowater flow direction of the braided river is completed.

[0123] Example 4

[0124] The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory includes the following specific steps:

[0125] S1. Collect drilling data of known units and draw a planar distribution map of the ancient water flow direction of braided rivers in known units based on the drilling data;

[0126] S2. Coarsening the planar distribution map of the ancient flow direction of the braided river in the known unit, i.e. modeling, retaining the main, regular, and reliable branches, and removing the uncertain parts, to obtain the coarsened model of the known unit.

[0127] S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known paleocurrent nodes.

[0128] The specific operating method is as follows:

[0129] Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas.

[0130] xB1=xA1+L / v1 *cosα (1)

[0131] yB2=yA1+L / v1 *sinα (2)

[0132] xB2=xA2+L / v1 *cos(α+γ) (3)

[0133] yB2=yA2+L / v1 *sin(α-γ) (4)

[0134] xC2=xB2+L / v2 *cos(α+β) (5)

[0135] yC2=yB2+L / v2 *sin(α-β) (6)

[0136] xD2==xB2+L / v3 *cos(α+γ) (7)

[0137] yD2=yA2+L / v3 *sin(α-γ) (8)

[0138] The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions.

[0139] S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit, and draw a distribution map of the paleocurrent direction of the unknown unit.

[0140] The specific method is as follows: using the values ​​of the linear fractal parameters α, β, γ, v1, v2, v3, and L obtained from S3 and the linear calculation formula, the paleocurrent direction joints of the unknown unit are calculated. Based on the calculation of the paleocurrent joints of the unknown unit, the linear calculation formula is as follows:

[0141] x n+1 =k*x n +e (9)

[0142] y n+1 =g*x n +f (10)

[0143] Then, the distribution map of the ancient water flow direction of the unknown unit was drawn using the industrial mapping software Geomap 3.6.

[0144] S5. Based on the actual geological conditions to be predicted, modify and improve the planar distribution map of the ancient water flow direction of the unknown unit to complete the prediction of the ancient water flow direction of the braided river.

Claims

1. A method for predicting the paleocurrent direction of braided rivers based on linear fractal theory, characterized in that, The specific steps are as follows: S1. Collect drilling data of known units and draw a planar distribution map of the ancient water flow direction of braided rivers in known units based on the drilling data; S2. The planar distribution map of the ancient flow direction of the braided river in the known unit is coarsened to obtain the coarsened model of the known unit. S3. For the known unit coarsening model, select the linear fractal fitting formula and obtain the linear fractal parameters based on the known ancient flow nodes; S4. Using linear fractal parameters and linear calculation formulas, predict the paleocurrent direction of the unknown unit, and draw a distribution map of the paleocurrent direction of the unknown unit. S5. Modify and improve the ancient water flow direction distribution map of the unknown unit based on the actual geological conditions to be predicted, and complete the prediction of the ancient water flow direction of the braided river.

2. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 1, characterized in that, The drilling data in S1 includes the well location coordinates of the study area, the sand body thickness of the study layer, and the sand body distribution map.

3. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 1, characterized in that, Specifically, in S1, the industrial drawing software Geomap 3.6 is used to draw a planar distribution map of the ancient water flow direction of the braided river.

4. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 1, characterized in that, In S2, after coarsening the planar distribution map of the ancient flow direction of the known braided river unit, the main, regular, and reliable branches are retained, while the uncertain parts are removed.

5. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 1, characterized in that, The specific operation method of S3 is as follows: Assume the coordinates of the primary paleocurrent joints A1, B1, C1, and D1 are (xA1, yA1), (xB1, yB1), (xC1, yC1), and (xD1, yD1), respectively; and the coordinates of the secondary joints A2, B2, C2, and D2 are (xA2, yA2), (xB2, yB2), (xC2, yC2), and (xD2, yD2), respectively. The angle between the primary paleocurrent A1B1 and the horizontal direction is α; the angles between the primary paleocurrent A1B1 and the secondary paleocurrents B1D1 and B1C1 are β and γ, respectively; the contraction velocity of the primary paleocurrent is v1; and the contraction velocities of the secondary paleocurrents are v2 and v3. The parameters α, β, γ, v1, v2, and v3 are obtained through linear fractal formulas. xB1=xA1+L / v1 *cosα (1) yB2=yA1+L / v1 *sinα (2) xB2=xA2+L / v1 *cos(α+γ) (3) yB2=yA2+L / v1 *sin(α-γ) (4) xC2=xB2+L / v2 *cos(α+β) (5) yC2=yB2+L / v2 *sin(α-β) (6) xD2==xB2+L / v3 *cos(α+γ) (7) yD2=yA2+L / v3 *sin(α-γ) (8) The parameters α, β, γ, v1, v2, v3, and L are calculated using trigonometric functions.

6. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 5, characterized in that, The specific method of S4 is as follows: using the values ​​of the linear fractal parameters α, β, γ, v1, v2, v3, and L obtained in S3 and the linear calculation formula, the paleocurrent direction key points of the unknown unit are calculated. Based on the calculation of the paleocurrent key points of the unknown unit, the linear calculation formula is as follows: x n+1 =k*x n +e (9) y n+1 =g*x n +f (10) Then, the distribution map of the ancient water flow direction of the unknown unit was drawn using the industrial mapping software Geomap 3.

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7. The method for predicting the paleocurrent direction of braided rivers based on linear fractal theory according to claim 1, characterized in that, The specific method of S5 is as follows: using the unknown paleowater flow direction plane distribution map drawn in S4, modifying and improving the drawn paleowater flow direction plane distribution map in combination with the geological background, deploying well locations, and completing the prediction of the paleowater flow direction of the braided river.

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