Calculation method of stack thickness of sedimentary cutting plane in fluvial reservoirs at large well spacing

Abstract

The present invention provides a method for calculating the thickness of the cut-off surface of the river-facies reservoir sedimentary layer under large well spacing, and the method for calculating the thickness of the cut-off surface of the river-facies reservoir sedimentary layer under large well spacing includes: step 1, establishing a sequence stratigraphic framework in the study area; step 2, identifying the boundary of the reservoir corresponding to the stratigraphic slice; step 3, determining the cut-off pattern of the sand body between wells; step 4, establishing an initial lithofacies model based on phase control, and carrying out sparse pulse inversion in the study area; step 5, calculating the thickness n of the lateral cut-off part; step 6, when the connectivity between the two wells is good, adjusting the well network, designing the perforation depth and thickness, and realizing balanced injection and production. The method for calculating the thickness of the cut-off surface of the river-facies reservoir sedimentary layer under large well spacing designs an implementation method for well network deployment and perforation scheme according to the cut-off thickness of the river channel sand body, which has better operability than before, is innovative and practical, and is conducive to promotion.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum development geological fine reservoir description research, and in particular to a method for calculating the thickness of the cut surface of a fluvial phase reservoir sedimentation under large well spacing. Background Art

[0002] Chengdao Oilfield is located in the shallow waters of the southern Bohai Bay. The upper section of the Guandao Oilfield is the main oil-bearing stratum, with a proven oil-bearing area of ​​65.9 km2. 2 , the reported geological reserves are 1.94×10 8 t. The oil field was put into development in 1993, with an output of 324.6×10 4 t, accounting for 13.8% of the output of Shengli Oilfield.

[0003] During the water injection development of the upper section of Guan, in the river sand bodies distributed over a large area, the injection conditions between the injection and production wells were poor, the production conditions were unfavorable, there was a difference between the water absorption profile and the comprehensive water content of the single well on the plane, and the remaining oil was unevenly distributed, which seriously affected the further improvement of the oil field recovery rate. The main reasons for the analysis are three aspects: First, the reservoir of the upper section of Guan in Chengdao Oilfield belongs to river phase deposition. Due to the frequent migration of the river channel during the deposition process, different river channels cut each other and formed composite river channel sand bodies on the superimposed plane; second, due to the variable sedimentary environment of the river phase, the lithology, physical properties and thickness of the reservoir on the plane change rapidly (this is not only the concept of thickness, but also the meaning of lithology, physical properties and oil content), and the oil and water movement laws and influencing factors in the study area are lacking; third, due to the large offshore well spacing and the lack of dynamic monitoring data, the connectivity of the sand bodies between wells only relies on logging data, which cannot truly reflect the connectivity of the sand bodies and achieve balanced injection and production.

[0004] In the Chinese patent application with application number: CN201910332462.6, a method for calculating effective sand thickness based on stratification coefficient is involved, which relates to the field of oil and gas development technology, solves the problem that the thickness of a single sandstone layer is too small to achieve the purpose of storing oil and gas, and the accumulation of multiple layers of thin sand will cause the misidentification of the main river channel or sand bar. The key points of its technical solution are: comprising the following steps: determining the continental reservoir type according to the sedimentary genesis of the sandstone reservoir; obtaining the total formation thickness G of the continental reservoir; obtaining the effective sandstone thickness S and the thin layer overflow sandstone thickness L of the main reservoir genesis of the continental reservoir; calculating the effective reservoir coefficient F according to the total formation thickness G, the effective sandstone thickness S, and the thin layer overflow sandstone thickness L, F = S / GE1+L / GE2, wherein E1 is the effective stratification coefficient and E2 is the overflow stratification coefficient.

[0005] In the Chinese patent application with application number: CN201811492987.8, a method and device for predicting the thickness of a thin sandstone reservoir are involved. The method for predicting the thickness of a thin sandstone reservoir includes: generating a drilling comparison profile of a thin sandstone reservoir according to logging curve data and a core deposition sequence; calculating the rock physical parameters of the thin sandstone reservoir according to the logging curve data and the drilling comparison profile; calculating the top reflection coefficient sequence and the bottom reflection coefficient sequence of the thin sandstone reservoir according to the logging curve data; establishing a thickness prediction template according to the rock physical parameters, the logging curve data, the top reflection coefficient sequence and the bottom reflection coefficient sequence; calibrating the horizon of the thin sandstone reservoir using the reflection coefficient sequence and seismic data; extracting the seismic reflection peak amplitude parameter according to the horizon calibration result; and calculating the thickness of the thin sandstone reservoir according to the seismic reflection peak amplitude parameter and the thickness prediction template.

[0006] In the Chinese patent application with application number: CN201711133194.2, a method for predicting the cumulative thickness of thin interbedded sand bodies of sand and mudstone is involved. The method for predicting the cumulative thickness of thin interbedded sand bodies of sand and mudstone includes: step 1, loading seismic data; step 2, determining the time window range for extracting seismic attributes; step 3, extracting root mean square amplitude attributes and centroid frequency attributes; step 4, establishing a relationship between root mean square amplitude, centroid frequency and relative cumulative thickness of thin interbedded sand bodies; step 5, calculating the relative cumulative thickness of thin interbedded sand bodies of sand and mudstone and obtaining a correction coefficient; step 6, calculating the cumulative thickness of thin interbedded sand bodies of sand and mudstone and mapping them.

[0007] The above existing technologies are quite different from the present invention and fail to solve the technical problem we want to solve. The upper section of the Guanshang oil reservoir in Chengdao Oilfield adopts offshore platform drilling and well group development. Therefore, the economic benefit is the center and the goal is to improve the well network and increase the oil production rate and recovery rate during the effective life of the platform. For this reason, we have invented a new method for calculating the thickness of the cut-off surface of the river phase reservoir sedimentary section under large well spacing. Summary of the invention

[0008] The purpose of the present invention is to provide a method for calculating the lateral cut-off thickness of the sedimentary cut-off surface of the river phase reservoir under large well spacing conditions by combining seismic, well logging and geological comprehensive research, which can effectively understand the connectivity of the well point reservoir and the calculation method of the cut-off thickness of the sedimentary cut-off surface of the river phase reservoir under large well spacing.

[0009] The object of the present invention can be achieved by the following technical measures: a method for calculating the thickness of the cut-off surface of the river facies reservoir sedimentation under large well spacing, the method for calculating the thickness of the cut-off surface of the river facies reservoir sedimentation under large well spacing comprises:

[0010] Step 1, establish the sequence stratigraphic framework of the study area;

[0011] Step 2, identifying the boundary of the reservoir corresponding to the stratigraphic slice;

[0012] Step 3, determining the inter-well sand body cutting and stacking pattern;

[0013] Step 4: Establish an initial lithofacies model based on phase control and conduct sparse pulse inversion in the study area;

[0014] Step 5, calculating the thickness n of the lateral cut and overlapped portion;

[0015] Step 6: When the connectivity between the two wells is good, adjust the well pattern, design the perforation depth and thickness, and achieve balanced injection and production.

[0016] The purpose of the present invention can also be achieved by the following technical measures:

[0017] In step 1, based on the completion data and guided by the sub-layer and single sand body division marks determined by the core wells, genetic sand body comparison is carried out to establish the stratigraphic framework of the study area, thereby ensuring the relative isochronism of the same river deposition.

[0018] In step 1, rock electrical calibration is carried out according to the coring wells to identify the sedimentary cycles and determine the division interfaces of sand groups, sublayers and single sand bodies in turn. On this basis, by flattening the marker layers and applying the completed drilling data, vertically, the sand layer groups, sublayers and single sand bodies are controlled step by step. In the plane, the characteristics of fluvial phase deposition are used as a guide and the coring wells are used as the basis to carry out detailed stratigraphic comparison.

[0019] In step 1, vertical wells are selected, synthetic seismic records are developed, well-seismic time-depth conversion is performed, the seismic interpretation horizon is determined, and the comparison results of the stratification interfaces of each well are verified.

[0020] In step 1, based on the core data of the study area, combined with field outcrop and logging data, the core and logging response characteristics of a single channel sand body at the well point are determined, and the lateral cutting and stacking patterns of channel sand bodies of different periods are established.

[0021] In step 2, based on the seismic reflection plane of the subdivided sedimentary unit, with the top and bottom of each sand group as the boundary and a step length of about 1 ms, stratigraphic slices of each sand group were made to characterize the changes in seismic reflection energy in the vertical direction and identify the boundaries of the reservoirs corresponding to the stratigraphic slices. On this basis, the evolution process of the river channels of different periods in the vertical direction is displayed one by one from the bottom of the sand group upward, that is, the distribution range of different river channels changes from disconnected to connected with the increase of sedimentation time, and the degree of overlap of the two sand bodies in the vertical direction increases accordingly.

[0022] In step 3, according to the river channel evolution process in different periods depicted by the stratigraphic slices and combined with the actual drilling logging curves, the stratigraphic slices with a high degree of consistency with the well points are selected to determine the sand body superposition pattern formed by the cutting of the inter-well river channel deposition.

[0023] In step 4, an initial lithofacies model is established based on phase control, and sparse pulse inversion is carried out in the study area to predict the spatial scale of reservoir lithology. On this basis, geostatistical inversion is performed according to the statistical variation function of the river direction and width zoning in the study area to determine the thickness of the inter-well sand body.

[0024] In step 5, based on the lateral cutting and overlapping pattern of the sand body, the corresponding top and bottom times t1 and t2 are determined by the thickness change points of the reservoir inversion sand body. According to the time-depth relationship of the study area, the depths of the top and bottom surfaces of the lateral cutting and overlapping part are calculated respectively, thereby calculating the thickness n of the lateral cutting and overlapping part.

[0025] In step 6, based on the comparison between the thickness n of the overlapping parts of the two river channels and the thickness h of the thinnest sand body encountered by the two wells, if n>1 / 2h, it is considered that the connectivity between the two wells is good, and the well pattern is adjusted, and the perforation depth and thickness are designed to achieve balanced injection and production.

[0026] The method for calculating the thickness of the cut-off surface of the river-phase reservoir sedimentation under large well spacing in the present invention determines the thickness of the cut-off surface of the two-stage sand body sedimentation cut-off surface, aiming at the poor connectivity of the inter-well sand bodies caused by the lateral cut-off between different stages of river channels during the sedimentation of the river-phase reservoir. The present invention fully considers the complex connectivity of the river-phase reservoir due to the frequent changes of the river channel, breaks through the limitation that the distribution and connectivity of the reservoir between wells cannot be predicted due to the large well spacing, and designs an implementation method for the deployment of the well network and the perforation plan according to the cut-off thickness of the river channel sand body. Compared with the past, this technical achievement has better operability, innovation, practicality, and is conducive to promotion. This method was applied in Chengbei 11 well block and 22F well block of Chengdao Oilfield. Among them, 19 oil wells in Chengbei 11 well block were adjusted and measures were taken to increase liquid, 13 water wells were subdivided, and 61 water wells were measured and adjusted. After implementation, the average daily liquid per well increased from 99.8 t / d to 146.3 / d, an increase of 46.5 t / d; the average daily oil per well increased from 19.1 t / d to 27.8 t / d, an increase of 8.7 t / d; the water content increased from 80.9% to 81.0%, an increase of 0.1%. At present, the cumulative increase in oil production has reached 6.3×104t, and the profit increased by 164.78 million yuan, achieving good liquid extraction development effect and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A detailed stratigraphic comparison diagram of the upper section of the pavilion in a specific embodiment of the present invention;

[0028] Figure 2 The upper section 5 of the pavilion is a specific embodiment of the present invention. 2 Schematic diagram of longitudinal seismic slices of small layers;

[0029] Figure 3 It is a schematic diagram of a lateral cut-and-stack cross section of a sand body actually drilled in a specific embodiment of the present invention;

[0030] Figure 4 A side-cutting diagram of a specific embodiment of the present invention;

[0031] Figure 5 A schematic diagram of thickness calculation in a specific embodiment of the present invention;

[0032] Figure 6 It is a schematic diagram of a lateral cut-and-stack cross section of a sand body actually drilled in a specific embodiment of the present invention;

[0033] Figure 7 A schematic diagram of thickness calculation in a specific embodiment of the present invention;

[0034] Figure 8 It is a schematic diagram of a lateral cut-and-stack cross section of a sand body actually drilled in a specific embodiment of the present invention;

[0035] Fig. 9 This is a diagram of the middle lateral cutting and stacking mode under the condition of large well spacing of the present invention;

[0036] Fig.10 A schematic diagram of thickness calculation in a specific embodiment of the present invention;

[0037] Fig.11 The present invention is a flow chart of a specific embodiment of a method for calculating the thickness of a sedimentary cross-section of a fluvial facies reservoir at a large well spacing according to the present invention. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0040] like Fig.11 As shown, Fig.11 The present invention is a flow chart of a method for calculating the stacking thickness of a fluvial facies reservoir sedimentary cut surface under large well spacing.

[0041] Step 101, based on the completion data and the sub-layer and single-layer division marks determined by the core well, the genetic sand body comparison is carried out to establish the sequence stratigraphic framework of the study area, so as to ensure the relative isochronism of the same river deposition;

[0042] According to the coring wells, rock electrical calibration is carried out to identify the sedimentary cycle and determine the division interface of sand group, sublayer and single sand body in turn. On this basis, by leveling the marker layer and applying the completed drilling data, vertically from sand layer group to sublayer and then to single sand body are controlled step by step. On the plane, guided by the characteristics of fluvial phase deposition and based on the coring wells, fine stratigraphic comparison is carried out.

[0043] By selecting vertical wells, developing synthetic seismic records, converting well-seismic time to depth, determining seismic interpretation horizons, and verifying the comparison results of the stratified interfaces of each well, we can effectively solve the time-diachrony phenomenon caused by the rapid changes in the fluvial sedimentary environment and the drastic changes in reservoir lithology and thickness, and ensure the relative isochronism of the same river sedimentation.

[0044] Based on the core data of the study area, combined with field outcrop and logging data, the core and logging response characteristics of a single channel sand body at the well point were determined, and the lateral cutting and stacking patterns of channel sand bodies in different periods were established.

[0045] Step 102, based on the seismic reflection plane of the subdivided sedimentary unit, with the top and bottom of each sand group as the boundary, and a step length of about 1 ms, stratigraphic slices of each sand group are made to characterize the change of seismic reflection energy in the vertical direction, and identify the boundary of the reservoir corresponding to the stratigraphic slice. On this basis, the evolution process of the river channels of different periods in the vertical direction is displayed one by one from the bottom of the sand group upward, that is, the distribution range of different river channels changes from being disconnected to being connected as the deposition time increases, and the overlap degree of the two sand bodies in the vertical direction increases accordingly;

[0046] Step 103, based on the river channel evolution process at different periods depicted by the stratigraphic slices and in combination with the actual drilling and logging curves, the stratigraphic slices with the highest degree of conformity with the well points are selected to determine the sand body superposition pattern formed by the deposition and cutting of the inter-well river channel;

[0047] Step 104, based on phase control, an initial lithofacies model is established, sparse pulse inversion is performed in the study area, and the spatial scale of reservoir lithology is predicted; on this basis, geostatistical inversion is performed according to the statistical variation function of the river channel trend and width partition in the study area to determine the thickness of the inter-well sand body;

[0048] Step 105, based on the lateral cutting and stacking mode of the sand body, the corresponding top and bottom times t1 and t2 are determined by the thickness change points of the reservoir inversion sand body, and the depths of the top and bottom surfaces of the lateral cutting and stacking part are calculated respectively according to the time-depth relationship of the study area, so as to calculate the thickness n of the lateral cutting and stacking part;

[0049] Step 106, based on the comparison between the thickness n of the overlapping parts of the two-phase river channel and the thickness h of the thinnest sand body encountered by the two wells, if n>1 / 2h, it is considered that the connectivity between the two wells is good, and the well pattern is adjusted, and the perforation depth and thickness are designed to achieve balanced injection and production.

[0050] The following are several specific embodiments of the present invention.

[0051] Embodiment 1:

[0052] In a specific embodiment 1 of the present invention, the method for calculating the stacking thickness of the fluvial reservoir sedimentary section under large well spacing includes the following steps:

[0053] Step 1: Based on the completion data and the sub-layer and single-layer division marks determined by the core wells, core observation is used as a guide to carry out genetic sand body comparison based on the marker layers, sedimentary cycles and lithological combinations, and establish a fine isochronous stratigraphic framework for the study area ( Figure 1 ), thus ensuring the relative isochrony of sedimentation in the same river;

[0054] Step 2: Use seismic data to conduct stratigraphic slice analysis to characterize the river channel evolution process at different stages in the vertical direction. Figure 2 It is a longitudinal stratigraphic slice of the sand body. From slice 6 to slice 1, we can see the development and evolution of the two river channels. In the early stage, the two river channels were not in lateral contact and the sand bodies were not connected. In the middle stage, the river channels migrated and began to cut and overlap laterally, and the sand bodies began to connect. In the late stage, the degree of lateral cutting and overlapping increased, and the number of connected sand bodies increased. The sand body distribution boundary outlined by the boundary line on the stratigraphic slice ( Figure 2 ).

[0055] Step 3: According to the actual drilling sand body, Figure 3 The distance between wells 22E-3 and 22A-6 is 280 meters, and the distance between wells 22A-6 and 22A-2 is 310 meters. The thickness of the sand bodies at the well points is between 5 and 6 meters. Based on the sedimentary law of fluvial reservoirs, sparse pulse inversion is carried out to implement the spatial distribution law of sand bodies between wells and establish the lateral cutting and stacking model of sand bodies formed by the cutting of river channel deposition ( Figure 4 );

[0056] Step 4: Conduct geostatistical inversion to determine the thickness of the inter-well sand bodies;

[0057] Step 5: Based on the lateral cutting and stacking mode of the sand body, the top and bottom times t1 and t2 corresponding to the thickness change points of the reservoir inversion sand body are calculated. According to the time-depth relationship of the study area, the depths of the top and bottom surfaces of the lateral cutting and stacking part are calculated respectively, so as to calculate the thickness n( Figure 5 );

[0058] Step 6: Compare the thickness n of the overlapping parts of the two river channels with the thickness h of the thinnest sand body encountered by the two wells. If n>1 / 2h, it is considered that the connectivity between the two wells is good, and the well pattern is adjusted, and the perforation depth and thickness are designed to achieve balanced injection and production.

[0059] Embodiment 2:

[0060] In the specific embodiment 2 of the present invention, the method for calculating the stacking thickness of the fluvial reservoir sedimentary section under large well spacing includes the following steps:

[0061] Step 1: Based on the completion data and the sub-layer and single-layer division marks determined by the core wells, core observation is used as a guide to carry out genetic sand body comparison based on the marker layers, sedimentary cycles and lithological combinations, and establish a fine isochronous stratigraphic framework for the study area ( Figure 1 ), thus ensuring the relative isochrony of sedimentation in the same river;

[0062] Step 2: Use seismic data to conduct stratigraphic slice analysis to characterize the evolution of river channels at different stages in the vertical direction; Figure 2 It is a longitudinal stratigraphic slice of the sand body. From slice 6 to slice 1, we can see the development and evolution of the two river channels. In the early stage, the two river channels were not in lateral contact and the sand bodies were not connected. In the middle stage, the river channels migrated and began to cut and overlap laterally, and the sand bodies began to connect. In the late stage, the degree of lateral cutting and overlapping increased, and the number of connected sand bodies increased.

[0063] Step 3: According to the actual drilling sand body, Figure 6 The distance between Well 11NB-6 and Well CB11E-6 is 250 meters, and the thickness of the sand body at the well point is between 8 and 12 meters. According to the actual sand body encountered during drilling and the sedimentary law of fluvial reservoirs, sparse pulse inversion was carried out to determine the inter-well sand body cutting and stacking pattern;

[0064] Step 4: Conduct geostatistical inversion to determine the thickness of the interwell sand bodies;

[0065] Step 5: Based on the lateral cutting and stacking mode of the sand body, the top and bottom times t1 and t2 corresponding to the thickness change points of the reservoir inversion sand body are calculated. Figure 7 ), according to the time-depth relationship of the study area, the depths of the top and bottom surfaces of the lateral cut-overlapping part are calculated respectively, so as to calculate the thickness n of the lateral cut-overlapping part;

[0066] Step 6: Compare the thickness n of the overlapping parts of the two river channels with the thickness h of the thinnest sand body encountered by the two wells. If n>1 / 2h, it is considered that the connectivity between the two wells is good, and the well pattern is adjusted, and the perforation depth and thickness are designed to achieve balanced injection and production.

[0067] Embodiment 3:

[0068] In the specific embodiment 3 of the present invention, the method for calculating the stacking thickness of the fluvial reservoir sedimentary section under large well spacing includes the following steps:

[0069] Step 1: Based on the completion data and the sub-layer and single-layer division marks determined by the core wells, core observation is used as a guide to carry out genetic sand body comparison based on the marker layers, sedimentary cycles and lithological combinations, and establish a fine isochronous stratigraphic framework for the study area ( Figure 1), thus ensuring the relative isochrony of sedimentation in the same river;

[0070] Step 2: Use seismic data to conduct stratigraphic slice analysis to characterize the evolution of river channels at different stages in the vertical direction; Figure 2 It is a longitudinal stratigraphic slice of the sand body. From slice 6 to slice 1, we can see the development and evolution of the two river channels. In the early stage, the two river channels were not in lateral contact and the sand bodies were not connected. In the middle stage, the river channels migrated and began to cut and overlap laterally, and the sand bodies began to connect. In the late stage, the degree of lateral cutting and overlapping increased, and the number of connected sand bodies increased.

[0071] Step 3: According to the actual drilling sand body, Figure 8 The distance between well 11NA-5 and well CB11D-6 is 180 meters, and the distance between well 11D-6 and well 11NA-9 is 130 meters. The thickness of the sand body at the well point is between 2 and 6 meters. According to the actual drilling sand body, combined with the sedimentary law of fluvial reservoir, sparse pulse inversion is carried out to determine the inter-well sand body cutting and stacking mode ( Fig. 9 );

[0072] Step 4: Conduct geostatistical inversion to determine the thickness of the interwell sand bodies;

[0073] Step 5: Based on the lateral cutting and stacking mode of the sand body, the top and bottom times t1 and t2 corresponding to the thickness change points of the reservoir inversion sand body are calculated. Fig.10 ), according to the time-depth relationship of the study area, the depths of the top and bottom surfaces of the lateral cut-overlapping part are calculated respectively, so as to calculate the thickness n of the lateral cut-overlapping part;

[0074] Step 6: Compare the thickness n of the overlapping parts of the two river channels with the thickness h of the thinnest sand body encountered by the two wells. If n>1 / 2h, it is considered that the connectivity between the two wells is good. If n<1 / 2h, it is considered that the connectivity between the two wells is poor. Adjust the well pattern, design the perforation depth and thickness, and achieve balanced injection and production.

[0075] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0076] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for calculating the thickness of the cross-section of fluvial reservoir sediments under large well spacing, characterized in that: The calculation method of the stacking thickness of the fluvial reservoir sedimentary section under the large well spacing includes: Step 1, establish the sequence stratigraphic framework of the study area; Step 2, identifying the boundary of the reservoir corresponding to the stratigraphic slice; Step 3, determining the inter-well sand body cutting and stacking mode; Step 4: Establish an initial lithofacies model based on phase control and conduct sparse pulse inversion in the study area; Step 5, calculating the thickness n of the lateral cut and overlapped portion; Step 6: When the connectivity between the two wells is good, adjust the well pattern, design the perforation depth and thickness, and achieve balanced injection and production; In step 2, based on the seismic reflection plane of the subdivided sedimentary unit, with the top and bottom of each sand group as the boundary and 1ms as the step length, stratigraphic slices of each sand group were made to characterize the changes in seismic reflection energy in the vertical direction and identify the boundaries of the reservoirs corresponding to the stratigraphic slices. On this basis, the evolution of the river channels of different periods in the vertical direction was displayed one by one from the bottom of the sand group upwards, that is, the distribution range of different river channels changed from being disconnected to being connected with the increase of sedimentation time, and the overlap degree of the two sand bodies in the vertical direction increased accordingly; In step 3, according to the river channel evolution process at different periods depicted by the stratigraphic slices and in combination with the actual drilling and logging curves, the stratigraphic slices with a high degree of conformity with the well points are selected to determine the sand body superposition pattern formed by the deposition and cutting of the inter-well river channel; In step 4, an initial lithofacies model is established based on phase control, and sparse pulse inversion is carried out in the study area to predict the spatial scale of reservoir lithology. On this basis, geostatistical inversion is carried out according to the statistical variation function of the river channel trend and width partition in the study area to determine the thickness of the inter-well sand body. In step 5, based on the lateral cutting and stacking mode of the sand body, the corresponding top and bottom times t1 and t2 are determined by the thickness change points of the reservoir inversion sand body. According to the time-depth relationship of the study area, the depths of the top and bottom surfaces of the lateral cutting and stacking part are calculated respectively, so as to calculate the thickness n of the lateral cutting and stacking part. In step 6, based on the comparison between the thickness n of the overlapping parts of the two river channels and the thickness h of the thinnest sand body encountered by the two wells, if n>1 / 2h, it is considered that the connectivity between the two wells is good, and the well pattern is adjusted, and the perforation depth and thickness are designed to achieve balanced injection and production.

2. The method for calculating the thickness of the cross section of fluvial reservoir sediments under large well spacing according to claim 1 is characterized in that: In step 1, based on the completion data and guided by the sub-layer and single sand body division marks determined by the core wells, genetic sand body comparison is carried out to establish the stratigraphic framework of the study area, thereby ensuring the relative isochronism of the same river deposition.

3. The method for calculating the thickness of the cross section of fluvial reservoir sediments under large well spacing according to claim 2, characterized in that: In step 1, rock electrical calibration is carried out according to the coring wells to identify the sedimentary cycles and determine the division interfaces of sand groups, sublayers and single sand bodies in turn. On this basis, by flattening the marker layers and applying the completed drilling data, vertically, the sand layer groups, sublayers and single sand bodies are controlled step by step. In the plane, the characteristics of fluvial phase deposition are used as a guide and the coring wells are used as the basis to carry out detailed stratigraphic comparison.

4. The method for calculating the thickness of the cross section of fluvial reservoir sediments under large well spacing according to claim 2, characterized in that: In step 1, vertical wells are selected, synthetic seismic records are developed, well-seismic time-depth conversion is performed, the seismic interpretation horizon is determined, and the comparison results of the stratification interfaces of each well are verified.

5. The method for calculating the thickness of the cross section of fluvial reservoir sediments under large well spacing according to claim 2, characterized in that: In step 1, based on the core data of the study area, combined with field outcrop and logging data, the core and logging response characteristics of a single channel sand body at the well point are determined, and the lateral cutting and stacking patterns of channel sand bodies of different periods are established.

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