A method for characterizing microstructures of thin shale layers

Abstract

The present application belongs to the technical field of oil and gas field exploration and development, and particularly relates to a method for depicting microstructure of thin shale layer. The specific steps include: the present application divides marker beds within a target window of a horizontal well shale, uses natural gamma ray and cutting characteristics while drilling to judge the marker beds in real time, calculates the stratigraphic dip and tendency according to the intersection relationship between the marker beds and the well trajectory on the basis of the stratigraphic thickness variation between the marker beds, and further depicts the microstructure of the target area. The present application has the characteristics of lower cost, sufficient data source and high accuracy, can not only realize the depiction of the microstructure of thin shale layer, but also provide a strong basis for the adjustment of the well trajectory during the drilling of the horizontal well, and can further provide a basis for the optimization of the well trajectory of the adjacent horizontal well to be drilled under the well factory mode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas field exploration and development, and particularly relates to a method for depicting microstructure of thin shale. BACKGROUND

[0002] With the gradual consumption of conventional oil and gas resources and the increasing difficulty of exploitation, and the rising demand for energy from economic and social development, the contradiction between supply and demand of oil and gas is increasingly prominent, and unconventional oil and gas resources including coalbed methane, tight sandstone oil and gas, shale oil and gas are increasingly valued by people, and have become an important support for rapid increase of global oil and gas reserves. China's shale oil and gas resources are rich in potential, and at present, marine shale has built a number of hundred-billion-scale marine shale gas fields, and has realized large-scale commercial development. Compared with marine shale, widely existing continental shale has the characteristics of thin thickness, frequent sedimentary facies change and strong heterogeneity. With the breakthrough of continental shale oil and gas layer series in Songliao Basin, Bohai Bay Basin, Ordos Basin, Junggar Basin and Sichuan Basin, the Jurassic system in Sichuan Basin has become a hot research field for exploration and development of continental shale oil and gas, which also promotes the development process of continental thin shale oil and gas resources.

[0003] Although the shale layer series with Ro reaching 0.7 or more generally contains oil and gas, only in the layer section with good oil or gas content can horizontal well drilling and large-scale fracturing be implemented to realize the benefit development of shale oil and gas. In order to realize the effective and orderly development of continental thin shale oil and gas, the shale oil and gas horizontal well should preferably select the target window of shale layer series, and the well trajectory should be as parallel as possible to the target layer and pass through the target layer, which requires providing accurate well trajectory adjustment scheme to the drilling engineer in time, and the microstructure depiction of thin shale target layer is particularly important. Therefore, the fine depiction of microstructure of thin shale is also urgently needed, which lays a foundation for the exploration and development of continental shale oil and gas.

[0004] Microstructure refers to the local small structure of the stratum itself in the total oilfield background, the width is usually between 200-400m, and the amplitude is not more than 20m. In the process of horizontal well drilling, it is usually necessary to set a series of logging while drilling to judge the stratum dip angle and the position of the drill bit, and the research and use of logging while drilling are still in the primary stage in China. Due to the high price and use cost of logging while drilling instruments and interpretation software, the logging while drilling instrument with natural gamma and resistivity parameters is mainly used in China at present. The existing technology for microstructure description mainly includes the following two types: ①Using seismic data: using seismic data, combining with stratum division to interpret the layer microstructure or on the basis of structure analysis and stratum division, improving the accuracy of the velocity field to ensure the accuracy of the microstructure map. But limited by the low vertical resolution of seismic data, the microstructure with an amplitude of less than 10m in thin shale cannot be accurately identified by seismic data; ②Using the relationship between the horizontal well (highly deviated well) well trajectory and the layer surface to identify the microstructure or using logging while drilling imaging logging and other logging technology series to obtain the stratum dip angle and tendency, but in the existing microstructure description method using the intersection relationship between the layer surface and the well trajectory, the stratum dip angle is calculated based on the equal thickness of the stratum, or the intersection between the target window internal marker layer and the well trajectory is ignored. There are problems of large error and high cost in obtaining the stratum dip angle change. Therefore, it is urgent to establish a microstructure description technology with high cost performance and suitable for thin shale oil and gas layer, to lay a solid foundation for realizing the exploration and development of continental shale oil and gas. SUMMARY

[0005] The purpose of the present application is to provide a thin layer shale microstructure description method to solve the problem of inaccurate description of thin layer shale microstructure by using seismic data in the prior art, and the problem of high cost of thin layer shale microstructure description by using logging while drilling imaging logging.

[0006] To solve the above technical problems, the present application provides a thin layer shale microstructure description method, according to the geological characteristics of the core of the target layer of the drilled well, the marker layers are divided in the target layer; the marker layers drilled by the well trajectory are identified, the vertical thickness of the stratum between different marker layers is described, and the intersection relationship between the well trajectory and the stratum between each marker layer is combined to calculate the stratum dip angle and the azimuth angle of the stratum dip angle when the well trajectory passes through the same marker layer or adjacent two marker layers each time, so as to describe the microstructure of the target area.

[0007] The beneficial effects are that the problems of inaccurate description of microstructure of thin shale layer caused by seismic data and high cost of description of microstructure of thin shale layer caused by imaging logging while drilling are solved, the formation dip angle and tendency are calculated according to the intersection relationship of the marker bed and the well trajectory on the basis of the stratigraphic thickness change between the marker beds, and then the microstructure of the target area is described, the method has the characteristics of low cost, sufficient data source and high accuracy, can not only realize the microstructure description of thin shale layer, but also provide a strong basis for the adjustment of the well trajectory in the drilling process of the horizontal well, and can also provide a basis for the optimization of the well trajectory of the adjacent horizontal well to be drilled in the well factory mode.

[0008] Further, the intersection relationship of the marker bed and the well trajectory includes that the formation and the well trajectory are both downdip and the well trajectory is relatively downdip to the formation, the formation and the well trajectory are both downdip and the well trajectory is relatively updip to the formation, the formation is downdip and the well trajectory is updip, the formation and the well inclination are both updip and the well trajectory is relatively updip to the formation, the formation and the well inclination are both updip and the well trajectory is relatively downdip to the formation, the formation is updip and the well trajectory is downdip, and the formation and the well trajectory are nearly parallel.

[0009] Further, when the formation and the well trajectory are both downdip and the well trajectory is relatively downdip to the formation, the calculation formulas of the formation dip angles of the well trajectory drilling the first marker bed and the second marker bed are respectively:

[0010]

[0011]

[0012] When the formation and the well trajectory are both downdip and the well trajectory is relatively updip to the formation, the calculation formulas of the formation dip angles of the well trajectory drilling the first marker bed and the second marker bed are respectively:

[0013]

[0014]

[0015] When the formation is downdip and the well trajectory is updip, the calculation formulas of the formation dip angles of the well trajectory drilling the first marker bed and the second marker bed are respectively:

[0016]

[0017]

[0018] When the formation and the well inclination are both updip and the well trajectory is relatively updip to the formation, the calculation formulas of the formation dip angles of the well trajectory drilling the first marker bed and the second marker bed are respectively:

[0019] When the formation and the well inclination are both updip and the well trajectory is relatively updip to the formation, the calculation formulas of the formation dip angles of the well trajectory drilling the first marker bed and the second marker bed are respectively:

[0020]

[0021] When the stratum and the hole inclination are both up-dip and the well trajectory is down-dip relative to the stratum, the calculation formulae of the stratum dip angles drilled by the well trajectory at the first marker layer and the second marker layer are respectively:

[0022]

[0023]

[0024] When the stratum is up-dip and the well trajectory is down-dip, the calculation formulae of the stratum dip angles drilled by the well trajectory at the first marker layer and the second marker layer are respectively:

[0025]

[0026]

[0027] When the stratum is nearly parallel to the well trajectory, the calculation formula of the stratum dip angle is:

[0028]

[0029] Wherein, a is the horizontal projection displacement length drilled at the two marker layers; b is the vertical thickness of the two marker layers at the coordinate calculated by the interpolation method when the second marker layer is drilled; c is the vertical thickness of the two marker layers at the coordinate calculated by the interpolation method when the first marker layer is drilled; a is the hole inclination when the marker layer is drilled; θ1 is the stratum dip angle drilled at the first marker layer; θ2 is the stratum dip angle drilled at the second marker layer; (X, Y, Z) and (X', Y', Z') are the geodetic coordinates drilled at the same marker layer or two different marker layers in sequence.

[0030] The beneficial effects are: the position relationship between the well trajectory and the marker layers in the target layer is accurately calculated, the target area is micro-structurally depicted, the well trajectory adjustment in the drilling process of the horizontal well is provided with a strong basis, and the basis for the optimization of the well trajectory of the adjacent horizontal well to be drilled in the well factory mode is provided.

[0031] Further, the azimuth angle of the calculated stratum dip angle is calculated according to the following formula:

[0032]

[0033] Wherein, δ is the azimuth angle of the stratum dip angle; (X, Y, Z) and (X', Y', Z') are the geodetic coordinates of the two marker layers drilled in sequence.

[0034] The beneficial effect is that the drilling direction of the well trajectory in the target layer is accurately calculated to depict the microstructure of the target area, and the adjustment of the well trajectory in the drilling process of the horizontal well can be provided with a strong basis, and in addition, the optimization of the well trajectory of the adjacent horizontal well to be drilled in the well factory mode can be provided with a basis.

[0035] Further, the means for identifying the marker layer drilled by the well trajectory is that the marker layer drilled by the well trajectory is judged according to the lithology characteristics of the cutting logging of each marker layer and the standardized natural gamma value.

[0036] The beneficial effect is that the marker layer is judged in real time by using the while-drilling natural gamma and cutting characteristics, the cost of depicting the microstructure of the target area is lower, the data source is more sufficient, and the accuracy is higher.

[0037] Further, the specific steps of the standardization processing of the natural gamma value include: selecting the natural gamma of the stable section of the standard well in the target area as the standard value, and standardizing the natural gamma of the actual drilled well in the target area based on the standard well, and the standardization formula is as follows:

[0038]

[0039] Wherein, GR sta is the standardized natural gamma value; is the natural gamma average value of the stable section of the selected standard well; is the natural gamma average value of the corresponding standard section to be standardized; and GR is the measured natural gamma value.

[0040] Further, the interpolation method is used to depict the vertical thickness of different marker layers.

[0041] The beneficial effect is to provide data basis for calculating the formation dip angle of the marker layer.

[0042] Further, the lithology characteristics of the cutting logging are judged by dripping hydrochloric acid on the cutting.

[0043] The beneficial effect is that the lithology of the cutting can be quickly judged to judge the marker layer drilled by the actual drilled well.

[0044] Further, the geological characteristics of the core of the target layer include: lithology, mineral composition, paleontology and sedimentary cycle. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is the flowchart of the thin shale microstructure depiction based on the natural gamma and cutting logging of the present application;

[0046] Figure 2-1 is the illustration of the stratum and the well trajectory both dipping and the well trajectory relatively dipping downward;

[0047] Figure 2-2 is a schematic view of the stratum and the well trajectory of the present application both being inclined downward and the well trajectory being relatively inclined upward;

[0048] Figure 2-3 is a schematic view of the stratum and the well trajectory of the present application both being inclined upward;

[0049] Figure 2-4 is a schematic view of the stratum and the well trajectory of the present application both being inclined upward and the well trajectory being relatively inclined upward;

[0050] Figure 2-5 is a schematic view of the stratum and the well trajectory of the present application both being inclined upward and the well trajectory being relatively inclined downward;

[0051] Figure 2-6 is a schematic view of the stratum and the well trajectory of the present application both being inclined upward and the well trajectory being relatively inclined downward;

[0052] Figure 2-7 is a schematic view of the stratum and the well trajectory of the present application both being inclined upward and the well trajectory being relatively inclined downward;

[0053] Figure 3 is a target well marker layer of the present application;

[0054] Figure 4 is a vertical thickness between two adjacent marker layers of the present application;

[0055] Figure 5 is a micro-structure profile of the target layer of the XXY1-1HF well area of the present application. DETAILED DESCRIPTION

[0056] The basic idea of the present application is to divide the marker layers within the shale target window of the horizontal well, to determine the marker layers in real time by using the natural gamma ray and the characteristics of the cuttings, to calculate the stratum dip angle and the tendency according to the intersection relationship between the marker layers and the well trajectory on the basis of the stratum thickness variation between the marker layers, and to further depict the micro-structure of the target area. Based on the idea, the thin-layer shale micro-structure depiction method of the present application can be realized.

[0057] The present application will be described in detail below with reference to the accompanying drawings and the method embodiments.

[0058] Method embodiment:

[0059] The thin-layer shale micro-structure depiction method of the present application has the flow chart as shown in Figure 1 The specific implementation steps include:

[0060] Step 1: The stable marker layers of the target layer and the upper and lower strata of the target layer are divided by using the core geological characteristics of the target area in the early stage of the drilled well, and the lithology, electrical property and sedimentation characteristics of each marker layer are determined; wherein the core geological characteristics include the geological characteristics such as the lithology, mineral composition, paleontology and sedimentary cycle, and the electrical property characteristics such as the natural gamma ray.

[0061] Step two, the natural gamma of the target area is standardized to a unified natural gamma interval, and the distribution range of the standardized natural gamma value is determined, which specifically includes: selecting the natural gamma of the stable section of the standard well in the target area as the standard value, and standardizing the natural gamma of the real drilled well in the target area based on the standard well. The standardization formula is as follows:

[0062]

[0063] Wherein, GR sta is the standardized natural gamma value; and respectively, the natural gamma mean of the selected standard well stable section and the corresponding standard section natural gamma mean of the standardization; GR is the measured natural gamma value, unit API.

[0064] Step three, according to the lithology characteristics of the cutting logging and the standardized natural gamma in step two, the marker bed drilled by the real drilled horizontal well is identified.

[0065] Step four, based on the interpolation method, the mark layer determined in step one is described, and the vertical thickness between adjacent mark layer bottom surfaces is described, which is used for calculating the formation dip angle.

[0066] Step five, according to the intersection relationship between the drilled marker bed and the well trajectory, the formation dip angle of the well trajectory crossing adjacent two marker beds and the azimuth angle of the formation dip angle are calculated, which are shown as follows:

[0067] 1) as shown in Figure 2-1 When the formation and the well trajectory are both inclined and the well trajectory is inclined relative to the formation, the calculation formula of the formation dip angle of the first marker bed drilled is:

[0068]

[0069] The calculation formula of the formation dip angle of the second marker bed drilled is:

[0070]

[0071] 2) as shown in Figure 2-2 When the formation and the well trajectory are both inclined and the well trajectory is inclined relative to the formation, the calculation formula of the formation dip angle of the first marker bed drilled is:

[0072]

[0073] The calculation formula of the formation dip angle of the second marker bed drilled is:

[0074]

[0075] 3) asFigure 2-3 As shown in FIG. 4, when the formation dips and the well trajectory inclines, the formula for calculating the formation dip angle drilled through the first marker layer is:

[0076]

[0077] The formula for calculating the formation dip angle drilled through the second marker layer is:

[0078]

[0079] 4) As shown in FIG. 5, when both the formation and the hole inclination angle incline and the well trajectory inclines relative to the formation, the formula for calculating the formation dip angle drilled through the first marker layer is: Figure 2-4

[0080] The formula for calculating the formation dip angle drilled through the second marker layer is:

[0081]

[0082]

[0083] 5) As shown in FIG. 6, when both the formation and the hole inclination angle incline and the well trajectory dips relative to the formation, the formula for calculating the formation dip angle drilled through the first marker layer is: Figure 2-5

[0084] The formula for calculating the formation dip angle drilled through the second marker layer is:

[0085]

[0086] 6) As shown in FIG. 7, when the formation inclines and the well trajectory dips, the formula for calculating the formation dip angle drilled through the first marker layer is:

[0087] Figure 2-6

[0088] The formula for calculating the formation dip angle drilled through the second marker layer is:

[0089]

[0090] 7) As shown in FIG. 8, when the well trajectory passes through the same marker layer, the formation can be considered to be nearly parallel to the well trajectory, at this time, the formula for calculating the formation dip angle is:

[0091] Figure 2-7

[0092] 8) The azimuth angle of the calculated formation dip angle is calculated according to the following formula:

[0093]

[0094] ​​​​

[0095] wherein, a is the horizontal projection displacement length of drilling two marker layers, unit m; b is the vertical thickness of two marker layers calculated by using interpolation method under the coordinate when drilling the second marker layer, unit m; c is the vertical thickness of two marker layers calculated by using interpolation method under the coordinate when drilling the first marker layer, unit m; α is the inclination angle when drilling the marker layer, unit °; θ1 is the strata dip angle when drilling the first marker layer, θ2 is the strata dip angle when drilling the second marker layer, unit °; (X, Y, Z) and (X', Y', Z') are the geodetic coordinates of two marker layers drilled in sequence.

[0096] Step six, based on the strata dip angles and azimuth angles of the two marker layers drilled through calculated in step five, the interlayer microstructure of the target area horizontal well and high angle well drilling the marker layer is depicted, and the microstructure of the target area thin shale target layer is depicted by combining the marker layer stratification of all the drilled vertical wells in the target area.

[0097] The specific implementation of the thin shale microstructure depiction method of the present application is as follows:

[0098] A set of typical semi-deep lacustrine facies high clay dark shale is developed in the X number of small layers of the first member of XXX group in XX area of XX basin, two sets of dark shale are developed from top to bottom, with thicknesses of about 10m and about 6m respectively, XXY1 well deployed in the area in 2020 obtained a high yield gas flow of 104,000 cubic meters per day, and the breakthrough of exploration also promoted the development process of shale gas in the area. XXY1-1HF well is the first shale gas horizontal well of the first unconventional test well group deployed in the area. The specific steps of the thin shale target layer microstructure depiction of XXY1-1H well in Puguang gas field are as follows:

[0099] ①According to the previous core, element logging and logging cuttings data, geological feature analysis is carried out, and small layer fine correlation is carried out on adjacent wells, the marker layers of three small layers in the XXY1-1HF well area of Puguang east syncline are as shown in the table, ten geological marker layers are determined from top to bottom, and the lithology, electrical property and sedimentary characteristics of the marker layers are determined, wherein the characteristics of the marker layers of the first member of XXY1-1HF well area are shown in the following table 1: Figure 3

[0100] Table 1

[0101]

[0102] ​② Select XXY1 well as the target area of the standard well, the shale section 3383.45-3393.35m is the stable stratum in the region, the average is 130.75 API; such as Puguang 4 well corresponding depth section is 3211.88-3222.4m, the average of natural GR is 103.11 API, the conversion coefficient is 1.27, using formula (1) to standardize the natural gamma of all the real drilled wells in the target area to the unified natural gamma interval, as shown in the following figure: Figure 3

[0103] ③ According to the natural gamma of the standardization of each marker layer in step two and the lithology and paleontological characteristics of the cutting logging, the marker layer drilled by the real drilled horizontal well is judged: the natural gamma and the cutting change obviously, supplemented by drop acid to judge whether it is a marker layer. When drilling K3-2, K3-3, K3-4 and K3-5, the cutting shows shell layer, which contains shell fossils composed of calcite, and bubbles violently when dropping acid. When drilling K3-1, the cutting shows black shale, the natural gamma value is high, and there is no bubble when dropping acid.

[0104] ④ Based on the interpolation method, the vertical thickness equal thickness graph between the adjacent marker layers determined in ① is drawn: the vertical depth between the marker layers of all the drilled vertical wells in the target area is counted, and the interpolation method is used to draw the vertical thickness equal thickness graph between different marker layers, as shown in the following figure: Figure 4

[0105] ⑤ According to the intersection relationship between the drilled marker layer and the well trajectory, the strata dip angle and the azimuth angle of the strata dip angle where the well trajectory crosses through two adjacent marker layers are calculated. As shown in the following figure: Figure 5 (wherein, T is the top of the marker layer, B is the bottom of the marker layer), taking the first drilling of K3-1T and K3-2T marker layer as an example, the two points of geodetic coordinates and elevation are (18767398.48, 3494395.27, -2617.5) and (18767370.19, 3494472.74, -2615), the intersection relationship between the strata and the well trajectory is that the strata is inclined downward and the well trajectory is inclined downward relative to the strata, the inclination angle α is 1.89°, the vertical thickness c and b of K3-1T and K3-2T marker layer calculated by interpolation under the coordinates are 0.245m and 0.245m respectively, the well trajectory length a is 10.31m, the strata dip angle of the two marker layers is calculated by formula (2) and formula (3) respectively, which is 3.25° and 3.25° respectively, and the azimuth angle is calculated by formula (15), which is 339.94°; the strata dip angle and the azimuth angle of the strata dip angle when drilling the remaining marker layers are calculated, the results are shown in the following table 2:

[0106] Table 2

[0107]

[0108] ​​

[0109] ⑥Based on the calculated strata dip angles and azimuth angles of the two marker beds penetrated, the interlayer microstructure of the marker beds drilled by the horizontal well and the high-inclination well in the target area is described, and the microstructure of the thin shale target layer in the target area is described by geological statistics interpolation in combination with the marker bed stratification of all the drilled vertical wells in the target area.

[0110] The present application divides the marker beds within the shale target window of the horizontal well, judges the marker beds in real time by using the while-drilling natural gamma ray and the cuttings characteristics, calculates the strata dip angle and the tendency according to the intersection relationship between the marker bed and the well track on the basis of the thickness change of the strata between the marker beds, and further describes the microstructure of the target area, which has the characteristics of lower cost, sufficient data source and high accuracy, can not only realize the microstructure description of the thin shale, but also provide a strong basis for the adjustment of the well track in the drilling process of the horizontal well, and can also provide a basis for the optimization of the well track of the adjacent horizontal well to be drilled in the well factory mode.

Claims

1. A method for characterizing the microstructure of thin-layer shale, characterized in that, According to the geological characteristics of the obtained core of the drilled target layer, the marker layers in the target layer are divided; the marker layers drilled by the well trajectory are identified, the vertical thickness of the strata between different marker layers is depicted, and the strata dip angle and the azimuth angle of the strata dip angle of the well trajectory each time crossing the same marker layer or adjacent two marker layers are calculated in combination with the intersection relationship between the well trajectory and the strata between the marker layers, so as to depict the microstructure of the target area. The intersection relationship between the marker bed and the well trajectory includes that both the stratum and the well trajectory are downdip, and the well trajectory is relatively downdip to the stratum, the calculation formula of the stratum dip angle of the well trajectory drilled through the first marker bed is θ 1 and the stratum dip angle of the well trajectory drilled through the second marker bed is θ 2 respectively. wherein, a is the horizontal projection displacement length of the two marker beds drilled; b is the vertical thickness of the two marker beds calculated by interpolation at the coordinate when the second marker bed is drilled; c is the vertical thickness of the two marker beds calculated by interpolation at the coordinate when the first marker bed is drilled; α is the inclination angle when the marker bed is drilled.

2. The method of claim 1, wherein, The intersection relationship between the marker layer and the well trajectory further includes that the strata and the well trajectory are both down-dip and the well trajectory is up-dip relative to the strata, the strata are down-dip and the well trajectory is up-dip, the strata and the well inclination angle are both up-dip and the well trajectory is up-dip relative to the strata, the strata and the well inclination angle are both up-dip and the well trajectory is down-dip relative to the strata, the strata are up-dip and the well trajectory is down-dip, and the strata and the well trajectory are nearly parallel.

3. The thin-layer shale microstructure depiction method according to claim 2, characterized in that, when the strata and the well trajectory are both down-dip and the well trajectory is up-dip relative to the strata, the calculation formulas of the strata dip angles of the well trajectory drilled through the first marker layer and the second marker layer are respectively: when the strata are down-dip and the well trajectory is up-dip, the calculation formulas of the strata dip angles of the well trajectory drilled through the first marker layer and the second marker layer are respectively: when the strata and the well inclination angle are both up-dip and the well trajectory is up-dip relative to the strata, the calculation formulas of the strata dip angles of the well trajectory drilled through the first marker layer and the second marker layer are respectively: when the strata and the well inclination angle are both up-dip and the well trajectory is down-dip relative to the strata, the calculation formulas of the strata dip angles of the well trajectory drilled through the first marker layer and the second marker layer are respectively: when the strata are up-dip and the well trajectory is down-dip, the calculation formulas of the strata dip angles of the well trajectory drilled through the first marker layer and the second marker layer are respectively: when the strata and the well trajectory are nearly parallel, the calculation formula of the strata dip angle is: Wherein, (X1, Y1, H1) and (X2, Y2, H2) are the geodetic coordinates of the same marker layer or two different marker layers drilled successively. X , Y , Z ) and are the geodetic coordinates of the same marker layer or two different marker layers drilled successively.

4. The method of claim 1, wherein, the calculation formula of the azimuth angle of the calculated strata dip angle is as follows: wherein, δ is the azimuth of the stratigraphic dip; X , Y , Z ) and are the geodetic coordinates of two marker horizons drilled in succession, respectively.

5. The method of claim 1, wherein, The means for identifying the marker layers drilled by the well trajectory is that the marker layers drilled by the well trajectory are determined according to the lithology characteristics of the cuttings logging of each marker layer and the standardized natural gamma value.

6. The method of claim 5, wherein, The specific steps of the standardization processing of the natural gamma value include that the natural gamma of the stable section of the standard well in the target area is selected as the standard value, the natural gamma of the actual drilled well in the target area is standardized based on the standard well, and the standardization formula is as follows: wherein, GR sta is the normalized natural gamma value; is the average natural gamma value of the stable section of the selected standard well; is the average natural gamma value of the standard section corresponding to the normalization; GR is the measured natural gamma value.

7. The method of claim 1, wherein, The interpolation method is adopted to depict the vertical thickness of the strata between different marker layers.

8. The method of claim 5, wherein, The lithology characteristics of the cuttings logging are determined by dripping hydrochloric acid on the cuttings.

9. The method of claim 1, wherein, The obtained geological characteristics of the core of the target layer include the lithology, the mineral composition, the paleontology and the sedimentary cycle.

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