A three-stage sequence division method based on Mitchell cycle

Abstract

The application discloses a three-level sequence division method based on Mitchell cycle, comprising the following steps: obtaining a natural gamma logging curve in a target area; determining the signal energy and cycle number of the natural gamma logging curve based on spectrum analysis, and then judging whether the natural gamma logging curve contains Mitchell cycle; selecting a time anchor point with determined age and depth; selecting a slope track parameter as a target curve; determining the initial corresponding position of the natural gamma logging curve and the target curve based on the time anchor point, and tuning the natural gamma logging curve to the target curve from the initial corresponding position as a starting point to obtain a time-depth conversion table, and then determining an astronomical age scale; filtering the astronomical age scale to obtain a filter curve, and performing three-level sequence division based on the envelope line of the filter curve. The envelope line of the filter curve reflecting the characteristics of sea level change is obtained by filtering the astronomical age scale, and the three-level sequence division is performed based on the envelope line, so that the three-level sequence division conclusion is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geology analysis, in particular to a three-level sequence division method based on Milankovitch cycle, a computer readable storage medium and an electronic device. BACKGROUND

[0002] Sequence stratigraphy is an important discipline in the field of oil and gas exploration. For oil exploration, due to the problem of limited seismic resolution, the identification of three-level sequence is more practically significant than that of one-level and two-level sequence. The existing three-level sequence division mainly has the following problems: since the division standard of three-level sequence has not been established and the formation reason of three-level sequence is not clarified, the sequence division is relatively chaotic, mainly manifested as chaotic sequence grading and non-uniformity of drilling and seismic sequence division, and the chaotic problem of sequence division results in low accuracy and reliability of the current division results. SUMMARY

[0003] In view of the problems existing in the prior art, the present application provides a three-level sequence division method based on Milankovitch cycle, a computer readable storage medium and an electronic device. Compared with the existing three-level sequence division scheme, the division result of the present application is accurate and has high reliability.

[0004] The present application discloses a three-level sequence division method based on Milankovitch cycle, comprising:

[0005] S1: obtaining a natural gamma ray logging curve representing the depth domain in a target area;

[0006] S2: determining the signal energy and cycle number of the natural gamma ray logging curve based on spectrum analysis, and judging whether the natural gamma ray logging curve contains Milankovitch cycle based on the signal energy and cycle number;

[0007] S3: selecting a set of strong amplitude continuous seismic interfaces with determined age and depth in the target area as time anchor points;

[0008] S4: selecting a slope orbit parameter from an astronomical orbit model as a target curve representing the time domain;

[0009] S5: determining the initial corresponding position of the natural gamma ray logging curve and the target curve based on the time anchor points, and tuning the natural gamma ray logging curve to the target curve according to the curve change of the target curve from the initial corresponding position as the starting point, to obtain a time-depth conversion table reflecting the corresponding relationship between the depth domain and the time domain; determining an astronomical age scale based on the time-depth conversion table;

[0010] S6: filtering the astronomical age scale to obtain a filtered curve, and taking the cycle low points of the envelope line of the filtered curve as sequence boundaries for three-level sequence division.

[0011] Further, before the step S2, the method further comprises pre-processing the natural gamma ray logging curve.

[0012] The natural gamma ray logging curve is subjected to outlier removal and detrending to remove the influence of trend signal and noise signal.

[0013] Further, the step S2 comprises:

[0014] The natural gamma ray logging curve is processed by using a multi-window spectral analysis method to obtain a spectral analysis graph for determining the spectrum of the dominant main peak, wherein the ordinate of the spectral analysis graph represents the energy of a cycle, and the reciprocal of the abscissa represents the thickness of the stratum corresponding to the cycle.

[0015] If the ratio between the thicknesses of the strata corresponding to the dominant main peak determined based on the spectral analysis graph is similar to the ratio of the orbital parameters in the astronomical orbit model, it is determined that the natural gamma ray logging curve contains Milankovitch cycle signals, and the step S3 is continued.

[0016] Further, in the step S3, the seismic interface selected as the time anchor point is expressed as a set of regional continuous strong amplitude seismic reflection events on the seismic profile.

[0017] The seismic interface selected as the time anchor point is determined by an obvious regional continuous sedimentary-tectonic unconformity interface.

[0018] Further, the step S4 comprises:

[0019] The slope is selected from the Laskar 2004 model as the target curve representing the time domain.

[0020] Further, the step S5 comprises:

[0021] Based on the time anchor point, the initial corresponding position of the natural gamma ray logging curve and the target curve is determined, and the natural gamma ray logging curve is tuned and corrected to the target curve according to the curve change of the target curve, starting from the initial corresponding position. According to the point position corresponding relationship between the natural gamma ray logging curve and the target curve, a time-depth conversion table for reflecting the age value corresponding to the depth is obtained.

[0022] Based on the time-depth conversion table, the time domain astronomical age scale corresponding to the natural gamma ray logging curve is determined.

[0023] The abscissa of the natural gamma ray logging curve represents the depth, and the abscissa of the astronomical age scale represents the age.

[0024] Further, before the step S6, the method further comprises:

[0025] Perform time-domain spectrum analysis on the astronomical time scale. If the frequency spectrum peak corresponding to the orbital parameter selected as the target curve is significantly higher than the others, then the astronomical time scale obtained in step S5 is determined to be correct, and proceed to step S6. Otherwise, return to step S5 to obtain the astronomical time scale again.

[0026] Furthermore, the step S6 includes:

[0027] Using different filter bandwidths for filtering to obtain envelopes with different resolutions;

[0028] Select the envelope that mainly contains the slope periodic signal;

[0029] The low-value points of the envelope cycle are used as sequence boundaries for third-level sequence division.

[0030] The present invention also discloses a computer-readable storage medium, wherein the storage medium stores a computer program, and the computer program is used to execute the above-mentioned three-level sequence division method based on the Michaelis cycle.

[0031] The present invention also discloses an electronic device, comprising:

[0032] processor;

[0033] a memory for storing instructions executable by the processor;

[0034] The processor is configured to read the executable instructions from the memory and execute the instructions to implement the above-mentioned three-level sequence division method based on Michaelis cycles.

[0035] The present invention has at least the following beneficial effects:

[0036] The present invention uses seismic interfaces with absolute time as time anchor points, converts natural gamma-ray log curves from the depth domain to the time domain, and obtains an astronomical age scale. This astronomical age scale is then filtered to obtain the filter envelope, which is then used to perform a three-level sequence division. Compared to existing technologies, the present invention provides more accurate conclusions on the three-level sequence division.

[0037] Other beneficial effects of the present invention will be described in detail in the specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 is a flow chart of the method for three-level sequence division based on the M ichel's rotation disclosed by the preferred embodiment of the present application.

[0040] Figure 2 is a spectrum analysis chart of the depth domain of the LW13 well disclosed by the preferred embodiment of the present application.

[0041] Figure 3 is a superimposed chart of the natural gamma ray logging curve and the depth domain filter curve of the LW13 well disclosed by the preferred embodiment of the present application.

[0042] Figure 4 is a seismic interface feature chart disclosed by the preferred embodiment of the present application.

[0043] Figure 5 is a seismic interface feature chart disclosed by the preferred embodiment of the present application.

[0044] Figure 6 is a target curve of each orbit parameter of the Laskar 2004 model disclosed by the preferred embodiment of the present application.

[0045] Figure 7 is a process chart of the natural gamma ray logging curve of the LW13 well tuned to the target curve disclosed by the preferred embodiment of the present application.

[0046] Figure 8 is a segmented slope tuning astronomic time scale chart of the LW13 well disclosed by the preferred embodiment of the present application.

[0047] Figure 9 is an MTM spectrum analysis chart of the astronomic time scale disclosed by the preferred embodiment of the present application.

[0048] Figure 10 is a depth domain natural gamma ray logging curve and preprocessed curve chart of the LW13 well disclosed by the preferred embodiment of the present application.

[0049] Figure 11 is a T6-T7 segment slope tuning astronomic time scale of the LW13 well disclosed by the preferred embodiment of the present application.

[0050] Figure 12 is a spectrum analysis chart of the astronomic time scale established by the natural gamma ray logging curve of the T6-T7 segment of the LW13 well after slope tuning disclosed by the preferred embodiment of the present application.

[0051] Figure 13 is an envelope superimposed comparison chart of the global sea level change curve and the astronomic time scale filter curve disclosed by the preferred embodiment of the present application.

[0052] Figure 14 is a three-level sequence division chart disclosed by the preferred embodiment of the present application.

[0053] Figure 15 It is a comparison diagram of the three-level hierarchical division of different schemes disclosed in the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0054] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0055] This paper discloses a three-level sequence division method based on Michaelis cycles, primarily applying cyclostratigraphy. Cyclostratigraphy is based on the theory that periodic or quasi-periodic variations in Earth's orbital parameters, such as eccentricity, slope, and precession, induce quasi-periodic variations in Earth's insolation. These quasi-periodic variations in insolation, in turn, induce quasi-periodic variations in Earth's climate system, which ultimately influences sedimentary responses under different sedimentary settings.

[0056] like Figure 1 As shown, the present invention includes:

[0057] S1: Obtain the natural gamma ray logging curve representing the depth domain in the target area.

[0058] Certain cyclical variations in sediments within the sedimentary record can reflect cyclical characteristics of paleoclimate. Milankovitch theory posits that cyclical variations in the three parameters of Earth's orbit cause variations in insolation, which in turn affect environmental systems, leading to cyclical paleoclimate variations. Therefore, cyclostratigraphic studies often utilize various proxy indicators recorded in strata to reconstruct paleoclimate. These include oxygen isotopes, well logs, paleomagnetism, carbon isotopes, organic carbon content, rock thickness, rock type, and color reflectance.

[0059] The natural gamma ray logging measures the intensity of the gamma ray emitted by the radioactive elements (such as thorium, uranium, potassium, etc.) in the stratum in the process of nuclear decay, and also measures the total concentration change of the radioactive elements thorium, uranium and potassium in the stratum, and the intensity of the gamma ray is determined by the decay process of the radioactive elements in the stratum. The reason why the total amount of natural gamma ray (GR) can reflect the change of sea level is that clay and organic matter particles have a strong ability to adsorb radioactive elements, and clay and organic matter particles are very sensitive to the change of the sedimentary environment. Since the size of the GR value mainly reflects the properties of the particles, the GR value increases with the increase of the argillaceous content in the stratum, and therefore the GR value is mainly used in geology to determine the sand-mud ratio or the median grain size and the sand content, and can also be applied to the estimation of the argillaceous content and the division of the sequence stratigraphy. Compared with other logging curves, the natural gamma ray logging curve can most sensitively reflect the change of the argillaceous content, and since the argillaceous content is directly related to the sedimentary cycle and climate change, the natural gamma ray logging data is a valuable reference index for the recovery of the paleoenvironment and paleoclimate of the sedimentary basin. The present application uses the natural gamma ray logging curve as a proxy index for cycle analysis, which has the advantages of small sampling interval, good continuity and sensitivity to sea level change.

[0060] S2: determining whether the natural gamma ray logging curve contains Milankovitch cycle signals based on frequency analysis. Although the astronomical force acting on the climate can cause the appearance of rhythmic cycles in the sedimentary stratum, it cannot be considered that all the cycles in the sedimentary stratum are Milankovitch cycles, because the stratum deposition conditions in different regions will not be completely the same, and even the cycles shown by the strata in the same region may be different due to different post-reconstruction, so it is necessary to verify whether the natural gamma ray logging contains Milankovitch cycle signals.

[0061] Preferably, the step S2 specifically comprises: processing the natural gamma ray logging curve by using a multi-window spectral analysis method to obtain a frequency spectrum analysis graph, which is used to determine the frequency spectrum of the dominant main peak, wherein the vertical coordinate of the frequency spectrum analysis graph represents the energy of the cycle within a period, and the reciprocal of the horizontal coordinate represents the stratum thickness corresponding to the cycle. If the ratio between the stratum thicknesses corresponding to the dominant main peaks based on the frequency spectrum analysis graph is similar to the ratio of the orbital parameters in the astronomical orbital model, it is determined that the natural gamma ray logging curve contains Milankovitch cycle signals, and therefore the astronomical time scale can be established through the natural gamma ray logging curve.

[0062] As Figure 2As shown in the figure, the horizontal coordinate of the spectrum analysis diagram is frequency, unit is cycle / meter, the vertical coordinate is relative power spectrum, unit is none, the greater the value of the vertical coordinate, the greater the energy of the cycle, the reciprocal of the horizontal coordinate represents the thickness of the stratum corresponding to the cycle. Since the Milankovitch cycle is generated by the astronomical force acting on the earth, it has relative stability, and the ratio between the parameters is relatively fixed in a certain geological period. Therefore, if the ratio between the thicknesses of the strata corresponding to the peak values of the dominant power spectrum found by depth domain spectrum analysis has the three-parameter ratio relationship of the Milankovitch cycle, it can be considered that this section of stratum is affected by the Milankovitch cycle. It is worth mentioning that the geological conditions are complex and diverse, and the sedimentary phenomena such as diagenesis will affect the preservation of the Milankovitch cycle in the stratum to some extent. Therefore, if the ratio between the dominant frequencies of the main peaks analyzed has a certain difference from the ratio between the three parameters of the relatively fixed Milankovitch cycle, it is still considered that the stratum is affected by the Milankovitch cycle.

[0063] The present application can determine the spectrum of the dominant main peak by the Multitaper Method (MTM for short), and can extract the specific main peak frequency by the method of digital filtering. Specifically, the present application selects bandwidth filtering as the selected filtering method. The parameters of bandwidth filtering include center frequency and bandwidth. The present application selects the center frequency as the frequency corresponding to the dominant main peak, and selects the bandwidth as the frequency range that can cover the peak range most. After selecting a center frequency and a bandwidth, it means that the information of the spectrum peak with a certain width corresponding to the center frequency is extracted. When selecting the bandwidth, it should cover all the signals of the selected dominant peak as much as possible, and should also cover both sides appropriately, but should not be too large.

[0064] As shown in the figures Figure 2 and Figure 3 , by analyzing the ratio between the peak values of the depth domain spectrum diagram, and combining the stratum thickness corresponding to 405kyr calculated by the average deposition rate, it is considered that the 71m (0.014m -1 ) peak in this section of data represents the 405kyr eccentricity cycle, the 18m (0.056m -1 ) represents the 100kyr short eccentricity cycle, the 7.1m (0.14m -1 ) represents the obliquity cycle, and the 3.5m (0.28m -1 ) represents the precession cycle. It can be seen that even though the data amount of this selected section of data is small and the stratum thickness is not large, it still can show almost the same dominant main peak frequency as the whole, and the peak values of the obliquity cycle and the eccentricity cycle are more obvious, so it can be considered that the stratum interpreted by the drilling in this area contains the signals of the eccentricity, obliquity and precession cycles of the Milankovitch cycle.

[0065] S3: selecting a set of strong-amplitude continuous seismic interfaces with determined age and depth in the target area as time anchor points. The geological age of the seismic interface selected as a time anchor point is determined by the last occurrence of calcareous nannofossils and the first occurrence of planktonic foraminifera. The specific method is the existing technology in the field, which will not be described herein.

[0066] The seismic interface selected as a time anchor point in the present application is expressed as a set of continuous strong-amplitude seismic reflection events on a seismic profile. The seismic interface selected as a time anchor point not only has absolute time, but also must be easy to track. As shown in Figure 4 and Figure 5 As a set of regional structural unconformities, T6 with absolute time is shown as a set of continuous strong-amplitude seismic reflection events on a seismic profile. It is just because of this characteristic of T6 seismic reflection events that T6 seismic interface has the characteristic of being easy to track, and the possibility of explaining errors is very small. Therefore, the seismic interface T6 can be selected as a time anchor point, and it is considered that the depth position is accurate for logging and the corresponding geological age is determined.

[0067] S4: selecting the slope orbit parameter as the target curve representing the time domain from the astronomical orbit model. The astronomical orbit model refers to the variation model of the three parameters of the earth's orbit established according to the influence of the inner orbit planets on the three parameters of the earth's orbit. Laskar 2004 is one of the representatives of the astronomical orbit model.

[0068] Specifically, the orbit parameters that can be selected from the Laskar 2004 model include eccentricity, slope, precession, and insolation. The commonly used astronomical orbit parameter models include Berger 1978, Laskar 1993, Laskar 2004, Laskar 2010, etc. Among them, the Cenozoic stable Laskar 2004 and the later Laskar 2010 are the models that best match the variation of the earth's orbit parameters in the geological period. Therefore, the theoretical astronomical orbit parameter model used in the present application is Laskar 2004. Through the Laskar 2004 model, the variations of three parameters, i.e. eccentricity, slope, and precession, can be calculated. See Figure 6 wherein the three target curves a, b, and c represent the cycle curves corresponding to the eccentricity, slope, and precession from 16000 Ka to 31000 Ka, i.e. the target curves.

[0069] Preferably, the present application selects the slope as the orbit parameter. The slope is the main orbit parameter controlling climate change since the Cenozoic era, and its theoretical curve has a good correlation with the change of sea level. The correlation between the envelope curve of the astronomical time scale filter curve and the sea level change curve can be seen in Figure 15, it can be considered that the slope is the main controlling factor of sea level change. Therefore, the application uses the slope of the natural gamma ray logging curve for astronomical tuning, establishes an astronomical age scale tuned by the slope, compares the envelope of the slope-tuned astronomical age scale filter curve with the global sea level change curve, and finds good similarity, which is used as a basis for dividing three-level sequences.

[0070] S5: determining the initial corresponding position of the natural gamma ray logging curve and the target curve based on the time anchor point, and tuning and correcting the natural gamma ray logging curve to the target curve from the initial corresponding position as the starting point according to the curve change of the target curve to obtain a time-depth conversion table reflecting the corresponding relationship between the depth domain and the time domain; determining an astronomical age scale based on the time-depth conversion table.

[0071] Specifically, the initial corresponding position of the natural gamma ray logging curve and the target curve is determined based on the time anchor point, and the natural gamma ray logging curve is tuned and corrected to the target curve from the initial corresponding position as the starting point according to the curve change of the target curve, and a time-depth conversion table for reflecting the corresponding geological age value of the depth is obtained according to the point position corresponding relationship of the natural gamma ray logging curve and the target curve; an astronomical age scale reflecting the time domain data corresponding to the natural gamma ray logging curve is determined based on the time-depth conversion table. Wherein, the horizontal coordinate of the natural gamma ray logging curve represents the depth, and the horizontal coordinate of the astronomical age scale represents the age.

[0072] As shown in Figure 7 and Figure 8 , this embodiment corrects the logging curve to the Laskar 2004 theoretical curve according to the cyclic change, which is the astronomical tuning process. This process needs to be verified repeatedly until the spectral analysis diagram of the obtained astronomical age scale is closest to the theoretical curve (i.e. the energy of the frequency spectrum peak of the applied tuning orbital parameter is concentrated and much higher than the surrounding values, and the frequency spectrum peak corresponding to other orbital parameters is also displayed). After astronomical tuning, the time-depth conversion table can be obtained (see Table 1).

[0073] Table 1

[0074] LW13 LW13 Depth (m) Time (kyr) Slope (40 kyr) Depth (m) Time (kyr) Slope (40 kyr) 3399.42 24989.88 O1 3581.09 25913.49 O24 3406.11 25027.41 O2 3588.39 25953.08 O25 3411.50 25065.98 3O 3595.14 25993.65 O26 3419.30 25107.25 4O 3602.56 26032.65 O27 3430.13 25147.67 5O 3608.31 26071.83 O28 3438.84 25189.09 6O 3614.99 26110.80 O29 3444.87 25225.71 7O 3620.88 26151.27 O30 3453.72 25267.26 8O 3627.19 26191.36 O31 3460.89 25310.81 9O 3635.25 26231.02 O32 3470.08 25357.12 10O 3641.31 26267.77 O33 3477.77 25390.97 11O 3646.97 26307.93 O34 3484.75 25429.57 12O 3652.88 26349.86 O35 3491.61 25476.01 13O 3659.59 26386.63 O36 3497.48 25515.78 14O 3665.74 26426.18 O37 3507.79 25558.37 15O 3673.26 26470.39 O38 3515.03 25593.84 16O 3680.63 26506.96 O39 3523.32 25638.00 17O 3689.27 26549.81 O40 3529.70 25675.98 18O 3697.65 26588.41 O41 3538.18 25713.77 19O 3704.74 26627.00 O42 3545.92 25757.13 20O 3711.88 26673.49 O43 3556.47 25795.03 21O 3719.16 26708.67 O44 3564.39 25833.94 22O 3728.61 26747.33 O45 3572.95 25874.90 23O 3741.01 26792.27 O46

[0075] In Table 1, one depth value corresponds to one age value. The depth domain data can be converted into time domain data through the depth-time conversion table, and the time domain data is the astronomical tuning age scale.

[0076] S6: filtering the astronomical time scale to obtain a filtered curve, and performing three-level sequence division on the envelope of the filtered curve. The step S5 can establish the slope-tuned astronomical time scale, and the step S6 extracts the slope signal of the slope-tuned astronomical time scale by using bandwidth filtering, and then draws the envelope of the bandwidth filtering, and takes the envelope as the basis for the three-level sequence division.

[0077] The existing research has proved that the climate change driven by the astronomical orbit is the main factor controlling the sea level change, and the sea level change is the main control factor of the three-level sequence development. Because the sea level change mainly controls the deposition of the marine sediment, and the change of the sediment will lead to the formation of the depositional sequence, the three-level depositional sequence division should mainly consider the sea level fluctuation amplitude and the deposition duration. Therefore, the envelope of the filtered curve of the slope-tuned astronomical time scale can be taken as the basis for the three-level sequence division.

[0078] Different filter bandwidths will obtain filtered curves with different resolutions, as shown in FIG. 4. Figure 13 As shown in FIG. 4, the envelope of the filtered curve formed by selecting the center frequency of 0.025 (40kyr) and the bandwidth of 0.002 and 0.001 is shown. Through the comparison of the envelopes of the filtered curves of the two slope-tuned astronomical time scales, it can be found that the envelope of the 0.002 bandwidth has higher resolution and richer information, but it also naturally includes a lot of non-slope signals; the envelope of the 0.001 bandwidth is smoother, and the amount of information covered is less, but the slope signal is more prominent. In summary, the envelope of the 0.001 bandwidth of the slope period is more conducive to the three-level sequence division.

[0079] In the present application, before the step S2, the natural gamma logging curve is preprocessed, and the preprocessing technique is to suppress useless signals and highlight the Miller cycle signals. Specifically, the natural gamma logging curve is subjected to outlier removal processing and trend removal processing to remove the influence of the trend signal and the noise signal.

[0080] The outlier refers to a small part of isolated values that are far away from the change trend of other values. The cause of the outlier may be the error in the measurement or the random error caused by the accidental factor. The existence of the outlier has little effect on the mean value of the whole signal, but it will overall raise the energy background of the power spectrum, so as to seriously affect the authenticity of the frequency spectrum analysis.

[0081] After the outliers are removed, the trend is also needed to be removed. Although the logging data and other data collected from the outcrop are depth domain data, there is a corresponding relationship between the deposition time and the deposition thickness, that is, the numerical value may increase or decrease with the deepening of the depth, and this data is called non-static data. The non-static data will generate a strong low-frequency signal during the frequency spectrum analysis, so that the correctness of the frequency spectrum analysis result is affected, and therefore a method for removing the linear trend is needed to eliminate the linear trend.

[0082] In the present application, the astronomical time scale obtained in step S5 is further needed to be verified before step S6. Specifically, the time domain spectrum analysis is performed on the astronomical time scale, if the frequency spectrum peak corresponding to the orbit parameter selected as the target curve is obviously higher than the others, it is judged that the astronomical time scale obtained in step S5 is correct, and the step S6 is continued; otherwise, the step S5 is returned to reacquire the astronomical time scale.

[0083] As shown in Figure 9 After the astronomical tuning, the astronomical time scale of the single well can be obtained, and at this time, it is needed to verify whether the tuning process is correct. The verification standard is to analyze whether the spectrum energy of 405kyr, 100kyr and 41kyr period is concentrated and obviously higher than the background noise energy to judge whether the tuning result is accurate.

[0084] The following embodiments are disclosed for detailed description.

[0085] Embodiment one

[0086] This embodiment is based on the establishment of the astronomical time scale of the LW13 well in the determination area. The about 346m thick stratum (3397m-3743m) with stable deposition rate of LW13 is selected to perform the cycle stratum analysis.

[0087] As shown in Figure 10 The depth domain natural gamma logging curve of the 3397-3743m section of the LW13 well shows good rhythm. As shown in Figure 2As shown in the figure, the numerical value on the dominant peak represents the frequency corresponding to the peak, and the thickness of the stratum corresponding to the frequency is in the brackets. There are multiple dominant peaks in the depth domain spectral analysis diagram, including 0.014 (71 meters), 0.056 (18 meters), 0.14 (7.1 meters), and 0.28 (3.5 meters), which are close to 405kyr: 100kyr: 40kyr: 20kyr. According to the known thickness of the drilling sequence and the rough sedimentation time estimation, the 0.014 peak should correspond to a 405kyr long eccentricity cycle. The information of the 0.014 dominant peak is extracted by the method of band-pass filtering, and the center frequency selected is 0.014 and the bandwidth is 0.004. The preprocessed natural gamma ray logging curve is superimposed with the filtered curve to check whether the parameters selected by the band-pass filtering are correct. It can be seen that the filtered curve extracted by the two parameters selected by the application contains the main cycle information of the logging curve, and the cycle period is obvious (see Figure 3 ).

[0088] By slope tuning, that is, comparing the depth domain data to the theoretical slope curve according to the cyclicity change (see Figure 7 ), a time-depth conversion table as shown in Table 1 can be established, that is, one depth corresponds to one time, and two time points are separated by a slope period. Through the time-depth conversion table, the depth domain logging curve can be converted into a time domain astronomical age scale tuned by the slope (see Figure 8 ).

[0089] This tuning process needs to be repeatedly verified many times until the spectrum diagram of the time domain astronomical age scale obtained is closest to the theory.

[0090] Finally, the astronomical age scale needs to be tested by time domain spectral analysis. MTM spectral analysis can not only be used to analyze whether the depth domain data has typical cyclicity, but also can be used to test whether the tuned astronomical age scale is accurate. The test standard is that if the dominant main peak obtained by the spectral analysis of the tuned astronomical age scale is obviously higher than the surrounding spectrum peak, it is considered that the tuning result is correct. As shown in Figure 9 , through the spectrum diagram of the astronomical age scale of the 3397-3743m section of the LW13 well, it can be seen that the main peak corresponding to the 40kyr slope period cycle is very prominent, and the 476kyr long eccentricity cycle, the 175kyr short eccentricity cycle, and the 20kyr precession cycle are also displayed, so it can be considered that the tuning result is in line with the actual situation, and the established astronomical scale is correct.

[0091] By tuning the LW13 well in sections and repeating the above steps, a slope-tuned astronomical age scale of about 1500m (3046-4482m) of the whole section of the LW13 well is obtained (see Figure 11), and the result is shown in Fig. 4. Figure 12 Figure 12 In the figure, the 40kyr slope period signal is outstanding, and the 454kyr eccentricity period signal and 20kyr obliquity period signal are also shown, so the tuning result is considered to be in accordance with the reality, and the astronomical time scale is correct.

[0092] Example Two

[0093] Previous studies have confirmed that the astronomical orbit driven climate change is the main factor controlling sea level change, which is the main controlling factor of the development of three-level sequences. Because sea level change mainly controls the deposition of marine sediments, and the change of sediments will lead to the formation of sedimentary sequences, therefore the division of three-level sedimentary sequences should mainly consider the amplitude of sea level fluctuation and the duration of deposition. Therefore, the envelope curve of the slope tuning astronomical time scale filter curve can be used as the basis for the division of three-level sequences.

[0094] Figure 13 The comparison chart of sea level change curve and the envelope curve of 0.002 bandwidth and 0.001 bandwidth of slope tuning astronomical time scale. It can be seen that there is a good similarity, which further confirms the correlation between the slope period envelope curve and the sea level change. Especially in the period of 24Ma-30Ma, the global sea level change and the slope period envelope curve of the astronomical time scale are highly consistent, almost synchronous rise and fall, and each peak of the global sea level change is reflected in the slope period curve envelope. Although there is a slight phase difference between some peaks, these phase differences can be considered as the influence of large-scale fluctuations caused by seafloor spreading in local areas. At 23.03Ma, there is no very sharp change in global sea level, only a slight decrease, but at 23.03Ma, the regional sea level change reflected by the slope period envelope curve has a short duration but a strong change amplitude, which can be considered as the performance of the start of seafloor spreading. This phenomenon also proves that the astronomical time scale established by tuning the well logging curve through astronomy is feasible, and the slope period envelope curve as an alternative indicator of regional sea level change is feasible. The global sea level change curve and the slope period envelope curve both reach a low value at 24Ma, which may be affected by the overall thermal subsidence of the region. From 24Ma to 22Ma, the change amplitude of the slope period envelope curve is significantly reduced; the global sea level change curve is a relatively regular and gentle fluctuation, and the fluctuation amplitude is lower than before. From 22Ma to 16Ma, the fluctuation amplitude of the slope period envelope curve is greatly reduced compared to before, and compared with the global sea level change curve, it can be found that the peak values between the two curves are generally similar, but there is a certain phase difference, which may be due to the influence of seafloor spreading activities in the target area. In summary, the slope period envelope curve has a high correlation with the sea level change.​

[0095] like Figure 14 As shown in the figure, the low-value points of the envelope cycle are used as sequence boundaries to divide the stratigraphic units, and a total of 14 third-order sequences are divided. The third-order sequence boundaries are named according to their boundary ages: SB16.3, SB17.2, SB18.2, SB19.2, SB20.5, SB21.3, SB22.2, SB23.7, SB24.7, SB25.8, SB27, SB27.7, SB28.9, and SB30.0.

[0096] like Figure 15 As shown, the third-order sequence division results of the present invention (left curve) are compared with two existing division results (the middle curve is the first existing solution, and the right curve is the second existing solution) for the same area. The first existing solution divides the 15.5Ma-30.0Ma strata into 11 third-order sequences, while the second existing solution divides this section into 8 third-order sequences. Although the number of third-order sequences in these two solutions is different, the third-order sequence interfaces overlap, such as SB15.5, SB17.5, and SB21. With the continuous deepening of basic geological research, there is reason to believe that the research results obtained by the first existing solution are more accurate than those obtained by the second existing solution.

[0097] Comparing the present invention with the existing scheme 1 reveals good comparability. Among the 12 third-order sequence interfaces, eight have inter-age differences of less than 0.2 Ma (SB16.3 and SB16.5, SB17.2 and SB17.1, SB18.2 and SB18, SB21.3 and SB21, SB23.7 and SB23.8, SB25.8 and SB26, SB27 and SB27, and SB28.9 and SB29). Only four third-order sequence interfaces in the present scheme, SB17.5, SB19.2, SB20.5, and SB22.2, do not correspond because they are located between two third-order sequences in scheme 1. Considering that the astronomical age scale obtained through sequence stratigraphic analysis has advantages over traditional methods, with higher analytical accuracy and resolution, the ages of the third-order sequence interfaces obtained by the present invention are considered to be closer to the actual situation.

[0098] The sequence division scheme disclosed by the present application is obviously superior to the prior scheme one in view of the need for quantitative sequence division. In the division scheme disclosed by the present application, the interval between two sequences is at most 1531 kyr and at least 687 kyr. In the prior scheme one, the interval between two sequences is at most 3000 kyr and at least 400 kyr. The duration of the three-level sequences divided in the present application is more stable and more in line with the requirements of quantitative sequence division; the duration of the three-level sequences in the prior scheme one varies too greatly. Considering that the main factor controlling the three-level sequences is sea level change, and the rise and fall amplitude and duration of the sea level change cannot possibly vary so greatly, it is believed that the three-level sequence division scheme derived by tuning the slope of the astronomical time scale is more in line with the actual situation in which the sea level as the main controlling factor controls the development of the three-level sequences.

[0099] Embodiment three

[0100] The present application also discloses a computer readable storage medium, which stores a computer program for executing the three-level sequence division method based on the Mitchell cycle.

[0101] Embodiment four

[0102] The present application also discloses an electronic device, which comprises a processor and a memory for storing executable instructions of the processor. The processor is used to read the executable instructions from the memory and execute the instructions to realize the three-level sequence division method based on the Mitchell cycle.

[0103] The above is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which shall be covered within the protection scope of the present application.

Claims

1. A method for dividing three-level sequences based on Michaelis cycles, characterized in that: include: S1: Obtain the natural gamma ray logging curve representing the depth domain in the target area; S2: Determine the signal energy and number of cycles of the natural gamma ray log based on spectrum analysis, and judge whether the natural gamma ray log contains Mie cycles based on the signal energy and number of cycles, including: The multi-window spectrum analysis method is used to process the natural gamma ray logging curve to obtain a spectrum analysis diagram, which is used to determine the spectrum of the dominant peak. The ordinate of the spectrum analysis diagram represents the energy of the cycle within the period, and the inverse of the abscissa represents the thickness of the formation corresponding to the cycle. If the ratio of the formation thickness corresponding to the dominant main peak determined based on the spectrum analysis is close to the ratio of each orbit parameter in the astronomical orbit model, it is determined that the natural gamma ray log contains a Mie cycle signal, and the process proceeds to S3; S3: Select a set of strong amplitude continuous seismic interfaces with certain age and depth in the target area as time anchor points; S4: Select the slope orbit parameter from the astronomical orbit model as the target curve representing the time domain; S5: Determine the initial corresponding position of the natural gamma ray logging curve and the target curve based on the time anchor point, and use the initial corresponding position as the starting point to tune the natural gamma ray logging curve to the target curve according to the curve change of the target curve to obtain a time-depth conversion table reflecting the corresponding relationship between the depth domain and the time domain; determine the astronomical age scale based on the time-depth conversion table; S6: Filter the astronomical age scale to obtain a filtering curve, and use the low-value points of the cycle on the envelope of the filtering curve as sequence boundaries to divide the three-level sequences.

2. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: Before S2, the natural gamma ray logging curve preprocessing is also included: The natural gamma ray logging curve is processed by removing outliers and detrending to remove the influence of trend signals and noise signals.

3. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: In said S3, the seismic interface selected as the time anchor point is expressed on the seismic section as a set of regionally continuous strong-amplitude seismic reflection sync axes; The seismic interface selected as the temporal anchor point is defined by a distinct regionally continuous sedimentary-tectonic unconformity.

4. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: Said S4 comprises: The slope is selected from the Laskar2004 model as the target curve representing the time domain.

5. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: Said S5 comprises: The initial corresponding position of the natural gamma ray logging curve and the target curve is determined based on the time anchor point, and the natural gamma ray logging curve is tuned and corrected to the target curve according to the curve change of the target curve with the initial corresponding position as the starting point. According to the point correspondence relationship between the natural gamma ray logging curve and the target curve, a time-depth conversion table for reflecting the age value corresponding to the depth is obtained; Determine the astronomical age scale in the time domain corresponding to the natural gamma ray logging curve based on the time-depth conversion table; Among them, the horizontal axis of the natural gamma ray logging curve represents depth, and the horizontal axis of the astronomical time scale represents age.

6. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: Said S6, before also includes: Perform time domain spectrum analysis on the astronomical age scale. If the frequency spectrum peak corresponding to the orbital parameter selected as the target curve is significantly higher than the others, then the astronomical age scale obtained in S5 is determined to be correct, and continue to S6; otherwise, return to S5 to re-acquire the astronomical age scale.

7. The method for dividing the third-level sequence based on the Michaelis cycle according to claim 1, characterized in that: Said S6 comprises: Using different filter bandwidths for filtering to obtain envelopes with different resolutions; Select the envelope that mainly contains the slope periodic signal; The low-value points of the envelope cycle are used as sequence boundaries for third-level sequence division.

8. A computer-readable storage medium storing a computer program, wherein the computer program is configured to execute the method according to any one of claims 1 to 7.

9. An electronic device, comprising: processor; a memory for storing instructions executable by the processor; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method according to any one of claims 1 to 7.

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