Carbonate rock sedimentary cycle division method and system based on element logging

Abstract

The invention relates to the technical field of carbonate rock sedimentary cycle division, in particular to a carbonate rock sedimentary cycle division method and system based on element logging. The method comprises the following steps: S1, acquiring stratum element logging data; s2, according to the stratum element logging data, solving intermediate parameters, and performing normalization processing; s3, obtaining sensitive parameters by using the normalized intermediate parameters; s4, according to the intermediate parameters, the intermediate parameters after normalization processing and the sensitive parameters, a continuous well section is drawn according to the borehole depth; s5, according to the continuous well section, analyzing the change rule of the sensitive parameters, and performing deposition cycle division; on the basis of element logging data, through data processing and parameter calculation, the problem that the logging curve and lithology differentiation degree in carbonate rocks is small is solved; when logging, rock core and other data are lacked, accurate sedimentary cycle division can be carried out when only element logging is carried out, and the reliability and timeliness of stratigraphic contrast are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbonate sedimentary cycle division, and particularly to a method and system for dividing carbonate sedimentary cycles based on element logging. Background Art

[0002] Traditional sedimentary cycle division mainly relies on logging curves and logging lithology. However, in carbonate rocks, the differentiation degree of logging curves and logging lithology in different sedimentary cycles is small, and their sensitivity is relatively low, which will lead to inaccurate division of sedimentary cycles, or when well conditions do not allow logging, sedimentary cycle division cannot be carried out, thus affecting the stratigraphic correlation ability of adjacent wells, making it impossible for us to determine the extension of the target formation or whether it has been drilled through, and further leading to low efficiency and poor accuracy in geological interpretation and exploration work.

[0003] The prior art CN114428358B discloses an isochronous stratigraphic division method based on geological-geophysical analysis. By introducing clastic component content analysis data and element analysis data, and combining seismic reflection data to jointly carry out stratigraphic division work. By introducing clastic component content analysis data and element analysis data as the basis for stratigraphic division, quantitative data information is provided, making the stratigraphic division process in the region more standard. The stratigraphic division and comparison work is carried out by integrating multi-parameter methods, improving the accuracy, and being not limited by regional tectonic differences and sedimentary environment differences, providing an accurate data basis for subsequent geological research.

[0004] The prior art CN106680879B discloses a method and device for sedimentary cycle division. The method includes the following steps: obtaining a peak frequency attribute curve according to seismic data; performing frequency division filtering on the peak frequency attribute curve to obtain a band-pass frequency component curve of low-frequency attributes and a band-pass frequency component curve of high-frequency attributes; respectively performing polyline processing on the band-pass frequency component curve of low-frequency attributes and the band-pass frequency component curve of high-frequency attributes to obtain a first sedimentary cycle curve and a second sedimentary cycle curve.

[0005] However, either the above method is for stratigraphic division of clastic rocks or relies on seismic data for sedimentary cycle division, and neither can solve the problem that the low differentiation degree of logging curves and lithology in carbonate sedimentary cycle division leads to inaccurate sedimentary cycle division.

[0006] Therefore, there is an urgent need to provide a method and system for dividing carbonate sedimentary cycles based on element logging, which can improve the accuracy of sedimentary cycle division compared with the prior art. Summary of the Invention

[0007] The present invention solves the technical problems existing in the prior art, and provides a method and system for dividing carbonate sedimentary cycles based on element logging.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for dividing carbonate rock sedimentary cycles based on elemental logging includes the following steps:

[0010] S1. Collect formation elemental logging data;

[0011] S2. According to the formation elemental logging data collected in step S1, intermediate parameters are obtained. The intermediate parameters at least include the content ratios of Sr and Ba, the content ratios of Mn and Fe, and the offshore index, and the intermediate parameters are normalized;

[0012] S3. According to the intermediate parameters after normalization in step S2, sensitive parameters are obtained;

[0013] S4. According to the intermediate parameters, the intermediate parameters after normalization, and the sensitive parameters, a continuous well profile is drawn according to the wellbore depth;

[0014] S5. According to the continuous well profile, the variation law of the sensitive parameters is analyzed to divide the sedimentary cycles.

[0015] Further, S5 specifically includes the following steps:

[0016] S501. Starting from the set formation boundary of seismic calibration or biologic calibration, if the set sensitive parameter is a relatively low value, it is defined as the starting point of a positive cycle; if it is a relatively high value, it is defined as the starting point of a reverse cycle;

[0017] S502. According to the sedimentary sequence, upwards in accordance with the third-order cycle, find the second-highest value or the second-lowest value of the cycle curve, and define it as the ending point of the positive cycle or the ending point of the reverse cycle. At the same time, the defined ending point is the starting point of the next cycle;

[0018] S503. When there is a sharp decrease or increase in the cycle curve value at the starting point of the next cycle defined within the set scale, define the nature of this cycle as the same as that of the previous cycle, otherwise it is the opposite;

[0019] S504. According to the determination result of whether the cycle nature of the next cycle in S503 is different from that of the previous cycle, set the ending point of the corresponding next cycle;

[0020] S505. Repeat steps S501 - S504, continue to find each node of the cycle upwards, then distinguish and mark the positive cycle and the reverse cycle to form a continuous sedimentary cycle sequence, and complete the division of the sedimentary cycle.

[0021] Further, step S504 is specifically as follows: When the cycle property of the next cycle determined in S503 is the same as that of the previous cycle, the determination method of the end point of the next cycle is the same as the definition method of the end point of the previous cycle described in S502; when the cycle property of the next cycle determined in S503 is opposite to that of the previous cycle, search upward for the next sub-low value or sub-high value of the set sensitive parameter, and define the sub-low value or sub-high value as the end point of the next cycle.

[0022] Further, the set sensitive parameter is a cycle curve parameter.

[0023] Further, the third-level cycle described in step S502 is defined as a scale of 30 - 50m.

[0024] Further, the set scale in step S503 is 2 - 3m.

[0025] Further, the determination method for the sharp decrease or increase of the cycle curve data in step S503 is: within the set scale thickness, the cycle curve value decreases to the sub-low value within the previous cycle, or the cycle curve value increases to the sub-high value within the previous cycle, and the upward values gradually show a reverse change trend.

[0026] Further, in step S5, set the content ratios of Sr and Ba, Mn and Fe, and the offshore index as auxiliary parameters for cycle division, and set the sensitive parameter as the basis parameter for cycle division.

[0027] Further, in step S4, specifically use Gxplorer or Resform software to draw the continuous well profile.

[0028] Further, the formation element logging data collected in step S1 includes elements reflecting shale content, elements reflecting sand content, elements reflecting the content of limestone and dolomite in carbonate rocks, elements reflecting marine provenance, and elements reflecting terrestrial provenance.

[0029] Further, the elements reflecting shale content are: Fe, Al, K; the elements reflecting sand content are: Si; the elements reflecting the content of limestone and dolomite in carbonate rocks are: Ca, Mg; the element reflecting marine provenance is: Sr; the element combination reflecting marine provenance is: Mn + Ca + Mg + K + Na; the element reflecting terrestrial provenance is: Ba; the element combination reflecting terrestrial provenance is: Fe + Si + Al.

[0030] Further, the offshore index described in step S2 is expressed by the following formula:

[0031]

[0032] In the above formula, DIS represents the offshore index, and Q Mn represents the content value of Mn, and Q Ca represents the content value of Ca, and Q Mg represents the content value of Mg, and Q K represents the content value of K, and Q Na represents the content value of Na, and Q Fe represents the content value of Fe, and Q Si represents the content value of Si, and Q Al represents the content value of Al.

[0033] Further, the normalization process in step S2 is specifically carried out by the following formula:

[0034]

[0035] In the above formula, Q n represents the value of the intermediate parameter represented by n, where n represents the intermediate parameter generated in step S2, represents the maximum value in the numerical sequence of the intermediate parameter represented by n, represents the minimum value in the numerical sequence of the intermediate parameter represented by n, and Q' n represents the value of the intermediate parameter represented by n after normalization.

[0036] Further, after step S5, there is also a step of verifying the cycle division result obtained in step S5, specifically:

[0037] (1) Compare the sedimentary cycle division result with the logging curve characteristics of this well. When the sedimentary cycle division result meets the first determination condition, use this sedimentary cycle division result as the intermediate result of the sedimentary cycle division of this well; otherwise, repeat step S5;

[0038] (2) Compare the intermediate result of the sedimentary cycle division with the division results of several adjacent wells. When the second determination condition is met, recognize this sedimentary cycle division result as the final sedimentary cycle division result of this well; otherwise, repeat steps S5 and (1) until the second determination condition is met.

[0039] The carbonate rock sedimentary cycle division system based on elemental logging includes a first module, a second module, a third module, a fourth module, and a fifth module connected in sequence; the first module is used to execute the content in step S1, the second module is used to execute the content in step S2, the third module is used to execute the content in step S3, the fourth module is used to execute the content in step S4, and the fifth module is used to execute the content in step S5.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] Based on the elemental logging data, through data processing and parameter calculation, the present invention improves the differentiation degree of sensitive parameters, realizes the accurate division of sedimentary cycles, and solves the problem of small differentiation degree of logging curves and lithology in carbonate rocks; when there is a lack of data such as logging and core, it can accurately divide sedimentary cycles only with elemental logging, providing a new method for stratigraphic sedimentary correlation and helping to improve the timeliness and accuracy of geological interpretation and exploration work. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flow chart of the method of the present invention.

[0043] Figure 2 is a schematic diagram of four different superposition methods in the sedimentary cycle division of the present invention.

[0044] Figure 3 is a schematic diagram of the single-well sedimentary cycle division result of the present invention.

[0045] Figure 4 is a schematic diagram of the comparison result of multi-well sedimentary cycle division of the present invention.

[0046] Figure 5 is a schematic diagram of the system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The technical solution of the present invention will be clearly described below in conjunction with the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0048] As Figure 1 shown, the present invention provides a method for dividing carbonate rock sedimentary cycles based on elemental logging, including the following steps:

[0049] S1. Collect formation elemental logging data. The logging data includes elements reflecting shale content, elements reflecting sand content, elements reflecting limestone content and dolomite content in carbonate rocks, elements reflecting marine provenance, and elements reflecting terrestrial provenance. That is, the logging data at least includes the content measurement value data of elements such as Al, Ba, Ca, Fe, K, Mg, Mn, Na, Si, and Sr. Among the above elements, Fe, Al, and K reflect shale content and are positively correlated with shale content; Si reflects sand content, Ca and Mg reflect limestone content and dolomite content in carbonate rocks, Sr represents marine provenance, Ba represents terrestrial provenance, and the elemental combination also reflects the sediment source. The combination of "Mn + Ca + Mg + K + Na" represents marine provenance, and the combination of "Fe + Si + Al" represents terrestrial provenance. The collected logging data is shown in the following table:

[0050] Table 1 is the data table of elemental logging measurements of Well X1 (partial)

[0051]

[0052]

[0053] Furthermore, after obtaining samples of the actual formation, elemental logging data is measured by an X-ray diffractometer to obtain the elemental content of the formation, as shown in Table 1.

[0054] S2. Using the elemental logging data of the formation collected in S1, intermediate parameters are obtained according to empirical formulas. The intermediate parameters include at least the content ratio of Sr and Ba, the content ratio of Mn and Fe, and the offshore index, and the intermediate parameters are normalized so that these intermediate parameters are in the same scale range. The calculation formulas for the intermediate parameters are as follows:[[]]

[0055]

[0056]

[0057] In the above formula, Sr:Ba represents the content ratio of Sr element to Ba element, Q Sr represents the content of Sr element, Q Ba represents the content of Ba element, Mn:Fe represents the content ratio of Mn element to Fe element, Q Mn represents the content of Mn, Q Fe represents the content of Fe.

[0058]

[0059] In the above formula, DIS represents the offshore index, Q Mn represents the content of Mn, Q Ca represents the content of Ca, Q Mg represents the content of Mg, Q K represents the content of K, Q Na represents the content of Na, Q Fe represents the content of Fe, Q Si represents the content of Si, Q Al represents the content of Al.

[0060] The normalization processing expression is as follows:[[]]

[0061]

[0062] In the above formula, Q n represents the value of the intermediate parameter represented by n, and n represents the intermediate parameter generated in step S2, represents the maximum value in the numerical sequence of the intermediate parameter represented by n, represents the minimum value in the numerical sequence of the intermediate parameter represented by n, Q' n represents the normalized numerical value of the intermediate parameter represented by n.

[0063] The above intermediate parameters are shown in Table 2.

[0064] S3. Using the intermediate parameters after the normalization process in S2, calculate through the formula of the present invention to obtain the sensitive parameter. Usually, Excel software is used for processing, and other equivalent software can also be used for processing to obtain the corresponding sensitive parameter.

[0065] Furthermore, the sensitive parameter is the derived cycle curve parameter, and the specific calculation formula of the sensitive parameter is as follows:

[0066] S = (Sr:Ba)' × (Mn:Fe)' × DIS'

[0067] In the above formula, S represents the cycle curve parameter, (Sr:Ba)' represents the content ratio of Sr element to Ba element after normalization, (Mn:Fe)' represents the content ratio of Mn element to Fe element after normalization, and DIS represents the normalized offshore index.

[0068] Even further, the cycle curve parameter is obtained by multiplying the content ratio of Sr element to Ba element after normalization, the content ratio of Mn element to Fe element after normalization, and the normalized offshore index, which are three parameters reflecting the water depth, simultaneously. The larger the value, the deeper the water body. Multiplying them simultaneously has the effect of enhancing the data effect.

[0069] Even further, the results after processing the data in Table 1 through steps S2 and S3 are shown in the following table:

[0070] Table 2 is the table of the element logging data processing results of Well X1 (partial)

[0071]

[0072] S4. According to the aforementioned intermediate parameters, the intermediate parameters after normalization, and the sensitive parameter, draw a continuous well profile according to the wellbore depth. When drawing the continuous well profile, Gxplorer or Resform software can be used for drawing.

[0073] S5. As Figure 3As shown in the figure, analyze the variation law of sensitive parameters, conduct sedimentary cycle division, and determine the boundaries of different sedimentary cycles according to the vertical variation trend of ratios or parameters during the division process. At the same time, take the three intermediate parameters of Sr:Ba, Mn:Fe, and the offshore index DIS, as well as the cycle curve parameters as the basis parameters for sedimentary cycle division; the logging curve GR reflecting lithology is a low value in carbonate rocks, and the amplitude is relatively gentle. The variation amplitude of the caliper curve CAL is also small, while the resistivity curves RD and RS more reflect the development of formation fractures and pores. In the present invention, the cycle curve parameter is a relatively low value at the starting point of the positive cycle reflecting the rising water body and a relatively high value at the end point of the positive cycle. The reverse cycle reflecting the falling water body is opposite to the positive cycle, with a relatively high value at the starting point and a relatively low value at the end point. From the deep part of the wellbore upwards, the positive and reverse cycles appear alternately, constituting a complete sedimentary profile sequence. Generally, there are peak-shaped relatively high values of GR near the end point of the positive cycle and the starting point of the reverse cycle, while GR is a relatively gentle low value near the starting point of the positive cycle and the end point of the reverse cycle. The specific sedimentary cycle division is carried out according to the following steps:

[0074] S501. Starting from the formation boundary of the set level (high level) calibrated by seismic or biologic calibration, for sensitive parameters, preferably cycle curve parameters, if it is a relatively low value, it is defined as the starting point of the positive cycle, and if it is a relatively high value, it is defined as the starting point of the reverse cycle;

[0075] S502. Then, according to the sedimentary sequence, upwards in accordance with the third-level cycle, that is, on the scale of 30 - 50m, find the second-highest data of the cycle curve and define it as the end point of the positive cycle, or find the second-lowest value of the cycle curve and define it as the end point of the reverse cycle. At the same time, the defined end point is the starting point of the next cycle;

[0076] S503. Starting from the starting point of the next cycle defined, if there is a sharp decrease or increase in the cycle curve value within the set scale and the value gradually shows a reverse change trend upwards, then define the nature of the next cycle as the same as that of the previous cycle. The above set scale is preferably 2 - 3m, otherwise it is the opposite. Further, the method for judging the sharp decrease or increase in the cycle curve value is: starting from the starting point of the next cycle defined, there is a decrease in the cycle curve value within the set scale to the second-lowest value within the previous cycle or an increase to the second-highest value within the previous cycle;

[0077] S504. According to the judgment of the cycle nature of the next cycle and the cycle nature of the previous cycle carried out in S503, set the end point of the corresponding next cycle. Specifically:

[0078] (1) If the cycle property of the next cycle determined in S503 is the same as that of the previous cycle, the method for determining the end point of the next cycle is the same as the method for defining the end point of the previous cycle described in S502.

[0079] (2) When the cycle property of the next cycle determined in S503 is opposite to that of the previous cycle, search upward for the sensitive parameter, preferably the next sub-low or sub-high value on the cycle curve, and define this sub-low or sub-high value as the end point of the next cycle.

[0080] S505. Repeat steps S501 - S504 to continue searching upward for each node of the cycle, and then use an equilateral triangle to represent a positive cycle and an inverted triangle to represent a negative cycle (as Figure 2 shown), to form a continuous sequence of sedimentary cycles and complete the division of sedimentary cycles (as Figure 3 shown).

[0081] Furthermore, Figure 2 from left to right in Figure 2 are schematic diagrams of a positive cycle superimposed upward by a negative cycle, a positive cycle superimposed upward by a positive cycle, a negative cycle superimposed upward by a positive cycle, and a negative cycle superimposed upward by a negative cycle. The broken line in

[0082] represents the numerical change trend of the sedimentary cycle curve. The left side of each schematic diagram represents a high value, and the right side of each schematic diagram represents a low value.

[0083] S6. Verify the result of the sedimentary cycle division in S5, which specifically includes the following steps:

[0084] S601. Compare the result of the sedimentary cycle division with the logging curve characteristics of this well. When the result of the sedimentary cycle division meets the first determination condition, and the first determination condition is that there is a peak-shaped relatively high GR value within 5 m above and below the end point of the positive cycle and the start point of the negative cycle, while the GR is a relatively flat low value near the end point of the negative cycle and the start point of the positive cycle, then take this result of the sedimentary cycle division as the intermediate result of the sedimentary cycle division of this well; otherwise, repeat step S5. Figure 4As shown in the figure, the intermediate result of the sedimentary cycle division passed by S601 is compared with the division results of several adjacent wells. After meeting the second determination condition, the sedimentary cycle division result is determined as the final sedimentary cycle division result of this well and can be used for other applications. Otherwise, steps S5 and S601 are repeated until the above second determination condition is met. The second determination condition is that the divided sedimentary cycle conforms to the characteristics of stable carbonate platform deposition in this area, that is, the change in cycle thickness does not exceed 20% compared with adjacent wells, and the division boundary is in a corresponding position in the stratigraphic framework, that is, the relative position of the same boundary relative to the top and bottom of the formation is basically the same. For example, if Well A is in the middle and lower position, it is unreasonable if the adjacent Well B is in the middle and upper position.

[0085] Furthermore, in steps S601 and S602, the intermediate result of the sedimentary cycle division can also be compared with the core data. The determination criterion is that the shale content in the core is high at the end point of the positive cycle and the starting point of the reverse cycle, while the particle content in the core is high at the end point of the reverse cycle and the starting point of the positive cycle. However, the coverage rate of the core data in the wellbore is generally low.

[0086] Based on the element logging data, through data processing and parameter calculation, and by analyzing the vertical variation law of the derived cycle curve parameters, the present invention divides the sedimentary cycle. The sensitive parameter reflecting the start point of the positive cycle of water body rising is a relatively low value, corresponding to a relatively high value at the end point of the positive cycle, while the reverse cycle reflecting the water body decline is opposite to the positive cycle, with the starting point being a relatively high value and the end point being a relatively low value, realizing the accurate division of the sedimentary cycle and solving the problem of small differentiation degree of logging curves and lithology in carbonate rocks. Using an X-ray diffractometer for element analysis and combining data processing and analysis software to complete the calculation and division process, when there is a lack of data such as logging and core, accurate sedimentary cycle division can be carried out only with element logging, providing a new method for stratigraphic sedimentary correlation and helping to improve the timeliness and accuracy of geological interpretation and exploration work.

[0087] As Figure 5 shown, the present invention also provides a carbonate rock sedimentary cycle division system based on element logging, including a first module, a second module, a third module, a fourth module, a fifth module, and a sixth module. The output end of the first module is connected to the input end of the second module, the output end of the second module is connected to the input end of the third module, the output end of the third module is connected to the input end of the fourth module, the output end of the fourth module is connected to the input end of the fifth module, and the output end of the fifth module is connected to the input end of the sixth module. This system outputs through the output end of the fifth module or the output end of the sixth module. The first module is used to execute the operation content in step S1, the second module is used to execute the operation content in step S2, the third module is used to execute the operation content in step S3, the fourth module is used to execute the operation content in step S4, the fifth module is used to execute the operation content in step S5, and the sixth module is used to execute the operation content in step S6.

[0088] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Simple modifications or equivalent replacements made by those of ordinary skill in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. Method for dividing carbonate sedimentary cycles based on elemental logging, characterized in that, it includes the following steps: S1. Collect formation elemental logging data; S2. According to the formation elemental logging data collected in step S1, calculate intermediate parameters, where the intermediate parameters at least include the content ratios of Sr and Ba, the content ratios of Mn and Fe, and the offshore index, and perform normalization processing on the intermediate parameters; S3. Obtain sensitive parameters according to the intermediate parameters after normalization processing in step S2; S4. Draw a continuous well profile according to the wellbore depth based on the intermediate parameters, the intermediate parameters after normalization processing, and the sensitive parameters; S5. Analyze the variation law of the sensitive parameters according to the continuous well profile to divide the sedimentary cycles.

2. The method for dividing carbonate sedimentary cycles based on elemental logging according to claim 1, characterized in that, step S5 specifically includes the following steps: S501. Starting from the set formation boundary of seismic calibration or biologic calibration, if the corresponding sensitive parameter is a relatively low value, it is defined as the starting point of a positive cycle, and if it is a relatively high value, it is defined as the starting point of a negative cycle; S502. According to the sedimentary sequence, search for the second-highest value or the second-lowest value of the cycle curve upward according to the third-order cycle, and define it as the ending point of the positive cycle or the negative cycle. At the same time, the defined ending point is the starting point of the next cycle; S503. When there is a sharp decrease or increase in the cycle curve value of the starting point of the next cycle defined within the set scale, it is defined that the nature of this cycle is the same as that of the previous cycle, otherwise it is the opposite; S504. According to the determination result of whether the cycle nature of the next cycle in step S503 is different from that of the previous cycle, set the ending point of the corresponding next cycle; S505. Repeat steps S501 - S504, continue to search for each node of the cycle upward, then distinguish and mark the positive cycle and the negative cycle to form a continuous sedimentary cycle sequence, and complete the division of the sedimentary cycles.

3. The method for dividing carbonate sedimentary cycles based on elemental logging according to claim 2, characterized in that, step S504 is specifically as follows: When the cycle nature of the next cycle determined in S503 is the same as that of the previous cycle, the determination method of the ending point of the next cycle is the same as the definition method of the ending point of the previous cycle described in S502; when the cycle nature of the next cycle determined in S503 is opposite to that of the previous cycle, search upward for the next second-lowest value or the second-highest value of the set sensitive parameter, and define this second-lowest value or the second-highest value as the ending point of the next cycle.

4. The method for dividing carbonate sedimentary cycles based on elemental logging according to claim 3, characterized in that, the set sensitive parameter is a cycle curve parameter.

5. The method for dividing carbonate sedimentary cycles based on elemental logging according to claim 2, characterized in that, the third-order cycle defined in step S502 is a scale of 30 - 50m.

6. The method for dividing carbonate sedimentary cycles based on elemental logging according to claim 2, characterized in that, the set scale in step S503 is 2 - 3m.

7. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 2, characterized in that, the method for judging the sharp decrease or increase of the cycle curve data in step S503 is as follows: within the set scale thickness, the cycle curve value decreases to the second lowest value within the previous cycle, or the cycle curve value increases to the second highest value within the previous cycle, and the upward value gradually shows a reverse change trend.

8. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, in step S5, the content ratios of Sr and Ba, the content ratios of Mn and Fe, and the offshore index are set as auxiliary parameters for cycle division, and the sensitive parameters are set as the basis parameters for sedimentary cycle division.

9. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, in step S4, Gxplorer or Resform software is specifically used to draw the continuous well profile.

10. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, the formation element logging data collected in step S1 includes elements reflecting shale content, elements reflecting sand content, elements reflecting the limestone content and dolomite content of carbonate rocks, elements reflecting marine provenance, and elements reflecting terrestrial provenance.

11. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 10, characterized in that, the elements reflecting shale content are: Fe, Al, K; the elements reflecting sand content are: Si; the elements reflecting the limestone content and dolomite content of carbonate rocks are: Ca, Mg; the elements reflecting marine provenance are: Sr; the element combination reflecting marine provenance is: Mn + Ca + Mg + K + Na; the elements reflecting terrestrial provenance are: Ba; the element combination reflecting terrestrial provenance is: Fe + Si + Al.

12. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, the offshore index described in step S2 is expressed by the following formula: In the above formula, DIS represents the offshore index, Q Mn represents the content value of Mn, Q Ca represents the content value of Ca, Q Mg represents the content value of Mg, Q K represents the content value of K, Q Na represents the content value of Na, Q Fe represents the content value of Fe, Q Si represents the content value of Si, Q Al represents the content value of Al.

13. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, the normalization process in step S2 is specifically carried out by the following formula: In the above formula, Q n represents the value of the intermediate parameter represented by n, where n represents the intermediate parameter generated in step S2, represents the maximum value in the numerical sequence of the intermediate parameter represented by n, represents the minimum value in the numerical sequence of the intermediate parameter represented by n, and Q′ n represents the normalized value of the intermediate parameter represented by n.

14. The method for dividing carbonate rock sedimentary cycles based on element logging according to claim 1, characterized in that, after step S5, it further includes a step of verifying the cycle division result obtained in step S5, specifically: (1) Compare the sedimentary cycle division result with the logging curve characteristics of this well. When the sedimentary cycle division result meets the first determination condition, take this sedimentary cycle division result as the intermediate result of the sedimentary cycle division of this well; otherwise, repeat step S5; (2) Compare the intermediate result of the sedimentary cycle division with the division results of several adjacent wells. When the second determination condition is met, recognize this sedimentary cycle division result as the final sedimentary cycle division result of this well; otherwise, repeat step S5 and step (1) until the second determination condition is met.

15. A system using the carbonate rock sedimentary cycle division method based on element logging according to any one of claims 1-14, characterized in that, it includes a first module, a second module, a third module, a fourth module, and a fifth module connected in sequence; the first module is used to execute the content in step S1, the second module is used to execute the content in step S2, the third module is used to execute the content in step S3, the fourth module is used to execute the content in step S4, and the fifth module is used to execute the content in step S5.

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