Quantitative recovery method for ancient water depth of salinized lake basin

Abstract

The invention relates to a quantitative recovery method for the paleo-water depth of a salinized lake basin, and belongs to the technical field of paleo-sedimentary environment research. According to the quantitative recovery method for the paleo-water depth of the salinized lake basin, the paleo-water depth of each deposition cycle can be recovered, the paleo-water depth accurate to different lithologic deposition periods in five-stage deposition cycles of a quasi-sequence can be recovered, and the accuracy is high; according to the quantitative recovery method for the paleo-water depth of the salinized lake basin, the paleo-water depth is calculated and determined through the mathematical physical relation, and compared with a fitting empirical formula calculation method, the method has the advantages of being accurate and reliable; the quantitative recovery method for the paleo-water depth of the salinized lake basin is suitable for research on paleo-environments of the salinized lake basin in different geological historical deposition periods, and the average paleo-water depth of the lake basin in different lithologic deposition periods in each quasi-sequence can be accurately recovered; and a basis is provided for research on stratigraphic sequence, sedimentary evolution, paleo-climate change in a sedimentary period and the like of the salinized lake basin.

Description

Technical Field

[0001] The present invention relates to a method for quantitatively restoring the paleo-water depth of a salinized lake basin, belonging to the technical field of paleo-sedimentary environment research. Background Art

[0002] As an important basin type in oil and gas exploration, salinized lake basins are relatively common in oil and gas resource basins such as the Bohai Bay Basin, Qaidam Basin, Jianghan Basin, Ordos Basin, and Sichuan Basin in China. By quantitatively restoring the paleo-water depth and then studying the water level changes of the salinized lake basin, it provides a basis for the study of the sedimentary stratigraphic sequence, sedimentary filling evolution, and paleoclimate during sedimentation in the salinized lake basin, and has important guiding significance for oil and gas exploration in this type of basin.

[0003] At present, the methods for restoring the paleo-water depth of salinized lake basins include paleontological marker method, sedimentology method, geochemical element analysis method, geophysical method, etc. Among them, the paleontological marker method mainly relies on the differentiation of organisms living in different environments to determine the paleo-water depth. This method can qualitatively determine the change of the paleo-water depth, but it is difficult to effectively quantitatively restore the paleo-water depth; the sedimentology method mainly comprehensively judges the paleo-water depth through information such as sediment distribution, sedimentary structure, seismic characteristics, and the formation law of authigenic minerals. Although this method combines sedimentary factors, it is still a qualitative restoration of the paleo-water depth and cannot effectively quantitatively restore it; the geochemical element analysis method mainly judges the paleo-water depth through the distribution characteristics of elements at different water depths. At present, the thorium-uranium ratio is mainly used to qualitatively determine the size of the paleo-water depth. A small thorium-uranium ratio indicates a reducing environment, indicating a relatively shallow water depth, and a large thorium-uranium ratio indicates an oxidizing environment, indicating a relatively deep water body. In addition, there is also a method of fitting the mathematical relationship between the iron-cobalt ratio of trace elements in mudstone and the known paleo-water depth to calculate the paleo-water depth; the geophysical method mainly includes well logging method and seismic method. The well logging method mainly uses the correlation relationship between gamma well logging and energy spectrum well logging, combined with sedimentary laws to restore the paleo-water depth. In addition, there is also a method of using seismic profiles, calculating the amount of erosion to restore the paleo-burial depth, and then using empirical formulas to calculate the paleo-water depth.

[0004] Most of the above methods for restoring the paleo-water depth are qualitative restoration or semi-quantitative restoration (by establishing empirical fitting formulas for calculation). Although the above methods for restoring the paleo-water depth can restore the paleo-water depth in different geological periods, they cannot accurately restore the specific values of the paleo-water depth in each sedimentary period, especially the paleo-water depth values within parasequences are difficult to effectively restore, which has certain limitations for the reconstruction of the paleo-environment and the restoration of the sedimentary evolution process. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for quantitatively restoring the paleo-water depth of a salinized lake basin, which can solve the problem that the existing methods for restoring the paleo-water depth cannot accurately restore the paleo-water depth within parasequences.

[0006] To achieve the above object, the technical solution adopted by the method for quantitatively restoring the paleo water depth of a salinized lake basin according to the present invention is as follows:

[0007] A method for quantitatively restoring the paleo water depth of a salinized lake basin, comprising the following steps:

[0008] S1. Conduct parasequence division on the target interval in the study area to determine the distribution area of each rock layer within each parasequence in the target interval;

[0009] S2. Determine the mass of the salt rock within each parasequence in the target interval; the mass of the salt rock within a certain parasequence is equal to the product of the average thickness of the salt rock within this parasequence, the distribution area of the salt rock within this parasequence, and the density of the salt rock within this parasequence;

[0010] S3. Determine the paleo water salinity of each rock layer within each parasequence in the target interval of the study area;

[0011] S4. Calculate the paleo water volume during the deposition period of each rock layer within each parasequence, and the calculation formula is as follows: V = M(1 - Wt) / (Wt×ρ 水 ), where V is the paleo water volume during the deposition period of a certain rock layer within a certain parasequence, M is the mass of the salt rock within a certain parasequence, Wt is the paleo water salinity of a certain rock layer within a certain parasequence, and ρ 水 is the paleo water density;

[0012] S5. Calculate the average paleo water depth during the deposition period of each rock layer within each parasequence in the target interval of the study area according to the distribution area and paleo water volume of each rock layer within each parasequence in the target interval of the study area.

[0013] The method for quantitatively restoring the paleo water depth of a salinized lake basin according to the present invention can restore the paleo water depth of each sedimentary cycle, and can restore the paleo water depth during the deposition period of different lithologies in the fifth-order sedimentary cycle accurate to parasequences, with high accuracy; the method for quantitatively restoring the paleo water depth of a salinized lake basin according to the present invention calculates and determines the paleo water depth using mathematical and physical relationships, and has the advantages of accuracy and reliability compared with the calculation method of fitting empirical formulas; the method for quantitatively restoring the paleo water depth of a salinized lake basin according to the present invention is applicable to the study of the paleoenvironment during different geological historical deposition periods of salinized lake basins, can relatively accurately restore the average paleo water depth of the lake basin during the deposition period of different lithologies within each parasequence, and further provides a basis for studying the stratigraphic sequence, sedimentary evolution, and paleoclimate change during the deposition period of salinized lake basins.

[0014] Preferably, the method for conducting parasequence division on the target interval in the study area is as follows: Obtain the logging data and mud logging data of each drilled well in the study area, conduct fine stratigraphic correlation on each drilled well, and then conduct stratigraphic division on each drilled well in the study area; on the basis of the stratigraphic division of each drilled well in the study area, establish a cross-well stratigraphic correlation profile, determine the development characteristics of each rock layer during the deposition period of the target interval in the study area, and then conduct parasequence division on the target interval in the study area.

[0015] It is understandable that in the present invention, the distribution ranges of each rock stratum within each parasequence in the target interval are delineated on the well location coordinate map by using the dual-arc geological software, and then the distribution areas of each rock stratum within each parasequence in the target interval are obtained by reading.

[0016] In order to improve the calculation accuracy of the average thickness of salt rock within a parasequence, preferably, the average thickness of salt rock within a certain parasequence is equal to the average value of the thicknesses of the salt rock encountered in each drilled well in the study area within this parasequence.

[0017] Preferably, the method for determining the paleo-water body salinity of each rock stratum within each parasequence is as follows: Obtain the primary brine inclusions captured during the deposition period of each rock stratum within different parasequences, and conduct test analysis on the primary brine inclusions to obtain the freezing point temperature of the primary brine inclusions, and then calculate the paleo-water body salinity of each rock stratum within each parasequence in the target interval of the study area. The paleo-water body salinity determined by the above method has high accuracy and the advantages of simple and convenient operation.

[0018] It is understandable that the calculation formula for the paleo-water body salinity of each rock stratum within each parasequence in the target interval of the study area is as follows: Wt = -1.76958×D - 0.042384×D 2 - 0.00052778×D 3 , where Wt is the paleo-water body salinity and D is the freezing point temperature of the primary brine inclusion, with the unit of °C. Calculating the paleo-water body salinity using the above formula has the advantages of simple calculation and accurate calculation results.

[0019] It is understandable that the freezing point temperature of the primary brine inclusion is measured by the freezing method.

[0020] Preferably, the calculation formula for the average paleo-water depth during the deposition period of each rock stratum within each parasequence is as follows: H = V / S, where H is the average paleo-water depth during the deposition period of a certain rock stratum within a certain parasequence in the target interval of the study area, V is the paleo-water body volume during the deposition period of a certain rock stratum within a certain parasequence in the target interval of the study area, and S is the distribution area of a certain rock stratum within a certain parasequence in the target interval of the study area. The paleo-water depth calculated by the above calculation method has high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic flow chart of the method for quantitatively restoring the paleo-water depth of a salinized lake basin according to an embodiment of the present invention;

[0022] Figure 2 is a distribution map of each rock stratum within parasequence I in the target interval of the study area according to an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of the quantitative change curve of the paleo-water depth during the deposition period according to an embodiment of the present invention;

[0024] Figure 4 It is a schematic diagram of the natural gamma ray curve (GR curve), spontaneous potential curve (SP curve), acoustic travel time logging curve (AC curve), density logging curve (DEN curve), lithology profile, sedimentary cycle division result, paleo-water body salinity change curve during the sedimentary period, quantitative paleo-water depth change curve during the sedimentary period, and sedimentary facies division result of the target interval in the study area in the embodiment of the present invention. Specific Embodiments

[0025] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0026] Embodiment

[0027] The quantitative restoration method of the paleo-water depth in the salinized lake basin in this embodiment takes a certain area as the study area, as Figure 1 shown, and specifically includes the following steps:

[0028] (1) Obtain core samples from the target interval in the study area, determine the sedimentary cycle and lithological combination characteristics of the target interval in the study area, and at the same time obtain the inclusion test samples of each rock segment within the sedimentary cycle from the core samples;

[0029] (2) Obtain the logging data and mud logging data of each drilled well in the study area, conduct fine stratigraphic correlation on each drilled well, and then conduct stratigraphic division on each drilled well in the study area;

[0030] On the basis of the stratigraphic division of each drilled well in the study area, establish a cross-well stratigraphic correlation profile, determine the development characteristics of each rock layer during the sedimentary period of the target interval in the study area, conduct parasequence division on the target interval in the study area, and use double-arc geological software to draw the distribution range of each rock layer within each parasequence of the target interval on the well location coordinate map to obtain the distribution area of each rock layer within each parasequence of the target interval; among them, the distribution map of each rock layer within parasequence Ⅰ of the target interval in the study area is as Figure 2 shown;

[0031] (3) Statistically calculate the thickness of salt rock drilled in each parasequence in each drilled well in the study area, then calculate the average value of the thickness of salt rock drilled in a certain parasequence in each drilled well to obtain the average thickness of salt rock within this parasequence, and then calculate the mass of salt rock within each parasequence of the target interval; the mass of salt rock within a certain parasequence is equal to the product of the average thickness of salt rock within this parasequence, the distribution area of salt rock within this parasequence, and the density of salt rock within this parasequence. The calculation formula is: M 盐 =S 盐 ×h 盐 ×ρ 盐 , where M 盐 is the mass of salt rock within a certain parasequence, with the unit of kg; S 盐 is the distribution area of salt rock within a certain parasequence, with the unit of m 2 ; h 盐is the average thickness of the salt rock within a certain parasequence, with the unit of m; ρ 盐 is the density of the salt rock within a certain parasequence. In this implementation, the value is 2165 kg / m 3 ; In this embodiment, the distribution area, average thickness, and mass of the salt rock within each parasequence are shown in Table 1;

[0032] Table 1 Distribution area, average thickness, and mass of the salt rock within each parasequence

[0033]

[0034] (4) From the core samples of the target interval in the study area, obtain the primary brine inclusions captured during the deposition period of each rock layer within different parasequences, and conduct test analysis on the primary brine inclusions. Measure the freezing point temperature of the primary brine inclusions using the freezing method, and then calculate the paleo-water salinity of each rock layer within each parasequence in the target interval of the study area according to the calculation formula of paleo-water salinity in the petroleum industry standard SY / T6010-2011 "Microthermometry Method for Fluid Inclusions in Sedimentary Basins"; the calculation formula of paleo-water salinity is as follows: Wt = -1.76958×D - 0.042384×D 2 - 0.00052778×D 3 , where Wt is the paleo-water salinity, %; D is the freezing point temperature of the primary brine inclusions, with the unit of °C; in this embodiment, the paleo-water salinity of each rock layer within each parasequence in the target interval of the study area calculated is shown in Table 2;

[0035] (5) According to the physical relationship among the paleo-water salinity of each rock layer within each parasequence in the target interval of the study area, the mass of the salt rock within each parasequence, and the paleo-water volume within each parasequence, calculate the paleo-water volume during the deposition period of each rock layer within each parasequence. The calculation formula is as follows: V = M(1 - Wt) / (Wt×ρ 水 ), where V is the paleo-water volume during the deposition period of a certain rock layer within a certain parasequence, with the unit of m 3 ; M is the mass of the salt rock within a certain parasequence, with the unit of kg; Wt is the paleo-water salinity of a certain rock layer within a certain parasequence, %; ρ 水 is the paleo-water density. In this embodiment, the paleo-water density is taken as 1.0×10 3 kg / m 3 ; In this embodiment, the paleo-water volume during the deposition period of each rock layer within each parasequence calculated is shown in Table 2;

[0036] (6) Based on the distribution area and paleo - water volume of each rock layer within each parasequence in the target interval of the study area, the average paleo - water depth during the deposition period of each rock layer within each parasequence in the target interval of the study area is calculated. The calculation formula is as follows: H = V / S, where H is the average paleo - water depth during the deposition period of a certain rock layer within a certain parasequence in the target interval of the study area, with the unit of m; V is the paleo - water volume during the deposition period of a certain rock layer within a certain parasequence in the target interval of the study area, with the unit of m 3 ; S is the distribution area of a certain rock layer within a certain parasequence in the target interval of the study area (i.e., the lake - basin area during the deposition period), with the unit of m 2 ; In this embodiment, the average paleo - water depths during the deposition periods of each rock layer within each parasequence in the target interval of the study area are shown in Table 2.

[0037] Table 2 Paleo - water salinity, paleo - water volume and average paleo - water depth of each rock layer within each parasequence in the target interval of the study area

[0038]

[0039]

[0040] After calculating the average paleo - water depths during the deposition periods of each rock layer within each parasequence in the target interval of the study area, a quantitative change curve of the paleo - water depth during the deposition period of the target interval of the study area can be drawn, and the result is as Figure 3 shown; Based on the quantitative change curve of the paleo - water depth during the deposition period, it can provide a basis for the division of other sequences (similar sequences that cannot be quantitatively restored for paleo - water depth due to lack of coring), system tracts, sedimentary facies, and understanding of the paleo - environment. Finally, the natural gamma ray curve (GR curve), spontaneous potential curve (SP curve), acoustic travel - time log curve (AC curve), density log curve (DEN curve), lithology profile, sedimentary cycle division result, quantitative change curve of the paleo - water salinity during the deposition period, quantitative change curve of the paleo - water depth during the deposition period, and sedimentary facies division result of the target interval of the study area are plotted, and the result is as Figure 4 shown.

Claims

1. A method for quantitatively restoring the paleo water depth of a salinized lake basin, characterized in that, it includes the following steps: S1. Conduct parasequence division on the target interval in the study area to determine the distribution area of each rock layer within each parasequence in the target interval; S2. Determine the mass of the salt rock within each parasequence in the target interval; The mass of the salt rock within a certain parasequence is equal to the product of the average thickness of the salt rock within this parasequence, the distribution area of the salt rock within this parasequence, and the density of the salt rock within this parasequence; S3. Determine the paleo water salinity of each rock layer within each parasequence in the target interval of the study area; S4. Calculate the paleo-water body volume during the deposition period of each rock stratum within each parasequence. The calculation formula is as follows: V = M(1 - Wt) / (Wt × ρ 水 ), where V is the paleo-water body volume during the deposition period of a certain rock stratum within a certain parasequence, M is the mass of salt rock within a certain parasequence, Wt is the paleo-water body salinity of a certain rock stratum within a certain parasequence, and ρ 水 is the paleo-water body density; S5. Calculate the average paleo water depth during the deposition period of each rock layer within each parasequence in the target interval of the study area according to the distribution area and paleo water volume of each rock layer within each parasequence in the target interval of the study area.

2. The method for quantitatively restoring the paleo water depth of a salinized lake basin according to claim 1, characterized in that, The average thickness of the salt rock within a certain parasequence is equal to the average value of the thickness of the salt rock encountered in each drilled well in the study area within this parasequence.

3. The method for quantitatively restoring the paleo water depth of a salinized lake basin according to claim 1, characterized in that, The method for determining the paleo water salinity of each rock layer within each parasequence is as follows: Obtain the primary brine inclusions captured during the deposition period of each rock layer within different parasequences, and conduct test analysis on the primary brine inclusions to obtain the freezing point temperature of the primary brine inclusions, and then calculate the paleo water salinity of each rock layer within each parasequence in the target interval of the study area.

4. The method for quantitatively restoring the paleo water depth of a salinized lake basin according to claim 3, characterized in that, The calculation formula for the paleo-water body salinity of each rock layer within each parasequence is as follows: Wt = -1.76958×D - 0.042384×D 2 - 0.00052778×D 3 , where Wt is the paleo-water body salinity and D is the freezing point temperature of the primary brine inclusion, with the unit of °C.

5. The method for quantitatively restoring the paleo water depth of a salinized lake basin according to any one of claims 1 - 4, characterized in that, The method for conducting parasequence division on the target interval in the study area is as follows: Obtain the logging data and mud logging data of each drilled well in the study area, conduct fine stratigraphic correlation on each drilled well, and then conduct stratigraphic division on each drilled well in the study area; On the basis of the stratigraphic division of each drilled well in the study area, establish a cross - well stratigraphic correlation profile, determine the development characteristics of each rock layer during the deposition period of the target interval in the study area, and then conduct parasequence division on the target interval in the study area.

6. The method for quantitatively restoring the paleo water depth of a salinized lake basin according to any one of claims 1 - 4, characterized in that, The calculation formula for the average paleo water depth during the deposition period of each rock layer within each parasequence is as follows: H = V / S, where H is the average paleo water depth during the deposition period of a certain rock layer within a certain parasequence in the target interval of the study area, V is the paleo water volume during the deposition period of a certain rock layer within a certain parasequence in the target interval of the study area, and S is the distribution area of a certain rock layer within a certain parasequence in the target interval of the study area.

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