Method and device for determining primary productivity of ancient lake

Abstract

The invention discloses a method and device for determining the primary productivity of an ancient lake, and the method comprises the steps: sampling a black shale section in a drilling core, and determining the total organic carbon content, the element lanthanum La abundance value and the element cobalt Co abundance value in a core sample; according to the element La abundance value and the element Co abundance value, calculating the water depth of the ancient lake and the time of organic matters in the shallow burying stage of the ancient lake bottom when the rock core sample is deposited; determining the organic carbon flux of the ancient lake bottom according to the determined time of the organic matters in the shallow burying stage of the ancient lake bottom and the density of the rock core sample; and determining the primary productivity of the ancient lake by using a primary productivity formula according to the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake.

Description

Technical Field

[0001] The present invention relates to the technical field of basic research on petroleum geology, and in particular to a method and device for determining the primary productivity of ancient lakes. Background Art

[0002] Since the Mesozoic and Cenozoic, lake facies strata have been generally developed in my country's major oil and gas-bearing basins, and organic-rich black shales are very developed, such as the 7th member of the Yanchang Formation of the Triassic in the Ordos Basin and the Qingshankou Formation of the Cretaceous in the Songliao Basin. These black shales are important source rocks for my country's conventional oil and gas resources and important exploration targets for unconventional oil and gas resources.

[0003] At present, the original hydrocarbon generation potential evaluation based on organic geochemical analysis in the study of black shales is far from meeting the needs of shale oil and gas exploration. Lake primary productivity refers to the total amount of organic matter produced by plant communities in lake ecosystems per unit time and per unit area. As an indicator that directly reflects the enrichment of organic matter in ancient lake environments and lake strata, it is of great significance to accurately evaluate the potential and exploration value of shale oil and gas resources. Summary of the invention

[0004] The present application provides a method and device for determining the primary productivity of ancient lakes. The method utilizes drilling coring data, fully considers the presence of exogenous organic matter input into the lake, and the varying degrees of loss of organic matter during sedimentation, shallow burial, and later thermal evolution stages. A quantitative recovery method for the primary productivity of ancient lakes is established, thereby improving the accuracy of the recovery of the primary productivity of ancient lakes.

[0005] In a first aspect, the present application provides a method for determining the primary productivity of an ancient lake, the method comprising:

[0006] Sampling the black shale section in the drill core and measuring the total organic carbon content (TOC) in the core sample 测 , the abundance value of lanthanum La and the abundance value of cobalt Co;

[0007] The water depth of the ancient lake when the core sample was deposited and the time that the organic matter spent in the shallow burial stage at the bottom of the ancient lake were calculated according to the abundance value of the element La and the abundance value of the element Co;

[0008] According to the time that the organic matter was buried in the shallow stage of the ancient lake bottom and the density of the core sample, the organic carbon flux of the ancient lake bottom was determined;

[0009] The primary productivity of the ancient lake is determined according to the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake using the primary productivity formula.

[0010] In a second aspect, an embodiment of the present invention further provides a device for determining the primary productivity of an ancient lake, the device comprising: a memory and a processor; the memory is used to store a program for determining the primary productivity of an ancient lake, and the processor is used to read and execute the program for determining the primary productivity of an ancient lake, and execute any one of the methods described in the above embodiments.

[0011] In a third aspect, an embodiment of the present invention further provides a computer-readable storage medium having a data processing program stored thereon, and the data processing program is executed by a processor to perform the method for determining the primary productivity of ancient lakes described in any one of the above embodiments.

[0012] Compared with the related art, the present application provides a method and device for determining the primary productivity of an ancient lake, the method comprising: sampling the black shale section in the drill core, and determining the total organic carbon content, the abundance value of the element lanthanum La and the abundance value of the element cobalt Co in the core sample; calculating the water depth of the ancient lake when the core sample was deposited and the time that the organic matter experienced in the shallow burial stage of the ancient lake bottom according to the abundance value of the element lanthanum La and the abundance value of the element cobalt Co; determining the organic carbon flux at the bottom of the ancient lake according to the determined time that the organic matter experienced in the shallow burial stage of the ancient lake bottom and the density of the core sample; determining the primary productivity of the ancient lake according to the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake using the primary productivity formula. The present application, based on the petrological and geochemical analysis of the drill core, removes the exogenous organic matter, and restores the loss of organic matter in the thermal evolution hydrocarbon generation stage, the shallow burial stage of the lake bottom, and the sinking stage to the lake bottom in steps, thereby realizing a more accurate method for determining the primary productivity of an ancient lake.

[0013] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by implementing the present application. Other advantages of the present application can be realized and obtained by the schemes described in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0015] Figure 1 A flow chart of a method for determining primary productivity of ancient lakes according to an embodiment of the present application;

[0016] Figure 2 A schematic diagram of a device for determining primary productivity of ancient lakes according to an embodiment of the present application;

[0017] Figure 3A graph showing the relationship between organic carbon recovery coefficient and maturity, hydrocarbon expulsion efficiency and organic matter type in some exemplary embodiments;

[0018] Figure 4 In some exemplary embodiments, k and t′ k Schematic diagram of the meaning of key parameters in the calculation formula;

[0019] Figure 5 A comprehensive histogram of the core of section 73 of the G135 well in the Ordos Basin in some exemplary embodiments;

[0020] Figure 6 A schematic diagram of shale lithology characteristics of the 73rd section of the G135 well in some exemplary embodiments;

[0021] Figure 7 TOC of the black shale section below the 73rd section of Well G135 in some exemplary embodiments 测 , La, Co content test results schematic diagram;

[0022] Figure 8 TOC of the black shale section below the 73rd section of Well G135 in some exemplary embodiments 内 and

[0023] TOC 埋 Schematic diagram of calculation results;

[0024] Fig. 9 Schematic diagram of calculation results of paleo-sedimentation rate V and paleo-water depth D of the black shale section below the 73rd section of the G135 well in some exemplary embodiments;

[0025] Fig.10 It is a schematic diagram of the calculation results of the time t and the organic matter settling time t0 experienced in the shallow burial stage of the black shale section under the 73rd section of the G135 well in some exemplary embodiments;

[0026] Fig.11 Schematic diagram of the calculation results of the paleo-lake bottom organic carbon flux CF and paleo-lake primary productivity PP in the black shale section below the Chang 73 section of the G135 well in some exemplary embodiments. DETAILED DESCRIPTION

[0027] The present application describes multiple embodiments, but the description is exemplary rather than restrictive, and it is obvious to those skilled in the art that there may be more embodiments and implementations within the scope of the embodiments described in the present application. Although many possible feature combinations are shown in the drawings and discussed in the specific embodiments, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with any other feature or element in any other embodiment, or may replace any other feature or element in any other embodiment.

[0028] The present application includes and contemplates combinations of features and elements known to those of ordinary skill in the art. The embodiments, features and elements disclosed in the present application may also be combined with any conventional features or elements to form a unique invention scheme defined by the claims. Any features or elements of any embodiment may also be combined with features or elements from other invention schemes to form another unique invention scheme defined by the claims. Therefore, it should be understood that any feature shown and / or discussed in the present application may be implemented individually or in any appropriate combination. Therefore, except for the limitations made according to the attached claims and their equivalents, the embodiments are not subject to other restrictions. In addition, various modifications and changes may be made within the scope of protection of the attached claims.

[0029] In addition, when describing representative embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, to the extent that the method or process does not rely on the specific order of the steps described herein, the method or process should not be limited to the steps of the specific order described. As will be understood by those of ordinary skill in the art, other sequences of steps are also possible. Therefore, the specific sequence of the steps set forth in the specification should not be interpreted as a limitation to the claims. In addition, the claims for the method and / or process should not be limited to the steps of performing them in the order written, and those skilled in the art can easily understand that these sequences can be changed and still remain within the spirit and scope of the embodiments of the present application.

[0030] The restoration of ancient primary productivity currently generally relies on empirical formulas constructed based on organic carbon abundance, stratum density, and ancient sedimentation rate, such as:

[0031]

[0032] Among them, PP is the primary productivity of the ancient lake, is the shale porosity, TOC is the organic carbon abundance, ρ is the formation density, and V is the paleo-sedimentation rate.

[0033] The inventors found that since the organic matter in the lake includes both endogenous organic matter and exogenous organic matter brought in by rivers, wind, volcanic eruptions, etc., these exogenous organic matter obviously cannot be used to calculate the paleoprimary productivity of the lake. In addition, as the endogenous organic matter in the lake sinks to the bottom of the lake, a large amount of organic matter is consumed by the metabolism of aquatic organisms and bacteria during the shallow burial stage at the bottom of the lake, resulting in the traditional paleoprimary productivity recovery method and recovery accuracy being unable to meet the current needs of shale research.

[0034] Therefore, the inventors provide a method for quantitatively restoring the primary productivity of ancient lakes. Based on the petrological and geochemical analysis of the drilling cores, after eliminating the exogenous organic matter, the inventors restore the loss of organic matter in the thermal evolution hydrocarbon generation stage, the shallow burial stage at the lake bottom, and the sinking stage to the lake bottom in steps, so as to achieve a more accurate determination of the primary productivity of the ancient lakes.

[0035] The embodiment of the present invention provides a method for determining the primary productivity of ancient lakes, such as Figure 1 As shown, the method includes steps S100-S130:

[0036] S100: Sampling the black shale section in the drill core and measuring the total organic carbon content (TOC) in the core sample 测 , element La abundance value and element Co abundance value;

[0037] S110: Calculating the water depth of the ancient lake when the core sample was deposited and the time that the organic matter spent in the shallow burial stage at the bottom of the ancient lake according to the abundance value of the element La and the abundance value of the element Co;

[0038] S120: Determine the organic carbon flux at the bottom of the ancient lake based on the time that the organic matter was buried at the shallow burial stage at the bottom of the ancient lake and the density of the core sample;

[0039] S130: Determine the primary productivity of the ancient lake using the primary productivity formula based on the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake

[0040] In this embodiment, the black shale section in the drilling core is sampled, wherein the black shale identification standard can be: the black shale is black to grayish black in appearance, a small amount of carbonized organic matter can be seen, and it can stain hands, the mineral components of the rock include clay minerals, quartz, feldspar, etc., with a small amount of carbonate rock components, and more than 50% of the particles have a diameter less than 0.0625 mm.

[0041] The standards and requirements for sampling the black shale section include: within a stratigraphic unit (such as a group, section, or subsection), the sampling interval for the black shale section should be less than 1 meter, and the recommended sampling interval is 0.1-0.3m. The number of sampling points for the black shale section should be greater than 10, and the sample collected at each sampling point should be in block shape, not contaminated by any organic matter, and the sample volume should be greater than 100g. The sample number increases from the bottom of the section to the top.

[0042] In an exemplary embodiment, after sampling the black shale section in the drill core, the method further includes:

[0043] Step 1, determining the endogenous organic carbon content of the ancient lake based on the content of sapropelite in the organic matter micro-components of the core sample;

[0044] In this step, the organic matter microscopic components of the core sample are identified and the total organic carbon content (TOC) of the core sample is determined. 测 {%), trace element La and Co abundance values ​​(10 -6 ), including: identification and statistics of sample organic matter microscopic components according to the method described in SY / T6414-2014; determination of the total organic carbon content of the sample according to the method described in SY / T5116-1997; determination of the trace element content of the sample according to the method described in GB / T14506.30-2010.

[0045] The organic matter microscopic components refer to organic components that can be identified under reflected light, transmitted light and fluorescence when the shale is ground into thin slices.

[0046] In this embodiment, the total organic carbon content is the total amount of organic matter in the rock expressed in terms of carbon content.

[0047] Step 2, determining the organic carbon recovery coefficient k according to the thermal maturity and hydrocarbon expulsion efficiency of the formation and the organic carbon recovery coefficient chart;

[0048] In this embodiment, the organic carbon recovery coefficient chart is a "type I kerogen recovery coefficient and organic matter maturity, hydrocarbon expulsion efficiency relationship chart" drawn based on a large amount of experimental data, such as Figure 2 As shown, the organic carbon recovery coefficient k can be determined based on the thermal maturity and hydrocarbon expulsion efficiency of the formation in combination with the organic carbon recovery coefficient chart.

[0049] The hydrocarbon expulsion efficiency refers to the mass percentage of hydrocarbons expelled from source rocks to the mass percentage of generated hydrocarbons.

[0050] The thermal maturity of the formation is represented by vitrinite reflectance, wherein the vitrinite reflectance is the percentage of the reflected light intensity of the vitrinite to the vertical incident light intensity.

[0051] Step 3, according to the organic carbon recovery coefficient and the endogenous organic carbon content of the ancient lake, using an organic carbon content calculation formula to determine the buried organic carbon content before the organic matter starts to generate hydrocarbons;

[0052] The organic carbon content calculation formula is:

[0053] TOC 埋 =TOC 内 ×k;

[0054] In the above formula, TOC 内 is the endogenous organic carbon content of the ancient lake, TOC 埋 is the buried organic carbon content before the organic matter starts to generate hydrocarbons, and k is the organic carbon recovery coefficient.

[0055] In an exemplary embodiment, the process of calculating the water depth of the ancient lake when the core sample was deposited according to the abundance value of the element La and the abundance value of the element Co is as follows:

[0056] Step 1, according to the abundance value of the element La and the abundance value of the element Co, using the sedimentation rate formula to calculate the ancient lake sedimentation rate when the core sample was deposited;

[0057] The deposition rate formula is:

[0058]

[0059] In the above formula, V is the sedimentation rate of the ancient lake, V0 is the standard sedimentation rate, N Co is the average content of Co in normal lake sediments, S co is the Co content in the sample, T Co is the average value of Co content in terrigenous clastic rocks, S La is the La content in the sample, T La It is the average value of La content in terrigenous clastic rocks.

[0060] The above parameters, V0 is the standard sedimentation rate of normal lacustrine black shale, which is 20cm / ka; N co is the average content of Co in normal lake sediments, which is generally taken as 20×10 -6 ; T Co is the average value of Co content in terrigenous clastic rocks, which is generally taken as 4.68×10 -6 ; T La is the average value of La content in terrigenous clastic rocks, which is generally taken as 38.99×10 -6 .

[0061] Step 2, calculating the ancient lake water depth when the core sample was deposited according to the ancient lake sedimentation rate and using the ancient lake water depth formula.

[0062] The formula for the water depth of the ancient lake is:

[0063]

[0064] In the above formula, D is the water depth of the ancient lake, in meters; V is the sedimentation rate of the ancient lake.

[0065] In an exemplary embodiment, the time t experienced by organic matter in the shallow burial stage at the bottom of the ancient lake is calculated based on the abundance value of the element La and the abundance value of the element Co, such as Figure 4 Shown are:

[0066] Step 1: According to the time-velocity relationship formula, the time t required to determine the stratum thickness between two adjacent samples No. k and No. k+1 is k In the above calculation, it is assumed that the stratum deposition rate between two adjacent samples is consistent with the deposition rate of the sample at the bottom of the stratum, and the time required for the deposition of the stratum thickness between two adjacent samples is calculated, that is:

[0067]

[0068] t k H is the time required to deposit the thickness of the stratum between two adjacent samples. k is the stratum thickness between two adjacent samples, No. k and No. k+1, V k is the ancient lake sedimentation rate when the kth sample was deposited, in cm / ka.

[0069] Step 2: According to the time-velocity relationship formula, determine the thickness of the stratum H′ deposited between the two samples No. k and No. k+1. k The time required t′ k ;

[0070]

[0071] t′ k H′ is the time required to deposit any layer thickness between two adjacent samples. k is any thickness of the stratum between the two samples No. k and No. k+1, V k is the ancient lake sedimentation rate when the kth sample was deposited, in cm / ka.

[0072] Step 3: According to the above relationship, determine the time t that the i-th sample has experienced in the shallow burial stage i ;

[0073]

[0074] Among them, the shallow burial stage refers to the period from when organic matter settled to when it was buried at the bottom of the lake, with a depth of 0.5 m (measured in core stratum thickness); V k is the ancient lake sedimentation rate when the kth sample was deposited, in cm / ka; t i is the time that the i-th sample spent in the shallow burial stage at the bottom of the ancient lake, t′ i+j+1 The burial depth of the i+j+1th sample reaches H′ i+j+1 The time required, t k is the thickness of the stratum between two adjacent samples, H k the time elapsed; H k is the stratum thickness between two adjacent samples, V k is the paleo-lake sedimentation rate when any sample was deposited, V i+j+1 is the ancient lake sedimentation rate when the i+j+1th sample was deposited.

[0075] Because the strata are deposited continuously and the samples are discretely sampled, in practical applications it is necessary to assume that the strata deposition rate between samples is the same. Here, it is assumed that the strata deposition rate between two adjacent samples is consistent with the deposition rate of the sample at the bottom of the stratum.

[0076] In an exemplary embodiment, determining the organic carbon flux at the bottom of the ancient lake according to the determined time that the organic matter experienced in the shallow burial stage at the bottom of the ancient lake and the density of the core sample includes:

[0077] Step 1, according to the sampling depth of the core sample, using the drilling density logging curve to determine the density value at the sampling depth;

[0078] In this step, if there is a drilling density logging curve and the logging curve is normal, the drilling density logging curve is used to determine the density value at the sampling depth;

[0079] If there is a drilling density logging curve, and the formation well diameter logging curve at the current sampling depth has a significant expansion, exceeding 50% of the drill bit diameter, and other logging curves have a sudden change in shape, then the density logging of this section is considered to be distorted, and the rock density value of the distorted section sample is taken as 2.4g / cm 3 .

[0080] If there is no drilling density logging curve, the rock density value is 2.4g / cm 3 .

[0081] Step 2: Using the Power organic matter degradation model, the time that organic matter experienced in the shallow burial stage of the ancient lake bottom, and the shale density, the flux formula is used to determine the organic carbon flux of the restored ancient lake bottom;

[0082] Among them, the Power organic matter degradation model is:

[0083]

[0084] According to the above Power organic matter degradation model and the relationship between organic carbon flux and lake bottom organic carbon content, the flux formula is determined:

[0085]

[0086] Among them, the relationship between organic carbon flux and lake bottom organic carbon content is:

[0087] TOC 底 =CF / (ρV);

[0088] CF is the organic carbon flux of the ancient lake bottom, TOC 埋 is the buried organic carbon content before the organic matter starts to generate hydrocarbons, ρ is the shale density, and V is the sedimentation rate of the ancient lake; D is the depth of the ancient lake, V 沉 is the average sedimentation rate of organic matter, which is a constant.

[0089] In an exemplary embodiment, the primary productivity of the ancient lake is determined using a primary productivity formula according to the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake;

[0090] The formula for primary productivity is:

[0091]

[0092] Among them, PP is the primary productivity of the ancient lake, the unit is gC / m 2 a; CF is the organic carbon flux of the restored ancient lake bottom, in gC / m 2 a; D is the depth of the ancient lake.

[0093] In this embodiment, when any calculated parameter is negative or significantly higher (or lower) than the adjacent sample point, the sample point is considered to be a noise point and is no longer used to calculate PP. When the number of noise points is less than 5% of the total number of samples, the paleoproductivity recovery result of the stratum is considered to be credible.

[0094] An embodiment of the present invention also provides a device for determining the primary productivity of an ancient lake, the device comprising: a memory 200 and a processor 210; the memory is used to store a program for determining the primary productivity of an ancient lake, and the processor is used to read and execute the program for determining the primary productivity of an ancient lake, and execute any one of the methods described in the above embodiments.

[0095] An embodiment of the present invention further provides a computer-readable storage medium, on which a data processing program is stored, and the data processing program is executed by a processor to perform the method for determining the primary productivity of ancient lakes described in any one of the above embodiments.

[0096] Example 1

[0097] According to the method of the present invention, the black shale section (1844.5m-1835.0m) below the core of the Chang 73 section of the Upper Triassic in Well G135 of the Ordos Basin was taken as the research object, and the realization process of the primary productivity of the ancient lake was determined as follows:

[0098] Step 1. Draw the core comprehensive logging histogram of the Chang 73 section of the Upper Triassic in Well G135 through core observation; Figure 5 As shown;

[0099] Step 2. Identify shale development sections through core observation

[0100] The shale development sections were identified, such as Figure 6 As shown in the figure, three shale development sections were identified. Among them, the lower black shale section (1844.5m-1835.0m) is mainly dark gray shale, with relatively stable GR curve characteristics and medium GR value (distribution range 142.3-239.3, average 168.3). According to the sampling standards and requirements, 38 pieces of the lower black shale section were sampled and numbered in sequence, with sampling intervals ranging from 0.2m to 0.65m.

[0101] Step 3. Test the core sample

[0102] Identify the microscopic components of organic matter in the collected samples and determine the total organic carbon content (TOC) of the core samples 测 (%), trace elements La and Co content (10 -6 The results are shown in Table 1. The composition characteristics of organic matter micro-components of black shale in the Chang 73 section of Well G135 in the Ordos Basin.

[0103] Table 1 Characteristics of organic matter microscopic components in the black shale of Chang 73 section in Well G135, Ordos Basin

[0104]

[0105] Step 4. Calculate the endogenous organic carbon content of the ancient lake based on the proportion of sapropelite in the sample microscopic components. 内 (%), the calculation results are shown in Table 2, Figure 7 .

[0106] Table 2 Key parameters and calculation results for restoration of primary productivity of ancient lakes in the 73rd section of Well G135 in the Ordos Basin

[0107]

[0108] Step 5. Determine the organic carbon recovery coefficient k based on the thermal maturity and hydrocarbon expulsion efficiency of the formation and the organic carbon recovery coefficient chart;

[0109] According to literature research, the thermal maturity of the shale formation under study is Ro = 0.9%, and the hydrocarbon expulsion efficiency of shale is about 50%. Figure 3 The “Relationship chart between organic carbon recovery coefficient and maturity, hydrocarbon expulsion efficiency and organic matter type” shows that the kerogen organic carbon recovery coefficient k is 1.17.

[0110] Step 6. According to the organic carbon recovery coefficient and the endogenous organic carbon content TOC of the ancient lake 内 , using the organic carbon content calculation formula to determine the buried organic carbon content TOC before the organic matter begins to generate hydrocarbons 埋 (%); In this step, TOC 埋 =TOC 内 ×k;

[0111] In the above formula, TOC 内 is the endogenous organic carbon content of the ancient lake, TOC 埋 is the buried organic carbon content before the organic matter starts to generate hydrocarbons, and k is the organic carbon recovery coefficient.

[0112] Step 7. Calculate the ancient lake sedimentation rate when the sample was deposited using the sedimentation rate formula according to the abundance value of the element La and the abundance value of the element Co;

[0113] The deposition rate formula is:

[0114]

[0115] In the above formula, V is the sedimentation rate of the ancient lake, V0 is the standard sedimentation rate, N Co is the average content of Co in normal lake sediments, S co is the Co content in the sample, T Co is the average value of Co content in terrigenous clastic rocks, S La is the La content in the sample, T LaIt is the average value of La content in terrigenous clastic rocks.

[0116] The average values ​​of Co and La contents in the provenance of the Chang 73 section of the Ordos Basin are: Co =4.68×10-6 and T La =38.99×10-6.

[0117] Step 8. Calculate the depth of the ancient lake:

[0118]

[0119] In the above formula, D is the water depth of the ancient lake (m), and V is the sedimentation rate of the ancient lake (cm / ka).

[0120] The calculation results of V and D are shown in Table 2 Key parameters and calculation results of primary productivity restoration of ancient lakes in the 73rd section of Well G135 in the Ordos Basin. Fig. 9 shown.

[0121] Step 9. Calculate the time t that the organic matter experienced in the shallow burial stage at the bottom of the ancient lake according to the abundance value of the element La and the abundance value of the element Co;

[0122] The shallow burial stage time limit t (the time it takes for the burial depth to reach 0.5 m) of each sample point is calculated, as follows: Fig.10 As shown, for the topmost sample No. 38, due to the insufficient number of control points for the deposition rate, it can be considered that the deposition rate of this sample remained constant during the shallow burial stage.

[0123] Based on the average sedimentation rate of suspended particulate organic matter in the lake (315 m / a) and the calculated ancient water depth, the time t0 (t0) it takes for organic matter to settle to the bottom of the lake after forming on the surface can be obtained. Fig.10 The calculation results are shown in Table 2. Key parameters and calculation results for restoration of primary productivity of ancient lakes in the 73rd section of Well G135 in the Ordos Basin.

[0124] Step 10. Substitute the sample density, sedimentation rate, shallow burial stage duration, organic matter settling time and other parameters into the organic carbon flux formula:

[0125]

[0126] The organic carbon flux CF at the bottom of the ancient lake was calculated. The calculation results are shown in Table 2 Key parameters and calculation results of primary productivity restoration of the ancient lake in the 73rd section of the G135 well in the Ordos Basin. Fig.11 shown.

[0127] According to the sampling depth of each sample, read the corresponding density value ρ (g / cm 3). When reading the density value, it is necessary to ensure that there is no significant expansion of the wellbore.

[0128] Step 11. Calculate the primary productivity of the ancient lake according to the primary productivity formula.

[0129] The formula for primary productivity is:

[0130]

[0131] The calculation results are shown in Table 2 Key parameters and calculation results of primary productivity restoration of ancient lakes in the 73rd section of Well G135 in the Ordos Basin, such as Fig.11 The changes in primary productivity of the ancient lake during the sedimentation process can be determined.

[0132] In this example, after eliminating exogenous organic matter based on petrological and geochemical analysis of the drilling cores, the loss of organic matter in the thermal evolution hydrocarbon generation stage, the shallow burial stage at the lake bottom, and the sinking stage to the lake bottom are restored in steps, achieving a high-precision restoration of ancient primary productivity and better serving oil and gas exploration and development work.

[0133] It will be appreciated by those skilled in the art that all or some of the steps, systems, and functional modules / units in the methods disclosed above may be implemented as software, firmware, hardware, and appropriate combinations thereof. In hardware implementations, the division between the functional modules / units mentioned in the above description does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed by several physical components in cooperation. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium (or non-transitory medium) and a communication medium (or temporary medium). As known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, it is well known to those of ordinary skill in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

Claims

1. A method for determining the primary productivity of ancient lakes, characterized in that: The method comprises: The black shale section in the drill core was sampled, and the total organic carbon content, the abundance of the element lanthanum La and the abundance of the element cobalt Co in the core samples were determined; The water depth of the ancient lake when the core sample was deposited and the time that the organic matter spent in the shallow burial stage at the bottom of the ancient lake were calculated according to the abundance value of the element La and the abundance value of the element Co; According to the time that the organic matter was buried in the shallow stage of the ancient lake bottom and the density of the core sample, the organic carbon flux of the ancient lake bottom was determined; The primary productivity of the ancient lake is determined according to the water depth of the ancient lake and the organic carbon flux at the bottom of the ancient lake using the primary productivity formula.

2. The method for determining the primary productivity of ancient lakes according to claim 1, characterized in that: After sampling the black shale section in the drill core, the method further comprises: The endogenous organic carbon content of the ancient lake was determined based on the content of sapropelite in the organic matter micro-components of the core samples; The organic carbon recovery coefficient is determined based on the thermal maturity and hydrocarbon expulsion efficiency of the formation and in combination with the organic carbon recovery coefficient chart; According to the endogenous organic carbon content of the ancient lake and the organic carbon recovery coefficient, the buried organic carbon content before the organic matter starts to generate hydrocarbons is determined using an organic carbon content calculation formula; The hydrocarbon expulsion efficiency refers to the mass percentage of hydrocarbons expelled from the source rock to the mass percentage of hydrocarbons generated.

3. The method for determining the primary productivity of ancient lakes according to claim 2, characterized in that: The thermal maturity of the formation is represented by vitrinite reflectance; The vitrinite reflectance is the percentage of the reflected light intensity of the vitrinite to the vertical incident light intensity.

4. The method for determining the primary productivity of ancient lakes according to claim 2, characterized in that: The organic carbon content calculation formula is: TOC 埋 =TOC 内 ×k: In the above formula, TOC 内 is the endogenous organic carbon content of the ancient lake, TOC 埋 is the buried organic carbon content before the organic matter starts to generate hydrocarbons, and k is the organic carbon recovery coefficient.

5. The method for determining the primary productivity of ancient lakes according to claim 1, characterized in that: The process of calculating the water depth of the ancient lake when the core sample was deposited according to the abundance value of the element La and the abundance value of the element Co is as follows: According to the abundance value of the element La and the abundance value of the element Co, the ancient lake sedimentation rate when the core sample was deposited is calculated using a sedimentation rate formula; The ancient lake water depth when the core sample was deposited was calculated based on the ancient lake sedimentation rate and the ancient lake water depth formula.

6. The method for determining the primary productivity of ancient lakes according to claim 5, characterized in that: The deposition rate formula is: In the above formula, V is the sedimentation rate of the ancient lake, V0 is the standard sedimentation rate, N Co C in normal lake sediments o The average content of S co is the Co element content in the core sample, T Co is the average value of Co content in terrigenous clastic rocks; S La is the La content in the core sample, T La It is the average value of La content in terrigenous clastic rocks.

7. The method for determining the primary productivity of ancient lakes according to claim 5, characterized in that: The formula for the water depth of the ancient lake is: In the above formula, D is the water depth of the ancient lake and V is the sedimentation rate of the ancient lake.

8. The method for determining the primary productivity of ancient lakes according to claim 1, characterized in that: The process of calculating the time that organic matter experienced in the shallow burial stage at the bottom of the ancient lake according to the abundance value of the element La and the abundance value of the element Co is: According to the time-velocity relationship formula, the stratum thickness H between two adjacent samples is determined. k Time required k ; According to the thickness H of the stratum between two adjacent samples k Time required k , determine the time t that the i-th sample experienced in the shallow burial stage at the ancient lake bottom i : The shallow burial stage refers to the stage that organic matter goes through from settling to the bottom of the lake to being buried at a depth of 0.5 m; i is the time that the i-th sample spent in the shallow burial stage at the bottom of the ancient lake, t′ i+j+1 The burial depth of the i+j+1th sample reaches H′ i+j+1 The time required, t k is the thickness of the stratum between two adjacent samples, H k the time elapsed; H k is the stratum thickness between two adjacent samples, V k is the paleo-lake sedimentation rate when any sample was deposited, V i+j+1 is the ancient lake sedimentation rate when the i+j+1th sample was deposited.

9. The method for determining the primary productivity of ancient lakes according to claim 2, characterized in that: Determining the organic carbon flux at the bottom of the ancient lake according to the determined time that the organic matter experienced in the shallow burial stage at the bottom of the ancient lake and the density of the core sample includes: According to the sampling depth of the core sample, the density value at the sampling depth is determined using the drilling density logging curve; The organic carbon flux at the bottom of the ancient lake was determined using the Power organic matter degradation model, the time that organic matter experienced during the shallow burial stage at the bottom of the ancient lake, and the shale density, using the organic carbon flux formula; Wherein, the organic carbon flux formula is: In the above formula, CF is the organic carbon flux at the bottom of the ancient lake, TOC 埋 is the buried organic carbon content before the organic matter starts to generate hydrocarbons, ρ is the shale density, and V is the sedimentation rate of the ancient lake; D is the depth of the ancient lake, V 沉 is the average sedimentation rate of organic matter in the lake, which is a constant.

10. The method for determining the primary productivity of ancient lakes according to claim 1, characterized in that: The primary productivity formula is: Among them, PP is the primary productivity of the ancient lake, CF is the organic carbon flux at the bottom of the ancient lake, and D is the water depth of the ancient lake.

11. A device for determining the primary productivity of ancient lakes, characterized in that: The device comprises: a memory and a processor; the memory is used to store a program for determining the primary productivity of ancient lakes, and the processor is used to read and execute the program for determining the primary productivity of ancient lakes, and execute the method described in any one of claims 1-10.

12. A computer-readable storage medium having a data processing program stored thereon, wherein the data processing program is executed by a processor to implement the method for determining the primary productivity of an ancient lake as described in any one of claims 1 to 10.

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