Method for improving organic parameters and recovering ocean ancient productivity

Abstract

The invention belongs to the technical field of ancient productivity recovery, and particularly relates to a method for improving organic parameters to recover marine ancient productivity. The method comprises the following steps: firstly, acquiring a rock sample, and measuring parameters such as total organic carbon content, sediment density, porosity, sterane, free hydrocarbon, pyrolytic hydrocarbon, hydrogen index, highest pyrolysis temperature and deposition rate; then calculating the residual degradation rate of the organic matter, determining the type of the organic matter through a graphical method, and determining the original degradation rate through a plummet diagram based on the residual degradation rate and the highest pyrolysis temperature; determining the original organic carbon content according to the total organic carbon content, the residual degradation rate and the original degradation rate; finally, the endogenous biological ratio is calculated based on the sterane, the paleo-productivity is calculated in combination with the original organic carbon content, according to the scheme, the sterane replaces n-alkanes to calculate the endogenous ratio, the original organic carbon content is combined to calculate the paleo-productivity, a more accurate calculation effect is achieved, and the method has important research significance on ocean understanding, oil-gas exploration and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of ancient productivity restoration, and in particular relates to a method for improving organic parameters to restore ocean ancient productivity. Background Art

[0002] Paleoproductivity refers to the amount of inorganic carbon converted into organic carbon by organisms through photosynthesis per unit time and per unit area during the geological history period. Currently, paleoproductivity can be restored using paleontological parameters (foraminifera, radiolarians, etc.), inorganic geochemical parameters (Ba, Fe, Cu, etc.) or organic geochemical parameters (TOC, biomarker compounds, etc.).

[0003] There are many implementation plans for restoring ancient productivity using organic parameters. For example, the ancient productivity calculation formula first proposed by Muller and Suess in 1979 is: R = C0 × ρs × (1-Φ) / (0.0030 × S 0.30 ), which is the most widely used method in various paleoproductivity studies around the world. Based on this method, considering that the organic carbon content in water bodies comes not only from endogenous organisms, but also from terrestrial organic matter (such as plant fragments transported to the ocean through rivers, atmosphere, etc.); Xu et al. proposed a calculation formula for paleoproductivity on this basis in 2024: R=C0 ×β×ρs ×(1-Φ) / (0.0030×S 0.30 ) ; β = (C 15 +C 17 +C 19 )(C 27 +C 29 +C 31 ) ; Where R is paleoproductivity; C0 is the total organic carbon content (TOC) in the sediment; ρs is the dry sediment density; Φ is the porosity; S is the sedimentation rate; β is the endogenous biomass ratio, which is determined by the n-alkane C 15 , C 17 , C 19 , C 27 , C 29 , C 31 Obtained by calculation.

[0004] However, the new calculation formula for paleoproductivity proposed by Xu et al. has problems of inapplicable and unstable parameters: (1) Parameter not applicable: The organic carbon content used is the existing total organic carbon content (TOC) in the sediment, which refers to the organic carbon generated by surface organisms (original total organic carbon content TOC ini) After settling and being preserved in sediments, it has undergone biodegradation, diagenesis, thermal maturation and other transformations, and the amount of organic carbon that remains in the rock. TOC ini During the sedimentation and burial process, it will be oxidized and decomposed; and for mature source rocks, organic matter has already generated and expelled hydrocarbons, and organic carbon will also be lost. Therefore, it is not appropriate to calculate paleoproductivity using TOC content; (2) Parameter instability: n-alkanes can reflect the source of organic matter and thus calculate the endogenous ratio, C 15 +C 17 +C 19 represents the contribution of phytoplankton (endogenous), C 27 +C 29 +C 31 Represents the contribution of terrestrial plants (terrestrial or allogeneic). (C 15 +C 17 +C 19 )(C 27 +C 29 +C 31 ) represents the endogenous ratio. However, considering that n-alkanes are unstable and easily affected by thermal maturation, redox conditions and other chemical reactions, using unstable parameters for calculation will reduce the accuracy of the results. Summary of the invention

[0005] In order to solve the existing problems of inapplicable parameters and unstable parameters in paleoproductivity calculation, which lead to low accuracy of paleoproductivity calculation, a method of improving organic parameters to restore paleoproductivity is proposed. ini The paleoproductivity calculation is combined with the endogenous biological ratio calculated based on steranes to achieve more accurate calculation results.

[0006] The present invention is implemented by adopting the following technical scheme: a method for improving organic parameters to restore marine ancient productivity, comprising the following steps: Step 1: Obtain rock samples and determine their paleoproductivity-related parameters; The paleoproductivity-related parameters include total organic carbon content TOC, sediment density ρs, porosity Φ, sterane, free hydrocarbon S1, pyrolysis hydrocarbon S2, hydrogen index HI, maximum pyrolysis temperature T max and the deposition rate S; Step 2: Determine the original organic carbon content TOC of the rock sample ini ; (1) Calculate the residual degradation rate D of organic matter rem and determine the type of organic matter by graphical method; (2) Based on the residual degradation rate D rem and the maximum pyrolysis temperature T max, the original degradation rate D0 is determined by plotting the points; According to the distribution of organic matter type data points, the residual degradation rate D of this specific organic matter type is determined. rem The upper limit of the distribution is the original degradation rate D0; (3) According to the total organic carbon content TOC and the residual degradation rate D rem The original organic carbon content TOC is determined by the original degradation rate D0 ini ; TOC ini = [TOC (1- D rem )] / (1- D0); Step 3, calculating the endogenous biological ratio β based on steranes; β = C 27 Steranes / (C 27 Steranes + C 28 Steranes + C 29 sterane); Step 4: Combine the original organic carbon content TOC ini and the endogenous biomass ratio β, determine the ancient productivity R: R=TOC ini ×β×ρs ×(1-Φ) / (0.0030×S 0.30 ).

[0007] Compared with the prior art, the advantages and positive effects of the present invention are: This scheme uses sterane to calculate the endogenous ratio and combines it with TOC ini By calculating paleoproductivity, researchers can more accurately assess the productivity of ancient lakes or ancient oceans, which is of great significance for reconstructing the marine environment, scientifically understanding the modern marine environment, and predicting future trends in marine environmental change. Moreover, the level of paleoproductivity directly affects the formation and distribution of source rocks, which are the basis for oil and gas generation. Accurately calculating paleoproductivity is of great significance for predicting the distribution of source rocks and determining favorable areas for oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A schematic diagram of a process for calculating paleoproductivity according to an embodiment of the present invention; Figure 2 To utilize HI and T max Identify the type of organic matter illustrated schematically; Figure 3 To utilize D rem and T max Determine D0 diagram schematic. DETAILED DESCRIPTION

[0009] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below: Embodiment, a method for improving organic parameters to restore marine paleoproductivity, such as Figure 1 As shown, the following steps are included: Step 1: Obtain rock samples and determine their paleoproductivity-related parameters; The paleoproductivity-related parameters include total organic carbon content (TOC), sediment density (ρs), porosity (Φ), steranes, free hydrocarbons (S1), pyrolysis hydrocarbons (S2), hydrogen index (HI), maximum pyrolysis temperature (T max ) and deposition rate (S); Step 2: Determine the original organic carbon content (TOC) of the rock sample ini ); (1) Calculate the residual degradation rate of organic matter (D rem ), and determine the type of organic matter through graphical method; among them, the residual degradation rate (D rem ) is calculated using the following formula: D rem =(S1 + S2) × 0.083 / TOC; (2) Based on D rem and T max , the original degradation rate (D0) was determined by plotting the points; According to the distribution of data points of each organic matter type, the upper limit of the data point distribution is drawn and extended to the Y axis. The intersection of the drawn curve and the Y axis is the original degradation rate D0 (approximately equal to the D rem the upper limit of the distribution);

[0010] (3) According to TOC, D rem and D0 to determine the original organic carbon content (TOC ini );TOC ini = [TOC (1- D rem )] / (1- D0), to provide parameters for subsequent paleoproductivity calculations.

[0011] Step 3, calculating the endogenous biomass ratio (β) based on steranes; β = C 27 Steranes / (C 27 Steranes + C 28 Steranes + C 29 sterane); It is usually considered that C 27Steranes come from phytoplankton (endogenous), C 28 Steranes come from chlorophyll-related organisms; C 29 Steranes are mainly derived from terrestrial plants (terrigenous or exogenous).

[0012] Step 4: Combine with TOC ini and β, calculate paleoproductivity (R): R=TOC ini ×β×ρs ×(1-Φ) / (0.0030×S 0.30 ).

[0013] In step 1, when determining the relevant parameters of various ancient productivity, relatively mature technical means can be used, such as using the combustion oxidation method to determine its total organic carbon content (TOC); obtaining sediment density (ρs) by weighing and volume measurement; measuring porosity (Φ) by mercury injection or nuclear magnetic resonance; measuring steranes by gas chromatography-mass spectrometry (GC-MS); obtaining free hydrocarbons (S1), pyrolysis hydrocarbons (S2), hydrogen index (HI), and maximum pyrolysis temperature (T max ); the sedimentation rate (S) is obtained according to the literature or calculation (stratum thickness / time), which will not be elaborated here.

[0014] In the field of petroleum geology, the use of HI and T max The graphical method for determining organic matter types is a widely recognized and used method. Figure 2 As shown, Figure 2 The organic matter types, curve shapes and boundaries in the above are widely used in the industry. max By projecting the data, the type of organic matter in the sample can be known. max =442℃, HI=725.24 mg / g TOC, according to Figure 2 It can be determined that the organic matter type of the sample is Type I. In addition, using D rem and T max Graphical determination of D0 is also a commonly used method in organic geochemistry and source rock evaluation. rem and T max For example, for samples with organic matter type Type I, draw a hand-drawn curve along the upper limit of the data point distribution and extend it to the Y-axis. The intersection with the Y-axis is 0.94, so the D0 value of Type I is uniformly 0.94.

[0015] In this example, to accurately calculate the ancient productivity, the original organic carbon content TOC ini, that is, the organic carbon content generated by surface organisms is more appropriate and accurate. Because it takes into account the possible oxidation and degradation of organic matter during burial, it can more accurately reflect the level of biological productivity at the time of deposition and calculate TOC ini There are many methods, and this embodiment adopts the following method: Assuming that the absolute content of inert carbon in organic matter remains unchanged, the left and right sides of formula (1) represent TOC ini and the content of inert carbon in the existing TOC. Formula (2) is a variation of formula (1). Combined with the empirical formula (3), TOC can be directly calculated. ini .

[0016] TOC ini (1- D0) = TOC (1- D rem ) (1) TOC ini = [TOC (1-D rem )] / (1- D0) (2) D rem = (S1 + S2) × 0.083 / TOC (3) Among them, S1 is the free hydrocarbon content, S2 is the pyrolysis hydrocarbon content, and D rem is the residual degradation rate of organic matter, and D0 is the original degradation rate of organic matter.

[0017] The order of biomarker compounds' ability to resist degradation is generally: n-alkanes < isoprenoids < steranes. Steranes have a much longer half-life in sediments than n-alkanes, and are thus more completely preserved in geological records; the cyclic structure and carbon-carbon bond stability of steranes make them relatively less susceptible to cracking during thermal maturation, and even under high ground temperatures and pressures, steranes can maintain their original structure; the molecular structure of steranes makes them highly resistant to redox conditions and other chemical reactions, and compared with n-alkanes, sterane compounds are more stable in sediments. The stability of steranes allows their original signals in sediments to be preserved, which helps reduce errors caused by organic matter degradation and thermal evolution, thereby improving the reliability of paleoproductivity assessments.

[0018] This embodiment creatively uses steranes instead of normal alkanes to calculate the endogenous ratio, and TOC ini Combined with paleoproductivity calculations, it is generally believed that C 27 Steranes come from phytoplankton (endogenous), C 28 Steranes come from chlorophyll-related organisms; C 29 Steranes are mainly derived from terrestrial plants (terrestrial or exogenous). Therefore, the present invention uses sterane data, i.e., C 27 Steranes / (C 27 Steranes + C28 Steranes + C 29 Steranes) replace normal alkanes (C 15 +C 17 +C 19 ) / (C 27 +C 29 +C 31 ) to calculate the endogenous ratio, which helps to improve the accuracy of paleoproductivity assessment. Researchers can more accurately assess the productivity of ancient lakes or ancient oceans, which is of great significance for reconstructing the marine environment, scientifically understanding the modern marine environment, predicting future marine environmental change trends, predicting the distribution of source rocks, and determining favorable areas for oil and gas exploration.

[0019] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for improving organic parameters to restore marine paleoproductivity, characterized in that: The following steps are involved: Step 1: Obtain rock samples and determine their paleoproductivity-related parameters; The paleoproductivity-related parameters include total organic carbon content TOC, sediment density ρs, porosity Φ, sterane, free hydrocarbon S1, pyrolysis hydrocarbon S2, hydrogen index HI, maximum pyrolysis temperature T max and the deposition rate S; Step 2: Determine the original organic carbon content TOC of the rock sample ini ; (1) Calculate the residual degradation rate D of organic matter rem and determine the type of organic matter by graphical method; (2) Based on the residual degradation rate D rem and the maximum pyrolysis temperature T max , the original degradation rate D0 is determined by plotting the points; (3) According to the total organic carbon content TOC and the residual degradation rate D rem The original organic carbon content TOC is determined by the original degradation rate D0 ini ; OCD ini = [TOC (1 - D rem )] / (1 - D0); Step 3, calculating the endogenous biological ratio β based on steranes; β = C 27 Steranes / (C 27 Steranes + C 28 Steranes + C 29 sterane); Step 4: Combine the original organic carbon content TOC ini and the endogenous biomass ratio β, determine the ancient productivity R: R=TOC ini ×β×ρs ×(1-Φ) / (0.0030×S 0.30 )。 2. The method for improving organic parameters and restoring marine paleoproductivity according to claim 1, characterized in that: In step 2, the remaining degradation rate D rem Use the following formula to calculate: D rem =(S1 + S2) × 0.083 / TOC.

3. The method for improving organic parameters and restoring marine paleoproductivity according to claim 1, characterized in that: In step 2, the hydrogen index HI and the maximum pyrolysis temperature T max The type of organic matter is determined by the graphical method. According to the distribution of data points of organic matter type, the residual degradation rate D of each organic matter type is calculated. rem and the maximum pyrolysis temperature T max Carry out the casting to determine the residual degradation rate D of this specific organic matter type rem The upper limit of the distribution is the original degradation rate D0.

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