Method for identifying shale paleoenvironment based on element geochemical analysis

Abstract

The invention belongs to the technical field of oil and gas development, and discloses a shale paleoenvironment identification method based on element geochemical analysis. The method comprises the following steps: preparing necessary element geochemical data, and completing required ratio and index calculation; based on element geochemical data, paleo-humidity and paleo-temperature recovery is carried out on a target interval; on the basis of single well paleo-humidity and paleo-temperature recovery, paleo-climate characteristics are recovered, and a paleo-climate vertical evolution characteristic graph is drawn; the change of the paleosalinity is analyzed by combining qualitative analysis and quantitative analysis of the paleosalinity; redox recovery is carried out from the two aspects of redox conditions and oxygen deficit-oxygen enrichment properties; and on the basis of single well paleo-salinity and redox recovery, drawing a paleo-water body environment vertical evolution characteristic graph. According to the method, the precision and accuracy of paleo-environment identification are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development, and in particular to a method for identifying shale paleoenvironment based on elemental geochemical analysis. Background Art

[0002] As the source rock of shale oil and gas with huge resource potential, the formation mechanism of organic-rich shale is a key scientific issue in shale oil and gas accumulation. The formation of organic-rich fine-grained sediments usually has abundant organic sources, good organic preservation conditions and later mineral preservation conditions. These conditions are the result of the combined effects of geological factors such as paleoclimate, paleostructure and paleo-sedimentary environment.

[0003] The distribution, allocation and migration of trace elements in strata are closely related to the formation environment of sedimentary rocks. Since the properties of some elements are stable and their occurrence state is less affected by subsequent diagenesis, it has been widely used to identify the paleoenvironment by using the contents of major and trace element components and the ratios of certain elements.

[0004] Commonly used methods for determining paleoclimate, such as the CIA index method and the Sr / Cu ratio, can effectively indicate cold and dry climates and hot and humid climates. Sr / Ba and other ratios are often used as the basis for determining paleo-salinity. V / (V+Ni) and other ratios are often used as important references for the redox properties of sedimentary environments.

[0005] However, the various element identification methods are relatively independent and have not been well combined to restore the ancient environment when shale was formed. Summary of the invention

[0006] In view of the current status of the ancient environment when shale was formed through elemental geochemical analysis, the present invention provides a method for identifying the ancient environment of shale based on elemental geochemical analysis. It can make comprehensive use of various element identification methods to identify the ancient environment of shale formation, and then more accurately restore the ancient environment of shale, effectively solving the problems existing in the background technology.

[0007] The present invention provides the following technical solution: a method for identifying shale deposition environment based on elemental geochemical analysis, comprising the following steps:

[0008] Step 1: Prepare the necessary elemental geochemical data and complete the required ratio and index calculations;

[0009] Step 2: Restore the paleohumidity and paleotemperature of the target layer based on element geochemical data;

[0010] Step 3: Based on the restoration of paleohumidity and paleotemperature of a single well, restore the paleoclimate characteristics and draw a paleoclimate vertical evolution characteristic map;

[0011] Step 4: Analyze the changes in paleo-salinity by combining qualitative and quantitative analysis of paleo-salinity;

[0012] Step 5: Redox recovery from two aspects: redox conditions and anoxic-oxygen-rich properties;

[0013] Step 6: Based on the restoration of the ancient salinity and redox properties of a single well, draw a vertical evolution characteristic map of the ancient water environment.

[0014] Furthermore, the paleohumidity change curve was estimated based on the Th / U, Sr / Cu, Fe / Mn, Al / Ti and CIA index change curves.

[0015] Furthermore, the paleotemperature change curve was estimated based on the Mg / Sr change curve.

[0016] Furthermore, by combining paleo-humidity and paleo-temperature, the paleoclimate characteristics of the target layer are inverted and a paleoclimate vertical evolution characteristic map is drawn.

[0017] Furthermore, the relative level of paleo-salinity was determined based on the Sr / Ba and Rb / Sr ratios, and the corresponding variation curve was established.

[0018] Furthermore, the paleo-salinity was quantitatively calculated based on the boron element method and verified with the variation curves of Sr / Ba and Rb / Sr.

[0019] Furthermore, based on the quantitative calculation results of paleo-salinity and referring to the modern lake salinity classification standards, paleo-salinity is classified into different levels.

[0020] Furthermore, the redox conditions of the deposition environment were determined based on V / (V+Ni) and Th / U, and the oxygen-deficient and oxygen-rich properties of the deposition environment were analyzed based on V / Cr.

[0021] Furthermore, the redox properties of the sedimentary environment are determined based on the redox conditions and the anoxic-oxic nature of the paleoenvironment.

[0022] Furthermore, based on the restoration of paleo-salinity and redox properties of individual wells, a vertical evolution characteristic map of the paleo-water environment was drawn.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This method of identifying shale paleoenvironment based on elemental geochemical analysis divides paleoenvironment identification into two major aspects: paleoclimate and paleowater environment, and four minor aspects: paleohumidity, paleotemperature, paleosalinity, and redox. Multiple identification methods are applied to each minor aspect to verify and constrain each other, thereby improving the precision and accuracy of paleoenvironment identification. By dividing paleoclimate into paleohumidity and paleotemperature and discussing them separately, identifying paleoclimate characteristics by combining paleohumidity and paleotemperature is more accurate than simply using ratios to discriminate paleoclimate. Warm and humid conditions and warm and semi-humid conditions can be subdivided on the basis of the original warm and humid conditions. In terms of paleosalinity, qualitative and quantitative analysis are combined to greatly improve the accuracy of the analysis. In terms of redox, the original reduction conditions can be subdivided into strong anoxic reduction and anoxic reduction by analyzing from the two aspects of redox conditions and anoxic-oxygen-rich properties, with higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attached Figure 1 It is the operation flow chart of the present invention;

[0026] Attached Figure 2 Vertical evolution characteristics of paleoclimate in a single well Figure 1 ;

[0027] Attached Figure 3 Vertical evolution characteristics of paleoclimate in a single well Figure 2 ;

[0028] Attached Figure 4 Vertical evolution characteristics of paleo-water environment in a single well Figure 1 ;

[0029] Attached Figure 5 Vertical evolution characteristics of paleo-water environment in a single well Figure 2 . DETAILED DESCRIPTION

[0030] The following will be combined with the appended Figure 1-5 , the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] A method for identifying shale paleoenvironment based on elemental geochemical analysis, including preparing necessary elemental geochemical data; calculating various parameters required for analysis based on corresponding elemental data; estimating paleohumidity change curves based on Th / U, Sr / Cu, Fe / Mn, Al / Ti and CIA index change curves; estimating paleotemperature change curves based on Mg / Sr change curves; analyzing paleoclimate change characteristics in combination with paleohumidity and paleotemperature change curves; qualitatively analyzing the relative high and low of paleosalinity based on Sr / Ba and Rb / Sr ratios, and establishing corresponding change curves; quantitatively calculating paleosalinity based on boron element method, verifying with the change curves of Sr / Ba and Rb / Sr, and determining the paleosalinity level of the target layer; determining the redox conditions of the paleoenvironment based on V / (V+Ni) and Th / U, and analyzing the anoxic and oxygen-rich properties of the paleoenvironment based on V / Cr; determining the redox properties of the paleoenvironment based on the determination of the redox conditions and anoxic-oxygen-rich properties of the paleoenvironment; and drawing a vertical evolution characteristic map of the paleowater environment based on the restoration of the paleosalinity and redox properties of a single well.

[0032] Among them, comprehensive consideration of multiple element ratio methods for paleohumidity restoration and estimation of the paleohumidity change curve greatly improved the reliability of paleohumidity analysis, which serves as an important basis for paleoclimate restoration.

[0033] Among them, the Mg / Sr change curve is used as the main basis for ancient temperature changes.

[0034] Among them, the paleoclimate is divided into two aspects: paleohumidity and paleotemperature, and the two aspects are analyzed separately. Finally, the paleoclimate characteristics are analyzed in combination with each other, which helps to improve the accuracy of paleoclimate restoration and can more intuitively see the changing trend of the paleoclimate.

[0035] Among them, the qualitative analysis of paleo-salinity changes was carried out based on Sr / Ba and Rb / Sr, and the quantitative analysis of paleo-salinity was carried out using the boron element method. By combining qualitative and quantitative analysis, the accuracy of paleo-salinity was improved.

[0036] Among them, the redox conditions of the paleoenvironment are determined according to V / (V+Ni) and Th / U, the anoxic and oxygen-rich properties of the paleoenvironment are analyzed based on V / Cr, and then the redox properties of the shale paleoenvironment are comprehensively considered. It can be subdivided on the basis of the original grade, which improves the accuracy of the redox analysis of the shale paleoenvironment.

[0037] Among them, combining the results of paleo-salinity and redox restoration to draw a vertical evolution diagram of paleo-water salinity helps to intuitively reflect the relationship between paleo-salinity and redox, and thus reflect the changing trend of the shale depositional environment.

[0038] Taking the first member of the Qingshankou Formation in the Changling Sag in the southern Songliao Basin as an example, the vertical evolution maps of the paleoclimate and the paleo-water sedimentary environment of two wells were established, reflecting the changing trends of the paleoclimate and paleo-water sedimentary environment of the first member of the Qingshankou Formation in the Changling Sag in the southern Songliao Basin.

Claims

1. A method for identifying shale depositional environment based on elemental geochemical analysis, characterized in that: The following steps are involved: Step 1: Prepare the necessary elemental geochemical data and complete the required ratio and index calculations; Step 2: Restore the paleohumidity and paleotemperature of the target layer based on element geochemical data; Step 3: Based on the restoration of paleohumidity and paleotemperature of a single well, restore the paleoclimate characteristics and draw a paleoclimate vertical evolution characteristic map; Step 4: Analyze the changes in paleo-salinity by combining qualitative and quantitative analysis of paleo-salinity; Step 5: Redox recovery from two aspects: redox conditions and anoxic-oxygen-rich properties; Step 6: Based on the restoration of the ancient salinity and redox properties of a single well, draw a vertical evolution characteristic map of the ancient water environment.

2. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The paleohumidity change curve described in step 2 is estimated based on the Th / U, Sr / Cu, Fe / Mn, Al / Ti and CIA index change curves.

3. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The ancient temperature change curve described in step 2 is estimated based on the Mg / Sr change curve.

4. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The paleohumidity, paleotemperature and paleosalinity described in step 3 are combined to invert the paleoclimate characteristics of the target layer and draw a paleoclimate vertical evolution characteristic map.

5. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: In step 4, the relative high and low of paleo-salinity are determined based on the ratios of Sr / Ba and Rb / Sr, and a corresponding variation curve is established.

6. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The paleo-salinity described in step 4 is quantitatively calculated using the boron element method and verified with the variation curves of Sr / Ba and Rb / Sr.

7. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The classification of paleo-salinity described in step 4 is based on the quantitative calculation results of paleo-salinity and refers to the modern lake salinity classification standards.

8. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: In step 5, the oxygen-deficient-oxygen-rich properties determine the redox conditions of the deposition environment based on V / (V+Ni) and Th / U, and the deposition environment is analyzed based on V / Cr.

9. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: Step 5: Determine the redox properties of the sedimentary environment based on the redox conditions and the anoxic-oxygen-rich properties of the paleoenvironment.

10. The method for identifying shale deposition environment based on elemental geochemical analysis according to claim 1, characterized in that: The vertical evolution characteristic map of the ancient water environment described in step 6 is drawn based on the restoration of the ancient salinity and redox properties of a single well.

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