Paleosalinity recovery method based on improved Couch formula

Abstract

The invention discloses a paleo-salinity recovery method based on an improved Couch formula, and belongs to the technical field of paleo-salinity recovery method.The paleo-salinity recovery method comprises the following steps that multiple clay mineral combinations of a marine clay shale stratum in a research area are determined, and for the clay mineral combinations containing illite smectite mixed layers, equal-ratio calculation should be conducted according to the interlayer ratio, and the content of the clay mineral combinations is calculated according to the interlayer ratio; according to the method, the boron content in illite and montmorillonite is corrected, the quantitative relation between the boron element and the clay mineral content is established according to the absorption strength of each clay mineral to boron in a research area, correction is performed on the basis of a Couch formula B * = B sample / (4Xi + 2Xm + Xk), and a new formula model is established.

Description

Technical Field

[0001] The present invention relates to a method for restoring paleosalinity, in particular to a method for restoring paleosalinity based on an improved Couch formula, belonging to the technical field of methods for restoring paleosalinity. Background Art

[0002] Boron is sensitive to salinity and relatively easy to determine, so boron is often used as an effective indicator to reflect paleosalinity.

[0003] Clay minerals can quickly fix a considerable amount of boron and do not desorb due to the decrease in boron concentration in the solution. Since the boron concentration in natural water bodies is a linear function of salinity, the boron content absorbed by clay minerals from water bodies has a double logarithmic relationship with the salinity of the water body, that is, there is the Freundlich absorption equation lgB = C1lgS + C2. Later, Couch considered that different clay minerals and their contents have different absorption intensities for boron. Among them, the boron absorption capacity of illite is 2 times that of montmorillonite and chlorite, and 4 times that of kaolinite. Therefore, Couch corrected the boron content of the sample and proposed the Couch correction formula B * = B 样品 / (4Xi + 2Xm + Xk). Because of its characteristics suitable for mudstones with complex clay mineral compositions, it is usually used for quantitative calculation of paleosalinity.

[0004] However, in many marine ancient mudshales in China, the clay mineral assemblages are complex. For example, in the Wufeng-Longmaxi Formation in the southeastern part of Chongqing, China, the clay mineral composition is mainly illite, illite-smectite mixed layer and chlorite;

[0005] The clay mineral assemblage in the Datangpo Formation in Songtao area is illite, kaolinite and chlorite;

[0006] The clay mineral assemblage in the Chentangwu Formation in Zhejiang is illite, montmorillonite, kaolinite and chlorite, and the clay mineral assemblage in the Dazi section in the Changdu area is illite, illite-smectite mixed layer, kaolinite, chlorite and chlorite-smectite mixed layer. At this time, the Couch formula has certain limitations and cannot meet the quantitative calculation of paleosalinity under the corresponding clay mineral assemblages. Therefore, a method for restoring paleosalinity based on an improved Couch formula is designed to solve the above problems. Summary of the Invention

[0007] The main purpose of the present invention is to provide a method for restoring paleosalinity based on an improved Couch formula.

[0008] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0009] A method for restoring paleosalinity based on an improved Couch formula includes the following steps:

[0010] Step 1: Calculate according to the percentage content of montmorillonite in illite-smectite mixed layer to obtain the boron contents in corrected illite and montmorillonite.

[0011] Step 2: Establish a quantitative relationship between boron element and clay mineral content according to the absorption intensity of clay minerals for boron.

[0012] Step 3: Modify on the basis of Couch formula to establish a new formula model and calculate the corrected boron element content.

[0013] Step 4: Calculate the paleosalinity through the corrected boron content and the paleosalinity calculation formula of polymineral mudstone.

[0014] Preferably, before Step 1, it also includes determining various clay mineral combinations in the marine shale formation in the study area and performing equi-ratio calculation according to the interlayer ratio.

[0015] The clay mineral combination is composed of illite, montmorillonite, illite-smectite mixed layer, kaolinite and chlorite clay minerals.

[0016] Preferably, in Step 2, the Couch formula is Couch formula B * = B 样品 / (4Xi + 2Xm + Xk);

[0017] In the formula:

[0018] B * is the corrected boron content with the unit of 10 -6 B 样品 is the measured boron content in the sample with the unit of 10 -6 ;

[0019] Xi, Xm, and Xk respectively represent the boron contents of measured illite, montmorillonite and kaolinite in the sample, and the coefficients represent the absorption intensities of various clay minerals for boron.

[0020] Preferably, the new formula model established under the clay mineral combination of illite, montmorillonite, illite-smectite mixed layer and chlorite is:

[0021] B i = B0 / (4I + 2M + 2Ch);

[0022] In the formula:

[0023] B i is the corrected boron content with the unit of 10 -6 B0 is the measured boron content in the sample with the unit of 10 -6 ;

[0024] I, M, and Ch represent the corrected illite, montmorillonite, and chlorite contents respectively, and the coefficients represent the boron absorption intensities of various clay minerals.

[0025] Preferably, the new formula model established under the clay mineral combination of illite-smectite mixed layer, kaolinite + chlorite is:

[0026] B i = B0 / (4I + 2M + K + 2Ch);

[0027] In the formula:

[0028] B i is the corrected boron content in units of 10 -6 , B0 is the measured boron content in the sample in units of 10 -6 , I, M, K, and Ch represent the corrected illite, montmorillonite, kaolinite, and chlorite contents respectively, and the coefficients represent the boron absorption intensities of various clay minerals.

[0029] Preferably, the new formula model established under the clay mineral combination of illite-smectite mixed layer, illite, and montmorillonite is:

[0030] B i = B0 / (4I + 2M);

[0031] In the formula:

[0032] B i is the corrected boron content in units of 10 -6 , B0 is the measured boron content in the sample in units of 10 -6 , I and M represent the contents of corrected illite and montmorillonite respectively, and the coefficients represent the boron absorption intensities of various clay minerals.

[0033] Preferably, in step three, the formula for calculating the paleosalinity of polymineral mudstone is lgB i = 1.28lgSp + 0.11;

[0034] In the formula:

[0035] Sp is the paleosalinity, in units of ‰.

[0036] The beneficial technical effects of the present invention:

[0037] The present invention provides a method for restoring paleosalinity based on an improved Couch formula. The idea of establishing a new formula model under different clay mineral combinations makes it applicable to many marine ancient mud shale formations, increasing the reliability of paleoenvironment restoration and laying an important foundation for further analyzing the distribution laws of source rocks and reservoirs.

[0038] In the analysis process, for clay mineral assemblages containing illite-smectite mixed layers, correction is carried out according to the interlayer ratio to obtain the contents of illite and montmorillonite after correction, further improving the accuracy and reliability of the analysis results. At the same time, the quantitative calculation results of paleosalinity completed by applying this method can provide strong guidance for the prediction of various types of high-quality marine reservoirs, and also have certain reference significance for the restoration of paleosalinity of other types of sediments. The process of the present invention is simple, the calculation is convenient, and the scheme has strong universality, and it is suitable for application in marine shale formations with various clay mineral assemblages. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG. is a flowchart of a preferred embodiment of a method for restoring paleosalinity based on an improved Couch formula according to the present invention;

[0040] Figure 2 FIG. is a longitudinal variation diagram of paleosalinity in the study area of a preferred embodiment of a method for restoring paleosalinity based on an improved Couch formula according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] To make the technical solutions of the present invention clearer and more definite to those skilled in the art, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0042] As Figure 1 - Figure 2 shown, a method for restoring paleosalinity based on an improved Couch formula provided in this embodiment mainly includes determining the clay mineral assemblage of the marine shale formation in the study area, establishing a quantitative relationship between boron element and clay mineral content, establishing a new formula model under various clay mineral assemblages, calculating the corrected boron element content, and quantitatively calculating the paleosalinity using the paleosalinity calculation formula of multi-mineral mudstone, as Figure 1 shown.

[0043] First, determine various clay mineral assemblages in the marine shale formation in the study area. For clay mineral assemblages containing illite-smectite mixed layers, perform an equal ratio calculation according to the interlayer ratio, that is, calculate according to the percentage content of montmorillonite in the illite-smectite mixed layer to obtain the boron contents in the corrected illite and montmorillonite;

[0044] According to the absorption intensity of clay minerals for boron, establish a quantitative relationship between boron element and clay mineral content, and correct and establish a new formula model on the basis of the Couch formula to calculate the corrected boron element content;

[0045] Calculate the paleosalinity through the finally corrected boron content and the paleosalinity calculation formula of multi-mineral mudstone;

[0046] Next, the calculation results of the present invention will be elaborated with five regions in the study area.

[0047] In this case, the boron element content was calculated using the modified Couch formula for five areas of the Wufeng-Longmaxi Formation in the southeastern Chongqing region, and then the paleosalinity was quantitatively calculated. The test results and calculation results are shown in the following table.

[0048] Table 1 Boron element content and paleosalinity of the Shiqiao shale in the Wufeng-Longmaxi Formation in the southeastern Chongqing region

[0049]

[0050]

[0051] Table 2 Boron element content and paleosalinity of the Lujiao shale in the Wufeng-Longmaxi Formation in the southeastern Chongqing region

[0052]

[0053]

[0054] Table 3 Boron element content and paleosalinity of the Zhonghe shale in the Wufeng-Longmaxi Formation in the southeastern Chongqing region

[0055] Sample Number Depth I I / M M / ％ Corrected I Corrected M C <![CDATA[B0 / 10 -4 > <![CDATA[B i / 10 -5 > Sp / ‰ ZH - 1 11.41 42 45 10 82.5 4.5 13 137 3.75 13.93 ZH - 2 19.91 47 38 10 81.2 3.8 15 80 2.21 9.20 ZH - 3 20.91 50 35 10 81.5 3.5 15 123 3.39 12.86 ZH - 4 22.01 49 34 10 79.6 3.4 17 114 3.17 12.22 ZH - 5 23.64 48 43 10 86.7 4.3 9 123 3.29 12.58 ZH - 6 25.84 48 42 10 85.8 4.2 10 102 2.74 10.91 ZH - 7 28.04 48 38 10 82.2 3.8 14 106 2.91 11.42 ZH - 8 29.24 45 40 10 81 4 15 116 3.20 12.31 ZH - 9 32.84 48 37 10 81.3 3.7 15 68 1.88 8.10 ZH - 10 41.46 48 51 10 93.9 5.1 1 92 2.37 9.74 ZH - 11 46.46 57 38 10 91.2 3.8 5 66 1.73 7.59 ZH - 12 53.24 50 42 10 87.8 4.2 8 56 1.49 6.77 ZH - 13 59.93 54 36 10 86.4 3.6 10 67 1.80 7.84 ZH - 14 61.43 56 35 10 87.5 3.5 9 64 1.71 7.53 ZH - 15 62.53 57 36 10 89.4 3.6 7 47 1.24 5.87 ZH - 16 62.93 52 47 10 94.3 4.7 1 58 1.49 6.78 ZH - 17 71.2 64 35 10 95.5 3.5 1 27 0.69 3.71 ZH - 18 73.3 81 13 10 92.7 1.3 6 29 0.75 3.97 ZH - 19 76.3 44 46 10 85.4 4.6 10 35 0.94 4.74

[0056] Table 4 Boron element content and paleosalinity of the Daxi shale in the Wufeng-Longmaxi Formation in the southeastern Chongqing region

[0057]

[0058]

[0059] Table 5 Boron element content and paleosalinity of the Hongyanxi shale in the Wufeng-Longmaxi Formation in the southeastern Chongqing region

[0060] Sample Number Depth I I / M M / ％ Corrected I Corrected M C <![CDATA[B0 / 10 -4 > <![CDATA[B i / 10 -5 > Sp / ‰ HYX - 1 4.01 57 38 10 91.2 3.8 5 125 3.27 12.51 HYX - 2 10.6 54 37 10 87.3 3.7 9 120 3.20 12.31 HYX - 3 24.8 54 19 10 71.1 1.9 27 127 3.71 13.81 HYX - 4 28.1 47 21 10 65.9 2.1 32 106 3.19 12.29 HYX - 5 30.8 46 25 5 69.75 1.25 29 93 2.74 10.89 HYX - 6 34.8 48 27 10 72.3 2.7 25 131 3.80 14.07 HYX - 7 45.1 49 25 10 71.5 2.5 26 112 3.27 12.50 HYX - 8 61.6 52 23 10 72.7 2.3 25 135 3.91 14.38 HYX - 9 65.6 54 20 10 72 2 26 114 3.31 12.64 HYX - 10 76.1 61 30 10 88 3 9 72 1.91 8.24 HYX - 11 80.95 51 36 10 83.4 3.6 13 77 2.10 8.85

[0061] The calculation results show that the paleosalinity concentration range in the study area is between 1.73 - 16.12‰, with an average value of 9.69‰. The overall state shows medium salinity water. Among them, the paleosalinity range of the Wufeng Formation is between 1.73 - 14.20‰, with an average value of 7.71‰, and the paleosalinity range of the Longmaxi Formation is between 4.52 - 16.12‰, with an average value of 10.06‰. Vertically, except for the Daxi section showing a relatively stable high paleosalinity value from bottom to top, the Shiqiao, Lujiao, Zhonghe, and Hongyanxi sections all show the change characteristics that the paleosalinity first increases rapidly from the Wufeng Formation to the Longmaxi Formation and then remains relatively stable at a high value; horizontally, from west to east, the overall trend of the paleosalinity from the Shiqiao section to the Hongyanxi section shows a change characteristic of first decreasing and then increasing, and the average paleosalinity concentration distribution is 10.01‰, 8.69‰, 8.84‰, 10.63‰, and 12.04‰( Figure 2 ).

[0062] The design of the present invention is reasonable and rigorous, and the prediction results have strong reference value. In the analysis stage, there is a large amount of typical data as support, making an important technical contribution to accurate calculation. It should be said that the present invention has well broadened the existing methods for calculating paleosalinity, keeping up with the trend of scientific and technological development, and well meeting the research needs for restoring the paleosalinity of sedimentary water bodies at the current stage.

[0063] The above are only further embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention, making equivalent substitutions or changes according to the technical solution and concept of the present invention, shall fall within the protection scope of the present invention.

Claims

1. A paleosalinity restoration method based on an improved Couch formula, characterized in that: The steps include: Step 1: Calculate the percentage of montmorillonite in the illite-montmorillonite mixed layer to obtain the corrected boron content in illite and montmorillonite; Step 2: Establish a quantitative relationship between boron and clay mineral content based on the absorption intensity of clay minerals to boron; Step 3: Based on the Couch formula, a new formula model is established to calculate the corrected boron content; Step 4: Calculate the paleo-salinity using the corrected boron content and the paleo-salinity calculation formula for multi-mineral mudstone.

2. The method for paleosalinity restoration based on the improved Couch formula according to claim 1, characterized in that: Before step 1, it also includes determining the combination of various clay minerals in the marine shale formation in the study area and calculating the equal ratio according to the interlayer ratio; The clay mineral combination is composed of illite, montmorillonite, illite-montmorillonite mixed layer, kaolinite and chlorite clay minerals.

3. A paleosalinity restoration method based on the improved Couch formula according to claim 2, characterized in that: In step 2, the Couch formula is Couch formula B * =B 样品 / (4Xi+2Xm+Xk); Where: B * To calibrate the boron content, the unit is 10 -6 , B 样品 The unit of boron content in the sample is 10 -6 ; Xi, Xm, and Xk represent the measured boron contents of illite, montmorillonite, and kaolinite in the samples, respectively, and the coefficient represents the absorption intensity of various clay minerals to boron.

4. The method for paleosalinity restoration based on the improved Couch formula according to claim 2, characterized in that: The new formula model established under the clay mineral combination of illite, montmorillonite, illite-montmorillonite mixed layer and chlorite is: Bi=B0 / (4I+2M+2Ch); Where: B i To calibrate the boron content, the unit is 10 -6 , B0 is the boron content in the sample, unit is 10 -6 ; I, M, and Ch represent the corrected contents of illite, montmorillonite, and chlorite, respectively, and the coefficient represents the absorption intensity of various clay minerals to boron.

5. The method for paleosalinity restoration based on the improved Couch formula according to claim 2, characterized in that: The new formula model established under the clay mineral combination of illite-montmorillonite mixed layer, kaolinite + chlorite is: B i =B0 / (4I+2M+K+2Ch); Where: B i To calibrate the boron content, the unit is 10 -6 , B0 is the boron content in the sample, unit is 10 -6 , I, M, K, and Ch represent the corrected contents of illite, montmorillonite, kaolinite, and chlorite, respectively, and the coefficient represents the absorption intensity of various clay minerals to boron.

6. A paleosalinity restoration method based on the improved Couch formula according to claim 2, characterized in that: The new formula model established under the clay mineral combination of illite and montmorillonite is: <h2 style=";text-align:left;direction:ltr">B<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> (B0 / (4I+2M)) Where: B i To calibrate the boron content, the unit is 10 -6 , B0 is the boron content in the sample, unit is 10 -6 , I and M represent the corrected contents of illite and montmorillonite, respectively, and the coefficient represents the absorption intensity of various clay minerals to boron.

7. A paleosalinity restoration method based on the improved Couch formula according to claim 6, characterized in that: The paleosalinity calculation formula of the multi-mineral mudstone in step 3 is lgBi=1.28lgSp+0.11; Where: Sp is the paleo-salinity, in ‰.

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