Quantitative evaluation method and system for ancient productivity of well-free and few-well depression hydrocarbon source rock

Abstract

The invention belongs to the technical field of quantitative data processing of ancient productivity, and discloses a quantitative evaluation method and system for ancient productivity of well-free and few-well depression hydrocarbon source rocks. The method comprises the following steps: testing the organic carbon content of a well-drilling rich depression actual hydrocarbon source rock sample, quantitatively calculating the ancient productivity based on the organic carbon content, and establishing a function relationship between the actual well-drilling ancient productivity and three geological elements, namely the activity rate, the settlement rate coefficient and the sand-to-land ratio, of the depression-control fault through experience statistics; obtaining three geological elements of the depression control fault activity rate, the settlement rate coefficient and the sand-to-land ratio of the series of virtual wells by means of three-dimensional seismic data of well-free and few-well depression, and substituting the three geological elements into the function relation formula to obtain the ancient productivity of the virtual wells; and finally, a well-free-less-well depression ancient productivity plane distribution diagram is compiled based on the sedimentary facies, and well-free-less-well depression ancient productivity quantitative evaluation is completed. The method effectively solves the problems of few actual samples and high difficulty in quantitative development of ancient productivity evaluation of well-free and few-well depression.

Description

Technical Field

[0001] The present invention belongs to the technical field of paleoproductivity quantitative data processing, and particularly relates to a method and system for quantitatively evaluating the paleoproductivity of source rocks in a fault depression with few or no wells. Background Art

[0002] At present, the quantitative evaluation of paleoproductivity mainly adopts indirect methods for estimation. Previous studies have shown that TOC and nutrient elements such as P and Ba can be used for the quantitative evaluation of paleoproductivity.

[0003] In the prior art, regarding the quantitative calculation method based on organic carbon content, Muller and Suess (1979) earliest restored the paleoproductivity conditions based on the organic carbon content of surface sediments in the sea, and proposed a paleoproductivity calculation formula with phytoplankton as the main productivity. Li Shoujun et al. (2002) proposed a paleoproductivity calculation formula for lake basins based on modern continental fault depression lake basin sediment samples, and it has been widely used (Ye Jiaren et al., 2020; Chen Guo, 2019). The calculation formula is as follows:

[0004] R = C × ρ × (1 - Φ) / (0.00421 × S^0.0826)

[0005] In the formula: R is the paleoproductivity, with the unit of gC·m -2 ·a -1 ; C means the organic carbon content, with the unit of %; ρ means the sediment density, with the unit of g·cm -3 ; Φ is the porosity, with the unit of %; S is the sedimentation rate, with the unit of cm·10 -3 ·a -1 .

[0006] In the prior art, regarding the quantitative calculation method based on major and trace elements, generally, the contents of P and Ba have a good positive correlation with paleoproductivity. This is because P is one of the constituent elements of organisms, and at the same time, organisms have an adsorption effect on Ba. High paleoproductivity (i.e., rich organisms) will directly lead to the enrichment of P and Ba. However, under reducing conditions, BaSO4 will start to dissolve, resulting in deviation in estimating paleoproductivity with Ba; similarly, the reducing environment will cause a large amount of P to be released into the water body, thereby affecting the accuracy of estimating paleoproductivity with P.

[0007] Schoepfer et al. (2015) proposed a quantitative calculation method based on major and trace elements, such as P, Ba, etc., based on 94 modern marine sediment samples globally. The calculation formula is as follows:

[0008] For phosphorus element: PORD prim =(10 3.46 *PAR) 1.14 , PAR = P org*ρ* LSR

[0009] Barium element: PORD prim =(10 1.63 *BaAR) 1.98 , PAR = Ba bio *ρ* LSR

[0010] Where: PORDprim: Ocean primary productivity, mgC / cm 2 · kyr; PAR / BaAR: Phosphorus / barium element accumulation rate, mg / cm 2 · kyr; Porg / Babio: Organic phosphorus / bio-barium; ρ: Sediment density, g / cm 3 ; LSR: Linear sedimentation rate, cm / kyr.

[0011] Through the above analysis, the problems and defects of the prior art are as follows: The defects and deficiencies of the existing quantitative evaluation methods for paleoproductivity mainly lie in the inability to carry out quantitative evaluation work for well-less or few-well depressions.

[0012] The key of the prior art lies in the test analysis of actual drilling samples. The quantitative calculation method based on the organic carbon content (TOC) requires testing the organic carbon content of actual source rock samples and then substituting into an empirical formula to obtain the paleoproductivity value of the samples; while the quantitative calculation method based on major and trace elements requires testing the major and trace element compositions of actual source rock samples and then substituting into an empirical formula to obtain the paleoproductivity value of the samples.

[0013] It can be seen that for well-less or few-well depressions, due to limited or no drilling, the number of source rock samples is limited or there are no source rock samples, so it is impossible to carry out tests on the organic carbon content and major and trace element compositions of large-scale source rock samples, and thus it is impossible to carry out quantitative evaluation of paleoproductivity. Summary of the Invention

[0014] To overcome the problems existing in the related art, the disclosed embodiments of the present invention provide a method and system for quantitatively evaluating the paleoproductivity of source rocks in well-less or few-well depressions, specifically relating to a method and system for quantitatively evaluating the paleoproductivity of source rocks in well-less or few-well depressions based on geological elements.

[0015] The technical solution is as follows: A method for quantitatively evaluating the paleoproductivity of source rocks in well-less or few-well depressions includes the following steps:

[0016] S1. In different structural parts of the deep depression zone and slope zone of the rich sag drilled in the same basin, select n≥10 representative wells that drill through the source rock interval. Based on the analysis of the organic carbon content of the source rock samples from the actual drilled wells and the geological elements of a single well, use the least squares method to fit and establish the empirical function relationship between the paleoproductivity of the source rock and the geological elements. The geological elements include: the activity rate of the depression-controlling fault, the subsidence rate coefficient, and the sand-to-shale ratio. Among them, the sand-to-shale ratio is the ratio of the thickness of the sandstone formation to the total thickness in the interval where the source rock develops.

[0017] S2. Based on the planar distribution of sedimentary facies during the development period of the source rock in the wellless - less well sag, evenly select n≥10 virtual wells along the seismic profile within the planar range of the source rock development facies belt. Based on the 3D seismic data of the wellless - less well sag, use the means of post-stack constrained sparse pulse wave impedance inversion, root mean square amplitude attribute, and basin simulation to obtain the data of the three geological elements, namely the activity rate of the depression-controlling fault, the subsidence rate coefficient, and the sand-to-shale ratio, of a series of virtual wells.

[0018] S3. Apply the empirical function relationship formula to calculate the paleoproductivity of the source rock of the virtual wells. Based on the paleoproductivity of the source rock of the virtual wells, with the boundary of the shallow lake facies sedimentary facies as the constraint, use the interpolation method to compile the isopach map of the paleoproductivity of the source rock in the wellless - less well sag, and complete the quantitative evaluation of the paleoproductivity of the source rock in the wellless - less well sag based on the geological elements in steps S1 and S2.

[0019] Step S1 specifically includes:

[0020] S101. Obtain the average paleoproductivity of the source rock of a single actual drilled well.

[0021] S102. Use geophysical data to obtain the activity rate of the depression-controlling fault of a single actual drilled well.

[0022] S103. Obtain the subsidence rate coefficient of a single actual drilled well.

[0023] S104. Obtain the sand-to-shale ratio of a single actual drilled well.

[0024] S105. Use the least squares method to fit and establish the empirical function relationship between the paleoproductivity of the source rock and the three geological elements.

[0025] In step S102, using geophysical data to obtain the activity rate of the depression-controlling fault of a single actual drilled well includes: intercepting the geophysical profile passing through the single actual drilled well and approximately perpendicular to the strike of the depression-controlling fault, and calculating the fault activity rate by dividing the fault displacement by the fault activity time.

[0026] In step S103, obtaining the single-well subsidence rate coefficient of the actual well drilled includes: using geophysical data, intercepting a geophysical profile passing through the single well of the actual well drilled and approximately perpendicular to the strike of the depression-controlling fault, and uniformly selecting virtual wells along the profile from the center of the deep depression zone of the depression to the edge of the depression; applying the PetroMod basin simulation software to restore the burial history of the single well of the actual well drilled and the virtual wells, dividing the total thickness of the formation to which the source rock layer belongs by the formation sedimentation time to obtain the single-well subsidence rate of the actual well drilled and each virtual well, and defining the ratio of the single-well subsidence rate of the actual well drilled to the maximum subsidence rate of the profile as the single-well subsidence rate coefficient.

[0027] In step S104, obtaining the sand-to-shale ratio of the single well of the actual well drilled includes: using the cuttings logging data of the actual well drilled, counting the total thickness of the sandstone in the formation to which the source rock section belongs, and dividing the sandstone thickness by the total thickness of the formation to obtain the sand-to-shale ratio of the single well.

[0028] In step S105, using the least squares method to fit and establish the empirical function relationship between the paleoproductivity of the source rock and three geological elements includes: standardizing the geological element evaluation indexes of ≥10 representative wells used for fitting and establishing the function relationship; respectively dividing the single-well depression-controlling fault activity rate by the maximum activity rate of the depression-controlling fault among all the representative wells, dividing the sand-to-shale ratio by the maximum value of the sand-to-shale ratio among all the representative wells, and keeping the single-well subsidence rate coefficient unchanged. After standardizing the three evaluation indexes, using the least squares method to fit and establish the linear function relationship between the paleoproductivity of the source rock and the three geological elements of the depression-controlling fault activity rate, subsidence rate coefficient, and sand-to-shale ratio. The expression is:

[0029] log 10 P = a×F + b×D + c×R + d

[0030] In the formula, P is the paleoproductivity, F is the single-well depression-controlling fault activity rate, D is the single-well subsidence rate coefficient, R is the single-well sand-to-shale ratio, a, b, and c are the coefficients obtained by fitting, and d is a constant.

[0031] Step S2 specifically includes:

[0032] S201, obtaining the single-well depression-controlling fault activity rate of the virtual well;

[0033] S202, obtaining the single-well subsidence rate coefficient of the virtual well;

[0034] S203, obtaining the single-well sand-to-shale ratio of the virtual well.

[0035] In step S201, obtaining the single-well depression-controlling fault activity rate of the virtual well includes: intercepting a geophysical profile passing through the virtual well and approximately perpendicular to the strike of the depression-controlling fault along the seismic survey line, obtaining the fault throw on the profile, and dividing it by the geological time to obtain the single-well depression-controlling fault activity rate of each virtual well on the profile.

[0036] In step S202, obtaining the single-well subsidence rate coefficient of the virtual well includes: obtaining the formation thickness of each single well of the virtual well by using seismic data, restoring the burial history of each single well of the virtual well by using the PetroMod basin simulation software, and obtaining the subsidence rate of the formation to which the source rock section of each virtual well belongs, and obtaining the single-well subsidence rate coefficient of the virtual well by dividing the virtual well formation subsidence rate by the maximum subsidence rate in the seismic profile passing through the virtual well.

[0037] In step S203, obtaining the single-well sand-to-shale ratio of the virtual well includes:

[0038] (1) In the area with few wells, obtaining the single-well sand-to-shale ratio of the virtual well by using the post-stack constrained sparse pulse impedance inversion method; impedance is a composite parameter related to the comprehensive characteristics of formation velocity and density, and is closely related to formation lithology. Impedance inversion is one of the most effective methods in seismic lithology inversion; the constrained sparse pulse inversion method is the most widely used method in the post-stack seismic impedance inversion process; this method requires at least one real drilled well in the work area, mainly using seismic data and using logging data as constraints to predict the formation lithology of the work area; applying the post-stack constrained sparse pulse impedance inversion technology to predict the lithology of the formation where the source rock is located in the area with few wells; based on the acoustic wave and density logging curves of the real drilled well, conducting rock physics analysis and statistics to obtain the impedance boundary values of different lithology formations such as mudstone and sandstone in the work area. Those higher than the impedance boundary value are sandstone, and those lower than the impedance boundary value are mudstone; obtaining the lithology profile passing through the real drilled well through post-stack sparse constrained pulse impedance inversion and the impedance boundary values of different lithologies of mudstone and sandstone, correcting the lithology inversion results with the lithology data of the cuttings logging of the real drilled well as constraints, and then using the inversion software to obtain the plane distribution map of the sand-to-shale ratio of the formation section where the source rock is located, and reading the single-well sand-to-shale ratio of each virtual well therefrom;

[0039] (2) In the area without wells, obtaining the single-well sand-to-shale ratio of the virtual well by using the linear correlation between the root mean square amplitude attribute of the real drilled well and the sand-to-shale ratio; statistically analyzing the linear relationship between the root mean square amplitude attribute of the real drilled well in the adjacent area and the sand-to-shale ratio, uniformly reading the root mean square amplitude attribute values of multiple points from top to bottom along the formation where the source rock is located in the seismic profile passing through the virtual well, obtaining the average value of the root mean square amplitude attribute of this formation, and obtaining the single-well sand-to-shale ratio of the virtual well by using the linear relationship between the root mean square amplitude attribute of the real drilled well in the adjacent area and the sand-to-shale ratio.

[0040] Step S3 specifically includes:

[0041] S301, substituting the single-well fault activity rate, subsidence rate coefficient, and sand-to-shale ratio values of the virtual well obtained in step S2 into the function relationship between the paleoproductivity of the source rock and geological elements established in step S1:

[0042] log 10 P = a×F + b×D + c×R + d

[0043] P is the paleoproductivity, F is the single-well controlled subsag fault activity rate, D is the single-well subsidence rate coefficient, R is the single-well sand-to-ground ratio, a, b, and c are coefficients obtained by fitting, and d is a constant) to calculate the paleoproductivity values of each virtual well in the wellless - less well subsag;

[0044] For S302, taking the sedimentary facies belt boundary of the source rock development in the wellless - less well subsag as the boundary for depicting the paleoproductivity of the source rock, and based on the paleoproductivity values of each virtual well in the subsag, an interpolation method is used between the determined virtual well with the maximum paleoproductivity and other virtual wells to compile the paleoproductivity isopach map of the source rock.

[0045] Another object of the present invention is to provide a quantitative evaluation system for the paleoproductivity of the source rock in a wellless - less well subsag, which implements the quantitative evaluation method for the paleoproductivity of the source rock in the wellless - less well subsag. The system includes:

[0046] A function relationship establishment module between the paleoproductivity of the actual drilled source rock and geological elements, which is used to select n≥10 representative wells in the deep sag zone and slope zone of different structural parts in the sag with rich drilling in the same basin, and establish the function relationship between the paleoproductivity of the source rock and geological elements based on the analysis of the organic carbon content of the source rock samples of the actual drilled wells and geological elements. The geological elements include the controlled subsag fault activity rate, subsidence rate coefficient, and sand-to-ground ratio;

[0047] A geological element acquisition module for virtual wells, which is used to evenly select n≥10 virtual wells along the seismic line within the plane range of the source rock development facies belt based on the planar distribution of the sedimentary facies belt in the wellless - less well subsag, and based on the 3D seismic data of the wellless - less well subsag, use means such as post-stack constrained sparse pulse wave impedance inversion, root-mean-square amplitude attribute acquisition, and basin simulation to obtain the data of three geological elements, namely the controlled subsag fault activity rate, subsidence rate coefficient, and sand-to-ground ratio, of a series of virtual wells;

[0048] A quantitative evaluation module for the subsag paleoproductivity, which is used to comprehensively evaluate the paleoproductivity of the source rock in the wellless - less well subsag by combining the function relationship establishment module between the paleoproductivity of the actual drilled source rock and geological elements and the geological element acquisition module for virtual wells.

[0049] Combining all the above technical solutions, the beneficial effects of the present invention are as follows: By drilling to enrich the organic carbon content test of actual source rock samples in the sag, the paleoproductivity is quantitatively calculated based on the organic carbon content, and the functional relationship between the paleoproductivity of actual wells and the three geological elements of the fault activity rate controlling the sag, the subsidence rate coefficient, and the sand-to-shale ratio is established through empirical statistics; then, the three geological elements of the fault activity rate controlling the sag, the subsidence rate coefficient, and the sand-to-shale ratio of a series of virtual wells are obtained from the 3D seismic data of the sag with few or no wells, and the paleoproductivity of the virtual wells is obtained by substituting them into the functional relationship formula; finally, the paleoproductivity plane distribution map of the sag with few or no wells is compiled based on the sedimentary facies, and the quantitative evaluation of the paleoproductivity of the sag with few or no wells is completed; effectively solving the problem of few actual samples and great difficulty in quantitatively evaluating the paleoproductivity in the sag with few or no wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure;

[0051] Figure 1 is a flowchart of a method for quantitatively evaluating the paleoproductivity of a sag with few or no wells provided by an embodiment of the present invention;

[0052] Figure 2 is a schematic diagram of a system for quantitatively evaluating the paleoproductivity of a sag with few or no wells provided by an embodiment of the present invention;

[0053] Figure 3 is a correlation diagram between the predicted value and the measured value of the paleoproductivity provided by an embodiment of the present invention;

[0054] Figure 4 is a rock physical analysis diagram of a representative well in a certain formation in a certain sag during the acquisition of the sand-to-shale ratio of a single well in the area with few wells provided by the present invention;

[0055] In the figure: 1. Function relationship establishment module between the vertical paleoproductivity of actual wells and geological elements; 2. Geological element acquisition module of virtual wells; 3. Quantitative evaluation module of sag paleoproductivity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be made in conjunction with the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0057] The present invention provides a method for calculating the average paleoproductivity of a single well in a drilled well, as well as a method for obtaining the numerical values of geological elements such as the activity rate of the fault controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio by means of geophysical data. Through the test of the organic carbon content of the actual source rock samples in the depression by drilling, the paleoproductivity of the source rock is quantitatively calculated based on the organic carbon content. The least squares method is used to fit and establish an empirical function relationship between the paleoproductivity of the source rock in the actual drilled well and the three geological elements of the activity rate of the fault controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio. Then, based on the 3D seismic data of the depression with few or no wells, a series of virtual well data of the three geological elements of the activity rate of the fault controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio are obtained by means of post-stack constrained sparse pulse wave impedance inversion, root mean square amplitude attribute acquisition, basin simulation, etc., and the paleoproductivity of the source rock of the virtual well is calculated by applying the foregoing empirical function relationship formula. Finally, based on the paleoproductivity of the source rock of the foregoing virtual well, with the boundary of the shallow lake facies sedimentary facies as the constraint, the planar distribution map of the paleoproductivity of the source rock in the depression with few or no wells is compiled by the interpolation method, and the quantitative evaluation of the paleoproductivity of the source rock in the depression with few or no wells is completed. The present invention solves the problems of few actual source rock samples in the depression with few or no wells and great difficulty in quantitatively evaluating the paleoproductivity of the source rock.

[0058] Example 1, as Figure 1 shown, the method for quantitatively evaluating the paleoproductivity of the depression with few or no wells provided by the embodiment of the present invention includes the following steps:

[0059] S1, in different structural parts of the deep depression zone and the slope zone of the depression with rich drilling in the same basin, select n≥10 representative wells that drill through the source rock layer segment. Based on the analysis of the organic carbon content of the source rock samples in the actual drilled well and the single well geological elements, use the least squares method to fit and establish an empirical function relationship between the paleoproductivity of the source rock and the geological elements; the geological elements include: the activity rate of the fault controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio; wherein, the sand-to-shale ratio is the ratio of the thickness of the sandstone formation in the source rock development layer segment to the total thickness;

[0060] A total of ≥10 representative wells (TW1, TW2,..., TWn, n≥10) that drill through the source rock layer segment are selected in different structural parts of the deep depression zone and the slope zone of the depression with rich drilling. Based on the analysis of the actual drilled well, a function relationship between the paleoproductivity and the geological elements (fault activity rate, subsidence coefficient, sand-to-shale ratio) is established.

[0061] Specifically, it includes:

[0062] S101. Obtain the average paleoproductivity of the hydrocarbon source rock in a single well of the actual drilled well: Taking Well TW1 as an example, collect samples evenly from the hydrocarbon source rock interval and ensure that the total number of samples is greater than or equal to 10. Measure the organic carbon content of the samples and calculate the average organic carbon content of the hydrocarbon source rock interval in Well TW1 using the weighted average method. Then, use the paleoproductivity calculation formula to obtain the average paleoproductivity of the hydrocarbon source rock in Well TW1. The calculation formula is R = C × ρ × (1 - Φ) / (0.00421 × S 0.0826 ), where R is the paleoproductivity, with the unit of gC·m -2 ·a -1 ; C is the organic carbon content, with the unit of %; ρ represents the sediment density, with the unit of g·cm -3 ; Φ is the porosity, with the unit of %; S is the sedimentation rate, with the unit of cm·10 -3 ·a -1 . The sediment density, porosity, and sedimentation rate depend on the situation of the study area;

[0063] S102. Obtain the activity rate of the single-well controlling depression fault in the actual drilled well using geophysical data: That is, intercept the geophysical profile passing through the single well of the actual drilled well and perpendicular to the strike of the controlling depression fault, and calculate the fault activity rate by dividing the fault offset by the fault activity time. The expression is: Fault activity rate = Fault offset / Fault activity time;

[0064] S103. Obtain the subsidence rate coefficient of the single well in the actual drilled well: To obtain the subsidence rate coefficient of the single well in the actual drilled well, it includes: using geophysical data, intercept the geophysical profile passing through the single well of the actual drilled well and approximately perpendicular to the strike of the controlling depression fault, and evenly select virtual wells along the profile from the center of the deep depression zone to the edge of the depression; apply the PetroMod basin simulation software to restore the burial history of the single well of the actual drilled well and the virtual wells, divide the total thickness of the formation to which the hydrocarbon source rock belongs by the formation sedimentation time to obtain the subsidence rate of the single well of the actual drilled well and each virtual well, and define the ratio of the subsidence rate of the actual drilled well to the maximum subsidence rate of the profile as the single-well subsidence rate coefficient;

[0065] S104. Obtain the sand-to-shale ratio of the single well in the actual drilled well: To obtain the sand-to-shale ratio of the single well in the actual drilled well, it includes: using the cuttings logging data of the actual drilled well, count the total thickness of the sandstone in the formation to which the hydrocarbon source rock interval belongs, and divide the sandstone thickness by the total formation thickness to obtain the sand-to-shale ratio of the single well;

[0066] S105. Establish an empirical function relationship between the paleoproductivity of source rocks and three geological elements by least - squares fitting: Establish an empirical function relationship between the paleoproductivity of source rocks and three geological elements by least - squares fitting, including: standardize the geological element evaluation indexes of ≥10 representative wells used for fitting the function relationship; divide the single - well fault - controlling depression activity rate by the maximum activity rate of the fault - controlling depression in all representative wells, divide the sand - to - ground ratio by the maximum value of the sand - to - ground ratio in all representative wells, and keep the single - well subsidence rate coefficient unchanged. After standardizing the three evaluation indexes, use the least - squares method to fit and establish a linear function relationship between the paleoproductivity of source rocks and the three geological elements of the fault - controlling depression activity rate, subsidence rate coefficient, and sand - to - ground ratio. The expression is:

[0067] log 10 P = a×F + b×D + c×R + d

[0068] In the formula, P is the paleoproductivity, F is the single - well fault - controlling depression activity rate, D is the single - well subsidence rate coefficient, R is the single - well sand - to - ground ratio, a, b, and c are the coefficients obtained by fitting, and d is a constant.

[0069] S2. Based on the planar distribution of sedimentary facies during the source - rock development period in a well - less or less - well depression, uniformly select n≥10 virtual wells along the seismic line within the planar range of the source - rock development facies belt. Based on the 3D seismic data of the well - less or less - well depression, use the means of post - stack constrained sparse pulse wave impedance inversion, root - mean - square amplitude attribute, and basin simulation to obtain the data of the three geological elements of the fault - controlling depression activity rate, subsidence rate coefficient, and sand - to - ground ratio of a series of virtual wells;

[0070] S201. Obtain the single - well fault - controlling depression activity rate of virtual wells: Obtain the single - well fault - controlling depression activity rate of virtual wells, including: intercept a geophysical profile passing through the virtual well and approximately perpendicular to the strike of the fault - controlling depression along the seismic line, obtain the fault throw on the profile, and divide it by the geological time to obtain the single - well fault - controlling depression activity rate of each virtual well on the profile;

[0071] S202. Obtain the single - well subsidence rate coefficient of virtual wells: Use seismic data to obtain the formation thickness of each virtual well, use the PetroMod basin simulation software to restore the burial history of each virtual well and obtain the subsidence rate of the formation to which the source - rock interval of each virtual well belongs. Divide the virtual well formation subsidence rate by the maximum subsidence rate in the seismic profile passing through the virtual well to obtain the single - well subsidence rate coefficient of the virtual well.

[0072] S203. Obtain the single - well sand - to - ground ratio of virtual wells:

[0073] (1) In the area with few wells, the single-well sand-to-shale ratio of virtual wells is obtained by using post-stack constrained sparse pulse impedance inversion. Impedance is a composite parameter related to the comprehensive characteristics of formation velocity and density, and is closely related to formation lithology. Impedance inversion is one of the most effective methods in seismic lithology inversion. The constrained sparse pulse inversion method is the most widely used method in the process of post-stack seismic impedance inversion. This method requires at least one real drilled well in the work area. Based on seismic data and using well logging data as constraints, the formation lithology of the work area is predicted. The post-stack constrained sparse pulse impedance inversion technology is applied to predict the lithology of the formation where the source rock is located in the area with few wells. Through rock physics analysis and statistics based on the acoustic wave and density logging curves of real drilled wells, the impedance boundary values of different lithology formations such as mudstone and sandstone in the work area are obtained. Those higher than the impedance boundary value are sandstone, and those lower than the impedance boundary value are mudstone. Through post-stack sparse constrained pulse impedance inversion and the impedance boundary values of different lithologies of mudstone and sandstone, the lithology profile passing through the real drilled well is obtained. Using the lithology data of the cuttings logging of the real drilled well as a constraint, the lithology inversion result is corrected. Then, using the inversion software, the plane distribution map of the sand-to-shale ratio of the formation where the source rock is located is obtained, and the single-well sand-to-shale ratio of each virtual well is read from it.

[0074] (2) In the area without wells, the single-well sand-to-shale ratio of virtual wells is obtained by using the linear correlation between the root mean square amplitude attribute of real drilled wells and the sand-to-shale ratio. The linear relationship between the root mean square amplitude attribute of real drilled wells in the adjacent area and the sand-to-shale ratio is statistically analyzed. In the seismic profile passing through the virtual well, the root mean square amplitude attribute values of multiple points are evenly read from top to bottom along the formation where the source rock is located, and the mean value of the root mean square amplitude attribute of this formation is obtained. The single-well sand-to-shale ratio of the virtual well is obtained by using the linear relationship between the root mean square amplitude attribute of real drilled wells in the adjacent area and the sand-to-shale ratio.

[0075] S3. Calculate and obtain the paleoproductivity of the source rock of the virtual well by applying the empirical function relationship formula. Based on the paleoproductivity of the source rock of the virtual well and taking the boundary of the shallow lake facies sedimentary facies as a constraint, use the interpolation method to compile the isopach map of the paleoproductivity of the source rock in the well-free and few-well sag. Integrate Step S1 and Step S2 to complete the quantitative evaluation of the paleoproductivity of the source rock in the well-free and few-well sag based on geological elements.

[0076] S301. Substitute the single-well fault activity rate, subsidence rate coefficient, and sand-to-shale ratio value of the virtual well obtained in Step S2 into the function relationship between the paleoproductivity of the source rock and geological elements established in Step S1:

[0077] log 10 P = a×F + b×D + c×R + d

[0078] where P is the paleoproductivity, F is the single-well fault activity rate controlling the sag, D is the single-well subsidence rate coefficient, R is the single-well sand-to-shale ratio, a, b, and c are the coefficients obtained by fitting, and d is a constant) to calculate the paleoproductivity values of each virtual well in the well-free and few-well sag.

[0079] S302. Using the sedimentary facies belt boundary of the source rock development in the well - less to less - well sag as the boundary for characterizing the paleoproductivity of the source rock, based on the paleoproductivity values of each virtual well in the sag, an interpolation method is used between the determined virtual well with the maximum paleoproductivity and other virtual wells to compile an isopach map of the paleoproductivity of the source rock.

[0080] Example 2. As Figure 2 shown, the embodiment of the present invention provides a quantitative evaluation system for the paleoproductivity of a well - less to less - well sag, including:

[0081] A function relationship establishment module 1 for the paleoproductivity of the actual - drilled source rock and geological elements, which is used to select n≥10 representative wells drilling through the source rock formation in different structural parts of the deep - sag zone and slope zone in the sag with rich drilling in the same basin. Based on the analysis of the organic carbon content of the actual - drilled source rock samples and geological elements, a function relationship between the paleoproductivity of the source rock and geological elements is established. The geological elements include the activity rate of the depression - controlling fault, the subsidence rate coefficient, and the sand - to - ground ratio.

[0082] A geological element acquisition module 2 for virtual wells, which is used to evenly select n≥10 virtual wells along the seismic survey line within the plane range of the source rock development facies belt based on the planar distribution of the sedimentary facies belt in the well - less to less - well sag. Based on the 3D seismic data of the well - less to less - well sag, a series of geological element data of the activity rate of the depression - controlling fault, the subsidence rate coefficient, and the sand - to - ground ratio of the virtual wells are obtained by means of post - stack constrained sparse spike impedance inversion, root - mean - square amplitude attribute acquisition, and basin simulation.

[0083] A quantitative evaluation module 3 for the paleoproductivity of the sag, which is used to comprehensively evaluate the paleoproductivity of the source rock in the well - less to less - well sag by combining the function relationship establishment module for the paleoproductivity of the actual - drilled source rock and geological elements and the geological element acquisition module for virtual wells.

[0084] Taking a certain sag in a certain basin in a certain sea area as an example, the following experiment is carried out.

[0085] Step 1: First, 11 representative actual - drilled wells are cumulatively selected in the sag with rich drilling in the adjacent area, and the average paleoproductivity of the formation to which the source rock belongs, as well as the activity rate of the depression - controlling fault of a single well, the subsidence coefficient of a single well, and the sand - to - ground ratio of a single well, are obtained according to the aforementioned method (Table 1).

[0086] Table 1 List of parameters of the paleoproductivity of actual - drilled wells and geological elements

[0087]

[0088]

[0089] The function relationship formula between the paleoproductivity and geological elements is obtained by least - squares fitting:

[0090] Log10 P = 0.05×F + 0.09×D - 0.82×R + 2.99

[0091] And compare the predicted values with the measured values, such as Figure 3 The correlation diagram between the predicted value and the measured value of paleoproductivity shows a high positive correlation between the two, which proves the feasibility of the method and indicates that the functional relationship formula can be used for the prediction of paleoproductivity.

[0092] Step 2: In the process of obtaining the sand-to-shale ratio of a single well in a low-well area, based on the petrophysical analysis of the actually drilled wells, the plane distribution map of the sand-to-shale ratio is obtained by using post-stack P-wave impedance inversion. The specific process of obtaining the sand-to-shale ratio of a single well in a low-well area includes, in sequence, such as Figure 4 The petrophysical analysis map of a representative well in a certain formation in a certain depression in the process of obtaining the sand-to-shale ratio of a single well in a low-well area.

[0093] In the process of obtaining the sand-to-shale ratio of a single well in a wellless area, the sand-to-shale ratio of a single well in the wellless area is obtained based on the correlation between the root-mean-square amplitude attribute of the actually drilled wells in the adjacent area and the sand-to-shale ratio. Specifically, in the process of obtaining the sand-to-shale ratio of a single well in the wellless area, in sequence, it includes obtaining the root-mean-square amplitude attribute value and the sand-to-shale ratio parameter of a virtual well in a certain depression in the process of obtaining the sand-to-shale ratio of a single well in the wellless area, as shown in Table 2.

[0094] Table 2 Root-mean-square amplitude attribute value and sand-to-shale ratio parameter of a virtual well in a certain depression

[0095]

[0096]

[0097] Step 3: Select virtual wells in the wellless-low-well depression, and apply the formula in Step 1 to calculate the paleoproductivity of each virtual well (Table 3), based on the paleoproductivity values of each virtual well in the depression.

[0098] Table 3 List of geological element values and predicted paleoproductivity values of some virtual wells

[0099]

[0100]

[0101] As mentioned above, only the relatively optimal specific implementation manner of the present invention is described, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating the paleoproductivity of source rocks in a depression with few or no wells, characterized in that, The method comprises the following steps: S1. Drilling in different structural parts of deep depressions and slope zones of rich depressions in the same basin, select n≥10 representative wells that encounter source rock sections, and based on the organic carbon content of the source rock samples actually drilled and the analysis of the geological elements of a single well, use the least squares method to fit and establish an empirical functional relationship between the paleoproductivity of source rocks and geological elements; the geological elements include: the activity rate of depression-controlling faults, the sedimentation rate coefficient, and the sand-to-ground ratio; the sand-to-ground ratio is the ratio of the sandstone formation thickness to the total thickness of the source rock development section; S2, based on the plane distribution of sedimentary facies during the source rock development period in the depression with no wells or few wells, n ≥ 10 virtual wells were uniformly selected along the seismic survey line within the plane range of the source rock development facies belt, and based on the 3D seismic data of the depression with no wells or few wells, the three geological element data of the depression-controlling fault activity rate, sedimentation rate coefficient, and sand-to-ground ratio of the series of virtual wells were obtained by means of post-stack constrained sparse pulse wave impedance inversion, root mean square amplitude attributes, and basin simulation; S3, applying the empirical function relationship formula to calculate the paleoproductivity of the source rock of the virtual well, based on the paleoproductivity of the source rock of the virtual well, taking the shallow lake sedimentary phase boundary as a constraint, using the interpolation method to compile the paleoproductivity contour map of the source rock in the depression with no wells or few wells, and combining steps S1 and S2 to complete the quantitative evaluation of the paleoproductivity of the source rock in the depression with no wells or few wells based on geological factors.

2. The quantitative evaluation method for the paleoproductivity of source rocks in a depression with few or no wells according to claim 1, wherein Step S1 specifically includes: S101, obtain the average paleoproductivity of source rocks in a single well that has been drilled; S102, using geophysical data to obtain the activity rate of depression-controlling faults in a single well in actual drilling; S103, obtaining the settlement rate coefficient of a single well in actual drilling; S104, obtaining the sand-to-ground ratio of a single well in actual drilling; S105, the least squares method is used to fit and establish the empirical functional relationship between the paleoproductivity of source rocks and the three geological elements.

3. The quantitative evaluation method for paleoproductivity of source rocks in a well-free or less-well sag according to claim 2, wherein In step S102, the activity rate of the depression-controlling fault of the actual drilling single well is obtained by using geophysical data, including: intercepting a geophysical profile that passes through the actual drilling single well and is approximately perpendicular to the strike of the depression-controlling fault, and calculating the fault activity rate by dividing the fault distance by the fault activity time; In step S103, the settlement rate coefficient of the actual well is obtained, including: using geophysical data to intercept a geophysical profile that passes through the actual well and is approximately perpendicular to the direction of the depression-controlling fault, and evenly selecting virtual wells along the profile from the center of the deep depression zone to the edge of the depression; using PetroMod basin simulation software to restore the burial history of the actual well and the virtual well, dividing the total thickness of the stratum to which the source rock layer belongs by the stratum deposition time to obtain the settlement rate of the actual well and each virtual well, and defining the ratio of the actual well settlement rate to the maximum settlement rate of the profile as the single well settlement rate coefficient.

4. The quantitative evaluation method for the paleoproductivity of the source rocks in the well-free to less-well sag according to claim 2, wherein In step S104, the sand-to-formation ratio of a single well is obtained, including: using the actual drilling cuttings logging data, calculating the total thickness of the sandstone in the formation to which the source rock section belongs, and dividing the sandstone thickness by the total formation thickness to obtain the sand-to-formation ratio of the single well; In step S105, the empirical function relationship between the paleoproductivity of the source rock and three geological elements is established by least squares fitting, including: standardizing the geological element evaluation indexes of ≥10 representative wells used for fitting the function relationship; dividing the single-well depression-controlling fault activity rate by the maximum activity rate of the depression-controlling faults in all representative wells, dividing the sand-to-ground ratio by the maximum sand-to-ground ratio in all representative wells, and keeping the single-well subsidence rate coefficient unchanged. After standardizing the three evaluation indexes, the linear function relationship between the paleoproductivity of the source rock and the three geological elements of the depression-controlling fault activity rate, subsidence rate coefficient, and sand-to-ground ratio is established by least squares fitting. The expression is: log 10 P = a×F + b×D + c×R + d In the formula, P is the paleoproductivity, F is the single-well depression-controlling fault activity rate, D is the single-well subsidence rate coefficient, R is the single-well sand-to-ground ratio, a, b, and c are the coefficients obtained by fitting, and d is a constant.

5. The method for quantitatively evaluating the paleoproductivity of source rocks in a well-free or less-well sag according to claim 1, wherein Step S2 specifically includes: S201, obtaining the single-well depression-controlling fault activity rate of the virtual well; S202, obtaining the single-well subsidence rate coefficient of the virtual well; S203, obtaining the single-well sand-to-ground ratio of the virtual well.

6. The method for quantitatively evaluating the paleoproductivity of source rocks in a well-free or less-well sag according to claim 5, wherein In step S201, to obtain the single-well depression-controlling fault activity rate of the virtual well, it includes: intercepting a geophysical profile that passes through the virtual well and is approximately perpendicular to the strike of the depression-controlling fault along the seismic line, obtaining the fault throw on the profile, and dividing it by the geological time to obtain the single-well depression-controlling fault activity rate of each virtual well on the profile.

7. The quantitative evaluation method for the paleoproductivity of source rocks in a wellless or less-well sag according to claim 5, characterized in that In step S202, to obtain the single-well subsidence rate coefficient of the virtual well, it includes: using seismic data to obtain the formation thickness of each single well of the virtual well, using the PetroMod basin simulation software to restore the burial history of each single well of the virtual well and obtain the subsidence rate of the formation to which the source rock interval of each virtual well belongs, and obtaining the single-well subsidence rate coefficient of the virtual well by dividing the formation subsidence rate of the virtual well by the maximum subsidence rate in the seismic profile passing through the virtual well.

8. The method for quantitatively evaluating the paleoproductivity of a source rock in a wellless or less-well depression according to claim 5, characterized in that, In step S203, to obtain the single-well sand-to-ground ratio of the virtual well, it includes: (1) In the area with few wells, the single-well sand-to-ground ratio of the virtual well is obtained by using the post-stack constrained sparse pulse impedance inversion method. The lithology prediction of the formation where the source rock is located in the area with few wells is carried out by applying the post-stack constrained sparse pulse impedance inversion technology; based on the sonic and density logging curves of the actual drilled wells, the wave impedance boundary values of different lithology formations of mudstone and sandstone in the work area are obtained through rock physics analysis and statistics. Those higher than the wave impedance boundary value are sandstone, and those lower than the wave impedance boundary value are mudstone; the lithology profile passing through the actual drilled wells is obtained through post-stack sparse constrained pulse impedance inversion and the wave impedance boundary values of different lithologies of mudstone and sandstone. The lithology inversion result is corrected with the lithology data of the cuttings logging of the actual drilled wells as a constraint, and then the plane distribution map of the sand-to-ground ratio of the formation where the source rock is located is obtained by using the inversion software, and the single-well sand-to-ground ratio of each virtual well is read therefrom; (2) In the area without wells, the single-well sand-to-ground ratio of the virtual well is obtained by using the linear correlation between the root mean square amplitude attribute of the actual drilled wells and the sand-to-ground ratio; the linear relationship between the root mean square amplitude attribute of the actual drilled wells in the adjacent area and the sand-to-ground ratio is statistically analyzed. Along the formation where the source rock is located in the seismic profile passing through the virtual well, the root mean square amplitude attribute values of multiple points are evenly read from top to bottom, and the mean value of the root mean square amplitude attribute of this formation is obtained. The single-well sand-to-ground ratio of the virtual well is obtained by using the linear relationship between the root mean square amplitude attribute of the actual drilled wells in the adjacent area and the sand-to-ground ratio.

9. The method for quantitatively evaluating the paleoproductivity of a source rock in a well-free or less-well sag according to claim 1, wherein The specific steps of step S3 include: S301, substituting the single-well fault activity rate, subsidence rate coefficient, and sand-to-shale ratio value of the virtual well obtained in step S2 into the function relationship between the paleoproductivity of the source rock and geological elements established in step S1: log 10 P = a×F + b×D + c×R + d In the formula, P is the paleoproductivity, F is the single-well fault activity rate controlling the depression, D is the single-well subsidence rate coefficient, R is the single-well sand-to-shale ratio, a, b, and c are coefficients obtained by fitting, and d is a constant; Calculating the paleoproductivity values of each virtual well in the wellless-low-well depression; S302, using the sedimentary facies belt boundary of the source rock development in the wellless-low-well depression as the boundary for depicting the paleoproductivity of the source rock. Based on the paleoproductivity values of each virtual well in the depression, an interpolation method is used between the determined virtual well with the maximum paleoproductivity and other virtual wells to compile an isopach map of the paleoproductivity of the source rock.

10. A quantitative evaluation system for paleoproductivity of source rocks in a sag with few or no wells, characterized in that This system implements the method for quantitatively evaluating the paleoproductivity of the source rock in the wellless-low-well depression as described in any one of claims 1-9. This system includes: A function relationship establishment module (1) between the paleoproductivity of the actual drilled source rock and geological elements, which is used to select n≥10 representative wells drilled through the source rock formation in different structural parts of the deep depression zone and slope zone of the depression with rich drilling in the same basin. Based on the analysis of the organic carbon content of the source rock samples of the actual drilled wells and geological elements, a function relationship between the paleoproductivity of the source rock and geological elements is established. The geological elements include the fault activity rate controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio; A geological element acquisition module (2) for virtual wells, which is used to evenly select n≥10 virtual wells along the seismic line within the plane range of the sedimentary facies belt of the wellless-low-well depression based on the planar distribution of the sedimentary facies belt of the wellless-low-well depression. Based on the 3D seismic data of the wellless-low-well depression, a series of geological element data of the fault activity rate controlling the depression, the subsidence rate coefficient, and the sand-to-shale ratio of the virtual wells are obtained by means of post-stack constrained sparse pulse wave impedance inversion, root-mean-square amplitude attribute acquisition, and basin simulation; A quantitative evaluation module (3) for the paleoproductivity of the depression, which is used to comprehensively evaluate the paleoproductivity of the source rock in the wellless-low-well depression by the function relationship establishment module (1) between the paleoproductivity of the actual drilled source rock and geological elements and the geological element acquisition module (2) for virtual wells.

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