A quantitative characterization and prediction method for original organic matter abundance in highly mature shale formations

Abstract

The invention discloses a method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation. The invention solves the problems and shortcomings of the existing original organic matter abundance evaluation method for source rocks mainly based on analytical testing, such as high experimental difficulty, high cost, long cycle, and complex implementation. The invention comprises step 1, proposing characteristic parameters capable of characterizing the original organic matter abundance of the highly mature shale formation; step 2, calculating the volume content of organic matter remaining in the current formation and the characteristic parameters of the original organic matter abundance; step 3, establishing a prediction model for the characteristic parameters of the original organic matter abundance; step 4, obtaining the sensitive elastic parameters required by the prediction model for the characteristic parameters of the original organic matter abundance by using post-stack seismic inversion technology; and step 5, calculating the characteristic parameters of the original organic matter abundance for evaluating the quality and hydrocarbon generation capacity of the source rock of the shale formation. The invention improves the success rate of exploration of highly mature shale oil and gas reservoirs, reduces the risks of exploration and development to the greatest extent, and improves the economic benefits of shale oil and gas.

Description

Technical Field

[0001] The present invention belongs to the field of geophysical exploration, and in particular relates to a method for quantitatively characterizing and predicting the abundance of original organic matter in highly mature shale formations. Background Art

[0002] The shale oil and gas revolution is changing the world's energy landscape and has become a research hotspot in the global oil industry. In the exploration and development of shale oil and gas reservoirs, the quantitative evaluation and spatial distribution description of source rocks are important components of shale oil and gas resource evaluation, and the abundance of organic matter in source rocks, namely organic carbon content and TOC, is one of the most important indicators for evaluating its hydrocarbon generation capacity. At present, we have realized that as the generation and expulsion of hydrocarbons in source rocks proceed, the abundance of residual organic matter in source rocks gradually decreases. For highly mature and over-mature source rocks, if the current residual organic carbon content of the formation is used to evaluate the quality of source rocks and estimate the amount of shale oil and gas resources, the results will be seriously distorted, which will directly affect the exploration and development of shale oil and gas and the economic benefits. Therefore, how to quantitatively characterize the original abundance of organic matter in highly mature shale formations and make a precise prediction of its spatial distribution is of great importance for shale oil and gas reservoirs.

[0003] There are many existing methods for evaluating the abundance of original organic matter in source rocks, such as thermal simulation experiment method, element model method, hydrocarbon generation kinetics method, etc. These calculation methods are mainly based on analytical testing, and require a large amount of high-precision experimental data. They are difficult to operate, expensive, and have a long cycle. The implementation is complex, and some key parameters are difficult to obtain. In addition, there is no direct prediction method for the spatial distribution of the original organic matter abundance of source rocks using three-dimensional seismic data. For this reason, we have invented a quantitative characterization and prediction method for the abundance of original organic matter in highly mature shale formations, which solves the above technical problems. Summary of the invention

[0004] The purpose of the present invention is to provide a method for quantitatively characterizing and predicting the original organic matter abundance of highly mature shale formations. Starting from the evolution process of source rocks, sensitive elastic parameters of characteristic parameters of original organic matter abundance are optimized by statistical intersection analysis and a prediction model is established. The prediction of characteristic parameters of original organic matter abundance is realized by post-stack seismic inversion, and then the hydrocarbon generation capacity of highly mature shale formations and the spatial distribution of high-quality source rocks are evaluated, so as to improve the exploration and development accuracy of shale oil and gas reservoirs and reduce the risks of exploration and development.

[0005] In order to achieve the above objectives, the technical solution adopted by the present invention is: a method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation, comprising the following steps:

[0006] Step 1: Based on the nature of source rock evolution, characteristic parameters of original organic matter abundance that can characterize high-mature shale formations are proposed;

[0007] Step 2: Conduct rock physics experimental measurements, geochemical measurements and physical property measurements on shale samples to obtain rock physical parameters, residual organic carbon content and total porosity, and calculate the current residual organic matter volume content and original organic matter abundance characteristic parameters;

[0008] Step 3, performing intersection analysis on the rock physical parameters of the shale sample and the original organic matter abundance characteristic parameters, optimizing the sensitive elastic parameters of the original organic matter abundance characteristic parameters, and establishing a prediction model for the original organic matter abundance characteristic parameters;

[0009] Step 4, using post-stack seismic inversion technology to obtain the sensitive elastic parameters required by the original organic matter abundance characteristic parameter prediction model;

[0010] Step 5, using the original organic matter abundance characteristic parameter prediction model in step 3 and the sensitive elastic parameters inverted in step 4 to calculate the original organic matter abundance characteristic parameters for use in evaluating the quality and hydrocarbon generation capacity of the shale formation source rock.

[0011] Step 1 The specific approach is to use the sum of the residual organic matter volume of the current formation and the pore volume of organic hydrocarbon generation to reflect the original formation organic matter volume content, and evaluate the shale organic matter abundance and hydrocarbon generation capacity; for highly mature shale formations, organic hydrocarbon generation pores are the main pore type, and organic hydrocarbon generation pores account for more than 90% of the total pores, so the total porosity is used to replace the pore volume generated during the hydrocarbon generation and expulsion process; it is proposed that the characteristic parameter of the original organic matter abundance of highly mature shale formations can be characterized as the sum of the residual organic matter volume content of the current formation and the total porosity, and the formula is as follows:

[0012]

[0013] Where: P is the characteristic parameter of original organic matter abundance, unit is %;

[0014] is the volume content of residual organic matter, in %;

[0015] is the total porosity, in %.

[0016] The specific method of step 2 is that the rock physical parameters include longitudinal wave velocity, transverse wave velocity, shale skeleton density, organic matter density, longitudinal wave impedance, transverse wave impedance, Poisson's ratio and Young's modulus; the original organic matter abundance characteristic parameters of the shale sample are calculated using step 1; the current residual organic matter volume content is calculated using the measured residual organic carbon content, and the formula is as follows:

[0017]

[0018] Where: is the volume content of residual organic matter, in %;

[0019] ρ rock is the shale skeleton density, unit: g / cm 3 ;

[0020] ρ om is the density of organic matter, in g / cm 3 ;

[0021] k is the organic matter conversion coefficient, which is generally taken as 1.25;

[0022] w TOC is the residual organic carbon content, in %.

[0023] The specific method of step 3 is to select the rock physical parameter with the highest correlation coefficient as the sensitive elastic parameter of the original organic matter abundance characteristic parameter based on the original organic matter abundance characteristic parameter calculated in step 2 and the measured rock physical parameter through statistical intersection analysis, and use the fitted intersection analysis equation as the prediction model of the original organic matter abundance characteristic parameter;

[0024] The rock physical parameter with the highest correlation coefficient between the original organic matter abundance characteristic parameters and P-wave velocity, S-wave velocity, density, P-wave impedance, S-wave impedance, Poisson's ratio and Young's modulus is P-wave impedance. Therefore, P-wave impedance is selected as the sensitive elastic parameter of the original organic matter abundance characteristic parameters, and its fitted intersection analysis equation is used as the prediction model of the original organic matter abundance characteristic parameters. The formula is as follows:

[0025] P = -1.87 × AI + 25.74

[0026] Where: P is the characteristic parameter of original organic matter abundance, unit is %;

[0027] Al is the longitudinal wave impedance, in Gg·m -2 ·s -1 .

[0028] The specific approach of step 4 is to use post-stack seismic inversion technology based on seismic data to obtain the sensitive elastic parameter required for the original organic matter abundance characteristic parameter prediction model, which is the longitudinal wave impedance AI.

[0029] The specific method of step 5 is to substitute the longitudinal wave impedance AI obtained in step 4 into the original organic matter abundance characteristic parameter prediction model in step 3, calculate the original organic matter abundance characteristic parameters, reflect the change law of high-quality source rocks, and realize the quantitative description of the hydrocarbon generation capacity of shale formations.

[0030] The beneficial effects of the present invention are:

[0031] The present invention proposes characteristic parameters that can characterize the original organic matter abundance of highly mature shale formations based on the essence of source rock evolution. The method is simple in principle, easy to understand, and can be widely promoted and applied, effectively solving the problems and shortcomings of the existing original organic matter abundance evaluation methods for source rocks that mainly rely on analytical testing, such as high experimental difficulty, high cost, long cycle, and complex implementation. Through experimental measurement of typical shale samples, sensitive elastic parameters of the original organic matter abundance characteristic parameters are optimized by statistical intersection analysis and a prediction model is established. The original organic matter abundance characteristic parameters are predicted based on post-stack seismic inversion, and the hydrocarbon generation capacity of highly mature shale formations and the spatial distribution of high-quality source rocks are evaluated, filling the gap in the seismic prediction method for the original organic matter abundance of highly mature shale formations, fundamentally improving the success rate of shale oil and gas reservoir exploration and reducing the risks of exploration and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Description of the drawings: Figure 1 This is a schematic diagram of a process for quantitatively characterizing and predicting the abundance of original organic matter in highly mature shale formations according to the present invention;

[0033] Figure 2 It is a schematic diagram of the source rock evolution process;

[0034] Figure 3 It is the cross-plot of the characteristic parameter P of the original organic matter abundance and the P-wave velocity;

[0035] Figure 4 It is the cross-plot of the characteristic parameter P of the original organic matter abundance and the shear wave velocity;

[0036] Figure 5 It is the cross plot of the characteristic parameter P of the original organic matter abundance and density;

[0037] Figure 6 It is the cross plot of the characteristic parameter P of the original organic matter abundance and the longitudinal wave impedance;

[0038] Figure 7 It is the cross plot of the characteristic parameter P of the original organic matter abundance and the shear wave impedance;

[0039] Figure 8 It is the cross plot of the characteristic parameter P of original organic matter abundance and Poisson's ratio;

[0040] Fig. 9 is the cross plot of the characteristic parameter P of the original organic matter abundance and Young's modulus;

[0041] Fig.10 This is the profile of the prediction results of the characteristic parameter P of the original organic matter abundance through Well A;

[0042] Fig.11 It is the predicted plane diagram of the characteristic parameter P of the original organic matter abundance of the Q2 oil layer.

[0043] Specific implementation method: In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and detailedly described below with reference to the drawings in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0044] A method for quantitatively characterizing and predicting the abundance of original organic matter in a highly mature shale formation comprises the following steps:

[0045] Step 1: Based on the nature of source rock evolution, characteristic parameters of original organic matter abundance that can characterize high-mature shale formations are proposed;

[0046] Step 2: Conduct rock physics experimental measurements, geochemical measurements and physical property measurements on shale samples to obtain rock physical parameters, residual organic carbon content and total porosity, and calculate the current residual organic matter volume content and original organic matter abundance characteristic parameters;

[0047] Step 3, performing intersection analysis on the rock physical parameters of the shale sample and the original organic matter abundance characteristic parameters, optimizing the sensitive elastic parameters of the original organic matter abundance characteristic parameters, and establishing a prediction model for the original organic matter abundance characteristic parameters;

[0048] Step 4, using post-stack seismic inversion technology to obtain the sensitive elastic parameters required by the original organic matter abundance characteristic parameter prediction model;

[0049] Step 5, using the original organic matter abundance characteristic parameter prediction model in step 3 and the sensitive elastic parameters inverted in step 4 to calculate the original organic matter abundance characteristic parameters for use in evaluating the quality and hydrocarbon generation capacity of the shale formation source rock.

[0050] Embodiment: Well A in a real seismic work area of ​​the high-mature Gulong shale oil of the Qingshankou Formation in the northern Songliao Basin was selected for testing, and Well A was a post-test well.

[0051] Figure 1 The present invention is a flow chart of a method for quantitatively characterizing and predicting the abundance of original organic matter in highly mature shale formations. The method comprises the following steps:

[0052] Step 1: Based on the nature of source rock evolution, characteristic parameters that can characterize the original organic matter abundance of highly mature shale formations are proposed;

[0053] Figure 2The figure is a schematic diagram of the evolution process of source rocks. It can be seen that during the thermal maturation of organic matter, part of the original organic matter evolves into oil and pores, and the other part is retained in the formation as residual organic matter. The higher the degree of thermal evolution, the smaller the volume of residual organic matter, and the larger the volume of organic hydrocarbon-generating pores. Therefore, the sum of the residual organic matter volume of the current formation and the organic hydrocarbon-generating pore volume is used to reflect the original formation organic matter volume content, and evaluate the original organic matter abundance and hydrocarbon-generating capacity of the shale formation. Since the organic-rich shale formation needs to reach the oil generation threshold in depth and temperature before it can generate and expel hydrocarbons, the strong compaction of the overlying formation will cause the primary pores of the shale formation to be undeveloped and relatively small. The organic hydrocarbon-generating pores are the main pore type. Through experimental measurement, the organic hydrocarbon-generating pores account for more than 90% of the total pores. Therefore, the present invention uses total porosity to replace the organic pore volume generated in the hydrocarbon generation and expulsion process.

[0054] Based on the above source rock evolution process, a characteristic parameter that can characterize the original organic matter abundance of Gulong shale oil is proposed, which is the sum of the volume content of residual organic matter in the current formation and the total porosity. The formula is as follows:

[0055]

[0056] Where: P is the characteristic parameter of original organic matter abundance, unit is %; Volume content of residual organic matter in the formation, in %; is the total porosity, in %.

[0057] Step 2: Experimental measurement of typical shale samples to calculate the volume and characteristic parameters of residual organic matter;

[0058] Eleven typical shale samples were selected for rock physics experimental measurements, geochemical measurements and physical property measurements to obtain rock physical parameters, residual organic carbon content and total porosity of the samples; the rock physical parameters include P-wave velocity, S-wave velocity, shale skeleton density, organic matter density, P-wave impedance, S-wave impedance, Poisson's ratio and Young's modulus; the measured residual organic carbon content was used to calculate the current residual organic matter volume content, and the formula is as follows:

[0059]

[0060] Where: is the volume content of residual organic matter, in %; ρ rock is the shale skeleton density, unit: g / cm 3 ρ om is the density of organic matter, in g / cm 3 ; k is the organic matter conversion coefficient, which is generally taken as 1.25; w TOC is the residual organic carbon content measured in shale samples, in %;

[0061] Based on the total porosity measured in the core and the present residual organic matter volume content calculated above, the characteristic parameter formula proposed in step 1 is used to calculate the characteristic parameter of the original organic matter abundance.

[0062] Step 3, sensitive elastic parameters are optimized and the prediction model of original organic matter abundance characteristic parameters is established;

[0063] Based on the original organic matter abundance characteristic parameters of the shale sample calculated in step 2 and the measured rock physical parameters, the rock physical parameters with the highest correlation coefficient are selected as the sensitive elastic parameters of the original organic matter abundance characteristic parameters through statistical intersection analysis, and the fitted intersection analysis equation is used as the prediction model of the original organic matter abundance characteristic parameters;

[0064] Figure 3-Figure 9 These are the cross plots of the original organic matter abundance characteristic parameters calculated from 11 typical shale samples of Gulong shale oil in the northern Songliao Basin and the measured rock physical parameters such as P-wave velocity, S-wave velocity, density, P-wave impedance, S-wave impedance, Poisson's ratio and Young's modulus. The horizontal axis is the rock physical parameters and the vertical axis is the original organic matter abundance characteristic parameters. It can be seen that the correlation coefficients between the original organic matter abundance characteristic parameters and the rock physical parameters such as P-wave velocity, S-wave velocity, density, P-wave impedance, S-wave impedance, Poisson's ratio and Young's modulus are 0.79, 0.65, 0.78, 0.83, 0.71, 0.32 and 0.75 respectively. The rock physical parameter with the highest correlation coefficient is P-wave impedance. Therefore, P-wave impedance is selected as the sensitive elastic parameter of the original organic matter abundance characteristic parameters of Gulong shale oil, and its fitted cross analysis equation is used as the prediction model of the original organic matter abundance characteristic parameters. The formula is as follows:

[0065] P = -1.87 × AI + 25.74

[0066] Where: P is the characteristic parameter of original organic matter abundance, unit is %; Al is the longitudinal wave impedance, unit is Gg·m -2 ·s -1 .

[0067] Step 4: Based on the seismic data, the post-stack seismic inversion technology is used to obtain the longitudinal wave impedance required for the shale oil original organic matter abundance characteristic parameter prediction model.

[0068] Step 5, substituting the longitudinal wave impedance obtained in step 4 into the original organic matter abundance characteristic parameter prediction model in step 3, calculating the original organic matter abundance characteristic parameters, reflecting the variation law of the original organic matter abundance, and evaluating the hydrocarbon generation capacity of the shale formation.

[0069] Based on the actual seismic data of the work area, the P-wave impedance was obtained by using the post-stack seismic inversion technology. At the same time, the original organic matter abundance characteristic parameters were calculated in combination with the established prediction model of the original organic matter abundance characteristic parameters, reflecting the hydrocarbon generation capacity of the shale formation.

[0070] Fig.10 This is the prediction result of the characteristic parameters of original organic matter abundance in Well A. The ordinate is the seismic reflection time, and the abscissa is the seismic data line number. The color range displayed in Well A is the original organic matter abundance interpreted by well logging after core calibration, and the rest of the area is the predicted characteristic parameters of original organic matter abundance. It can be seen that the change trend of the predicted characteristic parameters of original organic matter abundance is consistent with that of the original organic matter abundance interpreted by well logging, and the agreement is good, indicating that the prediction result of the characteristic parameters of original organic matter abundance is reliable. Fig.11 It is a plane diagram of characteristic parameters of original organic matter abundance of Q2 oil layer. It can be seen that the source rock in the north is of better quality, has greater organic matter abundance and stronger hydrocarbon generation capacity than that in the south. In addition, near well A, horizontal well D was deployed toward the north with Q2 oil layer as the target layer. The oil test obtained high-yield industrial oil flow and the test production was stable, which further confirmed the feasibility and reliability of the quantitative characterization and prediction method of original organic matter abundance in high-mature shale formations proposed in the present invention.

Claims

1. A method for quantitatively characterizing and predicting the abundance of original organic matter in highly mature shale formations, characterized by: The steps include: Step 1: Based on the nature of source rock evolution, characteristic parameters of original organic matter abundance that can characterize high-mature shale formations are proposed; Step 2: Conduct rock physics experimental measurements, geochemical measurements and physical property measurements on shale samples to obtain rock physical parameters, residual organic carbon content and total porosity, and calculate the current residual organic matter volume content and original organic matter abundance characteristic parameters; Step 3, performing intersection analysis on the rock physical parameters of the shale sample and the original organic matter abundance characteristic parameters, optimizing the sensitive elastic parameters of the original organic matter abundance characteristic parameters, and establishing a prediction model for the original organic matter abundance characteristic parameters; Step 4, using post-stack seismic inversion technology to obtain the sensitive elastic parameters required by the original organic matter abundance characteristic parameter prediction model; Step 5, using the original organic matter abundance characteristic parameter prediction model in step 3 and the sensitive elastic parameters inverted in step 4 to calculate the original organic matter abundance characteristic parameters for use in evaluating the quality and hydrocarbon generation capacity of the shale formation source rock.

2. The method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation according to claim 1, characterized in that: Step 1: Based on the nature of source rock evolution, characteristic parameters that can characterize the original organic matter abundance of highly mature shale formations are proposed; The specific approach is to use the sum of the residual organic matter volume of the current formation and the pore volume of organic hydrocarbon generation to reflect the original formation organic matter volume content, and evaluate the shale organic matter abundance and hydrocarbon generation capacity; it is proposed that the characteristic parameter that can characterize the original organic matter abundance of highly mature shale formations is the sum of the residual organic matter volume content of the current formation and the total porosity, and the formula is as follows: Where: P is the characteristic parameter of original organic matter abundance, unit is %; is the volume content of residual organic matter, in %; is the total porosity, in %.

3. The method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation according to claim 1, characterized in that: Step 2: Conduct rock physics experimental measurements, geochemical measurements and physical property measurements on shale samples to obtain rock physical parameters, residual organic carbon content and total porosity, and calculate the residual organic matter volume content and original organic matter abundance characteristic parameters of the current formation; Specifically, the rock physical parameters include longitudinal wave velocity, transverse wave velocity, shale skeleton density, organic matter density, longitudinal wave impedance, transverse wave impedance, Poisson's ratio and Young's modulus; the original organic matter abundance characteristic parameters of the shale sample are calculated using step 1; the current residual organic matter volume content is calculated using the measured residual organic carbon content, and the formula is as follows: Where: is the volume content of residual organic matter, in %; ρ rock is the shale skeleton density, unit: g / cm 3 ; ρ om is the density of organic matter, in g / cm 3 ; k is the organic matter conversion coefficient, which is generally taken as 1.25; w TOC is the residual organic carbon content, in %.

4. The method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation according to claim 1, characterized in that: Step 3, performing intersection analysis on the rock physical parameters of the shale sample and the original organic matter abundance characteristic parameters, optimizing the sensitive elastic parameters of the original organic matter abundance characteristic parameters, and establishing a prediction model for the original organic matter abundance characteristic parameters; The specific method is that the rock physical parameter with the highest correlation coefficient between the original organic matter abundance characteristic parameter and P-wave velocity, S-wave velocity, density, P-wave impedance, S-wave impedance, Poisson's ratio and Young's modulus is P-wave impedance. Therefore, P-wave impedance is selected as the sensitive elastic parameter of the original organic matter abundance characteristic parameter, and its fitted intersection analysis equation is used as the prediction model of the original organic matter abundance characteristic parameter. The formula is as follows: P = -1.87 × AI + 25.74 Where: P is the characteristic parameter of original organic matter abundance, unit is %; Al is the longitudinal wave impedance, in Gg·m -2 ·s -1 .

5. The method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation according to claim 1, characterized in that: Step 4, using post-stack seismic inversion technology to obtain the sensitive elastic parameters required by the original organic matter abundance characteristic parameter prediction model; The specific approach is to use post-stack seismic inversion technology based on seismic data to obtain the sensitive elastic parameter required for the original organic matter abundance characteristic parameter prediction model, which is the longitudinal wave impedance Al.

6. The method for quantitatively characterizing and predicting the original organic matter abundance of a highly mature shale formation according to claim 1, characterized in that: Step 5, using the original organic matter abundance characteristic parameter prediction model in step 3 and the sensitive elastic parameters inverted in step 4 to calculate the original organic matter abundance characteristic parameters for use in evaluating the quality and hydrocarbon generation capacity of the shale formation source rock; The specific method is to substitute the longitudinal wave impedance Al obtained in step 4 into the original organic matter abundance characteristic parameter prediction model in step 3, calculate the original organic matter abundance characteristic parameters, reflect the change law of high-quality source rocks, and realize the quantitative description of the hydrocarbon generation capacity of shale formations.

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