Identification and Thickness Prediction Methods for Grading and Evaluation of High- to Overmature Marine Source Rocks

Abstract

This invention relates to a method for identifying and predicting the thickness of highly-to-overmature marine source rocks, determining the lower limit of total organic carbon (TOC) content; using this lower limit as a boundary, clarifying the electrical distribution characteristics of carbonate mudstones with TOC content greater than the lower limit, mudstones with TOC content greater than the lower limit, and mudstones with TOC content less than the lower limit; and then constructing a well logging quantitative identification scale. This allows for the determination of the thickness of carbonate mudstones with TOC content greater than the lower limit. This invention effectively solves the key problem of often missing the distribution intervals of some high TOC samples in the evaluation of the hydrocarbon generation potential of highly-to-overmature marine source rocks.

Description

Technical Field

[0001] This invention relates to the fields of geophysics and geochemistry, specifically to a method for identifying and predicting the thickness of highly-to-overmature marine source rocks in a classification and evaluation process. Background Technology

[0002] In evaluating the hydrocarbon generation potential of highly-to-overmature marine source rocks (Ro>1.3%), organic matter abundance (i.e., total organic carbon content, TOC) is a recognized core indicator. This is because, in the highly-to-overmature stage, traditional evaluation methods relying on geochemical experiments using core samples (such as chloroform bitumen "A", hydrocarbon generation potential S1+S2, total hydrocarbons HC, hydrogen index HI, etc.) become ineffective due to the large amount of hydrocarbon expulsion from organic matter and the influence of thermal maturity, resulting in significantly reduced or lost indicative values. Previous studies have shown that the residual total organic carbon content (TOC) value can relatively stably reflect the enrichment degree of original organic matter (the material basis for hydrocarbon generation), becoming a key parameter for evaluating the hydrocarbon generation capacity of source rocks at this stage. A TOC content ≥0.5% in mudstone is generally considered the lower limit standard for commercially viable source rocks. However, the TOC value obtained based on sparse core data is insufficient to characterize its spatial heterogeneity, and cannot meet the exploration requirements for accurate prediction of the effective thickness and volume of source rocks. Therefore, this patent aims to break through traditional limitations and explore a new method for predicting the thickness of marine source rocks with relatively high total organic carbon (TOC) content based on high-precision well logging data constraints.

[0003] Unlike the relatively homogeneous mudstone and shale source rocks developed in deep-water marine basins, carbonate platform facies source rocks exhibit significant lithological heterogeneity. This facies zone commonly features thin interbedded layers of multiple lithologies. The main lithologies include effective source rocks with hydrocarbon generation potential (such as dolomitic mudstone and marl / lime mudstone) and ineffective interlayers with low total organic carbon (TOC) or no hydrocarbon generation capacity (such as limestone and dolomite). This complex lithological combination leads to blurred or even invalidated characteristics of conventional well logging responses (such as natural gamma ray GR, sonic transit time AC, and density DEN). Specifically, it is difficult to effectively distinguish lithologies with similar natural gamma ray GR responses but significant differences in TOC (e.g., mudstone with high natural gamma ray GR and low natural gamma ray TOC versus effective dolomitic mudstone), and it is even more difficult to accurately define the boundary locations of TOC variations within thin interbedded layers.

[0004] Against this backdrop, the classification and evaluation of marine source rocks (i.e., the thickness evaluation of argillaceous carbonate source rocks with different total organic carbon (TOC) contents) is crucial, especially in carbonate platform facies with complex lithological heterogeneity. The classification and evaluation of marine source rocks is a core prerequisite for accurately identifying effective source rocks and quantifying their effective thickness. It directly controls the accuracy of spatial distribution characterization of source rocks and prediction of hydrocarbon generation volume, constituting a key geological basis for subsequent oil and gas resource evaluation and exploration deployment decisions. Addressing the traditional bottlenecks in evaluating the hydrocarbon generation potential of highly-to-overmature marine source rocks and the technical challenges posed by the complex lithology of carbonate platform facies, this patent proposes a classification and evaluation method for highly-to-overmature marine source rocks based on a high-precision well logging data model. The aim is to establish a high-precision, continuous technical system for predicting the spatial distribution characteristics (especially key effective source rocks) of the thickness of marine argillaceous carbonate source rocks with different TOC contents in complex lithological zones within carbonate platforms. Summary of the Invention

[0005] This invention aims to construct an efficient and accurate method for classifying and evaluating hydrocarbon source rocks and predicting their thickness, based on a high-precision well logging data model and integrating multi-source geophysical and geochemical information.

[0006] The technical solution of this invention is as follows:

[0007] (i) This invention proposes an identification method for the classification and evaluation of highly-to-over-mature marine source rocks.

[0008] A method for identifying highly-to-overmature marine source rocks in a classification and evaluation process is as follows:

[0009] Determine the lower limit of total organic carbon (TOC) content in the high- to over-mature marine source rocks of the target stratigraphy in the study area. 下限 ;

[0010] The lithology of the high- to over-mature marine source rock development section of the target stratigraphy in the study area was determined and denoted as carbonate mudstone;

[0011] The lower limit of total organic carbon (TOC) 下限 As a boundary, the total organic carbon content (TOC) is clearly defined as greater than the lower limit of the total organic carbon content (TOC). 下限 Carbonate mudstone, total organic carbon (TOC) content > lower limit of total organic carbon (TOC) content. 下限 The mudstone and the total organic carbon content (TOC) < the lower limit of total organic carbon (TOC) 下限 Electrical distribution characteristics of mudstone;

[0012] The electrical distribution characteristics specifically include longitudinal wave impedance (IMP), natural gamma (GR), and density (DEN).

[0013] Based on the aforementioned electrical distribution characteristics, a three-dimensional cross-sectional diagram consisting of longitudinal wave impedance (IMP), natural gamma ray (GR), and density (DEN) is constructed as a quantitative identification template for well logging.

[0014] This also includes, based on the total organic carbon content (TOC) being greater than the lower limit of total organic carbon content (TOC). 下限 Carbonate mudstone, total organic carbon (TOC) content > lower limit of total organic carbon (TOC) content. 下限 The mudstone and the total organic carbon content (TOC) < the lower limit of total organic carbon (TOC) 下限 The electrical distribution characteristics of mudstone were analyzed to obtain the distribution range of longitudinal wave impedance (IMP), natural gamma ray (GR), and density (DEN) of marine source rocks of different lithologies. Then, a three-dimensional cross-sectional diagram composed of longitudinal wave impedance (IMP), natural gamma ray (GR), and density (DEN) was constructed.

[0015] The lower limit of total organic carbon (TOC) content (TOC) 下限 The specific method for obtaining the total organic carbon (TOC) content is as follows: A sample well (Well A) from the target stratigraphic layer in the study area is taken. The lithology of sample well A is then precisely reconstructed. Using the reconstructed electrical characteristics of sample well A as a template, the remaining wells in the target stratigraphic layer of the study area are calibrated. This allows for the acquisition of the total organic carbon (TOC) content of marine source rock samples from all wells in the target stratigraphic layer of the study area. The average value of this average is taken as the lower limit of the total organic carbon (TOC) content. 下限 .

[0016] The selection rule for the marine source rock development section is as follows: by using the total organic carbon (TOC) content of marine source rock samples from all wells in the target strata of the study area, the lithology of the high-to-overmature marine source rock development section in the target strata of the study area is determined to be carbonate mudstone; then, based on the well logging curve characteristics of the carbonate mudstone in the target strata of the study area, the corresponding area is selected as the marine source rock development section on the comprehensive columnar section of the electrical characteristics of the marine source rocks in the target strata of the study area.

[0017] The comprehensive columnar section of electrical characteristics of marine source rocks in the target stratigraphic layer of the study area includes natural gamma (GR), deep lateral resistivity (RLLD), shallow lateral resistivity (RLLS), acoustic transit time (AC), and density (DEN).

[0018] (ii) This invention proposes a thickness prediction method.

[0019] A thickness prediction method, based on the aforementioned identification method for the classification and evaluation of high- to overmature marine source rocks, is characterized by obtaining the maximum P-wave impedance (IMP) of carbonate mudstone through the electrical distribution characteristics of carbonate mudstone; performing P-wave impedance (IMP) inversion on all wells in the target stratigraphic group of the study area; and, based on the three-dimensional intersection map, defining the portion of the inversion profile where the P-wave impedance (IMP) is less than the maximum P-wave impedance (IMP) of carbonate mudstone as the lower limit of the total organic carbon (TOC) content (TOC). 下限 The distribution range of carbonate mudstones was determined based on the inversion profile, and the total organic carbon content (TOC) of the target strata in the study area was determined to be greater than the lower limit of the total organic carbon content (TOC). 下限 The thickness of the carbonate mudstone.

[0020] The total organic carbon (TOC) content of all wells in the target stratigraphic unit of the study area must be greater than the lower limit of TOC. 下限 Kriging interpolation was performed on the thickness of the carbonate mudstone to obtain a total organic carbon content (TOC) greater than the lower limit of TOC. 下限 A planar distribution map of the thickness of carbonate mudstone.

[0021] The technical advantages of this invention are as follows:

[0022] 1. This invention effectively solves the key problem in the evaluation of hydrocarbon generation potential of high-to-overmature marine source rocks, where the commonly used arithmetic mean of total organic carbon (TOC) content in source rocks often misses the distribution of some high TOC samples.

[0023] 2. This invention clarifies the lower limit of total organic carbon (TOC) content in the high-to-overmature marine source rocks of the target stratigraphic layer in the study area. 下限 And based on the above-mentioned total organic carbon (TOC) lower limit value (TOC) 下限 A logging quantitative identification scale consisting of longitudinal wave impedance (IMP), natural gamma ray (GR), and density (DEN) was constructed as the boundary.

[0024] 3. In the past, the evaluation of marine source rocks was generally carried out by calculating the thickness of dark mudstone or analyzing the total organic carbon (TOC) contour maps in dark mudstone, which only evaluated the mudstone thickness or the distribution of TOC, without comprehensively reflecting the information on the relationship between TOC and source rock thickness. The purpose of this invention is to construct this logging quantitative identification version to obtain a TOC value greater than the lower limit of TOC. 下限 The thickness distribution of carbonate mudstone, where the total organic carbon content (TOC) is greater than the lower limit of total organic carbon content (TOC). 下限 The thickness map of carbonate mudstone includes both the lower limit of total organic carbon (TOC) and the TOC value. 下限The thickness information of the carbonate mudstone also includes the lower limit of total organic carbon (TOC). 下限 Information on the total organic carbon (TOC) content in carbonate mudstone;

[0025] 4. Using the constructed logging quantitative identification template as a constraint, longitudinal wave impedance IMP inversion was performed, yielding a total organic carbon content (TOC) greater than the lower limit of TOC. 下限 The vertical distribution characteristics of carbonate mudstone were determined; consequently, the total organic carbon content (TOC) in the study area was found to be greater than the lower limit of TOC. 下限 A vertical thickness distribution map of carbonate mudstone; based on this, kriging interpolation was performed to obtain a total organic carbon content (TOC) greater than the lower limit of TOC. 下限 A planar distribution map of the thickness of carbonate mudstone. Attached Figure Description

[0026] Figure 1 This is a comprehensive organic geochemical columnar section of the target stratigraphic layer for well A.

[0027] Figure 2 This is a histogram of total organic carbon (TOC) content in the marine source rocks of the target stratigraphic layer in the study area.

[0028] Figure 3 This is a comprehensive columnar section showing the electrical characteristics of the marine source rocks in the target strata of Well B.

[0029] Figure 4 This is a comprehensive columnar section showing the electrical characteristics of marine source rocks in the target strata of well C.

[0030] Figure 5 This is an electrical characteristic diagram.

[0031] Figure 6 This is a quantitative identification tool for marine hydrocarbon source rocks in the target stratigraphic layer of the study area.

[0032] Figure 7 The waveform impedance inversion profile of dolomitic mudstone with a total organic carbon (TOC) content > 0.22% in the target stratigraphic layer of the study area.

[0033] Figure 8 This is a planar distribution map of the thickness of dolomitic mudstone with a total organic carbon (TOC) content > 0.22% in the target stratigraphic layer of the study area. Detailed Implementation

[0034] Specific Experimental Case 1

[0035] A method for identifying highly-to-overmature marine source rocks in a classification and evaluation process is as follows:

[0036] Step 1: Select Well A, the target stratigraphic sample well in the study area. Based on comprehensive logging, well logging curves, and core data, conduct detailed lithological relocation to distinguish the dolomitic mudstone / mudstone stratigraphic interface. Perform systematic and intensive sampling on Well A, with a sampling interval of 1-2 m. Conduct experimental analysis of geochemical parameters such as total organic carbon (TOC), hydrocarbon generation potential (S1+S2), total hydrocarbons (HC), depth (H), deep lateral resistivity (RLLD), and hydrogen index (HI). Construct a comprehensive organic geochemical columnar section of the target stratigraphic section from Well A. (See attached image) Figure 1 .

[0037] Step 2: Select multiple wells from the target stratigraphic unit in the study area, excluding sample well A. Based on the Total Organic Carbon (TOC) data from these wells, plot a TOC histogram of the marine source rocks in the target stratigraphic unit of the study area. (See attached image) Figure 2 ;Depend on Figure 2 It can be seen that the total organic carbon (TOC) content exhibits a unimodal skewed distribution, with an average value of 0.22%, which is the lower limit of the total organic carbon (TOC) content. 下限 It is 0.22%.

[0038] Step 3: Select all wells in the target stratigraphic region of the study area except for sample well A, and perform conventional logging data analysis on them (including natural gamma ray GR, resistivity RLLD, sonic transit time AC, and density DEN, etc.). Draw a comprehensive columnar section of the electrical characteristics of marine source rocks in the target stratigraphic region of the study area. Taking wells B and C as examples, Figure 3 This is a comprehensive columnar section showing the electrical characteristics of the marine source rocks in the target strata of well B. Figure 4 This is a comprehensive columnar section showing the electrical characteristics of marine source rocks in the target strata of well C.

[0039] As shown in the sample well A, the marine source rocks in the study area exhibit a large natural gamma ray GR in the well logging curves. Based on this characteristic, the increasing natural gamma ray GR sections in wells B and C, i.e., the sections with a large natural gamma ray GR distribution, are analyzed. Figure 3 and Figure 4 The area marked by the black dashed box in the middle represents the section where marine source rocks are developed.

[0040] Combined with the aforementioned determined lower limit of total organic carbon (TOC) 下限 0.22%. Electrical characteristics analysis was performed on key logging curves (natural gamma ray GR, sonic transit time AC, resistivity RLLD, and density DEN) of the marine source rocks in the target strata of the study area. (See attached data). Figure 5 ;

[0041] Specifically, this includes dolomitic mudstone with a total organic carbon (TOC) content > 0.22%, mudstone with a TOC content > 0.22%, and mudstone with a TOC content < 0.22%. Dolomitic mudstone with a TOC content > 0.22% exhibits high gamma, high acoustic, high density, and low resistivity characteristics in its electrical properties. Mudstone with a TOC content > 0.22% exhibits medium gamma, high resistivity, medium density, and low acoustic characteristics in its electrical properties. Mudstone with a TOC content < 0.22% exhibits medium acoustic, high resistivity, low density, and low gamma characteristics in its electrical properties.

[0042] It can be seen that dolomitic mudstone with a total organic carbon (TOC) content > 0.22%, mudstone with a TOC content > 0.22%, and mudstone with a TOC content < 0.22% have significant statistical differences in electrical characteristics. This provides a basis for establishing a high-precision well logging data model for highly-permature marine source rocks.

[0043] based on Figure 5 Electrical analysis of marine source rocks from multiple wells in the target strata of the study area was conducted to clarify the distribution ranges of total organic carbon (TOC) content, natural gamma ray (GR), density (DEN), and longitudinal impedance (IMP) of marine source rocks with different lithologies.

[0044] Dolomitic mudstone with a total organic carbon (TOC) content > 0.22% has a natural gamma ray (GR) frequency of 140-170 API and a density (DEN) frequency of 2.73-2.785 g / cm³. 3 The longitudinal wave impedance (IMP) is less than 14800 (m / s·g / cm³); that is, the maximum longitudinal wave impedance (IMP) of dolomitic mudstone with a total organic carbon content (TOC) > 0.22% is 14800 (m / s·g / cm³).

[0045] Mudstone with a total organic carbon (TOC) content > 0.22% has a natural gamma ray (GR) frequency of 100-128 API and a density (DEN) frequency of 2.68-2.83 g / cm³. 3 The longitudinal wave impedance (IMP) is between 14557 and 17000 (m / s·g / cm³).

[0046] Mudstone with a total organic carbon (TOC) content of <0.22% has a natural gamma ray (GR) frequency of 68-130 API and a density (DEN) frequency of 2.68-2.8 g / cm³. 3 The longitudinal wave impedance (IMP) is between 14100 and 17400 (m / s·g / cm³).

[0047] Based on this constraint, a three-dimensional intersection map consisting of longitudinal wave impedance (IMP), natural gamma ray (GR), and density (DEN) is constructed as a quantitative identification template for well logging. (See...) Figure 6In the figure, triangles represent dolomitic mudstone with a total organic carbon (TOC) content > 0.22%, rhombuses represent mudstone with a TOC content > 0.22%, and ellipses represent mudstone with a TOC content < 0.22%. It can be seen that this logging quantitative identification scale can easily identify the distribution of dolomitic mudstone and mudstone with different TOC contents, thereby realizing the hierarchical identification of high- to over-mature marine source rocks.

[0048] Specific Experimental Case 2

[0049] A thickness prediction method is as follows: Using the established well logging quantitative identification template as a constraint, the P-wave impedance (IMP) inversion is performed on sample well A. The portion of the inversion profile where the P-wave impedance (IMP) < 14,800 (m / s·g / cm³) represents the distribution range of dolomitic mudstone with a total organic carbon (TOC) content > 0.22%. (See...) Figure 7 Based on this inversion profile, the thickness of dolomitic mudstone with a total organic carbon (TOC) content > 0.22% in sample A well can be determined. Similarly, the thickness of dolomitic mudstone in wells B, C, and others can be determined using the same method. Finally, kriging interpolation is performed on the thickness of dolomitic mudstone in multiple wells of the target strata in the study area, yielding a planar distribution map of the thickness of dolomitic mudstone with a TOC content > 0.22%, as shown in [reference needed]. Figure 8 .

Claims

1. A method for identifying a high-overmature marine source rock grading evaluation, characterized in that, The method is as follows: Determine the total organic carbon content TOC lower limit value TOC of the high-mature marine hydrocarbon source rock of the target layer system in the area to be studied 下限 ; Determine the lithology of the high-mature marine hydrocarbon source rock development section of the target layer system in the area to be studied, which is recorded as carbonate mudstone; with a total organic carbon content TOC below a lower limit value TOC 下限 as a limit, the total organic carbon content TOC is unambiguously greater than the lower limit value TOC 下限 of the carbonate rock mudstone, the total organic carbon content TOC is greater than the lower limit value TOC 下限 of the mudstone and the total organic carbon content TOC is less than the lower limit value TOC 下限 of the mudstone; The electrical distribution characteristics specifically include P-wave impedance IMP, natural gamma ray GR, and density DEN; Further, according to the above electrical distribution characteristics, a three-dimensional intersection map composed of P-wave impedance IMP, natural gamma ray GR, and density DEN is constructed as a quantitative identification version for well logging.

2. The method according to claim 1, wherein, Also included, according to the total organic carbon content TOC > total organic carbon content TOC lower limit value TOC 下限 carbonate mudstone, total organic carbon content TOC > total organic carbon content TOC lower limit value TOC 下限 mudstone and total organic carbon content TOC < total organic carbon content TOC lower limit value TOC 下限 The electrical distribution characteristics of the mudstone are obtained, the distribution ranges of the P-wave impedance IMP, the natural gamma ray GR and the density DEN of different lithology marine hydrocarbon source rocks are obtained, and a three-dimensional intersection diagram composed of the P-wave impedance IMP, the natural gamma ray GR and the density DEN is constructed.

3. The method according to claim 2, wherein the high-overmature marine source rock classification evaluation is characterized by, The total organic carbon content TOC lower limit value TOC 下限 The specific obtaining method is: taking a sample A well of a target layer system in a to-be-studied area, performing fine lithology homing on the sample A well, taking the homed electrical characteristics of the sample A well as a template, calibrating the remaining wells of the target layer system in the to-be-studied area, and then obtaining the total organic carbon content TOC of the marine hydrocarbon source rock samples in all the wells of the target layer system in the to-be-studied area, taking the average value as the total organic carbon content TOC lower limit value TOC 下限 .

4. The method according to claim 3, wherein the high-overmature marine source rock classification evaluation is characterized by, The selection rule of the marine hydrocarbon source rock development section is: through the total organic carbon content TOC of the marine hydrocarbon source rock samples in all wells of the target layer system in the area to be studied, it is determined that the lithology of the high-mature marine hydrocarbon source rock development section of the target layer system in the area to be studied is specifically carbonate mudstone; further, according to the well logging curve characteristics of the carbonate mudstone of the target layer system in the area to be studied, the corresponding area on the electrical property characteristic comprehensive columnar chart of the marine hydrocarbon source rock of the target layer system in the area to be studied is selected as the marine hydrocarbon source rock development section.

5. The method according to claim 4, wherein the high-overmature marine source rock classification evaluation is identified by, The electrical property characteristic comprehensive columnar chart of the marine hydrocarbon source rock of the target layer system in the area to be studied includes natural gamma ray GR, deep lateral resistivity RLLD, shallow lateral resistivity RLLS, acoustic time difference AC, and density DEN.

6. A method for predicting thickness, based on the identification method of the high-overmature marine source rock classification evaluation according to any one of claims 1-5, characterized in that, The maximum value of longitudinal wave impedance IMP of the carbonate rock argillite is obtained through the electrical distribution characteristics of the carbonate rock argillite; the longitudinal wave impedance IMP inversion is carried out on all wells of the target layer system in the research area; according to the three-dimensional intersection diagram, the part of the inversion profile in which the longitudinal wave impedance IMP is less than the maximum value of the longitudinal wave impedance IMP of the carbonate rock argillite is taken as the distribution range of the carbonate rock argillite with the total organic carbon content TOC greater than the lower limit value TOC of the total organic carbon content TOC 下限 ; the thickness of the carbonate rock argillite with the total organic carbon content TOC greater than the lower limit value TOC of the total organic carbon content TOC 下限 in the target layer system of the research area is determined according to the inversion profile.

7. The thickness prediction method of claim 6, wherein The total organic carbon content TOC of all wells in the target layer system of the study area is greater than the total organic carbon content TOC lower limit value TOC 下限 The thickness of the carbonate rock mudstone with the total organic carbon content TOC greater than the total organic carbon content TOC lower limit value TOC 下限 The thickness of the carbonate rock mudstone with the total organic carbon content TOC greater than the total organic carbon content TOC lower limit value TOC

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