Identification and thickness prediction method for grading evaluation of high-over mature marine hydrocarbon source rocks

Abstract

The invention relates to an identification and thickness prediction method for grading evaluation of high-over mature marine facies hydrocarbon source rocks. The method comprises the following steps: determining the lower limit value of the total organic carbon content TOC; with the lower limit value of the total organic carbon content TOC as a boundary, determining electrical distribution characteristics of carbonate mudstone with the total organic carbon content TOC larger than the lower limit value of the total organic carbon content TOC, mudstone with the total organic carbon content TOC larger than the lower limit value of the total organic carbon content TOC and mudstone with the total organic carbon content TOC smaller than the lower limit value of the total organic carbon content TOC; and constructing a logging quantitative identification quantity version. The total organic carbon content TOC is larger than the lower limit value of the total organic carbon content TOC. The method effectively solves the key problem that part of distribution layer sections of high total organic carbon (TOC) samples are missed in hydrocarbon generation potential evaluation of high-over mature marine hydrocarbon source rocks.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geophysics and geochemistry, and particularly relates to a method for identification and thickness prediction of high-mature and over-mature marine source rock grading evaluation. BACKGROUND

[0002] In the evaluation of the hydrocarbon generation potential of high-mature and over-mature marine source rock (Ro>1.3%), the evaluation of organic matter abundance (i.e. total organic carbon content TOC) is a recognized core index. This is because at the high-mature and over-mature stage, the traditional evaluation method relying on core samples to carry out geochemical experiments (such as chloroform bitumen "A", hydrocarbon generation potential S1+S2, total hydrocarbon HC, hydrogen index HI, etc.) is invalid due to the influence of a large amount of organic matter expulsion and thermal maturity, and the index value is significantly reduced or loses its indication. Previous studies have shown that the residual total organic carbon content TOC value can relatively stably reflect the enrichment degree of original organic matter (hydrocarbon generation material basis), and has become a key parameter for evaluating the hydrocarbon generation capacity of source rock at this stage. Generally, total organic carbon content TOC≥0.5% of mudstone is regarded as the lower limit standard of commercial source rock. However, the total organic carbon content TOC value obtained based on sparse core data is difficult to depict the spatial heterogeneity, and it is even more difficult to meet the exploration demand for accurate prediction of the thickness and volume of effective source rock. Therefore, this patent aims to break through the traditional limitations and explore a new method for predicting the thickness of marine source rock with relatively high total organic carbon content TOC based on high-precision logging data constraints.

[0003] Unlike the relatively homogeneous shale source rock developed in deepwater marine basins, carbonate platform facies source rock shows significant lithologic heterogeneity. This facies generally develops a multi-lithology thin interbedded structure, including effective source rock with hydrocarbon potential (such as dolomitic mudstone, marl / lime mudstone) and ineffective interlayer with low total organic carbon content TOC or no hydrocarbon generation capacity (such as limestone and dolomite). This complex lithologic combination leads to ambiguous or even ineffective conventional logging responses (such as natural gamma ray GR, acoustic time AC, density DEN), which is specifically manifested in the difficulty in effectively distinguishing lithologies with similar natural gamma ray GR responses but significantly different total organic carbon content TOC (for example, high natural gamma ray GR low natural gamma ray TOC mudstone and effective dolomitic mudstone), and even more difficult to accurately define the boundary position of the change of total organic carbon content TOC in thin interbeds.

[0004] In this context, the hierarchical evaluation of marine source rocks (i.e. the thickness evaluation of argillaceous carbonate source rocks with different total organic carbon content TOC) is crucial, especially in the carbonate platform facies with complex lithological heterogeneity. The hierarchical evaluation of marine source rocks is the core prerequisite for accurately identifying effective source rocks and quantifying their effective thickness, directly controlling the accuracy of the spatial distribution of source rocks and the prediction of hydrocarbon volume, and constituting the key geological basis for subsequent oil and gas resource evaluation and exploration deployment decisions. In view of the traditional bottleneck of high-mature marine source rock hydrocarbon potential evaluation and the technical challenges brought by complex lithology in carbonate platform facies, the present invention proposes a high-precision logging data model constrained high-mature marine source rock hierarchical evaluation and thickness prediction method, aiming to establish a high-precision, continuous prediction technology system for the spatial distribution characteristics of marine argillaceous carbonate source rock thickness in complex lithology areas of carbonate platforms (especially key effective source rocks) with different total organic carbon content TOC. SUMMARY

[0005] The present invention aims to establish an efficient and accurate source rock hierarchical evaluation and thickness prediction method based on high-precision logging data models, integrating multi-source geophysical and geochemical information.

[0006] The technical solution of the present invention is as follows: (I) The present invention proposes a method for identifying the hierarchical evaluation of high-mature marine source rocks.

[0007] A method for identifying the hierarchical evaluation of high-mature marine source rocks, the method being as follows: Determine the total organic carbon content TOC lower limit value TOC 下限 of the high-mature marine source rocks of the target layer system in the area to be studied; Determine the lithology of the high-mature marine source rock development section in the area to be studied, denoted as carbonate rock mudstone; Take the total organic carbon content TOC lower limit value TOC 下限 as the boundary to clearly define the electrical distribution characteristics of carbonate rock mudstone with total organic carbon content TOC > total organic carbon content TOC lower limit value TOC 下限 , mudstone with total organic carbon content TOC > total organic carbon content TOC lower limit value TOC 下限 , and mudstone with total organic carbon content TOC < total organic carbon content TOC lower limit value TOC 下限 ; The electrical distribution characteristics specifically include longitudinal wave impedance IMP, natural gamma ray GR, and density DEN; Further, according to the above electrical distribution characteristics, a three-dimensional intersection diagram composed of longitudinal wave impedance IMP, natural gamma ray GR, and density DEN is constructed as a logging quantitative identification template.

[0008] 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.

[0009] The lower limit of total organic carbon (TOC) content. 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 .

[0010] 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.

[0011] 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).

[0012] (ii) This invention proposes a thickness prediction method.

[0013] 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.

[0014] 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.

[0015] The technical advantages of this invention are as follows: 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. 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. 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; 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thickness plan distribution of carbonatite argillutite. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 comprehensive column chart of organic geochemistry for the target layer system of sample well A.

[0017] Figure 2 histogram of total organic carbon content TOC of marine hydrocarbon source rock of the target layer system in the area to be studied.

[0018] Figure 3 comprehensive column chart of electrical characteristics of marine hydrocarbon source rock of the target layer system of well B.

[0019] Figure 4 comprehensive column chart of electrical characteristics of marine hydrocarbon source rock of the target layer system of well C.

[0020] Figure 5 electrical characteristics chart.

[0021] Figure 6 logging quantitative identification scale for marine hydrocarbon source rock of the target layer system in the area to be studied.

[0022] Figure 7 impedance inversion profile of dolomitic mudstone with total organic carbon content TOC > 0.22% in the target layer system in the area to be studied.

[0023] Figure 8 thickness plan distribution chart of dolomitic mudstone with total organic carbon content TOC > 0.22% in the target layer system in the area to be studied. DETAILED DESCRIPTION

[0024] Specific experimental case 1 A method for grading evaluation of high-over mature marine hydrocarbon source rock, the method is as follows: Step 1: Select sample well A in the target layer system of the area to be studied, and comprehensively record well logging, logging curve and core data, carry out fine lithology orientation, and distinguish dolomitic mudstone / mudstone layer interface; carry out systematic dense sampling on sample well A, sampling interval 1-2m, complete experimental analysis of total organic carbon content TOC, hydrocarbon generation potential S1+S2, total hydrocarbon HC, depth H, deep lateral resistivity RLLD and hydrogen index HI and other geochemical parameters, and construct comprehensive column chart of organic geochemistry for the target layer system of sample well A, see Figure 1 .

[0025] Step 2: Select multiple wells in the target layer system of the area to be studied except sample well A, based on total organic carbon content TOC data of the multiple wells, draw histogram of total organic carbon content TOC of marine hydrocarbon source rock of the target layer system in the area to be studied, see Figure 2 ; from Figure 2It can be seen that the total organic carbon content TOC is unimodal skew distribution, the average value is 0.22%, that is, the total organic carbon content TOC lower limit value TOC 下限 0.22%.

[0026] Step 3: Select the remaining wells in the target layer system of the study area except for the sample A well, and analyze the conventional logging data (including natural gamma GR, resistivity RLLD, acoustic time difference AC and density DEN, etc.) thereof, draw the comprehensive column chart of the electrical characteristics of the marine hydrocarbon source rock in the target layer system of the study area, take wells B and C as examples, Figure 3 the comprehensive column chart of the electrical characteristics of the marine hydrocarbon source rock in the target layer system of well B, Figure 4 and the comprehensive column chart of the electrical characteristics of the marine hydrocarbon source rock in the target layer system of well C.

[0027] It can be seen from the sample A well that the marine hydrocarbon source rock in the study area has a large natural gamma GR on the logging curve. According to this feature, by analyzing the increasing segment of the natural gamma GR curve in wells B and C, that is, the layer segment with a larger natural gamma GR distribution range (the black dotted box in Figure 3 and Figure 4 ), this area represents the development segment of the marine hydrocarbon source rock; Combined with the total organic carbon content TOC lower limit value TOC 下限 0.22% determined in the foregoing, the electrical characteristics of the key logging curves such as natural gamma GR, acoustic time difference AC, resistivity RLLD and density DEN of the marine hydrocarbon source rock in the target layer system of the study area are analyzed, see Figure 5 ; Specifically, dolomitic mudstone with total organic carbon content TOC>0.22%, mudstone with total organic carbon content TOC>0.22% and mudstone with total organic carbon content TOC<0.22%; dolomitic mudstone with total organic carbon content TOC>0.22% has the characteristics of high gamma, high acoustic wave, high density and low resistivity; mudstone with total organic carbon content TOC>0.22% has the characteristics of medium gamma, high resistivity, medium density and low acoustic wave; mudstone with total organic carbon content TOC<0.22% has the characteristics of medium acoustic wave, high resistivity, low density and low gamma.

[0028] It can be seen that dolomitic mudstone with total organic carbon content TOC>0.22%, mudstone with total organic carbon content TOC>0.22% and mudstone with total organic carbon content TOC<0.22% have great statistical differences in electrical characteristics, which provides a basis for the establishment of a high-precision logging data model of high-over mature marine hydrocarbon source rock.

[0029] Based on Figure 5Based on the electrical analysis of marine hydrocarbon source rocks in the target layer system of the study area, the distribution ranges of GR, DEN and IMP of different TOC and different lithology marine hydrocarbon source rocks are determined: Dolomitic mudstone with TOC>0.22%: GR main frequency of 140-170 API, DEN main frequency of 2.73-2.785 g / cm 3 , and IMP less than 14800 (m / s·g / cm³); that is, the maximum value of IMP of dolomitic mudstone with TOC>0.22% is 14800 (m / s·g / cm³).

[0030] Mudstone with TOC>0.22%: GR main frequency of 100-128 API, DEN main frequency of 2.68-2.83 g / cm 3 , and IMP between 14557 and 17000 (m / s·g / cm³); Mudstone with TOC<0.22%: GR main frequency of 68-130 API, DEN main frequency of 2.68-2.8 g / cm 3 , and IMP between 14100 and 17400 (m / s·g / cm³).

[0031] Based on this constraint, a three-dimensional crossplot composed of IMP-GR-DEN is constructed as a quantitative logging identification chart, as shown in Figure 6 ; in the figure, the triangle represents dolomitic mudstone with TOC>0.22%, the rhombus represents mudstone with TOC>0.22%, and the oval represents mudstone with TOC<0.22%. It can be seen that the distribution of dolomitic mudstone and mudstone with different TOC can be easily identified in the quantitative logging identification chart, and the classification identification of high-over mature marine hydrocarbon source rocks is realized.

[0032] Specific experimental case 2 A thickness prediction method, the method is as follows: based on the above established quantitative logging identification chart, the IMP inversion of sample A well is carried out, the part of the inversion profile with IMP<14,800 (m / s·g / cm³) is the distribution range of dolomitic mudstone with TOC>0.22%, as shown in Figure 7, according to the inversion profile, the thickness of dolomitic mudstone with TOC > 0.22% in sample A well can be determined. By analogy, the thickness of dolomitic mudstone in B well, C well and other wells can be determined by the same method. Finally, the thickness of dolomitic mudstone in the target layer system of the study area is kriged, and the thickness distribution map of dolomitic mudstone with TOC > 0.22% is obtained, as shown in Figure 8 .

Claims

1. A method for identifying highly-to-overmature marine source rocks in a classification and evaluation process, characterized in that, The method is as follows: 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 ; 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; 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; The electrical distribution characteristics specifically include longitudinal wave impedance (IMP), natural gamma (GR), and density (DEN). 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.

2. The identification method for the classification and evaluation of highly-to-overmature marine source rocks according to claim 1, characterized in that, 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.

3. The identification method for the classification and evaluation of highly-to-overmature marine source rocks according to claim 2, characterized in that, The lower limit of total organic carbon (TOC) content. 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 .

4. The identification method for the classification and evaluation of highly-to-overmature marine source rocks according to claim 3, characterized in that, 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.

5. The identification method for the classification and evaluation of highly-overmature marine source rocks according to claim 4, characterized in that, 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).

6. A thickness prediction method, based on the identification method for the classification and evaluation of highly-to-overmature marine source rocks as described in claims 1-5, characterized in that, The maximum P-wave impedance (IMP) of carbonate mudstone was obtained by analyzing its electrical distribution characteristics. IMP inversion was performed on all wells in the target stratigraphic sequence of the study area. Based on the three-dimensional intersection map, the portion of the inversion profile where the P-wave impedance IMP is less than the maximum value of the carbonate mudstone P-wave impedance IMP was taken 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.

7. The thickness prediction method according to claim 6, characterized in that, 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.

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