Method for drawing planar distribution map of continental shale facies combination based on well-seismic combination
By combining well-seismic methods and utilizing sonic transit time and density logging curves with seismic attribute optimization, the problem of planar distribution of lithofacies assemblages in shale oil and gas development has been solved, enabling rapid and accurate identification of lithofacies assemblages. This method is applicable to drawing planar distribution maps of lithofacies assemblages in continental lacustrine basins.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA UNIV OF PETROLEUM (EAST CHINA)
- Filing Date
- 2026-03-09
- Publication Date
- 2026-06-12
AI Technical Summary
Existing technologies struggle to efficiently and accurately delineate the planar distribution of lithofacies assemblages in shale oil and gas development, especially in China's continental lacustrine basins where lithofacies types are complex and rapidly changing. Current methods rely on extensive core sampling and analysis, resulting in low efficiency.
A well-seismic combined approach was adopted to determine the lithofacies assemblage type by using sonic transit time and density logging curves. Combined with seismic attribute optimization and adjustment, a lithofacies assemblage planar distribution map was drawn, and data processing and matching were performed using ResForm and CorelDRAW software.
It enables rapid identification of lithofacies assemblages in uncored wells, improving the efficiency and accuracy of lithofacies assemblages classification, meeting the needs of shale oil and gas development, and is applicable to drawing planar distribution maps of lithofacies assemblages in continental lacustrine basins.
Smart Images
Figure CN122190743A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of shale oil and gas exploration and development technology, specifically involving a method for drawing a planar distribution map of continental shale lithofacies based on well-seismic combination. Background Technology
[0002] Since the commercial development of shale oil and gas, a surge in unconventional oil and gas exploration and development has swept across the world, with the proportion of shale oil and gas production increasing year by year. China is rich in shale oil and gas resources, with recoverable shale oil resources estimated at 322 × 10⁻⁶. 8 Shale oil and gas (BBL) ranks third in the world, after Russia and the United States. It is mainly distributed in continental lacustrine basins such as the Ordos Basin, Bohai Bay Basin, Junggar Basin, Songliao Basin, and Sichuan Basin. It has great development potential, and increasing the development of shale oil and gas has become an important measure for China to reduce its dependence on foreign energy.
[0003] Lithofacies, as the basic geological unit for studying mudstone and shale, is widely used in stratigraphic correlation, distribution prediction, and comprehensive evaluation of shale. However, in the actual production and development of shale oil in China, it is rare for a single lithofacies type to develop continuously; they generally appear as combinations of two or more lithofacies, exhibiting complex and rapid vertical changes. Compared to lithofacies, the developmental characteristics of lithofacies assemblages are the core basic evaluation unit that meets the needs of shale oil and gas development in China's continental lacustrine basins. Furthermore, the planar distribution of lithofacies assemblages is the prerequisite and foundation for this core evaluation unit to function effectively. Therefore, the planar distribution of lithofacies assemblages is crucial for the development of shale oil and gas in China's continental lacustrine basins.
[0004] In the patent application number CN202211510515.7, a TOC prediction model and a brittle mineral content calculation model were established based on well logging curves. After verifying and modifying the estimated values with the measured values, the lithofacies types were classified based on "TOC-mineral". A planar map of the predicted TOC and brittle mineral content was made. Furthermore, the planar distribution map of the lithofacies was drawn according to the lithofacies identification parameters of each lithofacies, combining the TOC and brittle mineral content distribution map and the single-well lithofacies map.
[0005] In the patent application number CN201711170899.1, the mineral composition content of shale samples was used to compile three-terminal maps of silica mineral content, carbonate mineral content, and clay mineral content. Planar distribution maps of organic matter, silica minerals, clay minerals, and carbonate minerals were also compiled. Based on the three-terminal maps and the planar distribution maps of organic matter, silica minerals, clay minerals, and carbonate minerals, the shale was classified into lithofacies. Finally, the four planar distribution maps were overlaid and intersected, and the planar distribution of shale lithofacies was determined according to the lithofacies classification criteria.
[0006] In the patent application CN201510404879.0, conventional three-porosity (acoustic, density, neutron) logging measurements of N core samples are obtained through steps such as thin section identification, X-ray diffraction analysis, and core repositioning. Then, the relative distance between the two parameters of conventional three-porosity logging is obtained. Based on the relative distance between the two parameters and the mineral composition of the N core samples, a quantitative relationship between the relative distance between the two parameters and the main mineral components of X-ray diffraction whole-rock analysis is obtained. Furthermore, a rock classification based on the relative distance between the two parameters is established, which can be applied to the lithology identification of logging in fine-grained sedimentary facies zones, enabling continuous lithology identification of formations without core samples.
[0007] The above techniques are only applicable to the classification and distribution of shale lithofacies types, and rely on a large number of core samples for analysis, which is labor-intensive. They are suitable for the classification of shale lithofacies in well sections with a large number of core samples, but are inefficient. Summary of the Invention
[0008] This invention provides a method for drawing a planar distribution map of continental shale lithofacies based on well-seismic analysis, comprising the following steps: (1) Determine the lithofacies assemblage type of the area to be tested A core well with abundant logging data is selected as a control well in the area to be tested. Based on its logging data, the lithofacies types developed in the area to be tested are determined. Based on the superposition relationship of the lithofacies types in the area, the lithofacies assemblage types existing in the area to be tested are further clarified. (2) Obtain the optimal boundary values of the sonic transit time and density logging curves. In the logging data of the control well, two logging curves, sonic transit time and density, are selected. The boundary values of the two logging curves are adjusted so that they intersect each other. When the D value of each layer in the vertical direction of the control well matches its lithofacies assemblage type, the boundary values of the sonic transit time logging curve and density logging curve at this time are recorded. (3) Determine the lithofacies assemblage type of each stratigraphic level in the uncored well. High-frequency stratigraphic framework division was performed on the uncored wells, and the acoustic wave and density of the uncored wells were measured to obtain the acoustic transit time logging curves and density logging curves. The boundary values of the acoustic transit time logging curves and density logging curves were set to the boundary values recorded in step (2) above, and the D value of each layer of the uncored wells was calculated to determine the lithofacies assemblage type of each layer. (4) Draw a lithofacies assemblage projection map Mark the lithofacies assemblages of each layer in all wells on the well location map to obtain the lithofacies assemblages projection map of each layer in the area to be tested; (5) Preliminary planar distribution map of lithofacies assemblage. Based on the plotted facies assemblages of each stratum, and in conjunction with the sedimentary environment and provenance, a preliminary planar distribution map of the facies assemblages of each stratum was drawn, thus obtaining the preliminary boundaries of the facies assemblages of each stratum on the planar distribution map of the facies assemblages; (6) Optimization of seismic attributes The seismic attributes of the area to be measured are matched with the lithofacies combination types of each layer determined in step (3) above. The seismic attribute with the best matching degree is used as the main reference seismic attribute for lithofacies plane mapping. (7) Correcting the boundaries of lithofacies assemblage types The seismic attributes selected in step (6) are overlaid with the lithofacies assemblage planar distribution map drawn in step (5) above; the lithofacies assemblage type boundaries are further adjusted so that the lithofacies assemblage type boundaries are further corrected on the basis of step (5) above, and finally the lithofacies assemblage planar distribution map of each layer is obtained.
[0009] In the above-mentioned method for drawing a planar distribution map of lithofacies, in step (1), the lithofacies types include felsic shale facies, dolomitic shale facies, mixed shale facies, clayey shale facies, sand-bearing shale facies, and tuff-bearing facies, etc. The lithofacies types of shale in different areas to be tested may be different. When classifying lithofacies types, they can be determined based on the well logging data of the area to be tested.
[0010] In the above method for drawing a planar distribution map of lithofacies, in step (1), the determination of the lithofacies assemblage type is based on the content of felsic and dolomitic substances as the basic principle for classification.
[0011] In the above method for drawing a planar distribution map of lithofacies, in step (1), the lithofacies types include felsic type, felsic interbedded carbonate type, mixed type, carbonate interbedded felsic type and carbonate type.
[0012] In the above method for drawing a planar distribution map of lithofacies, step (2) is performed in ResForm software; that is, the two logging curves of sonic transit time and density are imported into ResForm software, and the boundary values of the two logging curves are adjusted so that the D value of each layer conforms to its lithofacies combination type.
[0013] In the above method for drawing a planar distribution map of lithofacies, in step (2), the D value is the proportion of the thickness of felsic lithofacies in the thickness of its stratum; the thickness is the vertical thickness.
[0014] The following formula is established for determining the felsic facies in stratigraphic layers: ; ΔL represents the distance between the superimposed (overlapping) acoustic and density logging curves, L2 is the acoustic transit time curve, L1 is the density curve, ρ is the bulk density, which is the measured logging value read from the density logging curve, Δt is the acoustic transit time, which is the measured logging value read from the acoustic logging curve, ρ1 and ρ2 are density boundary values, and Δt1 and Δt2 are acoustic transit time boundary values. When ΔL>0, it indicates that the acoustic curve is on the right and the density curve is on the left, which means high acoustic wave and low density. This indicates that the content of felsic and clay minerals is relatively high, and it is regarded as felsic rock facies.
[0015] In the above method for drawing a planar distribution map of lithofacies, in step (2), the correspondence between the D value and the lithofacies type is as follows: felsic type, D > 80%; felsic interbedded carbonate type, 60% < D ≤ 80%; mixed type, 40% < D ≤ 60%; carbonate interbedded felsic type, 20% < D ≤ 40%; carbonate type, D ≤ 20%.
[0016] In the above method for drawing a planar distribution map of lithofacies assemblage, in step (6), the seismic attributes include amplitude, frequency, phase, energy, waveform, wave impedance, wave velocity, correlation, and ratio; Among them, amplitude includes instantaneous amplitude, root mean square (RMS) amplitude, maximum amplitude, and average amplitude; frequency includes instantaneous frequency, dominant frequency, average frequency, and bandwidth; phase includes instantaneous phase, phase difference, apparent phase, and phase coherence; energy includes total energy, half-time energy, relative energy, and energy attenuation; waveform includes waveform similarity coefficient, waveform curvature, waveform width, and waveform distortion; wave impedance includes absolute wave impedance, relative wave impedance, wave impedance difference, and wave impedance gradient; wave velocity includes layer velocity, RMS velocity, average velocity, and superposition velocity; correlation includes coherence coefficient, cross-correlation, autocorrelation, and similarity coefficient; and ratio includes amplitude ratio, frequency ratio, velocity ratio, and wave impedance ratio.
[0017] In the above method for drawing a planar distribution map of lithofacies assemblages, in step (6), CorelDRAW software is used to match seismic attributes and lithofacies assemblage types.
[0018] In the above-mentioned method for drawing a planar distribution map of lithofacies, in step (6), the seismic attribute that has a strong matching regularity with the lithofacies as the main reference seismic attribute for lithofacies planar mapping is used; the matching regularity refers to the good correspondence between the strength of the seismic attribute and the lithofacies assemblage type.
[0019] In the above-mentioned method for drawing a planar distribution map of lithofacies, in step (7), the boundary of lithofacies combination type is adjusted according to the matching law between seismic attributes and lithofacies combination type; the purpose is to eliminate lithofacies combination types that fail to match the seismic attributes well in the overlay map as much as possible, so that the boundary of lithofacies combination type can be further corrected.
[0020] The beneficial effects of this invention are as follows: This invention leverages the strong correlation between sonic transit time logging curves, density logging curves, and mineral composition. Based on the confirmed lithofacies assemblages in the work area, and using core wells to obtain material composition and logging data, the boundary values of the sonic-density logging curves for different lithofacies assemblages in the work area are determined. This allows for rapid identification of lithofacies assemblages using logging and well data from uncorked wells. Employing the "dominant lithofacies assemblage projection method," which uses the dominant lithofacies assemblages of a single well as constraints and combines seismic attribute analysis, a planar distribution map of lithofacies assemblages is created. This method offers a simple and user-friendly approach to classifying shale lithofacies assemblages. The combination of sonic, density, and seismic attributes results in high accuracy, improving the efficiency and accuracy of existing methods. It meets the requirements of geological evaluation and drilling engineering practices in continental lacustrine basin shale oil, thus possessing significant application value and promising prospects in the field of shale oil and gas exploration and development. Attached Figure Description
[0021] Figure 1 This is a schematic diagram of a felsic lithofacies assemblages.
[0022] Figure 2 This is a schematic diagram of a felsic interbedded carbonate rock facies assemblage.
[0023] Figure 3 This is a schematic diagram of a mixed-sedimentary lithofacies assemblage.
[0024] Figure 4 This is a schematic diagram of a carbonate-felsic rock facies assemblage.
[0025] Figure 5 This is a schematic diagram of a carbonate-type lithofacies assemblage.
[0026] Figure 6 Schematic diagrams of typical logging characteristics for different lithologies and ∆L distance diagrams (Δt1<Δt2, ΦN1<ΦN2, ρ1<ρ2, L1 is the density curve, L2 is the sonic curve).
[0027] Figure 7 This is a well logging feature map for identifying felsic lithofacies.
[0028] Figure 8 This is a well logging feature map for identifying felsic carbonate-type lithofacies.
[0029] Figure 9 This is a logging feature map for mixed-sedimentary lithofacies.
[0030] Figure 10 This is a well logging feature map for identifying carbonate-intercalated felsic lithofacies.
[0031] Figure 11 This is a feature map for identifying carbonate-type lithofacies well logging.
[0032] Figure 12 This represents the dominant lithofacies assemblage types of each stratum in well G108-8, section 2, in a depression in the Bohai Bay Basin.
[0033] Figure 13 This is a projection map showing the dominant lithofacies assemblage type of shale in the C1③ stratum of the second section of a depression in the Bohai Bay Basin.
[0034] Figure 14 This is a preliminary planar distribution map of the rough lithofacies assemblage types.
[0035] Figure 15 This is a schematic diagram showing the overlay of the root mean square amplitude of earthquakes and lithofacies combination types at the C1③ layer of a borehole section 2 in the Bohai Bay Basin.
[0036] Figure 16 A planar distribution map of lithofacies assemblage for the C1③ layer of the second section of a depression in the Bohai Bay Basin, drawn using a combination of well and seismic data. Detailed Implementation
[0037] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.
[0038] Taking the second section of a depression in the Bohai Bay Basin as an example, this paper explains the method for drawing a planar distribution map of lithofacies based on well-seismic combination.
[0039] In this embodiment, a well with relatively abundant data from the second section of a depression in the Bohai Bay Basin was selected as a control well (coring well). The control well has relatively abundant logging data, the high-frequency stratigraphic framework has been well defined, and the lithofacies assemblage type of each layer is also very clear.
[0040] The steps for drawing a planar distribution map of lithofacies assemblages are as follows: 1. Determine the lithofacies assemblage type of the area to be tested. Based on existing data in the analysis area, the lithofacies types developed in the study area were determined through core observation, thin section identification, and analytical testing. Furthermore, lithofacies assemblage types were classified according to the repeated occurrence of lithofacies superposition, with the content of felsic and dolomitic materials as the basic principle for classification.
[0041] Based on the mineral content (XRD mineral content), sedimentary structures (core observation combined with thin section identification), and mixed-type data from the control well, and following the sedimentary rock naming tradition with 50% end-member mineral content as the boundary, the following five lithofacies types were identified in the second member of a certain depression in the Bohai Bay Basin: laminated felsic shale facies, laminated mixed shale facies, massive mixed shale facies, laminated dolomitic shale facies, and massive dolomitic shale facies. The lithofacies classification is shown in Table 1.
[0042] Table 1. Lithofacies type table Based on the superposition relationship of various lithofacies types (such as...) Figures 1-5 As shown in the figure, the following lithofacies assemblage types are further identified in the area to be tested: felsic type (Type A), felsic interbedded with carbonate type (Type B), mixed type (Type C), carbonate interbedded with felsic type (Type D) and carbonate type (Type E).
[0043] The lithofacies assemblage classification table is shown in Table 2: Table 2 Classification of Lithofacies Assemblages 2. Obtain the optimal boundary values of sonic transit time and density logging curves. Based on the existing data of the reference well, two logging curves, sonic transit time and density, were selected. In ResForm software, the boundary values of the two logging curves were adjusted so that they intersect each other. When the D value of each layer in the vertical direction of the reference well matches its lithofacies assemblage type, the boundary values of the sonic transit time logging curve and density logging curve at this time were recorded.
[0044] Because different rocks have different mineral compositions and contents, and these different mineral compositions have significantly different geophysical information such as acoustic wave, density, radioactivity, and neutron absorption characteristics, the logging responses of shale, carbonate rocks, and sandstone exhibit regular variations on a macroscopic scale. For fine-grained sedimentary rocks, porosity is generally less than 10%, and for shale it is generally less than 6%. When one type of information is weakened or suppressed, another type of information can be reflected more prominently. This results in layers with higher felsic content (oil and gas-bearing sections) in fine-grained sedimentary rocks exhibiting relatively high acoustic wave, low density, and high neutron absorption characteristics on the logging curves, while layers with higher carbonate content exhibit relatively low acoustic wave, high density, and low neutron absorption characteristics. Therefore, acoustic logging curves and density logging curves, in the vertical direction, can themselves reflect the lithofacies assemblage type of each layer to a certain extent.
[0045] After the high-frequency stratigraphic framework is established, many layers will be formed vertically (each layer may contain multiple lithofacies). To better reflect the lithofacies assemblages of each layer using sonic and density logging curves, the boundary values of the two logging curves are adjusted so that they intersect, forming enclosed regions. Each layer may contain multiple enclosed regions, and each enclosed region corresponds to a lithofacies assemblage. An enclosed region with the sonic curve on the right and the density curve on the left indicates a lithofacies facies of high sonic intensity and low density, suggesting a high content of felsic and clayey minerals, and should therefore be considered a felsic lithofacies.
[0046] In the above processing, the surrounding area representing the felsic rock facies can be filled with red (red patterning) to make it easier to visualize, such as... Figure 6 As shown.
[0047] For the determination of felsic rock facies, sonic transit time logging curves and density logging curves can also be selected to establish the following formula: ΔL represents the distance between the superimposed (overlapping) acoustic and density logging curves, L2 is the acoustic transit time curve, L1 is the density curve, ρ is the volume density, which is the measured logging value read from the density logging curve, Δt is the acoustic transit time, which is the measured logging value read from the acoustic logging curve, ρ1 and ρ2 are density boundary values, and Δt1 and Δt2 are acoustic transit time boundary values.
[0048] The above formula can be seen as a normalization of density and sonic transit time, that is, converting well logging data into dimensionless indices. Then, based on ΔL, i.e., the difference between AC (acoustic wave) and DEN (density), the mineral content is initially determined. When ΔL>0, it indicates that the sonic wave curve is on the right and the density curve is on the left, which means high sonic wave and low density, indicating a high content of felsic and clay minerals, and is considered a felsic lithofacies.
[0049] The D value mentioned above represents the proportion of the thickness of felsic facies within the thickness of its stratigraphic layer. The reason for defining the D value based on felsic content is that, during oil and gas extraction, a high felsic content often indicates relatively abundant oil and gas resources.
[0050] Based on the established high-frequency stratigraphic framework, the total thickness (d) of each layer is recorded, and the thicknesses of all felsic facies within that layer are denoted as d1, d2, d3, ... d. n The formula for calculating the thickness percentage (D value) of felsic facies is as follows: .
[0051] The magnitude of the D value corresponds to one of the five lithofacies assemblage types, as shown in Table 3 and... Figures 7-11 As shown in: Table 3 Corresponding relationship between D value and lithofacies combination (1) D > 80%: felsic lithofacies combination High acoustic travel time, low compensated density, the largest difference between AC and DEN curves, the largest filling area in the red region, and the red filling area is greater than 80%.
[0052] (2) 60% < D ≤ 80%: felsic intercalated with carbonate lithofacies combination The AC and DEN curves intersect frequently, and the difference between the curves is relatively large, showing obvious serrated undulations, mainly in the red region, between 60 and 80%, with a small amount of white regions intercalated.
[0053] (3) 40% < D ≤ 60%: mixed sedimentary lithofacies combination The changing trends of the AC and DEN curves are slightly slower than those in combination (2), with the characteristics of uniform alternation of red and white, and the red filling area is between 40 and 60%.
[0054] (4) 20% < D ≤ 40%: carbonate intercalated with felsic lithofacies combination The AC and DEN curves show obvious serrated undulations, with a small overlapping amplitude, only overlapping locally to form a "red pattern", featuring that the white area dominates, and the red filling area is between 20 and 40%.
[0055] (5) D ≤ 20%: carbonate lithofacies combination Logging shows that the difference between the AC and DEN curves is the smallest, the AC curve changes relatively frequently, the DEN curve is basically stable, there is basically no intersection, and the white area dominates in the "red pattern", with the red area less than 20%.
[0056] Since the lithofacies of each layer in the control well have been clearly defined in advance, during the process of adjusting the boundary values of the two logging curves, the D values of each layer will change continuously. When the D values of each layer meet the lithofacies combination type, the boundary values at this time are the optimal values, and record these boundary values. These boundary values can be used as the boundary values of the acoustic travel time and density logging curves of all un-cored wells (other wells) in the待测区域.
[0057] Based on the above method, the optimal boundary values of the acoustic travel time logging curve of the second member of the Kongdian Formation in a sag of the Bohai Bay Basin are finally determined to be 200 μs / m and 400 μs / m, and the optimal boundary values of the density logging curve are 2 g / m 3 and 3 g / m 3 .
[0058] 3. Determine the lithofacies combination types of each layer in the un-cored wells High-frequency stratigraphic frameworks were constructed for the uncored wells, and the sonic logging and density logging data were measured to obtain sonic transit time logging (STL) curves and density logging curves. The boundary values of the STL and density logging curves were set to the optimal values obtained in step 2 above, and the D value of each layer was calculated to determine the lithofacies assemblage type of each layer.
[0059] Taking well G108-8 in the second section of a depression in the Bohai Bay Basin as an example, the dominant lithofacies assemblage types of each stratum in well G108-8 were obtained, such as... Figure 12 As shown.
[0060] 4. Draw a lithofacies assemblage projection map. Taking the C1③ layer as an example, a lithofacies assemblage plot is drawn. The lithofacies assemblages of all wells in the C1③ layer (all layers of all wells have been determined in step 3 above) are marked on the well location map to obtain the lithofacies assemblage plot of the C1③ layer. For example... Figure 13 As shown.
[0061] 5. Preliminary planar distribution map of lithofacies assemblage. Based on the lithofacies assemblage plot of stratigraphy C1③, and combined with the sedimentary environment and provenance (which are generally determined before drilling), a preliminary planar distribution map of the lithofacies assemblage of stratigraphy C1③ is drawn (this is a standard drawing method). Figure 14 As shown, the boundary (rough boundary) of the lithofacies assemblage type of the C1③ stratum can be preliminarily obtained.
[0062] 6. Optimal selection of seismic attributes Seismic attributes were optimized for multiple key horizons, such as root mean square amplitude, relative wave impedance, sweet spot, instantaneous frequency, amplitude envelope, and instantaneous bandwidth. The seismic attribute with the best correlation to the lithofacies assemblage type of the area to be measured was selected (a seismic attribute with relatively good matching degree was selected).
[0063] Taking layer C1③ as an example, seismic attribute optimization is performed. Using various sensitive seismic attributes of the area to be measured (including root mean square amplitude, relative impedance, sweet spot, instantaneous frequency, amplitude envelope, instantaneous bandwidth, etc.), and based on the lithofacies assemblages of each layer determined in step 3 above, different types of seismic attribute characteristics are matched (using CorelDRAW software). Among these, the root mean square amplitude attribute shows a certain regularity with lithofacies assemblages during the matching process. Strong amplitude corresponds to felsic lithofacies assemblages, while weak amplitude mostly corresponds to carbonate lithofacies assemblages. The matching effect between the two is better than other seismic attributes. Therefore, the root mean square amplitude is selected as the primary seismic attribute for lithofacies plan mapping.
[0064] 7. Correcting the boundaries of lithofacies assemblage types Then, the root mean square amplitude of the earthquake at layer C1③ is overlaid with the preliminary lithofacies assemblage planar distribution map obtained in step 5 above to obtain... Figure 15 The purpose of overlaying seismic attributes is to make the boundaries of lithofacies assemblage types more precise.
[0065] The boundaries of the initially drawn lithofacies assemblages were finely adjusted to ensure that strong amplitude corresponded to high felsic materials, thus determining the boundaries of the lithofacies assemblages. Then, a planar distribution map of the lithofacies assemblages in the C1③ layer was compiled, as shown below. Figure 16 As shown.
[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.
Claims
1. A method for drawing a planar distribution map of continental shale lithofacies based on well-seismic analysis, characterized in that, Includes the following steps: (1) Determine the lithofacies assemblage type of the area to be tested A core well with abundant logging data is selected as a control well in the area to be tested. Based on its logging data, the lithofacies types developed in the area to be tested are determined. Based on the superposition relationship of the lithofacies types in the area, the lithofacies assemblage types existing in the area to be tested are further clarified. (2) Obtain the optimal boundary values of the sonic transit time and density logging curves. In the logging data of the control well, two logging curves, sonic transit time and density, are selected. The boundary values of the two logging curves are adjusted so that they intersect each other. When the D value of each layer in the vertical direction of the control well matches its lithofacies assemblage type, the boundary values of the sonic transit time logging curve and density logging curve at this time are recorded. (3) Determine the lithofacies assemblage type of each stratigraphic level in the uncored well. High-frequency stratigraphic framework division was performed on the uncored wells, and the acoustic wave and density of the uncored wells were measured to obtain the acoustic transit time logging curves and density logging curves. The boundary values of the acoustic transit time logging curves and density logging curves were set to the boundary values recorded in step (2) above, and the D value of each layer of the uncored wells was calculated to determine the lithofacies assemblage type of each layer. (4) Draw a lithofacies assemblage projection map Mark the lithofacies assemblages of each layer in all wells on the well location map to obtain the lithofacies assemblages projection map of each layer in the area to be tested; (5) Preliminary planar distribution map of lithofacies assemblage. Based on the plotted facies assemblages of each stratum, and in conjunction with the sedimentary environment and provenance, a preliminary planar distribution map of the facies assemblages of each stratum was drawn, thus obtaining the preliminary boundaries of the facies assemblages of each stratum on the planar distribution map of the facies assemblages; (6) Optimization of seismic attributes The seismic attributes of the area to be measured are matched with the lithofacies combination types of each layer determined in step (3) above. The seismic attribute with the best matching degree is used as the main reference seismic attribute for lithofacies plane mapping. (7) Correcting the boundaries of lithofacies assemblage types The seismic attributes selected in step (6) are overlaid with the lithofacies assemblage planar distribution map drawn in step (5) above; the lithofacies assemblage type boundaries are further adjusted so that the lithofacies assemblage type boundaries are further corrected on the basis of step (5) above, and finally the lithofacies assemblage planar distribution map of each layer is obtained.
2. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (1), the lithofacies types include felsic shale facies, dolomitic shale facies, mixed shale facies, clayey shale facies, sand-bearing shale facies, and tuff-bearing shale facies.
3. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (1), the determination of the lithofacies assemblage type is based on the content of felsic and dolomitic materials as the basic principle for classification.
4. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (1), the lithofacies assemblage types include felsic type, felsic-carbonate type, mixed type, carbonate-felsic type and carbonate type.
5. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, Step (2) is performed in ResForm software; the two logging curves, sonic transit time and density, are imported into ResForm software, and the boundary values of the two logging curves are adjusted so that the D value of each layer conforms to its lithofacies combination type; the D value is the proportion of the thickness of felsic lithofacies in the thickness of its layer; the thickness is the vertical thickness.
6. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (2), the correspondence between the D value and the lithofacies assemblage type is as follows: felsic type, D > 80%; felsic interbedded carbonate type, 60% < D ≤ 80%; mixed type, 40% < D ≤ 60%; carbonate interbedded felsic type, 20% < D ≤ 40%; carbonate type, D ≤ 20%.
7. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (6), the seismic attributes include amplitude, frequency, phase, energy, waveform, wave impedance, wave velocity, correlation, and ratio.
8. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (6), CorelDRAW software is used to match seismic attributes and lithofacies assemblage types.
9. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (6), the seismic attributes that have a strong matching regularity with the lithofacies assemblage are used as the main reference seismic attributes for lithofacies plane mapping; the matching regularity refers to the good correspondence between the strength of the seismic attribute and the lithofacies assemblage type.
10. The method for drawing a planar distribution map of lithofacies assemblages according to claim 1, characterized in that, In step (7), the boundary of the lithofacies combination type is adjusted according to the matching law between seismic attributes and lithofacies combination type; lithofacies combination types that fail to match well with seismic attributes in the overlay map are eliminated, so that the boundary of lithofacies combination type is further corrected.