Downhole core replacement method for mudstone outcrop based on plate
By correcting and repositioning the depth of mudstone outcrops and utilizing well logging and charting techniques, the problem of obtaining mudstone cores downhole was solved, enabling accurate substitution of mudstone and three-dimensional geomechanical modeling.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA NATIONAL OFFSHORE OIL (CHINA) CO LTD
- Filing Date
- 2026-03-03
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies are insufficient to effectively simulate the elastic properties and mechanical parameters of mudstone in underground mines, and obtaining mudstone cores from underground mines is difficult, resulting in insufficient research on underground strata.
By comprehensively utilizing well logging, downhole core samples, and charts, the depth of mudstone outcrops is corrected and repositioned, and the density, velocity, and mechanical properties of the mudstone are obtained, enabling precise three-dimensional geomechanical modeling.
It achieves accurate replacement of mudstone in the well, provides high-quality underground strata information, and supports three-dimensional geomechanical modeling.
Smart Images
Figure CN122017200A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil and gas drilling engineering technology, and in particular to a method for substituting downhole cores for mudstone outcrops based on charts. Background Technology
[0002] In geological research, oil and gas exploration, and mineral resource evaluation, downhole cores are underground rock samples obtained through drilling. Downhole cores are the core carriers for directly obtaining information about underground rock formations, providing crucial data for analyzing lithology, physical properties, hydrocarbon potential, and structural characteristics. However, due to factors such as high drilling costs, high acquisition costs of downhole cores, limited core sampling ratios, stringent preservation conditions, and technical limitations in some areas making core sampling difficult, obtaining complete or high-quality downhole cores is often challenging. In such cases, outcrop cores—natural rock samples exposed at the surface, or artificially or naturally exposed rock blocks in natural rock profiles—can serve as important substitutes. Through scientific selection and reasonable analysis, they can provide crucial supplementary information for downhole core research under similar geological conditions.
[0003] Currently, there are relatively few downhole core substitution techniques for outcrop cores. One approach involves obtaining outcrop samples using specific drilling methods, analyzing characteristics such as gravel quantity, size, and sorting coefficient, defining a "gravel characteristic coefficient S," comparing the similarity between downhole and outcrop cores, and selecting outcrop core plungers with matching physical properties to supplement laboratory experiments. This primarily addresses the difficulty of obtaining downhole cores from sandstone and conglomerate formations and is suitable for reservoir research in oil and gas exploration and development. Another approach utilizes a mixture of outcrop cores, quartz sand, and epoxy resin to prepare heterogeneous core models, simulating vertical reservoir heterogeneity. This can be used for sedimentary physics simulation experiments. The key feature of this technique is the precise preparation of multi-layered heterogeneous cores by controlling the binder permeability, making it suitable for studying sedimentary processes and reservoir evolution. However, this method has stringent requirements and cannot effectively simulate the elastic properties and related mechanical parameters of rocks under downhole conditions.
[0004] In response to the scarcity of mudstone cores in oil and gas field development and the inadequacy of current core substitution table technology, this study comprehensively utilizes well logging, downhole cores, experiments, and charts to reposition mudstone outcrops at the same stratum using depth correction charts. This allows for the acquisition of density, velocity, and mechanical properties of mudstone at different depths, enabling precise three-dimensional geomechanical modeling of underground strata. Summary of the Invention
[0005] The purpose of this invention is to provide a method for substituting mudstone outcrops with a plot based on a map. This method integrates well logging, downhole core analysis, experiments, and plots to reposition mudstone outcrops at the same stratum using depth correction on the plot. This allows for the acquisition of density, velocity, and mechanical properties of mudstone at different depths, thereby achieving a fine three-dimensional geomechanical modeling of underground strata.
[0006] To achieve the above objectives, the present invention adopts the following technical solution, comprising the following steps: S1. Conduct field mudstone outcrop collection and core preparation; obtain existing core experimental data, and create charts based on existing core experimental data and well logging acoustic waves and density data. S2. Conduct initial density determination of mudstone outcrops under normal pressure; perform initial burial depth repositioning and density numerical correction of outcrop cores under the chart. S3. Calculate the rock parameters of the mudstone outcrop relocation site under the above-mentioned map; if there is overpressure in the target formation, perform overpressure correction of the mudstone outcrop relocation site formation; S4. Determine whether the relevant parameters of the mudstone outcrop core after correction meet the quality requirements.
[0007] Preferably, in step S1, the existing core experimental data includes lithology, depth, density, rock velocity, uniaxial compressive strength, and Young's modulus; the charts include mudstone density-depth cross-plots, mudstone density-velocity cross-plots, depth-confining pressure cross-plots, pressure-mudstone density change cross-plots, overpressure-mudstone density change cross-plots, and overpressure-mudstone velocity change cross-plots.
[0008] Preferably, in step S2, the initial density of the mudstone outcrop under normal pressure is determined by obtaining the initial density of the outcrop rock through a rock electrical experiment. .
[0009] Preferably, in step S2, the method for repositioning the initial burial depth of the outcrop core under the chart is as follows: in the mudstone density-burial depth cross-plot, the initial density of the mudstone outcrop is used as the reference value. As an indicator, the first repositioning depth value of the original burial depth of the mudstone outcrop is read. In the depth-confining pressure intersection chart, read the first repositioning depth of the mudstone outcrop. Corresponding confining pressure value Read the confining pressure value from the pressure-mudstone density change cross plot. The corresponding change in mudstone density is the first density correction value of the mudstone outcrop. Density corresponding to the first original burial depth correction of mudstone outcrops Then read the data from the mudstone density-depth cross plot. Corresponding depth value This refers to the original burial depth of the mudstone outcrop. .
[0010] Preferably, in step S2, the density value correction method is as follows: the density value is corrected at the original burial depth of the mudstone outcrop. Corresponding confining pressure Below, the confining pressure is read from the cross-plot of pressure-mudstone density change. Corresponding correction value for density change of mudstone outcrops and then utilize = Obtain the mudstone density under the original burial depth correction of the mudstone outcrop. .
[0011] Preferably, in step S3, the rock parameters include Poisson's ratio, Young's modulus, and rock strength; the calculation method for the rock parameters of the mudstone outcrop location on the chart is as follows: Density corrected using mudstone outcrops The density-velocity intersection chart of mudstone can be used to read the original burial depth. The corresponding mudstone velocity is used to obtain Poisson's ratio, Young's modulus, and rock strength from mudstone density and mudstone velocity.
[0012] Preferably, in step S3, the formation overpressure correction method for mudstone outcrop relocation points is as follows: The mudstone density under formation overpressure is re-corrected using a mudstone overpressure-density change cross-plot, and the corrected mudstone density is read using the formation pressure gradient. Density of mudstone outcrops at original burial depth and under formation pressure for: in, The density of mudstone under the original burial depth correction of the mudstone outcrop.
[0013] Preferably, in step S4, the uniaxial compressive strength of existing downhole core test results is used for quality inspection; if the uniaxial compressive strength of the mudstone outcrop core after initial burial depth correction is more than 90% consistent with that of the core at the same depth, then it meets the quality requirements.
[0014] The beneficial effects of this invention are: by comprehensively utilizing well logging, downhole cores, experiments, and charts, mudstone outcrops at the same stratum can be repositioned through depth correction on the charts, thereby obtaining the density, velocity, and mechanical properties of mudstone at different depths, and realizing a fine three-dimensional geomechanical modeling of underground strata. Attached Figure Description
[0015] Figure 1 This is a density-depth cross plot of mudstone in the example.
[0016] Figure 2 This is a density-velocity cross plot of mudstone in the example.
[0017] Figure 3 This is a diagram showing the intersection of burial depth and confining pressure in the example.
[0018] Figure 4 This is a cross-plot of pressure-mudstone density changes in the examples.
[0019] Figure 5 This is a cross-plot of overpressure-mudstone density changes in the examples.
[0020] Figure 6 This is a cross-plot of mudstone overpressure-velocity changes in the example. Detailed Implementation
[0021] The invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.
[0022] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.
[0023] Example The present invention provides a method for substituting mudstone outcrops for downhole core samples based on charts, comprising: S1. Conduct field collection of mudstone outcrops and core preparation; acquire existing core experimental data, and create charts based on the existing core experimental data and combined with well logging sonic logging and density data; the existing core experimental data includes lithology, depth, density, rock velocity, uniaxial compressive strength, and Young's modulus; the charts include mudstone density-depth cross-plots (…). Figure 1 ), mudstone density-velocity cross plot ( Figure 2 ), Burial depth-confining pressure intersection chart ( Figure 3 ), cross plot of pressure-mudstone density change ( Figure 4 ), Cross plot of overpressure-mudstone density variation ( Figure 5 ) and cross plot of overpressure-mudstone velocity change ( Figure 6 ).
[0024] S2. Obtain the initial density of the outcrop rock through rock electrical experiments. The average density of the three Dongying Formation mudstone cores is 2.56 g / cm³. 3 The uniaxial compressive strength (UCS) of the rock is 42.1 MPa.
[0025] The initial burial depth of the outcrop core was determined on the chart, using the mudstone density-burial depth cross plot ( Figure 1 In the context of mudstone outcrops, the initial density is used as the basis for calculation. =2.56g / cm 3 Instructions to read the first repositioning depth value of the original burial depth of the mudstone outcrop. =3000m; on the depth-confining pressure intersection chart ( Figure 3 In the data, the depth of the first return of the mudstone outcrop was read. =3000m corresponding confining pressure value It is 64.6 MPa; in the cross plot of pressure-mudstone density change ( Figure 4 Read the confining pressure value on the device. The change in mudstone density corresponding to 64.6 MPa is the first density correction value for the mudstone outcrop. 0.3 g / cm 3 Density corresponding to the first original burial depth correction of mudstone outcrops =2.86g / cm 3 Then, in the mudstone density-burial depth intersection chart ( Figure 1 Read from ) =2.86g / cm 3 Corresponding depth value =3300m is the original burial depth of the mudstone outcrop. .
[0026] Density numerical correction: Restoring the original burial depth of the mudstone outcrop to its original depth. =3300m corresponding confining pressure =64.6MPa, based on the cross-plot of pressure-mudstone density change ( Figure 4 Read confining pressure Correction value for density change of mudstone outcrops corresponding to 64.6 MPa =2.86g / cm 3 and then utilize = =2.86g / cm 3 Obtain the mudstone density under the original burial depth correction of the mudstone outcrop. .
[0027] S3. Calculate the rock parameters of the mudstone outcrop at the location indicated on the chart; the rock parameters include Poisson's ratio, Young's modulus, and rock strength; and use the density corrected for the mudstone outcrop. The density-velocity intersection chart of mudstone can be used to read the original burial depth. The corresponding mudstone velocity is used to obtain Poisson's ratio, Young's modulus, and rock strength from mudstone density and mudstone velocity.
[0028] Formula for calculating Poisson's ratio in core samples: Formula for calculating Young's modulus of rock core: Formula for calculating the uniaxial compressive strength of rock core: in: The longitudinal wave velocity is given in m / s. The transverse wave velocity is in m / s; Density of rock, g / cm³ 3 ; Poisson's ratio for rocks, without units; Young's modulus, GPa; The rock mud content, decimal; If overpressure exists in the target formation, perform formation overpressure correction at the mudstone outcrop location; then, under the mudstone overpressure-density change cross-plot, perform a second correction of the mudstone density under formation overpressure, and use the formation pressure gradient to read the corrected mudstone density. Density of mudstone outcrops at original burial depth and under formation pressure for: in, The density of mudstone under the original burial depth correction of the mudstone outcrop.
[0029] Since there was no overpressure in the X1 core section of the comparison well, there is no need to perform overpressure correction.
[0030] S4. Determine whether the relevant parameters of the mudstone outcrop core after correction meet the quality requirements. The quality inspection is carried out using the uniaxial compressive strength of existing downhole core test results; if the uniaxial compressive strength of the mudstone outcrop core after initial burial depth correction has a higher than 90% consistency with the core at the same depth, then it meets the quality requirements.
[0031] Core sampling parameters from the existing X1 well in the Dongying Formation mudstone of the target area were selected. The vertical depth of the core in this well is 3877m, and the uniaxial compressive strength (UCS) under normal pressure is 44.6MPa. The uniaxial compressive strength (UCS) of the outcrop core, after correction from the initial burial depth (3300m) of the field outcrop (35.69MPa), was corrected to 42.1MPa at 44.6m. Comparing this to the uniaxial compressive strength (UCS) of the X1 well at the same depth (35.69MPa), the UCS substitution accuracy of the mudstone is 94%, and the density accuracy is 98% (see Tables 1 and 2). This demonstrates the feasibility and reliability of the downhole core substitution method for mudstone outcrops.
[0032] Table 1 Quality Control of Outcrop Core Placement and Density Correction Table 2 Quality Control of Outcrop Core Relocation and Uniaxial Compressive Strength Correction In summary, this invention provides a method for substituting mudstone outcrops for underground core samples based on charts. By comprehensively utilizing well logging, underground core samples, experiments, and charts, mudstone outcrops at the same stratum are repositioned using depth correction on the charts. This allows for the acquisition of density, velocity, and mechanical properties of mudstone at different depths, thus achieving precise three-dimensional geomechanical modeling of underground strata.
[0033] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.
Claims
1. A method for substituting mudstone outcrops from underground core samples based on charts, characterized in that, Includes the following steps: S1. Conduct field mudstone outcrop collection and core preparation; obtain existing core experimental data, and create charts based on existing core experimental data and well logging acoustic waves and density data. S2. Conduct initial density determination of mudstone outcrops under normal pressure; perform initial burial depth repositioning and density numerical correction of outcrop cores under the chart. S3. Calculate the rock parameters of the mudstone outcrop relocation site under the above-mentioned map; if there is overpressure in the target formation, perform overpressure correction of the mudstone outcrop relocation site formation; S4. Determine whether the relevant parameters of the mudstone outcrop core after correction meet the quality requirements.
2. The downhole core substitution method based on mudstone outcrops according to claim 1, characterized in that: In step S1, the existing core experimental data includes lithology, depth, density, rock velocity, uniaxial compressive strength, and Young's modulus; the charts include mudstone density-depth cross plots, mudstone density-velocity cross plots, depth-confining pressure cross plots, pressure-mudstone density change cross plots, overpressure-mudstone density change cross plots, and overpressure-mudstone velocity change cross plots.
3. The downhole core replacement method based on mudstone outcrops according to claim 1, characterized in that: In step S2, the initial density of the mudstone outcrop under normal pressure is determined by obtaining the initial density of the outcrop rock through a rock electrical experiment. .
4. The method for substituting mudstone outcrops based on charts according to claim 3, characterized in that, In step S2, the method for repositioning the initial burial depth of the outcrop core under the chart is as follows: In the mudstone density-depth cross plot, the initial density of the mudstone outcrop is used. As an indicator, the first repositioning depth value of the original burial depth of the mudstone outcrop is read. ; In the depth-confining pressure intersection chart, read the first repositioning depth of the mudstone outcrop. Corresponding confining pressure value Read the confining pressure value from the pressure-mudstone density change cross plot. The corresponding change in mudstone density is the first density correction value of the mudstone outcrop. Density corresponding to the first original burial depth correction of mudstone outcrops ; Then read from the mudstone density-burial depth cross plot. Corresponding depth value This refers to the original burial depth of the mudstone outcrop. .
5. The downhole core replacement method based on mudstone outcrops according to claim 2, characterized in that, In step S2, the density numerical correction method is as follows: the original burial depth of the mudstone outcrop is returned to its original position. Corresponding confining pressure Below, the confining pressure is read from the cross-plot of pressure-mudstone density change. Corresponding correction value for density change of mudstone outcrops and then utilize = Obtain the mudstone density under the original burial depth correction of the mudstone outcrop. .
6. The method for substituting mudstone outcrops based on charts according to claim 5, characterized in that, In step S3, the rock parameters include Poisson's ratio, Young's modulus, and rock strength; the calculation method for the rock parameters of the mudstone outcrop location on the chart is as follows: Density corrected using mudstone outcrops The density-velocity intersection chart of mudstone can be used to read the original burial depth. The corresponding mudstone velocity is used to obtain Poisson's ratio, Young's modulus, and rock strength from mudstone density and mudstone velocity.
7. The method for substituting mudstone outcrops based on charts according to claim 6, characterized in that, In step S3, the method for correcting formation overpressure at mudstone outcrop relocation points is as follows: The mudstone density under formation overpressure was recalibrated using the cross-plot of mudstone overpressure and density change, and the corrected mudstone density was read using the formation pressure gradient. Density of mudstone outcrops at original burial depth and under formation pressure for: in, The density of mudstone under the original burial depth correction of the mudstone outcrop.
8. The method for substituting mudstone outcrops based on charts according to claim 1, characterized in that, In step S4, the uniaxial compressive strength of existing downhole core test results is used for quality inspection; if the uniaxial compressive strength of the mudstone outcrop core after initial burial depth correction is higher than 90% compared with the core at the same depth, it meets the quality requirements.