A method for calculating acoustic curves by using elastic parameters of drilling cores as constraints
By constraining the elastic parameters of the drilling core and calculating the acoustic curve, the problem of insufficient acoustic data in sandstone-type uranium deposit exploration was solved, the accuracy of the formation acoustic curve was improved, and the lithological detection effect was enhanced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BEIJING RES INST OF URANIUM GEOLOGY
- Filing Date
- 2023-03-20
- Publication Date
- 2026-06-09
AI Technical Summary
In the exploration of sandstone-type uranium deposits, due to historical reasons and drilling and logging techniques, well logging data lacks acoustic data or contains errors, making seismic impedance inversion impossible and affecting the effectiveness of stratigraphic lithology detection.
By obtaining the elastic parameters of drilling core samples, especially acoustic velocity and resistivity, a mathematical relationship between resistivity and acoustic velocity is established. The acoustic velocity curve is then calculated using a drilling geological model, providing accurate formation acoustic data.
It improves the accuracy of stratigraphic acoustic curves, solves the problem of not being able to obtain accurate acoustic data in traditional methods, enhances the lithological detection effect, and provides a reliable basis for sandstone-type uranium deposit exploration.
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Figure CN116400409B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of geophysical exploration, specifically relating to a method for calculating acoustic curves using elastic parameters constrained by well core samples. Background Technology
[0002] Seismic impedance inversion is an effective method for lithological exploration in sandstone-type uranium deposits. It is usually based on seismic data and well logging sonic data. After well-seismic calibration, impedance inversion is carried out, and rock physical analysis is performed on the impedance inversion results to determine the lithology of the formation.
[0003] However, in the actual work of sandstone-type uranium exploration, due to historical reasons, drilling technology, logging technology and other factors, well logging data often lacks acoustic data or contains large errors, making it impossible to carry out seismic impedance inversion, which further affects the effectiveness of stratigraphic lithology detection. Summary of the Invention
[0004] The purpose of this invention is to provide a method for calculating acoustic curves using the elastic parameters of drilling cores. This method calculates pseudo-acoustic curves by constraining the elastic parameters of drilling cores, which can obtain accurate formation acoustic curves, thereby providing support for subsequent seismic impedance inversion.
[0005] Technical solution to achieve the purpose of this invention:
[0006] A method for calculating acoustic waveforms constrained by elastic parameters of drill cores, the method comprising the following steps:
[0007] Step 1: Obtain the well logging resistivity curves of the wells in the study area;
[0008] Step 2: Obtain core samples of different lithologies at various drilling depths;
[0009] Step 3: Measure the elastic parameters of the core sample, including acoustic velocity and resistivity;
[0010] Step 4: Establish mathematical relationships between resistivity and acoustic velocity parameters for different strata and lithologies;
[0011] Step 5: Based on the well logging results, establish a geological model of the well;
[0012] Step 6: Calculate the acoustic velocity curve of the well based on the drilling geological model and the fitted mathematical relationship.
[0013] In step 2, the diameter of the sample should be greater than 3cm and the length should be greater than 5cm.
[0014] The method for measuring the velocity of sound waves in step 3 is as follows:
[0015] The ultrasonic pulse transmission method was used to determine the acoustic velocity. Longitudinal wave transducers were fixed at both ends of the rock sample. The longitudinal wave transducer at one end was used to excite the longitudinal wave signal, and the longitudinal wave transducer at the other end was used to receive the longitudinal wave signal. The excitation time and reception time of the longitudinal wave signal were recorded, and the acoustic velocity of the rock core sample was calculated.
[0016] The formula for calculating the acoustic velocity of the core sample in step 3 is as follows:
[0017] VP = L / (T2-T1),
[0018] In the formula, VP represents the velocity of sound waves, L represents the length of the rock sample, T1 represents the excitation time of the longitudinal wave transducer at one end for longitudinal wave signal excitation, and T2 represents the reception time of the longitudinal wave transducer at the other end for longitudinal wave signal reception.
[0019] The method for measuring resistivity in step 3 is as follows:
[0020] The resistivity was measured using a two-stage method. Positive and negative electrodes were placed at both ends of the rock sample. An excitation current was flowed from the positive electrode to the negative electrode, and the potential difference between the positive and negative electrodes was measured to calculate the resistivity of the rock sample.
[0021] The formula for calculating the resistivity of the rock sample in step 3 is as follows:
[0022] RES=[πd 2 / (4L)]×(Δν / I)
[0023] In the formula, RES is the resistivity of the rock sample, d is the diameter of the rock sample, L is the length of the core sample, I is the current passing through the rock sample, and Δν is the potential difference between the two ends of the rock sample.
[0024] The mathematical relationship between resistivity and sound velocity parameters in step 4 is as follows:
[0025] VP = a1RES 2 +b1RES+c1,
[0026] In the formula, VP represents the longitudinal wave velocity, RES represents the resistivity, a1 represents the fitting constant of the quadratic term, b1 represents the fitting constant of the linear term, and c1 represents the constant term.
[0027] Step 6 specifically involves calculating the acoustic velocity curve using the resistivity curve from resistivity logging, based on the fitting mathematical relationship between resistivity and acoustic velocity.
[0028] The beneficial technical effects of this invention are as follows:
[0029] 1. Existing acoustic logging technologies in sandstone-type uranium deposits are limited by factors such as equipment, drilling processes, and logging techniques, making it impossible to obtain accurate formation acoustic data. This invention provides an acoustic curve calculation method that utilizes the elastic parameters of drill cores for constraint. This method can calculate acoustic curves using laboratory measurement results from drill cores combined with resistivity logging curves, providing a new approach for obtaining acoustic curves in sandstone-type uranium deposit formations.
[0030] 2. The present invention provides a method for calculating sonic curves using elastic parameters of drilling cores as constraints. Compared with traditional fitting methods, this method introduces measured data from drilling cores, overcoming the drawback of traditional methods that can only be adjusted based on existing data. By using additional real data for constraints, the accuracy of the fitting results is improved.
[0031] 3. The present invention provides a method for calculating acoustic curves constrained by the elastic parameters of drilling cores. By using the elastic parameters of drilling cores for constraint, the obtained pseudo-acoustic curves are closer to the true values than traditional fitting methods. This method can effectively solve the problem of lack of acoustic curves in seismic impedance inversion in sandstone-type uranium deposit exploration, thereby further improving the effect of lithological detection and providing a basis for uranium deposit exploration. Attached Figure Description
[0032] Figure 1 This is a resistivity curve obtained from resistivity logging in Embodiment 1 of the present invention;
[0033] Figure 2 This is a graph of the sound wave velocity calculated in Embodiment 1 of the present invention. Detailed Implementation
[0034] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.
[0035] This invention provides a method for calculating acoustic curves constrained by elastic parameters of drilling core samples, which specifically includes the following steps:
[0036] Step 1: Obtain the logging resistivity curves of wells drilled in the study area.
[0037] Select a well that can represent the stratigraphic lithological variations in the study area. This well should cover the main strata within its depth range. Obtain the resistivity logging curve of this well using resistivity logging techniques. The well that can represent the stratigraphic lithological variations in the study area must meet the following conditions: the drilling depth penetrates the main target layer; the lithology revealed by the well includes the main lithologies of the study area, such as mudstone, silt, fine sand, medium sand, coarse sand, and gravel.
[0038] Step 2: Obtain core samples of different lithologies at various drilling depths.
[0039] Core samples of different lithologies at various depths are obtained through drilling. Within depths where lithology changes are relatively stable, the sampling depth interval can be appropriately increased; conversely, within depths where lithology changes are more frequent, the sampling depth interval can be appropriately decreased. The sample diameter should be greater than 3 cm, and the length should be greater than 5 cm.
[0040] Step 3: Measure the elastic parameters of the core sample, including acoustic velocity and resistivity.
[0041] The laboratory prepared rock samples according to the cylindrical shape. First, the samples were placed in a drying oven for 24 hours to dry. Then, the diameter d and length L of the cylindrical rock samples were measured using vernier calipers.
[0042] In the laboratory, an automated servo rock physical properties and rock mechanics experimental testing system (such as the AutoLab1000 in the United States) is used to test the acoustic velocity parameters of rock samples. The main testing process includes sample preparation, cleaning and drying, density measurement, ambient temperature and pressure velocity measurement, high temperature and high pressure velocity measurement, and measurement result inspection, and finally obtains the acoustic velocity of the rock core sample.
[0043] The acoustic velocity was measured using the ultrasonic pulse transmission method. The specific method is as follows: longitudinal wave transducers are fixed at both ends of the rock sample. The longitudinal wave transducer at one end is excited with a longitudinal wave signal for a time of T1, and the longitudinal wave transducer at the other end is received with a time of T2. The length L of the rock sample is then measured. The acoustic velocity of the rock is then calculated as VP = L / (T2-T1).
[0044] The resistivity was measured using a two-stage method. The specific measurement method was as follows: electrodes were placed at both ends of the rock sample, namely a positive electrode and a negative electrode. The excitation current flowed from the positive electrode to the negative electrode, and the potential difference between the positive and negative electrodes was measured. The resistivity value of the rock sample was calculated according to the following formula.
[0045] RES=[πd 2 / (4L)]×(Δν / I)
[0046] In the formula, RES is the resistivity of the rock sample, d is the diameter of the rock sample, L is the length of the core sample, I is the current passing through the rock sample, and Δν is the potential difference between the two ends of the rock sample.
[0047] Step 4: Establish mathematical relationships between resistivity and acoustic velocity parameters for different strata and lithologies.
[0048] Based on the geological understanding of the study area, stratigraphic correlation methods were used to geologically stratify the wells, classifying different well depths into corresponding stratigraphic units. Within each geological stratum, lithology was further classified, generally into six categories: mudstone, silt, fine sand, medium sand, coarse sand, and gravel. For each geological stratum, the acoustic parameters of the core samples were fitted and analyzed to calculate the mathematical relationship between resistivity and acoustic velocity.
[0049] The mathematical relationship between resistivity and sound velocity, expressed as a quadratic polynomial, is as follows:
[0050] VP = a1RES 2 +b1RES+c1,
[0051] In the formula, VP represents the longitudinal wave velocity, RES represents the resistivity, a1 represents the fitting constant of the quadratic term, b1 represents the fitting constant of the linear term, and c1 represents the constant term.
[0052] Step 5: Based on the well logging results, establish a geological model of the well.
[0053] Based on the well logging results, a geological model is established that includes information on depth, formation, lithology, and resistivity.
[0054] Step 6: Calculate the acoustic velocity curve of the well based on the drilling geological model and the fitted mathematical relationship.
[0055] Based on the drilling geological model, for different strata and lithologies, the acoustic velocity curve is calculated using the resistivity curve from resistivity logging according to the corresponding mathematical relationship between resistivity and acoustic velocity, which is the pseudo-acoustic curve.
[0056] Example 1
[0057] Taking actual data from a basin in northern China as an example, this invention provides a method for calculating pseudo-acoustic curves constrained by core elastic parameters, comprising the following steps:
[0058] Step 1: Obtain the logging resistivity curves of representative wells in the study area.
[0059] A representative well was selected for the study area, covering the main formations within its depth range. This example focuses on the Yaojia Formation. Resistivity logging was used to obtain the resistivity logging curves for this well.
[0060] Step 2: Obtain core samples of different lithologies at various depths in the well.
[0061] Core sampling is conducted to obtain core samples from various depths and with different lithologies. The core samples should be representative of the characteristics of a specific lithology within a given depth range. In depths where lithology changes are relatively stable, the sampling depth interval can be appropriately increased, with one sample taken every 50 meters. In depths where lithology changes are more frequent, the sampling depth interval can be appropriately decreased, with one sample taken every 10 meters. The sample diameter should be greater than 3 cm and the length should be greater than 5 cm.
[0062] Step 3: Measure the acoustic velocity parameters of the core sample in the laboratory.
[0063] In the laboratory, an automated servo rock physical properties and rock mechanics experimental testing system (such as the AutoLab1000 in the United States) is used to test the elastic parameters of rock samples. The main testing process includes sample preparation, cleaning and drying, density measurement, ambient temperature and pressure velocity measurement, high temperature and high pressure velocity measurement, and measurement result inspection. Finally, the acoustic velocity of the rock core sample is obtained.
[0064] The resistivity of rock samples was measured using the diode method.
[0065] In this example area, the measurement conditions were selected as high temperature and high pressure saturated solution, the solution used was 3% NaCl solution, the temperature was 23℃, and the pressure was calculated according to the formula P=10.51*H (H is the burial depth, 0m≤H≤1000m).
[0066] The measurement results of the rock sample in this example are shown in the table below.
[0067]
[0068]
[0069] Step 4: Establish mathematical relationships between resistivity and acoustic velocity parameters for different strata and lithologies.
[0070] Based on the geological understanding of the study area, the wells were geologically stratified. Within each geological stratum, they were classified according to different lithologies, generally into six categories: mudstone, silt, fine sand, medium sand, coarse sand, and gravel. For each geological stratum with different lithologies, the acoustic velocity parameters of the core samples were fitted and analyzed to calculate the mathematical relationship between resistivity and acoustic velocity.
[0071] In this example area, only the Yaojia Formation is considered; therefore, stratigraphic subdivision is not performed, and lithology is classified only into mudstone and sandstone. Resistivity is represented by RES, and P-wave velocity by VP, and mathematical relationships can be established as shown in Table 1. The relationships and parameters in Table 1 are all calculated based on data from laboratory sample measurements.
[0072] Table 1. Resistivity-sonic velocity fitting equations for different strata and lithologies.
[0073]
[0074] Step 5: Based on the well logging results, establish a geological model of the well.
[0075] Based on the well logging results, a geological model is established that includes information on depth, formation, lithology, and resistivity.
[0076] In the instance area, the geological model application is shown in Table 2.
[0077] Table 2 Depth-Stratigraphy-Lithology-Resistivity Geological Model
[0078]
[0079]
[0080] Step 6: Calculate the acoustic velocity curve of the well based on the drilling geological model and the fitted mathematical relationship.
[0081] Based on the drilling geological model, for different strata and lithologies, the acoustic velocity curve is calculated using the resistivity curve according to the corresponding mathematical relationship between resistivity and acoustic velocity, which is the pseudo-acoustic curve.
[0082] In the instance area, the fitting results are shown in Table 3. Table 3 only lists part of the data; the completed calculation results are as follows: Figure 2 As shown.
[0083] Table 3 Fitting formulas and parameters for P-wave velocity curves, S-wave velocity curves, and density curves from well logging.
[0084]
[0085]
[0086] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. All contents not described in detail in the present invention can be derived from existing technologies.
Claims
1. A method for calculating acoustic curves using elastic parameters of a drilling core, characterized in that, The method includes the following steps: Step 1: Obtain the well logging resistivity curves of the wells in the study area; Step 2: Obtain core samples of different lithologies at various drilling depths; Step 3: Measure the elastic parameters of the core sample, including acoustic velocity and resistivity; Step 4: Establish mathematical relationships between resistivity and acoustic velocity parameters for different strata and lithologies; Step 5: Based on the well logging results, establish a geological model of the well; Step 6: Calculate the acoustic velocity curve of the well based on the drilling geological model and the fitted mathematical relationship; The mathematical relationship between resistivity and sound velocity parameters in step 4 is as follows: VP = a1RES 2 + b1RES + c1, In the formula, VP represents the longitudinal wave velocity, RES represents the resistivity, a1 represents the fitting constant of the quadratic term, b1 represents the fitting constant of the linear term, and c1 represents the constant term. Step 6 specifically involves: based on the drilling geological model, and for different formations and lithologies, calculating the acoustic velocity curve using the resistivity curve from resistivity logging according to the fitting mathematical relationship between resistivity and acoustic velocity.
2. The method of claim 1, wherein, In step 2, the diameter of the sample should be greater than 3cm and the length should be greater than 5cm.
3. The method of claim 1, wherein, The method for measuring acoustic velocity in step 3 is as follows: the acoustic velocity is determined by ultrasonic pulse transmission method. Longitudinal wave transducers are fixed at both ends of the rock sample. The longitudinal wave transducer at one end is used to excite the longitudinal wave signal, and the longitudinal wave transducer at the other end is used to receive the longitudinal wave signal. The excitation time and reception time of the longitudinal wave signal are recorded, and the acoustic velocity of the rock core sample is calculated.
4. The method of claim 3, wherein, The formula for calculating the acoustic velocity of the core sample in step 3 is as follows: VP = L / (T2 - T1) In the formula, VP represents the velocity of sound waves, L represents the length of the rock sample, T1 represents the excitation time of the longitudinal wave transducer at one end for longitudinal wave signal excitation, and T2 represents the reception time of the longitudinal wave transducer at the other end for longitudinal wave signal reception.
5. The method of claim 4, wherein, The resistivity measurement method in step 3 is as follows: the resistivity is measured using a two-stage method. Positive and negative electrodes are arranged at both ends of the rock sample. The excitation current flows from the positive electrode direction to the negative electrode direction. The potential difference between the positive and negative electrodes is measured, and the resistivity of the rock sample is calculated.
6. The method of claim 5, wherein, The formula for calculating the resistivity of the rock sample in step 3 is as follows: RES = [πd 2 / (4L)] x (Δv / I) In the formula, RES is the resistivity of the rock sample, d is the diameter of the rock sample, L is the length of the core sample, I is the current passing through the rock sample, and Δν is the potential difference between the two ends of the rock sample.