A method for predicting coal measure stratum shear wave time by using conventional logging data

Abstract

This invention discloses a method for predicting shear wave transit time in coal-bearing formations using conventional well logging data. The method first determines the shear wave transit time curve data, sonic transit time, density, and natural gamma curve data for coal-bearing formations. Based on the correlation between the shear wave transit time curve and conventional well logging curves for different lithologies, a prediction formula model for shear wave transit time in different lithologies of coal-bearing formations is established. Based on the lithology of the wellbore section of the conventional well logging data to be calculated, a suitable shear wave transit time prediction model is selected for calculation. This invention, by establishing a formula for predicting the shear wave transit time of a work area using conventional well logging data in coal-bearing formations, calculates the shear wave transit time curve of wells without measured dipole sonic imaging logging. This achieves the quantitative acquisition of continuous shear wave transit time parameter profiles using conventional well logging data with good continuity and economic reliability, providing key parameters for calculating the rock mechanical stress and evaluating the fracturing capability of coal-bearing formations.

Description

Technical Field

[0001] This invention belongs to the field of well logging interpretation and evaluation, and specifically relates to a method for predicting shear wave time difference in coal-bearing formations using conventional well logging data. Background Technology

[0002] In oilfield reservoir rock mechanics parameter calculation, in-situ stress calculation, fracturing capability evaluation, stratification and segmentation, and hydraulic fracturing engineering evaluation and fracturing operations, shear wave transit time data is indispensable. While dipole acoustic imaging logging can obtain shear wave transit time, it is costly and complex, and generally only a few exploration wells in coal-bearing strata study areas undergo dipole acoustic imaging logging. To obtain rock mechanics parameters, in-situ stress, and fracturing capability evaluations for other wells, shear wave transit time can only be predicted using economical and abundant conventional logging data. Domestic and international scholars have conducted some research on shear wave transit time prediction, obtaining empirical formulas. For example, Gan Lideng fitted data based on full-wavelength logging data from Shengli, Liaohe, and Zhongyuan oilfields. R.A. Anderson et al. used the relationship between Poisson's ratio and clay content for fitting. Li Qingzhong used quasi-parabolic fitting based on seismic P-wave and S-wave velocity measurements. Examples include Li Qingzhong's shear wave velocity calculation formula, the Greenberg-Castagna shear wave prediction method, and the shear wave velocity relationship established by Ma Zhonggao et al. However, many empirical methods have limited adaptability and cannot meet the needs of accurately predicting the shear wave time difference of different lithologies in coal-bearing strata in actual applications. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for predicting shear wave time difference in coal-bearing strata using conventional well logging data. This solves the problem that empirical methods are difficult to meet the prediction requirements for shear wave time difference of different lithologies in the bottom layer of coal-bearing strata in actual coal-bearing strata applications.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A method for predicting shear wave time difference in coal-bearing formations using conventional well logging data includes the following steps:

[0006] Step 1: Obtain formation shear wave transit time (DTS) curves, acoustic transit time (AC), density (DEN), natural gamma ray (GR), and resistivity curve data of coal-bearing strata.

[0007] Step 2: Determine the lithology of the coal-bearing strata, obtain conventional logging curve values ​​through the lithology, and calculate the different lithology content curves of strata at different depths through the conventional logging curve values;

[0008] Step 3: Based on the lithology of the coal-bearing strata, and according to the correlation between the shear wave transit time (DTS) curve and conventional logging curves of different lithologies, establish a prediction formula model for the shear wave transit time of different lithologies in the coal-bearing strata.

[0009] When the lithology is coal and rock, the formula for calculating shear wave transit time is:

[0010] DTS=a*(AC / DEN)+b (5)

[0011] When the lithology is sandstone and mudstone, the formula for calculating shear wave transit time is:

[0012] DTS=c*AC+d (6)

[0013] When the lithology is limestone, the formula for calculating shear wave transit time is:

[0014] DTS=e*(AC / DEN)+f (7)

[0015] In the formula: DTS is the calculated shear wave transit time, μs / m; AC is the conventional logging sonic transit time data, μs / m; DEN is the conventional logging density data, g / cm³. 3 a, b, c, d, e, and f are the fitting parameters to be determined.

[0016] Step 4: Substitute the acoustic transit time AC and density DEN from Step 1 into formulas (5), (6) and (7) to obtain the transverse wave transit time of the coal-bearing strata.

[0017] A further improvement of the present invention is that:

[0018] Preferably, in step 1, the formation shear wave time difference (DTS) curve of the coal-bearing strata is obtained by dipole acoustic imaging logging.

[0019] Preferably, in step 1, sonic transit time (AC), density (DEN), natural gamma ray (GR), and resistivity curve data are obtained using conventional logging methods.

[0020] Preferably, in step 2, the formula for calculating the clay content in the coal-bearing strata is:

[0021]

[0022] Where GR is the natural gamma value of the calculation point; GR MIN The minimum natural gamma within the depth range; GR MAX This represents the maximum natural gamma value within the depth range.

[0023] Preferably, in step 2, when the density of DEN is between A1 and A2 g / cm³ 3 At that time, the lithology was coal and rock.

[0024] Preferably, when the lithology is coal-lithology, the formula for calculating coal content is:

[0025] VCOAL = 100 - VSH (2)

[0026] Wherein, VCOAL represents coal content, %; and VSH represents clay content, %.

[0027] Preferably, in step 2, when the density of DEN is between B1 and B2 g / cm³ 3 When the resistivity RT is within the range of B3 to B4 Ω·m, the lithology is sandstone and mudstone.

[0028] Preferably, in step 2, when the lithology is sandstone and mudstone, the formula for calculating the sand content is:

[0029] VSAND = 100 - VSH (3).

[0030] Wherein, VSAND represents sand content, %; VSH represents clay content, %.

[0031] Preferably, in step 2, when the density of DEN is between C1 and C2 g / cm³ 3 Within the range of C3Ω·m, and when the resistivity RT is greater than C3Ω·m, the lithology is limestone.

[0032] Preferably, when the lithology is limestone, the formula for calculating the lime content is:

[0033] VLIME = 100 - VSH (4)

[0034] Wherein, VLIME represents ash content, %; and VSH represents clay content, %.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention discloses a method for predicting shear wave transit time in coal-bearing formations using conventional well logging data. The method first determines the shear wave transit time curve data, sonic transit time, density, and natural gamma curve data for coal-bearing formations. Based on the correlation between the shear wave transit time curve and conventional well logging curves for different lithologies, a prediction formula model for shear wave transit time in different lithologies of coal-bearing formations is established. Based on the lithology of the wellbore section of the conventional well logging data to be calculated, a suitable shear wave transit time prediction model is selected for calculation. This invention, by establishing a formula for predicting the shear wave transit time of a work area using conventional well logging data in coal-bearing formations, calculates the shear wave transit time curve of wells without measured dipole sonic imaging logging. This achieves the quantitative acquisition of continuous shear wave transit time parameter profiles using conventional well logging data with good continuity and economic reliability, providing key parameters for calculating the rock mechanical stress and evaluating the fracturing capability of coal-bearing formations.

[0037] This method first identifies different lithologies of coal-bearing strata through well logging. Based on lithology differentiation, it establishes a relationship between shear wave transit time and conventional well logging parameters, enabling relatively accurate calculation of shear wave transit time parameters for different lithological variations in coal-bearing strata. This solves the problem that the original calculation model could not accurately calculate shear wave transit time due to the multi-lithological variations in coal-bearing strata. It can accurately meet the needs of actual coal-bearing strata production, fulfilling the requirements of coal-bearing strata geomechanics, engineering evaluation, and fracturing operations, and can promptly serve and meet the needs of coal-bearing strata evaluation. Attached Figure Description

[0038] Figure 1 This is a flowchart of a method for predicting shear wave time difference in coal-bearing formations using conventional well logging data, provided by an embodiment of the present invention.

[0039] Figure 2 This invention relates to the correlation between shear wave transit time in coal and rock measurements in coal-bearing formations and conventional logging curves, as provided in this embodiment.

[0040] Figure 3 This invention relates to the correlation between shear wave transit time in coal-bearing sandstone and mudstone formations and conventional logging curves, as provided in this embodiment.

[0041] Figure 4 This invention relates to the correlation between shear wave transit time in coal-bearing limestone formations and conventional logging curves, as provided in this embodiment.

[0042] Figure 5 This is a comparison diagram of the predicted shear wave time difference and the measured shear wave time difference in coal-bearing strata provided by an embodiment of the present invention. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings:

[0044] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] A method for predicting shear wave time difference in coal-bearing formations using conventional well logging data, see [link to relevant documentation]. Figure 1 The method includes the following steps:

[0046] Step 1: Obtain formation shear wave time-of-flight (DTS) curve data of coal-bearing strata using dipole acoustic imaging logging. Measure the coal-bearing strata using conventional logging methods to obtain acoustic time-of-flight (AC), density (DEN), natural gamma (GR), and resistivity (RT) curve data.

[0047] Step 2: Determine the lithology based on core or logging data of the coal-bearing strata, and obtain conventional logging curve values ​​for the corresponding depth using the lithology data determined by the lithology or logging. Analyze the logging response characteristics of the conventional logging curves and different lithologies to identify and judge the lithology of the coal-bearing strata, and calculate the lithology content curves of different lithologies in the wellbore using the conventional logging curve values;

[0048] Conventional well logging is used to identify and determine different lithologies in coal-bearing strata and to calculate the content of different lithologies, as follows:

[0049] When the density DEN is between A1 and A2 g / cm³ 3 At that time, the lithology was coal-rock;

[0050] When the density of DEN is between B1 and B2 g / cm³ 3 Furthermore, when the resistivity RT is between B3 and B4 Ω·m, the lithology is sandstone and mudstone.

[0051] When the density of DEN is between C1 and C2 g / cm³ 3 Furthermore, when the resistivity RT is greater than C3Ω·m, the lithology is limestone.

[0052] The above A1, A2, B1, B2, B3, B4, C1, C2, and C3 are adjusted according to different regions.

[0053] The clay content in coal-bearing strata is calculated using the following formula:

[0054]

[0055] When the lithology is coal-lithology, the formula for calculating coal content is:

[0056] VCOAL = 100 - VSH (2)

[0057] When the lithology is sandstone and mudstone, the formula for calculating sand content is as follows:

[0058] VSAND = 100 - VSH (3)

[0059] When the lithology is limestone, the formula for calculating the lime content is as follows:

[0060] VLIME = 100 - VSH (4)

[0061] In the formula: VSH is the clay content, %; VCOAL is the coal content, %; VSAND is the sand content, %; VLIME is the ash content, %; GR is the natural gamma value at the calculation point, API; GR MIN API; GR is the minimum natural gamma within the depth segment. MAX API is the maximum natural gamma value within the depth range; GCUR is an empirical coefficient related to the formation, with 3.7 for new formations and 2.0 for old formations.

[0062] Step 3: Using the coal-bearing lithology obtained in Step 2, and based on the correlation between the shear wave time difference curve (DTS) measured by dipole acoustic imaging logging in Step 1 and the conventional logging curve data of different lithologies in the work area measured by conventional logging methods, establish a prediction formula model for shear wave time difference of different lithologies in coal-bearing strata.

[0063] The following formula is established for predicting shear wave time differences in different lithologies of coal-bearing strata:

[0064] When the lithology is coal and rock, the formula for calculating shear wave transit time is:

[0065] DTS=a*(AC / DEN)+b (5)

[0066] When the lithology is sandstone or mudstone, the formula for calculating shear wave transit time is as follows:

[0067] DTS=c*AC+d (6)

[0068] When the lithology is limestone, the formula for calculating shear wave transit time is:

[0069] DTS=e*(AC / DEN)+f (7)

[0070] In the formula: DTS is the calculated shear wave transit time, μs / m; AC is the conventional logging sonic transit time data, μs / m; DEN is the conventional logging density data, g / cm³. 3 a, b, c, d, e, and f are the fitting parameters to be determined.

[0071] Step 4: Based on the conventional logging data of the continuous interval well section to be calculated, substitute the data from Step 3 into the prediction formula model for shear wave time difference of different lithologies, and the shear wave time difference of coal-bearing strata can be continuously predicted and calculated.

[0072] This invention, by addressing the multi-lithological variation characteristics of coal-bearing strata, predicts the shear wave transit time of coal-bearing strata using conventional well logging data for different lithologies, and calculates the shear wave transit time curves of wells without measured dipole acoustic imaging logging. This achieves the quantitative acquisition of continuous shear wave transit time parameter profiles using conventional well logging data that offers good continuity and is economically reliable. This provides key parameters for calculating rock mechanics and in-situ stress in coal-bearing strata and evaluating their fracturing capability. The method is simple to operate, applicable to coal-bearing strata, and can promptly serve and meet the needs of geomechanical and engineering fracturing evaluation in coal-bearing strata.

[0073] Example

[0074] A method for predicting shear wave time difference in coal-bearing formations using conventional well logging data.

[0075] Step (1): Dipole acoustic imaging logging is used to obtain the formation transverse time-of-flight (DTS) curve data of coal-bearing strata. Conventional logging is used to obtain the acoustic time-of-flight (AC), density (DEN), natural gamma (GR), resistivity (RT) curve data.

[0076] Step (2): Determine the lithology based on the core or logging data of the coal-bearing strata, calibrate the logging curve data based on the lithology data determined by the lithology or logging data, analyze the logging response characteristics of conventional logging curves and different lithologies, identify and judge the lithology of the coal-bearing strata, and calculate the lithology content curves of different lithologies in the wellbore based on the conventional logging curve data.

[0077] Conventional well logging is used to identify and determine different lithologies in coal-bearing strata and to calculate the content of different lithologies, as follows:

[0078] When the density of DEN is between 1.10 and 1.50 g / cm³ 3 At that time, the lithology was coal-rock;

[0079] When the density of DEN is between 2.20 and 2.85 g / cm³ 3 Furthermore, when the resistivity RT is between 10 and 1000 Ω·m, the lithology is sandstone and mudstone.

[0080] When the density of DEN is between 2.50 and 2.72 g / cm³ 3 Furthermore, when the resistivity RT is greater than 1000 Ω·m, the lithology is limestone.

[0081] The clay content is calculated using the following formula:

[0082]

[0083]

[0084] When the lithology is coal-lithology, the formula for calculating coal content is:

[0085] VCOAL = 100 - VSH

[0086] When the lithology is sandstone and mudstone, the formula for calculating sand content is as follows:

[0087] VSAND = 100 - VSH

[0088] When the lithology is limestone, the formula for calculating the lime content is as follows:

[0089] VLIME = 100 - VSH

[0090] In the formula: VSH is the clay content, %; VCOAL is the coal content, %; VSAND is the sand content, %; VLIME is the ash content, %; GR is the natural gamma value at the calculation point, API; GR MIN API; GR is the minimum natural gamma within the depth segment. MAX API is the maximum natural gamma value within the depth range; GCUR is an empirical coefficient related to the formation, with 3.7 for new formations and 2.0 for old formations.

[0091] Step (3): Using the coal-bearing lithology obtained in step (2), and based on the correlation between the shear wave time difference measured by dipole acoustic imaging logging and the conventional logging curve data of different lithologies, establish a prediction formula model for the shear wave time difference of different lithologies in coal-bearing strata.

[0092] For step (3), see Figure 2 , Figure 3 , Figure 4 The following formula is established for predicting the shear wave time difference of different lithologies in coal-bearing strata in this invention:

[0093] When the lithology is coal and rock, the formula for calculating shear wave transit time is:

[0094] DTS=a*(AC / DEN)+b

[0095] When the lithology is sandstone or mudstone, the formula for calculating shear wave transit time is as follows:

[0096] DTS = c * AC + d

[0097] When the lithology is limestone, the formula for calculating shear wave transit time is:

[0098] DTS=e*(AC / DEN)+f

[0099] In the formula: DTS is the calculated shear wave transit time, μs / m; AC is the conventional logging sonic transit time data, μs / m; DEN is the conventional logging density data, g / cm³. 3 a, b, c, d, e, and f are the fitting parameters to be determined, with a = 1.6893, b = 156.76, c = 2.4673, d = -136.62, e = 3.6609, and f = 92.446.

[0100] Step (4) Based on the conventional logging data of the continuous interval well section to be calculated, substitute the data from step (3) into the prediction formula model for shear wave time difference of different lithologies, and the shear wave time difference of coal-bearing strata can be continuously predicted and calculated.

[0101] Figure 5 This is a diagram showing the predicted shear wave time difference calculated by this invention. As can be seen from the diagram, comparing the calculated shear wave time difference with that measured by dipole acoustic imaging logging, the calculated shear wave time difference for coal-bearing formations exhibits a low relative error rate, high accuracy, and good application results.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting shear wave time difference in coal-bearing formations using conventional well logging data, characterized in that, Includes the following steps: Step 1: Obtain formation shear wave transit time (DTS) curves, acoustic transit time (AC), density (DEN), natural gamma ray (GR), and resistivity curve data of coal-bearing strata. Step 2: Determine the lithology of the coal-bearing strata, obtain conventional logging curve values ​​through the lithology, and calculate the different lithology content curves of strata at different depths through the conventional logging curve values; Step 3: Based on the lithology of the coal-bearing strata, and according to the correlation between the shear wave transit time (DTS) curve and conventional logging curves of different lithologies, establish a prediction formula model for the shear wave transit time of different lithologies in the coal-bearing strata. When the lithology is coal and rock, the formula for calculating shear wave transit time is: （5） When the lithology is sandstone and mudstone, the formula for calculating shear wave transit time is: （6） When the lithology is limestone, the formula for calculating shear wave transit time is: （7） In the formula: DTS is the calculated shear wave transit time, μs / m; AC is the conventional logging sonic transit time data, μs / m; DEN is the conventional logging density data, g / cm³. 3 a, b, c, d, e, and f are the fitting parameters to be determined. Step 4: Substitute the acoustic time difference AC and density DEN from Step 1 into formulas (5), (6) and (7) to obtain the transverse wave time difference of the coal-bearing strata.

2. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 1, the formation shear wave time difference (DTS) curve of the coal-bearing strata is obtained by dipole acoustic imaging logging.

3. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 1, sonic transit time (AC), density (DEN), natural gamma ray (GR), and resistivity curve data are obtained using conventional logging methods.

4. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 2, the formula for calculating the clay content in coal-bearing strata is: （1） Where GR is the natural gamma value of the calculation point; GR MIN The minimum natural gamma within the depth range; GR MAX This represents the maximum natural gamma within the depth range; In the formula: VSH is the clay content, %; GCUR is an empirical coefficient related to the formation, which is 3.7 for new formations and 2.0 for old formations.

5. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 2, when the density of DEN is between 1.10 and 1.50 g / cm³ 3 At that time, the lithology was coal and rock.

6. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 5, characterized in that, When the lithology is coal-lithology, the formula for calculating coal content is: （2） Wherein, VCOAL represents coal content (%), and VSH represents clay content (%).

7. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 2, when the density of DEN is between 2.20 and 2.85 g / cm³ 3 When the resistivity RT is within the range of 10~1000Ω·m, the lithology is sandstone and mudstone.

8. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 7, characterized in that, In step 2, when the lithology is sandstone and mudstone, the formula for calculating the sand content is: （3） Wherein, VSAND represents sand content (%), and VSH represents clay content (%).

9. The method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 1, characterized in that, In step 2, when the density of DEN is between 2.50 and 2.72 g / cm³ 3 Within the range of resistivity RT, when the resistivity RT is greater than 1000 Ω·m, the lithology is limestone.

10. A method for predicting shear wave time difference in coal-bearing formations using conventional well logging data according to claim 9, characterized in that, When the lithology is limestone, the formula for calculating the lime content is: （4） Wherein, VLIME represents ash content (%), and VSH represents clay content (%).

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