Stratum interval transit time combined measurement device and method

Abstract

The invention provides a formation sound wave time difference combined measuring device and method.The device comprises a digital sound wave logging instrument and a dipole sound wave logging instrument, and when a to-be-measured well is arranged, the digital sound wave logging instrument and the dipole sound wave logging instrument are sequentially arranged from the bottom to the upper portion of the to-be-measured well; the arrangement distance between the digital acoustic logging instrument and the dipole acoustic logging instrument is larger than or equal to a preset threshold value. According to the method, the measurement advantages of the dipole acoustic logging instrument and the digital acoustic logging instrument are used for complementary combination; the risk of instrument data acquisition failure under complex well conditions such as high-temperature and high-pressure highly-deviated wells and horizontal wells can be effectively controlled, and the reliability of formation interval transit time and the success rate of one-time acquisition of data are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of well logging in petroleum exploration and development, and particularly relates to a formation acoustic wave time difference combined measurement device and method. Background Art

[0002] Acoustic logging is a type of logging method that determines the geological characteristics of the wellbore formation and the wellbore engineering conditions by measuring the acoustic properties of the wellbore medium. The original waveform time domain data collected by the acoustic logging instrument can extract the three-time difference information of the wellbore formation, including the longitudinal wave time difference, the transverse wave time difference and the Stoneley wave time difference. The above time difference information can be used to evaluate geological information such as lithology, anisotropy and porosity of the formation. At present, the commonly used acoustic logging instruments are dipole acoustic logging instruments and digital acoustic logging instruments. The former can provide three-time difference information of the formation at the same time, and the latter only provides the longitudinal wave time difference information of the formation. It is generally believed that the longitudinal wave time difference provided by digital acoustic waves is more reliable. As the oil exploration and development reservoir gradually moves from shallow layers to deep layers and even ultra-deep layers, complex well conditions such as highly deviated wells and horizontal wells have become the main well types. At the same time, due to the increase in well depth, the downhole temperature and pressure increase significantly, and high temperature and high pressure and even ultra-high temperature and high pressure measurement environments become the norm, which brings uncertainty to the success rate of obtaining data from a single logging instrument in one go. Summary of the invention

[0003] In order to ensure high logging timeliness and a high success rate in acquiring logging data in one go, the purpose of the present invention is to provide a formation acoustic time difference combined measurement device and method to increase the reliability of formation acoustic time difference measurement and greatly improve the success rate in acquiring formation acoustic time difference in one go.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a formation acoustic time difference combined measurement device, which includes a digital acoustic logging instrument and a dipole acoustic logging instrument. When the well to be logged is arranged, the digital acoustic logging instrument and the dipole acoustic logging instrument are arranged from the bottom to the top of the well to be logged, and the arrangement spacing between the digital acoustic logging instrument and the dipole acoustic logging instrument is greater than or equal to a preset threshold.

[0006] Preferably, other logging instruments are arranged between the digital acoustic logging instrument and the dipole acoustic logging instrument.

[0007] Preferably, the other logging instruments include a dual lateral logging instrument, a four-arm caliper logging instrument, an insulating short joint, a spectral gamma ray spectral logging instrument and a flexible short joint, wherein, when the well to be logged is arranged, from the bottom to the top of the well to be logged, there are in order the dual lateral logging instrument, the four-arm caliper logging instrument, the insulating short joint, the spectral gamma ray spectral logging instrument and the flexible short joint.

[0008] Preferably, the dipole acoustic logging instrument comprises a first far monopole transmitter, a dipole transmitter, a first near monopole transmitter, a first sound insulator and eight array receivers, wherein the first far monopole transmitter, the dipole transmitter, the first near monopole transmitter, the first sound insulator, the first array receiver, the second array receiver, the third array receiver, the fourth array receiver, the fifth array receiver, the sixth array receiver, the seventh array receiver and the eighth array receiver are arranged in sequence from the bottom to the top of the well to be logged.

[0009] Preferably, the digital acoustic logging instrument comprises a second far monopole transmitter, a second near monopole transmitter, a second sound insulator and four array receivers, wherein the second far monopole transmitter, the second near monopole transmitter, the second sound insulator, the first array receiver, the second array receiver, the third array receiver and the fourth array receiver are arranged in sequence from the bottom to the top of the well to be logged.

[0010] Preferably, the preset threshold is 10 meters.

[0011] A combined measurement method of formation acoustic wave time difference, based on the device, comprises the following steps:

[0012] Set the optimal center operating frequency of the dipole sonic logging tool and the digital sonic logging tool respectively;

[0013] Using a dipole acoustic logging instrument to collect a first far monopole acoustic waveform time domain signal, a dipole acoustic waveform time domain signal, and a first near monopole acoustic waveform time domain signal;

[0014] Using a digital acoustic logging instrument to collect a second far monopole acoustic waveform time domain signal and a second near monopole acoustic waveform time domain signal;

[0015] The longitudinal wave time difference, shear wave time difference and Stoneley wave time difference of the formation acoustic wave of the well to be measured are obtained according to the obtained acoustic wave waveform time domain signal.

[0016] Preferably, the optimal central operating frequencies of the dipole sonic logging tool and the digital sonic logging tool are set respectively, and the specific method is:

[0017] Establishing target signal thresholds for dipole sonic logging tools and digital sonic logging tools respectively;

[0018] The least square method is combined with the target signal threshold to establish the optimal design objective functions of the central working frequency of the dipole acoustic logging tool and the digital acoustic logging tool respectively.

[0019] Set the constraints of the central operating frequency optimization design objective function;

[0020] The optimal central operating frequency of the dipole acoustic logging tool and the optimal central operating frequency of the digital acoustic logging tool are obtained by using the optimization objective function and constraint conditions combined with the least square method.

[0021] Preferably, the center operating frequency optimization design objective functions of the dipole sonic logging tool and the digital sonic logging tool are:

[0022] arg min f(fre_Txi)=(signal(fre_Txi)-Signal Txi ) 2

[0023] arg min f(fre_Ti)=(signal(fre_Ti)-Signal Ti ) 2

[0024] Among them, arg min represents the value of the variable when the following formula reaches the minimum value; fre_Txi represents the central operating frequency of the dipole acoustic logging tool; fre_Ti represents the central operating frequency of the digital acoustic logging tool; Signal Txi Indicates the acoustic signal amplitude required by each receiver of the dipole acoustic logging tool; Signal Ti It represents the acoustic signal amplitude required by each receiver of the digital acoustic logging instrument; signal(fre_Txi) represents the signal amplitude of the dipole acoustic logging instrument at different central operating frequencies; signal(fre_Ti) represents the signal amplitude of the digital acoustic logging instrument at different central operating frequencies.

[0025] Preferably, the constraint condition for setting the center operating frequency optimization design objective function is:

[0026] fre_Tx min ≤fre_Txi≤fre_Tx max

[0027] fre_T min ≤fre_Ti≤fre_T max

[0028] Among them, fre_Tx min Indicates the lower limit of the central operating frequency of the dipole acoustic logging tool; fre_Tx max Indicates the upper limit of the central working frequency of the dipole acoustic logging instrument; fre_Txi indicates the central working frequency of the dipole acoustic logging instrument; fre_Ti indicates the central working frequency of the digital acoustic logging instrument; fre_T min Indicates the lower limit of the central operating frequency of the digital acoustic logging tool; fre_T max Indicates the upper limit of the central operating frequency of the digital acoustic logging tool.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a formation acoustic time difference combined measurement device, which utilizes the respective measurement advantages of a dipole acoustic logging instrument and a digital acoustic logging instrument for complementary combination, and can effectively control the risk of instrument data acquisition failure under complex well conditions such as high temperature and high pressure, high-angle wells and horizontal wells, thereby improving the reliability of the formation acoustic time difference and the success rate of one-time data acquisition.

[0031] At the same time, the present invention does not change the mechanical structure of the original dipole sonic logging instrument and the digital sonic logging instrument. By ensuring the minimum spacing between the two sonic instruments and optimizing the central operating frequency of the sonic transmitting transducer, the sonic signals of different transmitting-receiving combinations do not interfere with each other, and the optimized combination of formation longitudinal wave time difference, transverse wave time difference and Stoneley wave time difference information can be obtained. The risk of low data acquisition rate under complex well conditions such as high temperature and high pressure, high-angle wells and horizontal wells can be effectively controlled, thereby improving the reliability of formation sonic time difference and the success rate of one-time acquisition of logging data, and at the same time improving the time efficiency of logging operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A combined formation acoustic wave time difference measurement device provided by an embodiment of the present invention;

[0033] Figure 2 The optimization design process of the central operating frequency of the acoustic wave transducer provided by the embodiment of the present invention;

[0034] Figure 3 The present invention provides a combined measurement process of formation acoustic wave time difference. DETAILED DESCRIPTION

[0035] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0036] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0037] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0038] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0039] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0040] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0041] Example 1

[0042] like Figure 1 As shown, this embodiment provides a formation acoustic wave time difference combined measurement device, which comprises a digital acoustic wave logging instrument, other logging instruments and a dipole acoustic wave logging instrument from the bottom to the top.

[0043] The dipole acoustic logging instrument is composed of a first far monopole transmitter Tx1, a dipole transmitter Tx2, a first near monopole transmitter Tx3, a first sound insulator and eight array receivers Rx1-Rx8.

[0044] The first far monopole transmitter Tx1, the dipole transmitter Tx2, the first near monopole transmitter Tx3, the first sound insulator, the first array receiver Rx1, the second array receiver Rx2, the third array receiver Rx3, the fourth array receiver Rx4, the fifth array receiver Rx5, the sixth array receiver Rx6, the seventh array receiver Rx7 and the eighth array receiver Rx8 are arranged in sequence from bottom to top.

[0045] The digital acoustic logging tool is composed of a second far monopole transmitter T1, a second near monopole transmitter T2, a second sound insulator and four array receivers R1-R4.

[0046] The second far monopole transmitter T1, the second near monopole transmitter T2, the second sound insulator, the first array receiver R1, the second array receiver R2, the third array receiver R3 and the fourth array receiver R4 are arranged in sequence from bottom to top.

[0047] Different transmitting-receiving combinations can be used to simultaneously obtain the formation acoustic longitudinal wave time difference, shear wave time difference and Stoneley wave time difference information. At the same time, in order to ensure that there is enough acoustic signal attenuation distance between the two acoustic logging instruments, it is necessary to ensure that the length of the other logging instrument combination is more than 10 meters. Usually, other logging instruments include dual lateral logging instruments, four-arm caliper logging instruments, insulating short sections, energy spectrum gamma spectrum logging instruments and flexible short sections from bottom to top.

[0048] Other logging instruments can also measure other formation parameters, while ensuring that there is sufficient spacing between the two acoustic logging instruments.

[0049] Example 2

[0050] like Figure 2 As shown in the flowchart of the optimal design of the central working frequency of the dipole acoustic logging instrument and the digital acoustic logging instrument, the present embodiment provides a method for optimizing the central working frequency of the formation acoustic time difference combined measurement device. The dipole acoustic logging instrument and the digital acoustic logging instrument are matched and combined into an acoustic instrument string. In order to realize that the acoustic signals transmitted by each transmitting-receiving combination do not interfere with each other, a plurality of transmitting-receiving combinations are added between the two. Figure 1 In addition to increasing the spacing of the other logging instrument combinations shown, it is necessary to optimize the central operating frequency of the transmitting transducer. The specific optimization method includes the following steps:

[0051] S1, establish target signal thresholds for dipole acoustic logging tools and digital acoustic logging tools, where the dipole acoustic logging tool corresponds to three emission signal thresholds Signal Txi (i=1,2,3), digital acoustic logging tool corresponds to 2 emission signal thresholds Signal Ti (i=1, 2),

[0052] S2, using the least squares method, establish the optimal design objective function of the central working frequency of the dipole acoustic logging tool and the digital acoustic logging tool:

[0053] arg min f(fre_Txi)=(signal(fre_Txi)-Signal Txi )2 (1)

[0054] arg min f(fre_Ti)=(signal(fre _ Ti)-Signal ri ) 2 (2)

[0055] S3, according to the formation acoustic wave modes that can be excited by different working frequencies, set the constraints of the central working frequency optimization design objective function, which are:

[0056] fre_Tx min ≤fre_Txi≤fre_Tx max (3)

[0057] fre_T min ≤fre_Ti≤fre_T max (4)

[0058] Among them, arg min represents the value of the variable when the following formula reaches the minimum value; fre_Txi represents the central operating frequency of the dipole acoustic logging tool; fre_Tx min Indicates the lower limit of the central operating frequency of the dipole acoustic logging tool; fre_Tx max Indicates the upper limit of the central working frequency of the dipole acoustic logging instrument; fre_Ti indicates the central working frequency of the digital acoustic logging instrument; fre_T min Indicates the lower limit of the central operating frequency of the digital acoustic logging tool; fre_T max Indicates the upper limit of the central working frequency of the digital acoustic logging tool. Txi Indicates the acoustic signal amplitude required by each receiver of the dipole acoustic logging tool; Signal Ti It represents the acoustic signal amplitude required by each receiver of the digital acoustic logging instrument; signal(fre_Txi) represents the signal amplitude of the dipole acoustic logging instrument at different central operating frequencies; signal(fre_Ti) represents the signal amplitude of the digital acoustic logging instrument at different central operating frequencies.

[0059] The optimal central operating frequency fc_Txi of the dipole acoustic logging instrument and the optimal central operating frequency fc_Ti of the digital acoustic logging instrument are obtained by using the optimization objective function and constraint conditions combined with the least squares method. At this operating frequency, the time domain signal quality of the acoustic waveform received by the dipole acoustic logging instrument and the digital acoustic logging instrument is good and they do not interfere with each other.

[0060] Example 3

[0061] like Figure 3As shown, this embodiment provides a formation acoustic wave time difference combined measurement method, specifically:

[0062] S11, connecting a dipole acoustic logging instrument, other logging instruments and a digital acoustic logging instrument to form a logging instrument string, which can simultaneously measure dipole acoustic time difference and digital acoustic time difference information when it is run down the well once.

[0063] On the basis of ensuring that the distance between the dipole acoustic wave and the digital acoustic wave is more than 10 meters, the optimal center operating frequency of the dipole acoustic logging instrument and the digital acoustic logging instrument are set respectively. As the instrument string changes with the well depth in the well, at different formation depths, the dipole acoustic logging instrument collects the first far monopole, dipole, and first near monopole acoustic waveform time domain signals. At the same time, the digital acoustic logging instrument collects the second far monopole and the second near monopole acoustic waveform time domain signals. The collected acoustic waveform time domain signals can be used to obtain the acoustic time difference information of the formation. Among them, the dipole acoustic logging instrument can obtain the formation acoustic longitudinal wave time difference DTC1, shear wave time difference DTS and Stoneley wave time difference DTST, and the digital acoustic logging instrument can obtain the formation acoustic longitudinal wave time difference DTC2. The formation longitudinal wave time difference is obtained by the optimized combination of DTC1 and DTC2 to obtain the longitudinal wave time difference DTC.

[0064] The specific method of optimizing the combination is:

[0065] The dipole sonic logging instrument and the digital sonic logging instrument measure and obtain DTC1 and DTC2 respectively. According to the rock acoustic parameter information of the formation to be measured (such as Young's modulus and Poisson's ratio, etc.), a more reasonable formation P-wave time difference value is selected. Since the transmission and receiving distance of the digital sonic logging instrument is closer, the P-wave time difference is less affected by the adjacent formations and wellbore. Usually, the final P-wave time difference DTC=DTC2.

[0066] In summary, the complementary combination of the measurement advantages of dipole acoustic logging instruments and digital acoustic logging instruments can effectively control the risk of instrument data acquisition failure under complex well conditions such as high temperature and high pressure, high-angle wells and horizontal wells, greatly improve the reliability of formation acoustic time difference and the success rate of data acquisition in one time, and also promote the improvement of the timeliness of logging operations.

[0067] From the bottom to the top, the digital acoustic logging instrument, other logging instrument combinations and dipole acoustic logging instruments are combined and matched in sequence. The instrument combination string includes the far monopole and near monopole transmission and 4 array receiving transducers of the digital acoustic instrument, and the far monopole, dipole and near monopole transmission and 8 array receiving transducers of the dipole instrument. The other logging instrument combinations from the bottom to the top include lateral, wellbore, insulation short section, energy spectrum and flexible short section in sequence, ensuring that their total length is more than 10m. On the basis of not changing the existing mechanical structure of the two acoustic instruments, on the one hand, the distance between the two acoustic instruments is ensured to be more than 10 meters, and on the other hand, the target response threshold is set for each acoustic transmitting transducer. Through the optimization design of the central working frequency of the acoustic transducer, it is ensured that the acoustic signals of each part do not interfere with each other, and the effectiveness of the receiving transducer in collecting the acoustic waveform time domain signal is ensured. According to the collected acoustic waveforms, the dipole acoustic wave instrument can obtain the longitudinal wave time difference, transverse wave time difference and Stoneley wave time difference information of the formation acoustic wave, and the digital acoustic wave instrument can obtain the longitudinal wave time difference information of the formation, optimize the time difference results and combine them for output, and finally obtain the three time difference information of the formation acoustic wave.

[0068] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A combined measurement device for formation acoustic wave time difference, characterized in that: The device comprises a digital acoustic logging instrument and a dipole acoustic logging instrument, wherein, when the well to be logged is arranged, the digital acoustic logging instrument and the dipole acoustic logging instrument are arranged in sequence from the bottom to the top of the well to be logged, and the arrangement spacing between the digital acoustic logging instrument and the dipole acoustic logging instrument is greater than or equal to a preset threshold.

2. A combined formation acoustic wave time difference measurement device according to claim 1, characterized in that: Other logging instruments are arranged between the digital acoustic logging instrument and the dipole acoustic logging instrument.

3. A combined formation acoustic wave time difference measurement device according to claim 2, characterized in that: The other logging instruments include a dual lateral logging instrument, a four-arm caliper logging instrument, an insulating short joint, a spectral gamma spectral logging instrument and a flexible short joint. When the well to be logged is arranged, from the bottom to the top of the well to be logged, they are the dual lateral logging instrument, the four-arm caliper logging instrument, the insulating short joint, the spectral gamma spectral logging instrument and the flexible short joint.

4. A combined formation acoustic wave time difference measurement device according to claim 1, characterized in that: The dipole acoustic logging instrument comprises a first far monopole transmitter, a dipole transmitter, a first near monopole transmitter, a first sound insulator and eight array receivers, wherein the first far monopole transmitter, the dipole transmitter, the first near monopole transmitter, the first sound insulator, the first array receiver, the second array receiver, the third array receiver, the fourth array receiver, the fifth array receiver, the sixth array receiver, the seventh array receiver and the eighth array receiver are arranged in sequence from the bottom to the top of the well to be logged.

5. The combined formation acoustic wave time difference measurement device according to claim 1, characterized in that: The digital acoustic logging instrument comprises a second far monopole transmitter, a second near monopole transmitter, a second sound insulator and four array receivers, wherein the second far monopole transmitter, the second near monopole transmitter, the second sound insulator, the first array receiver, the second array receiver, the third array receiver and the fourth array receiver are arranged in sequence from the bottom to the top of the well to be logged.

6. The combined formation acoustic wave time difference measurement device according to claim 1, characterized in that: The preset threshold is 10 meters.

7. A combined measurement method of formation acoustic wave time difference, characterized in that: The device according to any one of claims 1 to 6 comprises the following steps: Set the optimal center operating frequency of the dipole sonic logging tool and the digital sonic logging tool respectively; Using a dipole acoustic logging instrument to collect a first far monopole acoustic waveform time domain signal, a dipole acoustic waveform time domain signal, and a first near monopole acoustic waveform time domain signal; Using a digital acoustic logging instrument to collect a second far monopole acoustic waveform time domain signal and a second near monopole acoustic waveform time domain signal; The longitudinal wave time difference, shear wave time difference and Stoneley wave time difference of the formation acoustic wave of the well to be measured are obtained according to the obtained acoustic wave waveform time domain signal.

8. A combined formation acoustic wave time difference measurement method according to claim 7, characterized in that: The optimal central operating frequencies of the dipole sonic logging tool and the digital sonic logging tool are set respectively. The specific method is: Establishing target signal thresholds for dipole sonic logging tools and digital sonic logging tools respectively; The least square method is combined with the target signal threshold to establish the optimal design objective functions of the central working frequency of the dipole acoustic logging tool and the digital acoustic logging tool respectively. Set the constraints of the central operating frequency optimization design objective function; The optimal central operating frequency of the dipole acoustic logging tool and the optimal central operating frequency of the digital acoustic logging tool are obtained by using the optimization objective function and constraint conditions combined with the least square method.

9. A formation acoustic wave time difference combined measurement method according to claim 8, characterized in that: The objective functions for optimizing the center operating frequency of dipole acoustic logging tools and digital acoustic logging tools are: arg min f(fre_Txi)=(signal(fre_Txi)-Signal Txi ) 2 arg min f(fre_Ti)=(signal(fre_Ti)-Signal Ti ) 2 Among them, arg min represents the value of the variable when the following formula reaches the minimum value; fre_Txi represents the central operating frequency of the dipole acoustic logging tool; fre_Ti represents the central operating frequency of the digital acoustic logging tool; Signal Txi Indicates the acoustic signal amplitude required by each receiver of the dipole acoustic logging tool; Signal Ti It represents the acoustic signal amplitude required by each receiver of the digital acoustic logging instrument; signal(fre_Txi) represents the signal amplitude of the dipole acoustic logging instrument at different central operating frequencies; signal(fre_Ti) represents the signal amplitude of the digital acoustic logging instrument at different central operating frequencies.

10. A formation acoustic wave time difference combined measurement method according to claim 8, characterized in that: The constraints for setting the central operating frequency optimization design objective function are: fre_Tx min ≤fre_Txi≤fre_Tx max fre_T min ≤fre_Ti≤fre_T max Among them, fre_Tx min Indicates the lower limit of the central operating frequency of the dipole acoustic logging tool; fre_Tx max Indicates the upper limit of the central working frequency of the dipole acoustic logging instrument; fre_Txi indicates the central working frequency of the dipole acoustic logging instrument; fre_Ti indicates the central working frequency of the digital acoustic logging instrument; fre_T min Indicates the lower limit of the central operating frequency of the digital acoustic logging tool; fre_T max Indicates the upper limit of the central operating frequency of the digital acoustic logging tool.

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