Model-based dispersive processing of borehole dipole wave data using an equivalent-tool theory

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. D35-D43 ◽  
Author(s):  
Sheng-Qing Lee ◽  
Xiao-Ming Tang ◽  
Yuan-da Su ◽  
Chun-Xi Zhuang
Keyword(s):  
Data Processing ◽  
Dispersion Curve ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Flexural Wave ◽  
Dispersion Characteristics ◽  
Acoustic Data ◽  
Model Based ◽  
Dispersion Data ◽  
Application Procedure

We have developed a model-based processing technique for borehole dipole S-wave logging data to estimate formation shear slowness from the data. During dipole acoustic logging, the presence of the logging tool can significantly affect the dispersion characteristics of flexural waves. Therefore, modeling the effects of the tool is essential for model-based processing. We have determined that an equivalent-tool theory using only two parameters, tool radius, and modulus, can adequately model the flexural-wave-dispersion characteristics. We used this theory, together with a calibration procedure, to determine the tool parameters to formulate an inversion method for the logging data processing. Our use of the equivalent tool theory played an important role in fitting the theoretical dispersion curve to the actual flexural-wave-dispersion data, enabling fast processing of the field acoustic data. An advantage of this model-based method is its prediction power, which, in the absence of low-frequency dispersion data, allows for predicting formation shear slowness from the low-frequency limit of the model-fitted dispersion curve. We have also developed an application procedure of the method for field-data processing and demonstrated its effectiveness in the dispersion correction using field acoustic data from fast and slow formations.

Mapping formation radial shear-wave velocity variation by a constrained inversion of borehole flexural-wave dispersion data

Geophysics ◽  
2010 ◽  
Vol 75 (6) ◽  
pp. E183-E190 ◽  
Author(s):  
Xiao-Ming Tang ◽  
Douglas J. Patterson
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
High Frequency ◽  
Wave Dispersion ◽  
Velocity Variation ◽  
Flexural Wave ◽  
Inversion Method ◽  
Dispersion Characteristics ◽  
Dispersion Data

We have developed a novel constrained inversion method for estimating a radial shear-wave velocity profile away from the wellbore using dipole acoustic logging data and have analyzed the effect of the radial velocity changes on dipole-flexural-wave dispersion characteristics. The inversion of the dispersion data to estimate the radial changes is inherently a nonunique problem because changing the degree of variation or the radial size of the variation zone can produce similar wave-dispersion characteristics. Nonuniqueness can be solved by developing a constrained inversion method. This is done by constraining the high-frequency portion of the model dispersion curve with another curve calculated using the near-borehole velocity. The constraint condition is based on the physical principle that a high-frequency dipole wave has a shallow penetration depth and is therefore sensitive to the near-borehole shear-wave velocity. We have validated the result of the constrained inversion with synthetic data testing. Combining the new inversion method with four-component crossed-dipole anisotropy processing obtains shear radial profiles in fast and slow shear polarization directions. In a sandstone formation, the fast and slow shear-wave profiles show substantial differences caused by the near-borehole stress field, demonstrating the ability of the technique to obtain radial and azimuthal geomechanical property changes near the wellbore.

scholarly journals Estimation of <i>Vs</i> profile using its natural frequency and Rayleigh-wave dispersion characteristics

2008 ◽  
Vol 14 ◽  
pp. 75-77 ◽  
Author(s):  
K. Tokeshi ◽  
M. Karkee ◽  
C. Cuadra
Keyword(s):  
Rayleigh Wave ◽  
Dispersion Curve ◽  
Natural Frequency ◽  
Numerical Test ◽  
Wave Dispersion ◽  
Test Site ◽  
Dispersion Characteristics ◽  
Rayleigh Wave Dispersion

Abstract. The evaluation of the natural frequency of random Vs profiles before analyzing the fundamental Rayleigh-wave dispersion characteristics is proposed in this paper. The inclusion of this parameter optimizes the effectiveness of random inverse searching to estimate Vs profiles. To demonstrate this method, a numerical test was performed using the "experimental" Rayleigh-wave dispersion curve obtained for a fictitious TEST site.

Advances in Cased Hole Acoustic Slowness Measurements and Its Application in a Depleted Reservoir Drilled with Highly Inclined Well: A Case Study from Offshore Malaysia

2021 ◽  
Author(s):  
M. Amin C. A. Razak ◽  
Ayham Ashqar ◽  
Saikat Das ◽  
Ahmad Izzuddin B. Yusof ◽  
Arie Purba Tata ◽  
...  
Keyword(s):  
Data Quality ◽  
Data Acquisition ◽  
Low Frequency ◽  
Flexural Wave ◽  
Bond Quality ◽  
Acoustic Data ◽  
Challenging Environment ◽  
Open Hole ◽  
Well Data ◽  
Cement Bond Quality

Abstract Acquiring acoustic slowness data in open & cased hole and a reliable cement bond log in one run without jeopardising data quality or increasing rig time is desired for fast and optimize data acquisition. This paper reviews the steps taken to ensure acoustic slowness and cement bond data acquisition fulfils the objective, while minimising the cost in an offshore challenging environment for formations with variable acoustic velocities that could be masked by strong casing arrivals. Crossed dipole acoustic logging is typically preferred to acquire within open hole environment for best quality signal. However, due to drilling challenges this could not be done in the subject well. Data was acquired in 6in open hole and 7" liner (8.5 in Open hole behind) cased hole section together in one run. Shear slowness in slow formation requires propagation of the low frequency dipole flexural wave whereas compressional slowness acquisition and cement bond evaluation requires high frequency monopole data. An improved understanding of cased-hole acoustic modes allowed developing the ability to transmit acoustic energies at optimal frequencies in order to acquire formation slowness concurrently with cement bond. Acoustic data quality in cased hole is dependent on cement bond quality. Poor bonding or presence of fluid between casing and the formation inserts noise in the data by damping the acoustic signal. Hence, understanding of the cement bond quality is critical in interpreting the cased hole acoustic data. The low amplitude of the compressional first arrival indicated the presence of cement bonded with the casing. Absence of casing ringing signal at the beginning and presence of strong formation signal in the VDL indicated good bonding of cement with formation. Filtration of the cased hole acquired semblances were necessary to remove the casing and fluids noises. Acquired data shows good coherency and continuous compressional and shear slowness's were extracted from the good quality semblances. This integrated strategy to acquire the formation slowness and to evaluate the cement bond quality and top of cement allowed meeting all objectives with one tool in single run. The risk of casing waves that could have masked the formation slowness signal was mitigated by transmitting acoustic energies at optimal frequencies with wider bandwidth followed by the semblance processing. The effects of borehole ovality, tool centralization, or casing centralization on waveform propagation were studied to supplement the interpretation. The first times strategic logging application in PETRONAS allowed time and cost saving and fulfilled all data acquisition plan. Data quality assurance and decision tree allowed drafting a workflow to assure data quality. This solution showed importance of smart planning to maximise advanced tools capabilities to acquire acoustic slowness data and cement evaluation in single run in offshore challenging environment.

Lateral variation of rayleigh-wave dispersion characteristics in Australia

1970 ◽  
Vol 60 (6) ◽  
pp. 1897-1906
Author(s):  
Harsh K. Gupta ◽  
Janardan G. Negi
Keyword(s):  
Rayleigh Wave ◽  
Wave Dispersion ◽  
Dispersion Characteristics ◽  
Lateral Variation ◽  
Lateral Velocity ◽  
Entire Family ◽  
Period Range ◽  
Velocity Gradients ◽  
Dispersion Data ◽  
Rayleigh Wave Dispersion

Abstract Rayleigh wave dispersion data on Australia by Bolt and Niazi (1964) and Thomas (1969) are examined in detail in the period range of 20 to 40 sec. The dispersion characteristics correspond well to region 7 in Santô's (1965) classification. A further and similar inspection of the African mass, Brazilian shield, Canadian shield etc. reveals that the entire family of shield areas systematically belongs to Santô's regions 6 and/or 7. They are uniformly characterized by the absence of appreciable lateral velocity gradients in clear contrast to corresponding extremely steep gradients for high seismicity areas.

Determining formation S-wave transverse isotropy from borehole flexural-wave dispersion data

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. D47-D55 ◽  
Author(s):  
Song Xu ◽  
Xiao-Ming Tang ◽  
Yuan-Da Su ◽  
Sheng-Qing Lee ◽  
Chun-Xi Zhuang
Keyword(s):  
Transverse Isotropy ◽  
Transversely Isotropic ◽  
Wave Dispersion ◽  
Flexural Wave ◽  
Stoneley Wave ◽  
S Wave ◽  
Acoustic Logging ◽  
Wave Measurements ◽  
Dispersion Data ◽  
Ti Media

Many earth formations are characterized as transversely isotropic (TI) media. In acoustic logging through a vertical borehole, the S-wave TI property has traditionally been determined from borehole monopole Stoneley-wave measurements, but the feasibility of shear-TI estimation from dipole flexural waves has not been fully investigated. We have developed a methodology to determine the TI parameters from borehole dipole-flexural wave data. Our analysis shows that the Stoneley wave is sensitive to the TI property mainly in an acoustically slow formation, and the sensitivity diminishes when the formation becomes faster. The advantage of the flexural wave over the Stoneley wave is that the former wave is sensitive to the TI property in the slow and fast formations, provided the wave measurement is made in a broad frequency range in which the flexural-wave dispersion characteristics from low to high frequencies can be used. By calculating the theoretical flexural-wave dispersion curve for the TI formation and using it to fit the measured wave dispersion data, we can simultaneously determine the vertical and horizontal S-wave velocities, from which the S-wave TI parameter is obtained. Application of our methodology to field data processing shows that the TI parameter estimated from the flexural wave is almost identical to that from the Stoneley wave for a slow formation. For a fast formation, the flexural-wave result is more accurate and reliable compared with the Stoneley-wave result. Our study, thus, introduces a novel application of dipole acoustic logging.

Sign in / Sign up

Export Citation Format

Share Document