scholarly journals Travel-Time Inversion Method of Converted Shear Waves Using RayInvr Algorithm

2021 ◽  
Vol 11 (8) ◽  
pp. 3571
Author(s):  
Genggeng Wen ◽  
Kuiyuan Wan ◽  
Shaohong Xia ◽  
Huilong Xu ◽  
Chaoyan Fan ◽  
...  
Keyword(s):  
Travel Time ◽  
Wave Velocity ◽  
P Wave ◽  
Inversion Method ◽  
Time Inversion ◽  
Ocean Bottom Seismometer ◽  
S Wave ◽  
S Waves ◽  
Inversion Model ◽  
Travel Time Inversion

The detailed studies of converted S-waves recorded on the Ocean Bottom Seismometer (OBS) can provide evidence for constraining lithology and geophysical properties. However, the research of converted S-waves remains a weakness, especially the S-waves’ inversion. In this study, we applied a travel-time inversion method of converted S-waves to obtain the crustal S-wave velocity along the profile NS5. The velocities of the crust are determined by the following four aspects: (1) modelling the P-wave velocity, (2) constrained sediments Vp/Vs ratios and S-wave velocity using PPS phases, (3) the correction of PSS phases’ travel-time, and (4) appropriate parameters and initial model are selected for inversion. Our results show that the vs. and Vp/Vs of the crust are 3.0–4.4 km/s and 1.71–1.80, respectively. The inversion model has a similar trend in velocity and Vp/Vs ratios with the forward model, due to a small difference with ∆Vs of 0.1 km/s and ∆Vp/Vs of 0.03 between two models. In addition, the high-resolution inversion model has revealed many details of the crustal structures, including magma conduits, which further supports our method as feasible.

A case study: travel time inversion for P-wave velocity using OBS data of South China Sea

2012 ◽  
Vol 33 (4) ◽  
pp. 389-396 ◽  
Author(s):  
Xiangchun Wang ◽  
Timothy A. Minshull ◽  
Changliang Xia ◽  
Xuewei Liu
Keyword(s):  
South China Sea ◽  
Travel Time ◽  
Wave Velocity ◽  
South China ◽  
P Wave ◽  
Time Inversion ◽  
P Wave Velocity ◽  
Travel Time Inversion ◽  
Obs Data

scholarly journals OBS Data Analysis to Quantify Gas Hydrate and Free Gas in the South Shetland Margin (Antarctica)

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3290 ◽  
Author(s):  
Sha Song ◽  
Umberta Tinivella ◽  
Michela Giustiniani ◽  
Sunny Singhroha ◽  
Stefan Bünz ◽  
...  
Keyword(s):  
Velocity Field ◽  
Wave Velocity ◽  
Gas Hydrate ◽  
P Wave ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
S Wave ◽  
Free Gas ◽  
Hydrate Reservoir ◽  
Gas Hydrate Reservoir

The presence of a gas hydrate reservoir and free gas layer along the South Shetland margin (offshore Antarctic Peninsula) has been well documented in recent years. In order to better characterize gas hydrate reservoirs, with a particular focus on the quantification of gas hydrate and free gas and the petrophysical properties of the subsurface, we performed travel time inversion of ocean-bottom seismometer data in order to obtain detailed P- and S-wave velocity estimates of the sediments. The P-wave velocity field is determined by the inversion of P-wave refractions and reflections, while the S-wave velocity field is obtained from converted-wave reflections received on the horizontal components of ocean-bottom seismometer data. The resulting velocity fields are used to estimate gas hydrate and free gas concentrations using a modified Biot‐Geertsma‐Smit theory. The results show that hydrate concentration ranges from 10% to 15% of total volume and free gas concentration is approximately 0.3% to 0.8% of total volume. The comparison of Poisson’s ratio with previous studies in this area indicates that the gas hydrate reservoir shows no significant regional variations.

Direct nonlinear inversion of multiparameter 1D elastic media using the inverse scattering series

Geophysics ◽  
2009 ◽  
Vol 74 (6) ◽  
pp. WCD15-WCD27 ◽  
Author(s):  
Haiyan Zhang ◽  
Arthur B. Weglein
Keyword(s):  
Wave Velocity ◽  
Material Properties ◽  
Value Added ◽  
P Wave ◽  
Added Value ◽  
Inversion Method ◽  
Elastic Media ◽  
Nonlinear Inversion ◽  
Model Matching ◽  
S Wave

In the direct nonlinear inversion method and in algorithms for 1D elastic media, P-wave velocity, S-wave velocity, and density are depth dependent. “Direct nonlinear” means that the method uses explicit formulas that (1) input data and directly output changes in material properties without the need for indirect procedures such as model matching, searching, optimization, or other assumed aligned objectives or proxies and that (2) the algorithms recognize and directly invert the intrinsic nonlinear relationship between changes in material properties and the recorded reflection wavefields. To achieve full elastic inversion, all components of data (such as PP, SP, and SS data) are needed. The method assumes that only data and reference medium propertiesare input, and terms in the inverse series for moving mislocated reflectors resulting from the linear inverse term are separated from amplitude correction terms. Although in principle this direct inversion approach requires all components of elastic data, synthetic tests indicate that a consistent value-added result may be achieved given only PP data measurements, as long as the PP data are used to approximately synthesize the PS and SP components. Further value would be derived from measuring all components of the data as the method requires. If all components of data are available, one consistent method can solve for all of the second terms (the first terms beyond linear). The explicit nonlinear inversion formulas provide an unambiguous data requirement message as well as conceptual and practical added value beyond both linear approaches and all indirect methods.

Shear‐wave logging with dipole sources

Geophysics ◽  
1988 ◽  
Vol 53 (5) ◽  
pp. 659-667 ◽  
Author(s):  
S. T. Chen
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Wave Train ◽  
P Wave ◽  
Dipole Source ◽  
Stoneley Wave ◽  
S Wave ◽  
S Waves ◽  
On Line ◽  
First Arrival

Laboratory measurements have verified a novel technique for direct shear‐wave logging in hard and soft formations with a dipole source, as recently suggested in theoretical studies. Conventional monopole logging tools are not capable of measuring shear waves directly. In particular, no S waves are recorded in a soft formation with a conventional monopole sonic tool because there are no critically refracted S rays when the S-wave velocity of the rock is less than the acoustic velocity of the borehole fluid. The present studies were conducted in the laboratory with scale models representative of sonic logging conditions in the field. We have used a concrete model to represent hard formations and a plastic model to simulate a soft formation. The dipole source, operating at frequencies lower than those conventionally used in logging, substantially suppressed the P wave and excited a wave train whose first arrival traveled at the S-wave velocity. As a result, one can use a dipole source to log S-wave velocity directly on‐line by picking the first arrival of the full wave train, in a process similar to that used in conventional P-wave logging. Laboratory experiments with a conventional monopole source in a soft formation did not produce S waves. However, the S-wave velocity was accurately estimated by using Biot’s theory, which required measuring the Stoneley‐wave velocity and knowing other borehole parameters.

Inversion of the shear velocity of the cement in cased borehole through ultrasonic flexural waves

Geophysics ◽  
2017 ◽  
Vol 82 (2) ◽  
pp. D57-D68 ◽  
Author(s):  
Feilong Xu ◽  
Hengshan Hu
Keyword(s):  
Wave Velocity ◽  
Error Rate ◽  
Shear Velocity ◽  
P Wave ◽  
Inversion Method ◽  
Flexural Waves ◽  
S Wave ◽  
Additional Time ◽  
Full Waveforms ◽  
Cased Borehole

Young’s elastic modulus and Poisson’s ratio of the cement in a cased borehole are important in the prediction of the cement sheath integrity under hydraulic fracturing. Although these mechanical properties can be derived in principle from the bulk velocities, the inversion of these velocities of the cement from the received full waveforms remains a challenging problem, especially the S-wave velocity. We have developed an inversion method based on the round-trip traveltimes of the leaked flexural waves (TTL) to invert the bulk velocities of the medium behind the casing. The traveltime difference between the casing wave and the delayed casing wave is the additional time for the leaked wave to travel in the interlayer to the formation and back to the casing. To demonstrate the effectiveness of this method, synthetic full waveforms with a changing interlayer are calculated when an ultrasonic acoustic beam is incident obliquely on the casing. The traveltimes of the wave packets are picked from the envelope curve of the full waveform and then used to invert the bulk velocities in the TTL method. The inverted S-wave velocity of cement is quite accurate with an error rate smaller than 3%, no matter whether the cement is of the ordinary, heavy, or light type. When the interlayer is mud, the P-wave is inverted with an error rate of less than 2%. The P-wave velocity is inverted roughly with an error rate of approximately 10% when the medium behind the casing is light cement.

Temperature‐dependent propagation of P‐ and S‐waves in Cold Lake oil sands: Comparison of theory and experiment

Geophysics ◽  
1993 ◽  
Vol 58 (6) ◽  
pp. 863-872 ◽  
Author(s):  
John Eastwood
Keyword(s):  
Theoretical Model ◽  
Wave Velocity ◽  
Oil Sands ◽  
Seismic Wave Propagation ◽  
P Wave ◽  
S Wave ◽  
Temperature Dependent ◽  
S Waves ◽  
Fluid Properties ◽  
Cold Lake

The measured dependence of ultrasonic velocity in Cold Lake oil sands on temperature is compared to theoretical model predictions for seismic wave propagation in porous media. The experiments indicated that change in fluid properties with temperature most greatly affect observed velocities. The theoretical model was constructed to account for temperature dependent fluid properties using correlations independent of the ultrasonic experiments. Theoretical and experimental P‐wave velocities agree within 5 percent for temperatures between 22°C to 125°C and effective stresses of 1 MPa and 8 MPa. The modeling indicates that the change in fluid bulk modulus with temperature dominates the observed 15 percent P‐wave velocity decrease between 22°C to 125°C. Over the same temperature range the model predicts the S‐wave velocity remains almost constant (<1 percent increase).

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