A study on the influence of salinity interfaces on borehole seismoelectric wavefields

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. D167-D180
Author(s):  
Yunda Duan ◽  
Hengshan Hu ◽  
Wei Guan
Keyword(s):  
Large Amplitude ◽  
Wave Amplitude ◽  
Amplitude Ratio ◽  
Experimental Studies ◽  
Pore Fluid ◽  
Head Wave ◽  
Stoneley Wave ◽  
Mud Cake ◽  
Porous Formation ◽  
Cake Layer

Previous theoretical and experimental studies on seismoelectric logging suggest that the electromagnetic head wave (EH wave) is much weaker than the electric field accompanying the Stoneley wave (ESt wave). Nevertheless, recent in situ measurements show that the EH wave amplitude can be greater than that of the ESt wave. We have addressed this issue according to the simulation of borehole seismoelectric wavefields and find that the amplitude ratio of EH to ESt waves is sensitive to the salinity contrast at the interfaces. Specifically, the EH wave amplitude can be greater than that of the ESt wave if the salinity of the borehole fluid is much higher than that of the pore fluid in a homogeneous porous formation. When an impermeable mud cake layer is taken into account between the borehole fluid and the formation, the amplitude ratio of EH to ESt waves can be even larger, although the amplitudes of the EH and ESt waves become smaller. For a radially stratified porous formation, the large amplitude ratio of EH to ESt waves also occurs if the salinity of the borehole fluid is much higher than that of the pore fluid in the inner layer, or if the salinity of the pore fluid in the inner layer is much higher than that in the outer layer. The large amplitude ratio of EH to ESt waves has potential for detecting interfaces with high salinity contrast, or it can be used as an indicator of mud cake.

Effects of in situ permeability on the propagation of Stoneley (tube) waves in a borehole

Geophysics ◽  
1987 ◽  
Vol 52 (9) ◽  
pp. 1279-1289 ◽  
Author(s):  
C. H. Cheng ◽  
Zhang Jinzhong ◽  
Daniel R. Burns
Keyword(s):  
Phase Velocity ◽  
Wave Amplitude ◽  
Pore Fluid ◽  
Stoneley Wave ◽  
Published Data ◽  
Intrinsic Attenuation ◽  
Wave Phase ◽  
In Situ Permeability ◽  
Wave Properties

We investigated the theoretical relationship between propagation characteristics of Stoneley (tube) waves in a borehole and in situ permeability by using a modified formulation of a borehole model with a formation that behaves as a Biot porous medium. We found that Stoneley‐wave attenuation and phase‐velocity dispersion increased with increasing permeability and porosity, and decreased with increasing frequency. In rocks with low to medium permeabilities (less than 100 mD), variations in formation velocity and attentuation were major contributors to variations in Stoneley‐wave properties at normal logging frequencies. However, in high‐permeability rocks (greater than 100 mD), coupling between the borehole and pore fluids associated with in situ permeability was more important than lithological changes in controlling Stoneley‐wave properties. Pore‐fluid viscosity had an effect on Stoneley‐wave propagation equal but opposite to permeability, and hence must he taken into account. We compared our theoretical results with published data on core permeability and Stoneley‐wave phase velocities and amplitudes. The Stoneley‐wave amplitude was more sensitive to the permeability of the formation than Stoneley‐wave phase velocity. By assuming an appropriate average value of intrinsic attenuation, we obtained reasonable agreements between theory and the published data. We conclude that relative permeability within a formation can be determined quite well using Stoneley‐wave amplitude and phase velocity, but absolute permeability determination requires accurate measurements of parameters such as the intrinsic attenuation of the formation and the viscosity and compressibility of the pore fluid.

Simple Formula to Study the Large Amplitude Free Vibrations of Beams and Plates

2008 ◽  
Vol 75 (1) ◽  
Author(s):  
G. Venkateswara Rao ◽  
K. Meera Saheb ◽  
G. Ranga Janardhan
Keyword(s):  
Free Vibration ◽  
Large Amplitude ◽  
Simple Formula ◽  
Space Variable ◽  
Linear Time ◽  
Amplitude Ratio ◽  
Compressive Load ◽  
Maximum Amplitude ◽  
Free Vibrations ◽  
Structural Members

A simple formula to study the large amplitude free vibration behavior of structural members, such as beams and plates, is developed. The nonlinearity considered is of von Karman type, and after eliminating the space variable(s), the corresponding temporal equation is a homogeneous Duffing equation. The simple formula uses the tension(s) developed in the structural members due to large deflections along with the corresponding buckling load obtained when the structural members are subjected to the end axial or edge compressive load(s) and are equal in magnitude of the tension(s). The ratios of the nonlinear to the linear radian frequencies for beams and the nonlinear to linear time periods for plates are obtained as a function of the maximum amplitude ratio. The numerical results, for the first mode of free vibration obtained from the present simple formula compare very well to those available in the literature obtained by applying the standard analytical or numerical methods with relatively complex formulations.

scholarly journals Resurrecting dead-water phenomenon

2011 ◽  
Vol 18 (2) ◽  
pp. 193-208 ◽  
Author(s):  
M. J. Mercier ◽  
R. Vasseur ◽  
T. Dauxois
Keyword(s):  
Internal Waves ◽  
Large Amplitude ◽  
Experimental Studies ◽  
Nonlinear Effects ◽  
Stratified Fluid ◽  
Nonlinear Internal Waves ◽  
Induced Drag ◽  
Wave Induced ◽  
Dead Water ◽  
Peculiar Phenomenon

Abstract. We revisit experimental studies performed by Ekman on dead-water (Ekman, 1904) using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects. Dedicated to Fridtjöf Nansen born 150 yr ago (10 October 1861).

Influence of Cement Coarse Particle on the Self-Healing Ability of Concrete Based on Ultrasonic Method

2010 ◽  
Vol 177 ◽  
pp. 526-529 ◽  
Author(s):  
Zhi Qiang Li ◽  
Zong Hui Zhou ◽  
Dong Yu Xu ◽  
Jing Hua Yu
Keyword(s):  
Particle Size ◽  
Wave Amplitude ◽  
Ultrasonic Method ◽  
The Self ◽  
Experimental Results ◽  
Coarse Particle ◽  
Head Wave ◽  
Self Healing ◽  
Before And After ◽  
The Relationship

The influences of particle size and mixing content of coarse cement on the self-healing ability of concrete were researched by ultrasonic method. Damaged degree was measured through the decrease of ultrasonic head wave amplitude (UHA) before and after loading. The relationship between damaged degree and self-healing ratio of concrete was built based on the experimental results as well as the relationship between cement diameter and self-healing ratio of concrete. Analyzing results show that UHA can evaluate the damaged degree of concrete clearly. There exists a damaged threshold of the concrete during loading. Under the same mixing content of coarse cement, when the damaged degree is higher than the threshold, the self-healing ratio of concrete decreases with the increase of damaged degree and increases with the increase of coarse cement diameter, however, while the damaged degree is less than the threshold, the self-healing ratio of concrete increases with both the increase of damaged degree and coarse cement diameter.

Shear velocity logging in slow formations using the Stoneley wave

Geophysics ◽  
1986 ◽  
Vol 51 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Jeffry L. Stevens ◽  
Steven M. Day
Keyword(s):  
Error Estimates ◽  
Shear Velocity ◽  
Low Noise ◽  
Head Wave ◽  
Inversion Method ◽  
Stoneley Wave ◽  
Fluid Viscosity ◽  
High Quality ◽  
Stoneley Waves ◽  
Compressional Velocity

We apply an iterative, linearized inversion method to Stoneley waves recorded on acoustic logs in a borehole. Our objective is to assess inversion of Stoneley wave phase and group velocity as a practical technique for shear velocity logging in slow formations. Indirect techniques for shear logging are of particular importance in this case because there is no shear head wave arrival. Acoustic logs from a long‐spaced sonic tool provided high‐quality, low‐noise data in the 1 to 10 kHz band for this experiment. A shear velocity profile estimated by inversion of a 60 ft (18 ⋅ 3 m) section of full‐wave acoustic data correlates well with the P‐wave log for the section. The inferred shear velocity ranges from 60 to 90 percent of the sound velocity of the fluid. Formal error estimates on the shear velocity are everywhere less than 5 percent. Moreover, application of the same inversion method to synthetic waveforms corroborates these error estimates. Finally, a synthetic acoustic waveform computed from inversion results is an excellent match to the observed waveform. On the basis of these results, we conclude that Stoneley‐wave inversion constitutes a practical, indirect, shear‐logging technique for slow formations. Success of the shear‐logging method depends upon availability of high‐quality, low‐noise waveform data in the 1 to 4 kHz band. Given good prior estimates of compressional velocity and density of the borehole fluid, only rough estimates of borehole radius and formation density and compressional velocity are required. The existing inversion procedure also yields estimates of formation Q inferred from spectral amplitudes of Stoneley waves. This extension of the method is promising, since amplitudes of Stoneley waves in a slow formation are highly sensitive to formation Q. Attenuation caused by formation Q dominates over attenuation caused by fluid viscosity if the viscosity is less than about [Formula: see text]. However, Stoneley‐wave amplitudes are also sensitive to gradients in shear velocity in the direction of propagation. In some cases, correction for the effects of shear‐velocity gradients is required to obtain the formation Q from Stoneley‐wave attenuation.

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