K.K. Sekharan

Interpretability and resolution in post‐migration time‐slices

A surprising result was that data which were acquired on an adequate spacing (as predicted by plane-wave theory) were nevertheless still improved in interpretability by interpolation onto a finer grid. In our experiments, we found that Kirchhoff migration performed a better job of interpolation than a cheaper two-pass post-migration algorithm. In this regard, we feel that the Neidell hypothesis may contain a valuable intuitive insight: specifically, that interpolation aids visual interpretability (the most important criterion for seismic data).

AVO studies of gas sands via physical modeling

A physical modeling experiment was conducted over a simple model consisting of three layers. The three layers were epoxy, Foamglas, and epoxy. The materials of these layers correspond to shale, gas sand and shale in the real earth. A trench was drilled in this model and the ground roll was successfully attenuated prior to seismic data acquisition over this model. Transducer directivity corrections were made based on empirically derived least square function. An elastic synthetic based on wave equation and an acoustic synthetic based on ray tracing were computed over this model. Elastic, and acoustic modeling data corresponding to the top interface (epoxy and Foamglas) were compared to the AVO data of the physical model. The results show a consistent decrease of amplitude versus offset at this interface. This amplitude decrease with offset is due to the anomalous density contrast between epoxy and Foamglas material. This experiment demonstrates that the physical modeling can be used to simulate gas sand reservoirs in the actual field AVO studies.

Nine‐component data collection over a reflection dome: A physical modeling study

All components of plastic waves in an isotropic medium (Plexiglas) have hvc>n recorded in a reflection seismics geometry. This was accomplished by using a source polarizable in any of threr directions (in-line horizontal or SV, cross-line horizontal or SH, and vertical or P) and a receiver similarly polarizal+. Nine acquisition polarization pairs were thus recordc\d. The struct,ure in the model was a simljle dome embetldrd in a flat plain, and lines of acquisil,ion passed over bol.h the crest of the dome and its flanks. The lines were acquired at a constant offset, and no summing of traces has been performed. S-wave, P-wave, and mode conversion ( S-wa.ve to P-wave and P-wave to S-wave) events are all present on the sections. The P/P, P/SV, SV/P, and SV/SV sections enhance those events whose rays lie in the vertical plane below the line of acquisition. The sections incorporating an SH transducer as either source or receiver (or both) enhance thos_e events whose rays reflect from out. of the plane. Although the sources and receivers are (#errned SV, SH, and P, in fact any of the polarizations can receive any of the wave types given an appropriate ray angle.

3-D imaging of seismic data from a physical model of a salt structure

Seismic data from a physical model of the SEG/EAGE salt structure were imaged to evaluate the quality of imaging of a complex structure and benchmark imaging codes. The physical model was constructed at the University of Houston. Two simulated marine surveys were collected from it: a conventional towed streamer survey, and a vertical receiver cable survey.

The Effect of Fold On Horizontal Resolution In a Physical Model Experiment

S u m m a r y inal fold of 30. The CMP binning of this dataset was Using two datasets with different acquisition geometries equivalent to 30 by 30 foot squares, corresponding to the collected over the same physical model, we attempted to spacing between the closest pegs. That dataset was used test Neidell’s conjecture. We found that fold contributes by Ebrom et al. in 1995 to demonstrate the power of a significantly to spatial resolution. However, given an Kirchhoff migration as an interpolation operator. equal number of traces, finer bin spacing provided a much Subsequently, greater increase in resolution than fold. a new single fold dataset has been collected over model 94. The new survey is collected on 8 by 8 foot bin centers. The new dataset has coincident source and

3-D AVO Physical Modeling Experiment Over a Simulated Fracture Medium

Physical modeling, as an adjunct to numerical simulation, is a very useful tool which can provide insights into complex structural and stratigraphic problems. A 3-D physical modeling experiment was conducted over a simulated fracture system. The objective was to understand the quantitative differences in the 3-D AVO signatures for line orientations parallel and perpendicular to fracture orientation.

Imaging shear‐wave diffractions from pier terminations

many older bridge structures, there are no surviving to document the sub-surface length of the individual and/or piles that support the load. This information is in current evaluations of bridge integrity when and/or rehabilitation are planned. In many cases, tops of the piers and/or piles are inaccessible owing to the geometry of the mating between the pier (pile) and the supported structure. Standard tap tests to determine length by timing are not feasible when the tops of the piers piles) are inaccessible.

A physical model experiment for turning ray study

Several preliminary tests have been conducted to establish the feasibility of a physical model study to record turning ray signals in the laboratory. Clear resin and aluminum powder are used as the model materials. By mixing aluminum powder to clear resin in different proportions, controlled velocities of the materials have been achieved. Without adding any aluminum, the resin has a velocity of 2,525 m/s. By adding aluminum powder, the maximum velocity that can be achieved is 3,320 m/s. For a model of thickness 0.127 meter, the velocity gradient will be 0.5/s, which is adequate to achieve turning rays. Attenuation has also been tested and compared among different materials selected to construct the physical model. It is found that adding aluminum powder into clear resin does not increase attenuation of the mixture. The results from preliminary tests give confidence that a physical model study to detect turning rays is feasible.

Data acquistion geometry and 3‐D DMO

A physical model study was designed to better understand the effects of data acquisition geometry on 3D DMO process. In particular, when sourcereceiver azimuths are consistently within narrow range on a 3D seismic survey, the 3D DMO is generally successful in correcting the CMP gathers to zero-offset. On the other hand, the wide-range azimuth data may or may not be well handled by 3D DMO when compared with narrow-azimuth data. To better understand the azimuth influence, we are gathering 3D physical model data over a simple structure to demonstrate the different results of 3D DMO applied to wideand narrow-azimuth data with similar offset parameters. In this manner, we record two contrasting surveys, one with a wide range of azimuths and one with a narrow range (in this study, we specified “narrow” as 30°). The wide azimuth survey contains six azimuths from 15° to 165° (Figure l(a)); the narrow azimuth survey contains six azimuth from 75° to 105° (Figure l(b)). For each survey, the CMP bins contain five offsets for each azimuth, from 1000 ft to 11000 ft, with an increment of 2500 ft.

Measurement of Attenuation In Composite Media

k is wavenumber: Composite media are being investigated at the Seismic Acoustics Laboratory in order to assess their utility in conB is particle radius, structing realistic scaled models of geologic structures. The P-wave Q of these composite media can be continuously varied u is the ratio of particle density to fluid density, to encompass a range of intermediate values. This variation in Q is accomplished by changing the volume fraction and dis=&(I+&), ameter of the particles embedded in the matrix. Experiments have been conducted to test a theoretical model for predictr=;+J?ing attenuation in these media against actual measurement8 at 4pa’