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Petroleum Seismological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Petroleum seismological survey is one of the most important geophysical studies of the earth including for oil/gas prospecting. The theory is based on the elastic disturbance (vibration) of the medium (rock) particles, by artificially generated and propagating seismic energy. The propagating wave interacts with strata, is affected accordingly and bears the subsurface geological history of the traveled path. The horizontal and vertical variation in the wave velocity, along with the modification in the characteristics of the seismic wave, forms the basis of seismological survey. The survey takes into consideration three kinds of waves, reflection, refraction and direct waves. A transmitted wave is of no value in seismology. The reflection and refraction propagating waves through a medium (rock) are mainly utilized for the characterizing of subsurface rock structure and to a small extent the rock stratigraphy. Surface, direct, ghost reflection and refraction, diffraction and environmental waves are unwanted noise signals and are eliminated through raw seismic data processing for improving the signal to noise ratio. Artificial seismic waves are generated by chemical explosion or mechanical thrust through laterally laid shot points at the earth’s surface. The waves propagate all around including underground, which is of interest to the survey. The seismic waves are monitored through laterally placed receivers (detector/geophone) offset array at the ground surface. Seismic data are gathered in the form of a seismogram, a collection of huge numbers of seismic traces drawn side by side as a function of travel time/offset distance versus amplitude/frequency on two-dimensional seismographs (x-y plot). Reflection and refraction seismology bears the same theory but the application varies. Underground reflected and refracted seismic waves propagate through different paths and distances. The waves bear different degrees of attenuation (variation) during propagation. Reflection seismology is employed for recording the amplitude and shape of a seismic wave and ground motion (wave velocity) as a result of reflection from an underground interface. Reflection seismology is used to determine a subsurface geological structure. On the other hand, refraction seismology is based on the time of first arrival of ground motion, generated by the propagating seismic wave, from different subsurface distances. The first arrival time is computed and interpreted in terms of depth (thickness) and change of ground motion in different layers. The acquired data are improved, first by electrical manipulation automatic gain control (AGC) and then by computerized processing, and then interpreted. Three-dimensional (3D) seismic data modeling has introduced greater certainty in oil/gas findings. A three-dimensional survey is carried out by laying down three sets of sources-receivers offset (grid) at right angles to each other above the subsurface targeted volumetric area. The processed data are interpreted and related to the geological features. There can be different interpretations and different models depending upon the opinion and skill of the interpreter. The most probable geological model of the subsurface is constructed.
On reflection and transmission of qP waves in initially stressed viscoelastic triclinic layer between distinct triclinic geomedia with sliding interface
Published in Waves in Random and Complex Media, 2021
Pato Kumari, Rupali Srivastava
The seismic energy released during an earthquake undergoes several reflection/refractions between different inhomogeneous layers before reaching the crustal region. Therefore, study of reflection/transmission phenomenon is vital for understanding earthquake mechanism, which define the centreline objective of theoretical seismology. Reflection seismology also plays a vital role in understanding the earth’s structure. Reflection and transmission techniques are further used in determining water depths, in the evaluation of soil, in geotechnical applications such as detection of bedrock and natural ground cavities, ground water exploration, mapping a saline and freshwater interface in coastal areas etc. These diverse applications emphasize the importance of investigating the reflection/transmission characteristics in different geomedia.
An inverse source identification by nonlinear optimization in a two-dimensional hyperbolic problem
Published in Inverse Problems in Science and Engineering, 2021
Murat Subaşı, Faika Derya Şendur, Cavide Yaşar
Considering the spatial variables in the region and time variable in the interval , let us write the hyperbolic equation on the domain in the form where In vibration modelling, the external forces with the form of separation of variables have special meanings. For example, the selection of describes a harmonic spatial force. Generally, the problem (1.1)–(1.3) is admitted as a model for flexible waves corresponding to a point slipping source. This kind of point source can be connected with models in ground-penetrating radar, reflection seismology, oil and gas exploration and many other physical systems [1].
Acoustic multi-parameter full waveform inversion based on the wavelet method
Published in Inverse Problems in Science and Engineering, 2021
The second example is the Marmousi model [50] with complex structures. The exact velocity is shown in Figure 5 and it will be used in the inversion computations. The computational domain is . The spatial step is and the time step is . The thickness of PML is . The shots and receivers are arranged under the surface . The sketch map of the data acquisition system is shown in Figure 2. This data observation geometry is analogous to the acquisition system of reflection seismology in geophysical exploration. In Figure 2, the blue points denote the shots and the red crosses denote the receivers. Figure 3(a) is a shot gather with the shot located at the left side of the model. Figure 3(b) is another shot gather with the shot located at the middle of the model. In both Figure 3(a,b), we can see the boundary reflections are eliminated obviously. For comparison with Figure 3, the corresponding shot gather by the staggered-grid method is shown in Figure 4. Comparing Figure 4 with Figure 3, we can clearly see that the waveform in Figure 3 by the wavelet method has much less dispersion.