Pramik B.,Geokinetics Inc.
SEG Technical Program Expanded Abstracts | Year: 2011
Our ability to process and deliver proper broadband seismic data to our colleagues and customers is dependent on the selection of appropriate seismic acquisition parameters. Inadequate survey design can result in insufficient signal to noise ratios in the final data which will lead to an inferior product. Consideration of all seismic events present in the recorded data with respect to proper spatial sampling in all appropriate domains relevant to the seismic processing will help ensure that the broadband signal that is imparted into the earth, detected by the receivers and delivered to the processing center can be faithfully preserved throughout data processing. © 2011 Society of Exploration Geophysicists. Source
Gaiser J.E.,Geokinetics Inc.
73rd European Association of Geoscientists and Engineers Conference and Exhibition 2011: Unconventional Resources and the Role of Technology. Incorporating SPE EUROPEC 2011 | Year: 2011
It is well established that similar vertical wavelength ranges must be preserved in multicomponent data and that wavelengths of P- and S-waves must match in order to sample reflectivity in an equivalent manner. Conversion of a wavefield to another time or depth domain is described by transformation functions that depend on average VP/VS ratios and velocity. Although these functions align corresponding stratigraphic events of different wavefields, they distort the seismic wavelet because global average velocity properties are independent of local interval properties that define wavelength. In this study we develop a theory of velocity-based wavelet corrections for domain transformations, which are expressed as functions of interval and average VP/VS and velocity, to match wavelength of multicomponent wavefields. We examine the effects for both land and marine data examples and find that land surveys are affected more than marine, and may require spectral broadening of the wavelet. Data from the Marcellus shale in northeast Pennsylvania, USA, shows significant bandwidth improvements for C-waves when wavelet corrections based on velocity match their wavelengths with P-waves. Application of these wavelet corrections should benefit registration fidelity, joint AVO/A (offset and azimuth) inversions and attribute analyses. Source
Geokinetics Inc. | Date: 2011-10-24
A method for spatial sampling of a seismic wavefield at the bottom of a water layer at an effective spatial sampling denser than the physical layout of the sensors. The sensors comprise a sensing element for vertical particle motion and a sensing element for rotational motion around a horizontal axis. Stress and wavefield conditions allow the rotational sensing element to yield the transverse horizontal gradient of the vertical particle motion wavefield, used in ordinate and slope sampling to yield improved transverse spatial sampling of the vertical particle motion wavefield.
Zhou Z.,University of Houston |
Hilterman F.J.,Geokinetics Inc.
Geophysics | Year: 2010
Three seismic attributes commonly used to predict pore fluid and lithology are the fluid factor (ΔF), Poisson impedance (PI), and lambda-rho (γρ). We evaluated the pore-fluid sensitivity of these attributes with both well-log and seismic data in Tertiary unconsolidated sediments from the Gulf of Mexico where sand and shale are the only expected lithologies. While the sensitivity of one attribute versus another to discriminate pore fluid is often debated in the literature, the sensitivities of the three attributes are not independent but can be traced back to the fluid factor, which is a function of the P- and S-wave normal-incident reflection coefficients. Interestingly, the fluid factor, which is a reflectivity attribute, at the top of a hydrocarbon-saturated reservoir, is basically independent of the shale properties above the reservoir. It is a function of the brine and hydrocarbon impedances of the reservoir. The next attribute, Poisson impedance, is thenequal to the fluid factor times the sum of the brine and hydrocarbon impedances. Finally, the lambda-rho attribute is equal to the Poisson impedance multiplied by the same impedance sum. Essentially, the same scale factor differentiates these attributes, which does not significantly affect the sensitivity of the attributes. PI is the basis of the sensitivity for these attributes. As a means of testing their sensitivity for predicting pore fluid, we generated the three attributes along with their statistical distributions for different pore fluids for 183 reservoirs. The well-log statistical descriptions were then used to calibrate the seismic amplitude in a 3D survey to reflectivity values, thus allowing pore-fluid classification schemes based on Bayes' decision rules. In essence, seismic-amplitude quantification was based on regional statistics rather than individual wells within the 3D seismic survey to delineate the portions of the reservoir that were saturated with oil, gas, or brine. © 2010 Society of Exploration Geophysicists. Source
Gaiser J.,Geokinetics Inc. |
Verm R.,Geokinetics Inc.
74th EAGE Conference and Exhibition Incorporating SPE EUROPEC 2012 | Year: 2012
Most shear-wave (S-wave) surveys in exploration seismology are acquired with compressional-wave (P-wave) sources. These are primarily for the purpose of recording P to S converted-wave (PS-wave) reflections to image deep oil and gas targets. Essential for processing, is to have a good model of S-wave properties in the overburden and near surface. These properties include not only velocities and statics, but also the presence of S-wave birefringence (splitting) in azimuthally anisotropic media. In addition to PS-waves, pure mode shear-waves (SS-waves) are excited by P-wave sources due to the elastic nature of the near surface and these can aid in velocity model building. The purpose of this presentation is to examine several applications of SS-waves and PS-waves to characterize S-wave properties of the overburden using SS-wave modes from land and marine surveys. Synthetic seismic data from an HTI medium is used to demonstrate that fast and slow SS-waves can be recovered. Also in the marine environment, S-wave resolution is typically very high near the seabed, and can provide accurate S-wave statics and velocities for prestack depth migration (PSDM). An interferometry example shows that SS-waves can be retrieved from OBC data, and a PSDM example illustrates the high resolution that can be achieved with PS-wave data. Source