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Long A.,PGS
Leading Edge (Tulsa, OK) | Year: 2010

Conventional 3D streamer seismic processing generally ignores any azimuth component in the data. We are used to the convenience of acquiring overlapping shot gathers in straight lines, as we can sort the data into common midpoint gathers, and then exploit the power of stack in processing to attenuate random noise. The higher the fold, the more random noise we attenuate. Conventional 3D surveys are acquired using "swath"or "racetrack" vessel shooting, wherein the survey has a single line orientation (or "survey azimuth"), and a long, narrow spread of streamers are towed by a single vessel. Apart from the front of the streamers (short source-receiver offsets), most source-receiver combinations have a relatively common azimuth (the angle between their particular vector and the survey orientation, Figure 1). Thus, the subsurface geology is illuminated only from one particular shooting direction. We assume that most coherent noise types are well behaved and we can remove them in processing. We assume that the target illumination is acceptably uniform, and we can produce clean seismic images. Most of the time these assumptions are in the ballpark of truth and our resultant seismic data allow us to achieve our exploration and appraisal objectives. © 2010 Society of Exploration Geophysicists. Source

Van Borselen R.G.,PGS | Fokkema J.,Technical University of Delft | Van den Berg P.,Technical University of Delft
Geophysics | Year: 2013

marine seismic acquisition, the free surface generates seismic events in our recorded data that are often categorized as noise because these events do not contain independent information about the subsurface geology. Ghost events are considered as such noise because these events are generated when the energy generated by the seismic source, as well as any upgoing wavefield propagating upward from the subsurface, is reflected downward by the free surface. As a result, complex interference patterns between up- and downgoing wavefields are present in the recorded data, affecting the spectral bandwidth of the recorded data negatively. The interpretability of the data is then compromised, and hence it is desirable to remove the ghost events from the data. Rayleigh's reciprocity theorem is used to derive the relevant equations for wavefield decomposition for multisensor and single-sensor data, for depth-varying and depth-independent recordings from marine seismic experiments using a single-source or dual-source configuration. A comparison is made between the results obtained for a 2D synthetic example designed to highlight the strengths and weaknesses of the various acquisition configurations. It is demonstrated that, using the proposed wavefield decomposition method, multisensor data (measurements of pressure and particle velocity components, or multidepth pressure measurements) allow for optimal wavefield decomposition as independent measurements are used to eliminate the interference patterns caused by the free surface. Single-sensor data using constant-depth recordings are found to be incapable of producing satisfactory results in the presence of noise. Single-sensor data using a configuration with depth-varying measurements are able to deliver better results than when constant-depth recordings are used, but the results obtained are not of the same quality when multisensor data are used. © 2013 Society of Exploration Geophysicists. Source

The goal of vibroseis data acquisition and processing is to produce seismic reflection data with a known spatially-invariant wavelet, preferably zero phase, such that any variations in the data can be attributed to variations in geology. In current practice the vibrator control system is designed to make the estimated groundforce equal to the sweep and the resulting particle velocity data are cross-correlated with the sweep. Since the downgoing far-field particle velocity signal is proportional to the time-derivative of the groundforce, it makes more sense to cross-correlate with the time-derivative of the sweep. It also follows that the ideal amplitude spectrum of the groundforce should be inversely proportional to frequency. Because of non-linearities in the vibrator, bending of the baseplate and variable coupling of the baseplate to the ground, the true groundforce is not equal to the pre-determined sweep and varies not only from vibrator point to vibrator point but also from sweep to sweep at each vibrator point. To achieve the goal of a spatially-invariant wavelet, these variations should be removed by signature deconvolution, converting the wavelet to a much shorter zero-phase wavelet but with the same bandwidth and signal-to-noise ratio as the original data. This can be done only if the true groundforce is known. The principle may be applied to an array of vibrators by employing pulse coding techniques and separating responses to individual vibrators in the frequency domain. Various approaches to improve the estimate of the true groundforce have been proposed or are under development; current methods are at best approximate. © 2009 European Association of Geoscientists & Engineers. Source

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A new synthetic material that’s strong enough to fill gaps in bone while stimulating new bone growth could advance the grafting treatments needed by people suffering from bone cancer and other bone defects, says a biomedical engineer at Texas A&M University who is developing the technology. The material serves as a biodegradable scaffold that can be surgically implanted within the body to promote healing by triggering bone regeneration at the cellular level, says Akhilesh Gaharwar, assistant professor of biomedical engineering at Texas A&M. His research is detailed in the scientific journal Acta Biomaterialia. With more than two million bone-grafting operations occurring worldwide each year, bone is the second-most transplanted organ, following blood, Gaharwar notes, but existing procedures can be limited by the amount of viable bone a patient can surrender. Some synthetic replacements are available, he adds, but they can cause side effects, be outright rejected by the body or become brittle and break under the loads they experience. In addition they can be difficult to cut and shape to fit a bone defect, particularly in instances where pieces of bone are removed to facilitate the extraction of a bone tumor, he says. Looking to overcome these obstacles, Gaharwar created a biomaterial that is strong yet flexible — think tire rubber— and that has the ability to boost the healing process by essentially telling pre-osteoblast cells (those cells in the body responsible for forming bone) to begin the regeneration process. For Gaharwar, the work is an extension of his previous research developing an injectable material aimed at inducing bone formation for hard-to-heal bone fractures. This new material, however, is significantly harder and can absorb a greater load, he says, noting that it is intended for surgical implantation rather than injection. Gaharwar’s material is made from embedding incredibly small particles of minerals called nanosilicates into a substance known as polyglycerol sebacate (PGS). Because PGS contains components already present in the body, it is rarely rejected and doesn’t cause side effects when it degrades, Gaharwar notes. Those properties, he says, make PGS a widely used material for a number of biomedical applications, but for bone engineering PGS needed to be stronger and interactive — in terms of “talking” to bone cells to initiate bone formation. So small that they are actually referred to as two-dimensional materials, these ultrathin nanosilicates have a high surface area but a thickness of a few nanometers or less. Think of a sheet of paper but on a much smaller scale. For example, a sheet of paper is 100,000 nanometers thick; Gaharwar’s nanosilicates are one nanometer thick and they contain orthosilicic acid, magnesium and lithium — minerals that induce bone formation. By embedding these nanosilicates in PGS, Gaharwar was able to enhance the mechanical stiffness of the material by four times without affecting its elasticity. This allows the material the strength to sustain force while not breaking, he explains. In addition, the nanosilicates, once in place, signal bone cells to increase production of bone tissue. Early tests have demonstrated a 300 percent increase in alkaline phosphatase activity, a marker for early bone formation, and a six-fold increase in the presence of calcium phosphate, a main component of bone, Gaharwar notes. This is achieved, he says, without the use of proteins known as growth factors, which are used in conventional bone therapy treatments but can lead to serious side effects due to the large amounts required to stimulate cells. What’s more, Gaharwar can control the rate of degradation for his material so that it works like a true scaffold, giving support when necessary and removing itself through natural degradation at the same rate as bone tissue is formed. Other commercial technology often fails when it degrades, leaving behind gaps, breaks and unsupported bone, Gaharwar notes. Given these properties, Gaharwar believes his material can significantly help in bone regeneration for patients suffering from trauma, infection, congenital anomalies and oncologic resection. “The addition of nanosilicates to PGS matrix significantly enhances the mechanical stiffness without affecting the elastomeric properties,” Gaharwar says. “The increase in mechanical stiffness and in vitro stability is mainly attributed to enhanced interactions between nanosilicates and PGS.” Release Date: November 18, 2015 Source: Texas A&M

Van der Neut J.,Technical University of Delft | Frijlink M.,PGS | van Borselen R.,PGS
Geophysical Journal International | Year: 2012

A common strategy for surface-related multiple elimination of seismic data is to predict multiples by a convolutional model and subtract these adaptively from the input gathers. Problems can be posed by interfering multiples and primaries. Removing multiples by multidimensional deconvolution (MDD) (inversion) does not suffer from these problems. However, this approach requires data to be consistent, which is often not the case, especially not at interpolated near-offsets. A novel method is proposed to improve data consistency prior to inversion. This is done by backpropagating first-order multiples with a time-gated reference primary event and matching these with early primaries in the input gather. After data matching, multiple elimination by MDD can be applied with a deterministic inversion scheme. © 2012 PGS Geophysical Journal International © 2012 RAS. Source

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