Reflection seismic data from block F3 in the Dutch North Sea exhibit many large-amplitude reflections at shallow horizons typically categorized as bright spots. In most cases, these bright reflections show a significant “flatness” that contrasts with local structural trends. Although flat spots in thick reservoirs are often easily identified, others within thin beds or near reservoir edges can be difficult to identify and are poorly understood. Many of the shallow large-amplitude reflections in this block are dominated by flat spots. We (...) investigated the tuning effects that such flat spots cause as they interacted with reflections from the top of the reservoir. We first studied the zero-offset “wedge-model” tuning effects of the flat spot with overlying bright spots, dim spots, or polarity reversals. We then expanded that model to examine prestack tuning effects, as well as the results from inclusion of postcritical flat spot reflections in the final stack. We observed that under certain conditions, the reflections could appear to be somewhat flattened bright spots; those conditions might be met frequently in practice, and they should be considered in routine interpretation. In the North Sea case, we concluded that this tuning effect was the primary cause of the brightness and flatness of these reflections. (shrink)
A comprehensive knowledge of the development and connectivity of fractures and vugs in carbonate reservoirs plays a key role in reservoir evaluation, ultimately affecting the gas prediction of this kind of heterogeneous reservoir. The carbonate reservoirs with fractures and vugs that are well developed in the Longwangmiao Formation, Sichuan Basin are selected as a research target, with the fractal dimension calculated from the full-bore formation microimager image proposed to characterize the fractures and vugs. For this purpose, the multipoint statistics algorithm (...) is first used to reconstruct a high-resolution FMI image of the full borehole wall. And then, the maximum class-variance method realizes the automatic threshold segmentation of the FMI image and acquisition of the binary image, which accurately characterizes the fractures and vugs. Finally, the fractal dimension is calculated by the box dimension algorithm, with its small value difference enlarged to obtain a new fractal parameter. The fractal dimensions for four different kinds of reservoirs, including eight subdivided models of vugs and fractures, show that the fractal dimension can characterize the development and the connectivity of fractures and vugs comprehensively. That is, the more developed that the fractures and vugs are, the better the connectivity will be, and simultaneously the smaller that the values of the fractal dimensions are. The fractal dimension is first applied to the gas production prediction by means of constructing a new parameter defined as a multiple of the effective thickness, porosity, and fractal dimension. The field examples illustrate that the fractal dimensions can effectively characterize the fractures and vugs in the heterogeneous carbonate reservoir and predict its gas production. In summary, the fractals expand the characterization method for the vugs and fractures in carbonate reservoirs and extend its new application in gas production prediction. (shrink)
In this paper, a heterogeneous diffusive prey-predator system is first proposed and then studied analytically and numerically. Some sufficient conditions are derived, including permanence and extinction of system and the boundedness of the solution. The existence of periodic solution and its stability are discussed as well. Furthermore, numerical results indicate that both the spatial heterogeneity and the time-periodic environment can influence the permanence and extinction of the system directly. Our numerical results are consistent with the analytical analysis.
Seismic interpretation is often based on the analysis of amplitude anomalies, which depend strongly on the seismic wavelet presented in the data. However, if the wavelet polarity or phase is unknown or fine-scale impedance variations are complex, interpretation of the anomaly can be ambiguous. The Stratton data volume contains a dome-like feature that may be interpreted as the top of a potential gas target, the top of a buried tight reef, or as a thin layer of either higher or lower (...) impedance, depending on the interpreter’s assumption of polarity and phase. This observation provoked our interest in modeling the seismic response of domes using wavelets of differing polarity and phase on stacked data. Because there appears to be only a single event, perhaps the top of an anomalous feature, and not its base, a “gradational” decrease in impedance contrast with depth is included among our models. We have determined that the seismic response from a layer with an impedance contrast decreasing with depth is quite different from that of a layer with constant impedance contrast when the bed thickness exceeds one quarter of the wavelength; that is, a reflection from the base of a “thick” gradational layer is not visible, as expected. We independently determine the polarity and phase of the Stratton data, finding that the surface-based seismic and VSP data are of opposite polarity, and concluding that the dome structure represents the top of a gradational thick bed. A model based on a nearby reservoir containing thin gas, oil, and water zones supports this conclusion. This anomaly in the Stratton data appears to represent a hydrocarbon reservoir with thin layers of gas and oil, each with lower impedance than the surrounding beds but with stepwise decreasing contrast over a sufficient thickness to avoid a basal reflection at these wavelengths. (shrink)
Guo Qiyong’s edited volume offers a detailed look at research on Chinese philosophy published in Chinese from 1949-2009. The chapters in this volume are broken down into either the major themes or time periods in the history of Chinese philosophy.