Identification and Prediction of the High Heterogeneous Channel Sand in Southern Turgay Basin
With the development of high quality 3D seismic exploration in Southern Turgay Basin, the exploration targets are being shifted from the structural traps to stratigraphic traps. As for one of the most important reservoir, the identification and prediction of the high heterogeneous channel-sands is the key to enhance drilling success rate and reduce the investment risk. The multi-geophysical methods and integrated studies of geology and geophysics have been applied to determine the distributed area of the channel-sands in Southern Turgay Basin of Kazakhstan. The channel-sands are widely distributed from Upper Jurassic to Cretaceous. The channel-sands in the mature explored Cretaceous strata are meandering or braided river bars. On well-logging, the SP curve of the channel sand presents the block - shape and positive cycle with bell – shape with high porosity and permeability, and lower self-potential, gamma ray and density; Whereas in seismic profiles, channel sands presented the „bright spot‟ with the low frequency, high amplitude and short reflection. No obvious rules of „bright spot‟ can be found in the seismic profiles. The multi-geophysical methods, such as strata slice, 3D visualization and spectral decomposition, etc., have been applied to identify more than 50 pieces of channel-sands with the cutting and overlying each other vertically and horizontally. As for the relatively lower explored Upper Jurassic strata, the channel-sands developed in submerged distributary channel, branching mouth bars of deltaic system or fan deltaic system. On well-logging, channel sand presents the middle porosity and permeability, and lower selfpotential, gamma ray and density; Low-frequency and varied amplitude presents in seismic profiles. The area distribution of the deltaic or fan deltaic can be determined by sequence stratigraphy and the distribution of the channel-sands in different cycles vertically can be identified by chronostratigraphic interpretation in wheeler domain. Several cases suggested that the integration of strata slice, chronostratigraphic interpretation in wheeler domain, 3D visualization and spectral decomposition is an effective method to identify the high heterogeneous channel-sand, which has been confirmed by drilling results.
Stratal slicing, Part I: Realistic 3-D seismic model
Two-dimensional, fenced 2-D, and 3-D isosurface displays of some realistic 3-D seismic models built in the lower Miocene Powderhorn Field, Calhoun County, Texas, demonstrate that a seismic event does not necessarily follow an impedance boundary defined by a geological time surface. Instead, the position of a filtered impedance boundary relative to the geological time surface may vary with seismic frequency because of inadequate resolution of seismic data and to the en echelon or ramp arrangement of impedance anomalies of sandstone. Except for some relatively time-parallel seismic events, the correlation error of event picking is large enough to distort or even miss the majority of the target zone on stratal slices. In some cases, reflections from sandstone bodies in different depositional units interfere to form a single event and, in one instance, an event tying as many as six depositional units (interbedded sandy and shaly layers) over 50 m was observed. Frequency independence is a necessary condition for selecting time-parallel reference events. Instead of event picking, phantom mapping between such reference events is a better technique for picking stratal slices, making it possible to map detailed depositional facies within reservoir sequences routinely and reliably from 3-D seismic data.
Collagen dynamics in articular cartilage under osmotic pressure
Cartilage is a complex biological tissue consisting of collagen, proteoglycans and water. The structure and molecular mobility of the collagen component of cartilage were studied by 13C solid‐state NMR spectroscopy as a function of hydration. The hydration level of cartilage was adjusted between fully hydrated (∼80 wt% H2O) and highly dehydrated (∼30 wt% H2O) using the osmotic stress technique. Thus, the conditions of mechanical load could be simulated and the response of the tissue macromolecules to mechanical stress is reported. From the NMR measurements, the following results were obtained. (i) Measurements of motionally averaged dipolar 1H–13C couplings were carried out to study the segmental mobility in cartilage collagen at full hydration. Backbone segments undergo fast motions with amplitudes of ∼35° whereas the collagen side‐chains are somewhat more mobile with amplitudes between 40 and 50°. In spite of the high water content of cartilage, collagen remains essentially rigid. (ii) No chemical shift changes were observed in 13C cross‐polarization magic angle spinning spectra of cartilage tissue at varying hydration indicating that the collagen structure was not altered by application of high osmotic stress. (iii) The 1H–13C dipolar coupling values detected for collagen signals respond to dehydration. The dipolar coupling values gradually increase upon cartilage dehydration, reaching rigid limit values at ∼30 wt% H2O. This indicates that collagen is essentially dehydrated in cartilage tissue under very high mechanical load, which provides insights into the elastic properties of cartilage collagen, although the mechanical pressures applied here exceed the physiological limit. Copyright © 2006 John Wiley & Sons, Ltd.