Seismic velocity gradient stratification of the mantle at Ukrainian Shield

2020 ◽  
Author(s):  
Y. I. Dubovenko ◽  
L. A. Shumlianska ◽  
M. P. Kuzminets
Keyword(s):  
Velocity Gradient ◽  
Seismic Velocity ◽  
Ukrainian Shield

THE MUTINEER COMPLEX AND EXETER OIL DISCOVERIES: MUTINY IN THE DAMPIER

2003 ◽  
Vol 43 (1) ◽  
pp. 273
Author(s):  
K.A. Auld ◽  
J.E.P. Redfearn
Keyword(s):  
Velocity Gradient ◽  
Seismic Velocity ◽  
Oil Fields ◽  
3D Seismic ◽  
Time Data ◽  
Southern Limit ◽  
Integration Of Technology ◽  
Critical Components ◽  
Structural Closure ◽  
Commercial Oil

The oil discoveries at Norfolk–1 and Exeter–1 in the Northern Dampier Sub-basin (permit WA-191-P) have realised major commercial potential in an area with a prolonged exploration history. This paper presents the results of the drilling campaign which was undertaken in 2002 comprising two successful exploration discovery and five appraisal wells. The Norfolk–1 (28 m gross oil column), Norfolk–2 (9 m oil column), Exeter–1 (23 m oil column), Mutineer–3 (8 m oil column) and finally Exeter–2 (12 m oil column) confirmed a significant commercial oil volume within the Jurassic Angel Sandstones.The recent exploration of this area has improved understanding of the geology through the integration of technology with geoscientific understanding. Highs have been revealed from seismic time data using advanced 3D seismic techniques and sophisticated depth conversion processes.The time structural high of the Mutineer area was first tested by Bounty–1 in 1983 which is now mapped outside the southern limit of closure. Pitcairn–1 was drilled in 1997 discovering three thin oil columns and was followed by a near crestal well at Mutineer–1B drilled 2.6 km northwest of Pitcairn–1 in 1998, discovering an 8m column. The key issue was the understanding of the velocity gradient and depth conversion over the Mutineer Complex which revealed the true structural picture.This paper summarises results of the exploration and appraisal wells drilled and describes the evolution of the structural/stratigraphic understanding of the area, covering critical components hindering the oil field’s early detection. The first component is a significant seismic velocity gradient which causes true structural closure to be significantly offset from the time closure. The second component is the reservoir pressures within the oil reservoir and older sandstone intervals within the Angel and Legendre Sandstones show differences due to hydrodynamic cells and/or depletion resulting from production from the adjacent NWS Venture oil fields. The final component is the oil is primarily reservoired in the top Angel Sandstone, belonging to the J40 sequence and is sealed by a thin shale from the underlying mainly water bearing sandstones (J35/J30 and Legendre Sandstones).The combined reserves for the Mutineer Complex and Exeter Oil Fields reservoired in these laterally continuous turbidites are estimated to be 70–160 MMBBL recoverable.

scholarly journals 2.5 dimensional model of mantle heterogeneities under the Ukrainian shield according to the gradients of the velocities of seismic waves

2020 ◽  
Vol 29 (2) ◽  
pp. 431-441
Author(s):  
Liudmyla O. Shumlianska ◽  
Yurii I. Dubovenko ◽  
Petro H. Pigulevskyy
Keyword(s):  
Velocity Gradient ◽  
Upper Mantle ◽  
Seismic Waves ◽  
Deep Structure ◽  
Ukrainian Shield ◽  
Depth Range ◽  
Tectonic Structures ◽  
P Waves ◽  
Useful Signal ◽  
Background Density

We analyze the basic techniques for the investigation of the deep structure of the mantle and the shortcomings of the models of mantle structures derived from them. Thus, we reveal that there is no analysis of the velocity field by means of analytical transformants. Therefore, we developed and tested a new approach to define the mantle boundaries based on the calculations of the sequence of P-waves velocity derivatives. As a result, we obtain some new set of velocity gradient distributions for the principal tectonic structures of the Ukrainian Shield along the composite profile. The boundaries of the mantle discontinuities according to the velocity gradient we define in a special manner to eliminate the false anomalies and the fluctuations of the velocity curves that occur due to the conversion of the hodograph into the mean velocities. The smoothing of the velocity curve we perform with a previously defined wavelength step being equal to 50 km. We treat the calculated velocity gradient anomalies as the useful signal response above the appropriate sections, which have different velocity accelerations levels inside the upper mantle. We assume that the mantle anomalies have the same physical background (density/viscosity distributions, temperature gradients etc.) within each range with the equal acceleration value. However, the singular points determined by the inflections of the gradient curve could be the possible boundaries of additional inhomogeneities within the mantle. We calculate both the 1st and the 2nd derivatives for the velocity curves obtained. The excesses 2.5-D model of the 1-th and 2-th gradient curves (the acceleration of the gradvp itself) determine the position of the max / min anomalies of gradvp at the consolidated seismic profile within the Ukrainian Shield. Finally, we analyze in detail the distribution of velocity gradients of P-waves within the upper mantle in the depth range of 50–750 km. It results in the identification of a series of additional gradient velocity boundaries within three principal structural horizons of the upper mantle (under ~ 200–300 km, ~ 410–500 km, and ~ 600–650 km respectively).

Imaging the Upper Plate Lithosphere and Asthenosphere beneath Alaska with Sp Converted Waves

2021 ◽  
Author(s):  
Isabella Gama ◽  
Karen M. Fischer ◽  
Junlin Hua
Keyword(s):  
Free Surface ◽  
Velocity Gradient ◽  
Mantle Wedge ◽  
Seismic Velocity ◽  
Receiver Functions ◽  
The North ◽  
West Central ◽  
Subduction Zone Processes ◽  
The Us ◽  
Moho Depths

<p>To resolve the signatures of subduction zone processes in the mantle wedge, and how subduction has interacted with the upper plate, we imaged seismic velocity gradients beneath the US state of Alaska with Sp receiver function common conversion point (CCP) stacking.  Pacific plate lithosphere, and lithosphere bearing the thicker crust of the Yakutat terrane, subduct to the northwest beneath the southern margin of Alaska.   We employed data from hundreds of stations of the US NSF EarthScope Transportable Array, as well as other portable arrays and permanent networks. We calculated waveform components using a free-surface transform with improved estimates of free-surface velocities that were determined from P and SV particle motions. Sp receiver functions were calculated with time-domain deconvolution, and the CCP stack was generated with weighting functions that incorporate the properties of Sp scattering kernels. The CCP stack shows a clear interface between the North American and underthrust Yakutat crust, as well as Yakutat Moho depths of up to 60 km.  Sp phases from the negative velocity gradient at the base of the upper plate are strongest in west-central Alaska, where lithosphere-asthenosphere boundary (LAB) depths lie at 65-100 km.  In west-central Alaska, joint inversions of Sp data at single stations with Rayleigh phase velocities show comparable LAB depths as well as low asthenospheric velocities. This zone includes active magmatism and the upper plate appears to have been thinned by mantle wedge volatiles, melt, and flow.  The LAB phase deepens to the north, reaching depths of ~120 km beneath the northern Arctic Alaska terrane.  This increase in the depth of the LAB phase from the arc to the back-arc is consistent with the sculpting of the upper plate by subduction-related processes. Sp phases also delineate a prominent positive velocity gradient that represents the base of a low-velocity asthenospheric layer at depths of 100-130 km.  The positive velocity gradient is consistent with the onset of partial melting in the asthenosphere.</p><p> </p>

Upper lithospheric seismic velocity structure across the Pripyat Trough and the Ukrainian Shield along the EUROBRIDGE'97 profile

2003 ◽  
Vol 371 (1-4) ◽  
pp. 41-79 ◽  
Author(s):  
H. Thybo ◽  
T. Janik ◽  
V.D. Omelchenko ◽  
M. Grad ◽  
R.G. Garetsky ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Ukrainian Shield ◽  
Seismic Velocity Structure

Effect of Temperature, Velocity Gradient and I.V. Heparin on in Vitro Blood Coagulation and Platelet Aggregation

1967 ◽  
Vol 17 (01/02) ◽  
pp. 112-119 ◽  
Author(s):  
L Dintenfass ◽  
M. C Rozenberg
Keyword(s):  
Blood Coagulation ◽  
Velocity Gradient ◽  
Elevated Temperatures ◽  
Morphological Changes ◽  
Effect Of Temperature ◽  
Clotting Time ◽  
Progressive Change ◽  
Aggregation Of Platelets ◽  
Microscopic Techniques

SummaryA study of blood coagulation was carried out by observing changes in the blood viscosity of blood coagulating in the cone-in-cone viscometer. The clots were investigated by microscopic techniques.Immediately after blood is obtained by venepuncture, viscosity of blood remains constant for a certain “latent” period. The duration of this period depends not only on the intrinsic properties of the blood sample, but also on temperature and rate of shear used during blood storage. An increase of temperature decreases the clotting time ; also, an increase in the rate of shear decreases the clotting time.It is confirmed that morphological changes take place in blood coagula as a function of the velocity gradient at which such coagulation takes place. There is a progressive change from the red clot to white thrombus as the rates of shear increase. Aggregation of platelets increases as the rate of shear increases.This pattern is maintained with changes of temperature, although aggregation of platelets appears to be increased at elevated temperatures.Intravenously added heparin affects the clotting time and the aggregation of platelets in in vitro coagulation.

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