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Cairo, Egypt

Abdeen M.M.,Cairo University | Abdelghaffar A.A.,Western Geco
Precambrian Research | Year: 2011

The Allaqi-Heiani suture (AHS) is the western part of the main Allaqi-Heiani-Gerf-Onib-Sol Hamed-Yanbu suture and represents one of the Neoproterozoic, arc-arc sutures in the Arabian-Nubian Shield (ANS). It separates the ca. 750. Ma South Eastern Desert terrane in the north from the ca. 830-720. Ma Gabgaba terrane in the south. The AHS is a deformed belt of ophiolitic rocks, syn-tectonic granitoids and metasediments. The central AHS zone is divided into three structural domains. The western domain (I) is characterized by NNE dipping thrusts and SSW-vergent folds. The central domain (II) includes upright tight to isoclinal NNW-SSE oriented folds and transpressional faults. The eastern domain (III) shows NNW-SSE oriented open folds. Structural analysis indicates that the area has a poly-phase deformation history involving at least two events. Event D1 was an N-S to NNE-SSW regional shortening generating the SSW-verging folds and the NNE dipping thrusts. Event D2 was an ENE-WSW shortening producing NNW-SSE oriented folds in the central and eastern parts of the study area and reactivating older thrusts with oblique-slip reverse fault movement. The tectonic evolution of the area involves two episodes of collision: an early collision between the South Eastern Desert terrane and the Gabgaba terrane along the AHS after the consumption of a basin floored by oceanic crust above a north-dipping subduction zone; and a later collision between East- and West-Gondwanas at ca. 750-650. Ma, leading to the closure of the Mozambique Ocean. This collision deformed the AHS along N-S trending shortening zones and produced NW-SE and NE-SW oriented sinistral and dextral transpressional faults, respectively. The early collision episode is related to the terrane accretion during the early Pan-African orogen, while the later phase is related to a late Pan-African or Najd orogen. © 2011 Elsevier B.V. Source


Lira J.M.,Petrobras | Innanen K.A.,University of Houston | Weglein A.B.,University of Houston | Ramirez A.C.,Western Geco
Journal of Seismic Exploration | Year: 2010

Western-Geco, Houston, TX, U.S.A. The objective of extracting the spatial location of a reflector, and its local angle-dependent reflection coefficient, from seismic data, depends on the ability to identify and to remove the effect on primary amplitudes of propagation down to and back from the reflector. All conventional methods that seek to correct for such transmission loss require estimates of the properties of the overburden. In this paper we propose a fundamentally new approach that will in principle permit correction of primaries for such transmission loss without requiring overburden properties as input. The approach is based on the amplitude of the first term of the inverse scattering series internal multiple attenuation algorithm, which predicts the correct phase and approximate amplitude of first order internal multiples. The amplitude is estimated to within a factor determined by plane wave transmission loss down to and across the reflector producing the event's shallowest downward reflection. Hence, the amplitude difference between a given predicted and actual multiple, both of which are directly available from the data and the algorithm output, in principle contain all necessary information to correct specific primary reflections for their overburden transmission losses. We identify absorptive overburdens/media as requiring particular focus, so as a first step, previous amplitude analysis of the internal multiple attenuation algorithm is here extended to include stratified absorptive media. Using this newly derived relationship between predicted and actual internal multiples, and existing results for acoustic/elastic media, correction operators, to be applied to specific, isolated primaries in both types of media, are then computed using combinations of multiples and their respective predictions. We illustrate the approach on synthetic data for the absorptive case with three earth models with different Q profiles. Further research into the amplitudes of the plane wave internal multiple predictions in 2D and 3D media is a likely pre-requisite to field data application of this concept-level algorithm. © 2010 Geophysical Press Ltd. Source


Johnson C.L.,University of Utah | Semple I.L.,Western Geco | Creem-Regehr S.H.,University of Utah
Journal of Geoscience Education | Year: 2013

The scale of features shown on outcrop photographs can be critical to geoscience interpretations, yet little is known about how well individuals estimate scale in images. This study utilizes a visualization test in which participants were asked to estimate the absolute size of several boxes shown in outcrop images using high resolution, stitched photopanoramas (Gigapans). Participants viewed two different outcrops that highlight different kinds of photographic distortion, first using static images and then with "interactive" Gigapans that permitted zooming and panning. A test group was given basic scaling cues in the form of distance to and height of the outcrops, whereas a control group completed the test without any scaling cues. Other population comparisons were investigated (e.g., gender, age, experience level, and major) but no other statistically significant population difference was observed. Therefore, scaling cues seem to invoke a primary effect at least in the first part of the exercise. Results show that scaling cues increase accuracy overall, but with wider spread and a tendency to cause overestimation of size. The control group, which was not given any scaling information, was less accurate overall and tended to underestimate the size of features. Both groups gave more accurate scale estimates with smaller standard deviations for the extension-distorted photopanorama than the compression-distorted image. Participants also generally showed improved accuracy in the second part of the test, which probably reflects the impact of interactivity, although a training effect cannot be discounted. These results suggest that nonembedded scaling cues (as opposed to physical objects denoting scale in photographs) can be useful for some individuals to estimate the size of features shown in outcrop images. Results also underscore the importance of interactivity and multiple exposures in classroom applications. © 2013 National Association of Geoscience Teachers. Source


Laake A.W.,Schlumberger | Sheneshen M.S.,Western Geco | Strobbia C.,Schlumberger | Velasco L.,Schlumberger | Cutts A.,Schlumberger
Petroleum Geoscience | Year: 2011

Reservoir mapping in the Gulf of Suez petroleum system is challenging because rift-parallel and cross-rift faults disrupted the sediments, leaving the reservoirs confined to stratigraphic, structural, and combined traps. We have developed a technique to address this challenge that integrates fault outcrop mapping using satellite image interpretation, seismic near-surface characterization techniques such as Rayleigh wave velocity mapping and ray parameter interferometry, as well as ant tracking of faults and geobody delineation on a prestack time-migrated (PSTM) cube. The technique uses a combination of geographic information system (GIS) and geological modelling software such as Petrel for surface/subsurface integration. The joint analysis of Rayleigh wave data with satellite imagery provides a near-surface structural geological model. The acquisition, processing, and interpretation of point-receiver seismic data enables the interpretation of near-surface geological structures. Detailed shallow structural geology can be imaged in the near surface, a data regime that is conventionally masked by the acquisition noise from the seismic acquisition. The shallow geological model comprises shallow lithological horizons as well as fault zones, the mapping of which may assist with the mitigation of shallow drilling risks. The integration of surface and subsurface structural mapping provides a tectonic framework for the delineation of reservoirs in the rift-faulted environment of the Gulf of Suez. © 2011 EAGE/Geological Society of London. Source

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