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" Fracture distribution in faulted basement blocks, Gulf of Suez, Egypt: "
A. I. Younes
T. Engelder
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Latin Dissertation
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| Language of Document
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English
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| Record Number
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1113511
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| Doc. No
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TLpq304311586
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| Main Entry
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A. I. Younes
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T. Engelder
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| Title & Author
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Fracture distribution in faulted basement blocks, Gulf of Suez, Egypt:\ A. I. YounesT. Engelder
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| College
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The Pennsylvania State University
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| Date
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1996
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| student score
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1996
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| Degree
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Ph.D.
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| Page No
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170
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| Abstract
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Fractures, faults and dikes within granite outcrops at Gebel El Zeit, Egypt correlate within the same structures in the offshore Ashrafi field. Fractures occur in three sets: a rift-parallel (310/67) and a rift-normal (060/79), fault-related fracture sets; and a sheet fracture set (143/45). The fault-related fractures are pervasive whereas the sheet fractures are absent in the northeastern side of Gebel El Zeit and in the Nubia sandstone. The frequency of the fault-related fractures increases near faults, whereas that of sheet fractures increases towards the top of the basement. The intersection of the three fracture sets localizes the fracture density along the crest, or at the edges of fault blocks. Rotation and uplift, however, erodes the uplifted corners or edges and thus removes rocks with the highest fracture density. In the subsurface, slightly eroded fault blocks such as those covered by the pre-rift sediments, have higher fracture density than deeply eroded blocks covered only by syn-rift Miocene rocks. Thus, the level of erosion contributes to the fracture density of a fault block. Dikes of andesitic composition in Gebel El Zeit and Ashrafi field are oriented normal to the rift, but are occasionally found parallel to the rift. Dikes show the highest fracture frequency and are frequently bounded by dike-parallel fractures. Consequently, dikes can be zones of high permeability and production, however, dikes extending below the oil-water contact can draw water into the well. Fractures in the layered basement rocks of Gebel El Zeit rotate from north-south in the upper red and grey layers to rift-parallel in the lower pink layer. The younger pink layer has the highest fracture frequency of the rift-parallel fractures which are the most conductive fractures as indicated by borehole image processing techniques. Their higher conductivity is related to their position relative to present-day stresses. Thus layering of the basement can compartmentalize a reservoir and may control its local fracture permeability. Abrupt changes in rift-parallel and cross-rift dike-wall geometry at Gebel El Zeit indicate that the dike material filled in previously existing fractures. Microgranite dikes injected during the intrusion of the pink granite parallel the present-day rift-parallel orientation and indicate a regional NE Eocambrian extension. This Eocambrian fabric suggests that an inherited fabric may have controlled Miocene rifting.
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Applied sciences
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Earth sciences
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Geology
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Petroleum production
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