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| Titel |
Structural analysis of a fractured basement reservoir, central Yemen |
| VerfasserIn |
Resi Veeningen, Hugh Rice, Dave Schneider, Bernhard Grasemann, Kurt Decker |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075764
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| Zusammenfassung |
| The Pan-African Arabian-Nubian Shield (ANS), within which Yemen lies, formed as a result
of Neoproterozoic collisional events between c. 870-550 Ma. Several subsequent phases of
extension occurred, from the Mesozoic (due to the breakup of Gondwana) to the Recent
(forming the Gulf of Aden and the Red Sea). These resulted in the formation of numerous
horst- and-graben structures and the development of fractured basement reservoirs in the
southeast part of the ANS.
Two drill cores from the Mesozoic Marib-Shabwa Basin, central Yemen, penetrated the
upper part of the Pan-African basement. The cores show both a lithological and structural
inhomogeneity, with variations in extension-related deformation structures such as
dilatational breccias, open fractures and closed veins. At least three deformation events have
been recognized:
D1) Ductile to brittle NW-SE directed faulting during cooling of a granitic
pluton. U-Pb zircon ages revealed an upper age limit for granite emplacement
at 627±3.5 Ma. As these structures show evidence for ductile deformation, this
event must have occurred during the Ediacaran, shortly after intrusion, since
Rb/Sr and (U-Th)/He analyses show that subsequent re-heating of the basement
did not take place.
D2) The development of shallow dipping, NNE-SSW striking extensional faults
that formed during the Upper Jurassic, simultaneously with the formation of the
Marib-Shabwa Basin. These fractures are regularly cross-cut by D3.
D3) Steeply dipping NNE-SSW to ENE-WSW veins that are consistent with the
orientation of the opening of the Gulf of Aden. These faults are the youngest
structures recognized.
The formation of ductile to brittle faults in the granite (D1) resulted in a hydrothermally
altered zone ca. 30 cm wide replacing (mainly) plagioclase with predominantly chlorite, as
well as kaolinite and heavy element minerals such as pyrite. The alteration- induced porosity
has an average value of 20%, indicating that the altered zone is potentially a good fluid-flow
pathway and also a suitable reservoir for hydrocarbons.
The youngest faults (D3) are often filled with calcite, (saddle) dolomite and pyrite that
formed at temperatures between 100 and 150Ë C. Fluid inclusions within calcite have
abundant hydrocarbon-rich components indicating that these veins formed synchronously
with hydrocarbon migration. The same minerals were deposited within the ductile to brittle
faults within the granite (formed during D1). This resulted in significant porosity
reduction, especially in the faults themselves, reducing the fluid flow efficiency within
the altered granite, locking up hydrocarbons and reducing the reservoir quality. |
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