Log-derived petrophysical characteristics and oil potentiality of the Upper Qishn Clastic Member, Masila Basin, Yemen
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ORIGINAL PAPER
Log-derived petrophysical characteristics and oil potentiality of the Upper Qishn Clastic Member, Masila Basin, Yemen Awad A. Omran & Nabil M. Alareeq
Received: 18 August 2012 / Accepted: 25 January 2013 # Saudi Society for Geosciences 2013
Abstract The Lower Cretaceous Qishn Formation at Masila Basin, Yemen, contains substantial amounts of proven crude oil. It is divided into a lower shaly silisiclastic member and an upper carbonate member. In the present work, detailed formation evaluation of the Upper Qishn Clastic Member was carried out using the digitized well logging data from 12 wells, via computer-assisted analysis, to accomplish its reservoir characteristics and oil potentiality. Accordingly, the true resistivity (Rt), porosity (total φt and effective φe), shale content (Vsh), permeability (K), water saturation (Sw), hydrocarbon saturation (Sh) (movable “Shm” and residual “Shr”) and lithologic composition in each well were estimated, analyzed, and illustrated versus depth on litho-saturation cross-plots. Likewise, the areal distribution of such parameters alongside the member in the investigated area and their relations to geological setting were defined from the constructed isoparametric contour maps. Based on the obtained results, the components of Upper Qishn Clastic Member of Masila Basin are mainly shaly sandstone and minor calcareous sandstone with considerable amount of shale. Regionally, the Member was deposited on an inner neritic to shallow-marine platform setting. It is interpreted as a good-quality reservoir rock which has been established from high total porosity (15–22 %), good effective porosity (8–13 %), and variable shale volume (24– 31 %). A number of high hydrocarbon saturation zones (exceeding 55 %) are detected through intervals having Sw 20 % which have been considered as economic oil producers. The storage and pay capacities of the reservoir intervals have been resolved. The obtained results were A. A. Omran (*) Department of Geology, Faculty of Science, Assiut University, Assiut 71516, Egypt e-mail: [email protected] N. M. Alareeq Department of Geology, Faculty of Science, Thamar University, Thamar, Yemen
confirmed from the available data of core analyses and production tests. The Upper Qishn Clastic Member reveals promising reservoir characteristics which should be taken into consideration during future development of the oilfields in the area. Keywords Formation evaluation . Well logging analysis . Hydrocarbon potentiality . Reservoir . Qishin Formation . Masila Basin . Yemen
Introduction Yemen abuts the most prolific hydrocarbon province in the world. Oil was only discovered there as recently as the early 1980s (Mills 1992). Hydrocarbon produced from the Masila region in the east central Republic of Yemen (Fig. 1) was discovered in 1991, and by November 2002, 656 millionbbl of oil had been produced with estimated reserves of at least 1.1 billion bbl of oil (Fig. 2) (Leckie and Rumple 2003). Masila block is an irregular-shaped concession falling in an area cov
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