Cyclo-Stratigraphy of the Lower Cretaceous Succession in Jade field, North Western Desert, Egypt
Journal Title: IOSR Journal of Applied Geology and Geophysics (IOSR-JAGG) - Year 2018, Vol 6, Issue 5
Abstract
The lower Cretaceous Alam Elbueib (AEB) Formation acts as a hydrocarbon reservoir in the subsurface of the Western Desert, Egypt. The objective of this paper is to investigate changes in the depositional settings of the early Cretaceous; mainly for Alam Elbueib Formation in Jade field using lithofacies characteristics and electrofacies analysis. It is subdivided into six units (AEB-1, 2, 3, 4, 5 and 6) and is composed mainly of sandstone with shale and siltstone interbeds at base while carbonate increases at top. AEB-3 unit consists of a succession of massive fluvial sand bodies separated by marine shale incursions and is divided into six subunits (AEB-3A, 3C, 3D, 3E, 3F and 3G). Ditch samples and well logs of six wells (Jade-1X, Jade-2X, Jade-3X, Jade-8, Jade-12 and Jade N-1X) were utilized in this study. The description of samples and logs revealed strata packages with a progradation to retrogradation timeline which defines two regressive to transgressive trends forming the lower Cretaceous succession in Jade field. The first cycle commences with a transgressed phase started during Tithonian at the base of AEB-6 and continued during Valangian (AEB-5) to early Hauterivian (AEB-4) with mainly shallow marine setting with a terrestrial input. This transgression came after a period of non-deposition and/or erosion which is regional in the North Western Desert of Egypt. A regressive phase started with the thick fluvial sand sequence of AEB-3G of early Hauterivian, culminating in non-deposition during the late Hauterivian. These sands occasionally interbedded with thin shale and siltstone layers. Also, it contains some recognized shale intervals in AEB-3C and AEB-3F subunits, which may represent shallow marine setting. The second cycle begins with the end of AEB Formation during Barremian by another transgressive phase that is reached its peak in the Aptian Alamien marine shelf dolomites. It is represented by the increase of dolomites and marine dinocysts enrichment which referee to increase of marine influence. Dahab shallow marine claystones represents the regressive phase and it marks the end of this cycle by a subaerial unconformity that separates it from the above sands of Kharita Formation. The results of lithofacies analysis were correlated with the wire line log response to perform electrofacies investigation. Four main facies associations could be recognized in the studied lower Cretaceous sequence in Jade field. The obtained results indicate that interested horizon within the lower Cretaceous succession in Jade field in general represents two 3rd order cycles of shallow marine to fluvial environments.
Authors and Affiliations
Abu Khadrah, A. M. 1 ,, Refaat, A. A. 1, Omar, M. 2
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