Sedimentology and sedimentary architecture of the Middle Ordovician Hawaz Formation in the subsurface of the Murzuq Basin (Libya)

Programa de Doctorat en Ciències de la Terra / Tesi realitzada conjuntament amb l'Institut de Recerca Geomodels [eng] The Hawaz Formation is a Middle Ordovician siliciclastic succession which extends for hundreds of kilometres across North Africa. This thesis uses a subsurface-based approach, mainly utilizing well data, complemented by data from nearby outcrops, with the aim of gaining new insight into the oil-prone Hawaz Formation in the emergent hydrocarbon province of the Murzuq Basin (SW Libya). The limited lateral continuity of this formation, often truncated by the Late Ordovician glaciation unconformities, has always presented a challenge to the interpretation of this reservoir in terms of large-scale sedimentary architecture and facies connectivity. This investigation has required a high resolution description and interpretation of the sedimentology and sedimentary architecture of this succession in the subsurface of the north central part of the Murzuq Basin through two well-differentiated phases: 1) sedimentological description and interpretation of lithofacies and facies associations together with a sequence stratigraphic analysis of the succession; 2) basin-scale reservoir characterization in terms of vertical and lateral continuity of facies belts and paleogeographic reconstruction of this unit in the area of study. This research has resulted in the identification and characterisation of fifteen distinctive lithofacies, defined on the basis of lithology and internal fabric, mainly using core and microresistivity image log data, grouped into seven correlatable facies associations distributed in broad and laterally extensive facies belts deposited in a shallow marine, intertidal to subtidal environment. These facies associations are: 1) tidal flat; 2) subtidal complex; 3) abandoned subtidal complex; 4) middle to lower shoreface; 5) burrowed shelfal and lower shoreface; 6) burrowed inner shelf and; 7) shelfal storm sheets. Three main depositional sequences and their respective systems tracts have also been identified and interpreted as deposited mainly during transgressive and high relative sea level stages. On this basis, a genetic-based stratigraphic zonation scheme has been proposed as a tool to improve subsurface management of this reservoir unit. Facies analysis and sedimentological interpretation provided the basis for the reconstruction of the sedimentary architecture of the Hawaz Formation by means of eight correlation panels oriented alo