The Hasdrubal field (offshore Tunisia) comprises an Early Eocene shallow-marine nummulitic limestone reservoir (the El Garia Formation) sourced by deep-marine mudstones and limestones of the generally age-equivalent Bou Dabbous Formation. The field is located on a NNW-SSE trending horst between a series of en-dchelon normal to oblique faults, and is dip-closed except to the north where a stratigraphic pinch-out into the Bou Dabbous Formation is inferred. Middle Eocene shales and dense limestones of the Cherahil Formation form the main seal.The El Garia Formation reservoirs signijkant volumes of hydrocarbons in Tunisia and Libya. A detailed micropalaeontological and nannofossil study has been undertaken of the El Garia Formation and the immediately over-and underlying formations which together form the Metlaoui Group, using subsu$ace data from the Hasdrubal field. This has permitted a detailed chronostratigraphic and sequence stratigraphic framework to be developed, including the recognition of three flooding events, which can partly be calibrated with second-order sequences, thus permitting the correlation of discrete reservoir units across the field. A further six microfaunal events are recognized between the Chouabine Formation and the "Compact Micrite Member" within the Metlaoui Group.Previous depositional models for the El Garia Formation are discussed and a new model is proposed. The model partly explains why a number of wells drilled along the El Garia nummulite "bank" trend have failed to encounter the nummulite reservoir facies, and why, even where this facies was encountered, the limestones were frequently tight and/or contained limited hydrocarbons. It is also suggested that proximity to source is a critical factor, with the development of dissolution porosity by acidic pore waters migrating in advance of hydrocarbons. This is critical for enhancing reservoir quality and thus promoting the capacity to reservoir hydrocarbons, as indicated by the location of existing discoveries.

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Fieldwork provides an efficient and economical way of obtaining genuine geological data that can be used to constrain, test and develop exploration models in frontier areas. This study of the Cretaceous outcrops of NW India has been used to characterize models for petroleum systems postulated to have developed beneath the Deccan volcanic sequence, offshore western India, where well data are not available. To date, exploration of ‘sub-Deccan plays’ has mainly been limited to the NW, where the presence of a working Cretaceous petroleum system has been proven in the offshore Kutch Basin.A revised chronostratigraphic framework has been defined for the Cretaceous section as a result of new biostratigraphic data collected during this study and a thorough revision of existing palaeontological data. The revised framework, together with lithofacies observations from the field, has provided a basis for regional sequence stratigraphic correlation, which has been used to link data from onshore outcrops to models of offshore petroleum systems.A Lower Cretaceous clastic package that, in part, corresponds to the Lower Goru and Bhuj Formation reservoirs of the Indus Basin of Pakistan and the Kutch Basin in India has been correlated across the region. Towards the top of this package, a transition from fluvial to shallow-marine sedimentation marks the onset of a marine transgression that reaches its peak in the Turonian. Marly limestones and claystones associated with this regionally mapped event are a potential topseal to the Lower Cretaceous clastic package. Geochemical evaluation of several outcrop locations has identified potential source-prone facies that, if present downdip in the offshore, may provide a mechanism for charging a pre-Deccan play.

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