Challenges in Characterisation of Jurassic Carbonates in an Underexplored Area

Abstract

The Atlantic Passive Margin, offshore Morocco is an underexplored area, especially North of the Mazagan Plateau. This part of the Moroccan margin has undergone rifting in late Triassic to Early Jurassic times (Central Atlantic opening) with some influence of Western Tethyan wrench deformation persisting in the Jurassic and Alpine compression subsequently affecting the margin.

A range of plays are recognised from Palaeozoic to Tertiary age with clastics predominating except in the Jurassic when a well developed carbonate system prevails. The Jurassic carbonates form an extensive platform that is segmented along the margin by faulting, particularly where Tethyan wrench deformation is influential and also where earlier halite beds are mobile. A variety of source rocks are proven effective in the area including Silurian oil prone shales, Early Jurassic marine shales and various substrates for biogenic gas generation.

This paper looks at both 2D and 3D seismic acquired over the platform margin where discrete, draped fault blocks and other anticlinal structures are identified at the Jurassic level. Carbonate build up geometries can be seen on the seismic data, with internal character that has been mapped in detail. Mapped seismic facies include mounded geometries, prograding events and planar sub-parallel events, which are interpreted to represent carbonate reservoir lithologies. These are overlain by a seismically quiet zone which can be interpreted to represent sealing lithology.

The only 2 wells in the vicinity of the study area do not penetrate the Jurassic platform hence there is no direct calibration of seismic facies, which are described from both reflection and pre-stack seismic inversion data. Nevertheless the potential lithofacies corresponding to the relevant seismic facies have been studied in outcrop in the onshore Atlas region and by comparison with the Deep Panuke field on the conjugate Nova Scotian margin. These analogues give good insight to potential reservoir development in the target area of interest. (Go to www.searchanddiscovery.com to see figures.)

AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015