--> Offshore Morocco Petroleum Systems: Major Revisions to the Prevailing Paradigm

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Offshore Morocco Petroleum Systems: Major Revisions to the Prevailing Paradigm

Abstract

The prevailing paradigm for offshore Morocco has changed very little since the Esso discovery of significant heavy oil resources in the Upper Jurassic at Cap Juby in 1969. Over a period of over four decades, periodic interest led to numerous work programs that made incremental advances, but mainly established and reinforced a petroleum systems paradigm that focused on heavy biodegraded oil being present in the Upper Jurassic reservoir, a source rock being present in the Jurassic, and a possible second source rock that may have charged a potential reservoir in the Middle Jurassic. The critical component of this study is focused on fluid inclusion stratigraphy (FIS) technologies, and includes the extraction and analysis of oil- and gas-phases from the fluid inclusions. The most important results establish that the Cap Juby structure was filled to spill in both the Upper and Middle Jurassic levels (350 and 200 meter oil columns, respectively), the Upper Jurassic reservoir contains biodegraded and nonbiodegraded oil (i.e., not diesel cut DST as previously reported), some areas have 100% nonbiodegraded oil, and there is Type B oil content in other Middle Jurassic reservoirs. This Type B oil also leaked vertically into the Upper Jurassic reservoir to account for the non-biodegraded oil charge. The correlative marine source rocks are genetically related with the primary difference being assigned to tectonic setting: Type A is a Type I/II kerogen associated with restricted water circulation / stratified molecular signal versus Type B is a Type II/III kerogen associated with higher dissolved oxygen in the water column. Type B oil is also proven to be present in the in the Lower Jurassic and Triassic reservoirs that also contain a charge (i.e., mixed) of Type K (i.e., Cretaceous sourced oil). This is the first report of hydrocarbons in Lower Jurassic and Triassic reservoirs, and the presence of Jurassic sourced oil at this stratigraphic level also contradicts the paradigm that these reservoirs would need to be charged from the Paleozoic source rock system. The documentation of Type K oil proves that a Cretaceous petroleum system charge is viable in offshore Morocco. Collectively these results indicate that offshore Morocco may not be an undercharged petroleum system, that additional focus should be directed to top seal capacity in evaluating prospective drilling targets, and provides additional support for including the Canadian conjugate margin analogues.