Unusual but Effective Petroleum Systems – Disseminated Terrestrial Organic Matter of the Upper Oligocene as the Primary Source Rock, Offshore Nile Delta, Egypt
Exploration in the oil industry commonly follows the paradigm of a “world class source rock” where an organic source must be of a certain quality and thickness to generate large volumes of hydrocarbons. However, recent experience from the Nile Delta shows that lower quality, transported terrigenous organic matter is sufficient to charge large volumes when closely coupled to a reservoir system.
Very little was known about the source rocks of the Nile Delta prior to the drilling of BP’s Satis field in 2007. Nile Delta production occurs from shallow, biogenic gas-dominated fields such as the Plio-Pleistocene Taurt and Ha’py fields, and deeper, thermogenic gas-dominated Miocene fields such as West Akhen and Temsah. In the past, thermogenic gas was generally attributed to deep Tertiary sources via biomarkers and maturity parameters, although contributions from Mesozoic sources were not completely ruled out.
The success of the offshore Miocene fields led to industry interest in the underlying Oligocene turbidite system, and BP successfully drilled the Oligocene play fairway in 2007 with Satis 1, followed by Satis 3 in 2010. Both of these wells prove the presence of disseminated terrestrial organic matter as a component of the fines within the Chattian turbidite systems. Although of relatively low quality (TOC from 1-2%; HI 150-300), the close coupling of the organic matter with the reservoir system results in direct charging with minimal migration losses. Satis 3 penetrated a reservoir compartment within the upper Oligocene that is solely sourced by a low maturity segment in the Chattian, proving further the relatively high quality of this type of source rock. Additional deeper marine systems of the Rupelian also contribute hydrocarbons into the system at Satis, although long distance vertical migration results in greater difficulty predicting the distribution of these hydrocarbons.
The newly-revealed potential of the Chattian source system in the Nile Delta has not only enabled understanding of its distribution (associated with the reservoir systems) but also has allowed refinement of predicted fluid properties and volumes in this emerging play fairway.
AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013