--> Abstract: Causes of High Formation Pressures in Deep Drilling in Western Greece, by Angelos Mavromatidis, Vassilios C. Kelessidis, and Dionisis Monopolis; #90072 (2007)

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Causes of High Formation Pressures in Deep Drilling in Western Greece

Angelos Mavromatidis1, Vassilios C. Kelessidis2, and Dionisis Monopolis2
1Petroleum Development Oman LLC, Muscat, Oman
2Technical University of Crete, Chania, Greece

This research analyzes data of high formation pressures encountered while deep drilling thick evaporitic sections in northwestern Greece. The stratigraphy of the area is composed of Jurassic to Tertiary carbonates underlain by Triassic evaporites. The well structure was an anticlinal dome, with uncertainty as to the nature of the interval beneath the Triassic evaporites. The hydrocarbon play system depended on the geological model applied. The most likely model comprised carbonate reservoir of Cretaceous-Eocene age, sealed by the Oligo-Miocene Flysch and over-thrusted Triassic evaporites. The reservoir was thought to be sourced from underlying Mesozoic source rock intervals. The alternate, less likely model, comprised of Permo-Triassic carbonate-dominated reservoir, sealed by Triassic evaporites and probably sourced from Triassic intervals.
During drilling at the depth of 4,000 m in the evaporitic section high pressures were encountered and the well was killed. A sidetrack well kicked off but at 3,600m, high formation pressures were encountered again which could not be overcome and the well was finally shut in.
We explore possible causes of the high pressures: flysch overpressure, laying beneath the evaporites, somehow charged the dolomitic lenses within the evaporites via faults; intra evaporite overpressure due to earlier isolation of carbonate lenses/rafts within anhydrite while they were at greater depths, followed by uplift of those lenses to shallower depths; and/or overpressures as a result of formation water migration from under laying potential oil-gas bearing formations.
We explore similarities and differences with similar situations reported worldwide in similar lithological environment (e.g. carbonates and evaporites). The difficulties in predicting high formation pressures while drilling thick evaporite sections are presented and we suggest possible actions for future developments.

 

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece