AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Regional pore pressure in challenging environments: how to get good results from old data.

Abstract

The Getic Depression and Bend Zone areas, located in the foothills of the South Carpathians are very old, well known prolific hydrocarbon basins. Traditional shallow plays have been drilled during last century with few drilling challenges. The deeper plays, however, are still a matter of discovery and it is here where overpressure plays an important role, not only because pore pressure prediction is a key element to drilling safely but also because the high pressures can negatively impact the economics of any future discovery. Compiling a comprehensive database can therefore bring valuable insights for the main problems of operating in this kind of environments (eg well design, drilling operations, data acquisition, well completion and production). Such a database can give a proper understanding of the regional pressure regime for the Oligocene s.l. formation and is the starting point for future seal analysis, well planning and evaluation of safety issues. A thorough methodology together with a clear interpretation of each of the different data sources has been applied to the area of study allowing us to establish solid conclusions that can be later polished to a more robust model as the projects advance. Uncertainty in old wells is key where sources include mud weight and observations; kicks reported while drilling; pressure estimates derived from old DST data but with no direct measurements from the formation. Our initial results suggest that the basin is close to hydrostatic pressure (or even sub-hydrostatic in the shallower formations); while abnormal pressure trends start to be visible below Meotian FM. For the Upper Oligocene s.l. shales, we have identified two separate overpressure trends which are linked to the amount of recent tectonic activity in the vicinity of the wells. The mechanisms for generating such overpressures are proposed to be a mix of disequilibrium compaction, mean stress increase as well as hydrocarbon generation and cracking.