Petroleum Systems Dynamics of the South Caspian Basin
Stephan J. Duppenbecker1, Gregory W. Riley2, Nazim R. Abdullayev2, Tim J. Green1, and Helen Doran1
1BP Exploration Ltd., Azerbaijan Business Unit, Chertsey Road, Sunbury-on-Thames, TW16 7LN, UK
2BP Exploration (Caspian Sea) Limited, 2 Neftchiler, Villa Petrolea, Baku, AZ 1003
The South Caspian Basin represents an extremely young petroleum system in which over 8 kilometres of sediment have been deposited in the past 6-10 million years. Within the last 1-2 million sediment deposition rates increased up to 3 kilometres. These high deposition rates have pushed the sedimentary section into significant disequilibrium with respect to the evolution of temperature and pore pressure. The basin dynamics are expressed in:
(1) Rapid, vertical and lateral pressure changes in the sediments that limit the capacity of seals to build and preserve petroleum columns and present challenges for well planning and execution.
(2) Low temperature gradients which delay petroleum generation from the source rock intervals and slow down diagenetic processes in the reservoirs.
(3) Tilted hydrocarbon contacts that lead to uncertainty of field development.
Basin Modelling has proven to be the key technology in understanding the South Caspian Basin dynamics and quantifying their impact on petroleum generation, migration and seal capacity evolution, as well as in assessing prospect drillability and field development options.
The Miocene Maykop Source Rock series is overlain by a group of world class reservoir systems and extensive lacustrine shales which are folded into extremely large anticlines. Depending on the regional extent of the sandstone “sheets” high pressure is transferred both regionally from the overpressured basin to the basin margins, and semi-regionally from syncline to crest, and this results in reduced seal capacity for petroleum accumulations and stacked pays. This complex regional aquifer pressure distribution can explain variations in fluid contacts observed in structures. The resultant low effective stress in the shallow section also creates substantial drilling and field development challenges.
From our early studies we learned that sedimentation rate, the aquifer extent and the nature of fine-grained sediments exert fundamental controls on pressure distribution. The complex interaction between the 3D connectivity of high permeability sediments (aquifers) and the 3D architecture of the low permeability sediments (aquitards) can be best understood using integrated basin modeling simulation techniques. Our methodology is strongly based on calibration of models to the observed pressures and temperatures in a number of exploration and appraisal wells across the Azerbaijan sector of the South Caspian Basin. The modeling results show how the basin plumbing structure transfers pressure regionally from the overpressured basin to the basin margins, and semi-regionally from syncline to crest. This enables the evaluation of seal capacity in petroleum accumulations and stacked pays.
AAPG Search and Discovery Article #90091©2009 AAPG Hedberg Research Conference, May 3-7, 2009 - Napa, California, U.S.A.