An Effective Basin Model for Pore Pressure Evaluation

Kenneth E. Williams¹ and Arkady G. Madatov^2
1Knowledge Systems, Inc.
²Murmansk State Technical University

An effective basin geopressure modeling (EBM) concept for geopressure simulation is introduced that is several orders of magnitude more rapid than conventional full-scale 3D grid-based modeling with no loss in resolution or accuracy of the pore pressure analysis.

The EBM hydrodynamic modeling approach is based on the identification of the interrelationships between the various processes involved in the development, maintenance and dissipation of overpressures. In addition to use in pre-drill pressure prediction, the modeling also allows real-time updating of pressure predictions based on new information acquired during drilling operations. The EBM approach has been thoroughly tested and used in pre-drill pressure predictions for over 150 wells, and for real-time updating of more than 50 of those wells.

Reduction of model parameters to a minimal but sufficient number of key variables allows significant simplification of the background earth model. For example, the largest uncertainty in pressure modeling is the permeability of the shale sealing compartment units. EBM uses a specific surface area parameter directly related to permeability and adjustable in calibration. Therefore the EBM calibration strategy is based on the use of well data inversion. The relevant solution is numerically stable within the range of reasonable model parameters and grid properties.

The EBM concept incorporates both 1D and 2D approaches to overpressure modeling through geologic time and is shown to be effective in accounting for the main overpressure generating mechanisms, including 3D pressure communication phenomena.

The model data is derived from three main sources: 1) Geologic data comes from well and seismic correlations supplemented by paleontological and formation ages. The construction of the model is faster and simpler because it is based on triangulation rather than the more conventional gridding algorithms. The ability to model salt deformation within the model’s mesh framework allows refinement of sediment geometry through time by applying a user-defined burial history concept. 2) Secondly, seismic velocity volumes are analyzed along pressure compartment boundary horizons and within pressure compartment intervals. A pressure volume is generated based on calibration, compartment and data quality analysis. 3) Thirdly, standard petrophysical pressure analysis of well log data incorporates all available drilling information to improve the pressure analysis. Well data quality is further improved through comparison of all well analyses in the context of the overall model geometric and stratigraphic framework.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands