Geocellular Modeling; Considerations for Estimating and Reporting Reserves

Jeffrey M. Yarus and Richard L. Chambers
Landmark Graphics/Halliburton

High resolution geological models are built upon 3D mathematical meshes that provide the numerical architecture for building the structural stratigraphic framework.   Models are generally constructed and parameterized through software products that allow professional geoscientists to approximate the static state of reservoir by interpolating or simulating geologic facies and their petrophysical properties within a 3D volume.   This process, however, is not done "willy-nilly," but is "model driven” from a scenario comprising a conceptual geological model.  The interpolation and simulation algorithms used to fill the inter-well space are performed using workflows based on these conceptual models and attempt to bind results to logical rules derived from underlying geologic principles.  While the workflows can vary based on individual interpretation of the data, the results are generally obligated to honor the observed data.  Within a given scenario, it is the interpolation algorithm that is responsible for providing the best estimate at every grid location and the simulation algorithm that is responsible for capturing the inherent variability, providing the basis for uncertainty analysis.  

However, there are less obvious aspects of uncertainty that go beyond the conceptual geological model, interpolation, and simulation. Many aspects of geocellular modeling are involved technology that is not well understood by modelers.  Grid design and volume support, stochastic principles including spatial modeling and algorithm selection, appropriate methods for capturing the space of uncertainty, how to integrate the “human” factor in the model.  All of these issues can significantly effect dynamic modeling and risk assessment, thus impact reserve estimation.  The presentations in this session highlight many of these issues and provide insights into appropriate geocellular modeling principles that can provide better input into the subsequent crucial steps that lead to reserve reporting. 

AAPG Search and Discovery Article #90098©2009 AAPG Education Department, Houston, Texas 9-11 September 2009