Recoverable Resource Assessment through 3D Reservoir Modeling

Emmanuel Gringarten, PARADIGM

Uncertainty exists at all levels of a reservoir study, starting with measurements of raw data and their interpretation.  For instance, uncertainty in seismic interpretation and in velocity functions affects time-to-depth conversion and thus the position in depth of the reservoir’s structural model.  The geological model depends on a conceptual understanding of deposition. The petrophysical model exhibits uncertainty that is due to a very limited sampling of an often complex and heterogeneous subsurface.  The parameters and equations controlling fluid flow also carry some uncertainty. The combination of these uncertainties affects one's ability to understand and predict reservoir behavior and to reliably forecast reservoir production, therefore impacting estimations of recoverable hydrocarbon resources.

In front of this overwhelming amount of uncertainty, it is important to follow a systematic methodology articulated along the following principles: (1) it is necessary to capture and integrate the complete spectrum of uncertainties, from time-to-depth conversion and structural modeling, to petrophysical property distribution and flow simulation; (2) one must then identify the critical sources of uncertainty; this is achieved by assessing their impact on specific reservoir management decisions; finally (3) these key uncertainties must be reduced to a level where a risk-acceptable decision can be made, either by refining the interpretation models or by gathering new data.

In view of the recently revised resources categorization, uncertainty quantified through 3D reservoir modeling can play a key role in the assessment of 1P, 2P, or 3P reserves (and 1C, 2C, and 3C contingent resources) values as they relate directly to P10, P50, and P90 reservoir models. However, it is important to understand that these are not merely the result of stochastic variations around a reference case or equiprobable realizations, but are the combination of alternative (possibly very different) scenarios and stochastic simulations describing all elements and parameters contributing to the construction of a realistic 3D representation of the subsurface.

This presentation will illustrate the above concepts and the importance of 3D reservoir modeling in quantifying uncertainty for recoverable resources evaluation.

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