Abstract: A Three-Dimensional Volume Estimation Technique

KELLY, BRYCE, Dynamic Graphics Inc., Alameda, CA; DEREK TAYLOR, Dynamic Graphics Inc., Alameda, CA; JEFFREY SCHWALM, Dynamic Graphics Inc., Alameda, CA

Accurate volume calculations of hydrocarbons are critical for evaluating development strategies of reservoirs. Despite the known limitations of two-dimensional hydrocarbon mapping and volume estimation techniques, these methods are still commonly used because of the simplicity in deriving a result. Three-dimensional geocellular models can be more accurate yet historically have been difficult to produce, especially in areas of complex faulting, and consequently have not been adopted as a common hydrocarbon estimation technique.

Presented in this paper is a rigorous yet simple approach for building a three-dimensional geological model that correctly handles geological boundaries, normal and reverse faulting, fluid contacts, and the distribution of pore-volume fluids.

Faults are modeled as continuous surfaces and assembled to form a fault framework. This framework is used to spatially transform horizon data (and if appropriate property data) so that gridding is done in a continuous unfaulted environment. The model is then projected back into the original faulted space using an inverse-transformation. To reflect the influence of fault traps and other post-faulted conditions, properties and fluid contacts can be gridded using the faulted geologic model to define boundaries. The result is a completely defined three-dimensional numerical geological model from which volumes (and other metrics) can be derived on a field-wide or block-by-block basis. By using continuous surfaces, geological units and the distribution of hydrocarbons are modeled as closed volumes. Numerical integration can then be applied, yielding more accurate results compared with two-dimensional maps or three-dimensional geocellular models.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California