The Influence of 3-D Property Modeling Protocols on Uncertainties in Net Pay and Hydrocarbons-in-Place

The emergence of geoscience 3D modeling protocols has raised questions about the compatibility of hydrocarbon volumetric deliverables with those derived from established 2D methodologies. Two key points of comparison are net pay and hydrocarbons in place. Net pay is an important parameter in the estimation of hydrocarbons resources, a practice that underpins the value of the petroleum industry. However, net/gross pay does constitute a major source of uncertainty in volumetric resources estimates.

The purpose of this study has been to compare static-volumetric estimates of net pay and thence hydrocarbons in place for various reservoir characters. This has been done at two levels. First, 3D geocellular models have been generated using two commercial software packages to allow comparisons of the deliverables within the 3D domain. Second, these data have then been compared with 2D reference models. Each 3D geocellular model is populated with an identical set of petrophysical properties that are internally self-consistent and tied to facies (rock type). The reservoir comprises an oil accumulation within a water-wet clean sandstone. The sandstone is made up of five rock types with different reservoir quality and discrete irreducible water saturations: these are further distinguished by different relationships between core total porosity and permeability.

This study has incorporated the influence of geological architecture, stratigraphic sequences of rock types, upscaling, variogram selection, and other property modeling protocols on the volumetric results as a basis for assessing uncertainty and for inter-model comparison. Net pay uncertainty is expressed in terms of a range of estimates of hydrocarbons in place that have resulted from comparisons of the 3D and 2D models for each reservoir scenario. The paper details not only the methodology for quantifying net pay but also the various uncertainty and sensitivity analyses used to evaluate the 3D and 2D model scenarios of the study. The results have exposed a significant difference between the 2D and 3D protocols in terms of the targeted deliverables. A high-level approach is proposed for managing the shift in hydrocarbon volumes as geoscience modeling continues to migrate to 3D practices.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California