Y. Shirakura

Japan Oil Development Company Ltd., Tokyo, Japan

ABSTRACT: Reservoir Characterization of An Offshore Abu Dhabi Lower Cretaceous Limestone Based Upon A Unique Method of Lithofacies Identification

This paper demonstrates the successful application of a unique method of lithofacies identification in a clean and algal dominant bioclastic limestone reservoir. The subject reservoir is contained within the Thamama group of the Lower Cretaceous, offshore Abu Dhabi and has to date produced a significant volume of oil.

The objective of the study was to construct a geological reservoir model for flow simulation of the reservoir. The key point of the modeling was to predict permeability distribution, especially distribution of high permeability streaks accelerating water breakthrough under a five spot pattern water injection scheme. Actually, a breakthrough of injected water has been observed in several producers. Core and thin section observations suggest that permeability is related to lithofacies. In this study, identification of lithofacies distribution was done using gamma-ray response, which behaves in a non-conventional manner, generally, grain-dominant lithofacies show a relatively higher gamma-ray response than mud-dominant lithofacies and, although the reservoir interval is composed of an upward-coarsening parasequence, the gamma-ray stacking pattern indicates an upward-deepening pattern.

As a result of this study a robust reservoir model was generated. Lithofacies distribution was modeled by prediction of lithofacies at uncored wells based on thickness and gamma-ray log profile. Permeability was predicted based on the lithofacies distribution model. Five rock types were classified for capillary pressure curves and relative permeability curves.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado