Naturally fractured reservoirs are important contributors to global petroleum reserves and production. Existing classification schemes for fractured reservoirs do not adequately differentiate between certain types of fractured reservoirs, leading to difficulty in understanding fundamental controls on reservoir performance and recovery efficiency. Three hundred naturally fractured reservoirs were examined to define a new classification scheme that is independent of the type of fracturing and describes fundamentally different matrix types, rock properties, fluid storage and flow characteristics.
This study categorises fractured reservoirs in three groups: 1) Type 1: characterized by a tight matrix where fractures and solution-enhanced fracture porosity provide both storage capacity and fluid-flow pathways; 2) Type 2: characterized by a macroporous matrix which provides the primary storage capacity where fractures and solution-enhanced fracture porosity provide essential fluid-flow pathways; and 3) Type 3: characterized by a microporous matrix which provides all storage capacity where fractures only provide essential fluid-flow pathways. Differentiation is made between controls imparted by inherent natural conditions, such as rock and fluid properties and natural drive mechanisms, and human controls, such as choice of development scheme and reservoir management practices.
The classification scheme presented here is based on reservoir and production characteristics of naturally fractured reservoirs and represents a refinement of existing schemes. This refinement allows accurate comparisons to be made between analogous fractured reservoirs, and trends and outliers in reservoir performance to be identified. Case histories provided herein demonstrate the practical application of this new classification scheme and the benefits that arise when applying it to the understanding of naturally fractured reservoirs.
© 2020 The Author(s). Published by The Geological Society of London for GSL and EAGE
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0/)
Written by Shaoqing Sun and David A. Pollitt
“This article represents the culmination of years of dedicated study to mature from concept to completion. We hope that our efforts will help advance the scientific application of global analogues in exploration, appraisal, and development. Unrestricted access to analogue knowledge is something I strongly believe in and I am therefore happy to say that this study is available for all via open access.
Our article defines a revised classification scheme that better describes the real-world performance of naturally fractured reservoirs, and further allows differentiation and improved understanding of controls imparted by both inherent rock and fluid properties, as well as human intervention, on reservoir performance and recovery efficiency.”