The appropriate economic balance between oil production rate, ultimate oil recovery and development cost can be difficult to find for complex naturally fractured reservoirs. This makes development drilling decisions and reservoir management of these reservoirs a very demanding task. Successful life cycle development of a naturally fractured reservoir can only be achieved by fully understanding the role of fractures on fluid flow at different scales, both inside the reservoir and near wellbores. Systematic fracture characterization becomes an essential prerequisite to gain the critical understanding crucial for successful development and economic success.
This publication presents a complex low matrix permeability naturally fractured reservoir case study from a mature giant Middle Eastern oil field. Examples are provided illustrating the impact of fractures of different scales on reservoir fluid flow and well productivity, ranging from large scale fractures, previously often termed fracture corridors or fracture lineaments, to small scale micro fractures.
Systematic efforts have been exerted over the past years to collect fracture characterization data, e.g. pressure transient, image logs and advanced formation tester data, including mini-DST (Drill Stem Test) formation tests. This data set has been complemented by other dynamic data like rate tests, pressure surveys and time lapse production logs, plus seismic and electromagnetic surveys. Based on the presented observations, it is evident that small scale micro features and associated connected fracture networks also play a role. If near wellbore large scale fracture features are not dominant, the small scale fracture networks determine the well drainage areas and become a controlling factor for reservoir well productivity and the overall reservoir recovery mechanism.
As presented in this paper, the reservoir development strategy, including development well type, has been modified as a direct result on the improved understanding of the reservoir fracture system.