This paper provides a case study in the reservoir description of a fractured carbonate by a multi-disciplinary team. It illustrates how the synergistic interaction of team members during data analysis and model building resulted in:the identification of previously unrecognized links between several reservoir characteristics;produced a superior reservoir model; andincreased the likelihood of successful development.
The significant role fractures played in the connectivity, and hence the productivity of the reservoir, became obvious early in the study. A multi-disciplinary team approach allowed for the study of the fracture system utilizing lull range of scales, from microscopic to regional. Team members analyzed cuttings, core, wireline logs, well tests and 3-D seismic. Due to the interaction of team members during data analysis and model building, previously unrecognized links between static and dynamic reservoir characteristics were identified.
It was recognized from the study of cuttings and core that microfractures provide reservoir-quality porosity and permeability in the Cretaceous deepwater carbonates of Yum Field. Further, the fractures are concentrated in dense, siliceouslcherty lime mudstone and wackestone facies. Log analysis supports these findings and shows these reservoir zones to be correlatable, high density-low garrnna intervals. Analysis of well test data suggests the presence of discrete reservoir zones within the Cretaceous carbonate succession. interpretation of 3-D seismic allows for delineation of the structural framework.
In summary, identification, characterization, and delineation of fractured intervals within the deepwater carbonate succession resulted in a preliminary 3-D model of both the static and dynamic properties for the Cretaceous reservoir of the Yum Field which, through reservoir simulation, will provide a predictive tool for development planning.
Introduction
Natural matrix porosity in the Cretaceous formations of the Yum field is less than 5%, with permeabilities less than 1 md. These formations could not be produced economically were it not for the swarms of fractures that provide "super-highways" for the fluids to migrate to the wellbores. Because of the importance of the fractures to the production rates, this multi-disciplinary study focused on characterizing the fracture network at multiple scales, from the microscopic to the megascopic.
The interaction of the team members in the day-to-day work of interpreting the data, coupled with weekly progress/review meetings, promoted a work environment conducive to sharing ideas, and streamlined the work progression.
Description of the reservoir framework is provided by 3-D seismic and inter-well correlations. Well log, core and cuttings data provide the finer detail required to "flesh-out" the structure. A 3-D geologic model, built using this information, acts as a data repository, provides enhanced visualization of the geologic model, and provides a stepping-stone to the next step in reservoir evaluation - reservoir simulation. It is within this model that the static properties of the reservoir are distributed in the inter-well space.
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