ABSTRACT: Characterizing carbonate reservoirs: Approaches for determining the boundaries and internal facies patterns of small-scale cycles

Harris, Paul M. , Chevron Petroleum Technology Company, Houston, TX

In many carbonate reservoirs, a key component that must be well understood for reservoir characterization purposes is the small-scale cycle, as it appears to exert a fundamental control over fluid flow behavior. Understanding the nature of these cycles can be challenging in cases where core control is less than optimum. Modern and outcrop analogs, as well as crosswell seismic data, may provide clues to better understand the boundaries and internal facies distribution of cycles.

Modern environments are valuable for conceptualizing the spatial distribution of facies for a time-slice. Combining remote sensing data such as satellite images and aerial photographs with surface sediment maps provide facies trends and dimensionality data that can be used to show patterns and assist the modeling of a reservoir relative to simulated well spacing. These map data are of even more value when combined with coring studies that provide the vertical dimension of facies within the modern cycle.

Outcrop exposures offer two- or even three-dimensional views of cycles with greater diagenetic overprint than found in the modern examples. Cycle boundaries and spatial facies variation can be examined in detail. Porosity and permeability measured on outcrop within a cycle and facies framework serve as a template for modeling flow-unit dimensions.

Crosswell seismic profiling may also prove to be a suitable method of directly measuring cycle-scale reservoir units and interwell changes of facies. High vertical resolution crosswell data has been collected in carbonate reservoirs with close well spacing. The data are capable of resolving cycles and show indications of detecting interwell variations of impedance. When combined with log and core data and compared with porosity models, the seismic data can reasonably be used to map "petrophysical" facies between wells.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia