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A New Genetic Classification of Carbonate Porosity and Its Application to Reservoir Characterization*
Wayne M. Ahr1
Search and Discovery Article #40357 (2008)
Posted October 24, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008.
1 Department of Geology, Texas A&M University, College Station, TX. ([email protected])
Abstract
Carbonate pore types are formed by depositional, diagenetic, or fracture processes such that the spatial distribution of porosity may or may not conform to depositional facies boundaries. Pores may be formed or altered by diagenesis and brittle fracture. Understanding carbonate porosity requires identifying pore characteristics that reflect the processes that created them. It requires determining how genetic pore types are related to petrophysical characteristics and how pore-forming processes have influenced bulk-rock properties.
Genetic pore types are part of a larger collection of rock properties formed by the three end-member processes; consequently, genetic pore types must have characteristics that correspond to petrological or stratigraphic attributes that serve as "tags" for the genetic pore types. Examples of "tags" may include unconformities, paleosols, evaporite horizons, predictable occurrences in stratigraphic cycles, or distinctive geochemical, fluid inclusion, and cathode luminescence signatures. Such tags may be recognizable in cores and thin sections, on outcrops, in sequence stratigraphic "stacking patterns", on wireline logs, and in seismic signatures.
If the mode and time of origin of the "tags" can be identified, it is then possible to predict the spatial distribution of the corresponding genetic pore types. Rock properties that correspond to genetic pore types can be put in larger stratigraphic context for use in reservoir characterization, flow unit mapping, and reservoir modeling.
Selected Figures
Conclusions
Genetic classification identifies rock properties and covariant genetic pore types "bundled" by common origin. Knowing cause-effect origin of pores, pore/rock-type bundles are mappable at field scale; e.g., diagenesis associated with unconformities, fractures associated with structural geometry, depositional pore systems associated with facies boundaries. The classification facilitates improved reservoir definition, flow unit mapping, and petrophysical rock typing based on pore type and pore/pore throat geometry instead of "facies type".
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