--> Abstract: Reservoir Heterogeneities Induced by Bitumen Cementation, by A. J. Lomando; #91012 (1992).

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ABSTRACT: Reservoir Heterogeneities Induced by Bitumen Cementation

LOMANDO, ANTHONY J., Chevron Overseas Petroleum, San Ramon, CA

Reservoir bitumen is precipitated in pore systems as a result of the alteration of trapped or migrating oil in carbonate and siliciclastic reservoirs. Reservoir bitumen is not readily identified on typical log suites, often being read as open porosity, which has hampered its broad recognition as a reservoir-altering cement. When present as a solid, it can be as influential on reservoir quality as carbonate, silica, or authigenic clay cements and therefore should be evaluated as part of the diagenetic evolution of any pore system whenever it is encountered.

Five morphotypes of reservoir bitumen have been identified and named: droplets, carpets, peanut brittle, vesicular, and digitate. Data from east Texas, Gulf Coast, and West African examples indicate that reservoir bitumen can reduce total effective porosity by more than 50%. Permeability can be significantly reduced by restricted or closed pore throats and by fines migration, even when bitumen occurs in only moderate amounts. The occurrence and distribution of bitumen on well, field, and regional scales can range from uniform and predictable to irregular and unpredictable, but are mappable through core and cuttings examination. Within a trap, bitumen can cause heterogeneity and form permeability barriers not related to depositional facies or prebitumen diagenesis and reservoir quality Its economic importance must be recognized when reservoir parameters are adversely affected, impacting reserves calculations, recovery factors, and secondary recovery programs. On a regional scale, predictive models can be developed to determine the areas of a trend or portions of a stratigraphic section that are most likely to be affected and can be incorporated with other data for evaluating expected reservoir quality in regional play assessments.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)