Abstract: Petrophysical Characterization of the Carito Norte, Mulata and Carito Fields, Norte de Monagas, Eastern Venezuela

Juan Carlos Porras, Manuel De J. Valle

The Norte de Monagas trend is located in the Eastern Venezuelan Basin and is characterized by high temperature, high initial pressure and production rates, variable PVT properties, GORs, and asphaltene content, and the presence of a tar mat at the base of the oil column.

These reservoirs were petrophysically characterized through the integration of core and log data. Productive sands are composed of very coarse- to medium-grained sands deposited primarily in deltaic to shallow marine environments. These sands are quartz-rich, with clay matrix averaging 3% in the Oligocene and 6% in the Cretaceous. The main difference is the presence of up to 30% feldspars in the Cretaceous. Clay mineralogy is dominated by illitic material in the Cretaceous and by kaolinite in the Oligocene.

Post-depositional changes dominated by cementation, mechanical compaction and subsequent dissolution processes have resulted in marked improvement or degradation of the productive characteristics of these reservoirs. Rocks were divided into four petrophysical categories based on grain size, pore throat radius, porosity and permeability.

Mercury saturation vs. mercury saturation over capillary pressure plots show the dominant interconnected pore system which controls flow rates is best defined by 50% saturation. Plots constructed using R50 pore aperture correlation indicate the pore throats to be macro to mega porous. Average log calculated water saturation is 14% compared with estimated from capillary pressure data of 12% at 1200^prime above free water level, and 15% from relative permeability data. Relative permeability data indicate the rocks behave preferably as water-wet.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela