ABSTRACT: Sequence stratigraphy and depositional environments of the Oficina Formation, Petrozuata, Orinoco Heavy Oil Belt, Venezuela

Suter, John R., Robert Kopper, Stephen D. Levine, and Thomas Demchuk , Conoco, Inc, Houston, TX (2) Petrozuata, Puerto La Cruz, Venezuela

The Petrozuata joint venture between Conoco and PDVSA utilizes horizontal drilling to produce heavy oil from Miocene sands of the Oficina Formation, located in the Zuata region of the Orinoco Heavy Oil Belt of the eastern Venezuela Basin. The main reservoir intervals are interpreted to represent a complex mix of fluvial, estuarine, incised valley and deltaic deposits. To more accurately predict the distribution and continuity of reservoir sands, a 3-D seismic survey was conducted. Major reflectors comprise marine flooding surfaces and candidate sequence boundaries at the tops and bases of amalgamated, channelized successions, as well as coupled coal-paleosol horizons. Stratigraphically significant surfaces and lithologic intervals were identified and correlated using seismic reflector geometries, seismic facies analysis, log character and correlation, whole core description and analysis, palynologic data, and Stratimagic. Stratimagic is a 3-D seismic analysis and interpretation tool that uses neural network technology to classify and map seismic trace shapes within a user-defined interval. The resulting "seismic facies" maps can reveal a surprising amount of geomorphologic detail, and show that depositional style differed spatially and temporally within the Petrozuata block. Amalgamated, narrow, sinuous channel systems dominate some portions of the survey, while large, straighter reaches characterize others. Whole core, palynology, and drilling results indicate that these comprise fluvial and tidal-estuarine deposits, respectively, with distinctly different reservoir characteristics. Efforts continue to map and predict these differing reservoir styles within a sequence stratigraphic framework to more effectively develop the Petrozuata field.

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