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Moros, J. Saul1, William S. Meddaugh2 
(1) ChevronTexaco Global Technology Services Company, Maracaibo, Venezuela 
(2) ChevronTexaco Exploration & Production Technology Co, Bellaire, TX

ABSTRACT: Facies, Sequence Stratigraphy and Flow Units in the Eocene C-4-X.01 Reservoir, LL-652 Area (Lagunillas Field), Western Venezuela

Facies and sequence stratigraphic analysis have aided in the development of a new geological model for the C-4-X.01 reservoir. This reservoir is located on the east flank of the LL-652 anticline (Lagunillas Field). The reservoir produces oil and gas from the Eocene C-3-X / C-4-X members of the Misoa Formation. 
The studied intervals are part of the large scale transgressive-regressive stratigraphic cycle that characterizes the Misoa Formation. This large scale cycle is punctuated by smaller-scale sequences which represent higher frequency regressive-transgressive cycles within the succession. Within the smaller-scale sequences, successive Lowstand (LST), Transgressive (TST) and Highstand (HST) Systems Track can be recognized and correlated throughout the entire LL-652 area. This sequence hierarchy is the basis for the sequence stratigraphic subdivision of the C-4-X.01 reservoir. 
Petrophysical characterization indicates that depositional facies exert the primary control over reservoir properties. Reservoir flow units are associated with the amalgamated distributary channels and tidal sand bars that define the LST of each sequence. Permeability baffles and barriers occur within the tidally-influenced TST and HST deposits. 
In the C-4-X.01 reservoir, facies and sequence stratigraphic analysis have been successfully applied to: (1) recognize the correlative reservoir intervals with confidence; (2) identify and map the LST of the low-order sequences which represent the major reservoir compartments and (3) demonstrate that significant differences in reservoir modeling result from varying the style of well-log correlation from a complex stratigraphic model with several lithofacies to a simple stratigraphic model that define systems tracts and only two “lithofacies” (reservoir or non-reservoir rock).


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.