Jean-Yves D Chatellier¹, Pablo Hernandez², Carlos Porras², Sergio Olave², Maria Eugenia Rueda²

(1) PDVSA Intevep, Caracas, Venezuela
(2) PDVSA Oriente, Puerto La Cruz, Venezuela

ABSTRACT: Recognition of Fault Bend Folding, Detachment and Decapitation in Wells, Seismic and Cores from Norte Monagas, Venezuela

Our study focussed on the compressive structure of the Santa Barbara Field with integration of our previous reviews of the neighboring Carito and Furrial fields; these three fields corresponding to the major producing area in Venezuela with in place reserves of 26 MMMbbls and 50 TCF. We will show examples and recognition criterias of various types of structural elements using cores, dipmeters, geochemistry, pressure data and 3-D seismic.

Fault Bend folding recognized on various structural sections has been corroborated by outstanding observations from cores. Regularly spaced flats and ramps of small scale fault bend folds are characterized by slickensides, pressure solution features and quartz cement precipitation.

The use of 3-D statistics enabled us to recognize highly prominent and laterally extensive detachment planes which have been corroborated by our stratigraphers and our reservoir engineers. Abnormal but highly characteristic RFT patterns have been successfully integrated in our study and confirm the small-scale observations made in cores.

One school book example of a large scale decapitation came out of our fault analysis that included generation of fault planes, fault throw maps, bird'eye maps and integration with dipmeter and seismic. Thus along the same low angle fault plane, perfectly tied by fifteen wells on an area of 5x5 km, apparent throws gradually change from a repetition of 510' to missing sections of more than 3000'. Folding occurred before the decapitation phase.

The 3-D seismic confirmed the existence of detachment and decapitation postdating a first folding and thrusting phase.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado