Abstract: High Resolution Sequence Stratigraphic Analysis from Subsurface Well Log Data Sets: An Example from Faja Field, Venezuela

RODRIGUEZ, M., D.S. HAMILTON

A high-resolution genetic stratigraphic analysis of the Oligocene and Oligocene-Miocene sediments at Faja field, Eastern Venezuela Basin, was undertaken from over 45 well logs and 2 cores. The genetic stratigraphic framework established was defined by thin, but laterally extensive, shale markers interpreted as maximum flooding surfaces. The shale markers were identified primarily by their high gamma-ray log response and consistent stratigraphic position from well to well, but marked changes in bedding architecture above these surfaces also facilitated their identification. The changes in bedding architecture reflect reorganization of the depositional systems from one depositional episode to the next.

A number of widespread lignite beds consistently occurring at the same stratigraphic level in neighboring wells also contributed to the high level of resolution in the stratigraphic framework. Because peat accumulation and preservation as lignite can only occur in the absence of significant clastic influx, these lignite beds record hiatuses in clastic deposition and, thus, have time-significance at least at field-wide scale. The lignite beds represent readily recognized and easily correlated operational boundaries allowing very fine subdivision of the reservoir sequence.

The stratigraphic analysis provided a reliable framework within which the depositional facies were mapped, and proved essential for unraveling sediment transport patterns and, thus, predicting reservoir sandstone distribution. The high resolution achieved by the stratigraphic framework also enabled accurate identification of missing section in faulted wells leading to superior fault modeling. The geologic model constructed from the combined stratigraphic, sedimentologic, and structural analysis formed the foundation for design of a 24-well horizontal drilling program commencing by the end of 1996.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria