WHITE, H. J.¹, D. W. JORDAN¹, E. E. ROBBS¹, R. BARRAGAN¹, and F. A. RAMIREZ^2
1Oryx Energy, Dallas, TX
²Oryx Ecuador, Quito, Ecuador.

Abstract: Predictability of Reservoir Facies within a Sequence Stratigraphic Framework, Oriente Basin, Ecuador

Cretaceous sandstones have been prolific producers for over 25 years in the Oriente Basin of Ecuador. Exploration within the basin has largely relied on seismic recognition of structural closures. Only within the last five years have sequence stratigraphic correlations been established for the Cretaceous interval. Predictability of the stratigraphic framework has been significantly enhanced using detailed facies interpretations from conventional cores and outcrops.

Five units (Albian to Campanian) contain reservoir quality sands: the Albian Hollin Sandstone and four sands within the overlying Napo Formation (Napo T, U, M1 and Basal Tena). The five units are separated by erosional or conformable boundaries. Each succession records general east to west shoreline progradation across the 200 kms of shallow Oriente shelf. Early workers envisaged south-flowing rivers systems depositing fluvial and deltaic mouth-bar sands derived from distal cratonic highlands. This study describes westward-flowing, low sinuosity fluvial to shoreline/deltaic and tidally-influenced estuarine sandstones alternating with marine shelf limestones and shales.

Reservoir sands within the five sequences reflect lowstand alluvial plain, early transgressive incised valley fill, transgressive tidal shoal, and highstand fluvial/deltaic deposition. To date, greater than 90% of the oil is produced in lowstand sandstones of the Main Hollin and early transgressive incised valley fill sands of the Napo T, U and M1 sequences. Comparatively minor volumes are currently produced from late transgressive and highstand shoreline facies of the M1 and Basal Tena sequences.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas