Sequence Stratigraphic Framework in a Humid Alluvial Fan Complex, Quiriquire Oil Field, Maturin Sub-Basin, Venezuela

Fanchen Kong: REPSOL YPF / MAXUS ENERGY CORPORATION, The Woodlands, TX; Guillermo Jalfin, Pujianto Lukito, and Ichsan Sarkawi

Abstract

The giant Quiriquire Shallow oil field is located in the southeastern foothills of the Serrania del Interior in northeastern Venezuela. The main reservoir interval, the Quiriquire Formation, consists of conglomerates and sandstones deposited during 2.4-0.9 Ma, in a humid alluvial fan complex that interfingers with axial fluvial systems. Sequence stratigraphic concepts are applied to interpreting 3D seismic volume to establish an accurate tectono-stratigraphic depositional model for facies prediction. Sequence boundary recognition criteria are explored for humid alluvial fans. Five regionally extensive erosional unconformities are recognized as sequence boundaries. Maximum fluvial/shallow lake flooding surfaces and correlatives are recognizable as continuous high amplitude reflectors having overlying wide troughs. Each sequence may have flooding, high base-level, and low base-level systems tracts. At least five levels of cycles are interpreted. The three higher levels are controlled by intermittent tectonic events of hill uplift and basin subsidence from SE-contraction in a clockwise wrench-fault setting. Episodic growth strata, strata truncations, and linear shale diapirs are associated with these tectonic events. Smaller cycles are nevertheless associated with sediment supply and climatic changes or autocyclic processes.

Analyses of seismic reflection facies, waveform facies, and various attributes reveal a general basinward decrease of conglomerates and sandstones but an increase of shales. Alluvial-fluvial evolution shows a general northward fluvial onlapping trend consisting of two major alluvial fan progradations, in which conglomerates and conglomeratic sandstones prograde more basinward. Analyzing and imaging alluvial and fluvial internal architectural complexity and vertical/lateral alluvial-fluvial boundaries played critical roles in our detailed reservoir correlation and characterization.