RAPOSO, ANTONIO and MURTHY INKOLLU, Sociedade Nacional de Combustiveis de Angola U.E.E.(Sonangol), Luanda, Republica de Angola

ABSTRACT: Albian Reservoirs: Congo Basin, Angola, West Africa

During the past decade, an upsurge in discovery of Albian reservoirs has added 11,600 MMSTBO(STOOIP) in Congo basin of Angola. Successes in localizing prolific reservoirs provided impetus for further exploration. The reservoirs are characterized by carbonate or sandstone lithologies and are referred as Pinda.

Pinda reservoirs are selectively associated with prominent hinge zones, underlain by basement ridges. Further, reservoir bearing carbonates at central and of sandstones in peripheral zones are noted along the basin's NNW-SSE long axis. The factors influencing the reservoir development are growth faulting and extension with concomitant salt movement, regional subsidence, eustatic sea level fluctuations, sedimentation and accumulation rates.

Reservoirs in carbonates are essentially dolomitized oolitic shoals, span the entire Albian and are distributed across the basin. Several shoal cycles are recognized. Reservoir heterogeneity is characteristic for shoals. Variations in porosity-permeability and lithofacies are seen in a shoal's west to east profile. Diagenetic changes are the key to reservoir quality. Significant non-dolomitized limestone shoal reservoirs show moderate porosities and low permeabilities.

Stacked sandstone reservoirs in upper portions of pinda are confined to north part of the basin. Contrast to this, sand-rich with carbonate intercalated reservoirs are in lower half of pinda, at southern region of the basin. These are heterogeneous reservoirs that show moderate to good porosities with variable permeabilities.

Structural complexity of the reservoirs necessitated to develop the fields with 3D interpretations.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.