Multi-Attribute Analysis of Six Upper Cretaceous and Jurassic Structural Closures in Belo Profond, Morondava Basin, Offshore West Madagascar

Abstract

Recent publications have brought attention to hydrocarbon prospectivity in the Morondava Basin off the west coast of Madagascar. This geological and geophysical interpretation yields more detail over an approximately 700 km² 3D seismic survey covering a structurally anomalous area 100 km offshore in the Belo Profond. Six prospects were identified as structural closures in the late Jurassic to late Cretaceous formations, and described using RMS amplitude extractions, spectral decomposition, and seismic-limited AVO analyses. Challenged by igneous lithologies, a Bouguer gravity map was applied to discriminate between the bright amplitudes of the prospects and of the intrusive sills that permeate the Early Jurassic units and spread upward through the section.

Distal siliciclastic sediment deposited from the east during the Late Jurassic to Upper Cretaceous in Morondava Basin, captures in its architecture the latent movement on failed Karoo rift faults, and the development of the Davie Ridge, which contributed sediment from the west. Abundant igneous sills lace the 1.5 km of sediment supplied during the drift phase in the Mesozoic, intruding along weak bedding planes and fault surfaces, and underpinning flower structures within the limits of this survey. The presence of intrusive sills increased trap sizes but may have locally impacted the reservoir quality and compartmentalized closures where they migrated up into the reservoir interval. The overlying sedimentation was deposited during the current passive margin structural domain, and is comprised of roughly 1 km of sediment thickness. It includes a dramatically thick and extensive Mass Transport Complex, originating to the east and associated with a possible Oligocene/Miocene shelf collapse.

Within the six prospects this study describes, there is little evidence for igneous lithologies. The Belo Profond study area contains considerable hydrocarbon reservoir potential: nearly 2.5 km of sand, shale; sufficiently deep organic material for thermal maturation; structures derived from uplift, erosion, transpression and transtension, and igneous intrusion, creating potential traps; faults and deep seal breaches providing migration pathways. Any fluid escape or leakage in the shallow regional seals across the survey are localized and minimal, given seepage records across the region. The vertically-overlapping stacked prospects appear to be the best area of interest.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018