Seal Analysis of Compressional Deepwater Structures

Sankar Muhuri¹, Gary P. Muscio¹, Carlos Rivero¹, Richard Eisenberg², Simon D. Harris³, and Robert Knipe^3
1Chevron Energy Technology Co., Houston, TX
²Chevron International Exploration Production, Houston, TX
³Rock Deformation Research, Leeds, United Kingdom

Exploration results in deep water Tertiary, compressional systems such as offshore Nigeria present formidable challenges to our understanding of the interactions between structural growth, coeval seal development and hydrocarbon charge. High quality seismic data helps to unravel the structural evolution but the efficiency of the hydrocarbon charge process in middle to outer fringes of the petroleum system remains uncertain. We discuss some results of our regional approach toward solving key issues that appear to control seal efficacy in Deepwater Nigeria.

Shales within the top seal intervals contain a significant quantity of clay minerals often in excess of 65% of the total mineral volume. Hydrocarbon column heights in under-filled anticlinal traps are in alignment with seal capacity predicted from top seal MICP data. Exploratory drilling of fault bounded traps has been less successful in Deepwater Nigeria. Regional fault seal efforts underline a preponderance of sand in the mid-early Miocene section promoting multiple sandy juxtaposition windows and a clay poor fault rock. Multiple stacked amplitude anomalies that are restricted to the hanging wall of toe-thrusts allude to flow along clay poor faults and a complex fill and spill history involving multiple reservoirs. Stochastic results incorporating uncertainties from varying net to gross, several fault zone mixing models and fluid properties are consistent with observed column height distributions in fault bounded traps. The critical elements of robust analytical techniques needed to model and understand flow along faults in compressional deepwater settings are reviewed and the basis for a new generation of basin modeling, that improves understanding of how the coupled dynamics of fault seal behavior and fill and spill histories affect fluid volumes and properties, is outlined.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery