Wytze van der Werff1,
(1) University of Liverpool, Liverpool, United Kingdom
(2) Statoil, Forus, Stavanger, Norway
(3) University of Stellenbosch, South Africa
Abstract: High-resolution 3-D architecture and pinchout geometries of fasin floor fans, Tanqua Karoo, South Africa
Permian turbidite sandstones of the Tanqua Karoo foreland basin were deposited in four stratigraphically sealed basin floor fans which are overlain by slope and shelf deposits. Each fan has a thickness of 20-60 m, and is separated by a 20-75 m thick interval of shales and silts. The completely exposed 30 km dip and 15 km strike sections permit seismic scale investigation of fan architecture. Fan 3 consists of six facies associations and four categories of architectural elements, which form the principal building blocks of the fan. The architectural elements include channel forms, transitional depositional styles, sheets and fines. A ‘midground’ area of the fan comprises sandstones with complex geometries, having characteristics of both channel and lobe environments. The down-dip pinchout of the system is not a simple radial fan fringe but a complex arrangement of minor channels and sheets. The identification of high frequency sequence boundaries and flooding surfaces within the fan has enabled the construction of a high resolution time slice stratigraphy with which to accurately delimit phases of active fan growth and decay. Although the fan shows a progradational style, care must be taken with stacking pattern analysis at single localities (equivalent to wells) because certain locations within the fan show misleading vertical facies arrangements. A similar approach has been undertaken for Fan 4, which has an overall aggradational growth history. This sequence stratigraphic approach allows better prediction of reservoir flow units and down-dip net sand distribution and serves as a basis for accurate reservoir modelling.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana