Slope Terrains: A Critical Factor in Explaining and Predicting the Distribution and Type of Slope Reservoirs

Donovan, Art¹ (1) BP, Houston, TX

Two fundamental first-order controls (delta position & slope terrains) can be used to better explain and predict both the type and distribution of slope reservoir systems (leveed, vs. confined, vs. sheet). Delta position controls the sediment entry points into the basin. Off-axis areas offer limited opportunity for slope reservoirs. Slope terrains, which are herein termed Simple, Chute, Ponded, and By-pass, are controlled by the rugosity of the slope, as well as the size of the slope channels (gullies vs. canyons). These terrains determine the architectures of dominant turbidite reservoir types deposited on slopes down-dip of the deltaic depocenters.

Simple Terrains form on slopes with limited to no rugosity. Because of the lack of rugosity, slope channels are free to move laterally across the slope and do so predominantly as Leveed Channel Complexes. Chute Terrains form due to two-dimensional confinement between salt and/or shale structures in areas of moderate rugosity. The structural movement in these areas leads to lower relief slopes and the development of confined channel complexes confined to the two-dimensional lows. Ponded Terrains form in response to three-dimensional confinement between salt and shale structures in areas of the slope with high rugosity. The structural movement in these areas leads to localized lows and the development from time to time of sheet complexes in ponded lows. By-pass Terrains form when a large canyon develops across the slope. These canyons form efficient by-pass systems that move turbidites from the shelf margin to basin floor drastically reducing reservoir potential of the slope.