ABSTRACT: Outcrop and subsurface characterization of basin floor to slope reservoir facies, Taranaki Basin, New Zealand

King, Peter R.¹, Greg H. Browne¹, and Roger M. Slatt²
(1) Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand
(2) Colorado School of Mines, Golden, CO

A Miocene deep-water progradational succession in Taranaki is well exposed along the present-day coastline, and in nearby oil fields contains several producing intervals. From a wealth of outcrop and subsurface data we deduce stratal geometries, stacking patterns, and lithologic variability within this basin floor to slope system, providing an analog and facies prediction tool for exploration and reservoir management alike. Our depositional model illustrates the temporal relationships between various facies types, and causal links to changes in relative base level. The model provides useful points of comparison and contrast to established Mutti-, Walker-, Reading-, and Exxon-type models.

The succession comprises several high-resolution (4^th -order) cycles, deposited rapidly in lower- to upper-bathyal water depths. Individual cycles fine upwards, as does the overall succession. Proximal fan and base-of-slope intervals are sand-rich (generally fine-grained), but otherwise the system is mudstone dominated. Basin floor fan lobe sandstones are thick- to thin-bedded, massive or slightly rippled, have sharp bases and tops, and are generally ungraded. They pinch and swell in compensation-style geometry, and fewer than 30% of individual beds can be traced for more than 200 m. Slope fan strata comprise "classical" Bouma-type beds within interleaved scour-fill-overbank packages. These beds can exhibit considerable vertical and horizontal permeability variation. Reservoir facies within confined slope canyons comprise debris flow conglomerates, thick-bedded sandstones similar in appearance to basin-floor fan sandstones, and thin-bedded, rippled sandstones that are broadly scoured.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia