ABSTRACT: Sediment Input and Evolution of Deltaic Systems in the Triassic Napperby Formation, Gunnedah Basin, N.S.W.: Implications for Reservoir Description and Characterization of Deltaic Systems

XU JIAN, FENG, and COLIN R. WARD, Department of Applied Geology, University of New South Wales, Australia

Increasing oil recovery efficiencies by waterflooding and EOR techniques requires a reservoir to be described realistically and characterized accurately. Regularly spaced and fully cored wells penetrating the lacustrine-deltaic sediments of the Napperby Formation in the Gunnedah Basin, New South Wales, provide an excellent database for studying the 3-D geometries and facies architecture of fluvial-dominated deltaic systems.

The fluvial-dominated deltaic systems of the Napperby Sequence evolved from a lobate, coalesced sandy fan delta complex with dominantly bed-friction processes in its mouth bars and low to high density underflows in the prodelta and distal delta front areas to an elongate or digitate deltaic system with inertia-dominated processes in the mouth bars and turbidites formed by slumping process in the prodelta and distal delta front.

The contrasting geometries and internal facies distribution patterns of the fluvial-dominated lacustrine deltas in the Napperby Sequence are considered to have been caused mainly by differences in sediment input to the delta systems. Existing delta classification schemes cannot accommodate variations in the nature and facies pattern of deltas caused by such differences in the sediment input, and a new scheme for delta characterization and description was developed, based on the results of the present study together with a review of available information on delta sedimentology. This scheme considers six different attributes, and should prove to be a useful tool for studying ancient deltaic sequences.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)