AAPG Bulletin, V. 82 (1998), No. 1 (January 1998), P. 160-180.

Deposition and Textural Evolution of Cool-Water Limestones: Outcrop Analog for Reservoir Potential in Cross-Bedded Calcitic Reservoirs¹

Alexis S. Anastas,² Noel P. James,³ Campbell S. Nelson,⁴ and Robert W. Dalrymple³

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received April 29, 1996; revised manuscript received January 3, 1997; final acceptance August 6, 1997.
²Department of Geological Sciences, Queen’s University, Kingston, Ontario K7L 3N6, Canada. Present address: Amoco Canada Petroleum Company Ltd., Calgary, Alberta T2P 2H8, Canada.
³Department of Geological Sciences, Queen’s University, Kingston, Ontario K7L 3N6, Canada.
⁴Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand.

This research was funded by the Natural Sciences and Engineering Research Council of Canada (grants to James and Dalrymple), PanCanadian Petroleum Ltd. (grant to Dalrymple), and Queen’s University (grant to Anastas). We would like to thank Scott Lindsay, H. and N. Shorten, R. Takiare, P. Pulman, Omya Corp., and the University of Waikato for support and assistance in the field. We thank former AAPG Elected Editor Kevin Biddle and reviewers C. G. St. C. Kendall and J. Dravis, as well as readers M. Coniglio, R. McNaughton, and E. C. Turner. 

ABSTRACT

The Eocene-Miocene Te Kuiti Group is a succession of cool-water carbonate and siliciclastic rocks on the North Island of New Zealand. The limestones are subtidal, bioclastic, and largely composed of bryozoans, echinoderms, and benthic foraminifers. These rocks can be divided into a horizontally bedded facies assemblage and a cross-bedded facies assemblage. The horizontally bedded facies assemblage represents deposition on a wave- (storm-) dominated shelf and is composed of grainstones and packstones containing textures resulting from biologic processes. The cross-bedded facies assemblage represents deposition on a current-dominated shelf and consists of grainstones with textures formed chiefly by physical processes.

The Te Kuiti Group can be used as an outcrop analog for cross-bedded, calcite-dominated hydrocarbon reservoirs. Porosity, permeability, and reservoir potential of the horizontally bedded facies assemblage decreased rapidly during late shallow burial owing to mechanical compaction and to the fine grain size, close packing, and ineffective early cementation of the rock. Coarser grain size, open framework, and earlier cementation within the cross-bedded facies assemblage resulted in significant heterogeneity and good reservoir potential before moderate burial. Tabular, lens-shaped, and sigmoidal reservoir units are proposed. Primary porosity and early developed traps are essential to reservoirs formed of cool-water limestones and those carbonates from "calcite seas." The influence of depositional setting extends into the eventual bedding style, texture, physical properties, and reservoir potential of the rock.