--> --> Abstract: Prerequisites, Processes, and Prediction of Chlorite Grain Coating Using Modern Estuarine Systems as Analogues, by Patrick J. Dowey, James Utley, David Hodgson, and Richard H. Worden; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Prerequisites, Processes, and Prediction of Chlorite Grain Coating Using Modern Estuarine Systems as Analogues

Patrick J. Dowey1; James Utley1; David Hodgson1; Richard H. Worden1

(1) School of Environmental Sciences, University of Liverpool, Liverpool, United Kingdom.

Chlorite cement in petroleum reservoirs can be responsible for preservation of anomalously high porosity and permeability in deeply buried sandstones. Fe-chlorite cement is common in reservoirs of shallow marine rocks. An understanding of the formation and distribution of chlorite pre-cursor clay minerals in modern coastal systems could aid the prediction of reservoir quality during subsurface exploration, appraisal and reservoir development.

To begin to understand how and where these pre-cursor minerals may be forming in a modern setting, a series of key questions are outlined:

1. How do depositional processes and estuarine environments control the variety and distribution of clay minerals?

2. What is the role of biological organisms in controlling the variety and distribution of clay mineral coatings?

3. How does hinterland geology and climate affect the variety of clay minerals forming?

4. How can clay mineral distributions from modern estuaries be applied to develop subsurface reservoir models to aid chlorite clay coat predictions?

To answer these questions, a field study of the Leir√°rvogur Estuary, SW Iceland was undertaken. The estuary is macro-tidal (2-3 m), has a short catchment (250 km2), and drains a simple hinterland geology (basalt extrusives). Raised shorelines, regraded drainage channels, and submerged peats indicate a regressive to transgressive relative sea-level trend during the Holocene. Core and surface sediment samples were collected from intertidal, upper tidal and the alluvial plain settings around the estuary. Analytical techniques include laser granulometry, x-ray diffraction, infrared spectroscopy and scanning electron microscopy.

Initial analyses suggest that there are variations in clay mineralogy and clay fraction abundance across the estuary. These appear to be controlled by depositional environment (proximity to fluvial and marine input points). There is also a weak correlation between areas of intense biological activity and clay coatings. Weathering of basalt and soil formation also has an influence on the mineralogy in the estuary sediments. Ongoing work aims to aid the development of subsurface reservoir models.