--> Abstract: Petrographic Analysis of Carbonate "End Member" Samples, by F. Anselmetti, G. Eberli, and S. Luthi; #90942 (1997).

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Abstract: Petrographic Analysis of Carbonate "End Member" Samples

ANSELMETTI, FLAVIO, GREGOR EBERLI, and STEFAN LUTHI

In carbonate reservoirs, the range of pore types and sizes is much wider than in clastic reservoirs and is a function of the depositional texture and subsequent diagenesis. In order to establish quantitative relationships between pore parameters and reservoir characteristics, we investigated the pore space of 17 carbonate samples selected as "end members" from a database of carbonates with a wide geographic, sedimentological and petrographic range. Using optical microscopy and an environmental scanning electron microscope (ESEM) we were able to quantify the pore space over more than 3 orders of magnitude, from less than 1 micron to greater than 1 mm in the same sample using digital image analysis. We extracted four pore parameters: The amount of macroporosity, amount of microporosity, shapes of the macropores and pore size distribution.

We define microporosity as pore size less than 20 microns, whereas all larger pore sizes constitute macroporosity. Microporosity was found to be widely present in our samples and is believed to have a major influence on total water saturation, irreducible water saturation and wettability. We used a dimensionless perimeter/area measurement for the pore shape parameter. In a parameter sensitivity analysis using neural networks we found that permeability is controlled mainly by

- Macropore shape in high-permeability samples

- Amount of microporosity in the low-permeability samples.

These parameters may be obtained explicitly or implicitly from a combination of wireline logging measurements, notably nuclear magnetic resonance (NMR), total porosity measurements and vug size quantification from borehole images.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria