Abstract: Concepts Relating Reservoir Mineralogy to Reservoir Interpretation, Completion and Economics

Robert J. Yedlosky

Reservoir interpretation using electric logs is affected by grain density and "irreducible water" saturation values. Standard assumptions used without direct well sample information is often dangerous and misleading. The grain density for "sandstone" is assumed to be 2.68 g/cc, but it may vary from 2.63 g/cc to 2.85 g/cc for Appalachian "sandstones". Examples are shown for various reservoirs.

Porosity/permeability relationships are determined by both pore size and shape. Examples of various Appalachian reservoirs are shown, demonstrating effects of diagenesis on pore sizes and shapes and the resultant permeability and irreducible water.

Reservoir composition and pore size are extremely important in determining completion methods. Examples of good and poor completion methods and the resultant well production (economics) are shown for some Appalachian Basin reservoirs.

Reservoir permeability as well as reservoir continuity and gas/fluid ratios are directly related to well drainage and thus well economics. Examples are shown.

Reservoir type and mineralogy are sometimes consistent within a given formation, but often are quite variable. The use of an average value for reserve interpretation or average type completion for a given formation is often dangerous. Examples are shown.

Electric logs have improved greatly over the past four decades, but studies of well samples and cores are still an extremely important aspect of reservoir analysis, well completion and well economics, and thus the success and economic stability of an oil and gas company.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas