Abstract: Visualisation with Quantification: New Approaches to Reservoir Petrophysics

Paul B. Basan, Ben D. Lowden, John J. Attard

Quantifying variations in the pore structure that regulates flow leads to a better understanding of reservoir quality. Mercury injection (MICP), nuclear magnetic resonance (NMR) and backscattered electron image analysis (BSEI) offer the visual depiction and the quantitative data needed to characterize pore systems. More important, each technique characterizes the pore system differently, and together furnishes a way to diagnose variations and calculate reservoir properties.

Porosity and permeability correlations reveal variations in the efficiency of pore structures to transmit fluid. MICP, NMR and BSEI distributions show the same variations in efficiency. However, NMR and MICP measure pore sizes connected to the total volume of the pore system, which include some non-hydraulic pores. BSEI measures the larger parts of pore channels, and therefore focuses on pore sizes associated with a "restricted" volume. Differences in these measurements identify the pore size and volume that contribute to permeability.

Calculating permeability based on a critical pore size and the pore volume it connects produce equations in the form of C(pore size² × porosity). Here pore size squared comes from NMR, MICP or BSEI, and gives the equation the dimensions of permeability. Total porosity raised to the exponent "n" is the adjusted pore volume associated with the critical pore size.

Using the visual and quantitative information from these different measurements, on a large database, shows that the constant is reservoir-specific, whereas the exponent is geometry-specific. Changes in the constant and exponent expose variations in reservoir quality that have important applications in formation evaluation.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela