The influence of macropore heterogeneity on the petrophysical properties of carbonates.

摘要

The objective of this research is to better understand the petrophysical properties of hydrocarbon bearing carbonate rocks. The specific properties that are investigated are: electrical properties, capillary pressure curves, permeability and displacement behavior. The relationship between the petrophysical properties and various geological classification systems is also explored.;A porous plate capillary desaturation cell that can simultaneously measure electrical properties, capillary pressure curves and displacement behavior has been built. Up to 12 cores can be simultaneously desaturated. Both gas and crude oil were used as the non-wetting phase.;In accordance with Lucia's carbonate porosity classification, two oil fields were chosen, one with vuggy porosity and the other with interparticle porosity. Cores from the Dune field and the Yates field in the San Andres-Grayburg formations in west Texas were used as examples of interparticle and vuggy porosity systems. Saturation exponents for the Dune field cores were found to be lie between 1.6 and 2.5, and the cementation exponents were approximately 2.2. Experimental results showed very poor correlation between the geologically defined lithofacies and the measured petrophysical properties.;The effect of vugularity on the petrophysical properties was evident from the Yates core experiments. For a constant porosity, as vugularity increases, m and n increase systematically. The irreducible water saturation, the capillary pressure curves and the displacement behavior are also substantially different.;CAT-scanning was used for characterizing the local heterogeneity of the core. Cores were CAT scanned at 1 mm increments to generate a 3-dimensional porosity map. Three dimensional resistivity maps were generated from these local porosities. A random walk method was used to estimate the resistivity of the core. Simulation results and experimental results showed good agreement.