Probing Pore Systems in Carbonates: Correlations toPetrophysical Properties

摘要

The understanding of petrophysical and multiphase flowproperties is essential for the assessment and exploitationof hydrocarbon reserves; these properties in turn are dependenton the geometric and connectivity properties ofthe pore space. The determination of the pore size distributionin carbonate rocks remains challenging; extremevariability in carbonate depositional environments andsusceptibility to a range of post-depositional processesresults in complex pore structures comprising length scalesfrom sub-micron to several centimeters. In this paper weillustrate that combining experimental techniques includingmicro-computed tomography and scanning electronmicroscopy (SEM) allows one to probe the pore scalestructure in carbonates across a continuous range overmany decades of length scales (from 10 nm to cm scales).Image data at nanoscales can be incorporated into theprediction of petrophysical properties of 3D images. Thisis especially important in limestones.We describe the study of the internal structure of over 30carbonate samples across this range of length scales. Thesamples include carbonates with different porosity classificationsincluding end members ranging from depositionalporosity, diagenetic porosity and fracture porosityand many hybrid samples with mixtures of pore types.Particular emphasis is placed on the quantification of thepore sizes, shapes and interconnectivities in three dimensions.Extreme variability in pore network structures isobserved. The pore network statistics (e.g., coordination,aspect ratio, pore size) for the connected samples are oftensimilar despite the clear visual difference in the networkstructures. This illustrates the danger of attemptingto stochastically generate pore networks for differentcarbonate samples based on matching network statisticsalone.Petrophysical properties including resistivity, acoustic responseand permeability are calculated on image data andwhere available, compared to experimental data. Comparisonsbetween simulation and experimental data onthe same core material are satisfactory. Flow propertiesof systems exhibiting significant microporosity requirefurther development.