A COMPARISON OF QUANTITATIVE ACOUSTIC, MAGNETIC AND PERMEABILITY ANISOTROPY MEASUREMENTS ON A NORTH SEA CAPROCK

摘要

Caprocks or seals are important components of a reservoir system,and are generally characterised by low permeability values.It is rare,however,that petrophysical measurements on caprock core material specify the direction in which the measurements such as permeability or acoustic velocity(which are generally one dimensional) are taken.It is therefore often assumed that the caprocks are isotropic.However,the effectiveness of a caprock may depend in part on how anisotropic that caprock is and the orientation of the principal anisotropy axes.The purpose of the present paper was to take an unconventional approach and compare and quantify the magnitude and orientation of the acoustic,magnetic and permeability anisotropy of a North Sea caprock.The magnetic anisotropy involved anisotropy of magnetic susceptibility(AMS) and anisotropy of isothermal remanent magnetization(AIRM).The samples studied showed significant acoustic,magnetic and permeability anisotropy parallel and perpendicular to the observed petrofabric.Comparisons between the magnitudes and orientations of the acoustic, magnetic and permeability anisotropies could potentially allow estimates of one type of anisotropic property from measurements of a different anisotropic property.In the samples studied all the techniques gave consistent results,with maximum acoustic velocity,permeability,AMS and AIRM axes being parallel to the observed petrofabric (the horizontal axis in these cases).