INFLUENCE OF PORE GEOMETRY, PRESSURE AND PARTIAL WATER SATURATION TO ELECTRICAL PROPERTIES OF RESERVOIR ROCK: MODEL AND LABORATORY INVESTIGATION

Pressure and saturation are of two important parameters to be considered to
evaluate the electrical properties of reservoir rock. As confining pressure can cause
pore space of the rock to collapse and rock properties to change, it is necessary to
examine in details how much the pressure and saturation changes affect the electrical
properties. Investigations of electrical properties of sandstones and carbonates are the
main focus in this work. The effects of pore geometries, confining pressure, and
partial water saturation on electrical properties are investigated. The new electrical
dispersion models from 0.1 Hz until 0.2 MHz for shaly sandstone are also developed.
Petrographic image analysis is carried out to asses pore geometry of the media.
Circularity, pore aspect ratio, pore size distribution and pore angle distribution are
calculated to evaluate their effect on electrical dispersion. Confining pressure and
water saturation observation are then evaluated to obtain their impact on pore
structure and complex resistivity.
The result of this work shows that surface conductivity plays as a dominant factor
particularly in shaly media and it is indicated by electrical resistivity dispersion in low
water saturation. When evaluating surface conductivity, the pore geometry has to be
considered because large structure is easier to saturate rather than small structure.
Moreover, the high water salinity can significantly reduce diffusive layer thickness
and if the pore radii are very small, the diffusive layer thickness will touch each other
and block the anion movement.
In addition to these results, it is found that pore radius distribution provides more
contribution to the electrical resistivity dispersion and becomes a basis to extract
porosity from resistivity. Confining pressure only contributes small changes in pore
geometry of media and the use of imaginary resistivity gives a better detection on it.
Modified D-model and Archie’s model are developed to calculate the dielectric
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permittivity and effective conductivity in high water salinity saturated-rock as a
function of water saturation degree.