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AAPG Bulletin

Abstract

AAPG Bulletin, V. 97, No. 4 (April 2013), P. 619637.

Copyright copy2013. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/10031212040

Insight into petrophysical properties of deformed sandstone reservoirs

Anita Torabi,1 Haakon Fossen,2 Alvar Braathen3

1Centre for Integrated Petroleum Research (Uni CIPR), Uni Research, Allegt. 41, N-5007 Bergen, Norway; anita.torabi@uni.no
2Department of Earth Science, University of Bergen, Bergen, Norway; haakon.fossen@geo.uib.no
3University Centre in Svalbard, Longyearbyen, Norway; alvar.braathen@unis.no

ABSTRACT

We use samples from undeformed and deformed sandstones (single deformation band, deformation band cluster, slip-surface cataclasite, and fault core slip zone) to characterize their petrophysical properties (porosity, permeability, and capillary pressure). Relationships between permeability and porosity are described by power-law regressions where the power-law exponent (D) decreases with the increasing degree of deformation (strain) experienced by the sample from host rock (D, sim9) to fault core (D, sim5). The approaches introduced in this work will allow geologists to use permeability and/or porosity measurements to estimate the capillary pressures and sealing capacity of different fault-related rocks without requiring direct laboratory measurements of capillary pressure. Results show that fault core slip zones have the highest theoretical sealing capacity (gt140-m [459-ft] oil column in extreme cases), although our calculations suggest that deformation bands can locally act as efficiently as fault core slip zones in sealing nonwetting fluids (in this study, oil and CO2). Higher interfacial tension between brine and CO2 (because of the sensitivity of CO2 to temperature and pressure) results in higher capillary pressure and sealing capacity in a brine and CO2 system than a brine and oil system for the same samples.

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