Accurate capillary pressure curves are essential for studying the reco
very of oil by gas injection in naturally fractured chalk reservoirs.
A simple and fast method to determine high-pressure drainage capillary
pressure curves has been developed. The effect of gas/oil interfacial
tension (IFT) on the capillary pressure of chalk cores has been deter
mined for a methane/n-pentane system. Measurements on a 5-md outcrop c
halk core were made at pressures of 70, 105, and 130 bar, with corresp
onding IFT's of 6.3, 3.2, and 1.5 mN/m. The results were both accurate
and reproducible. The measured capillary pressure curves were not a l
inear function of IFT when compared with low-pressure centrifuge data.
Measured capillary pressures were considerably lower than IFT-scaled
centrifuge data. it appears that the deviation starts at an LFT of abo
ut 5 mN/m. According to the results of this study, the recovery of oil
by gravity drainage in naturally fractured chalk reservoirs may be si
gnificantly underestimated if standard laboratory capillary pressure c
urves are scaled by IFT only. However, general conclusions cannot be m
ade on the basis of only this series of experiments on one chalk core.