--> Abstract: Capillary Seal or Permeability Barrier: Advances in Experimental and Theoretical Considerations of Caprock Wetting State, by Steve Larter, Andy Aplin, and Barry Bennett; #90039 (2005)
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Capillary Seal or Permeability Barrier: Advances in Experimental and Theoretical Considerations of Caprock Wetting State

Steve Larter1, Andy Aplin2, and Previous HitBarryTop Bennett1
1 University of Calgary, Calgary, AB
2 University of Newcastle, Newcastle, United Kingdom

Oilfield caprocks are generally assumed to be water wet with high capillary entry pressures preventing the leakage of oil from the underlying reservoir. Column heights are then estimated by measurement of a critical pore radius, use of assumed oil-water interfacial tensions and contact angles, and the assumption that the pore system is water-wet. Over the past few years we have been looking at the way in which petroleum non-hydrocarbons such as phenols (hydrophilic organic oxygen compounds) and carbazole derivatives (more hydrophobic nitrogen compounds) partition between oil, water and mineral surfaces in geological systems. These studies indicate that many non-hydrocarbon compounds partition substantially from oil to either/or both water and mineral surfaces, with the implication that the wetting state of a rock may change after contact with oil. Recent data from experimental corefloods, coupled with (a) theoretical and modelling considerations of wetting state and (b) field studies of leaking caprocks, support this assertion. Here, we review this body of work and suggest that there is substantial doubt as to the assumption that mudstone caprocks remain water wet after contact with oil. We also discuss the relevance of these results to gas shale scenarios.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005