Teige, Gunn Mari Grimsmo¹, Christian Hermanrud², Wibeke Hammervold Thomas³, Hege Marit Nordgård Bolås², Ove Bjørn Wilson⁴ 
(1) Statoil, Trondheim, Norway 
(2) Statoil ASA, N-7005 Trondheim, Norway 
(3) Statoil ASA, 4035 Stavanger, Norway
(4) Reslab, 4033 Forus, Norway

ABSTRACT: Capillary Resistance and Trapping of Hydrocarbons - A Laboratory Experiment

Low permeability cap rocks retain hydrocarbons by capillary sealing when pore throats of the seals are sufficiently small to prevent leakage. The extent to which aquifer overpressures work to push hydrocarbons through capillary seals is debated. This paper reports the results from a laboratory experiment that was designed to investigate this issue. 
Water pressure was applied to a water wet, oil saturated core sample, which was mounted to a low permeable membrane at the outlet. The oil was pressurized to 0.5 MPa, which is equivalent to the buoyancy of a 150 m oil column. The water pressure was high enough to ensure fluid flow through the sample. The intent of the experiment was to see whether water flushed oil through the membrane, or if oil was retained by capillary forces as water flowed through the core plug / membrane system. 
The result of the experiment was that water flowed through the core, while the oil remained in place. Accordingly, traps can leak water at the apex and still retain all of its hydrocarbons. Aquifer overpressures below the hydrocarbon-water contact should not be expected to increase the risk of capillary seal failure under such conditions.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.