Capillary Pressures--Examples of Their Use
Arnold H. Jennings
Capillary pressures can be useful in many different ways, including (1) regional mapping, (2) reservoir comparison, (3) choosing downdip well locations from a "tight" oil-stained dry hole, and (4) choosing updip well locations from a porous oil-stained dry hole.
Regional mapping:
Four regional Ordovician Red River maps, based on capillary pressure data, were
constructed for the western flank of the Williston basin. They delineated a
north-south trend of favorable reservoir rock, which was in close agreement with
successful Red River production and complimented conventional stratigraphic
studies in the area.
Reservoir comparison:
Two wells had very similar reservoir and oil entrapment parameters as measured
by conventional methods. Both wells had excellent porosity and oil shows but the
first produced only water whereas the second was a good oil discovery. Capillary
pressure data showed the first sand to be an ineffective, water-producing
multiple reservoir system, but the second sand had a good, oil-productive single
reservoir system. Thin section examination confirmed the capillary pressure
interpretation.
Downdip well location from a "tight" oil-stained dry hole:
An oil-water contact was calculated from capillary pressure data and
superimposed on a structure map of the producing formation. A theoretical
location, picked between the oil-water contact and the updip dry hole, would
have been a discovery as confirmed by production in the area.
Updip well location from a porous oil-stained dry hole:
An ancient downdip oil-water contact was interpreted from capillary pressure
data and a present oil-water contact was obtained from conventional well data.
The vertical distance between the two represented the amount of updip oil
migration that had occurred and gave a minimum updip limit to the oil
accumulation. Relative permeability calculations showed how far updip a location
should be for commercial oil production.
AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988