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