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→Water-gas coning
==Water-gas coning==
==Water-gas coning==
[[file:production-problems_fig1.png|thumb|{{figure number|1}}Wave coning.]]
[[file:production-problems_fig1.png|thumb|300px|{{figure number|1}}Wave coning.]]
When water underlies an oil column or a gas cap exists above, the phenomenon of ''coning'' can occur when the oil is produced. Muskat<ref name=pt09r18>Muskat, M., 1949, Physical principles of oil production: New York, McGraw-Hill, chap. 5.</ref> noted that coning is most likely to occur when a wellbore only penetrates a portion of the formation or when the perforations are placed only in the oil zone ([[:file:production-problems_fig1.png|Figure 1]]). The horizontal and vertical pressure gradients created by the production of oil causes a deformation of the oil-water (or oil-gas) contact. When the vertical pressure gradient exceeds the hydrostatic gradient down to the water zone, the water is pulled toward the well, resulting in a cone-shaped distortion of the oil-water contact. If a well is produced too hard, water breakthrough can occur. The same basic principles apply to the downward coning of gas from a gas cap.
When water underlies an oil column or a gas cap exists above, the phenomenon of ''coning'' can occur when the oil is produced. Muskat<ref name=pt09r18>Muskat, M., 1949, Physical principles of oil production: New York, McGraw-Hill, chap. 5.</ref> noted that coning is most likely to occur when a wellbore only penetrates a portion of the formation or when the perforations are placed only in the oil zone ([[:file:production-problems_fig1.png|Figure 1]]). The horizontal and vertical pressure gradients created by the production of oil causes a deformation of the oil-water (or oil-gas) contact. When the vertical pressure gradient exceeds the hydrostatic gradient down to the water zone, the water is pulled toward the well, resulting in a cone-shaped distortion of the oil-water contact. If a well is produced too hard, water breakthrough can occur. The same basic principles apply to the downward coning of gas from a gas cap.