Changes

==Anomalously thick transition zones==

==Anomalously thick transition zones==

The transition zones calculated for homogeneous reservoirs may be relatively thin, particularly in coarsegrained reservoirs. However, thick transition zones are observed in many fields due to reservoir heterogeneity. Interbedded lithologies with different capillary behaviors may result in a thick transition zone in which some lithologies produce hydrocarbons and others produce water. Rocks with complex pore networks (such as combined fracture and matrix [[porosity]]) may also have a thick transition zone, with different fluid types produced from different pore types. The cause of thick transition zones may be evaluated by combined core examination and capillary pressure tests. Some intervals within transition zones characterized by interbedded lithologies may be brought into low water production by selective perforation.

The [[What is a reservoir system?#Waste and transition zones|transition zones]] calculated for homogeneous reservoirs may be relatively thin, particularly in coarsegrained reservoirs. However, thick transition zones are observed in many fields due to reservoir heterogeneity. Interbedded lithologies with different capillary behaviors may result in a thick transition zone in which some lithologies produce hydrocarbons and others produce water. Rocks with complex pore networks (such as combined fracture and matrix [[porosity]]) may also have a thick transition zone, with different fluid types produced from different pore types. The cause of thick transition zones may be evaluated by combined core examination and capillary pressure tests. Some intervals within transition zones characterized by interbedded lithologies may be brought into low water production by selective perforation.

Upward movement of hydrocarbon-water contacts may leave a zone of residual hydrocarbon saturation below the present transition zone. The hydrocarbons might be interpreted as part of a transition zone from well log or core analysis, leading to an erroneous approximation of fluid contacts or rock properties. The presence of residual hydrocarbon saturation below an oil pool can sometimes be detected by the presence of two inflections in the plot of hydrocarbon saturation against depth, one at the present transition zone and another at the original transition zone.

Upward movement of hydrocarbon-water contacts may leave a zone of residual hydrocarbon saturation below the present transition zone. The hydrocarbons might be interpreted as part of a transition zone from well log or core analysis, leading to an erroneous approximation of fluid contacts or rock properties. The presence of residual hydrocarbon saturation below an oil pool can sometimes be detected by the presence of two inflections in the plot of hydrocarbon saturation against depth, one at the present transition zone and another at the original transition zone.