Abstract

A study utilizing core and log data was conducted to find an explanation of why wet sands are generally much tighter than hydrocarbon bearing ones. Within a single sand body the difference in reservoir characteristics above and below the oil-or gas-water contact, suggests that the presence of hydrocarbons has inhibited the process of porosity and permeability reduction by chemical diagenesis.

In deep exploration targets, one of the main questions is preservation of porosity and permeability within the zone of geopressure. Integration of structural data and time-temperature modelling of the deep Nilam stratigraphic section, showed early structuring and predicts hydrocarbon migration into stratigraphic traps; therefore, one might still expect adequate porosity and permeability in deep hydrocarbon-filled reservoirs in the Nilam area.

Another implication of the early migration of hydrocarbons is the formation of a diagenetic permeability barrier at the gas or oil-water contact. This permeability barrier could act as a diagenetic trap when restructuring occurred. This concept explains the trapping of gas beyond the combination closure of the present day Nilam structure.