THE DEPRESSURIZATION OF WATER-FLOODED RESERVOIRS - WETTABILITY AND CRITICAL GAS SATURATION

The influence of wettability on the formation, growth and mobilization of bubbles formed when solution gas is released from water-flood resi dual oil have been visually observed in a series of experiments. The e xperiments were performed using a mixture of low boiling point hydroca rbons, which had a positive spreading coefficient for the oil phase in contact with water and its own vapour. In an oil-wet matrix, nucleati on of gas bubbles occurred on the surface of the matrix. While it was impossible to determine where nucleation occurred in the water-wet con dition, the results suggest that wettability influences the gas nuclea tion behaviour. In a water-wet system, the oil-water interfacial tensi on controlled the growth pattern for the gas bubbles, but in an oil-we t system the gas-oil interfacial tension was the controlling parameter . As a result, it seems likely that wettability influences the critica l saturation for mobilization of the gas phase. The behaviour of the o il phase during depressurization is influenced by wettability. In a wa ter-wet system the physical form of the oil is changed from immobile d roplets into films which may be transported with the gas phase, and in which the oil is mobile. In contrast in an oil-wet system, the oil ph ase can move as films when the gas is released from solution but gener ally will not initially move over many pores.