The performance of a solution gas drive experiment is ultimately determined by a complex interaction of a variety of different petrophysical parameters,including the rate of pressure decline and the chemical and physical properties of the rock-fluid system itself(viz: the nucleation properties of the porous medium,the gas-oil diffusivity,oil viscosity,gas-oil interfacial tension,dissolved gas-oil ratio,pore connectivity,etc).Here,a pore-scale process simulator is used to interpret the underlying dynamic processes that characterise a long-core heavy oil depletion experiment.This is achieved by direct matching of experimental gas and oil production profiles under different depletion rates.Progressive nucleation is implemented in the simulator,whereby bubbles nucleate from sites of increased”nucleation potential”-in keeping with recent developments in the field.The complex phenomenon of nucleation is discussed here in terms of the combined effects of(i)the spatial distribution of nucleation potential,(ii)depletion rate and(iii)the characteristics of the oil under investigation.Different bubble densities are produced at different depletion rates via a physically-based nucleation algorithm.As a result excellent history-matches of two heavy oil depressurisation experiments are obtained.The associated relative permeability curves are also presented.Finally,close analysis of the simulation data also allows us to investigate the widely-held belief that recovery efficiency is directly linked to depressurisation rate-the higher the depletion rate,the larger the number of bubbles nucleated,and the higher the observed recovery.We show here that recovery is seen to depend not only upon the depletion rate and bubble density,but also upon the lengths of diffusion pathways,local supersaturation gradients,and gas cluster topology-all of which are related to the underlying connectivity of the pore system.
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