Relative permeabilities for blowdown of a near-critical oil reservoir: Issues and solutions emerging from pore-scale network modelling

I. Bondino, C. C. Ezeuko, S. R. McDougall, R. Ward, G. Hamon

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    5 Citations (Scopus)


    This work constitutes a practical attempt at addressing issues surrounding depletion gas-oil relative permeabilities in the case of a near-critical oil by using pore-scale network modelling techniques. Firstly a new model for gas buoyancy is presented that is able to track dynamically the movement of buoyant gas in the pore network; this framework is successfully used to model experimental visual observations of "coherent" channelized gas flow and dispersed "incoherent" gas flow that are seen to take place in porous media as permeability increases. We then apply the pore-scale network model to study the dynamics of gas flow during reservoir depressurization in virgin and waterflooded conditions with the dual purpose of understanding the microscopic flow behavior and producing predicted estimates for the variation of multi-phase flow properties: this is undertaken at two PVT extremes (fluid samples separated by a depth interval of 200m, from the top and bottom of the oil bearing column), and for two extremes of rock permeability (5mD and 252mD). It is found that the very low gas-oil interfacial tension at the onset of the pressure decline induces strong gas buoyancy effects, even at the pore scale. Moreover, the variation in PVT properties along the oil bearing column, coupled to permeability differences, causes a transition of behaviours in the reservoir: from vertical gravity-driven gas flow in virgin systems, to more capillary-controlled, isotropic gas patterns under conditions of lower permeability, heavier oil, and/or high water saturation. In particular, under strong buoyancy conditions, anisotropy in gas flow during depletion is seen to be time dependent, with vertical gas flow at low gas saturations dominating the process initially. The gradual formation of a gas cap, however, slowly increases the extent of horizontal flow near the top of the system. In light of these observations, the issue of flow anisotropy and its impact on gas-oil relative permeability is examined in some detail by computing network fluxes in both the horizontal and vertical (along-gravity) directions. Copyright 2008, Society of Petroleum Engineers.

    Original languageEnglish
    Title of host publicationSPE Annual Technical Conference and Exhibition, ATCE 2008
    Number of pages12
    Publication statusPublished - 2008
    EventSPE Annual Technical Conference and Exhibition 2008 - Denver, CO, United States
    Duration: 21 Sept 200824 Sept 2008


    ConferenceSPE Annual Technical Conference and Exhibition 2008
    Abbreviated titleATCE 2008
    Country/TerritoryUnited States
    CityDenver, CO


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