The presence of vugs in carbonate reservoir has strong influence on filtration processes. Porosity in this case can be low (less than 5%), but permeability can be higher than dozens of millidarcy. Common petrophysical models do not take into account vug type porosity.
For two fields two types of petrophysical models had been viewed. For the first field we used Wyllie-Rose model (relation between permeability and total porosity and irreducible water saturation). Wyllie-Rose equation coefficients had been empirically chosen to maximize fit with core analysis results. In comparison with previously used common petrophysical model, Wyllie-Rose model not only takes into account permeability of “low porosity zone” reservoir, but also better describes all core data for whole porosity interval. Wyllie-Rose model with empirically chosen coefficients was used for permeability grid construction in simulation model. For the second we choose a model with direct accounting of vug porosity (based on logging data, relation between permeability, total porosity and vug porosity). Obtained from logging data vug component of porosity was used in statical model and distributed by the same methods as total porosity. Permeability was calculated as function of two variables and exported to simulation model as initial data.
In case of common petrophysical model permeability in simulation model leads to necessity of its modification. Such simulation model has insufficient forecast ability because of local permeability modifications and high level of uncertainty in undrilled and between-well zones. Using of Wyllie-Rose model allowed to decrease permeability modifications volume and to cut down for one order of vertical conductivity multiplier median. Thus, using of Wyllie-Rose model allows to “reconstruct” wells exploitation data more accurate. On the base of this simulation model 2021-2022 years drilling results retrospective analysis was executed. Model showed high level of quality and quantity converging and was accepted for field development forecast. Geological and simulation models, based on vug porosity direct accounting model, are going to be justifying by drilling data. Simulation model fad been matched to historical data, on their basis the drilling prospects were determined.
References
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