Methodological issues of fl w simulation during WAG and gas injection

The article is concerned with physical processes, taking place in the oil reservoir during oil, water and gas filtration.Special issues are described in the article, that may be raised during the creation of simulation models for the calculation of WAG and gas injection and analysis of the results. Questions of the control setting for exploitation and recharge wells are examined by the author. Methodical recommendations for simulation of WAG and gas injection are given in the article.
Materials and methods
A black oil method, a Todd-Longstaff method, and a compositional model can be used for WAG simulation. The behavior of relative permeability of the fluids depends on the method of the hysteresis calculation (methods of Carlson, Killough or without hysteresis); the method of calculating oil relative permeability in three-phase saturation (Stone I, Stone II, linear interpolation) and the effect of gas-oil boundary tension. The interpolation method of VFP-tables canbe used for the limitations of formation fluids with HGQR on the well mouth.
Results
Three-phase flow of oil, water and gas is usually accompanied by complex physical phenomena, including the mass exchange between oil and gas and changing of their physicochemical properties, as well as hysteresis of relative permeability. Direct transfer of the quantitative results of core analyses into the hydrodynamic model sometimes is impossible. The measure expansion of gas can lead to the incorrect determination of the injection ratio. The restraining of bottom hole pressure of exploration wells should take into account the way of fluids lifting at high gas factor values. Traditional approaches, used in simulation of oil reservoirs waterflooding, can lead to discrepancies and errors.
Сonclusions
To improve the reliability of technological parameters calculation data during WAG and gas injection, constructing hydrodynamicmodel, one should:
• construct the model, true to scale of core and reproduce the available coreexperiments to determine the displacementefficiency of gas and WAG;
• make a correction for oil volume changes with gas dissolved in it, recalculating displacement coefficient of residual oilsaturation;
• correct the target quantity of injection ratio, taking into account the difference ofvolumes in bottomholes of exploitation andrecharge wells;
• to use the flow calculation along the wellbore and restraining of well head pressure;
• to set WAG cycles on the basis of target injection volumes of water and gas in reservoir conditions.