Analysis of Factors Influenced on Oil Rim Breaking up During Gas Cap Development

The main goal of the present paper is to determine main factors affected on oil rim breaking up ratio during gas cap development, to construct analytical model of this process and to develop method for movable oil reserves decrease estimation based on the analytical model. Field with underlaying oil rim is considered. Gas cap development leads to reservoir pressure decrease, oil viscocity increase due to dissolved gas liberation and underlaying water expands sweeping oil from oil rim and forming immobile oil reserves behind displacement front. For volume of penetrating water estimation material balance equation is considered. Equation is solved in analytical form using linearization of main oil and gas properties deopendencies from pressure. For immobile oil reserves calculation balance equation is considered taking into account initial and residual saturations of oil, gas and water. For determine main factors affected breaking up ratio dimensional analysis is used. In the present paper main factors affected oil rim breaking up ratio is determined. There are factors characterized reservoir energetic, oil and gas reserves, relative permeability properties, ratio of gas production. During dimensional analysis count of this factors was reduced to five, this is dimensionless potential of gas cap, dimensionless potential of aquifer, dimensionless gas production, displacement efficiency of oil by water and water's redisplacement efficiency of oil sweeping gas. Also it is shown that presence of strong aquifer intensifies breaking up because expanding water forms essential volume of immobile oil reserves. Novelty of this work consists of analytical model of oil rim breaking up during gas cap development and determination of main factors affected breaking up ratio. Results can be used for estimation of gas cap development on movable oil reserves in oil rim and for estimation of oil rim development efficiency with early gas cap development.