Gas Cycling and the Development of Miscibility in Condensate Reservoirs

Abstract

Summary This paper presents a detailed analysis of the development of miscibility during gas cycling in condensate displacements and the formation of condensate banks at the leading edge of the displacement front. Dispersion-free, analytical 1D calculations are presented for enhanced condensate recovery by gas injection. The analytical approach allows investigation of the possible formation of condensate banks (often at saturations that exceed the residual liquid saturation) and allows fast screening of optimal injection-gas compositions. We describe construction of the analytical solutions, a process that differs in some ways from related displacements for oil systems. All analytical solutions are verified by numerical calculations. We use an analysis of key equilibrium tie lines that are part of the displacement composition path to demonstrate that the mechanism controlling the development of miscibility in gas condensates may vary from first-contact miscible drives to pure vaporizing and combined vaporizing/condensing drives. Depending on the compositions of the condensate and the injected gas, multicontact miscibility can develop at or below the dewpoint pressure of the reservoir-fluid mixture. Finally, we discuss the possible impact on performance prediction of the formation of a mobile condensate bank at the displacement front in near-miscible gas-cycling/injection schemes.