Estimation of In-situ Compositions in Lean Gas Condensate Reservoirs

Abstract

There is a high degree of complexity in both fluid flow and phase-behavior of gas condensate reservoirs during the depletion period due to retrograde condensation. Natural depletion in gas condensate reservoirs results in low condensate recoveries at surface due to in-situ condensation and accumulation of condensate in the reservoir especially in vicinity of wellbore. During reservoir depletion, the overall composition of reservoir fluid varies and becomes different from initial reservoir composition as pressure decline to values less than dew-point pressure. In-situ gas and condensate composition in the reservoir are changing accordingly. This paper develops a novel approach to obtain initial gas condensate reservoir composition from gas and liquid compositions taken from separator tests during several depletion stages. Based on the composition of mixed sample and initial reservoir composition, a set of novel correlations is developed for estimating initial gas condensate reservoir composition. The generalized reduced gradient (GRG) algorithm of iteration was used to tune the constant and exponents of the correlation based on available field data. The convergence criteria were to minimize the value of the squared sum, SS, of the difference between the real data and the estimated one.