Three-Phase Equilibrium Computations for Hydrocarbon–Water Mixtures Using a Reduced Variables Method

• DOI: 10.1021/acs.iecr.9b00695
• Publication Date: 2019-07-22T13:28:47Z
• Authors: Michael Connolly; Huanquan Pan; Hamdi Tchelepi
• Keywords: Hydrocarbon mixtures; Flash evaporation

Thermal compositional simulation requires phase-equilibrium calculations for at least three fluid phases. The use of precomputed equilibrium ratios (K-values) has long been justified on the basis efficiency. However, this method may not appropriately represent thermal recovery mechanisms. An equation state (EOS) approach is more rigorous, though prohibitively costly. In processes injection steam results in hydrocarbon–water interactions elevated temperatures. Representation phase behavior these systems a nonisothermal context gives rise to set challenges owing polarity water molecule and resulting nonideal behavior. research we address two difficulties pertinent reservoir simulation: (i) robust phase-stability analysis using predetermined initial estimates ratios; (ii) numerical solution phase-split (flash) presence trace components. Phase-stability testing can be difficult mixtures. Three-phase regions extremely narrow pressure–temperature space, making resolution boundaries problematic. standard stability hydrocarbon fluids entails series guesses based variations Wilson correlation (Wilson, G. M. A modified Redlich-Kwong state, application general physical data calculations; 65th National AIChE Meeting, Cleveland, OH, 1969) trial-phase compositions dominated by each Nc components present. For mixtures, fewer are required. We propose physics-based strategy, sensitive distinct water. saturation pressure guide our selection trial compositions. Below saturated pressure, only sets required identify correct state. Above expand K-value account appearance near pure aqueous phase. K-values obtained from used perform two-phase flash computations. Then, mixture assessed. system following guides choice next K-values. This strategy direct benefits. First, number phases predetermined. Second, reliability tests ensuing greatly improved. procedure isothermal typically two-stage process that uses successive-substitution conjunction with Newton method. setting amounts hydrocarbons produce ill-conditioned linearized when (conventional) variables loop. have developed reduced order model three-phase split allows us circumvent difficulties. formulated take advantage sparsity binary interaction parameter matrix. first time, demonstrate efficacy reduced-variables formulation involving present protocol computations through comprehensive characterized literature. Through calculations, able consistently resolve boundaries.