Complex two and three-phase envelopes of reservoir fluids with asphaltenes: Understanding different behaviors and a new integral strategy for their calculation.

CISMONDI, MARTÍN

Congreso; PetroPhase 2017; 2017

Regardless theircubic or SAFT nature, equations of state (EoS) have been used to model asphaltenesphase behaviour in reservoir fluids for at least two decades already. The importanceof the upper and lower asphaltene onset pressures (AOP´s) is widely recognizedin the literature, where many studies of either experimental or modellingcharacter are available, with different approaches. In terms of algorithms orcalculation methods, most studies normally resort to a series of two-phase andmultiphase flashes. New flash algorithms were even proposed focused onasphaltenic systems. But, surprisingly, no explicit method for tracingdifferent phase boundaries like AOP lines and the intermediate bubble line arefound in the literature. No attention has been paid either to study thedifferent possible behaviours, i.e. how these and other related segments canarrange in the complete phase envelope of a specific asphaltenic reservoirfluid, as predicted by a model.In this work, anew integral algorithmic strategy for the construction of complete phaseenvelopes based on an EoS, including AOP lines and other related segments, hasbeen proposed and implemented. Every segment is treated as the boundary ofeither a two-phase or three-phase region in the pressure-temperature diagramfor a specific fluid. In other words, every point along these lines determinesthe T-P conditions where an incipient phase appears or disappears. In the firstcase, the method of Michelsen for tracing two-phase boundaries is used, whilefor three-phase saturation lines an equivalent method was designed, including asecond set of K factors and a phase fraction as extra independent variables.Several fluidsfrom the literature are taken as case studies to illustrate the application ofthe proposed strategy and discuss different types of behaviour. Specific issuesas recognition of unstable segments like false bubble curves, are alsodiscussed. In sum, computer codes based on the proposed strategy can become auseful tool for researchers or professionals dealing with asphaltene phasebehaviour in reservoir fluids.