A classification of phase envelopes for reservoir fluids with Asphaltene onset lines: Exploring topology transitions based on compositional changes

BENELLI, FEDERICO E.; PISONI, GERARDO O.; CISMONDI-DUARTE, MARTIN

FLUID PHASE EQUILIBRIA

ELSEVIER SCIENCE BV

Año: 2023

0378-3812

Reservoir fluids may present complex phasediagrams involving three-phase behavior, due to the presence of differentcompounds that -when exceeding certain quantities- can induce the separation ofa second liquid phase. Typical and important cases are carbon dioxide, water,and asphaltenes, while the mere asymmetry in the mixture of hydrocarbons canalso be responsible for a three-phase region in the fluid phase envelope.Although the behavior and practical implications are quite different in each ofthese cases, their phase diagrams may share some qualitative characteristicsand therefore require similar methods and strategies for their calculation. Ageneral calculation strategy, which includes details about the calculationmethod for certain types of three-phase envelopes and emphasizes the importanceof double saturation points, was presented in a previous publication. The mainobjective of this study is to explore the different possible topologies thatthe phase envelope of a reservoir fluid may adopt as a result of compositionalchanges, when using an equation of state (EOS). Reference fluids (compositionaldata and parameters) were taken from the literature. Based on these fluids,different alterations in the amounts of defined or pseudo-components of thesystem were used to analyze their effect on the predicted phase diagram. A newtype of behavior was identified, which is included in a classification thatcurrently consists of four different types. Additionally, a complete andupdated algorithm is presented, which enables the computation of the differenttopologies presented in this study. Finally, it is shown that transitionsbetween different types of phase diagram can be observed not only as aconsequence of compositional changes but also based on modeling or parametricchanges in the description of a given fluid, for example by changing thelumping strategy for the heavy fractions.