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

FEDERICO E.BENELLI; PISONI, GERARDO O.; CISMONDI, MARTÌN

FLUID PHASE EQUILIBRIA

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2023 vol. 575

0378-3812

Reservoir fluids may present complex phase diagrams involving three-phase behavior, due to the presence ofdifferent compounds that -when exceeding certain quantities- can induce the separation of a second liquid phase.Typical and important cases are carbon dioxide, water and asphaltenes, while the mere asymmetry in the mixtureof hydrocarbons can also be responsible for a three-phase region in the fluid phase envelope. Although thebehavior and practical implications are quite different in each of these cases, their phase diagrams may sharesome qualitative characteristics, and therefore require similar methods and strategies for their calculation.A general computation strategy, including details on the calculation method for three-phase envelopes andhighlighting the importance of double-saturation points, was presented in a previous publication. That workfocused on the behavior of asphaltenic reservoir fluids, illustrating three different possible topologies for thecomplete phase envelope, based on reservoir fluid cases taken from the literature.In the present work, different composition effects on these complex phase diagrams for reservoir fluids arestudied, with focus on the transitions between different topologies. Reference fluids considered in this studyconsisted again of compositions and parameters taken from the literature. Starting from those fluids, differentalterations in compositions were used to analyze the effect on the predicted phase diagram. A new type ofbehavior was identified, allowing to complete a classification consisting in four different types. Moreover, newways of arriving at phase diagrams of types I and II had to be considered in the extension of the computationalstrategy for constructing complete phase envelopes with two and three-phase boundaries. The effects andrelations observed could help to advance the understanding of asphaltenes phase behavior in reservoir fluids andthe relation between composition and/or fluid characterization and the corresponding predicted phase diagrams.