CO₂–Oil Miscibility and Minimum Miscibility Pressure (MMP) Prediction

This case study focuses exclusively on the use of CHEMCAD process simulation software to predict
CO₂–oil minimum miscibility pressure (MMP) and phase behavior. CHEMCAD was applied as a
thermodynamic and phase‐equilibrium modeling tool, enabling rapid miscibility assessment without the
need for specialized reservoir simulation software.

Challenge

Accurate determination of the minimum miscibility pressure (MMP) between injected CO₂ and crude oil is a critical design requirement for miscible CO₂‐EOR projects. However:

• Experimental MMP measurements are time‐consuming and expensive
• Early‐stage studies often lack access to dedicated reservoir simulators
• Crude oils exhibit complex, multicomponent compositions

The challenge was to determine whether CHEMCAD, a process simulator, could reliably predict CO₂–oil miscibility and MMP values without tuning to experimental PVT data.

Solution

CHEMCAD v7.1.8 was used to model CO₂–oil phase behavior using the FLASH unit operation.

Modeling Approach

• Crude oils represented as n‐alkane pseudo‐components (C6–C25+)
• Heavy fractions lumped into a C25 pseudo‐component
• Soave–Redlich–Kwong (SRK) equation of state
• Standard van der Waals mixing rules
• No EOS tuning or experimental matching applied

Sensitivity Studies

• CO₂‐to‐oil mass ratio
• Gas–oil ratio (GOR)
• Dead oil vs. live oil systems

Simulation Configuration

• Gaseous CO₂ feed stream
• Liquid crude‐oil feed stream
• Optional light‐gas stream (95 mol% CH₄, 5 mol% C₂H₆) to represent live oil
• Iterative pressure increase to identify the lowest pressure at which no free CO₂ gas phase remained after flashing → defined as first‐contact MMP