Numerical modeling of asphaltene precipitation in petroleum reservoirs is important in relation to precipitation around the wellbore and in the reservoir domain. Production from some reservoirs results in asphaltene precipitation in the wellbore region, leading to production loss and need for cleanup. Fluid injection can also lead to injectivity loss due to asphaltene precipitation. There are also desirable processes in which precipitation of asphaltene can lead to “in-situ” upgrading of heavy oil recovery. Reservoir compositional models that are currently in use rely on cubic equations of state for asphaltene precipitation. The cubic equations, despite their relative reliability in describing reservoir fluids phase behavior, become unreliable in asphaltene-rich phase description. A number of non-cubic equations of state have been introduced to overcome the shortcomings of cubic equations. The cubic-plus-association equation of state (CPA-EOS) is perhaps the method of choice in modeling asphaltene precipitation in compositional modeling. When there is no asphaltene precipitation, the CPA-EOS becomes the standard cubic equation. In this work we implement the CPA-EOS in compositional modeling and introduce a simple technique to speed up considerably the root finding. Our efficient algorithm makes the additional cost from CPA- EOS insignificant. We also derive the basic equations for the total compressibility and total potential molar volume in our implementation of the CPA-EOS compositional modeling. Our new algorithm is introduced in a simple finite difference code. This work introduces a general framework for widespread use of the CPA-EOS in compositional modeling.
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