Page 24 - PVT Property Correlations

Introduction Chapter | 1 5

FIGURE 1.3 Phase diagrams of equilibrium gas at different levels of depletion for an oil reser-
voir (gas near the GOC). GOC, gas oil contact.

volatile oils), it may drop some of the liquids it contains when it reaches the
surface. The concept of equilibrium is used in tracking the produced fluids
to surface. At every new pressure and temperature on the way of oil and gas
to surface, new equilibrium between the oil and gas is assumed for every
increment of pipe.

COMMON MODELS FOR PVT MODELING
Three common PVT models are used to handle the changes in PVT proper-
ties with the changes in pressure, temperature, and composition of the fluid.
These models are usually termed (1) black-oil, (2) MBO, and (3) composi-
tional models.
The choice of model to use in a particular situation depends on fluid type
and the process to be modeled in the reservoir and/or the production system
(El-Banbi et al., 2000; Fevang et al., 2000). The models differ in data
requirements, complexity, and accuracy. The following sections discuss the
differences between the three common PVT models.

Black-Oil Models

Black-oil models (not to be confused with the black-oil fluid type, to be dis-
cussed in Chapter 2) are fluid models that assume the composition of