10.7 Fluid Composition

Fluid composition refers to the mixture of fluid components in a hydrocarbon fluid. A fluid composition has a list of fluid components and the molar fraction of each.

Fluid components are the individual molecular types and are specified by referencing them inside the fluid component catalog. This method of describing fluid composition is used both in the fluid analysis and the fluid characterization objects. The roles of fluid composition, fluid component and fluid component catalog are shown in Figure 10.7-1 .

Figure 10.7-1 Fluid Composition model common to all PRODML

Within the fluid analysis and the fluid characterization objects, each instance of a component within a fluid composition refers to one of the members of the fluid component catalog in that same object, using the UID for reference. The inclusion of a fluid component catalog can be seen in Figure 10.6-1 showing fluid characterization. Examination of the hydrocarbon analysis class attributes (it is shown in outline in Figure 10.5.4-1 ) shows it too contains a fluid component catalog. What this means is that every characterization within a fluid characterization—and every hydrocarbon analysis within a fluid analysis—share the one set of possible fluid components within the parent analysis or characterization object. Note that every composition does not need to use all of the fluid components in the fluid component catalog, just that every component which is going to be used to describe a composition in a fluid analysis or fluid characterization must be included in the fluid component catalog.

An example of the use of a fluid composition within fluid analysis can be seen in Figure 10.5.6-1 , which shows constant composition expansion. Each test step (a pressure-temperature step) contains vapor, liquid and overall compositions. Each of these is shown in Figure 10.7-1 .

Examples of the use of referencing to a fluid component within the catalog within fluid characterization can be seen in Figure 10.6.1-2 : in the fluid component property class, the attribute at the bottom of the list is the fluid component reference. This will contain the UID for the fluid component which is within the catalog for the parent fluid characterization object. This class contains the various parameters required for that component. The binary interaction coefficient has the same referencing but for the two components whose binary interaction coefficient is being reported.

Figure 10.7-2 shows the fluid components in the catalog and includes:

• stock tank oil
• natural gas
• formation water
• pure fluid component
• plus fluid component

• pseudo fluid component

The first three are aimed at black oil descriptions and the second three at compositional descriptions; however, the two kinds may be mixed. Figure 10.7-2 shows the attributes of each type of fluid component.

Figure 10.7-2 Types of fluid components supported for fluid composition.

Section 12.1 Fluid Components Defined in the Model lists all the fluid components defined in the schema. However, the enumerated lists are extensible so user-defined components can be added.

Note that the Fluid Component Catalog and the Fluid Components are contained in the PRODML Common package, and are shared with the Simple Product Volume data objects, so are compatible with production volume reports created using PRODML v2.