Feasible C7+ Splitting Methods An Object-Oriented Approach

When using equations of state to predict the phase behavior of hydrocarbon mixtures, problems occur with the C7+ fraction that exists in such mixtures. Minimizing such problems requires breaking down (splitting) the C7+ fraction into a number of pseudo-components with a single carbon number; e.g. C7, C8, C9..., etc. Extensive compositional analyses of too many reservoir fluids from all over the world have shown exponential molar distributions (mole fraction/molecular weight relation) of the C7+ pseudo-components. Hence exponential methods are extensively used by many researchers as a first choice for splitting the C7+ fraction. Other researchers are still suggesting improvements and enhancements to such methods. This is due to their feasibility in the sense that they do not contain too many unknown or difficultto-determine parameters. In addition, C7+ characterization represents only a minor portion of the process of compositional reservoir simulation. This paper revisits the most common splitting methods that were presented in literature and have gotten a wide acceptance in the oil industry. A worthwhile aspect of the paper, however, is that it proposes an improvement to the Katz constant-parameter splitting method. The improved method compared well with other splitting methods for all tested data sets. Another aspect of the paper is that the program has been coded in an object-oriented manner, which offers flexibility in programming and allows the different parts of the code to be described easily and in a natural manner as if they were real world objects. Some examples that were cited in literature are presented. Index Term— C7+ splitting; hydrocarbon plus fractions; phase behavior; equations of state; OOP application