Z-Based Structural Index Correlation Method



What is Z-BaSICtm

Z-BaSICTM is a revolutionary advancement in the field of computational chemistry of petroleum and other mixtures of organic compounds. Z-BaSICTM describes molecular composition in numerical form that is used by computer applications for petroleum production, evaluation, transportation, refining and marketing. No other method is known to combine the precision of fundamental chemistry with real-time decision-making in the petroleum business.

Current evaluation methods

Nearly everyone in the petroleum field has experienced uncertainty about the value and process behavior of crude oil. Most methods used to estimate refining behavior (yields, product qualities, and costs) are based on measurements of bulk properties such as API gravity, sulfur content and boiling point yield. The problems with these methods derive from the fact that bulk properties are averages, and averages are not sensitive to important variations in the quantities and distributions of components of the mixture. This causes errors in evaluation and results in economic losses when actual behavior deviates from planned behavior.

Take, for example, two southwestern USA crude oils.

Comparison of yields from two crude oils with similar bulk properties

New Mexico - Permian age Texas - Lower Permian age

Dark green color Brown-green color

38.4 API, 0.55S, 0.062N 38.6 API, 0.47S, 0.057N

Vol % Vol %

Naphtha 41.7 29.8

Distillate 25.2 18.5

Gasoil 14.2 17.9

800+ resid 18.9 33.9

Looking solely at the bulk properties listed, these two crude oils are virtually equivalent, and if anything, a slightly higher value would be given to the Texas crude. But the difference in yield profiles between these two crude oils is remarkable. The New Mexico crude oil yields substantially more atmospheric distillate, the most valuable fraction, than does the Texas crude.

The variations seen between these two crude oils are caused by variations in the quantity and type of the compounds they contain. The New Mexico crude oil is of lower molecular weight and higher aromaticity while the Texas crude oil is of higher molecular weight and lower aromaticity. The example shows that these two characteristics offset each other in the API gravity and the differences are not detected by the three properties used. This inherent insensitivity of bulk properties to the underlying chemistry is the main cause of uncertainty when evaluating petroleum for refining purposes. This uncertainty produces less-than-optimum results all along the supply and process chain.

How Z-BaSICTM removes the uncertainties in petroleum process value

The Z-BaSICTM method solves the problems inherent with bulk properties by describing crude oil at the molecular level. When the molecular composition is known, fundamental chemical and engineering principals can be employed to construct accurate and precise models of processes, and to report properties, specifications and other quantitative information useful for decision-making. Z-BaSICTM consists of a complementary suite of methods and computer applications.

The composition and property file generator consists of:

The Z-BaSICTM applications suite consists of:

The aforementioned methods and applications have been developed to the stage where implementations at the assay, blend and unit operation monitor and control level are now available.


The major applications of Z-BaSICTM fall in the following categories.

A more detailed technical description of Z-BaSICTM can be found by clicking HERE.

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