Existing calculations in USC Assay

When crude oil is fractionated, the total volume of the liquid products is expected to differ slightly from the original crude volume. In most cases, the total product volume is slightly higher—typically by 0.1% to 1%. This occurs because molecules tend to pack less efficiently in more homogeneous fractions than in a complex mixture such as a whole crude. In AVEVA Unified Supply Chain Assay, this phenomenon is referred to as volume expansion and is represented using the density property.

Like other linearly blendable properties, the density of a typical cut is generally calculated from the density profile as follows:

(Equation 1)

(All densities and yields in this equation are defined at a consistent temperature—typically 15°C—independent of the boiling point, T.)

For density, however, AVEVA Unified Supply Chain applies the following exceptions to account for volume expansion:

• Whole-crude density value: In addition to the component-wise density profile, the crude representation includes a separate whole-crude density value. This whole-crude density is usually slightly higher than the value predicted by integrating the profile using Equation 1. When an assay is generated from measurements, values for both the profile and the whole-crude density are predicted.

• Whole-crude stream cut: When you request the density cut value for the whole-crude stream, the system returns the predicted whole-crude density instead of calculating density by integrating across the profile using Equation 1.

• Very wide cuts (>70% weight yield): For very wide cuts (where the weight yield exceeds 70%), the system applies a smooth transition between “normal” cutting and “whole-crude” cutting. As the cut width increases toward 100%, the cut density value approaches the whole-crude density value.

These rules apply consistently across all AVEVA Unified Supply Chain modules.