Crude oils from different locations on earth all started from a common source in the organisms, but with differing temperature- pressure and geologic histories. Gross patterns have always been obvious in crude (crudes with lower SpGr have more light components), etc, but detailed relationships have been difficult to see.

The use of only "whole crude" properties (density, sulfur, ConCarbon, metals, etc) would not at first seem likely to give good predictions of cut yields and properties. However, HPI has employed a number of techniques which make this possible. First, yields and whole crude properties are corrected to a C6+ basis, which eliminates a major (often man-made) impact on crude characteristics, i.e. varying stabilization levels. The Assay Simulator requires the user to enter the light ends yields (pentane and lighter) so that the yields and properties can be corrected for stabilization levels. Secondly, the World models use the overall K factor to characterize the crude. While this is not a measured property, it can be determined from a Base crude. Furthermore, K factor tuning corrections are determined for each cut and each property of the Base assay, to further refine the model.

The CCPP models capture two independent aspects of assay cut properties: 1) the effect of cut points, and 2) the effect of Whole Crude (WC) properties. Accuracy statistics from the prediction process show that WC properties often relate well to the cut properties, and small tuning ajustments can be made to an get exact to the Base assay. However, some properties do not show a good relationship to the WC properties, so an offset is determined to exactlt match the Base assay.

The CCPP TBP yield predictions have been shown to be generally more accurate than Simulated Distillations done by multiple laboratories. The SimDist can be a better process for estimating yields (especially for blends of very light and very heavy crudes), but requires diligence in the laboratories. In additon, corrections should be generated between known Still Distillations and corresponding SimDists. This is a complicated process that most assay users are not likely to perform. Even if the SimDist is used for estimating the TBP curve, the Assay Simulator may be useful for predicting other cut properties.

There are obvious limitations to this approach of using whole crude properties. One problem is the increasing use of synthetic crudes, the properties of which are so different from natural oils that blends with them will not necessarily correlate to whole crude properties. While blending of crudes can sometimes cause confusion, if the crudes are from the same region they should predict quite well if the blend did not create a "dumbell" crude (a very light with a very heavy). While many properties predict quite well, the predictions of the lighter cuts for sulfur and nitrogen are less accurate. The tuning factors for these properties are larger in magnitude.