Assay, crude oil

A crude-oil assay always includes a whole crude API gravity and a TBP curve. As discussed by Nelson (op. cit., pp. 89-90) and as shown in Fig. 13-85, a reasonably consistent correlation (based on more than 350 distillation curves) exists between whole crude API gravity and the TBP distillation curve at 101.3 kPa (760 torr). Exceptions not correlated by Fig. 13-85 are highly paraffinic or naphthenic crude oils. 

These analyses are valuable in order to formulate a general idea of the usefulness of the crude oil in producing various refined products. However, the results do not yield much information about the variety of final products which can be obtained. To gain this information, an additional evaluation termed crude oil assay is required. 

A crude oil assay is based on a number of standard tests. Some of the more important tests are listed as follows ... 

Assays of the crude types B and C will need frequent revisions in the crude oil assay libraries, but the nature will be different. With crude oils from group B there is a continuous need to update the crude assay in the databank, which can be platmed following two possible criteria on a fixed delta time basis or on a delta quaUty basis, which is the usual procedure. 

Figure 1. Conventional crude oil assay evaluation procedure...

Some authors suggest an existing tradeoff between improving LP predictions with rigorous models and the cost associated to continuously update the crude assay libraries. A conventional crude oil assay evaluation is... 

Some recent references have demonstrated the power of statistical techniques applied to crude assay prediction. The availability of large crude assay databases integrated with advanced statistical methods allows the prediction of updated crude oil assays or isolated physical properties. 

The acquisition of a commercial crude oil assay library with periodical updates is a common alternative, which could help refiners solve the planning problem appearing with crude oils type B (Figure 1). However, this approach is not effective with crude oils type C), and the cost is a factor to be considered. 

With the basis of the mentioned requirements and the shortage of commercially available tools, a new technology was developed with the objective to update/complete crude oil assays with limited experimental data using rigorous models. This new technology, registered under the name repCAPT (Repsol-YPF Crude Assay Prediction Tool) was intended to complement conventional evaluation procedures. ... 

The methodology has been designed with flexible inputs, allowing different levels of information to be used in the predictions. It is possible to supply incomplete evaluations from different sources, with the purpose to fill the incomplete information in the crude oil assay according to the standard fractions and properties defined. 

Although crude oil density, sulfur and viscosity are the minimum typical bulk properties required by the model, sometimes optional laboratory analysis may be required to improve the accuracy of the predictions. The methodology is independent of the available information for the crude oil, and partial crude oil assays can be used. The output information is always a complete updated assay. 

The system is integrated with unified libraries, updated through the intranet, compiling all the crude oil assay information available. Instant access is provided to crude assay updates, and software interfaces assure integration with other supply chain tools available in planning and operation areas (Figure 7). 

In this chapter we have reviewed a new methodology to generate complete and reliable crude oil assays from limited laboratory data. This... 

Hunger, JW and Associates, Inc., Z-Basic Crude Oil Assay , www.jwba.com. 

The ideal crude oil assay should be able to provide on-line, instantaneous and detailed determination of all crude oil properties across the boiling range. Unfortunately, such a method is not yet available. However, several efforts have been made to that end. The most successful approach has been the prediction of the physicochemical properties of crude oils by correlating the data obtained by a rapid, surrogate method (usually spectroscopic) to the data... 

Chapter 27 reviews a new methodology to generate complete and reliable crude oil assays from limited laboratory data. Better crude quality control can improve refinery planning to ensure the profitability to survive in highly competitive global markets. It has also potential to be used in upstream operations for preliminary assessment of the oil quality of new reservoirs and new wells. 

If at all possible, the concentration of light ends in the feed, ethane through the pentanes, should be taken directly from the parent crude oil assay. In the next section which describes the whole naphtha splitter, methods will be presented for estimating the componential composition for the whole feed, including light ends. Having determined the light ends makeup of the feed, tabulate the properties and flow rates of materials to be fed to the tower. 

A series of articles [4-9] illustrate the diversity of crude oil assay practices employed by major refiners in the United States and Austria. The dissimilarity of results reported in the literature [10 ] is a reflection of this independent development of analytical schemes, even though standardized approaches to crude oil analysis have previously been published 11,12 ]. Despite the complexity of crude oil composition and the diversity of analytical methodology, probably more crude oil analyses are routinely performed on a daily basis using inher-... 

The determination of the boiling range distribution is an essential requirement in crude oil assay. This information can be used to estimate refinery yields and, along with other information, to evaluate the economics of using one particular crude as opposed to another. 

Chapter 1 provides an in-depth introduction to topics related to heavy petroleum, such as definitions, properties, and crude oil assay. The problems that frequently occur while upgrading and refining heavy petroleum are also discussed in this chapter. 

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