Add a new property

In the following guide to adding and configuring a property using the Property Manager, the example of adding and configuring the property of Basic Nitrogen is used throughout.

Add a Property

Add a property by pressing the Add Property button , and choose a name for the new property. Additionally, you should choose a unit category for the new property and a DLL code. The unit category determines the unit category in which measurements for this property are made, while the DLL code is needed to refer to the property when using the DLL version of Process Model Manager Reference Manual.

In this example, a suitable property name would be Basic Nitrogen, and a suitable unit category would be Proportion, since Basic Nitrogen is measured in units such as ppm, or %. A suitable DLL code is BN.

Choose Names

In the General category, it is possible to alter the name and short name for the property. The name will be used in various controls throughout Process Model Manager Reference Manual to represent this property. The short name will be used in reports and other areas where an extended, long name might not fit neatly into the space available.

In our example, we retain the name Basic Nitrogen, and choose the short name BN2.

Enter Boiling Point Ranges

Boiling point ranges and cut types which are normally measured are set in the next section. For each property it is possible to set temperature ranges that are normally measured. In the measurement grid cells corresponding to cuts that are not normally measured have a darker shading, but these values are still used during generation.

The three check boxes associated with the fields 'Cuts', 'Residues' and 'Whole crude value' allow you to define, if necessary, boiling ranges that are normally measured for that property. To define a boiling range select the check box for the type and, if needed, enter the acceptable cut points. You must also choose the appropriate temperature unit for measurement of the boiling point.

In the example, basic nitrogen is declared as usually being measured for any cuts whose initial and final boiling points lie between 200 and 550ºC. For example, a cut 300-400°C is normally measured, but it would be unusual to measure the basic nitrogen of such cuts as IBP-300°C, 150-300°C, 300°C+, 300-600°C. Similarly, residue cuts such as 350°C+ may be expected to be measured, whereas 250°C+ would not be. The unchecked whole crude value box shows it would be unusual to measure the whole crude value.

The Boiling Point Range is used only to control shading of the Measurement Grid, indicating property/cut combinations which would normally be measured. If a particular property/cut combination is not normally measured (that is a cut for that property is not in the boiling point range as defined for that property), then the cell in the grid is shaded slightly grey. Values may still be entered in the cell for that property/cut combination, and these values will be used during generation.

In the above example the basic nitrogen cell of a cut IBP-70° would be shaded dark grey indicating the basic nitrogen is not normally measured for this cut, and if a value were entered in the cell the basic nitrogen measurement would be used during assay generation along with the other measurements.

Enter Value Ranges

The value range section allows setting of acceptable values for a property. Two acceptable ranges can be set: a warning range and an invalid range:

• Invalid Measurements - If entered measurements are in the invalid range they will be highlighted in red and are ignored during assay generation. If a property is modelled or based on a correlation generation results may be returned in the Measurement Grid but these are for reference only and are not used during generation.

• Warning Measurements - If entered measurements are in the warning range the measurements will be underlined in the grid but are still used during assay generation (warning ranges only apply to AssayEditor Documents).

In this example, we have chosen to say that the normal range for Basic Nitrogen is between 0.0 and 0.5%. If values are entered which lie outside these ranges, a warning will be seen.

Similarly, the valid range is entered as 0 to 100%. This is a hard range outside which a value for this property can never lie. For percentages, this is naturally 0 to 100%. For other types of measurement, natural valid ranges may be similarly determined.

Normally Process Model Manager Reference Manual checks to see if entered values are valid by comparing the entered value to expected values found in the statistical model. For example the statistical model may contain crudes with whole crude sulphur values between 0% and 4%. If a whole crude sulphur value of 12% is entered, this is outside the range expected so would be highlighted as a warning. This method of warning checking only applies to Documents based on the statistical model such as AssaySynthesis and ProductSynthesis.

For AssayEditor Documents which do not use the statistical model the entered value is checked against the warning range entered in the Property Manager. For example if the warning range for sulphur in the Property Manager is set as 0% - 3% then entering a whole crude sulphur value of 9% will show a warning for that value.

Choose Display Settings

A number of display settings can be configured from the General page.

You can choose the unit in which values for measurements or cuts of this property are displayed by default. This setting can be overridden in the measurement grid to display the property in any of the other possible units. In this example we have chosen to display Basic Nitrogen in ppm units.

You can also choose a display format for values for this property. Your can choose between various numbers of decimal places, significant figures or scientific notation (see Formats for a full explanation).

Finally, you may choose whether the property can be graphed against boiling point or not. In this example, Basic Nitrogen can indeed be graphed against boiling point, while other properties (for example, ethane content) would not naturally lend themselves to such graphing.

Choose Blending Behaviour

Blending behaviour can be configured in the Blending section of the Calculations page.

You may choose the basis for blending (both within a crude, and between crudes) to be one of the following:

• Weight - blending is linear by weight

• Volume - blending is linear by volume

• Mole - blending is linear by mole

• None - the blending behaviour cannot be defined

• Wgt or Vol - blending is linear by weight or volume

Since the units editor ("Unit Manager" on page 40) allows you to define non-linear unit transformations, it is necessary to specify the unit with respect to which blending is considered linear. The Linear As option allows you to specify this unit. In this example, any unit is acceptable (since transformations between units are linear).

Alternatively, if a blending index is used to linearise the blending, this option may be specified and the blending index explicitly entered, using the variable X to represent the property value expressed in the chosen unit. Any mathematical expression may be used. For more details, see Write Formulae.

Finally, some properties are best handled by assuming that the fitted profiles should "blend back to crude". This means that, given the profile, the value returned should correspond to the measured whole crude value upon integrating the whole profile with respect to the relevant yield curve. Simple properties such as sulphur measurement and metals measurement will have this box checked. Other values, such as pour point, are not normally expected to behave in this way, even when handled using a blending index. In these cases the box would normally not be checked.

Choose Correlations

If required, correlations can be chosen for the property in the Correlations section of the Calculations page.

It is often the case that no measurements are available for a particular property for a particular crude. Unless specified otherwise through this correlations section, in such cases, no values would be generated for that crude.

In practice, we might wish the property value to be calculated from other known values, in the case where it is absent. It is possible to add a number of correlations (to set up correlations, see Correlation Manager, by selecting from the list of valid correlations presented on pressing the Add button. In the case of absent data for this property, the correlations will be evaluated in order until a value is generated.

In our example, Basic Nitrogen might be calculated using an example Precise Correlation, which requires Total Nitrogen and Aniline point to be evaluated. In the case the Aniline Point, say, is not present in the measurements for a crude, this formula evaluation will fail. Process Model Manager Reference Manual will at this point attempt to evaluate the second example correlation in the list - the Simple Correlation - which requires only Total Nitrogen for evaluation.

Correlations can be removed from this list using the Remove button, and reordered by using the and buttons.

Specify Measurement Precisions

Precisions of measurements for this property can be defined in the Measurements section of the Test Methods page.

When making a measurement for any property, there will necessarily be uncertainties in the measurements due to measurement errors. It is possible to specify these measurement errors so that, when profiles are fitted for this property, matching tolerances correctly reflect the measurement uncertainties - it is sensible to try and match a nitrogen measurement of 10ppm to within 1ppm, but not sensible to try and match a measurement of 10% to within 1ppm.

Process Model Manager Reference Manual allows you to specify with a formula exactly what the precision associated with the measurement should be. In our example, we require measurement precision of either 5% relative of the measured value, or 1 ppm, whichever is the greater. This can be entered as max(1,0.05*X), where X is the measured value in ppm. The full range of possibilities for the formulae which may be entered is indicated in Write Formulae.

Specify Constraints

When profiles are fitted for this property, a number of complex constraints may be specified to govern the nature of the curve fitted. These can be found on the Fitting page. It is possible to govern:

• Constraints on value ranges for the curves

• The tension of the curve

• The extrapolation behaviour of the curve

Constraints can be added, edited and removed using the Add, Edit and Remove buttons in the

Constraints section of the Fitting page.

Constraints may be added which pertain to given boiling point ranges. Three types of constraint may be added, and as many of these constraints as you wish may be imposed:

• Value between - an upper and lower bound may be specified for the profile values for this boiling point range.

• Value fixed - a fixed value may be specified for this boiling point range

• Monotonicity - behaviour of the profile may be constrained to be monotonically either increasing or decreasing in this boiling point range.

Specify Fitting Behaviour

The default tension can be controlled by using the slider in the Fitting section of the Fitting page. When the tension is low, the fitted profiles try to match the measured values and guide points faithfully. When the tension is high, smoothness of the profile shape becomes more significant and values may not be matched so closely. Note that this setting controls the default, and can be overridden at any time when fitting a profile.

The extrapolation behaviour of the fitted profiles can be controlled in the Extrapolation section of the Fitting page. Three options are available for both upper and lower extrapolation. Upper extrapolation corresponds to extrapolation beyond the highest specified boiling point (either for a measurement or a guide point), and lower extrapolation to extrapolation below the lowest specified boiling point.

It is possible to specify one of three modes of extrapolation, for the lower and upper extrapolation behaviour separately:

• Intelligent - extrapolation follows the natural tendencies of the data

• Linear - extrapolation is constrained to be linear beyond the range of the data

• Fixed - a value which the fitted profile should take may be explicitly specified for the extrapolated range. In this case, the fixed value and associated unit may be entered in the corresponding boxes.

Process Model Manager Reference Manual allows you to specify with a formula exactly what the precision associated with the measurement should be. In our example, we require measurement precision of either 5% relative of the measured value, or 1 ppm, whichever is the greater. This can be entered as max(1,0.05*X), where X is the measured value in ppm. The full range of possibilities for the formulae which may be entered is indicated in Write Formulae.