Use AssaySynthesis

The normal process for creating model-based crude descriptions using AssaySynthesis is described in the following sequence:

1. Enter non-numeric information

   You can enter non-numeric information about the crude using the Information page. This page lists a number of properties associated with the crude being worked up in the document, such as name, reference and comments.

   

   The Information page contains all the fields and data present in the Crude Summary dialog available in the Database view for the crude currently being processed.

   Tip: The assay Name and Reference can be also edited directly from the document tab in the Navigator pane, by double-clicking the relevant field and entering the text directly into the field. See Crude summary dialog.

   When generating the crude, you can exploit any information provided about the origin and sample date of the crude by ticking the Origin and Sample Date check boxes respectively. Clearing the check boxes causes the crude origin and sample date to play no role in the generation process. By default, neither check box is selected.

   In depth: The geographical origin of a crude oil can say a lot about its nature. Crudes from different areas in the world are often from different rock strata and consequently will have widely different properties. For example, given no other information, it would be reasonable to assume that a crude oil from Venezuela will likely be dense (>0.9 g/cm3or <26 °API), whereas a crude oil from an Australian field will likely be light (say, 0.8 g/cm3or >45 °API).
   In addition to using the numerical property measurement data that is entered in the measurement grid, Assay can exploit any knowledge about the geographical origin of the oil. As the simple case above suggests, knowing the origin ties down (with a particular probability) some characteristics of the crude oil. The generation modules can use this data to increase the certainty of calculated values.
   Crude oil wells also change in character as they age. Wells may not be completely homogeneous (and in fact, often they are not, due to impermeable layers in the oil bearing rocks), or commercial blends may change due to the ageing of contributing fields. Thus, just as crude characteristics are known to vary with geographical origin, so too they may vary with the date of production.
   Assay can exploit information known about the sample date of a crude to predict ageing trends of a crude. Since all crude data used to train the model in Assay has an associated sample date, supplementing measurement data with a sample date will help increase the predictive accuracy of the generation module, provided that multiple crudes of this type were available when generating the model.

2. If required, set up flowsheets for commercial fractionation

   You can use imperfectly fractionated streams by importing a flowsheet or defining a new one in the Flowsheet page.

   Note: You can only use crude independent flowsheets in the Flowsheet page of an assay document.

   To create a flowsheet, use the following toolbar buttons to create, move and delete units. See the help topics about the Flowsheet Manager for more information on how to set up a flowsheet. See Create a flowsheet.

   • - add a distillation unit. See Configure the number of distillation units in Create a flowsheet.

   • - add a mixer. See Add mixers and splitters in Create a flowsheet.

   • - add a splitter. See Add mixers and splitters in Create a flowsheet.

   • - move the selected process unit up.

   • - move the selected process unit down.

   • - remove the selected unit.

     To delete a flowsheet, click the button in the toolbar.

     To import an existing flowsheet you have two options:

• Click the button to import a flowsheet from an external file.

• Click the button and select Copy from Managed Flowsheet to copy a flowsheet from the Flowsheet Manager.

  

  The Crude Independent Flowsheets dialog box opens. Choose a flowsheet and click Select to import it. Click Manage to open the Flowsheet Manager in case you want to create or edit a flowsheet in that environment before importing it. See Create a flowsheet.

  

  If you imported a flowsheet from the Flowsheet Manager, any changes you make in the Flowsheet page will not be automatically saved back to the Flowsheet Manager. To save a newly created or edited flowsheet, you have the following options:

  • Click the button to save the flowsheet to a file.

  • Click the button and select Copy to Managed Flowsheet to save the flowsheet to the Flowsheet Manager.

    Once you have created or imported a flowsheet, go to the Streams page, right-click and choose Add all flowsheet streams from the context menu.

    You can then use the flowsheet streams in the Measurements grid. Double click a column or row header (depending on whether the grid is transposed or not) and click the arrow icon to reveal a list of available streams. See Enter data.

    

    After defining a flowsheet and adding its streams to the Measurements grid, it is possible to associate assay data with these streams. If distillation data (i.e. D86, D1160 or Simdis) are included in the Measurements grid, the flowsheet parameters will be automatically calculated during assay generation.

    To prevent automatic flowsheet fitting from changing a flowsheet parameter, click the Lock Parameter icon next to the parameter in the Flowsheet page. The icon changes to a locked padlock . Note that you can still manually edit the value. Click the icon again to unlock the entry and refit the distillation unit data.

    To lock all parameters for a distillation unit, click the Lock all parameters icon for that unit.

    If distillation data is available for flowsheet streams, and fitting is enabled during generation, you can see the fitting results in the Distillation graph. See Distillation graph.

    3. Optionally set up streams included in the assay in the Streams page

       Before you enter assay measurements you may define the streams included in the assay on the Streams page. Streams can be added on the Streams page by defining the start and end cut points, or can be imported directly from a flowsheet. Streams will also automatically be created when you enter cut points for a stream in the measurement grid during data entry. See Streams page.

       

    4. Enter data into the Measurement Grid

       To enter measurement data for the crude, select the Measurements page in the Document Navigator. See Output grid.

       Enter your values into the grid, making use of the functionality of the grid as required to do so. See Enter data, Manipulate data in the grid and Additional features of the measurement grid.

    5. If required, set constraints on properties

       You can configure individual constraints governing the behaviour of property profiles in the Constraints page.

       

       Two types of constraints on properties are supported in Assay:

       • Global Constraints. Global constraints govern the default behaviour of properties throughout Assay in the absence of any other property constraining information. Global constraints on properties may be set up and managed on a property by property basis using the Property Manager. See Configure your properties.

       • Local constraints. Local constraints govern the behaviour of properties within a particular crude assay. They override any corresponding global constraints that would otherwise be applied to the property. However, they apply only to the individual assays in which they reside. Thus, for example, a local constraint specifying a monotonically increasing sulphur profile for a crude will not affect the behaviour of the sulphur profiles of other crudes in the database, although any global constraints on the sulphur profile will. Local constraints provide you with significant additional flexibility and control over property profiles and distributions that would otherwise not be available.

       Local constraints are embedded in the crude assay being worked up, so that they may be remembered within generated crudes, even after they have been saved to the database. However, they are created and managed at the point at which an assay is being worked up within a Generation module.

       You can also activate a number of predefined constraints on multiple properties by selecting the corresponding check boxes in the Multiple Property Constraints pane at the bottom of the page.

       

       The behaviour of local and global constraints when creating a new crude description from within a Generation module is determined as follows:

       • When beginning a new generation from scratch, the default property constraints are applied. In this case the local constraints and global constraints for the properties of the crude will be the same.

       • When copying or importing a crude to a Generation module, constraints are copied across with the crude if these are present in the crude assay. In this case, for these properties, the local constraints may differ from the global constraints.

       • When copying or importing a crude to a Generation module, default property constraints associated with the Property Manager are applied provided no constraints are present in the crude assay. In this case the local and global constraints for the properties of the crude will be the same.

       Note: In addition to constraints, you can also use guide points to have control over individual properties.

       

       To add a constraint for a property, select the property from the Properties pane on the left hand side of the constraints page. Click the Add button to open the Constraint Editor dialog.

       In the constraint dialog, select an effective boiling point range and temperature scale for the constraint. Then select an appropriate type of constraint:

       • Value between: Enter maximum and minimum values to ensure the value for the property remains between the selected range. You can set the units for this range from the associated drop down list.

       • Value fixed at: Enter a value to ensure a fixed value for the property. You can set the units for the fixed value from the associated drop down list.

       • Monotonically: Select increasing or decreasing to ensure the value for the property never decreases or increases, respectively.

       To add the new constraint, click OK. The new constraint is added to the list of constraints for the property given in the Constraints pane.

       To cancel adding the constraint, click Cancel. You are returned to the Constraints information page proper.

       To edit a constraint, either double click on it in the Constraints pane, or select it and click the Edit button at the bottom of the pane. This opens the Constraint Editor dialog box.

       To remove a constraint for a property, select it in the Constraints pane and click the Remove button at the bottom of the pane.

       Once constraints on a property have been configured, they will be applied in all subsequent operations involving the fitting of profiles for that property in the current assay.

    6. Check the entered data for consistency with the statistical model

       The Calculate Model Range option in Assay allows you to validate whether the measured values entered in the measurement grid lie within the range of the statistical model of Assay, where the range is fixed by the data used to train the model. You would like to check the measured values you have entered against the model range, since the measured value for atmospheric residue Nickel content is potentially ambiguous.

       To validate your data against the model range, click the Calculate Model Range button in the Assay group of the Home ribbon tab. Once the calculation is complete, Assay flags those values it finds outside the range of the model by underlining them in red in the measurement grid.

       In the following figure the atmospheric residue Nickel content has been underlined in red. Assay is warning you that the value entered lies outside the model range and hence is deemed improbable.

       

       You can use the measurement grid tooltips to obtain a better picture of why this value is underlined in red. Hover over the value 624 in the atmospheric residue Nickel content cell to view the tooltip.

       

       The tooltip shows both the model average and the model range. In this case you can see that the measurement lies outside the model spread indicated in the tooltip. Although the value for model spread will not always provide enough information for you to reasonably assess the value of a measurement, in this case, you can see that the value for atmospheric Nickel content was probably 6.24 rather than 624.

       Document pages You can choose to exclude any data point by clearing the check box of the corresponding cell in the measurement grid. You can also exclude entire properties or cuts by clearing the check boxes in the corresponding row or column headers.

    7. Generate the crude

       After entering all relevant data into the AssaySynthesis document, you can generate the crude at any time by clicking the Generate button in the Assay group of the Home ribbon tab Document pages.

       In depth: Often, when carrying out a generation, you will notice that the values Assay generates (as indicated in the top right hand corner of the grid cells) do not match the measurement values you have entered. There are two main reasons for this: measurement tolerances, and the intelligent modelling behaviour of Assay.
       All physical measurements are inherently uncertain to some degree. For crude oil property measurements, typical uncertainties or tolerances are usually stated in the test method as repeatability and reproducibility values. In particular, the reproducibility value represents the distribution in measurement value when a measurement is reproduced elsewhere, on like apparatus, by a different operator. Assay knows what typical reproducibilities are for any measurement, and when using entered values to generate a crude, will not strive to match values which are known to have high uncertainty.
       Owing to its intelligent modelling behaviour, Assay has the ability to extrapolate slightly beyond the range of its training set of crude oil data, but not more than statistically reliable. For example, a range of training data may include crudes with a density in the range 0.75-0.95 g/cm3. The extrapolative abilities of the model allow robust predictions in the extrapolated region out to densities as low as 0.70 and as high as 1.05 g/cm3, say. However, any density values below 0.70 or above 1.05 g/cm3will be in the unmodelled region too far from the training set to model reliably. Thus, if a density value is entered for a product which is, say, 2 g/cm3, Assay will correctly detect that to model a crude of this sort would be far beyond the range of the training data. Assay does not reject this data per se, but rather flags it in the measurement grid as lying outside the model range. A crude description can still be generated, but it will be contorted to make the generated values more consistent with Assay’s understanding of how the crude oil data should look.

    8. If required, additionally edit crude profiles

       Having generated the crude, you can additionally 'fine-tune' the crude description, by editing property profiles using the Profile Graphs and associated information tools and then regenerating the crude to reflect changes to the properties across the entire crude description.

       Make sure that the Property Profile Graph is visible and that the Show on Graph icon () is active in the AssaySynthesis tab in the Navigator pane. The icon is active when surrounded by a light blue box. This allows you to see property profiles for the generated crude in the graph. Select properties in the LY Axis and RY Axis boxes to view the corresponding profiles.

       The ability to edit property profiles for a crude description generated via an AssaySynthesis is provided in Assay to give you complete flexibility in working up your crude assay. Note however that since AssaySynthesis generates the crude description most statistically consistent with the input measurements, in practice it should almost never be necessary to modify property profiles in this way.

    9. Use the crude

       At any point in your workflow, you can save the crude to the Database by clicking the Save button in the Document group of the Home ribbon tab.

       After the crude has been added to the Database, all of the usual functionality of Assay can be used to analyse and study the crude.