Topaze NL (RTA) Tutorial #1

1. Introduction

This tutorial provides a description of the options and workflow in KAPPA-Workstation. This includes creation of new documents and analyses, loading of pressure and rate data, extraction of the loaded production data, Decline Curve Analysis, use of loglog analysis tools (new in G5), example of analytical and numerical modeling, specialized plots, sensitivity and forecast, and the creation of interpretation file templates (new in G5). The tutorial finishes by pointing to a few items that users may decide to explore on their own.

Before starting this session, the user is expected to have installed KAPPA-Workstation and started the RTA (Topaze NL) module. The tutorial will use the three files (below, left) located in the Examples folder in the Installation directory. Topaze NL starts (below, center) and brings the user to the ‘File’ page. The active option is ‘New and recent’ and a ‘Blank’ icon can be seen towards the top left of the screen (below, right).

2. Creating a new document

Click on the ‘Blank’ icon. This starts a wizard that will take the user through six steps to initialize a new document and its first analysis.

- Step 1: initialization of the main document options: reference time and location, general information, units and general comments. Keep everything as default and click .

- Step 2: main options of the first analysis in this document. Input the main test parameters. Those highlighted with red fields have a significant impact on the results and should not stay at default value. If the default happens to be the answer one may enter the same value or select ‘Accept default’ using a right mouse click. If any field remains, a red warning message will be carried out throughout the interpretation. For this session, set the pay zone (h) to 100 ft and the porosity () to 0.08. Click .

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- Step 3: definition of the fluid and its physical diffusion in the formation. Define the fluid as single phase gas. Advanced PVT is required when the reference phase is gas, in order to compute pseudo properties. To access the advanced PVT definition, click on . In the PVT definition page, change the reference pressure to 6650 psia and reference temperature to 300 °F. Validate the PVT definition with and proceed to Step 4 using .

- Step 4: definition of the constant parameters and/or pseudo-functions that will be used in analytical or linear numerical models (linearity is required for superposition). The computed pseudo-pressure and pseudo-time integral can be viewed in tabulated and graphical form using (below, right). The choice of pseudo pressures (none, not normalized or normalized) affects the plot axes only. The model is always generated in pseudo pressures. Click on .

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- Step 5: controls the level of complexity in the numerical model. The options in the left column are standard with Saphir NL and Topaze NL. The options in the right columns are Rubis facilities. Although these models can, in Generation 5, be directly built from Saphir NL or Topaze NL, they do require a Rubis license to be available. The default numerical settings will be largely sufficient for now but will be visited later in this tutorial, so click on .

- Step 6 (new in G5): Topaze NL G4 would initialize the default model as a fully penetrating vertical well in a homogeneous reservoir bounded by a circular boundary. This can now be overridden at any stage of the analysis, even at initialization stage. If the user knows or suspects that a given model should apply there is no need to start with an irrelevant default. For this session, do not change the default at this stage. Click on .

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The document and its first analysis are initialized and the main Topaze NL window appears. The active tab is ‘Analysis’ with an empty workspace. The document is only in the active computer memory and it is named ‘Untitled1’. Save it and call it ‘RTA Tutorial 1’ using the Ctrl+S shortcut or select ‘Save’ in the File menu.

3. Loading production data

Click on the ‘Load Q’, , icon in the control panel on the left to load the Rate History. The rate information is stored in ‘RTAEX01 Rates.xlsx’. Click on and select the file to load. A file preview is shown (below, left). with the possibility to change the tab/worksheet. brings a dialog where the file information is interpreted line by line (below, right). The collapsible panels on the left offer detailed load options. The top right section has a set of editable information while the bottom left window gives the result of the format processing. As the input file is very simple, with time stored as durations, the default format will work. Click on to proceed.

The main Topaze NL screen is displayed again with a history plot showing the loaded rates.

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4. Automatic extraction and Rate Decline curve analysis

It is possible to perform a Decline curve analysis as soon as a production history is available, regardless of the existence of a pressure gauge.

The ‘Extract p’, , icon in the control panel accesses the manual extraction dialog. We will revisit the dialog later. The ‘Automatic Extraction’, , icon appears in lieu of the ‘Extract p’ icon when the shift key is pressed. In this state, click on the icon and the entire loaded production history, using the default extraction settings will be extracted on a DCA plot, generated at the end of the extraction.

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Double clicking on the DCA plot title bar maximizes it, bringing additional options in the ribbon. Right-click in the plot to access the split options in the popup menu. Split horizontally and vertically to end with three plots.

Change the top right plot to q vs Q by right clicking on it and selecting the plot type in ‘Decline curve options’ (below left). Similarly, change the bottom one to log(q) vs log(t) to end up with something as shown below, right:

Click on the ‘Parameters’ icon in the ‘Plot options’ panel at the top and change the model to Duong. The slider bar at the bottom allows the user to set the relative weight of rates and cumulative production while regressing on the model parameters. Move the slider to mid-way between q and Q and run the regression on initial rate, M and A Exponents (each decline curve will have its own set of parameters):

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Change the abandonment rate to 500 Mscf/D, observe the abandonment time change (6.35 years) and the EUR (4.07 bscf). The results may vary slightly depending on the position of the slider between q and Q.

Abandonment ratio 1e-3 Abandonment rate 500 Mscf/D

Several DCA plots may be created with different decline models on each.

Close the dialog and restore the DCA plot by double clicking on the plot title bar.

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5. Loading Pressure data

Create a new analysis by clicking on the ‘New’ icon in the ribbon at the top. When creating a new analysis, different levels of duplication are offered to the user. For this session, select the existing ‘Analysis 1’ to duplicate and keep all the selections. Click on . Delete the existing DCA plot in Analysis 2.

Before proceeding with loading pressure data, access the ‘RTA Settings’ through located at the top right of the Topaze NL window and select the automatic plots as indicated below:

Based on the above selection, when an extraction is made only the normalized rate – cumulative plot will be created (in addition to the loglog plot and Blasingame plot which are always created on extraction). This allows the user to save overcrowding the workspace with plots the user is not intending to use. The unchecked plots can always be created at any time during the analysis using the ‘New plot’ option in the ribbon (subject to plot prerequisites being met). This will be visited later in the tutorial.

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Click on the ‘Load P’, , icon in the main control panel to load the Pressure History. The pressure data are stored in the Ascii file ‘RTAEX01 Pressures.txt’. Click on the icon and select the file to bring a preview of the file content (below, left). Click on to proceed to the next dialog. The dialog is the same as when loading rates, where the file information is being interpreted line by line (below, right). Again, the format is simple, so keep the defaults and click on to proceed.

Back in the Topaze NL main workspace, the history plot is displayed with both rate and pressure data.

Since an extraction already existed, even though we deleted the DCA plot, loading pressure data will also launch the extraction dialog. This time, the extraction will be based on both pressures and rates, unlike before, when we had rates only.

If no extraction had existed, the dialog can be manually called using the ‘Extract p’, , icon in the control panel.

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6. Extracting data interval and generating plots

In the extraction dialog (below, left) the loglog plot resulting from the current extraction options is displayed on the right (new in G5). Open the ‘Time range’ panel and click on to interactively select the extraction interval (below, right). The effect of the extracted interval on the resulting loglog plot can be seen instantaneously in the extraction preview (shown below).

Reset the interval to the complete history by clicking on , set the starting value to 1hr, then click on to proceed with extraction.

The main Topaze screen (below, right) has four plots (loglog, Blasingame, normalized rate - cumulative & history) and a result windows where a red warning indicates that some key parameters remain at their default value.

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Maximize the loglog plot. Among the plot options, the ‘Show tool parameters’ will display the permeability and drainage area results related to the horizontal line and PSS unit slope. Moving any of these lines will update the corresponding parameter. Moving any line with the ‘Ctrl’ key pressed actually moves both at the same time. After this, pressing the ‘Automatic Analytical’ option will generate the homogeneous model, bounded by a circular limit, taking the current values of k and Re and estimating a value of skin. All this is very similar to Topaze Generation 4. What is new in Generation 5 is that this default simple behavior can be overriden by the user using the Analysis Tools.

7. Analysis tools

Instead of a simple circular boundary, centered around the well, we will model the boundary with a centered rectangle i.e. North-South boundary distances are the same and East-West boundary distances are the same. Click on the 'Tools’ icon in the ‘Analysis control’ panel. This recalls the Analysis tool dialog, step 6 of the new document wizard (below, left). Change the Boundary model to ‘Rectangle (centered)’ and click on to validate.

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The 2 nodes controlling the distances to the boundaries, , can now be played with, to interactively adjust the component behaviors to the data, until we get something similar to the display above right.

Depending on the position of the limit markers on the loglog plot, the North-South and East-West distance values observed in the result window can be a little different.

Hide the tool parameters and restore the loglog plot by double clicking on the plot title bar.

7.1. Additional options

Some of the additional options, available in the ribbon at the top to edit the data and plots, are explained below:

When plots are not maximized and several plots exist in the workspace, the plot area may be reduced by the presence of plot scales. In such instances, the scales may be hidden using this option.

The extracted interval can be edited by clicking on ‘Selection’ and interactively changing the time range in the consequent popup plot. Its impact on the plots is immediate.

The loglog plot uses the equivalent time Te = Q/q. Small rate values can be filtered in order to avoid excessively large values of Te by clicking on ‘Filter’ and specifying the criteria in the filter dialog.

Certain data points can be selected in a lasso by clicking ‘Time interval selection’, then holding the left click down in a plot to draw a lasso around them. The corresponding points are automatically

highlighted in all other plots (below, right).

The ‘Show values’ option, , in the plot tool bar in any plot, can be used to display the time and data values inside the plot, e.g. in the loglog plot (below, left).

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8. Manual and Automatic Analytical Model

The ‘Analytical’, , icon in the control panel accesses the manual analytical dialog. Model and parameters have been initialized from the settings and results of the loglog tool. Clicking on the button would generate the model with these parameters, but we may as well call the automatic model directly. So click on to exit the manual analytical model dialog

The ‘Automatic Analytical’, , icon appears in lieu of the ‘Analytical’ icon when the shift key is pressed. In this state, click on the icon and the model is executed in a single command, with the resulting curves displayed on the visible plots.

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By default, the model curve displayed on the diagnostic plots is the single step model response i.e. corresponding to rate response to a constant pressure step. This removes the scattering effect of equivalent time, Te = Q/q, which is unstable when the pressure is not constant.

In the ribbon at the top, the single step response can be turned on/off using . Turn the option off to see the true pressure response on the loglog plot (inset image above).

Turn the single step response back on. It will be left on for the remainder of this tutorial.

9. Straight line (specialized) Analysis

The default Topaze workflow follows the control panel options and is based on the loglog plot. Users can also create additional commonly used plots and analyze production behaviors/estimate drainage area reserves by drawing appropriate straight lines on them. What is new in G5 is the ability to then transfer the model values from these straight lines to the analytical or numerical models.

In this session, the normalized rate – cumulative plot (which is already created) will be used to estimate the drainage area size. Maximize the normalized rate – cumulative plot and display results in the plot using the option in the ribbon at the top (below, left). Activate the ‘Line’ plot option from the ribbon at the top and select a range of data in boundary dominated flow by holding the left mouse click and highlighting the relevant data range. A straight line will be drawn based on regression on the data within the selected interval. The volumetric results will be updated when the line is redrawn (below, right). You may need to reset the zoom to see the complete line.

Note: the actual values may be different depending on the points selected for regression.

Restore the normalized rate – cumulative plot by double clicking on the plot title bar.

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10. Introduction to the model dashboard

This option is accessible from the ‘Dashboard’ icon in the analysis ribbon. It brings the dialog shown below. This new G5 feature allows results to be transferred from analysis tools, specialized analyses and models to the analytical and numerical models of the active analysis. From the top set of icons on the left, the user can select the source analysis tool, the analytical model, the numerical model or any of the specialized analyses. The corresponding results are displayed in the right table.

The destination model may be the analytical or numerical model at the bottom of the icons on the left. Clicking on one of these two buttons will transfer the relevant active ‘transferrable’ results to the model and execute the model at once. If for example you select the Analytical model in the top column and send to the numerical model you will do exactly what you just did when calling the numerical model with the analytical values. However, the dashboard establishes a more flexible bridge between the different sources of results.

In this session, select the normalized rate - cumulative plot from the list of specialized analyses and click on the ‘To analytical’ icon:

Since the PV has no information on the relative North-South and East-West boundary distances, they are all reset to the same value, which gives the same PV as calculated from the normalized rate – cumulative plot.

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11. Manual and Automatic Improve

The ‘Improve’, , icon in the control panel accesses the manual improve dialog with two tabs defining the targets (below, left) and the parameter controls (below, right). One can select the regression parameters, set their ranges and apply different weighting on various sections. One may also choose between a match on the cumulative production or the production rates or both. In this session, select the cumulative production as the target (below, left) and choose the permeability and boundary distances (below, right) as regression parameters.

Clicking on the button would run the regression with the defined settings.

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12. Numerical model and Forecast

Before accessing the numerical model dialog, let us turn the NL flag on, so the numerical model takes into account varying PVT properties with pressure. Access the ‘PVT and diffusion’ dialog using in the ‘Analysis control’ panel. This recalls the Analysis tool dialog, and switch to the ‘Numerical modeling’ tab, step 6 of the document initialization wizard. In the options on the left, check ‘Use real PVT’ (below left). Validate the selection with .

The existing analytical model is deleted, but the model parameters are still retained in memory. Click on the ‘Numerical’, , icon to access the manual numerical model dialog (above right). The numerical model can be defined automatically based on the diagnostics (analysis tools) or from the analytical model. To initialize the numerical model from the analytical one click on and click on . In addition to the model response at the well, a 3D plot with the reservoir geometry, the static and dynamic reservoir properties is also generated.

The boundary distanced for the numerical model are copied over from the analytical model. Go to the Map tab to see that the default boundary distances (5000 ft in each direction from the well) have been updated to the analytical model boundary distances:

With a numerical model initialized it is possible to consider many more complex options either geometrical (in the map ribbon), related to the fluid behavior (PVT), etc. In the following sections, we will look at the PVT a little. Switch back to the Analysis Tab.

Now that the model is generated, it can be used to forecast future production. Click on the ‘Forecast’, , icon to access the forecast setup. Select the ‘Constant pressure’ forecast option. Set a producing pressure of 1750 psia and forecast for a duration of 3 months and generate the forecast:

13. Adding further non-linearities in numerical models

We are now going to illustrate, using the same example, a case where desorption is incorporated in the NL numerical model. Create a duplicate of ‘Analysis 2’ using the ‘New’ icon at the top and accept to duplicate all levels. In ‘Analysis 3’, access the ‘PVT and diffusion’ dialog (below, left) and check ‘Desorption’ in the ‘PVT & diffusion’ tab. Click on to define the desorption isotherm (below, right) and accept the default relationship with .

In the ‘Numerical modeling’ tab (below, left), ‘Desorption’ is automatically enabled.

Validate the setup with . The model will be removed. Access the numerical model dialog and regenerate the model (a zoom reset on the history plot may be required).

Adding desorption to the model leads, quite logically, to an overall higher gas production.

Click on the ‘Improve’, , icon in the control panel accesses the manual improve dialog. Select the rates and the cumulative production as the regression targets (below, left) and the reservoir surface and the regression parameter (below, right). Click on .

Observe the reduction in the reservoir size as the regression progresses.

Repeat a forecast for 3 months and a constant pressure of 1750 psia:

14. Comparison of different analyses.

The two analyses can be compared on the various plots: history plot, loglog plot and normalized rate cumulative plot.

Click on the ‘Compare’, , icon in the Analysis ribbon at the top. In the compare dialog, select ‘Analysis 3’ and ‘Analysis 2’. The models, as well as the forecasts, are displayed with a specific color in the various plots:

The color assigned to each analysis in compare can be changed by right-clicking on the analysis in the compare dialog (below, left). Alternatively, this may also be done in the Analysis Information dialog.

With the compare mode active, click on the ‘Results’ icon in the ribbon at the top. Tabulated results from the 2 analyses may be compared in the consequent dialog. Using the ‘Show:’ drop down list at the bottom of the ‘Results’ dialog, show the ‘Results’ category only to compare the change in STGIIP and PV because of including desorption in the model (above, right).

Close the compare option.

15. Sensitivity

Once a model is generated, sensitivity on various model parameters can be run to see their influence on the model response or forecast.

Click on the ‘Sensitivity’, , icon to access the sensitivity dialog. The default is to generate 5 sensitivity runs between a minimum and maximum value. Select the ‘Forecast pressure’ as the sensitivity parameter and define to generate five sensitivity runs for forecast pressure between 1400 and 1800 psia (below, left). Click on to generate the sensitivities.

The computation of the various responses is executed on parallel threads on a multicore PC and the results are displayed on a dedicated history plot (below, right).

Alternatively the results of the Sensitivity runs can be displayed on the loglog plot by selecting in the Sensitivity dialog.

16. Creating a template

An important improvement in G5 is the ability to create interpretation templates. This may be done at any time by using the ‘Save as template’ option in the File menu (below left). Once a template is created, it is made available in the file menu (below right).

The template stores the setting of the document and the active analysis at the time it was saved. The next time the user wants to create a new document, they will just have to select the template. Notice that the wizard, which takes the user through the six initialization steps, has the settings of the current analysis. This can be checked with the parameter values in Step 2 (below left) or the PVT and diffusion setup (below right).

17. What’s next?

This tutorial is over. You may save the results and exit Topaze NL.

However, you may want to explore the capabilities of the numerical models a little further. In the session above we had just initialized the NL numerical model from the analytical model and gone one step further to add desorption in the NL model. You may go to the 2D-Map tab, load the field bitmap file ‘RTAEX01 Field.jpg’, scale the field, define the contour, faults, position the producing well properly, add an injection well and display the resulting grid in 2D or 3D, enter the interference well schedule, create layers, select a more complex PVT, etc.

KAPPA-Workstation also has a comprehensive contextual online help, including ‘How to’ topics, Examples and FAQs, to assist the users whilst using the software. Users are encouraged to consult these.