GAP Course Notes

Petroleum Experts

GAP Course Notes

Petroleum Experts

© Petroleum Experts Ltd 1 IPM GAP Manual

IPMTCSBS.5.00.20.09.2007

Step-By-Step Guide in building the Simple.GAP model

In this section of the manual we shall be exploring the procedure taken in order to build a full GAP model. These are the steps taken during the first four days of the course including calculations and generation of results.

1 Building the GAP network

1.1 Setting the options In order to build the network, one needs to setup GAP depending on what kind of model will be built. This can be done from Options/Method

and then choose the most appropriate options for your model:


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1.2 Building the network When putting the model together, the following toolbar is used:

The model can be constructed using the following path:


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1.3 Connecting the pieces of equipment For this we use the “Link” Icon. Please remember that whenever we need to construct a pipeline, we need to do this by linking two joints together.

Point the mouse cursor in the middle of one joint, left click, drag keeping the mouse button selected and drop in the middle of the second joint:

The rest of the equipment is linked together in the same way:


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2 Building the well model We are now ready to start filling in the data and describing the different elements of the system. Double click on the well icon Well1:

GAP requires a set of VLPs and an IPR for the well to work (When using the VLP/IPR intersection Model). These are the two fields which are highlighted red. They can be created through a well analysis package such as PROSPER.


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Please select the “Run PROSPER” button, in order to create a PROSPER model for this well:

We can start entering the data required and performing the matching for this well.


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2.1 Entering the well data (PVT, IPR and VLP) In PROSPER, we can follow a logical sequence from left to right and top to bottom on the main menu:

First we go to “Options” in order to make sure the well is set up correctly. The defaults are OK for this example:

Select “Done” and move to PVT/Input Data


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Enter the PVT Data given for Problem 1, page 10 of the example sheet:


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Then we use the match data (given in Problem 6, page 17) to decide which correlations to select and also make them reproduce the measured data. For this we click on “Match Data”:


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Select “Done” and then “Regression”:

We will now match all the correlations and select the one for which Parameter 1 is as close to 1 as possible and Parameter 2 as close to 0. Select “Match All”:

and then “Parameters”:


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On this screen we need to select one correlation that matches the best on Bubble Point, GOR and FVF. A different correlation needs to be selected for oil viscosity. The reason for selecting a single correlation for the first three parameters is to respect material balance. This is one of the fundamental strengths of BO models as opposed to EOS models which do not inherently respect material balance. In this case we select Glaso and Beal. These correlations have to be set in the main PVT screen:


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Next we move to System/Equipment:


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Please select All and Edit. This sequence will allow the program to bring the input data screens up one by one, eliminating the possibility of us missing a screen in the process. Enter the data in the following screens:


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As no surface equipment will be entered (no pipeline), then we simply select Cancel on this screen.

and finally the Cp database, which is left at default values:


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We select done in the main equipment screen and move to the IPR data now:

In this screen we are asked to choose the IPR model to use. Select PI entry, enter the data on the right section and then go to Input Data in order to enter the PI of the well:


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Then select “Calculate” to generate the IPR:

The input data is now entered and we can start matching the well model to some tests.


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2.2 Matching to Well Tests Go to:

Enter the match data as provided in Problem 6. For the Gas Oil Ratio, we know that the value of 600 is incorrect as the reservoir pressure is above the bubble point and the solution GOR for the fluid is 800 scf/stb. Therefore we will enter the correct value of 800 scf/stb


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Firstly we need to match the temperature measured at the well head. Select the point and then “Estimate U Value” as shown above.

Note down the number and go back to the equipment section, Geothermal Gradient and enter this number:

We go back to the Matching screen, select the point and then Correlation Comparison:


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Select “OK”:


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In the screen above, we will first quality check the point. If it is OK is has to be between Duns and Ross Modified and Fancher and Brown Correlations (Maximum and Minimum pressure drops in the tubing). Duns & Ross modified can be used as the maximum boundary only if it is predicting Slug Flow (usually Oil wells) Select these two correlations and then “Calculate” and “Calculate” again in the next screen.


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Note the temperature matches that of the test. Select “Plot” to see if the match point is between the two limit correlations:


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Now we can go back and select the correlations we are likely to use for commercial work in order to find out which one is the closest:

and Calculate followed by Plot:


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You can enlarge an area on the plot by dragging on that area with the mouse cursor:


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We can see that PE3 is the closest correlation; therefore we will match this one. Select “Finish” and done to go back to the main matching screen:

Select “match” as shown above and from the list of correlations only select the one you are intending to match:


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If we go back to the correlation comparison, you can see that the correlation now has been made unique to the particular well we are analysing:


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Now, from the main matching screen we will match the IPR:


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By selecting “Calculate” the program will create a VLP corresponding to the match point that we used earlier:


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The BHP and rate calculate should be a solution to the system, i.e. the IPR should pass through this point as well: By clicking on PLOT the intersection of VLP and IPR can be seen.

The ‘square’ point represents the bottom hole pressure and rate as observed in the well test data.


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The point shown by the “+” sign represents the intersection of the VLP and IPR as represented in the model. Clearly if the model represents the reality observed in the field, the IPR must pass through the ‘square’ point. This means that the IPR must be modified. This can be done by clicking on the IPR tab on the screen where the calculations were performed.

Click on ‘Input Data’ to access the PI screen


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And alter the PI here (a PI of 6.5 will make it):

Click on Calculate to register the changes made in the IPR section.


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This will show the IPR plot. Click on Finish | Done to go back to the VLP Matching Screen and click on Calculate.


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The model is now finished. Go back to the main screen and save the file as “Well 1”. Then select “GAP” to pass control back to GAP:


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Now the created PROSPER file will be associated to the GAP well model. We could also Browse and assign the PROSPER file to the corresponding well in GAP. The same procedure can be repeated with the other well, using the data in Problem 7.


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3 Building the Reservoir Model From the Main Screen of GAP, double click on the reservoir icon (Res 1):

We need to build the reservoir model using MBAL. Please select “Run MBAL” so that we create a new MBAL file: 3.1 Entering Basic Data

• On the menu bar go to Tools and click on Material Balance.

• On the menu bar go to Options


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Then again on the menu bar go to PVT | Fluid Properties and supply the following data:

The Matching procedure is very similar to PROSPER. Select “Match”:


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and then “Calc”:

Once the calculations are finished, select “Match Param.”


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In the above screen we select one correlation for Pb, Rs and Bo and another for viscosities. The selection should be set in the main PVT screen:

Now the next step is building you tank model. In the main menu bar go to Input | Tank Data, and supply the following information:


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You can follow the screens from Left to right as shown above. For the aquifer:


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The history data can be copied and pasted from Excel:

This finishes our setting up of basic tank model. It is advisable to save the file at this point. Next step would be to fine-tune the model, in terms of identifying and quantifying its various drive mechanisms.


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3.2 Matching to Production History data in MBAL In order to begin the history matching, go to “History Matching” and then “All”:

The following screen will appear:

Note that in the graphical methods the plot shown in the screen above is the Campbell plot. You may not get this initially. You should click on the graphical method screen and in the menu bar of the above screen as shown appears. Select Method | Campbell Plot. The Campbell Plot is showing the typical shape corresponding to additional energy required (in this case an aquifer), so the next step before proceeding to the matching will be to include an Aquifer to our model.


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Go back to the Tank Input Data screen by selecting Finish then \Input\Tank Data and add an aquifer model

Then go back to \Matching\All

activate the Analytical Method plot and select “Regression”:


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Select the variables you want to change and then “Calc”. Transfer the calculated variables onto the model by selecting “Accept All Fits”:


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After transferring the data if we click on Done we get the following plots.

3.3 Running Sensitivity Analysis on the Tank Model


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Select History Matching and then Sensitivity:


On this screen if you click on plot you get the following plot.


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We can see that there is a clear minimum on the plot so the solution is unique.


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3.4 Using Simulation Option to Quality check the History Matched Model

From the main menu we select History Matching | Run simulation as shown above. On the following screen select “Calc”:

Then we select “plot” in order to compare the simulated results to the history:


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From the plot screen, please select “Variables” and choose to display both History and simulation results:


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The results will be plotted together:

We will now concentrate on matching the Pseudo Relative Permeabilities Go to:


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Select “Regress” and “Save” in order to match the model (different weight can be given to the different points as required):


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No match can be done on the Fg as there is no free gas production. Now, in order to confirm that the relative permeabilities have been matched properly, we will do a prediction of history. Please go to:

and select the following options:


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Then select “Done” and go to:

Select “Copy” in order to transfer the average rates from the simulation over to this section:


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Select “Validate | Next | Validate | Done” and go to the next option which is:


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This screen simply needs to be activated so select “Done”. We are now ready to do the calculations from:


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Select “Calculate” and then “Plot” in order to compare the results of history, simulation and prediction (you may need to go to Variables in order to select History\Simulation and Prediction streams):

This concludes the History matching and verification process. We can now go to the main screen of MBAL and select “GAP” (after saving the file), in order to go back to GAP:


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Repeat the procedure for Reservoir 2


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4 Finishing the GAP model In the main GAP model, we have now built the well models and the reservoir models.

4.1 VLP and IPR Generation The next step is to Generate VLPs and IPRs for the wells. This can be done from the Generate options: Let us start from the IPR generation

:

Click “All” in order to select all the wells in the model. Then the following screen will appear:

Click “Generate”


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Click OK. Next we go to the main screen and go to the VLP generation:

Click on “data” in order to access the screen where the variables are entered:


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We can fill in the table with a wide range of numbers covering the full operating conditions of the well. After the table is finished, we can copy and paste this onto the other well using the following procedure:


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Select the well 1 and then “Copy”:

Then select the well 2 and “Paste” and then update the information for the GOR as shown below.:


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Then click “OK” and “Generate”:

When the VLPs are finished, the red circles around the wells will disappear:


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4.2 Pipe data In order to enter the pipeline description, we need to double click in the icon in the middle of the pipeline:


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This will bring up the pipe summary screen:

Select “Pipe Data” and the following screen will appear:


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Drop down the menu as shown above, select Line pipe and enter the necessary data: You can now select OK and the colourless box will become Cyan:


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Do the same with the other The model in now ready to use. Save it.


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