Common flow assurance study objectives include calculating the time it takes to reach hydrate conditions in a shutdown (typically starting from a steady state). This is commonly called ‘Cooldown’. It is extremely valuable for operators to be able to determine how much time they have to complete tasks safely, and how close they can operate a pipe before it runs into problems.
This article will discuss how to efficiently run large simulation matrices in order to cooldown with flotools. It will also compare flotools with other methods that use the OLGA GUI.
Pre-Processing

You can quickly set up and create many cases in flotools. We are interested in the cooling times for hydrate formation temperatures for systems with different parameters, such as Gas Lift Rate, Inlet Temperature and Flowrate. Using the Parametric Studies tool, flotools makes it easy to do this.

It can take a lot of time to create the various simulations in OLGA when you have a large case matrix. By replacing the base file’s text with new parameters, flotools Parametric Studies can create model files. If you have a boundary node that has PRESSURE=100 psig, flotools can create three separate key files. These are copies of the base data file. One with 100 psig; one with 150 and one with 200.

Only the variables that need to be changed are required. The parameters for each variable can only be defined once. Based on the parameters, cases can be interactively named.

Interactive inputs are required to name cases. Each variable is assigned an index, such as WC, which is associated with the %7 (seventh research variable). To have the index associated to each variable change with each variation in the parameters, the %n operator can be used to input the index into the naming line. Even linked variables can be created that aren’t used for anything other than naming. The generate cases button displays the total number to be generated with a small number badge (360 in this case). These are the cases that we will generate using these inputs.

5 flowrates x3 gas lift ratesx4 temperaturesx2 fluidsx3 water cuts = 360 cases

After the study parameters have been set, the flotools can create 360.key files at any location. flotools will output the.key/model files at any location within the directory structure. It can also generate a batch file, if required. The cases can then be run.
Post-processing

Post-processing the results took too much time due to the high number of cases. The OLGA GUI can only extract simulation results for a limited number of cases. Each case output file for this project was small, with a combined size of.tpl/.ppl files around 2 MB each. Only 47 fully-finished simulations were able to be loaded into the GUI at once. You can only extract trend and profile data from cases that have been loaded into the GUI at any given time. To get the complete data set, this project required eight separate extractions. This took a lot more time than loading cases into the OLGA GUI.

Instead, with the flotools route you can simply load your cases into a flotools workspace so that you are ready to plot immediately.

Both of these methods can be used to plot and tabulate results. To create a plot showing cooldown times in Excel, you will need to use a combination of INDEX/OFFSET formulas and MATCH for each series of MDTHYD outputs from the case matrix. The rest of the data should then be formatted correctly to create a table/pivottable that can be used to plot different parameters.

Flotools has built-in calculations to calculate DTHYD (MDTHYD/MDPHYD/MAXDTHYD/MAXDPHYD) and its (MDTHYD/MDPHYD/MAXDTHYD/MAXDPHYD). These can be used in place of OLGA’s hydrate curve input. During post-processing, hydrate curves can also be entered in flotools. These will be used to compare the temperatures and pressures along the entire flow path of the simulation.

With flotools, even large case matrices can be created quickly and easily. The entire set of cases were created without any pre-processing. It took less than two minutes to do this.

Post-processing with Excel and OLGA GUI took 5x as long to produce a final product of plots and tables. The OLGA software GUI limits the amount of information that can be stored at once. This means that it cannot load multiple cases simultaneously. It was time-consuming to export data in chunks.

This set of 360 cases required 11 plots to show the effects of each parameter.

Below are time breakdowns for each method (these times reflect the experience of an experienced user of each technique):

OLGA/EXCEL method:

Open cases in GUI (22 minutes) and export MDTHYD into.csv
Locate first MDTHYD >0 degC (2 Minutes)
All parameters and cooldown times should be formatted in a table format (five minutes).
In just 7 minutes, create pivot tables, slicers, or pivot charts
Format plots (create titles, axis labels, etc.) (20 minutes to create 11 plots).
Total (56 minutes).

flotools method

Load cases and open flotools (5 minutes).
Use the parametric study tool to select variables and filters/slicers. (2 minutes)
Modify plot formatting to your liking (2 minutes).
For 11 plots, duplicate the plot and make changes to filters/slicers in 2 minutes
Total (11 minutes).

This difference in time is particularly important if the case matrix has been updated or if simulations have been re-run. You can copy a parametric study from flotools to save time and make it similar to another one.

Conclusion

flotools makes it easy to run common flow assurance tasks like cooldowns, and even with multiple cases, create, report, and then run them again. Flotools is a time-saver when compared to the OLGA GUI. It can handle all cases in a project and plot them instantly, rather than requiring Excel post-processing.