One common objective of flow assurance studies is to calculate the time needed to reach hydrate conditions (typically from a steady-state). This is sometimes called “Cooldown”. Operators have a lot of valuable information that can help them understand how long it takes to complete certain tasks or how close they can get to the hydrate area before running into problems.
This discussion will focus on how large simulation matrices can be run efficiently for cooldown using flotools. We will also compare the flotools method with traditional methods using OLGA GUI.
Pre-Processing
With flotools you can easily set up large numbers of cases and then post-process them quickly. This case will show you how to cool down to the hydrate formation temperature of a system with various parameters such as gas lift rate, flowrate, inlet temperature, water cut and other fluids. This process is made easy by flotools’ Parametric Studies tool.
It can be difficult to create all simulations in OLGA software with a large case matrix. The flotools Parametrics tool can create model file by replacing text in a base files with new parameters. If you have a border node with PRESSURE=100psig, you can provide flotools a list with comma-separated numbers (100, 150 or 200). Flotools will then create 3 key files. Each key file is a copy of the base file.
Only inputs are needed for the variables to vary, and the parameters of each variable must be defined once. You can name cases interactively based on the parameters.
With the inputs above, interactive naming can be done for cases. Each variable has an associated index. For example, WC is associated to %7 (seventh variable in the study). You can input each variable’s index with the operator %n into the naming section to make them change according to the parameter variations. You can create linked variables that you don’t use for anything but naming. You can also see the total number generated cases on the generate cases button. In this example, it is 360. This is the number of cases we will generate with these inputs.
5 flowrates + 3 gas lift rates x 4, temperatures x 2 fluids = 360 cases
Once the matrix has been named and set up, flotools can generate the 360.key files in the location we choose. flotools can generate a batch file or output the.key/model files anywhere in the directory structure. These files can be used to create the cases.
Post-processing
The large number of cases meant that post-processing was slow. You are limited in the number of cases that you can load into the OLGA GUI at once when using the OLGA GUI for simulating many cases. The case output files were small for this project (.tpl/.ppl combined file sizes to approximately 2 MB per case). The GUI could only load 47 complete simulations at once. Trend and profile data can only be extracted from the cases loaded into the GUI at one time. The project required 8 separate extractions in order to obtain the complete data set. It took a lot longer to load the cases into the OLGA GUI.
You can also load the cases into the flotools workspace to begin plotting right away.
These are both the settings for tabulating and plotting results. Excel allows you to plot cooldown times using a combination MATCH and INDEX/OFFSET formulas. Next, you must format the rest of your data in a way that will allow you to make a table/pivottable based on different parameters.
Flotools includes built-in calculations for DTHYD. These include MDTHYD; MDPHYD; MAXDTHYD; MAXDPHYD. This can be used even without having to enter a hydrate curvature in OLGA. You can input hydrate curves in flotools during postprocessing. This will allow flotools to reference the temperatures and pressures for the entire flow path during simulation.
flotools makes it easy to create all model files for large case matrixes. This example shows how the entire set was created in under 2 minutes without pre-processing.
However, it took five times longer to produce a finished product using Excel and the OLGA Gui. This is due to the limitations of OLGA GUI in terms of how much information can be stored at once. For example, it limits how many cases can be loaded simultaneously. The process was complicated because you had to export the data in small chunks.
The goal of this 360-case set was to create 11 plots showing the effects of each parametric study parameter.
These are the time breakdowns of each method. They reflect an experienced user.
OLGA/EXCEL method:
Open cases in GUI and export MDTHYD (22 minutes).
Find the first MDTHYD > 0.02 degC (2 minutes).
In a table format, write down all parameters and cooldown times (5 minutes).
In 7 minutes create pivot tables, slicers and pivot charts
Format plots (create titles, axis labels, etc.) (20 minutes per 11 plots
Total (56 min)
flotools Method:
Open flotools and load boxes (5 minutes)
Open parametric study tools and choose variables, filters/slicers. (2 minutes)
2 minutes to change the plot formatting
Make a duplicate plot and then change the filters/slicers (about 2 minutes for 11 plots).
Total (11 Minutes)
This can be especially true if you update the case matrix or rerun simulations. A similar parametric study can be copied in flotools, and modified instead of creating a new one. This saves time and allows for future work.
Conclusion
flotools makes common flow assurance tasks, such as cooldowns, easy to create, run, and report on, even with many cases. Flotools saves time compared with the OLGA GUI. This is because flotools can handle multiple cases at once and can plot them immediately, instead of requiring Excel post processing.
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