No, not for the use case you describe.
There are two aspects to keep in mind here: the software application and its source code.
Even if you modify the source code of a GPL software for your use, you are under no obligation to distribute your modifications unless the software is part of the output (the product) of your consultation. Using a GPL licensed software to automate or process any kind of data also does not oblige you in any manner to make the processed data freely available to anyone.
Let's consider some examples.
Example 1: Your client gives you some data to analyse. You use a GPL licensed software to analyse the data and offer the output of the data from the software as part of your analysis.
- GPL doesn't even come to the picture here because you are not modifying the source code of the software application in any manner nor or you distributing it. You are simply using a software to do some work. If your clients wants to know how you do it, GPL doesn't force you to disclose to others that you are using a GPL software to analyse the data. Even if they ask you to share the GPL software with them, you have no obligation to do so.
Example 2: Your client gives you some data and they want you to offer them different analysis of this data. You customize an existing GPL licensed software that can process such data and create the different analysis the client wants. When the client gives you the data, you run it through the customised software, and only give them the output data feed from the software.
- GPL license allows you to modify the software code. But since you are not distributing the software to others, and only using it personally (even if for a commercial purpose), you are under no obligations to make the source code modifications available to anyone.
Example 3: Your client wants to do some data analysis and they want you to create some algorithms / processes for them to generate different outcomes by varying the data. You customize an existing GPL licensed software that can process such data. You hand over this software to the client so that they can feed it different data and generate the various outcomes from it they desire.
- In this case, the GPL license obliges you to make all the modifications you made to the software code public to anyone who demands it (including your clients if they ask for it) since you have modified and are distributing this modified software to others.
Note: Even if you distribute a GPL software, along with the source code of the modifications you made as required by the GPL, you are under no obligation to do it for free. You can still charge for it. But ofcourse, once the code is out there as open source, its commercial viability decreases.
GPL doesn't prohibit you from making commercial use of any GPL licensed software. Nor does it oblige you to reveal to anyone that you are using a GPL licensed software.
GPL doesn't force you to reveal any changes you make to a GPL licensed software unless you plan to share these modifications / customisation with anyone.
GPL doesn't prohibit you from charging for distribution or for your software skills in creating any code used in the GPL licensed software.
GPL does force you to make all source codes available to anyone who wants, if you distribute a GPL licensed software that you have created or modified in any manner.
(Disclaimer: Always consult a local lawyer as country specific / locale specific laws vary, and some or all of what is said here may not apply in some countries).