Multiple introduction in an academic report
It is good writing practice to think of any document as having a hierarchical -- even fractal, if you're into these things -- structure: Every section contains a mini-introduction that spells out how what you're going to discuss in the following connects to what you've done before, and a mini-summary at the end that sets the stage for how what you just did leads to the next question.

At the sub-sub-subsection level, these mini-introductions and mini-summaries may be just a sentence or two long, but it's good to get into the habit of seeing that every section could be read on its own by connecting it explicitly to material before and after. 

As such, it is entirely appropriate to have the mini-introductions you talk about in your question.