[Edit]
If I understand correctly, what you call the “outer loop” is just for building a two-column layout. If so, you don’t need to call two WordPress loops, just open a “fake” oeuvres at the beginning, close a “fake” oeuvres at the end, do a single loop (a single while have_posts()) and close and re-open an oeuvres DIV every 2 posts (when $iOeuvres%2 == 0).
Let me know if that makes sense.
[original answer]
First problem: If you do two loops, you should be using different names for the WP_Query objects (for example, $req1 and $req2 instead of two $req). Otherwise, the inner one will override the values from the outer one.
Second problem: You are missing $req->the_post() on the outer query. That means posts will never advance.
But do you really need a WP Loop within a WP Loop? I don’t see any request for posts for the inner query, you only do a single call for WP_Query() on line 3. Maybe if you clarify what you are trying to fetch (which post types, how they nest, etc.) I can help more.