I'd also like to see a photo of this barrel. I bought an 870 Competition years ago that came with two barrels, one of which had been ported. I sold that barrel but wonder if yours could be that barrel.
Nitro27man will have the official answer to this question I just talked to him about another 870 comp question. Kingman FYI he is a retired factory rep owns 3 870 comps and I currently own 2 with one as NIB.
The name of that porting pattern is on the tip of my tongue but it just won't move any farther! I owned a used Krieghoff Model 32 that had that same porting and there is a name for it but damned if I can think of it. The 870 Comp barrel I had was ported with oval ports with no separation between groups.