If somebody, due to forces out of his control, was unable to daven shachris before Zman tefillah has passed and then is able to do so before chatzos, is there anything for him to do as far as davening shachris other then 2 shemoneh esreis by mincha?
According to Shulchan Aruch (OC 89:1) one who did not daven shacharis until after the time for shacharis (four halachic hours) and davens after that time, until midday, still gets the reward for praying (although not for praying in its time). Rema adds that it is forbidden to daven shacharis after midday. Taz (ibid. 1) disagrees and says one may daven shacharis until the time for mincha (approximately half an hour after midday), and still gets the reward for praying.
If he intentionally missed shacharis, he cannot daven mincha twice as compensation, however, he can daven as a voluntary prayer, provided he adds an additional prayer to it (if he does this immediately after the following mincha he need not add anything) (ibid. 7).