See "The Rav Thinking Aloud" pg. 233 where it quotes a transcript of a dialogue with Rav J.B. Soloveitchik:
"...if you study the parshios of Avraham properly, you'll find out there are two brisos. One Bris is a combination of Hakadosh Baruch Hu, Avraham, and the aretz; and then a second bris for Eretz Yisrael…"
in the footnote 59* (by r' David Holzer, the rav's shamash who contributed the notes and recordings for this work) he explains:
"The two brisos of Avraham would seem to refer, respectively, to the bris bein ha'besarim (Bereishis 15:18), and the bris at which his name changes from Avrum to Avraham (Bereishis 17:2) which is explicitly called a "bris olam" (17:2)."
(See the continuation of both the dialogue, and the footnote, for an explanation of the difference between the brisos, and what Rav JBS was explaining using this concept.)