The Chaldeans in the OT are associated with the inhabitants of Babylon. The Hebrew word for “Chaldeans” is KeSeDiY (Strongs ,3679, 3777, 3778) meaning “the ones of KeSeD” or “the inhabitants of “KeSeD”. KeSeDiY is found 82 total times in the OT: Chaldeans 60, Chaldees 14, Chaldea 7. Who is “KeSeD” then? AVRaM was the oldest of three brothers from his father, TeRaK. (Gen 11:26ff) Avraham had two brothers, NaKoWR and HaRaN. NaKoWR had eight children by his wife, MiLKaH, and five children from his “PiYLeGeSH”, RAuWNaH, whose name means “the raised one”. (PiYLeGeSH, H6370, is translated concubine. This word could be derived from the Hebrew word, piyd (Strongs 6365) which has a meaning of misfortune. Thus, PiYLeGeSH is one who has come to misfortune. In this case Avram takes her in as a wife. This very well could be the essence of the meaning of the word which is most commonly translated “concubine”. It would be then a most honorable custom which would bestow honor on the one who took the person in.) The eight children of NaKoWR by MiLKaH were: UWTZ (his descendants were of the land Yob), BuWZ, QeMuWEL (father of the Arams/Syrians), KeSeD (father of those who are called Chaldeans), KaZoW, PiLDaSH, YaDaLaF, and BeTHuWEL. BeTHuWEL was the father of RiBeQaH who was the wife of Isaac. (Gen 22:20ff)
Thus, the Chaldeans or the KeSeDiY were most likely the people of the nephew of AVRaM, KeSeD, son of NaKoWR.