Hello,

If the oil reservoir is initially undersaturated(no gas cap) and above the bubble point pressure, then (Bti=Boi). Just have a look at this equation of the Total formation volume factor, Bt =Bo+(Rsi-Rs)*Bg . Above the bubble point pressure Rs = Rsi, therefore the term (Rsi-Rs)*Bg = 0, what left is Bt=Bo, as result at Pi=> Bti=Boi.

Regards