Volumetric oil reservoir with pressure dropped from 2000 psi to 1000 psi with 30 MM STB oil was produced. Gas oil ratio was 900 Scf/ STB at 1000 psi , while the current gas oil ratio is 2200 scf/STB . Porosity= 20% , Sw= 0.15 .the temperature of the reservoir is 160F. rsi =500 scf/STB , Boi = 1.3 bbl/STB, rs(1000 psia)= 300 scf/STB , Bo=1.20 bbl/STB 1. Calculate IOIP?