An　improved　model　for　calculating　physical　properties　and　phase　behavior　of　confined　fluids　(oil　and　gas　resources　in　shale　reservoirs)　by　considering　adsorption　film　theory　was　developed　based　on　the　square-well　chain-like　fluid　with　variable　well-width　range　(SWCF-VR)　equation　of　state.　The　accuracy　of　the　improved　model　is　greatly　increased　via　comparing　the　experimental　data　of　argon　in　cylindrical　pores　at　87.3　K.　The　physical　properties　of　pure　component　hydrocarbons,　mixture　hydrocarbons,　and　real　Bakken　oils　in　nanopores　were　predicted　and　analyzed.　The　results　show　that　the　properties　of　confined　fluids　are　very　different　from　those　of　bulk-phase　fluids,　where　confinement　decreases　the　gas-liquid　phase　equilibrium　constant　(K-value),　bubble　point　pressure,　and　interfacial　tension　of　the　fluid.　The　presence　of　the　adsorption　film　further　decreases　theK-value　and　bubble　point　and　increases　the　capillary　pressure,　and　these　properties　change　more　significantly　in　pore　radius　with　only　a　few　nanometers.　The　results　demonstrate　the　importance　of　improving　the　accuracy　in　calculating　the　properties　and　phase　behaviors　of　confined　fluids　and　also　draw　the　necessity　of　considering　the　adsorption　film　theory.　©　2021　American　Chemical　Society