Tight oil occurrence space of Triassic Chang 7 Member in Northern Shaanxi Area, Ordos Basin, NW China

Low-temperature adsorption experiment, high-speed centrifugal gas displacing water experiment and nuclear magnetic resonance (NMR) experiment were conducted on sealed coring samples taken from Triassic Yanchang Formation Chang 7 tight oil reservoir of Northern Shaanxi Area, Odos Basin, to analyze the tight oil occurrence space quantitatively. Micro-capillary bound water T2 (transversal relaxation time) spectra after 2.76 MPa centrifugation and distribution of micro-pores less than 50 nm obtained from low-temperature adsorption experiment both reflect less than 50 nm pore throats consistently, and conversion coefficient C of T2 and pore radius can be computed from comparing their distribution. The conversion coefficient of 15 cores in the study area is 5.80 nm/ms on average. Using C in oil phase T2 spectrum of sealed coring samples, the maximum pore radius of oil occurrence in the study area is 363−8 587 nm, 3 195 nm on average, and average pore radius of oil occurrence 50−316 nm, 166 nm on average, and main pore radius of oil occurrence is 97−535 nm, 288 nm on average. Tight oil mainly exists in nanometer pores.