鄂尔多斯盆地陕北地区三叠系长7致密油赋存空间

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

基于鄂尔多斯盆地陕北地区三叠系延长组长7段致密油储集层密闭取心岩样,进行低温吸附、气驱水高速离心和核磁共振实验分析,定量研究致密油储集层原油赋存空间。岩心2.76 MPa离心力离心后毛细管束缚水T2（横向弛豫时间）谱与低温吸附实验得到的50 nm以下微孔隙分布均主要反映孔径小于50 nm的孔喉,两者具有很好的一致性,对比两者分布可计算将横向弛豫时间转换为孔喉半径的转换系数C,研究区15块岩心C平均值为5.80 nm/ms。将C值应用于密闭取心岩样核磁共振油相T2谱,得到研究区油相赋存最大孔隙半径为363~8 587 nm,平均3 195 nm,平均孔隙半径为50~316 nm,平均166 nm,主要孔隙半径为97~535 nm,平均288 nm,致密油主要赋存于纳米级孔隙内。

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 maximmn pore radius ofoil 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.