准噶尔盆地车北地区浅层砂岩油藏顶底双油水倒置成因

Oil-water inversion and its generation at top and bottom of the shallow sandstone reservoir in the Northern Chepaizi area,Junggar Basin,NW China

基于油水性质及油水分布特征分析,从构造、岩性、碳酸盐胶结及原油稠化等方面研究准噶尔盆地车排子地区北部新近系沙湾组浅层砂岩油藏顶部和底部双油水倒置现象成因。车北地区原油为重质稠油,随油层深度增加,原油密度和黏度呈相应增大的趋势,储集层碳酸盐胶结作用和原油稠化作用是双油水倒置现象的决定性因素。当下降盘油层顶部超过一定深度后,由于原油稠化作用,原油密度可接近或大于地层水密度,导致油藏底部出现油水倒置;构造高部位碳酸盐胶结作用较强,导致储集层物性变差,后期运移的高黏度稠油无法进入高部位储集层中,从而导致构造高部位油水倒置。在构造中高部位聚集常规稠油,其密度小于地层水密度,油水分异较为完全。

Based on fluid property and distribution, the reason for oil-water inversion at top and bottom of the shallow sandstone reservoir of the Neogene Shawan Formation in the Northern Chepaizi area, Junggar Basin was researched from the perspective of structure, lithology, carbonate cementation and oil thickening. The oil of Northern Chepaizi area is heavy crude oil, whose density and viscosity increase with the depth of oil layer. Carbonate cementation and oil thickening are the controlling factors of oil-water inversion at both top and bottom. When the top surface of oil layer in downthrown side is deeper than a definite depth, the density of crude oil, due to oil thickening, is closer to or higher than that of the formation water, and oil-water inversion at the bottom of reservoir occurs. In the structural high part, carbonate cementation deteriorates the reservoir physical property, the late migrated oil has no access to the high position reservoir, and oil-water inversion forms in the structural high part. In the middle to upper area, conventional heavy oil accumulates, because it＇s lighter than the formation water, oil and water differentiation is complete.