准噶尔盆地西北缘吐孜阿克内沟中三叠统一下侏罗统油砂矿沉积和储层特征

摘要

Based on detailed field survey of oil sand outcrops at the top of the middle Triassic Upper Karamay Formation and on the bottom of lower Jurassic Badaowan Formation in Tuziakeneigou on the northwest edge of Junggar basin, the authors measured 11 single sand beds in the oil sand outcrop of Upper Karamay Formation whose lithology is mainly grayish-brown pebbly coarse sandstone and medium-coarse sandstone, and identified 12 single sand beds which are products of multistage migration and superposition of channels in the oil sand outcrop located on the bottom of Badaowan Formation, where every single sand is composed of fining-upward positive rhythm composed of pebbly sandstone, medium coarse sandstone, fine sandstone and siltstone.Thin section analysis reveals that oil sand beds are mainly lithic sandstone and the content of feldspar and quartz is very low, which indicates that rock compositional maturity is low, stability of sandstone is in a low degree and these beds are fairly close to the source area.Textural maturity of sandstone is in a medium degree.In Upper Karamay Formation, lake and delta sedimentary facies, 2 subfacies composed of shore and shallow lake and braided delta front and 3 microfacies composed of lacustrine swamp, subaqueous distributary channel and interdistributary bay were recognized, and it is found that oil sand beds are mainly developed in the subaqueous distributary channel sand bodies, with a high oil content of 9.62％, the average porosity of oil sands of 28.6 ％, and the average permeability of 65.3 × 10-3 μm2.In Badaowan Formation, 3 sedimentary subfacies were recognized, i.e., riverbed, bank and alluvial flat deposit of braided river, with 5 microfacies, namely, channel lag, mid-channel bar, natural levee, alluvial flat and back swamps.The oil sand beds are mainly developed in the mid-channel bar sand bodies of braided river, with an oil content of 5.8％, the average porosity of oil sands of 31 ％, and the average permeability of 2602 × 10-3 μm2.It is thus concluded that oil sand beds in Tuziakeneigou have good reservoir quality and oil-bearing property.Group composition of oil sand beds is mainly non-hydrocarbon and asphaltite, with only a small amount of saturated hydrocarbon and aromatic hydrocarbon, reflecting the serious degradation of oil sands.%通过对准噶尔盆地西北缘吐孜阿克内沟中三叠统克拉玛依上组顶部和下侏罗统八道湾组底部的油砂露头剖面的精细野外实测,在克拉玛依上组油砂露头共识别出11个单砂层,岩性以灰褐色含砾粗砂岩、粗砂岩以及中砂岩等粗粒岩石为主;在八道湾组底部砂岩中共识别出12个单砂层,为多期河道迁移叠加的产物,每一单砂层均以含砾砂岩、中粗砂岩、中细砂岩以及粉砂岩的向上变细正韵律组成.通过对油砂岩薄片鉴定发现油砂岩均以岩屑砂岩为主,长石和石英含量均很低,表明岩石的成分成熟度低,砂岩稳定性较差,距离物源较近,同时砂岩结构成熟度中等.克拉玛依上组剖面共识别出了湖泊和辫状河三角洲两种相,滨浅湖和辫状河三角洲前缘两种亚相,湖泊沼泽、水下分流河道、分流间湾3种微相,其中油砂主要发育于水下分流河道砂体中,油砂岩含油率高达9.62%;八道湾组剖面共识别出辫状河的河床、堤岸和河漫3种沉积亚相,河床滞留、心滩、天然堤、河漫滩及河漫沼泽5种微相,油砂主要发育于辫状河道心滩中,油砂岩含油率为5.8%.油砂岩的孔隙度渗透率均很好.油砂油族组分均以非烃和沥青质为主,仅含少量的饱和烃和芳烃,反映油砂遭到了严重的降解.