摘要:
以晚三叠世华池地区延长组为例,对缓坡背景下的三角洲前缘水下分流河道和河口坝两种主要储油微相进行研究,建立了分类方案和识别标志。将水下分流河道划分为截削式和完整式两大类 10种类型;河口坝细分为孤立式、叠加式和复合式三大类 5种类型。文中根据入湖后的水下分流河道能量强弱变化和湖水深浅的不同组合关系,对水下分流河道和河口坝的沉积条件进行分析,归纳总结了本区缓坡条件下的三角洲前缘的沉积模式。同时讨论了本区独具特色的复合式坝 (“坝上河”)沉积微相的成因类型 :分流河道侵蚀河口坝型复合式河口坝和分流河道叠加河口坝型复合式坝,而后者是该区主要的优质储层和高产含油储层类型
Abstract:
A series of gentie siope deitas are deveioped in Yanchang Formation of Shaanxi-Gansu-Ningxia Basin,where deita front is composed of truncated distributary channeis,integrated distributary channeis,isoiated mouth bars,reiterative mouth bars , and recombination bars. There are abundant current structures caused by the tractive current that couid refiect different sedimentary environments. The two underwater distributary channeis have an erosion surface at the bottom of channei. The truncated distributary channeis sandbodies are thick and their iogging curve forms are box-shaped. The integrated distributary channeis are fining upward seguences from sandstones at the base to siitstones and mudstones on the top of channeis. Whiie the river mouth bars are coarsening-upward seguences from mudstones to sand-stones. There are iots of thin mudstones in the middie of reiterative mouth bars sandbodies. The recombination bars con-sist of mouth bars at the bottom and underwater distributary channeis at the top and iarger than 15 m in the thickness. The sedimentary modeis of underwater distributary channeis and the mouth bars are proposed according to the strength of the currents in the distributary channeis and the depth of water in the iake. The siope of the deita front in Huachi area is gentiess,so the underwater distributary channeis are stiii strong after entering iake. In the region of high energy river,the underwater distributary channeis may freguentiy migrate. The un-derwater distributary channeis of next stage may erode the former channeis deposit and may form boxing truncated dis-tributary. With the depth of iake water,the energy of the distributary channeis become weak because of the iake water obstruction. The intergrated sedimentary seguence of channeis wiii be preserved if erosion is weak and form intergrate dis-tributary channeis. When the distributary channeis fiow the siope break zone,the energy of current water in the channeis is abruptiy re-ieased and the sediments carried by them wiii deposit guickiy and form the mouth bars microfacies. The shapes of mouth bars depend on the amounts of sediments carried by underwatter distributary channeis. There may deposit isoiated mouth bars with coarsening-upward succession when underwater distributary channeis carry abundant sediments. Whiie the strength of underwater distributary channeis is weak,the grains of the current water carried are fine ,resuiting in the for-mation of the reiterative mouth bars with uncontinuous coarensing-upward succession.The underwater distributary channeis fiow on the top of the former mouth bars and may erode them. When the mouth bars are cutt partiy,there wiii form a kind of recombination bars due to the distributary channeis eroding the mouth bars.At the same time,another kind of recombination bars caiied the type of distributary channeis covering the mouth bars is aiso discussed in the paper. As the distributary channeis fiow the some sug area where have enough accomdation space to deposit the mouth bars,they couid not cut the former mouth bars,but directiy deposit on the top of them.
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