【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更多还原

【Abstract】 A series of gentle slope deltas are developed in Yanchang Formation of Shaanxi Gansu Ningxia Basin, where delta front is composed of truncated distributary channels, integrated distributary channels, isolated mouth bars, reiterative mouth bars ,and recombination bars. There are abundant current structures caused by the tractive current that could reflect different sedimentary environments. The two underwater distributary channels have an erosion surface at the bottom of channel. The truncated distributary channels sandbodies are thick and their logging curve forms are box shaped. The integrated distributary channels are fining upward sequences from sandstones at the base to siltstones and mudstones on the top of channels. While the river mouth bars are coarsening upward sequences from mudstones to sandstones. There are lots of thin mudstones in the middle of reiterative mouth bars sandbodies. The recombination bars consist of mouth bars at the bottom and underwater distributary channels at the top and larger than 15 m in the thickness. The sedimentary models of underwater distributary channels and the mouth bars are proposed according to the strength of the currents in the distributary channels and the depth of water in the lake. The slope of the delta front in Huachi area is gentless, so the underwater distributary channels are still strong after entering lake. In the region of high energy river, the underwater distributary channels may frequently migrate. The underwater distributary channels of next stage may erode the former channels deposit and may form boxing truncated distributary. With the depth of lake water, the energy of the distributary channels become weak because of the lake water obstruction. The intergrated sedimentary sequence of channels will be preserved if erosion is weak and form intergrate distributary channels. When the distributary channels flow the slope break zone, the energy of current water in the channels is abruptly released and the sediments carried by them will deposit quickly and form the mouth bars microfacies. The shapes of mouth bars depend on the amounts of sediments carried by underwatter distributary channels. There may deposit isolated mouth bars with coarsening upward succession when underwater distributary channels carry abundant sediments. While the strength of underwater distributary channels is weak, the grains of the current water carried are fine , resulting in the formation of the reiterative mouth bars with uncontinuous coarensing upward succession. The underwater distributary channels flow on the top of the former mouth bars and may erode them. When the mouth bars are cutt partly, there will form a kind of recombination bars due to the distributary channels eroding the mouth bars. At the same time, another kind of recombination bars called the type of distributary channels covering the mouth bars is also discussed in the paper. As the distributary channels flow the some sug area where have enough accomdation space to deposit the mouth bars, they could not cut the former mouth bars, but directly deposit on the top of them.更多还原