辽河盆地冷家油田沙河街组三段储层岩相古地理

辽河盆地在沙河街组三段早期水体较深,主要形成扇三角洲及盆底扇;沙三晚期水体较浅,发育湖泊砂体.依据沉积相分布规律,沙三早、中、晚3个时期可进一步分别划分出湖泊扩张和收缩阶段.盆地西部凹陷的冷家油田为东陡西缓的箕状洼陷.研究区内沙三段的古地理格局是决定相分布的关键因素,河流和湖泊能量相对强弱决定扇体沉积的规模.受相对湖平面变化的影响,纵向扇三角洲主要形成于湖泊扩张时期,并且有相带窄、过渡快、以粗碎屑沉积为主的特点.扇体沉积中主要发育前缘分流河道充填沉积,但位于河口前缘或侧缘的滩坝及前三角洲中的盆底扇局部也较发育.

Sedimentary facies and palaeogeography of the third member of the Shahejie Formation in the Lengjia Oil Field,Liaohe Basin,Liaoning

During the early stage of the detposition of the third member of the Shahejie Formation in the Lengjia Oil Field, Liaohe Basin, Liaoning, the deeper lake water facilitated the formation of fan deltas and basin-floor fans in which the braided distributary channel and beach-bar reservoir microfacies are accentuated. Till the late stage of the deposition of the third member of the Shahejie Formation, the shallower lake water shoud be responsible for the development of lacustrine sandstones. According to the distribution of the sedimentary facies in the study area, the early, middle and late stages of the deposition of the third member of the Shahejie Formation may be involved into two phases of lake spreading and collapse. The Lengjia Oil Field in the western depression of the basin occurs as a half graben depression being steeper in the east and gentle in the west. The palaeogeographic framework is interpretated as the key factor which has an important effect on the sedimentary facies distribution in the third member of the Shahejie Formation. The sizes and scales of fan deposits depend on the energy intensity in the rivers and lakes. Influenced by the lake-level changes, the longitudinal deltas were formed in the spreading phases of the lakes, and characterized by narrower facies belts, sharp gradation and coarser clastics. The fan deposits consist dominantly of frontal distributary channel deposits. The basin-floor fans are often developed on the beaches and bars and profan deltas in the frontal parts or flanks of the estuary.