鄂尔多斯盆地陇东地区长7段重力流砂体构型及其主控因素

鄂尔多斯盆地陇东地区长7段重力流砂体规模巨大、油气资源丰富，但不同层系不同地区砂体的形态、规模及叠置关系差异巨大，砂体构型特征及发育规律认识程度低，制约了其油气滚动勘探和开发效率。在岩心观察基础上，基于单井砂体构型界面识别和区域性连井砂体对比，结合砂体沉积微相类型开展了砂体构型划分和发育特征研究。研究认为陇东地区长7段重力流砂体规模较大，主要发育西南物源体系，其次为东北物源。发育典型的重力流水道—湖底扇沉积，可细分为侵蚀型水道、过渡型水道、沉积型水道、溢岸、沟道化朵叶体、板状朵叶体和浊积席状砂7种沉积微相。自三角洲前缘斜坡至深湖沉积中心，除砂体形态从条带状向扇形转换外，砂体规模、垂向叠置关系、横向迁移方式等构型特征亦呈现规律性变化，平面上呈现良好的分带性。在靠近三角洲前缘斜坡的近岸半深湖区，单砂体厚度小，呈孤立条带状分布，叠置关系以薄互层或单层型为主；向盆地内部，单砂体厚度增大，横向连通性增强，砂体叠置导致垂向连通性增强，逐渐向连续叠加型转化；靠近沉积中心地区，单砂体厚度略有减小，但横向连通性显著增强，连片性明显，呈间隔叠加型。综合分析认为，该区重力流砂体构型受控于重力流沉积微相、基准面旋回变化以及物源供给速率。

Architecture and Main Controls of Gravity-flow Sandbodies in Chang 7 Member,Longdong Area,Ordos Basin

The Chang 7 member in the Longdong area of the Ordos Basin contains huge gravity-flow sandbodies and rich oil and gas resources. However， their shape， scale and superpositional relationships differ considerably in different strata regions， and very little is known about their architecture and development. This restricts the improvement of their oil and gas rolling exploration and development efficiency. A study based on core analysis， on the architectural division and the development characteristics of the sandbodies was carried out based on the identification of individual well sandbody architecture interface and their comparison at regionally connected wells， together with sandbody sedimentary facies analysis. The study suggests that the scale of gravity-flow sandbodies in this area is relatively large. The main provenance is a south?southwestern system， followed by a northeastern provenance system. The sandbodies are characterized as a typical lacustrine channel?fan system subdivided into seven sedimentary microfacies: erosional channel， transitional channel， sedimentary channel， levee， channelized lobe， tabular lobe and turbidite sheet sand. The thickness of the sandbody increases from the delta front slope to the deep-lake depocenter， and its shape changes from a strip to a fan. In addition， the architectural properties change （e.g.， the scale）. The vertical superpositional relationships and the lateral migration aspects of the sandbodies also show regular changes in the planar view. In the nearshore semi-deep lake delta front slope area individual sandbodies are relatively thin， and the isolated strips occur as thinly interbedded or single layers. The thickness of the single sand layer increases towards the center of the basin， and the lateral connectivity is enhanced. Superimposition of the bodies has led to an increase in vertical connectivity and a transition to continuous stacking. The thickness of individual sandbodies is slightly reduced near the depocenter， but the lateral connectivity is significantly enhanced with obvious continuity， evident as an interval-stacking type of deposition. Comprehensive analysis suggests that the configuration of the gravity-flow sandbodies in this area is controlled by gravity-flow sedimentary facies， base-level cyclic changes and provenance supply rate.