鄂尔多斯盆地陇东地区长9油层组砂体成因与油气差异分布

勘探实践表明，鄂尔多斯盆地延长组油气资源丰富，但不同层系或相同层系油气富集存在明显差异.以鄂尔多斯陇东地区三叠系延长组长9油层组为例，基于大量岩心及钻/测井资料，对其岩性和岩石组合、沉积相类型及石油差异聚集特征进行系统分析.结果表明，陇东地区长9油层组是在鄂尔多斯古湖盆迅速扩大、水体逐渐加深背景下形成的，发育以西南方向物源为主的河控三角洲沉积及湖泊（重力流）沉积，其中三角洲前缘水下分流河道、河口坝及浊积扇等砂体是长9油层组主要的储集砂岩成因类型.受水深、水动力强度以及古地貌等地质因素影响，三角洲前缘水下分流河相互切割叠置，沿主物源分散方向砂体具有“条”状、“带”状、“毯”状再到“席”状平面展布变化特征.陇东地区长9油层组内部原油差异聚集特征明显，油藏内部原油多聚集于水下分流河道、河口坝等厚层砂岩物性相对较好的部位，发育“自生自储”型和“上生下储”型两类油藏.长9油层组以长7黑色页岩为油源的Ⅰ类原油形成“上生下储”型油藏较为普遍，储层以水下分流河道、道-坝复合体砂岩为主，多为岩性、构造-岩性油气藏，沿各个主要物源口形成的三角洲连续分布.而以Ⅱ类原油为主“自生自储”型油藏的形成则与长9烃源岩互层产出浊积扇砂体密切相关，分布于志丹-华池-槐树庄林场一线临近长9油层组半深湖区.显然，“源”-“储”空间配置、砂体的空间连通性和储层物性是延长组长9油层组石油差异运聚的主控因素. 

Characteristics and Controlling Factors of Oil Accumulation in Chang 9 Member in Longdong Area,Ordos Basin

The exploration practice shows that the Yanchang Formation in Ordos basin is rich in oil and gas resources, but there are obvious differences in oil and gas accumulation in different or the same member. Based on a large number of core and drilling/logging data, in this paper it systematically analyzes the lithology and rock association, sedimentary facies and oil accumulation characteristics of the Triassic Yanchang Formation in Longdong area, Ordos basin. The results show that Chang 9 Member in Longdong area was formed under the background of rapid expansion of Ordos basin and gradual deepening of water. River controlled delta deposits and lake (gravity flow) deposits mainly developed in southwest direction. Among them, underwater distributary channel, mouth bar and basin floor fan of delta front are the main reservoir sandstone genetic types of Chang 9 member. Influenced by the changes of water depth and hydrodynamic intensity, the distributary rivers in the delta front are cut and overlapped with each other, and the sandbodies along the dispersion direction of main provenance have the characteristics of "strip", "belt", "blanket" and then "sheet". There are two types of oil reservoirs, i.e. "self generation and self storage" type and "upper generation and lower reservoir" type. It is common to form "upper generation and lower reservoir" type oil reservoirs of type Ⅰ crude oil with Chang 7 black shale as oil source. The reservoirs are mainly composed of underwater distributary channel and channel-bar sandstone, mostly lithologic and structural lithologic reservoirs, which are continuously distributed along the delta formed by each main source direction. However, the formation of "self generation and self storage" type oil reservoirs, mainly composed of type Ⅱ crude oil, is closely related to the basin floor fan sandbodies produced by the interbedding of Chang 9 source rocks, and are distributed in the semi deep lake area near the Chang 9 member along the Zhidan-Huachi-Huaishuzhuang. In addition, the oil in the reservoir is mainly concentrated in the parts with relatively good properties such as underwater distributary channel and mouth bar. This study considers that the spatial configuration of "source reservoir", physical properties of reservoir and spatial connectivity of sand body are the main controlling factors of oil differential migration and accumulation in Chang 9 member.