鄂尔多斯盆地环县地区上三叠统延长组长6_3砂层组沉积微相特征及新认识

Sedimentary microfacies characteristics and new understandings of the Upper Triassic Yanchang Formation Chang 6_3 interval in Huanxian area in Ordos Basin

通过岩心的详细观察,结合测井、录井资料综合分析,在环县地区上三叠统延长组长63砂层组中,识别出了三角洲前缘、前三角洲和深湖3种亚相,和水下分流河道、支流间湾、河口砂坝、远砂坝、前三角洲泥、砂质碎屑流沉积、浊流沉积、液化流沉积、滑塌沉积和深湖泥10种微相。编绘了一系列沉积微相连井剖面图和长63砂层组的沉积微相平面展布图,表明研究区西部、北部及东北部发育三角洲前缘亚相,研究区中部和东南部发育深湖亚相。在深湖亚相中除了深湖泥外,发育大量的砂质碎屑流和浊流等重力流沉积。作者首次提出了源于浅水区的砂级沉积物是通过前三角洲上的一系列水道搬运至深湖区形成重力流沉积的。综合以上研究成果,建立起了该区的沉积模式。论文最后分析了研究区的油气潜力,指出水下分流河道和砂质碎屑流沉积两种微相的储集性能最好。由于本区砂体横向尖灭现象普遍,可形成一些规模较大的岩性圈闭,是岩性油气藏勘探的有利目标区。

There were 3 subfacies including delta-front, prodelta and deep lake, and 10 microfacies including underwater distributary channel, tributary bay, channel mouth bar, distal bar, prodeha clay,sandy debris flow, turbidity current, fluidized sediment flow, slump deposit and deep lake mud of the Upper Triassic Yanchang Formation Chang 63 interval in Huanxian area by detailed core observation, com- bined with logging data integrated analysis. A series of sedimentary microfacies profile maps and sedimen- tary microfacies distribution maps of Chang 63 interval show that delta-front subfacies developed in western, northern and northeastern part of the study area, deep lake subfacies including deep lake mud, sandy debris flow and turbidity current developed in central and southeastern part of the study area. The authors firstly proposed that sand sediments can transport from shallow water area to deep water area through a se- ries of water channels on prodelta to form the gravity flow deposit. On the comprehension of above studies, the sedimentary model of study area was established. This paper finally analyses the hydrocarbon potential and points out that underwater distributary channel and sandy debris flow sedimentary microfacies are the best reservoirs in the study area. These sand bodies generally pinch out to form big lithologieal traps. The study area is the favorable lithologic reservoir exploration target zone.