龙门山前陆盆地南段须五段沉积特征

龙门山前陆盆地南段上三叠统须家河组须五段是该区重要的油气产层,由于长期被视为烃源岩与盖层,对其沉积相研究相对较少。文中利用野外实测剖面、测录井资料,并结合前人研究成果,对该地区须五段沉积相类型、砂体分布特征、沉积体系空间展布特征进行了系统分析,得出研究区须五段主要发育辫状河三角洲和湖泊2类沉积体系,识别出分流河道、分流间湾、河漫沼泽、河口砂坝、远砂坝及浅湖泥等微相。须五段沉积时期,研究区西北部主要发育大型辫状河三角洲,东南部多发育湖泊沉积体系。砂体厚度由西北部向东南部逐渐减薄,沉积相类型由辫状河三角洲沉积过渡到湖泊沉积,物源可能来自于西北方向。

Sedimentary characteristics of fifth Member of Upper Triassic Xujiahe Formation in southern section of Longmen mountains foreland basin

The fifth Member of Upper Triassic Xujiahe Formation in the southern section of Longmen mountains foreland basin is an important oil and gas reservoir in the area,but the current study of sedimentary facies is relatively low due to taking the formation as source rock and cover layer for a long time.According to the field measured profiles,logging data and the results of previous research,this paper systematically analyses the sedimentary facies type,sand body distribution characteristics and spatial distributing characteristics of sedimentary system of the fifth Member of Upper Triassic Xujiahe Formation in the southern section of Longmen mountains foreland basin.The following understandings are preliminarily obtained:braided river delta and lake sedimentary systems were developed in the study area,and sedimentary microfacies types,including distributary channel,interdistributary bay,backswamp,mouth bar and distal bar,shallow lake muds,are identified;during the fifth Member stage sedimentary period,a large braided river delta was developed in the northwest of the five study areas and a lake sedimentary system was developed in the southeast of the study area.The thickness of sand body was gradually thinned from northwest to southeast and sedimentary facies types transited from braided river delta sediment to lake sediment.The distribution characteristics of the sand body and sedimentary facies show that the source of the display may come from the northwest direction.