湿地的沉积特征及石油地质意义

根据野外露头和钻、测井资料中湿地沉积的观察对比研究,结合现代湿地的特征,从沉积学的角度对湿地进行定义:"一种地形平坦,地面常年潮湿,可有很浅积水(水深通常小于2 m),被繁茂植物广泛覆盖的沉积环境",根据沉积特征,可将湿地分为两类,即沼泽湿地(或称沼泽)和湿原湿地(或称湿原),并对湿原湿地的沉积特征及其与相关相类型的对比关系进行研究。结果表明:湿原湿地沉积物为灰色-黑色泥岩、粉砂质泥岩、碳质泥岩等,富含植物化石,有机碳含量高,电阻率测井曲线呈小锯齿状,数值介于纯泥岩和砂岩之间;古代湿原湿地与河漫滩沉积、湖泊沉积的区别标志在于沉积物颜色、岩性、植物化石、电测曲线等方面;湿地外围部分主要发育泛滥平原,且主要为河漫滩,湿地的边缘部位主要发育湿原,而中心部位发育沼泽;正确区分湿原湿地与湖泊沉积有利于正确恢复古地理面貌和气候演化,正确评价盆地的油气潜力及指导油气勘探。

Depositional characteristics and petroleum geological significance of wetland

Based on analysis and correlation of wetland in outcrops,drilling and logging information,and combined with the features of modern wetland,wetland was redefined from the view point of sedimentology as "a type of natural sedimentary environments which is flat and wet,may be covered by water less than 2 m deep,and is rich in plants".Wetland is classified into two types,swamp wetland(swamp in brief) and wet plain wetland(wet plain in brief).The sedimentary features in plain wetland and correlation among related facies were studied.The deposits of wet plain wetland are mainly dark colored mudstone,silty mudstone and carbonaceous mudstone.They are rich in plant fossils.The content of organic carbon of wet plain is high.The resistivity logging curve is notched,and the resistivity is in between those of pure mudstone and sandstone.The difference marks in geologic wet land,flood plain and lake lie in as follows: color of deposits,lithology,plant fossils and electric logs.Flood land always develops in the outside zone of wet land,while wet plain in the outer part and swamp in the central part.Correct differentiation between wet plain mudstone and lake mudstone contributes to reconstruction of paleogeography,evolution of paleoclimate,evaluation of the oil and gas potential of a basin,and guiding oil-gas exploration work.