鄂尔多斯盆地宜川富县地区古生界天然气勘探潜力分析

Analysis of the natural gas exploration potential of the Paleozoic erathem in Yichuan-Fuxian area,Ordos Basin

结合前人研究成果,分析了鄂尔多斯盆地宜川富县地区岩心、测井、地震、试气等资料,研究了其古生界生、储、盖、圈闭特征及油气富集规律,认为该区天然气勘探潜力较大.下古生界海相烃源岩为平凉组泥岩及马家沟组灰岩、泥灰岩,具有低丰度、过成熟的特点;储层为风化壳,主要储集空间为微裂缝、溶蚀孔隙和基质内微孔;盖层为上古生界石炭系本溪组铝土岩、铝土质泥岩及泥岩.上古生界烃源岩为暗色泥岩、太原组和山西组碳质泥岩、灰黑色泥岩、煤层和生物碎屑灰岩,具高丰度、高成熟的特点;储层为下石盒子组和山西组水下分流河道及滩坝类砂体,主要储集空间类型为混合孔隙、残余孔隙、裂缝-微孔隙、裂缝;盖层为上石盒子组泥岩.圈闭类型主要有岩性圈闭、地层圈闭,局部发育构造-岩性圈闭.油气成藏综合研究表明,下古生界以中央古隆起的马五段为有利勘探目标,上古生界以寻找三角洲前缘分流河道及滩坝等有利沉积相带控制的岩性圈闭为主要勘探目标.

Based on predecessors' research achievements,the source,reservoir,cap and trap features and the hydrocarbon accumulation features of the Paleozoic in the area are studied according to the current drilling,logging,seismic and gas-testing data.It is held that there is great potential of natural gas in the studied area.In the lower Paleozoic,the marine hydrocarbon source rocks are mainly the mudstone of Pingliang formation and the limestone and muddy limestone of Majiagou formation,and they are of the characteristics of low abundance and over-mature;the reservoir is weathering crust,and the main reservoir space is micro-cracks,dissolution pore and micro-pore in substrates;the cap rock is the bauxite,bauxitic mudstone and mudstone of Benxi formation,Carboniferous,upper Palaeozoic.In the upper Palaeozoic,the hydrocarbon source rocks are dark mudstone,the carbonaceous mudstone of Taiyuan formation and Shanxi formation,gray black mudstone,coal bed and biological clastic limestone,and they are of the characteristics of high abundance and high maturity;the reservoir is the underwater distributary channel and beach sandbodies of lower Shihezi formation and Shanxi formation,and its main reservoir space type is mixed pore,residual pore,crack-micropore and crack;the cap rock is the mudstone of upper Shihezi formation.The trap types are mainly lithologic trap and stratigraphic traps,locally developing tectonic-lithologic trap.The study on hydrocarbon accumulation indicates that 5th member of Majiagou formation of the lower Palaeozoic at central palaeouplift is favorable exploration target,and in the upper palaeozoic,the lithologic traps controlled by favorable sedimentary facies zones of delta front distributary channel and beach bar are main exploration target.