从岩相古地理论下扬子地区青龙群油气潜景

下扬子地区的青龙群地层分殷坑组、和龙山组、扁担山组和东马鞍山组.前三组属下三叠统,后者属中三叠统.根据“单因素分析综合作图法”,对青龙群各组进行了岩石学及岩相古地理学研究.殷坑期与和龙山期的古地理面貌以浅水碎屑岩台地、浅水碳酸盐岩台地、深水斜坡和深水盆地为特征,海水自南而北加深.在扁担山期,深水区域不断向北收缩,浅水区域向北扩展,浅滩发育.至东马鞍山期,整个下扬子海变为统一的浅水沉积区,膏泻湖、局限海、云坪、云灰坪、滩、准滩和雏滩发育.深水环境为有利的生油区.从青龙群的暗色岩层等厚图可以历史地和全面地看出有利生油岩的分布规律.浅滩环境形成的粒石灰岩、准同生后白云岩以及具构造裂缝的石灰岩,都可作为有利的油气储集岩.东马鞍山组的石膏和硬石膏层是良好的油气盖层,致密的灰泥石灰岩亦可作为油气盖层.综合本区的油气生、储、盖条件,可以看出:(1)东部的常州、漂阳地区及中部的铜陵、贵池,安庆地区,具有良好的生储盖组合.(2)西部殷坑组生储条件有利,盖层条件一般.(3)在深水环境的暗色岩层发育区,如果构造裂隙发育,则可望形成句容式的自生自储油气藏.

POTENTIAL OF OIL AND GAS OF QINGLONG GROUP OFLOWER-MIDDLE TRIASSIC IN LOWER YANGTZE RIVERREGION FROM THE VIEWPOINT OF LITHOFACIESPALEOGEOGRAPHY

The Qinglong Group can be divided into four formations,i.e.Yinkeng Formation,Helongshan Formation,Biandanshan Formation and Dongmaanshan Formation.The first three formations belong to the Lower Triassic and the last one to the Middle Triassic.According to"single factor analysis and comprehensive mapping method",the petrography and lithofacies paleogeography of every formation of Qinglong Group has been studied.The paleogeographical features of Yinkeng Age and Helongshan Age in this region were characterized by shallow water elastic platform,shallow water carbonate platform,deep water slope and deep water basin,with water becoming deeper northwards.In Biandanshan Age,the deep water area gradually narrowed northwards but the shallow water sedimentary area was widened.Meanwhile,the shallow water banks were well developed.In Dongmaanshan Age,the whole Lower Yangtze Sea became a shallow water sedimentary area where gypsum lagoons,restricted sea,dolomite flats,dolo-micrite flats,banks,parabanks and embryonic banks were developed.The deep water basin and slope are beneficial to the preservation and transformation of organic materials.The isopach map of Lower Triassic dark coloured rooks has been drawn showing the distribution of possible source rocks of oil and gas.Oosparite and intrasparite which formed in shallow water banks,postpenecontemporaneous dolomites and structurally fractured limestone may be favorable for reserving oil and gas.Gypsum and anhydrite in Dongmaanshan Formation and dense micrite in all formations may serve as good cap rocks of oil and gas.From the combination of the formation,preservation and cap of oil and gas,it can be seen:(1)The formation,preservation and cap conditions are very good in Changzhuu,Liyang area in the eastern part and Tongling,Guichi,Anqing in the middle part where all the profitable conditions are concentrated;(2)In the western part,the good conditions of petroleum formation exist in the Yinkeng Formation,but the cap rocks are not good enough;(3)It can be inferred that in this region where the deep water deposits and the dark colour rocks are well developed,the primary traps such as Jurong type might be formed if there are structural fractures in rocks.