琼东南盆地崖北凹陷崖城组煤系烃源岩分布及其意义

崖北凹陷位于南海北部大陆边缘西区琼东南盆地北部坳陷西段，是新生代凹陷，连续沉积了始新世到第四纪地层。该凹陷古近纪为裂谷期，发育始新世陆相、早渐新世崖城组海陆过渡相和晚渐新世陵水组海相3套地层。中新世到第四纪为热沉降和新构造期，均为海相地层。崖北凹陷主力烃源岩是崖城组海陆过渡相煤系和泻湖相泥岩，其中，煤层、炭质泥岩及其伴生的暗色泥岩是烃源岩的重要组成部分。已钻井揭示崖城组发育35层煤，累积厚度16.8m。煤层与炭质泥岩主要分布于崖一段和崖三段，形成于潮坪与辫状河三角洲。崖城组地震相与沉积相对应关系良好，据此建立了煤系烃源岩沉积模式，煤系主要发育在凹陷缓坡带的辫状河三角洲和潮坪环境中，其次是陡坡带的扇三角洲和潮坪，暗色泥岩主要发育在深洼漕的泻湖环境。崖北凹陷崖城组煤系和泻湖湘泥岩都是有利烃源岩，生烃潜力大，凹槽内部渐新统-中新统为有利成藏组合。 

Distribution of Yachen Formation Coal Measure in Yabei Sag in Qiongdongnan Basin

Yabei sag lies in the western part of northern depression of Qiongdongnan basin in the continental margin of South China Sea,covering an area of nearly 3 000km2.After the sag was rifted in Paleogene,it accepted the Eocene continental formation,early Oligocene Yacheng transitional formation and later Oligocene Lingshui marine formation.Yacheng Formation is the most important source rock by obsevasing the drilled souce rocks and measuring the gas geochemerstry and making the source-gas correlation in the basin.Coal measure and carbonaceous mudstone are the most important components of source rock,and the drilled wells indicate that they occur from Yacheng-3,Yacheng-2 and Yacheng-1.Rockcores of shallow water area in the Yabei sag shows that the Yacheng-3 formation was formed in the fan-deta,braided stream,the Yacheng-2 was in lagoon,and the Yacheng-1 was in tidal flat facies.The coal meaure and carbonaceous mudstone are distributed mostly in the formations of Yacheng-1 and Yacheng-3.The Yacheng-3 in the Yabei sag shows the chaos seismic faices,the Yacheng-2 exhibits weak amplitude and low frequency and well continuation seismic facies,and the Yacheng-1 is strong amplitude,strong continuation and low frequency.It is good conrespond between seimic facies and sedimentary facies.The sedimentary facies maps drawn by rockcorea,well logging and seismics suggest that the Yacheng-3 was mostly in braided delta,the Yacheng-2 in the lagoon extended a lot,and the Yacheng-1 was mostly in tidal flat.Coal is mostly distributed in the slope of sag in braided delta and tidal flat and second along steep slope in fan-delta and tidal flat;dark mudstone is mainly in the deep area of lagoon.So,we consider that the greater distribution of coal in south slope of Yabei sag and dark lagoon facies,and the giant gas potential in shallow water area of Qiongdongnan basin is strong.