川中地区须五段—须六段浅水三角洲沉积特征与模式

针对川中地区须五段—须六段,在大量露头观察、岩心描述基础上,结合测井和地震分析,认为研究区为典型的浅水三角洲。根据煤岩产状、砂岩中植物颈干与碎片、河道底部冲刷程度、滞留沉积类型、层理类型等特征将浅水三角洲划分为上三角洲平原、下三角洲平原、三角洲前缘及前三角洲4种亚相。并在此基础上,建立了两种浅水三角洲模式:一种为以须五段为代表的低物源供给浅水三角洲沉积模式;另一种为以须六段为代表的高物源供给浅水辫状河三角洲沉积模式。低物源供给型的下三角洲平原发育的煤是良好烃源岩,高物源供给型的下三角洲平原分流河道及决口沉积为优质储层发育相带,两者匹配,构成良好的生储组合,是岩性油气藏勘探的重点区块。

Characteristics and Depositional Models for the Shallow-water Deltas of the 5th-6th Interval, Xujiahe Formation, Upper Triassic in Central Sichuan Basin,China

The 5th-6th interval,of the upper part of Xujiahe Formation,in Central Sichuan Basin,is the main studying stratum in this paper.Based on many outcrops,cores,logging and seismic data,Xujiahe Formation is one typical kind of shallow-water delta.According to the characteristics of coal rocks,plant stems,leaves,channel scouring,lags,and the stratification,shallow-water delta could be divided into four kinds of subfacies.They are upper delta plain,lower delta plain,delta front and prodelta.Two types of models for shallow-water deltas are summarized in this paper.The first is of low supply,i.e.the 5th interval.The second is of high supply,i.e.the 6th interval.Coal rocks on the lower delta plain of the delta with low supply are good source rocks.Sandstones of distributary channel and crevasse splay on the lower delta plain of delta with high supply are the favorite reservoirs.Favorable generating-reserving assemblages could be found on the lower delta plain of shallow-water delta,which is the major exploration zone for lithological reservoirs.