惠民凹陷江家店地区古近系沙河街组物源体系特征与演化

Characteristics and Evolution of the Provenance Systems from the Paleogene Shahejie Formation in the Jiangjiadian Area,Huimin Sag

【目的】惠民凹陷江家店地区沙四上—沙三段物源体系认识薄弱,增加了砂体和储层预测的难度。系统分析物源体系特征及演化,可为砂体和储层预测奠定基础。【方法】通过特征元素、岩石组分Q型聚类和砂砾岩百分含量分布特征等分析,识别出研究区物源区和碎屑物质搬运路径,建立了物源体系演化模式。【结果与结论】沙四上—沙三段层序Ⅰ至层序Ⅴ的特征元素比值分布模式与中生界具有良好的吻合关系,表现为明显高Mg/Mn比值、Al/Mg比值和较高Al/Na比值、Ba/Mn比值的特点;岩石组分Q型聚类分析结果表现为五种QFR组合,揭示了三大物源体系,包括过夏27—夏斜98井区物源体系、过夏37井区物源体系、过夏222—夏223—夏225井区物源体系;层序Ⅰ、层序Ⅱ时期,研究区东南侧的鲁西隆起区提供大量的碎屑物质,砂体发育范围大,层序Ⅲ时期物源区明显后退,砂体规模变小,层序Ⅳ、层序Ⅴ时期物源区向湖盆推进,砂体展布范围再次扩大。

[Objective]Low understanding on the provenance system exists in the upper part of the Fourth member to Third member of the Paleogene Shahejie Formation(i.e.,E2 ss 4 and E2s3,respectively)in the Jiangjiadian area,in-creasing difficulties in the prediction of sand bodies and high-quality reservoirs.The characteristics and evolution of the provenance system are system natically studied,so as to lay a foundation for prediction of sand bodies and reser-voirs.[Methods]Characteristic elements analysis,Q-type cluster analysis of lithological components,and percent-age statistics of sand-conglomerates are performed to identify the provenance system and transport routes of clastic matter,subsequently build evolutionary model of provenance,and discuss its significance to petroleum exploration.[Results and Conclusions]Distributional patterns of the characteristic elements in sequenceⅠtoⅤ,i e.,E2 ss 4 and E2s3,are in agreement with those of Mesozoic formations,displaying obviously high Mg/Mn and Al/Mg ratios along with relatively high Al/Na and Ba/Mn ratios.Five QFR assemblages,extracted from Q-type cluster analysis results of all lithological components reveal that 3 prodominant provenance regions exist:across the Xia27-Xiaxie98,Xia37,and Xia222-Xia223-Xia225 well blocks.During development of sequenceⅠandⅡ,the provenance system,located in the Luxi uplift located in the southeast of the study area,supplied abundant clastic matter to the sedimentary region,forming a large scale of sandstones.The provenance systems recede during sequenceⅢ,causing the scale of sand-bodies to decrease.Subsequently,the provenance systems advance during sequenceⅣandⅤ,allowing the sand-bodies to develop.