准噶尔盆地车排子凸起新近系沙湾组一段1砂组钙质隔层“三元复合”成因及其油气地质意义

准噶尔盆地车排子凸起新近系沙湾组一段1砂组(N1 s 11)勘探程度整体较高,挖潜难度越来越大,急需转变研究思路,为后续油藏再认识和寻找新的勘探目标提供支撑。综合利用岩心、薄片、测井和地震等资料,对砂体内部钙质隔层识别标准、成因机制和盖层性能进行了研究,剖析了钙质隔层的油气地质意义。结果表明,钙质隔层位于1砂组砂体中上部,岩性主要为钙质胶结细砂岩,测井曲线上具有高Rt、低AC、高DEN、GR值变小、SP具有一定回返幅度的特征。钙质隔层具有“三元复合”成因,“短期旋回进积—退积作用转换面、干旱环境下的浅水辫状河三角洲沉积体系、沉积期—浅埋藏期强烈钙质胶结”三要素控制了钙质隔层的形成。根据盖层突破压力分析,钙质隔层可以作为有效盖层。以上述认识为指导,开展了基于隔层分布的油藏特征再认识,在储量区周缘新发现多个有利勘探区块,指导了多口井的成功钻探,发现了规模储量,取得了较好的勘探效果。

“Ternary composite”genesis and petroleum geological significance of calcareous barriers in the 1st sand group of Shawan-1 member of Neogene in the Chepaizi bulge of the Junggar Basin

The exploration degree of the 1st sand group of Shawan-1 member of Neogene(N1s11)in the Chepaizi bulge of Junggar Basin is generally high,and it is more and more difficult to tap the potential.Therefore,it is urgent to change research ideas to provide supports for subsequent re-understandings of reservoirs and searching for new exploration targets.Based on comprehensive analysis of core,thin section,well logging and seismic data,researches of identification standard,formation mechanism,and sealing capacity of calcareous barriers inside the sand bodies have been carried out,and petroleum geological significance of calcareous barriers has been analyzed.The results show that the calcareous barriers are developed in the middle and upper parts of sand bodies in the 1st sand group,and the lithology is mainly calcareous cemented fine sandstones.According to well loggings-it is characterized as high Rt,low AC,high DEN,decreasing GR,and SP with feature of a certain return range.There is“ternary composite”genesis for the calcareous barriers.The formation of the calcareous barriers is controlled by 3 factors:transition surface of progradation-retrogradation in short-period cycle,sedimentary system of shallow braided river delta in arid environment,and strong calcareous cementation during sedimentary to shallow burial stages.According to the analysis of caprock breakthrough pressure,the calcareous barriers can be served as effective caprocks.Guided by the above understandings,re-defining of reservoir characteristics based on barrier distribution has been carried out.Several favorable exploration blocks have been newly discovered around the reserve area,multiple wells have been successfully drilled,and large-scale reserves have been obtained.The achieved exploration performance is promising.