开鲁盆地奈曼凹陷北部地区下白垩统地层剥蚀量恢复及其对油气藏的影响

Denudation restoration of Lower Cretaceous formation erosion and its significance to hydrocarbon accumulation in the northern area of Naiman Depression, Kailu Basin

恢复地层剥蚀厚度是研究盆地演化史和进行油气资源评价的重要基础工作。奈曼凹陷作为开鲁盆地中一个重要的沉积凹陷,整体勘探程度不高。本文运用地震地层厚度趋势法辅之以构造沉积综合法恢复了奈曼凹陷北部地区下白垩统九佛堂组上段和下段的古地层厚度及地层剥蚀量分布范围;同时结合奈曼地区构造演化特征和沉积相特征确定了奈曼凹陷北部地区的沉降中心位于奈10井区域,明确了九佛堂组时期原始沉积相展布特征。在物源供给方面,北部物源受搬运距离远及剥蚀难以存留的影响未能沉积,主要来自于西部陡坡带发育的扇三角洲相沉积及东部缓坡带发育的辫状河三角洲相沉积。此外,研究还发现奈曼凹陷北部地区下白垩统古地层厚度地质模型特征为北东向受抬升剥蚀最严重,剥蚀范围广,剥蚀厚度大。此次研究对于揭示该区域的构造演化历史及油气成藏过程有一定的参考价值。同时,本次研究方法的应用对于类似沉积盆地的剥蚀量恢复研究也具有借鉴意义。

Restoring the thickness of stratigraphic erosion is a crucial foundational task in studying basin evolutionary history and evaluating oil and gas resources.In the Kailu Basin,the Naiman Sag is an important sedimentary depression with relatively low exploration.This study employed the seismic stratigraphic thickness trend method,complemented by structural and sedimentary synthesis,to restore the ancient stratigraphic thickness and delineate the range of stratigraphic erosion in the upper and lower sections of the Jiufotang Formation from the Lower Cretaceous in the northern area of the Naiman Sag.By integrating the structural evolution and sedimentary facies characteristics of the Naiman area,the study pinpointed the subsidence center in the northern part of the Naiman Sag near the Nai 10 well area.It also clarified the original sedimentary facies distribution characteristics during the Jiufotang Formation period.Regarding material source supply,it was determined that the northern material source,hindered by long transport distances and challenges in erosion preservation,failed to deposit significantly.The primary sources were identified as fan delta facies deposits from the western steep slope zone and braided river delta facies deposits from the eastern gentle slope zone.Additionally,the study revealed that the geological model of the ancient stratigraphic thickness in the Lower Cretaceous of the northern area of the Naiman Sag is characterized by intense uplift and erosion,particularly in the northeast direction,with a broad erosion range and significant erosion thickness.This study provides valuable insights into the structural evolution history and the oil and gas accumulation process of the region.The methodologies applied in this study are also of referential significance for erosion recovery studies in similar sedimentary basins.