松辽盆地苏家屯次洼初始裂陷期扇三角洲沉积特征

扇三角洲沉积砂砾岩体作为良好的油气储层,一直备受重视。为了深化对断陷盆地初始裂陷期扇三角洲沉积特征的认识,以松辽盆地苏家屯次洼火石岭组为研究对象,综合运用岩心、测井、三维地震资料和古地貌恢复技术,对初始裂陷期扇三角洲的发育规律、沉积特征和控制因素展开深入研究,建立了断陷湖盆初始裂陷期扇三角洲沉积模式。结果表明:①苏家屯次洼初始裂陷期发育东西双断的地堑式断陷湖盆,区内地形高差较大、构造运动活跃,沉积物源主要来自次洼西北、西南和东部等3个方向;②火石岭组形成时期广泛发育扇三角洲沉积体系,岩性以厚层杂色、灰色砂砾岩夹薄层灰色泥岩为主,测井曲线多呈高幅箱形或钟形,在地震剖面上多表现为斜交前积反射、楔状或丘状杂乱反射结构;③沉积体系展布受控盆断裂和古地貌控制,形成“中部凹陷带湖相、东西断阶带扇三角洲相”的沉积格局以及“中部生烃、两侧储集”的生储配置关系;④初始裂陷期构造活动是控制扇三角洲体系发育的主导因素,控盆断裂不仅控制着沉积相带和储层砂体的分布,也持续影响着断陷湖盆的沉积充填演化。该研究成果可为陆相盆地断陷深部的油气勘探提供地质依据。

Sedimentary characteristics of fan delta during initial rifting stage in Sujiatun sub-depression,Songliao Basin

As a kind of good oil and gas reservoir,sandy conglomerate bodies of fan delta have been paid more attention. In order to deepen the understanding of the sedimentary characteristics of the fan delta during the initial rifting stage in the fault basin,taking Huoshiling Formation in Sujiatun sub-depression of Songliao Basin as an example,the development rules,sedimentary characteristics and controlling factors of fan delta in the initial rifting stage were studied by using core,well logging,three-dimensional seismic data and paleogeomorphic restoring technology. The fan delta sedimentary model in the initial rifting stage of the faulted lacustrine basin was established. The results show that:(1)During the initial rifting stage of Sujiatun sub-depression,there was a grabentype faulted lake basin with EW double faults developed,the terrain height difference was large within the area, the tectonic movement was active,and the sediment source were mainly from the northwest,southwest and east of the sub-depression.(2)During the formation stage of Huoshiling Formation,fan delta sedimentary system was widely developed. The lithology was dominated by thick bedded variegated and gray sandy conglomerate with thin bedded gray mudstone. The logging curves were mostly box or bell shaped with high amplitude. The fan delta deposits are characterized by oblique progradation reflection,wedge-shaped or mound shaped disordered reflection structure on the seismic section.(3)The distribution of the sedimentary system was mainly controlled by basin faults and paleogeomorphology,forming the sedimentary pattern of "lacustrine facies across the central sag,fan delta facies in the east-west fault terrace" and the source reservoir assemblage of "hydrocarbon generation in the center and reservoirs on both sides".(4)The structural activity in the initial rifting stage is the main controlling factor for the development of fan delta system. The basin-controlling fault not only controls the distribution of sedimentary facies belt and reservoir sand bodies,but also continuously affects the sedimentary filling evolution trend of faulted lacustrine basins. The research results could provide a geological basis for oil and gas exploration in deep strata of fault depression of continental basin.