地层学杂志

西湖凹陷平湖斜坡带平湖组是重要的岩性勘探领域,主力勘探层系平中段以碎屑潮坪沉积为主,存在砂体变化快、规模砂体相类型及分布不清等问题。本次研究基于钻井、测井、分析化验、三维地震等资料开展平湖斜坡带宝团区潮坪层序特征分析,刻画潮坪层序控制下沉积响应差异,梳理潮坪层序内部砂体展布的控制因素。研究表明:(1)潮坪环境层序底界面为进积潮坪向退积潮坪转换的沉积作用转换面,界面特征不明显;层序顶界为进积潮坪向三角洲的转换面,顶部发育稳定潮坪相泥岩,潮坪层序内部最大海泛面处于温暖潮湿气候,发育小粒径草莓状黄铁矿和结核状、纹层状菱铁矿,水退期气候逐渐变冷,发育大粒径草莓状黄铁矿和条带状、团块状菱铁矿;(2)潮坪环境层序内退积潮坪受控于海平面快速上升,发育障壁相砂体,进积潮坪受控于海平面震荡式下降,发育潮下带潮汐砂坝;(3)潮坪环境层序砂体分布受物源供给强弱、地貌特征及基准面变化共同控制。该认识对于潮坪层序内部规模潮坪砂体的分布及预测具有指导意义。

The Pinghu Formation in the Pinghu slope belt of the Xihu Sag is a significant lithological exploration area,in which the main exploration horizons in the middle segment is dominated by clastic tidal flat deposits. However,issues such as rapid changes in sand bodies, unclear facies types and distributions of large-scale sand bodies persist. In this study, the tidal flat sequence characteristics in the Baotuan area were analyzed based on data from drilling, well logging, analytical testing, and 3D seismic surveys. Differences in sedimentary responses under the control of tidal flat sequences and the controlling factors on the distribution of sand bodies within these sequences were clarified.Results indicate:(1) The base boundary of the tidal flat sequence represents a sedimentary transition from progradational to retrogradational tidal flats with an indistinct interface, while the top boundary marks the transition from progradational tidal flats to deltas with stable mudstones of tidal flat facies developed atop. Within the sequence,the maximum flooding surface indicates a warm and humid climate, where fine-grained strawberry-like pyrite, and nodular or laminated siderite were developed. During the regression phase, the climate gradually cooled, leading to the formation of coarse-grained strawberry-like pyrite and banded or agglomerated siderite;(2) Retrogradational tidal flats within the sequence are controlled by rapid sea-level rise, resulting in the development of barrier sand bodies. In contrast, progradational tidal flats are governed by oscillating sea-level decline, giving rise to subtidal tidal sand bars;(3) The distribution of sand bodies within tidal flat sequences is jointly controlled by the sediment supply scale,geomorphological features, and base-level changes. This study provided guidance for the distribution and prediction of large-scale tidal flat sand bodies within tidal flat sequences.