高邮凹陷东部阜三段沉积特征及隐蔽油藏形成条件分析

Sedimentary characteristics and formation conditions of subtle reservoirs of the third member of Funing Formation in the east of Gaoyou Sag

高邮凹陷斜坡带东部阜三段构造圈闭不发育,勘探程度低,潜力大,是隐蔽油藏挖潜增储的重要领域。通过岩心及测录井资料分析,以砂层组为研究单元,精细刻画研究区沉积微相及砂体展布特征,认为研究区主要发育两支三角洲前缘朵叶体,由不同主水流控制,两侧水下分流河道砂体向中间的间湾减薄尖灭。由于水下分流河道频繁迁移改道,单层砂岩横向上变化快,在纵剖面上形成频繁的砂泥薄互层,砂体多呈透镜状并多有叠置。在此沉积背景下,研究区发育砂岩上倾尖灭油藏及构造-岩性复合油藏两类隐蔽油藏,前者受控于相变背景下的岩性尖灭及构造上的上倾产状,后者则还需要适配封闭性断层才能有效成藏。

The structural traps of the third member of the Funing Formation in the eastern slope belt of Gaoyou Sag are undeveloped,with low exploration degree and great potential. It is an important area for tapping potential and increasing reserves of subtle reservoirs. Through the analysis of core and logging data,taking the sand formation as the research unit,the sedimentary microfacies and sand body distribution characteristics in the study area are finely described. It is believed that the study area mainly develops two delta front lobes,which are controlled by different main water flows,and the underwater distributary channel sand bodies on both sides thin out toward the middle bay. Due to the frequent migration and re-routing of underwater distributary channels,the single-layer sandstone changes rapidly in the lateral direction,forming frequent thin interbeds of sand and mud on the longitudinal section,and the sand bodies are mostly lens-shaped and superimposed. Under this depositional background,two types of hidden oil reservoirs have developed in the study area: sandstone up-dip pinch-out reservoirs and structural-lithologic composite reservoirs. The former is controlled by lithological pinch-out and tectonic updip occurrence under the background of phase change,while the latter needs to be adapted to sealing faults for effective accumulation.