西湖凹陷断裂系统特征及其控藏机制

东海陆架盆地西湖凹陷断裂系统复杂,断裂组合样式多样,前人较少涉及凹陷整体断裂系统及其对油气成藏控制作用的研究。为此,基于地震资料解释成果,系统研究了该区断裂的展布特征和活动特征,探讨了断裂系统对油气成藏的控制作用。结果表明:1以渐新统花港组底界和上中新统柳浪组底界为界,可将断裂系统垂向上分为下部(张性)、中部(压性)和上部(张剪性)3套断裂系统;2下部张性断裂系统主要有断阶型、多米诺型、地堑、地垒等多种断裂组合样式,主要形成于凹陷裂陷发育阶段,断裂对沉积地层的控制(或改造)作用显著;3中部压性断裂系统主要有正"Y"、反"Y"字形和简单后冲型断裂组合样式,形成于凹陷反转期,上盘地层存在不同程度的剥蚀;4上部张剪性断裂系统剖面上为悬挂断裂,平面上呈带状和雁行状组合,形成于凹陷区域沉降阶段,对地层控制作用微弱。结论认为:断裂系统中不同性质的断裂对油气聚集的控制作用存在显著差异,深大断裂宏观上控制油气田的分布,裂陷期断裂是油气运移的主要通道,而反转期断裂形成有效圈闭,区域沉降期断裂则改造原生油气藏。

Characteristics of the fault systems and their control on hydrocarbon accumulation in the Xihu Sag,East China Sea Shelf Basin

A fault system is one of the main geological factors controlling the formation and preservation of hydrocarbon reservoirs. The Xihu Sag in the East China Sea Shelf Basin is characterized by a complex fault system and multiple fault configurations. Unfortunately, previous studies have rarely focused on the overall fault systems and their control on hydrocarbon accumulation. Based on the seismic interpretation of the whole Xihu Sag, this paper studied the control of fault systems on hydrocarbon accumulation in this sag. The following results were obtained. (1) The faults can be grouped vertically into the lower (extensional), the middle (compressional), and the upper (extensional shear) fault systems, with the bottom of the Oligocene Huagang Fm and the bottom of the Upper Miocene Liulang Fm as the boundaries. (2) The fault configurations of the lower fault system mainly include fault terrace type, domino type, graben type and horst type. They were mainly formed in the chasmic stage and played an important role in controlling and modifying the sedimentary strata. (3) The fault configurations of the middle fault system are mainly "Y" shaped, anti "Y" shaped and simple back thrusting types. They were formed in the inversion stage and the strata in the upper hanging wall experienced erosion to different degrees. (4) The fault configurations of the upper fault system are featured by suspended cross section, and ribbon and en echelon on map view. They were formed during the regional subsidence and had insignificant control on the strata. It is concluded that different fault configurations in the fault systems played different roles in controlling hydrocarbon accumulation. The deep rooted major faults exert different controls on the distribution of oil/gas fields. Specifically, the faults formed during the chasmic stage acted as the major pathways for hydrocarbon migration, the faults formed during the inversion stage controlled the formation of effective traps, while the faults formed during regional subsidence modified the primary oil/gas reservoirs.