渤南洼陷深层油气成藏特征及主控因素

Resrvoiring characteristics and main controlling factors for deep hydrocarbon accumulations in Bonan sag in Jiyang depression

渤南洼陷深层烃源岩主要为古近系沙河街组四段暗色泥岩、砂泥岩及膏盐层,有机碳含量为0.9%～2.39%,干酪根为Ⅰ和Ⅱ1型;深部储集层以沙河街组四段砂砾岩、细砂岩及泥灰岩为主,孔隙度为1.18%～23.5%,渗透率为0.1×10 - 3～36.67×10 - 3 μm2;按照圈闭类型可将深层油气藏划分为岩性圈闭油气藏和复合圈闭油气藏,按烃源岩类型可将其分为古近系腐泥型烃源岩油气藏和中、古生界煤成气藏,按生储盖组合又可将其划分为自生自储型油气藏和上生下储型油气藏.渤南洼陷深层油气成藏主要受充注期、流体动力系统及膏盐层控制.油气的晚期连续充注为深层油气藏的形成提供了雄厚的物质基础.深层特有的超压流体动力系统为深部油气的运聚提供了动力.区域性分布的膏盐层对油气成藏的控制作用主要体现在:1)区域性封盖作用;2)延缓了其下地层的成岩作用,改善了储集物性;3)有利超压流体系统的形成.因此,膏盐层的下部地层为深层勘探的有利区域.

In Bonan sag, the deep source rocks are predominantly dark shale, sandy shale and evaporites in the 4^th member of Paleogene Shahejie Fm, with the TOC content of 0.9%-2.39% and kerogens of type Ⅰ and Ⅱ1 ; deep reservoir rocks are mainly composed of glutinite, fine sandstone and muddy limestone in the 4^th member of Shahejie Fm, with the porosity of 1.18%-23.5% and permeability of 0.1×10^-3-36.67×10^-3μm^2. According to trap types, the deep oil-gas pools in Bonan sag can be divided into lithologic trap and composite trap oil-gas pools; based on types of source rock, they can be divided into oil-gas pools sourced by Paleogene sapropel-type source rocks and sourced by Paleo-Mesozoic coal measures （i. e. coal-derived gas pools） ; in the light of source-reservoir-cap rock combinations, they can be divided into “self-sourcing and self-reservoring” type oilgas pools （i. e. both the source rocks and reservoir rocks are in the 4^th member of Shahejie Fm） , and “uppersourcing and lower-reservoiring” type oil-gas pools （i. e. the oil-gas pools with the source rocks in the 3^rd member of Shahejie Fm and reservoir rocks in the 4^th member of Shahejie Fm）. Their reservoiring process is controlled dominantly by charging stages, fluid dynamic systems and evaporite layers. The continuous late-stage charging has provided huge quantities of hydrocarbons for deep reservoiring. The unique dynamic systems of overpressure fluid in deep strata have provided the driving force for hydrocarbons migration and accumulation. The control of evaporites on oil and gas accumulations is represented by （1） acting as regional seal rocks, （2） delaying the diagenetic process of underlying strata and improving the poroperrn characteristics of reservoir rocks and （3） conducing to the formation of overpressure fluid systems. Therefore, the strata overlain by evaporites are favorable targets for deep oil and gas exploration.