琼东南盆地块体搬运体系对天然气水合物形成的控制作用

CONTROL OF MASS TRANSPORT DEPOSITS OVER THE OCCURRENCE OF GAS HYDRATE IN QIONGDONGNAN BASIN

琼东南盆地深水区中新世以来构造运动不活跃,自中新世以来沉积物厚度达5 000～9 000m,Ya35-1-2井显示更新世地层沉积物主要以泥质与砂泥互层的细粒沉积物为主,深部流体垂向运移通道不发育。高分辨率地震资料和3D地震资料表明,琼东南盆地的上新世及其以上地层存在大量气烟囱和块体搬运体系。气烟囱为深部流体垂向运移提供通道,沉积物在搬运过程中发生重塑,由于沉积和压实作用使MTD具有相对较高电阻率、高密度异常和渗透率降低,是烃类气体聚集的良好盖层,有利于天然气水合物形成。

Tectonic movement has become inactive since the Miocene in the Qiongdongnan Basin.The thickness of sediments from the Miocene to present comes to 5000~9000 m.The well of Ya35-1-2 reveals that the Pleistocene are dominated by fine-grained sediments characterized by interbedded mudstone and silt.There is lack of vertical pathways for fluid migration.The interpretation of high resolution 2D and 3 D seismic data reveals that there are gas chimneys and mass transport deposits occurred in the Pliocene.The gas chimneys may provide vertical pathways for fluid migration from the deeper sediments to the shallower part.Sediments would be remolded during the transport.The MTD layer usually has higher resistivity,higher density and lower permeability than the bounding sediments due to compaction.It may act as a seal for hydrocarbon accumulation and favor the formation of gas hydrate.