琼东南盆地南部低凸起及其周缘区天然气水合物富集影响因素和成藏模式

Influencing Factors and Accumulation Modes of Gas Hydrate in South Low Uplift and Its Surrounding Area of Qiongdongnan Basin

为了厘清琼东南盆地南部低凸起及其周缘区天然气水合物富集影响因素及成藏模式,利用天然气水合物钻探获取的钻井、测井及2D/3D地震资料,分析了研究区天然气水合物赋存的地质、地球物理特征,探讨了水合物富集控制成藏的影响因素,建立了水合物成藏模式.结果表明:琼东南盆地南部低凸起及其周缘区位于中央坳陷带南坡的深部流体输导优势方向上.多个站位水合物钻探显示,水合物具有分层、多类型储集层的特征.测井上含水合物层段总体具有高电阻率、低声波时差特征.地震剖面分析显示气烟囱顶部气体横向充注现象明显,气体垂向运移受限.研究区水合物的气源兼具微生物成因和热解气成因.断层、气烟囱以及孔-缝渗漏体系为深层热解气的运移提供了良好的输导条件.浅层块体搬运沉积的快速堆积使得其内部孔隙流体难以迅速排出,从而其孔隙流体压力相比上覆和下伏地层要高,使得下伏流体的垂向输导受阻,形成封盖作用.超压封盖层是研究区多类型储集层水合物主要的控制因素.根据封盖能力的差异性及其对水合物富集程度的影响提出了封闭系统和开放系统两种类型的水合物成藏模式.

In order to clarify the influencing factors and accumulation model of gas hydrate in the southern low uplift and its surrounding area of Qiongdongnan basin, using drilling, logging and 2D/3D seismic data obtained from gas hydrate drilling, the geological and geophysical characteristics of gas hydrate occurrence in the study area are analyzed, and the influencing factors of hydrate accumulation control are discussed, and the gas hydrate accumulation model is established. The results show that the southern low uplift of Qiongdongnan basin and its surrounding areas are located in the dominant direction of deep fluid transport on the southern slope of the central depression zone. Gas hydrate drilling at multiple stations shows that the gas hydrate has the characteristics of stratified and multi-type reservoirs. In logging, gas hydrate formation is characterized by high resistivity and low acoustic. The seismic profile analysis shows that the gas filling at the top of gas chimney is obvious, and the gas vertical migration is limited. The gas source of hydrate in the study area is both biogenic and thermogenic gas. Faults, gas chimney and and pore fracture leakage system provide good transportation conditions for the migration of thermogenic gas. The rapid accumulation of shallow mass transport deposits makes it difficult for the internal pore fluid to discharge rapidly, so the pore fluid pressure is higher than that of the overlying and underlying strata, which hinders the vertical dispersion of the underlying fluid and forms a sealing effect. Overpressure sealing layer is the main controlling factor of hydrate in multi-type reservoirs in the study area. According to the difference of sealing ability and its influence on gas hydrate accumulation, two types of hydrate accumulation and enrichment models of closed system and open system are summarized.