琼东南盆地天然气水合物与浅层气共生体系成藏特征

Accumulation Characteristics of Gas Hydrate-Shallow Gas Symbiotic System in Qiongdongnan Basin

继我国在神狐海域两次天然气水合物试采成功之后,近几年来在琼东南盆地的勘探证实了天然气水合物的存在,而且钻探表明其与浅层气具有复杂的共生关系.为揭示琼东南盆地深水区天然气水合物与浅层气共生体系成藏特征,结合岩心、测井及三维地震数据,阐明了天然气水合物与浅层气的空间分布特征,研究结果表明,天然气水合物主要赋存在海底以下200 m范围内的沙质沉积物中,且其形成过程与浅层气的垂向运移有关.对天然气水合物与浅层气共生体系成藏特征的深入分析表明,深部热成因气和浅部生物成因气是其重要的气体来源,第四系未固结沙层是良好的储层,且天然气水合物和浅层气共生体系的分布主要受深部气烟囱和断层的控制.浅层气藏为天然气水合物提供稳定的气源条件;第四系块体流沉积与含天然气水合物地层能有效地封堵浅层气的纵向运移,进一步促进浅层气的成藏.因此,天然气水合物的形成与浅层气的发育具有正反馈的相互作用关系,有利于形成更大规模的天然气水合物矿体和浅层气藏,具有良好的商业开发潜力.

Following the successful production test of natural gas hydrate in the Shenhu area in China, the exploration in the Qiongdongnan basin in recent years has confirmed the existence of natural gas hydrate, which shows a complex symbiotic relationship with shallow gas by the drilling. In order to reveal the accumulation characteristics of gas hydrate-shallow gas symbiotic system in the deep water area of the Qiongdongnan basin, combining core photos, logging data, and three-dimensional seismic data, the spatial distribution characteristics of gas hydrate and shallow gas is expounded in the study area. The research results show that gas hydrate mainly exists in sandy sediments above-200 m below the seafloor, and its formation process is related to the vertical migration of shallow gas. The deep analysis of the accumulation characteristics of gas hydrate and shallow gas symbiotic system shows that deep thermogenic gas and shallow biogenic gas are the vital gas source. The unconsolidated sand layer in the Quaternary strata is a high-quality reservoir. The distribution of gas hydrate and shallow gas symbiotic system is mainly affected by deep gas chimneys and faults. Shallow gas has been providing stable gas source for gas hydrate. The mass transport deposits and gas hydrate-bearing sediments developed in the Quaternary strata can effectively block the vertical migration of natural gas and further promote the accumulation of shallow gas. Therefore, there are positive feedback interactions between the formation of gas hydrate and the development of shallow gas, which are conducive to the formation of larger gas hydrate ore bodies and shallow gas reservoirs, and have good commercial development potential.