琼东南盆地“气聚集带”的成藏特征与勘探潜力

Accumulation characteristics and exploration potentials of gas accumulation belt in Q iongdongnan Basin

琼东南盆地是中国近海的一个在浅水区、深水区、超深水区均发现煤型大气田的盆地,探讨其天然气地质特征及勘探新领域具有重要的理论和实际意义。笔者基于区域地质、地震、钻井、地球化学测试等数据分析了琼东南盆地的成藏特征和勘探潜力。研究结果表明:琼东南盆地在崖城组沉积期具有"两隆两坳"的构造格局,崖城组的煤型烃源岩(包括煤系烃源岩和陆源海相烃源岩)是主要的烃源岩,以渐新统崖城组(扇)三角洲为中心的煤型烃源岩的生烃灶,主要沿北部坳陷北缘、中央坳陷南缘和北缘呈串珠状分布;北部坳陷北缘的煤型烃源岩的成熟度低,未进入大量生气阶段;中央坳陷南缘和北缘的煤型烃源岩均已成熟,且已进入大量生气阶段;每个(扇)三角洲发育的煤系烃源岩及其周边的陆源海相泥岩均为1个富气生烃灶。受渐新世煤型烃源岩的生烃灶控制,形成了中央坳陷南缘和北缘2个大型气聚集带;气聚集带中的凸起、断阶带、缓坡带、凹中浊积体等圈闭是煤型天然气的主要勘探领域,勘探前景巨大,天然气资源量预计超过2×10^(12)m^(3)。

In China,Qiongdongnan Basin is the only place where large coal type gas fields have been discovered in shallow water,deep water,and ultra-deep water areas.Therefore,it is of important theoretical and practical significance to explore the geological characteristics of natural gas and new exploration fields in the basin.Based on regional geological,seismic,drilling,and geochemical testing,the paper analyzes the accumulation characteristics and exploration potentials of Qiongdongnan Basin.The results indicate that a tectonic framework of"two uplifts and two subbasins"was formed during the deposition period of Yacheng Formation in Qiongdongnan Basin.The coal-type source rocks(including coal-measure source rocks and terrestrial marine source rocks)of Yacheng Formation are the major source rocks,and the source kitchen of coal-type source rocks in the(fan)delta of the Oligocene Yacheng Formation mainly shows a bead-like distribution along the northern margin of the northern depression,the southern and northern margins of the central depression belt.The maturity of coal-type source rocks in the northern margin of the northern depression is low and has not come up to the main gas generation stage.The coal-type source rocks at the southern and northern margins of the central depression belt are mature and have entered the main gas generation stage.Coal-measure source rocks and the surrounding terrestrial marine mudstones developed in each(fan)delta are one source kitchen.As controlled by the source kitchen of the Oligocene coal-type source rocks,two large gas accumulation belts were formed at the southern and northern margins of the central depression belt.The main exploration areas for coal-type natural gas include uplifts,step-fault belts,gentle slope belts,and turbidite bodies inside sags in the gas accumulation belt,showing great exploration prospects,and the natural gas resources are expected to exceed 2×10^(12)m^(3).