南海北部陆坡区气烟囱的分布特征与成因机制

Distribution Characteristics and Genetic Mechanism of Gas Chimney at Slope Area,Northern South China Sea

气烟囱是地壳深部流体刺穿上部地层运移至浅层而形成的流体底辟构造。目前针对南海北部陆坡区的气烟囱研究仅限于地震反射特征和单一的成因分析。基于三维地震资料,旨在揭示白云凹陷内气烟囱的分布特征与多重成因机制。南海北部陆坡区下切水道密集分布,古水道充填砂体粒径粗、孔隙大,为陆坡低压区,是研究区域内气烟囱的泄压指向。根据气体来源,研究区内气烟囱主要有深部泥岩底辟成因和火山作用伴生成因两种类型。前者气体主要源于文昌—恩平组泥岩,超高压和构造活动是其诱发条件;后者远离烃源岩发育区,气体源于火山溢出,火山反复侵入是其主要形成条件。

Gas chimney is a fluid diapir formed by fluid at deep crust piercing upper formation and then migrating to shallow layers.At present, the research on gas chimney at slope area in the northern South China Sea is restricted to seismic reflection characteristics and single origin analysis. Based on 3D seismic data, its distribution characteristics and multiple genetic mechanism in Baiyun depression are revealed. Some incised paleochannels densely at the slope area are filled by sandbody which is characterized by coarse particle size, big pore size. This is a low-pressure region, also the pressure-relief instruction of gas chimney. According to gas origin,there are two genetic types of gas chimney in the study area, i.e.deep mudstone diapir and associated by volcanism. Gas of the former originated mainly from Wenchang- Enping formation mudstones, induced by ultra- high pressure and tectonic activity; far away from the development zone of source rock, gas of the latter was originated by the overflow of volcanoes with multiple intrusions.