珠—琼盆地新生界火山岩特征及其油气地质意义

Cenozoic volcanic rocks in the Pearl River Mouth and Southeast Hainan Basins of South China Sea and their implications for petroleum geology

采用钻井、重力、磁力、地震相结合的方法,对南海北部珠江口和琼东南盆地新生界火山岩进行识别,并对其岩性、分布特征及火山活动对油气成藏的影响进行了分析。共识别出新生界火山岩体70余个,主要包括两种类型:①夹于新生界沉积层序之中的火山熔岩和火山碎屑岩,主要为层状;②新生界沉积层下伏的刚性基底玄武岩,主要为锥状、丘状和楔状。新生代早期(E1—2)主要发育酸性、中性、基性火山岩,新生代中晚期(E3—Q)主要发育单一的基性岩,规模大。火山岩相主要发育喷溢相下部亚相、喷溢相中部亚相和爆发相热碎屑流亚相。空间展布上,由琼东南盆地至珠江口盆地,火山活动逐渐增强;由浅水区至中央海盆,火山岩体规模增大,时代逐渐变新。新生代火山活动提高了地层温度,降低了生烃门限深度,促进了油气成藏。文昌组(E2w)—珠江组(N1z)火山岩具有油气成藏的有利条件,在深层勘探中应给予重视。

Drilling, gravity, magnetic observation and seismic facies are combined to identify the Cenozoic volcanic rocks in the Pearl River Mouth Basin and the Southeast Hainan Basin in the northern South China Sea, and to analyze how their lithology, distribution characteristics and volcanic activity influence on hydrocarbon accumulation. As a result, more than 70 volcanic bodies are ascertained. They are divided into two types： （1） laminated lava and pyroclastic rocks in the Cenozoic sedimentary sequence; and （2） conoid, mounded or wedged basalt with rigid basement under the Cenozoic sedimentary sequence. In the early Cenozoic （El-E2）, the acidic, neutral and basic volcanic rocks developed, while in the mid-late Cenozoic （E3-Q）, single basic rocks existed intensively. The volcanic lithofacies mainly include the lower and middle effusive subfacies and the pyroclastic flow explosive subfacies. Spatially, from the Southeast Hainan Basin to the Pearl River Mouth Basin, the Cenozoic volcanic activity gradually enhances; from shallow water area to the central basin in the South China Sea, the scale of Cenozoic volcanic rocks increases gradually, and the age tends to be younger. These activities improve the formation temperature, reduce the hydrocarbon generation threshold, and promote the hydrocarbon accumulation. Volcanic rocks in Wenchang Formation （E2w） to Zhujiang Formation （Nl2） provide favorable conditions for hydrocarbon accumulation, so they are important targets in the deep exploration.