南海北部陆缘声浑浊体成因机制及地震响应特征

Genetic mechanism and seismic response characteristics of acoustic turbidites in the northern margin of the South China Sea

南海北部大陆边缘发育多个裂谷盆地,地震资料表明各盆地中均发育有反射成像模糊的声浑浊体,但这些模糊体地质类型不一,对油气成藏影响迥异。为弄清该区声浑浊体的地质类型及分布特征,总结了地震资料上模糊带的地震响应特征,结合各类地质异常体形成机制及演化规律,进行了地震相类比分析,并对异常体进行了三维可视化表征,在此基础上探讨了触发机制及对油气成藏的地质意义。研究认为,这些模糊带主要由泥底辟、泥火山、气烟囱、岩浆底辟、火山、潜山、礁、浅层气等地质现象所引起,这些模糊体在平面分布上具有成群成带、分布宽泛的赋存特征,底侵作用形成的异常体在盆地中央的沉积中心附近其单体发育规模大,往盆缘方向强度变小;结合钻孔资料分析,泥底辟、气烟囱是有利的油气渗漏系统,是油气运移活跃的有力指示,可作为有利油气富集区判断的依据。

Rift basins have been developed in the northern continental margin of the South China Sea.Seismic data shows that acoustic turbidites with fuzzy reflection and imaging are developed in these basins,which have different geological types and exert different effects on hydrocarbon accumulation.In order to make clear the geological types and distribution characteristics of acoustic turbidites in this area,we summarized the seismic response characteristics of the fuzzy belt in seismic data,conducted analogical analysis on seismic facies according to the formation mechanism and evolution law of various geological abnormal bodies,and carried out three-dimensional visual representation of abnormal bodies,based on which we studies the triggering mechanism and its geological significance for hydrocarbon accumulation.The study shows that these fuzzy belts are mainly caused by geological phenomena such as mud diapir,mud volcano,gas chimney,magma diapir,volcano,buried hill,reef,shallow gas,etc.The planar distribution of these fuzzy bodies shows the characteristics of zonation in groups and wide range.As for anomalous bodies formed by underplating,single body with large scale can be developed near the depocenter in the basin center,and its strength reduced towards the basin margin.After analyzing along with drilling data,mud diapir and gas chimney are the favorable oil-gas leakage systems and the powerful indication of active hydrocarbon migration,which can be taken as a basis in judging favorable oil and gas accumulation area.