莺歌海盆地泥底辟热流体上侵活动与天然气及CO_2运聚规律剖析

ANALYSIS ON THE UPINTRUSION OF THERMAL FLUID AND THE MIGRATION AND ACCUMULATION RULES OF NATURAL GAS AND CO_2 IN THE MUD DIAPIRS OF THE YINGGEHAI BASIN

莺歌海盆地属南海北部被动大陆边缘新生代高热盆地,其高地温场及高大地热流主要集中于盆地中部莺歌海坳陷泥底辟构造带,因此泥底辟热流体上侵活动,尤其是晚期泥底辟热流体活动控制了天然气及CO2的运聚富集规律。同时,由于热流体分区、分块与分层的局部性侵入,导致了壳源型CO2及烃类气运聚富集的差异性和分区、分块与分层的局部富集特点。总之,泥底辟热流体上侵活动是控制天然气及CO2运聚成藏的主控因素。根据CO2与烃类气的地化特征及其控制因素,可以分析和预测其运聚规律,为天然气勘探提供决策依据。

The Yinggehai Basin is a Cenozoic high-heat basin developed on the passive continental margin of the northern part of the South China Sea. Its high geotemperature field and high geothermal flux are mainly concentrated in the mud-diapir structural zone of the Yinggehai Depression in the central part of the basin. So, the upintrusion of thermal fluid in the mud diapirs, especially the thermal fluid action in the late stage controlled the migration, accumulation and enrichment rules of natural gas and CO_2. Meanwhile, the local intrusion of thermal fluid by different layers, different blocks and different districts resulted in the migration, accumulation and enrichment differences of crust-sourced CO_2 and hydrocarbon gases and the characters of local enrichment by different layers, different blocks and different districts. In a word, the upintrusion of thermal fluid in the mud diapirs was the key factor controlling the migration and accumulation of natural gas and CO_2. According to the geochemical characteristics of CO_2 and hydrocarbon gases and their controlling factors, the migration and accumulation rules of CO_2 and hydrocarbon gases can be analysed and predicted. This will provide decision basis for the exploration of natural gas.