琼东南盆地超压系统泄压带:可能的天然气聚集场所

Discharging Zones of Overpressure System in Qiongdongnan Basin, Northern South China Sea: Implications for Favorable Sites of Natural Gas Accumulation

泄压带是超压系统内部流体向外运移的通道和有利的油气聚集场所,对水溶相天然气析离成藏更有着重要意义.本文综合应用速度谱、测井、钻井和地层测试等资料预测了琼东南盆地超压系统的分布,将其划分为3种结构类型;结合粘土分析等资料识别出了4种类型的泄压带,并讨论了泄压带的分布与可能的天然气聚集区带.琼东南盆地中央坳陷带整体发育一个超压系统,其分布格局主要受陆坡带的形成和莺歌海盆地超压传递的影响,陆坡区的超压明显强于非陆坡区,西部的超压整体强于东部并在浅部呈现自西向东传递的趋势.泄压带内的天然气成藏主要取决于压力、温度和溶解气量,需满足溶解气量足够多和溶解度变化量足够大,相对而言,Ⅱ型泄压带成藏条件最优,既有断裂沟通深部水溶气和浅部储层,又有温压条件的显著变化,因而流体运移最活跃.Ⅲ型泄压带次之,但分布最广,该类型最有利部位分布在陵水低凸起和宝岛凹陷北坡.

Discharging zones are channels for fluid to move out from inside the overpressure system and favorable sites for petroleum accu mulaion, wbach are o（ great signi（icance to the accumulation of water muble gas by exso[utior~ The overpressure system distribution of Oiongdongnan basin is predicted and divided into three types based on the comprehensive analysis of the velocity spectrum, bgging, drill- ing and formation test data. In addition, four types of discharging zones are identified according to the mineral analysis The distribution of discharging zones and possible sites for petroleum accumulation are finally discussed. There exists only one overpressure system which is effected by the development of continental slop system and the pressure trarrsfer from Yinggebai basin, the pressure along the slop beh is much stronger and the top surface of overpressure system in the west is shallower than that in the east. Accumulation of water soluble gas in the pressure discharging zones is tot＇ally determined by pressure, temperature and the amount of dismlved gas, and it is vital whether there is adequate amount of dissolved gas and sufficient changes in mlubility. The accumulation conditions of type II di^barging zone are the morn favorable one, resulting in more active fluid activitie~ The favorable sites of type III discharging zone are distributed near the Lingshui low uplift and the northern slop of Baodao ~g, along boundary faults and close to the normal pressure zone Key words： discharge zones; overpressure system; fluid migration; degasification; hydrocarbon accumulation; Qiongdongnan basin; petroleum geology.