莺-琼盆地YA13-1气田成藏过程分析

根据埋藏史、热史恢复,运用有机地球化学指标和稳定碳同位素比值,判断出莺-琼盆地 YA13-1气田天然气的母质来自于以Ⅲ型干酪根为主的崖城-陵水组.有两个来源:一个是琼东南盆地崖南凹陷埋深在4450m以下的烃源岩,另一个是莺歌海盆地埋深在4700m以下的烃源岩.通过流体包裹体分析,确定出天然气以水溶相在5.8～2.0Ma和2.0Ma至现在期间发生两次高峰运聚.梅山组碳酸盐岩和钙质泥岩具7～10MPa的排替压力并发育有49～66MPa的异常超压,从而成为其有效盖层.陵水组储层因浅埋时间长,受大气淡水淋滤作用和有机酸对铝硅盐骨架颗粒和碳酸盐胶结物的溶解/沉淀,在后来的深埋过程中仍然保持平均14.9%的孔隙率和213×10^-3μm²的渗透率,披覆背斜的YA13-1圈闭形成于10.5Ma,远远早于天然气的运聚时间.从而在生、运、聚、保和圈闭、储-盖层演化诸方面奠定了在YA13-1地区形成我国迄今最大气田的必要条件.

NATURAL GASES REPLENISHMENT IN YA13-1 GAS FIELD IN YING-QIONG BASINS,SOUTH CHINA SEA

The gases in YA13-1 gas field in Ying-(along Basins mainly derived from the parent of type-Ⅲ kerogen in Yachen-Lingshui Fms,as indicated by the geochemical biomarkers,stable carbon isotope ratios and natural gas components.Measurements of fluid inclusion and restorations of the burial history and thermal history suggest that there are two sources for YA13-1 gas field:the first was from the source rocks buried beneath 4,450m in Yanan depression of Qiongdongnan Basin,the second was from the source rocks buried beneath 4,700m in Yinggehai Basin,two peak migration-accumulation ages in the range of 5.8-2.0Ma and 2.0Mapresent.The seal is Meishan Fm which has 7-10MPa expelling pressures and 49-66MPa overpressures to form an effective sealing far YA13-1 gas field.The reservoirs in Lingshui Fm has a good quality of averaged 14.9% porosity and 213×10^-3μm² permeability because of fresh water leaching and enhancement by dissolulion/precipitation of aluminosilicates and carbonate cements during the shallow burial stage.The trap of YA13-1 trape anticline formed at 10.5Ma that was much earlier than that of gas migration-accumulation.Therefore,a best match of generation,migration,accumulation with the trap formation occurred for YA13-1 petroleum system.