涟源凹陷流体包裹体特征与天然气成藏

CHARACTERISTICS OF FLUID INCLUSIONS AND FORMATION PROCESS OF NATURAL GAS RESERVOIRS IN LIANYUAN SAG

涟源凹陷属于典型的改造型盆地,是湘中坳陷最有利的含油气凹陷之一。应用流体包裹体分析技术,并结合盆地构造演化和圈闭发育史、烃源岩主要生、排烃史,对改造型盆地涟源凹陷主要目的层石炭系储层中流体包裹体特征及气藏形成时间和期次进行了分析。结果表明,研究区存在两种类型流体包裹体,第一类为单一液相或气/液比小于15%的气液两相盐水包裹体,第二类为气液两相含烃盐水包裹体,单一液相包裹体大小一般3～4μm,其它包裹体大小一般1～7μm;流体包裹体特征反映出该区气藏成藏期有两期,即第一期天然气注入时温度120.8～126.2℃,对应成藏时间为早三叠世,第二期天然气注入时温度154.4～169.7℃,对应成藏时间为晚三叠世,其中主要成藏期为晚三叠世。

Lianyuan sag is a kind of typical reformed basin, and is one of the best favorable oil ＆ gas sags in Xiangzhong depression. The characteristics of fluid inclusions and formation time of natural gas reservoirs in Carboniferous System, the principal hydrocarbon generation strata, in reformed basin-type Lianyuan sag, are studied based on fluid inclusions data in combination with age data for basin structure evolution, trap evolution, petroleum generation and expulsion from source rocks to reservoirs, and the results show that there are two types of fluid inclusions occurring in Lianyuan sag. One type of inclusions are brine inclusions, a kind of single liquid phase inclusions or twophase （gas-liquid） inclusions in which gas/liquid ratio is less than 15% , the other type are hydrocarbon-bearing brine inclusions, a kind of two-phase （gas-liquid） inclusions. The single liquid phase inclusions are commonly as big as 3 -4μm, while the other type of inclusions are generally as big as 1 -7μm; The characteristics of fluid inclusions in Lianyuan sag indicate that two episodes are involved in regard to formation time of gas reservoirs. The first episode for gas reservoir formation is early Triassic and the temperature ranges between 120.8 - 126.2℃ , the second episode for gas reservoir formation is late Triassic, which proves to be the principal episode for gas reservoir formation in Lianyuan sag, and the temperature ranges between 154.4 -169.7℃.