应用有机包裹体研究天然气成藏特征——以鄂尔多斯盆地苏里格气田西部山1段为例

通过对苏里格气田西部山1段成岩作用及成岩序列研究,利用有机包裹体岩相学观察和流体包裹体测试析技术,探讨苏里格气田西部山1段天然气成藏特征。研究表明苏里格气田西部山1段成岩作用主要有压实和压溶作用、胶结作用、石英次生加大作用、溶蚀和裂隙作用等。依据有机包裹体分布特征和包裹体物理相态特征可以识别出特征明显的2期包裹体。第一期油气包裹体主要相态为气态烃+盐水、气态烃+液态烃+盐水和气态烃+液态烃,气/液比较小,多呈串珠状定向分布在裂隙中,均一温度相对较低,温度主峰为120℃,代表了早期天然气充注作用,天然气开始形成并初次运移进入储层。第二期油气包裹体主要为纯气相和气态烃+少量盐水,气/液比较大,主要分布在溶蚀孔隙和晚期裂隙中,均一温度相对高,温度主峰为150℃,该期包裹体代表了生气高峰期天然气大规模运移成藏事件,也是研究区最重要的成藏事件。利用Tt曲线方法研究表明,苏里格西部地区山1段天然气开始运移进入储层的时间大约为170Ma(相当于中晚侏罗世),天然气规模成藏时间约为120Ma(相当于早白垩世晚期)。

Application of Organic Fluid Inclusion to Study the Characteristics of Gas Reservoir Formation: Example from the Sulige Gas Field in Western Ordos Basin

After studying the diagenesis sequence about the sandstone gas bed of the Sulige gas field in Western Ordos Basin, the petrography of organic fluid inclusions has been studied through carrying out petrographical observation and fluid inclusion microthermometry under microscope, the homogenization temperatures and salinities of these organic fluid inclusion shave been analyzed, and the formation characteristics of gas reservoir in the Sulige gas field have been discussed in this paper. Results indicate that the sandstone of gas bed had experienced diagenesis of compaction, pressolution, cementation, quartz secondary increase, dissolution and fracturing.According to the distribution characteristics and the physical phase state of organic fluid inclusions, two stages organic fluid inclusions have been identified by microscopeob servation. The first stage organic fluid inclusions mainly are oil/gas inclusions, which are featured with main phases, including gaseous hydrocarbon and brine, gaseous hydrocarbon and liquid hydrocarbon together with brine or gaseous hydrocarbon and liquid hydrocarbon.For the first stage organic fluid inclusions, their volumes of bubble are relatively small, and their homogenization temperatures are relatively low with the main peak around 120℃.These features of first stage organic fluid inclusions represent the formation and initial migration into reservoir of natural gas at early stage.The second stage organic fluid inclusions are characterized with mainly pure gas phase, with a small amount of brine. For the second stage organic fluid inclusions, their volumes of bubble are relatively big, and their homogenization temperatures are relatively high with the main peak around 150℃.The second organic fluid inclusionsare mainly distributed in the dissolution pores or filled in cracks.The second stage organic fluid inclusions stand for the gas formationpeak and large scale migration and accumulation, representing the most important reservoir formation event in this studying area. The T-t curve of chronology shows that the gas initially migrated into reservoir of natural gas since about 170Ma(Middle-Late Jurassic) and the gas accumulated peak happened at about 120Ma (late period of Early Cretaceous).