南祁连盆地哈拉湖坳陷青徳地2井三叠系天然气水合物储层特征及其意义

Characteristics and significance of natural gas hydrate reservoir of Triassic in well QH-2 in Harlahu Depression of Southern Qilian Basin

哈拉湖地区目前基本属于地质空白区,有关天然气水合物形成及分布的研究较少,尤其针对该地区天然气水合物储层研究与认识较为有限。青徳地2井(QH-2)位于南祁连盆地哈拉湖坳陷西部,为坳陷内首口天然气水合物调查深井,钻遇第四系、新近系—古近系和三叠系。以青徳地2井三叠系主要储集岩层段岩心为研究对象,通过岩石薄片观察以及孔隙度、渗透率、密度、铸体薄片等物性测试,结合测井资料开展哈拉湖坳陷储层特征研究,结果表明:青德地2井三叠系储层分布较广,厚度巨大,但储集性能整体较差,绝大部分属非常规储集层,且整体裂隙较不发育,较难形成类似木里地区固结岩层中的裂隙型水合物及孔隙型水合物,而该区冻土层下存在厚层第四系松散沉积物及裂隙相对发育的古近系—新近系,可为天然气水合物形成提供良好的储集空间。

Harlahu Depression is basically a geological blank area now.Few studies on the formation and distribution of natural gas hydrate have been published,especially the research and understanding of natural gas hydrate reservoir in this area.The borehole QH-2 is located in the western part of Harlahu Depression of South Qilian Basin,and it was the first deep drilling hole for natural gas hydrate investigation in this area,in which Quaternary,Neogene—Paleogene and Triassic strata were drilled.The authors took the core of Triassic reservoir in well QH-2 as the research object to study the reservoir characteristics of Harlahu Depression,through the thin section observation of rock,porosity,permeability,rock density,casting thin section and other physical property tests,as well as the logging data.The research shows that Triassic reservoir of well QH-2 is widely distributed with great thickness.However,the physical property of the reservoir is poor,and most parts of the reservoir were unconventional reservoirs.The fractures are not developed,so it is difficult to form fracture type hydrate and pore type hydrate in the consolidated rock stratum similar to Muli area.While,the thick Quaternary loose sediments and Tertiary strata with relatively developed fissures were developed under the permafrost regions in this area,which may provide a better reservoir space for the formation of natural gas hydrate.