鄂尔多斯盆地东北部上古生界太原组及下石盒子组碎屑岩储集层特征

Characteristics of clastic reservoir of the Upper Paleozoic Taiyuan and Xiashihezi Formations in northeastern Ordos Basin

鄂尔多斯盆地东北部上古生界太原组及下石盒子组是该区天然气的主力储集层。应用偏光显微镜、环境扫描电镜、恒压压汞以及近几年来发展起来的恒速压汞技术,对该地区上古生界太原组及下石盒子组储集层进行了研究。研究区储集层岩性以粗粒、巨—粗粒岩屑石英砂岩为主,石英砂岩、岩屑砂岩为次。由于成岩作用强烈,残余原生粒间孔基本全部丧失。由于煤系地层提供的大量有机酸以及丰富的可溶性组分,太原组形成了以溶孔为主的储集空间类型,下石盒子组则主要以高岭石晶间微孔为主。太原组及下石盒子组储集层孔隙结构差别巨大,太原组储集层孔径大、孔喉比大,而下石盒子组储集层孔径小,孔喉比接近于1:1,属于较差的孔喉配置。

The Upper Paleozoic Taiyuan and Xiashihezi Formations are the dominant reservoirs in the northeastern Ordos Basin. By means of microscope,ESEM,constant-pressure mercury penetration and constant-speed mercury penetration,the reservoir of the Taiyuan and Xiashihezi Formations in northeastern Ordos Basin has been studied in this paper.And it is shown that quartz sandstone and debris sandstone give priority to coarse grain sandstone and boulder-coarse debris quartz sandstone.Owing to the intense diagenesis,most residual primary pores were lost. Coal measure strata offers abundant organic acid and resoluble component. All these elements control the characteristics of the Taiyuan Formation reservoir in which dissolved pore commonly exists.Differently,the Xiashihezi Formation reservoir is characterized by kaolinite intercrystalline micropore.Based on the constant-speed mercury penetration test,it is shown that the pore texture of the Taiyuan and Xiashihezi reservoir is quite different. Compared with the Xiashihezi Formation,the Taiyuan Formation reservoir has larger pore diameter and higher ratio of pore throat,which builds up a favorable pore throat pattern.