碱山构造新近系气藏特征及天然气聚集主控因素

Characteristics and major controlling factors of the Neogene low-efficiency gas reservoirs in the Jianshan structure

碱山构造位于柴达木盆地一里坪坳陷西端,其天然气储集层主要分布于新近系下油砂山组、上干柴沟组和古近系下干柴沟组下段上部,具有含气井段长、储层物性差、气层产能低且气水同出的特点。综合利用地震、岩心观察及室内镜下鉴定、铸体薄片、扫描电镜和测井解释等方法,对控制碱山构造新近系天然气聚集的主控因素进行了分析。结果表明:烃源岩有机质丰度偏低是碱山构造新近系天然气不能形成规模聚集的根本原因,但存在溶解气以及低产气层;后期构造运动产生的断层、裂缝对碱山气藏的破坏以及新近系储集层条件较差,是碱山构造新近系天然气不能形成规模聚集的直接原因。

The Jianshan structure is located at the western end of Liping depression in the Qaidam Basin,where gas reservoirs are mainly distributed in the Neogene Xiayoushashan Fm,the Shangganchaigou Fm and the Paleogene Upper Xiaganchaigou Fm.The gas reservoirs here are featured by long gas-bearing interval,poor poroperm characteristics,low deliverability,and gas-water co-production.Various methods,including seismic interpretation,core observation,microscopic identification,cast thin section observation,electron microscopic scanning,well log interpretation,etc.are integrated to analyze the major factors controlling gas accumulation in the Neogene period in the Jianshan structure.The following results are obtained.The low abundance of organic matter in the source rocks is the fundamental factor preventing large-scale accumulation of gas in the Neogene period in the Jianshan structure.However,dissolution gas and low-productivity gas pay-zones occur in the study area.Moreover,the faults and fractures resulted from the late tectonic movement and the poor poroperm characteristics of the Neogene reservoirs directly lead to the result of no large scale gas accumulation in the Neogene period in the Jianshan structure.