摘要
尖北斜坡为柴达木盆地阿尔金山前东段天然气勘探重点区域之一，目前针对该区域基岩储层发育特征和成藏条件的分析研究尚很薄弱。在岩心观察、薄片鉴定的基础上，结合常量元素分析、XRD、SEM、压汞测试和井震资料分析，对柴达木盆地尖北斜坡基岩储层的发育特征及天然气成藏的有利地质条件进行了研究。结果表明，尖北斜坡基岩储层岩石类型主要为花岗闪长岩、花岗岩和片岩；发育风化壳型储层，其中半风化层孔渗物性最好；储集空间为基质微孔、溶蚀孔和裂缝，储层孔隙度主要分布在2.23%~3.77%，渗透率均值为0.06×10 μm，以Ⅱ类中等储层为主；基岩储层临近坪东以西侏罗系生烃凹陷，天然气自生烃凹陷沿基岩基底发育的深大断裂和不整合发生运移，经基岩顶部古近纪咸湖环境下形成的膏泥岩有效封堵，最终在更新世晚期形成的断背斜圈闭内富集成藏，发育基岩顶部风化壳型气藏。该研究成果对指导尖北斜坡基岩气藏下一步勘探具有重要的指导意义。
Abstract
Jianbei slope is one of the key areas for natural gas exploration in the eastern segment of the Altun Piedmont, Qaidam Basin, but the analysis of developing characteristics and gas accumulation conditions of the basement reservoirs in this area is still rarely seen.Based on observation of cores and thin sections, combined with major element analysis, XRD, SEM, MIP(mercury intrusion porosimetry)and log-seismic data analysis, we analyzed the developing characteristics of basement reservoirs and the favorable conditions for natural gas accumulation in Jianbei slope, Qaidam Basin.The results show that the basement reservoirs in the study area are dominated by granodiorite, granite and schist.The reservoirs of weathering crust type are developed there, with the semi-weathering crust reservoirs being the best in porosity and per-meability.The reservoir space is mainly matrix micropores, dissolved pores and cracks, with a reservoir porosity ranging between 2.23% and 3.77% and an average permeability of 0.06mD.So the reservoirs are mainly Type Ⅱ reservoirs of medium permeability.The distribution area of the basement reservoirs is adjacent to the Jurassic hydrocarbon kitchen to the west of Pingdong area.The natural gas generated in the kitchen migrated along the well-developed deep-rooted large faults and unconformities at the bottom of basement; then got effectively sealed by the gypsiferous mudstones deposited under the Paleogene saline lacustrine environment on the basement top; and ultimately got accumulated in the faulted anticline trap formed during the Late Pleistocene, resulting in the formation of weathering crust gas reservoir on the basement top.In all, the research results are of instructional significance to further exploration of basement gas reservoirs in Jianbei slope, Qaidam Basin.
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