准噶尔盆地西泉地区石炭系火山熔岩油气储层特征及成岩演化过程研究

Oil and gas resevoir characteristics and petrogenetic evolution of the Carboniferous volcanic lava in Xiquan area,Junggar Basin

火山熔岩油气藏是准噶尔盆地油气勘探和开发的重要目标之一。通过对准噶尔盆地西泉地区16口石炭系火山熔岩井的岩心观察、普通薄片和铸体薄片镜下鉴定和定量统计、扫描电镜和X-射线衍射等实验,研究玄武岩、安山岩、英安岩的岩石学特征、孔隙类型及储集特征及异同点,建立火山熔岩成岩演化序列,探讨成岩作用对火山熔岩孔隙演化的影响。研究表明,安山岩的储集空间最发育,孔隙类型及组合多样,多为气孔+斑晶溶孔+基质溶孔+溶蚀缝组合和气孔+斑晶溶孔+基质溶孔+溶蚀缝+构造裂缝组合。英安岩的孔隙组合为气孔+斑晶溶孔+基质溶孔和气孔+斑晶溶孔+基质溶孔+溶蚀缝。玄武岩孔隙类型及组合单一,为构造裂缝+溶蚀缝,构造裂缝+基质溶孔,气孔+溶蚀缝。挥发分逸出作用控制火山熔岩原生气孔的发育,岩浆期后热液作用和充填作用破坏了火山熔岩的储集空间,溶蚀作用、风化淋滤作用和构造破裂作用极大地改善了火山熔岩的储集性能。认为西泉地区石炭系顶部风化剥蚀淋滤带(距石炭系顶面0~20 m)的安山岩是油气聚集的最有利层段。

Junggar Basin is an important area for the exploration and development of volcanic lava in western China.16 volcanic lava wells were selected for core observation,ordinary thin-section and cast thin-section identification and quantitative statistic analysis under microscope,scanning electron microscopy and X-ray diffraction experiments to study petrological characteristics,pore types,combination characteristics,similarities and differences of basalt,andesite and dacite which are characterized by relative lack of research data on the characteristics of the volcanic lava reservoirs and petrogenetic evolution processes in the Xiquan area,eastern Junggar Basin.Besides,diagenetic evolutionary sequence of volcanic lavas was built and the influence of diagenesis on the pore evolution of volcanic lava was explored.The results show that andesite has a large reservoir space,and its pore types and pore combinations are complex and diverse,which include stoma+phenocryst solution pore+matrix solution pore+dissolution fracture combination,and stoma+phenocryst solution pore+matrix solution pore+dissolution fracture+structural fracture combination.Pore types and combinations of dacite are stoma+phenocryst solution pore+matrix solution pore and stoma+phenocryst solution pore+matrix solution pore+dissolution fracture.Pore types and combinations of basalt are simple,which include structural fracture+dissolution fracture combination,structural fracture+matrix solution pore combination,and stoma+dissolution fracture combination.Volatilization controls the development of original gas hole in volcanic lava.Dissolution,weathering,leaching,and tectonic fracture have greatly improved the reservoir performance of volcanic lava.Post-magmatic hydrothermal and filling have destroyed the reservoir space of volcanic lava.Overall,it is considered that andesite in the weathering and erosion-leaching belt at the top of the Carboniferous in Xiquan area(0−20 m from the top of the Carboniferous)is the most advantageous segment of hydrocarbon accumulation.