准噶尔盆地克拉美丽气田滴西14井区石炭系蚀变凝灰岩储层热液作用过程及时限

Hydrothermal Process and Duration of Carboniferous Altered Tuff Reservoir in Well Dixi 14 Area of Kelameili Gas Field(Junggar Basin),NW China

为明确克拉美丽气田滴西地区石炭系蚀变熔结凝灰岩储层经历的流体作用及成岩孔隙演化过程,利用铸体薄片观察、扫描电镜、电子探针、阴极发光、荧光、微量/稀土元素分析及U-Pb同位素定年等方法技术开展综合研究.结果表明,火山碎屑物质的溶解及成岩转化为自生矿物的形成提供了物质基础;成岩过程中因埋藏、生烃、热液充注等活动而产生的成岩环境改变是控制区内孔隙形成及演化的重要因素:伴随着有机质的成熟,有机酸溶蚀形成大量晶屑铸模孔并在孔隙中沉淀出高岭石及石英;随着酸性流体向碱性转变,在溶蚀孔隙中沉淀出钠长石以及方解石,其充填作用使孔隙急剧减少;燕山中期(135±27 Ma)的构造热事件对储层形成及演化起到关键作用:高温、含硅热液流体的充注使基质中的伊利石转变为钾长石,同时二次溶解形成的Ca^(2+)与流体携带的P^(5+)、Ti^(4+)、F^(-)等离子结合形成含氟磷灰石、榍石充填孔隙,多余的SiO;则在孔隙中沉淀出石英.随着成岩环境再次向碱性、还原环境转变,含砷黄铁矿进一步在孔隙中形成,高岭石则进一步向绿泥石转化.温度升高引起的脱玻化、黏土矿物/沸石矿物转化、重结晶作用以及溶解作用在一定程度上增加了岩石中的次生储集空间,有利于油气的储集.

To decipher the fluid action and pore evolution in the Carboniferous altered tuff reservoir in Kelameili gas field(Junggar basin,Northwest China),the petrography and geochemistry were studied by core and thin section observation,scanning electron microscopy,electron probe,cathodoluminescence,fluorescence,rare elements and U-Pb isotope dating,etc..The results show that the pore filling minerals of reservoir in the well Dixi 14 area mainly include kaolinite,albite,quartz,chlorite,pyrite,apatite,and the pore types are mainly residual pores of feldspar(K-feldspar and plagioclase)by dissolution-infilling and intergranular pores of various authigenic minerals.Firstly,the dissolution of pyroclastic materials and the transformation of diagenetic materials were fundamental for the formation of authigenic mineral.A large number of mold pores in crystal pyroclast were formed by acid fluid dissolution and kaolinite and quartz were precipitated from pores.More importantly,diagenetic environment changes caused by burial,hydrocarbon generation,hydrothermal charging and other activities are significant for pore formation and evolution.Albite and calcite were precipitated in dissolved pores by the fluid transformation from acid to alkaline,and resulted in the rapidly decrease of pores.During Middle Yanshanian(135±27 Ma),the thermal events were critical for the formation and evolution of the reservoir.(1)The illite of matrix was transformed into K-feldspar by the recharge of high temperature and rich-silicon hydrothermal fluid.(2)Simultaneously,fluoapatite and titanite were precipitated by combination of P,Ti,F ions with Ca^(2+) ion that derived by secondary dissolution,and filled the pores.Quartz was precipitated in the pore by the oversaturation of SiO;fluid.Thereafter,arsenopyrite and chlorite were formed by the transformation of alkaline and redox condition in the process of burial diagenesis.Thus,devitrification caused by temperature elevation,mineral transformation from clay to zeolite,recrystallization and dissolution partly increased the secondary reservoir space,which is beneficial to the enrichment of hydrocarbon.