苏北盆地黄桥地区富CO_2流体对二叠系龙潭组砂岩储层的改造与意义

The interaction of CO_2-rich fluid with sandstone and its significance for sandstone reservoirs of Permian Longtan Formation in Huangqiao area, Subei Basin

富CO_2流体-砂岩相互作用是砂岩储层次生孔隙的重要形成机制。苏北黄桥地区作为中国重要的CO_2气产区,富CO_2流体对上二叠统龙潭组砂岩储层的改造问题备受关注。为揭示富CO_2流体的作用特征及其对储层的影响,对黄桥地区典型钻井开展了系统的岩心描述和岩矿鉴定,并进行了微区原位观测和相关地球化学分析。结果表明,在靠近CO_2流体活动强烈的断裂带部位(特别是断层上盘),砂岩中碳酸盐胶结物基本溶蚀殆尽,仅存少量交代成因菱铁矿,同时钾长石类碎屑溶蚀非常强烈,并伴随高岭石等矿物沉淀,以及石英次生加大,还发育片钠铝石等指示高浓度CO_2作用的特征矿物,形成与CO_2流体作用相关的特征矿物组合(片钠铝石+高岭石+次生石英+菱铁矿);而在远离断裂的部位,受CO_2流体影响较弱,溶蚀作用也较弱,有较多的次生方解石沉淀,形成了以方解石+菱铁矿为主的自生矿物组合。前者次生孔隙发育,后者则更加致密。据此提出了深源断裂主控下与富CO_2流体作用相关的储层发育模式,为油气勘探和开发提供了新的思路。

The interaction between CO2-rich fluid and sandstone is the main factor for forming secondary porosity in sandstone res-ervoirs.As an important CO2 production area in China,the problem about the sandstone reformation by CO2-rich fluid in Permian Longtan Formation has attracted much attention.To reveal the interaction feature of the CO2-rich fluid and its influence on sand-stone reservoirs,the authors carried out systematic core description and micro-observation on typical coring wells as well as in-situ observation and major element analysis based on EPMA.The results show that carbonate cements in sandstone near the fracture zone have been almost completely dissolved with some displacement siderite left,especially in the upper wall where the CO2-rich fluid in-flux is active.Meanwhile,the dissolution of clastic grains such as K-feldspar is strong,and there are much kaolinite precipitation,quartz secondary enlargement and dawsonite,which indicates effects of high concentration of CO2.There exists the combination of typical minerals related to the CO2-rich fluid including dawsonite,kaolinite,secondary quartz and siderite.In the area away from faults where the CO2-rich fluid has relatively insignificant effects,the dissolution is weak and much calcite and siderite precipitated on the contrary.As for the former,reservoir has better secondary porosity,while for the latter the reservoir is much tighter.On such a basis,the genetic mode related to the interaction between CO2-rich fluid and sandstone as well as its effects on the objective reser-voir is set up in consideration of the fact that the deep faults play the main role in the sandstone reservoir improving.This viewpoint offers a new view angle for petroleum exploration and development.