神木气田石千峰组储层沉积微相与成岩作用

Study on sedimentary micro-facies and diageneses of Shiqianfeng Formation,Shenmu Gasfield,Northeastern Ordos Basin

神木气田上二叠统石千峰组千5段碎屑岩气藏是近年来发现的浅层气藏,具有一定的勘探开发潜力.为有助于千5段储层评价与预测,根据测井、录井、常规薄片、铸体薄片、物性、压汞、扫描电镜、X衍射和粒度资料,结合岩心描述,研究了神木气田千5段沉积相类型和成岩作用.认识到千5段砂岩粒度粗,成分和结构成熟度差—中等,大型交错层理发育,正粒序发育,属于干旱气候条件下的砂质曲流河沉积,砂体分布受边滩微相控制.成岩作用以压实、胶结和溶蚀为主,其中,绿泥石薄膜式胶结抑制石英或长石次生加大,伊蒙混层收缩形成的微裂隙,以及岩屑、长石和黑云母溶蚀均为建设性成岩作用;成岩作用阶段为早成岩B期到中成岩A期;成岩相可划分为5种类型,以绿泥石+硅质胶结粒间孔相、绿泥石+硅质胶结溶孔-粒间孔相和伊蒙混层胶结微裂隙相有利.储层孔隙以粒间孔为主,喉道以中、细喉为主,孔喉组合主要见中孔中喉、中孔细喉、低孔中喉和低孔细喉4种类型,属于中—低孔、中—特低渗透率储层.微裂隙显著改善了储层渗透率.

The fifth member (Q5) of the Upper Permian Shiqianfeng Formation in Shenmu Gasfield is been testified to be the recently found clastic gas reservoir of shallow burial depth,which has the potential of further exploration and development.The sedimentary micro-facies and the diageneses of Q5 are studied based on the data analysis of well logging,ordinary thin-section,cast thin-section,reservoir physical property,mercury-injection measurement,scanning electron microscope,X-ray diffraction and grain size measurement.It is held that Q5 is the deposit of sandy meandering rivers formed under the condition of dry climate,which shows the characteristics of coarse grain,low--moderate compositional and textural maturity,developed large-scale cross bedding and normal graded bed sequence.The distribution of sandbodies is controlled by the point bar microfacies of the meandering rivers.The sandstones principally undergone the diageneses of compaction,cementation and dissolution.Constructive diagenesis include:the filming cementation of chlorite restraining the secondary enlargement of quartz or feldspar and contributing to the reservation of primary intergrain pores,the contraction of illite-smectites mixed layer forming microfractures,and debris,feldspar and biotite dissolving.The diagenetic stage can be classified as from B period of early diagenesis to A period of middle diagenesis.Five diagenesis facies are discerned:the intergranular pore facies of chlorite--quartz cementation,the dissolution pore-intergranular pore facies of chlorite--quartz cementation,the microfracture facies of illite--smectite mixed layer cementation,the dissolution pore facies of siliceous cementation and the micropore facies of dense compaction.Of these,the first three are most favorable diagenesis facies.There are mainly intergrain pore and moderate--fine throat in reservoir.And there are four kinds of pore--throat assemblages:moderate pore--moderate throat,moderate pore--fine throat,low pore--moderate thoat and low pore--fine throat.The reservoir is of moderate--low porosity and moderate--super-low permeability.The microfracture improves the permeability of the reservoir.