四川盆地下寒武统豹斑灰岩成因机理及其对储层的影响

doi:10.11743/ogg20170413

摘要/Abstract

摘要： 豹斑灰岩（云岩）的广泛发育引起了地质学者的关注，目前其成因机理存在很大争议，因此研究豹斑灰岩（云岩）的特征、成因，以及与储层的关系，对于油气勘探具有重要意义。通过对4条基干剖面豹斑发育层段的宏观沉积相分析和镜下描述，结合X-射线衍射分析、扫描电镜、电子探针和同位素等分析手段，详细解剖了四川盆地下寒武统龙王庙组和天河板组豹斑灰岩的岩相及地球化学特征，并探讨了其成因机理。四川盆地下寒武统豹斑发育的基质灰岩主要有（含颗粒）泥微晶灰岩和砂屑亮晶灰岩，不同基质灰岩内的豹斑在斑块形态、泥质含量、白云石大小晶形方面具有较大差异，故可将豹斑分为3类：泥质云斑、含泥云斑和云斑。泥质云斑和含泥云斑主要发育于（含颗粒）泥微晶灰岩中，云斑内部由他形至半自形的泥粉晶白云石晶体组成；云斑主要发育于砂屑亮晶灰岩中，内部由自形-半自形粉细晶（部分中粗晶）白云石组成。（含颗粒）泥微晶灰岩的豹斑灰岩形成于海侵期潮下浅水低能环境，是交替沉积的灰泥质和云泥质软泥受后期风浪扰动或负载压实，再经历埋藏改造，形成纵向上具有韵律特征的云斑。亮晶砂屑灰岩的豹斑主要形成于浅埋藏期，与富镁高盐地层水沿孔渗较好的部位渗透至固结成岩地层中发生渗透回流白云化有关。豹斑内部粉细晶白云石的晶间孔十分发育，该类灰岩能否形成优质储层受控于豹斑在全岩中的含量。

关键词: 选择性白云化, 豹斑灰岩, 龙王庙组, 下寒武统, 四川盆地

Abstract: Wide occurrence of leopard-pattern limestones (dolostone) has aroused extensive attention of scholars,but origin of this type of rock remains disputable.So a study on its features,origin,and impact on reservoir properties is significant to petroleum exploration.Four reference cross sections were chosen in the Lower Cambrian Longwangmiao Formation and Tianheban Formation in the Sichuan Basin to analyze petrologic and geochemistry characteristics.Based on outcrop sedimentary facies study,microscopic observation,X-ray diffraction analysis,scanning electron microscopic observation,electron probe microanalysis,and stable isotope analysis,the origin of the limestone was discussed.Leopard pattern limestone occurs mainly in two types of rocks in the Lower Cambrian sediments in the Sichuan Basin:wackstone and packstone.According to their different features in patch morphology,clay content,dolomite size and crystal form,leopard pa-ttern limestone can be classified into three types:muddy leopard limestone,leopard limestone containing mud,and leopard limestone.The first two types mainly appear in wackstone,composed of muddy to silty,anhedral to semi-euhedral crystalline dolomite,while the third type of leopard pattern limestone occur in packstone,composed of silty to fine,semi-euhedral to euhedral crystalline dolomite.Leopard pattern limestone in wackstone deposited in subtidal environment with low water energy,lime mud and aragonite mud(transform to dolomite) deposited alternately in tune with the water body transform from open to restricted frequently due to sea level change.Leopard pattern are formed by wave disturbance and di-fferential load from overlying strata.Leopard pattern limestone in packstone was mainly formed during shallow burial stage,when formation water with high content of magnesium penetrated into the cemented sediments and dolomitization took place.Intercrystalline pore space is widely observed in leopard limestone,which shows much better reservoir properties than limestone,so the proportion of leopard pattern limestone to the whole rock determines the petrophysical properties of reservoir rocks.

Key words: selective dolomitization, leopard pattern limestone, Longwangmiao Formation, Lower Cambrian, Sichuan Basin

中图分类号:

TE122.2

韩波,冯菊芳,何治亮,等. 四川盆地下寒武统豹斑灰岩成因机理及其对储层的影响[J]. 石油与天然气地质, 2017, 38(4): 764-775,783. doi: 10.11743/ogg20170413 Han Bo,Feng Jufang,He Zhiliang,et al. Origin of the Lower Cambrian leopard-pattern limestones and its influence on reservoirs in the Sichuan Basin[J]. Oil & Gas Geology, 2017, 38(4): 764-775,783. doi: 10.11743/ogg20170413

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