摘要
近年在四川盆地开江-梁平海槽周缘下三叠统飞仙关组的勘探开发中,已发现普光、七里北、龙门等气田,获探明储量6316×108m3,展现出较大勘探潜力,其中储集层段主要为鲕滩相白云岩储层。为探讨该区域白云石化作用及其对储层发育的控制,本文以薄片观察及连井剖面对比等手段为基础,结合阴极发光、微区原位主微量元素、锶同位素及流体包裹体分析,对研究区白云石的类型、分布、形成机制及白云岩储层的孔隙演化进行了讨论。川东大竹—开江地区飞仙关组二段岩石类型主要有泥晶灰岩、颗粒灰岩及白云岩;白云岩主要包括残余颗粒白云岩和晶粒白云岩,过渡岩类如云质颗粒灰岩同样较为常见,而颗粒灰岩和白云岩的发育及分布主要受沉积相带控制。在飞一段沉积晚期—飞二段沉积早期,研究区西南部沙坪场构造一带为开阔台地沉积,鲕粒滩呈点状分布且白云石化程度相对较弱;随着飞二段沉积中晚期鲕粒滩向海槽方向的进积作用,形成滩后或滩间的局限环境,双家坝-龙门构造一带鲕粒滩白云石化作用增强,形成了分布范围广、厚度大的白云岩发育区。区内白云石在阴极射线下为暗红光—不发光,为同生—准同生期高盐度卤水渗透回流交代下的产物。云化流体主要为飞仙关组同期海水,部分形成于相对低能环境的白云岩云化流体是海水与大气淡水的混合流体,但仍以海水为主且不是白云石化流体的主要来源。Mg2+主要由飞二段沉积早期鲕粒滩的垂向加积作用形成的滩后灰质潟湖以及飞二段沉积中—晚期鲕粒滩加积及进积作用所形成的膏质潟湖和云质潟湖等局限环境提供。研究区飞仙关组二段储集岩中主要的储集空间为粒间孔、铸模孔及晶间孔等孔隙,裂缝不发育。结合成岩及孔隙演化序列以及流体包裹体的分析认为,孔隙发育与白云岩分布有较好的一致性,白云石一定程度上增加了储集岩的抗压实性,其晶间孔为烃类的充注提供了储集空间,因此白云石化作用为储层的发育提供了良好的基础。该地区飞二段储集岩中识别出液态烃及天然气充注,说明至少存在两期油气成藏,而孔隙发育与油气充注同样具有较好的耦合关系。
The Northern Qili and Longmen gas fields,with proven reserves of 6316×10~8 m~3 and great exploration potential,have been discovered the recent exploration of the Lower Triassic Feixianguan Formation around Kaijiang-Liangping trough in Sichuan basin,Puguang.The reservoir interval is mainly composed of dolomites from oolitic shoal.To explore the regional dolomitization and its control over the reservoir development,this paper analyzes the types,distribution,formation mechanism of dolomites and the pore evolution of the dolomite reservoirs in the study area based on thin section observations,well-tie correlation combined with cathodoluminescence,in-situ LA-ICP-MS major and trace elements strontium isotope and fluid inclusion analyses.The rock types of the second member of the Feixianguan Formation in the Dazhu-Kaijiang area of eastern Sichuan basin mainly include micritic limestone,grainstone and dolomite which mainly includes residual granular dolomite and crystalline dolomite,and transitional rocks such as dolomitic granular limestone are also common.The development and distribution of granular limestone and dolomite are mainly controlled by sedimentary facies.In the interval from the late stage of the first member of the Feixianguan deposition to the early stage of the second member,the southwest region of the study area like Shapingchang structure was an open platform facies deposit,and the oolitic shoals are sporadic,the degree of dolomitization is also weak.With the progradation and aggradation of the oolitic shoals in the middle to late stage of the second member of the Feixianguan Formation,a restricted environment is formed between or behind the oolitic shoals.As a result,the degree of dolomitization in the oolitic shoals in the Shuangjiaba-Longmen structure is enhanced,forming a widely distributed and thickly deposited dolomite area.The dolomites in the study area mainly show dull-red or non-luminance cathodoluminescence under cathode rays,and are the products of high salinity brine by infiltration and circumfluence in contemporaneous and penecontemporaneous period.The dolomitization fluid was mainly seawater at the time for the Feixianguan deposition.However,the dolomitization fluid of the dolomite that formed in a restricted environment is a mixture of meteoric freshwater and dominantly seawater.The Mg2+is mainly provided by lime lagoon formed by the aggradation of the oolitic shoals in the early stage of the second member of the Feixianguan Formation,and by the lime lagoon and dolomitic lagoon formed by the progradation and aggradation of the oolitic shoals in the middle to the late stage of the second member of the Feixianguan Formation.The main reservoir spaces in reservoir rocks of the second member of the Feixianguan Formation in the study area are intergranular pores,mould pores and intergranular pores,and fractures are not developed.A combination of diagenetic sequence,pore evolution and fluid inclusion analysis shows great consistency between pore abundance and dolomite distribution.As compaction resistance increases,intercrystalline pores in dolomite accommodate hydrocarbon charging,providing a good base for reservoir development.Liquid and gaseous hydrocarbon are identified in the reservoir rocks from the second member of the Feixianguan Formation,indicating there are at least two stages of hydrocarbon accumulation,and pore development and hydrocarbon charging also have a good coupling relationship.
作者
叶子旭
袁海锋
杨鹏
易娟子
谌辰
YE Zixu;YUAN Haifeng;YANG Peng;YI Juanzi;SHEN Chen(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu,Sichuan 610059,China;PetroChina Southwest Oil&Gas Field Company,Chongqing 400021,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2023年第1期150-167,共18页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号41572133、41872130)资助的成果。
关键词
四川盆地
飞仙关组二段
白云石化作用
台地边缘颗粒滩
孔隙演化
Sichuan basin
the Second Member of Feixianguan Formation
dolomitization
platform margin shoal
pore evolution
