【作者】 杨凯；

【导师】 王绪本；

【作者基本信息】 成都理工大学 ， 地球探测与信息技术， 2022， 博士

【摘要】 四川盆地志留系龙马溪组页岩是中国海相页岩中勘探程度高,并得到商业化开发的重要层系。地球物理方法是进行页岩气勘探的有力手段,面对川南复杂地形,电磁法因经济、探测深度大的优点被广泛应用于页岩气勘探。但是页岩的导电机理与极化机理极其复杂,使得页岩岩石电学属性特征的研究较为薄弱,极大限制了岩石电磁学的相关理论突破和电磁法勘探的应用。本文选取龙马溪组页岩为研究对象,首先对储层特征进行定量和定性表征,并通过复电阻率实验,分析页岩的频散特征及其影响因素;然后进行地质事件的识别和沉积古环境的重建,厘清沉积环境对矿物类型与组分、孔隙类型及连通性、有机质丰度等的影响;最后探讨不同沉积背景下页岩的电学属性差异,建立岩石电学机理模式,从而为页岩电磁法勘探提供岩石电学基础,达到岩心尺度的标尺作用。通过研究得出以下认识:(1)明确了龙马溪组页岩储层矿物、孔隙、有机地化特征,并划分出4种岩相类型。川南及周缘龙马溪组页岩主要矿物组成为石英和黏土矿物,并含有少量的白云石、方解石、长石、黄铁矿等,底部页岩脆性矿物较高,中上部页岩黏土矿物较高。研究区龙马溪组页岩生烃潜力较好,TOC含量平均为1.97%,成熟度平均为2.96%。通过氩离子抛光扫描电镜分析技术,识别出龙马溪组页岩发育三种主要的基质孔隙(粒间孔、粒内孔、有机质孔)和裂缝。并根据矿物组成、沉积构造和孔隙类型,将龙马溪组页岩划分为黏土质页岩、硅-黏土混合质页岩、含黏土混合硅质页岩、混合硅质页岩四种岩相。其中混合硅质页岩特征为高石英含量、高TOC含量、有机质孔发育,是龙马溪组页岩中优势岩相类型。(2)通过测定岩石的复电阻率,剖析了页岩发生频散的影响因素,并通过模型拟合明确了不同岩相的电阻率和极化率特征。通过岩心复电阻率测试发现页岩样品中均表现出实部、虚部及相位随频率的变化而变化,即发生了频散特征。研究发现矿物组成和有机碳含量均对页岩的频散特征产生了一定的影响,其中黄铁矿含量、有机质含量等对于页岩频散特征具影响较大。通过模型优选与计算,得出了阻尼最小二乘法结合Double Cole-Cole模型拟合效果最佳。通过电阻率和极化率参数,发现不同类型的页岩表现出不同的电学属性,其中混合硅质页岩的电阻率最低(34.53Ω·m)、极化率最高(平均为0.159)。(3)通过沉积学手段识别出4种地质事件,重建了页岩古沉积环境。通过元素地球化学分析测试手段结合岩心、露头观察,识别出晚奥陶系-早志留系沉积时期4种主要的地质事件:火山运动、赫南特冰期、上升流事件以及浊流。泥页岩沉积古环境受地质事件、地形等多方面因素共同影响。通过选取合适的地球化学指标,重建了龙马溪组页岩沉积期的古环境。龙马溪组页岩整体上处于温湿的气候条件,仅在底部见半干冷的气候条件。古生产力整体上较高,尤其是底部混合硅质页岩,火山运动及上升流为其生物生长提供了丰富的营养物质。氧化还原条件纵向上变化较大,从底部到顶部逐渐由还原、次氧化过渡到氧化条件。并且底部混合硅质页岩的陆源输入较低,而中上部陆源输入较高。(4)建立了宏观-微观联控作用下沉积环境对岩石电学属性影响机制。首先沉积环境影响矿物的组分及含量:底部页岩古生产力强,陆源输入较低,生物大量繁盛,使得混合硅质页岩石英多以生物成因为主,石英含量高;同时还原环境有利于草莓状黄铁矿的形成,促使黄铁矿含量较高且草莓状黄铁矿粒径较小。其次沉积环境影响有机质富集程度:还原硫化条件、高古生产力和低陆源输入是混合硅质页岩有机质富集的关键因素。然后在成岩过程中,高TOC含量的混合硅质页岩在干酪根热解生烃作用下会导致有机质孔大量发育,并得益于生物硅质的强抗压实能力,使得底部页岩孔隙连通性较好。最后厘清了页岩的导电机理与极化机制:龙马溪组页岩的电阻率变化主要与无机孔和有机孔形成的孔隙网络、高黄铁矿含量以及高比表面积的有机物表面官能团等因素在通电情况下,形成导电回路的路径长短有关,即其导电机理为孔隙流体离子导电主控岩石导电能力。龙马溪组页岩极化率主要受黏土矿物和黄铁矿两者的双电层发生界面极化现象影响,其极化机理为电子导体与离子导体共同控制岩石的极化特征。最终建立了宏观-微观联控作用下沉积环境对岩石电学属性影响机制。更多还原

【Abstract】 The Silurian Longmaxi formation shale in Sichuan Basin is an important series with high exploration degree and commercial development in China.The use of geophysical methods is a powerful means for shale gas exploration.Facing the complex terrain of southern Sichuan,electromagnetic method is widely used in shale gas exploration because of its advantages of economy and large detection depth.However,the electrical conduction mechanism and polarization mechanism of shale are extremely complicated,which makes the research on the electrical properties of shale rock relatively weak,which greatly restricts the relevant theoretical breakthroughs in rock electromagnetism and the application of electromagnetic exploration.In this paper,Longmaxi formation shale is selected as the research object.Firstly,the reservoir characteristics are characterized quantitatively and qualitatively,and the dispersion characteristics and influencing factors of shale are analyzed through complex resistivity experiment;Then,the geological events are identified and the sedimentary paleoenvironment is reconstructed,and the effects of sedimentary environment on mineral types and components,pore types and connectivity,organic matter abundance and so on are clarified;Finally,the differences of electrical properties of shale under different sedimentary backgrounds are comprehensively discussed,and the rock electrical mechanism model is established,so as to provide rock electrical basis for shale electromagnetic exploration and achieve the scale of core scale.Through the research,the following understandings are obtained:(1)The minerals,pores,and organic geochemical characteristics of Longmaxi Formation shale reservoirs are clarified,and four lithofacies types are classified.The main mineral composition of Longmaxi Formation shale in southern Sichuan and the periphery is quartz and clay minerals,and contains a small amount of dolomite,calcite,feldspar,pyrite,etc.The bottom shale has higher brittle minerals,the middle and upper shale has higher clay minerals.The Longmaxi Formation shale in the study area has good hydrocarbon generation potential,with an average TOC content of 1.97%and an average maturity of 2.96%.Through the argon ion polishing scanning electron microscope analysis technology,three main matrix pores(intergranular pores,intragranular pores,organic pores)and fractures were identified in the Longmaxi Formation shale.According to the mineral composition,sedimentary structure and pore type,the Longmaxi Formation shale is divided into four lithofacies: argillaceous shale,argillaceous/siliceous mixed shale,argillaceous-rich mixed siliceous shale and mixed siliceous shale.The mixed siliceous shale is characterized by high quartz content,high TOC content and organic matter pore development,which is the dominant lithofacies type in the shale of Longmaxi formation.(2)By measuring the complex resistivity of the rock,the factors affecting the frequency dispersion of shale are analyzed,and the resistivity and polarizability characteristics of different lithofacies are clarified through model fitting.Through the core complex resistivity test,it is found that the real part,imaginary part and phase of shale samples change with the change of frequency,that is,the characteristics of frequency dispersion occur.It is found that both mineral composition and organic carbon content have a certain impact on the dispersion characteristics of shale,among which pyrite content and organic matter content have a great impact on the dispersion characteristics of shale.Through model optimization and calculation,it is concluded that the damping least square method combined with double Cole Cole model has the best fitting effect.Through the resistivity and polarizability parameters,it is found that different types of shale show different electrical properties.Among them,the resistivity of mixed siliceous shale is the lowest(34.53 Ω· m)and the polarizability is the highest(0.159).(3)Four types of geological events were identified by means of sedimentology,and the shale paleosedimentary environment was reconstructed.By means of element geochemical analysis and testing,combined with core and outcrop observation,four main geological events in the sedimentary period of Late Ordovician and Early Silurian are identified: volcanic movement,hernantian ice age,upwelling event and turbidity current.Mud shale sedimentary paleoenvironment is affected by geological events,topography and other factors.By selecting appropriate geochemical indexes,the Paleoenvironment of shale sedimentary period of Longmaxi formation is reconstructed.The shale of Longmaxi formation is generally in warm and humid climate conditions,and only semi dry and cold climate conditions can be seen at the bottom.Paleoproductivity is generally high,especially the bottom mixed siliceous shale.Volcanic movement and upwelling provide rich nutrients for its biological growth.The redox conditions change greatly longitudinally,and gradually transition from reduction and secondary oxidation to oxidation conditions from bottom to top.And the terrigenous input of bottom mixed siliceous shale is low,while the terrigenous input of middle and upper part is high.(4)The influence mechanism of sedimentary environment on rock electrical properties under macro micro joint control is established.Firstly,the sedimentary environment affects the composition and content of minerals: the bottom shale has strong paleoproductivity,low terrigenous input and a large number of organisms,so that the mixed siliceous shale quartz is mainly biogenic and the quartz content is high;At the same time,the reduction environment is conducive to the formation of strawberry pyrite,which promotes the high content of pyrite and the small particle size of strawberry pyrite.Secondly,the sedimentary environment affects the degree of organic matter enrichment: reducing sulfide conditions,high paleoproductivity and low terrigenous input are the key factors for organic matter enrichment of mixed siliceous shale.Then,in the diagenetic process,the mixed siliceous shale with high TOC content will lead to a large number of organic matter pores under the effect of kerogen pyrolysis and hydrocarbon generation.Thanks to the strong anti compaction ability of biological siliceous,the pore connectivity of the bottom shale is good.Finally,the conductive mechanism and polarization mechanism of shale are clarified: the resistivity change of Longmaxi formation shale is mainly related to the pore network formed by inorganic and organic pores,high pyrite content and organic surface functional groups with high specific surface area.Under the condition of power on,the path length of conductive circuit is related,That is,its conductive mechanism is pore fluid ionic conductivity,which mainly controls the conductivity of rock.The polarizability of shale in Longmaxi formation is mainly affected by the interfacial polarization of electric double layers of clay minerals and pyrite.Its polarization mechanism is that electronic conductors and ionic conductors jointly control the polarization characteristics of rocks.Finally,the influence mechanism of sedimentary environment on rock electrical properties under macro micro joint control is established.更多还原