水岩反应蚀变矿物对模拟花岗岩断层泥摩擦系数与速度依赖性的影响  

Effect of water-rock reaction altered minerals on friction coefficient and velocity dependence of simulated granite fault gouges

作　　者：马泽强 刘金锋 范财源 MA Zeqiang;LIU Jinfeng;FAN Caiyuan(School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519082,China;Guangdong Provincial Key Lab of Geodynamics and Geohazards,Zhuhai 519082,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,China)

机构地区：[1]中山大学地球科学与工程学院,广东珠海519082 [2]广东省地球动力作用与地质灾害重点实验室,广东珠海519082 [3]南方海洋科学与工程广东省实验室(珠海),广东珠海519082

出　　处：《中山大学学报（自然科学版）（中英文）》2024年第5期13-27,共15页Acta Scientiarum Naturalium Universitatis Sunyatseni

基　　金：广东省基础与应用基础研究基金(2021A1515012202);国家自然科学基金(42293350,42293354)。

摘　　要：地热开采过程中水岩反应生成的蚀变矿物可能会影响储层断层的摩擦特性,进而诱发不稳定滑动。本文以深圳东北部潜在地热储层的断裂构造为背景,考虑了埋深约2.5 km、温度约150℃的储层条件及横岗-罗湖断裂带,估算得出流体注入导致断层滑动的临界孔隙流体压力(约50 MPa)及临界有效正应力(约20 MPa)。热力学计算表明,在临界流体压力及地热温度下,高产热燕山期花岗岩粉末与水反应在平衡状态下生成的蚀变矿物为:二氧化硅、高岭石和绿泥石,质量比为16∶7∶2。基于此,本文在室温、恒定含水率(10%)及恒定有效正应力(20 MPa)条件下,通过19个速度阶跃直剪试验,研究了3种蚀变矿物单独作用及其共同作用下对模拟花岗岩断层泥的摩擦系数及其速度依赖性的影响,并结合声发射及微观特征分析了其控制机理。试验结果表明:天然花岗岩粉末的摩擦系数为0.64,表现为速度弱化。单种蚀变矿物作用下,二氧化硅对模拟花岗岩断层泥的摩擦系数影响不显著,但能增强断层泥速度弱化特性,甚至引发黏滑;相反,黏土矿物(高岭石和绿泥石)可以显著降低断层泥的摩擦系数,并起速度强化的作用。3种蚀变矿物共同作用下,黏土矿物起主控作用:降低断层泥的摩擦系数,并起速度强化的作用。微观结构分析发现,相比于3种蚀变矿物总含量为33%的变形样品,总含量为67%的变形样品未观察到明显的剪切带且累计声发射事件数显著下降,暗示其变形可能从脆性转变为半塑性。如果在深圳东北部地热储层进行地热开采,应当控制流体注入压力避免断层滑动。Altered minerals introduced by water-rock reactions during geothermal energy recovery may play a role in the frictional properties of fault gouges,perhaps inducing earthquakes.Based on the geological conditions of potential geothermal reservoirs in northeastern Shenzhen,this paper considers the critical pore pressure(about 50 MPa)and critical effective normal stress(about 20 MPa),which may lead to reactivation of the Henggang-Luohu fault zone due to fluid injection into a potential geothermal reservoir at a buried depth of about 2.5 km with the temperature of 150℃.Under such hydrothermal conditions(50 MPa fluid pressure and 150℃),thermodynamic calculations suggest that the reaction of Yanshanian granular granite and water,at equilibrium,can produce silica,kaolinite,and chlorite at a mass ratio of 16∶7∶2.Here we report 19 direct shear experiments performed on simulated fault gouges consisting of the binary mixture of silica+granite,kaolinite+granite,and chlorite+granite,and the multivariate mixture of silica+kaolinite+chlorite+granite,to investigate the effects of altered minerals on frictional properties of simulated granite fault gouges.Velocity stepping experiments were conducted on the wet samples with 10%water content at an initial normal stress of 20 MPa under drained conditions at room temperature.On this basis and together with acoustic emission observation and microstructural analysis,we discussed the likely mechanism responsible for the observed behavior.The results show that,for the presence of a single altered mineral,silica has little effect on the friction coefficient,though it contributes to velocity weakening and even stick-slip events.Whereas,clay minerals can significantly decrease the friction coefficient,though they have a contribution to velocity strengthening.For the presence of a mixture of silica+kaolinite+chlorite,clay minerals play a dominant role in controlling frictional properties of the simulated fault gouges:altered minerals can also significantly decrease the friction coeffi

关 键 词：地热开采 摩擦特性 水岩反应 蚀变矿物 

分 类 号：TU45[建筑科学—岩土工程]