三轴压缩试验前后含气页岩微纳尺度裂隙空间分布特征研究
|
摘要
含气页岩受力后裂隙扩展分布方式与矿物之间的关系研究对页岩气勘探开采具有重要指示意义,但受制于前期仪器设备水平的不足,目前相关研究较少。本文以四川盆地志留纪龙马溪组页岩为例,分别选择三轴压缩试验前后的天然样和压缩样进行氩离子抛光,借助高性能场扫描电镜和能谱仪进行矿物晶体和微纳尺度的裂纹观察(分别设定扫描电镜像素大小10 nm和1μm,观察面积设为1 mm),结合空间统计分析技术,进行三轴压缩试验前后含气页岩微纳尺度裂隙空间分布特征及其与矿物组成的相关关系进行分析研究。研究表明,三轴压缩试验前后,样品内微纳尺度裂隙的空间分布均符合幂律分布,具有一定的自仿射性和层次结构性。但是不同矿物(石英、长石、碳酸盐、黏土等)在受压前后产生的微观裂隙分布特征值(D、logC)变化方式存在显著差异,反映了不同矿物的力学响应特征和机制的不同以及不同矿物对页岩压裂造缝的贡献作用的不同。脆性矿物中的长石、碳酸盐矿物组成以及脆性矿物与黏土矿物的相互作用可能对页岩缝网改造中起着较为重要的作用。不同矿物压缩前后的破坏模式总体存在从张性破坏到剪性破坏的转变过程,然而不同矿物类型在压缩前后裂隙展布形态特征及力学机制有很大不同,特别是碳酸盐类和黏土类矿物变化最为显著,容易形成较复杂的缝网,并存在复杂应力状态主导的多种不同力学机制裂纹共存的现象,在研究时需要考虑页岩复杂矿物构成和结构导致的破裂过程的不确定性等因素。
The spatial characterization of micro-cracks and their relationship with the mineral composition in the gas shale can provide scientific guidance for the shale gas exploration. However,there has been little research on this problem because of the limitation of experiment instruments. In this study,two samples from Longmaxi Shale,which had been preserved in Sichuan Basin since Silurian,are imaged using the high performance field Scanning Electron Microscope( SEM) and energy dispersive X-ray spectrometer( EDS). Triaxial compression test is conducted on one of the two samples which called compressed sample,while the other sample remains undistrubed.The SEM and EDS are ZEISS MERLIN SEM equipped with secondary electron( SE) detectors for crack investigations at a pixel size of 10 nm and Bruker QUANTAX energy dispersive X-ray spectrometer( EDS) system for automatic identification of minerals at a pixel size of 1 μm. The scanning area is 1 mm. Based on this,the microand nanoscale micro-cracks before and after triaxial compression test are characterized by spatial analysis methods.The relationship between micro-fractures and mineral compositions is also investigated. Results show that the spatial distribution of all micro-cracks in both disturbed and undisturbed samples follows the power law indicating the nature of self-organization and structural hierarchy of spatial distrubiton of micro-cracks in shale. However,the parameters of the distribution( D and log C) vary distinctly with the mineral types( quartz,feldspar,carbonate and clay) implicating that different minerals have different mechanisms in response to mechanical loading and thus different contributions to the shale fracturing. Some brittle minerals such as feldspar and carbonate and their interaction with clay may play vital role in shale fracturing. The transition from tensile failure to shearing failure dominates the failure patterns for all minerals under mechanical loading. However, the cracking spatial characterization and fracturing mechanism vary among different minerals. The spatial distribution of micro-cracks concerning carbonate minerals and clay mineral changes dramatically before and after triaxial compression test and more complicated crack networks could form. Multiple failure mechanisms could co-exist within single mineral due to the complex stress condition under triaxial compression test. The high uncertainty of failure process should be taken into account due to the complicated mineral composition and structure.
The spatial characterization of micro-cracks and their relationship with the mineral composition in the gas shale can provide scientific guidance for the shale gas exploration. However,there has been little research on this problem because of the limitation of experiment instruments. In this study,two samples from Longmaxi Shale,which had been preserved in Sichuan Basin since Silurian,are imaged using the high performance field Scanning Electron Microscope( SEM) and energy dispersive X-ray spectrometer( EDS). Triaxial compression test is conducted on one of the two samples which called compressed sample,while the other sample remains undistrubed.The SEM and EDS are ZEISS MERLIN SEM equipped with secondary electron( SE) detectors for crack investigations at a pixel size of 10 nm and Bruker QUANTAX energy dispersive X-ray spectrometer( EDS) system for automatic identification of minerals at a pixel size of 1 μm. The scanning area is 1 mm. Based on this,the microand nanoscale micro-cracks before and after triaxial compression test are characterized by spatial analysis methods.The relationship between micro-fractures and mineral compositions is also investigated. Results show that the spatial distribution of all micro-cracks in both disturbed and undisturbed samples follows the power law indicating the nature of self-organization and structural hierarchy of spatial distrubiton of micro-cracks in shale. However,the parameters of the distribution( D and log C) vary distinctly with the mineral types( quartz,feldspar,carbonate and clay) implicating that different minerals have different mechanisms in response to mechanical loading and thus different contributions to the shale fracturing. Some brittle minerals such as feldspar and carbonate and their interaction with clay may play vital role in shale fracturing. The transition from tensile failure to shearing failure dominates the failure patterns for all minerals under mechanical loading. However, the cracking spatial characterization and fracturing mechanism vary among different minerals. The spatial distribution of micro-cracks concerning carbonate minerals and clay mineral changes dramatically before and after triaxial compression test and more complicated crack networks could form. Multiple failure mechanisms could co-exist within single mineral due to the complex stress condition under triaxial compression test. The high uncertainty of failure process should be taken into account due to the complicated mineral composition and structure.
引文
Cahoon J R,Broughton W H,Kutzak A R.1971.The determination of yield strength from hardness measurements[J].Metallurgical and Materials Transactions B,2(7):1979-1983.
Chalmers G R,Bustin R M,Power I M.2012.Characterization of gas shale pore systems by porosimetry,pycnometry,surface area,and field emission scanning electron microscopy/transmission electron microscopy image analyses:Examples from the Barnett,Woodford,Haynesville,Marcellus,and Doig unit[J].Aapg Bulletin,96(6):1099-1119.
Chen C,Hu D,Westacott D,et al.2013.Nanometer-scale characterization of microscopic pores in shale kerogen by image analysis and pore-scale modeling[J].Geochemistry Geophysics Geosystems,14(10):4066-4075.
Chen J,Xiao X M.2013.Mineral composition and brittleness of three sets of Paleozoic organic-rich shales in China South area[J].Journal of China Coal Society,38(5):822-826.
Chen S B,Zhu Y M,Wang H Y,et al.2011.Characteristics and significance of mineral compositions of Lower Silurian Longmaxi Formation shale gas reservoir in the southern margin of Sichuan Basin[J].Acta Petrolei Sinica,32(5):775-782.
Diao H.2013.Rock mechanical properties and brittleness evaluation of shale reservoir[J].Acta Petrologica Sinica,29(9):3300-3306.
Dieterich M K B G A.2016.Characterization of Marcellus Shale and Huntersville Chert before and after exposure to hydraulic fracturing fluid via feature relocation using field-emission scanning electron microscopy[J].Fuel,(182):227-235.
Gu X S,Cole D R,Rother G,et al.2015.Pores in Marcellus Shale:Aneutron scattering and FIB-SEM study[J].Energy&Fuels,29(3):1295-1308.
Guo X S,Li Y P,Liu R B,et al.2014.Characteristics and controlling factors of micro-pore structures of Longmaxi Shale Play in the Jiaoshiba area,Sichuan Basin[J].Natural Gas Industry,34(6):9-16.
Guthrie J M,Houseknecht D W,Johns W D.1986.Relationships among vitrinite reflectance,illite crystallinity,and organic geochemistry in Carboniferous strata,Ouachita Mountains,Oklahoma and Arkansas[J].Aapg Bulletin,70(1):26-33.
Hou Z K,Yang C H,Wang L,et al.2016.Hydraulic fracture propagation of shale horizontal well by large-scale true triaxial physical simulation test[J].Rock and Soil Mechanics,37(2):407-414.
Jiao K,Yao S,Liu C,et al.2014.The characterization and quantitative analysis of nanopores in unconventional gas reservoirs utilizing FESEM-FIB and image processing:An example from the lower Silurian Longmaxi Shale,upper Yangtze region,China[J].International Journal of Coal Geology,128-129(3):1-11.
Klaver J,Desbois G,Littke R,et al.2016.BIB-SEM pore characterization of mature and post mature Posidonia Shale samples from the Hils area,Germany[J].International Journal of Coal Geology,158:78-89.
Klaver J,Desbois G,Littke R,et al.2015.BIB-SEM characterization of pore space morphology and distribution in postmature to overmature samples from the Haynesville and Bossier Shales[J].Marine&Petroleum Geology,59:451-466.
Klaver J,Desbois G,Urai J L,et al.2012.BIB-SEM study of the pore space morphology in early mature Posidonia Shale from the Hils area,Germany[J].International Journal of Coal Geology,103(23):12-25.
Li X Y,Lei X L,Li Q,et al.2015.Characteristics of acoustic emission during deformation and failure of typical reservoir rocks under triaxial compression:An example of Sinian dolomite and shale in the Sichuan Basin[J].Chinese Journal of Geophysics,58(3):982-992.
Lin D,Zhang T,Liao J,et al.2016.Mineral composition and brittleness analysis of organic-rich lower paleozoic shale in South Sichuan and North Yunnan Areas of China[J].Chemistry&Technology of Fuels&Oils,52(2):218-223.
Liu C,Shi B,Zhou J,et al.2011.Quantification and characterization of microporosity by image processing,geometric measurement and statistical methods:Application on SEM images of clay materials[J].Applied Clay Science,54(1):97-106.
Loucks R G,Reed R M,Ruppel S C,et al.2009.Morphology,genesis,and distribution of nanometer-scale pores in Siliceous Mudstones of the Mississippian Barnett Shale[J].Journal of Sedimentary Research,79(12):848-861.
Shi X,Cheng Y F,Jiang S,et al.2014.Experimental study of microstructure and rock properties of shale samples[J].Chinese Journal of Rock Mechanics and Engineering,33(S2):3439-3445.
Tang X,Jiang Z,Jiang S,et al.2016.Heterogeneous nanoporosity of the Silurian Longmaxi Formation shale gas reservoir in the Sichuan Basin using the QEMSCAN,FIB-SEM,and nano-CT methods[J].Marine&Petroleum Geology,78:99-109.
Wang P,Ji Y L,Pan R F,et al.2013.A comprehensive evaluation methodology of shale brittleness:A case study from the Lower Silurian Longmaxi Fm in Block W,Sichuan Basin[J].Natural Gas Industry,(12):48-53.
Wang P,Jiang Z,Ji W,et al.2016.Heterogeneity of intergranular,intraparticle and organic pores in Longmaxi shale in Sichuan Basin,South China:Evidence from SEM digital images and fractal and multifractal geometries[J].Marine&Petroleum Geology,72:122-138.
Wei Y L,Yang C H,Guo Y T,et al.2015.Experimental research on deformation and fracture characteristics of shale under cyclic loading[J].Chinese Journal of Geotechnical Engineering,37(12):2262-2271.
Yang F,Ning Z F,Kong D T,et al.2013.Pore structure of shales from high pressure mercury injection and nitrogen adsorption method[J].Natural Gas Geoscience,24(3):450-455.
Yang R,He S,Yi J,et al.2016.Nano-scale pore structure and fractal dimension of organic-rich Wufeng-Longmaxi shale from Jiaoshiba area,Sichuan Basin:Investigations using FE-SEM,gas adsorption and helium pycnometry[J].Marine&Petroleum Geology,70:27-45.
Zeng W,Zhang J,Ding W,et al.2013.Fracture development in Paleozoic shale of Chongqing area(South China).Part one:Fracture characteristics and comparative analysis of main controlling factors[J].Journal of Asian Earth Sciences,75(8):251-266.
Zhang P,Li S X,Zhang Z F.2011.General relationship between strength and hardness[J].Materials Science and Engineering:A,529(1):62-73.
Zhou S,Yan G,Xue H,et al.2016.2D and 3D nanopore characterization of gas shale in Longmaxi formation based on FIB-SEM[J].Marine&Petroleum Geology,73:174-180.
陈吉,肖贤明.2013.南方古生界3套富有机质页岩矿物组成与脆性分析[J].煤炭学报,38(5):822-826.
陈尚斌,朱炎铭,王红岩,等.2011.四川盆地南缘下志留统龙马溪组页岩气储层矿物成分特征及意义[J].石油学报,32(5):775-782.
刁海燕.2013.泥页岩储层岩石力学特性及脆性评价[J].岩石学报,29(9):3300-3306.
郭旭升,李宇平,刘若冰,等.2014.四川盆地焦石坝地区龙马溪组页岩微观孔隙结构特征及其控制因素[J].天然气工业,34(6):9-16.
侯振坤,杨春和,王磊,等.2016.大尺寸真三轴页岩水平井水力压裂物理模拟试验与裂缝延伸规律分析[J].岩土力学,37(2):407-414.
李霞颖,雷兴林,李琦,等.2015.油气田典型岩石三轴压缩变形破坏与声发射活动特征---四川盆地震旦系白云岩及页岩的破坏过程[J].地球物理学报,58(3):982-992.
时贤,程远方,蒋恕,等.2014.页岩微观结构及岩石力学特征实验研究[J].岩石力学与工程学报,33(S2):3439-3445.
王鹏,纪友亮,潘仁芳,等.2013.页岩脆性的综合评价方法---以四川盆地W区下志留统龙马溪组为例[J].天然气工业,(12):48-53.
魏元龙,杨春和,郭印同,等.2015.三轴循环荷载下页岩变形及破坏特征试验研究[J].岩土工程学报,37(12):2262-2271.
杨峰,宁正福,孔德涛,等.2013.高压压汞法和氮气吸附法分析页岩孔隙结构[J].天然气地球科学,24(3):450-455.
Chalmers G R,Bustin R M,Power I M.2012.Characterization of gas shale pore systems by porosimetry,pycnometry,surface area,and field emission scanning electron microscopy/transmission electron microscopy image analyses:Examples from the Barnett,Woodford,Haynesville,Marcellus,and Doig unit[J].Aapg Bulletin,96(6):1099-1119.
Chen C,Hu D,Westacott D,et al.2013.Nanometer-scale characterization of microscopic pores in shale kerogen by image analysis and pore-scale modeling[J].Geochemistry Geophysics Geosystems,14(10):4066-4075.
Chen J,Xiao X M.2013.Mineral composition and brittleness of three sets of Paleozoic organic-rich shales in China South area[J].Journal of China Coal Society,38(5):822-826.
Chen S B,Zhu Y M,Wang H Y,et al.2011.Characteristics and significance of mineral compositions of Lower Silurian Longmaxi Formation shale gas reservoir in the southern margin of Sichuan Basin[J].Acta Petrolei Sinica,32(5):775-782.
Diao H.2013.Rock mechanical properties and brittleness evaluation of shale reservoir[J].Acta Petrologica Sinica,29(9):3300-3306.
Dieterich M K B G A.2016.Characterization of Marcellus Shale and Huntersville Chert before and after exposure to hydraulic fracturing fluid via feature relocation using field-emission scanning electron microscopy[J].Fuel,(182):227-235.
Gu X S,Cole D R,Rother G,et al.2015.Pores in Marcellus Shale:Aneutron scattering and FIB-SEM study[J].Energy&Fuels,29(3):1295-1308.
Guo X S,Li Y P,Liu R B,et al.2014.Characteristics and controlling factors of micro-pore structures of Longmaxi Shale Play in the Jiaoshiba area,Sichuan Basin[J].Natural Gas Industry,34(6):9-16.
Guthrie J M,Houseknecht D W,Johns W D.1986.Relationships among vitrinite reflectance,illite crystallinity,and organic geochemistry in Carboniferous strata,Ouachita Mountains,Oklahoma and Arkansas[J].Aapg Bulletin,70(1):26-33.
Hou Z K,Yang C H,Wang L,et al.2016.Hydraulic fracture propagation of shale horizontal well by large-scale true triaxial physical simulation test[J].Rock and Soil Mechanics,37(2):407-414.
Jiao K,Yao S,Liu C,et al.2014.The characterization and quantitative analysis of nanopores in unconventional gas reservoirs utilizing FESEM-FIB and image processing:An example from the lower Silurian Longmaxi Shale,upper Yangtze region,China[J].International Journal of Coal Geology,128-129(3):1-11.
Klaver J,Desbois G,Littke R,et al.2016.BIB-SEM pore characterization of mature and post mature Posidonia Shale samples from the Hils area,Germany[J].International Journal of Coal Geology,158:78-89.
Klaver J,Desbois G,Littke R,et al.2015.BIB-SEM characterization of pore space morphology and distribution in postmature to overmature samples from the Haynesville and Bossier Shales[J].Marine&Petroleum Geology,59:451-466.
Klaver J,Desbois G,Urai J L,et al.2012.BIB-SEM study of the pore space morphology in early mature Posidonia Shale from the Hils area,Germany[J].International Journal of Coal Geology,103(23):12-25.
Li X Y,Lei X L,Li Q,et al.2015.Characteristics of acoustic emission during deformation and failure of typical reservoir rocks under triaxial compression:An example of Sinian dolomite and shale in the Sichuan Basin[J].Chinese Journal of Geophysics,58(3):982-992.
Lin D,Zhang T,Liao J,et al.2016.Mineral composition and brittleness analysis of organic-rich lower paleozoic shale in South Sichuan and North Yunnan Areas of China[J].Chemistry&Technology of Fuels&Oils,52(2):218-223.
Liu C,Shi B,Zhou J,et al.2011.Quantification and characterization of microporosity by image processing,geometric measurement and statistical methods:Application on SEM images of clay materials[J].Applied Clay Science,54(1):97-106.
Loucks R G,Reed R M,Ruppel S C,et al.2009.Morphology,genesis,and distribution of nanometer-scale pores in Siliceous Mudstones of the Mississippian Barnett Shale[J].Journal of Sedimentary Research,79(12):848-861.
Shi X,Cheng Y F,Jiang S,et al.2014.Experimental study of microstructure and rock properties of shale samples[J].Chinese Journal of Rock Mechanics and Engineering,33(S2):3439-3445.
Tang X,Jiang Z,Jiang S,et al.2016.Heterogeneous nanoporosity of the Silurian Longmaxi Formation shale gas reservoir in the Sichuan Basin using the QEMSCAN,FIB-SEM,and nano-CT methods[J].Marine&Petroleum Geology,78:99-109.
Wang P,Ji Y L,Pan R F,et al.2013.A comprehensive evaluation methodology of shale brittleness:A case study from the Lower Silurian Longmaxi Fm in Block W,Sichuan Basin[J].Natural Gas Industry,(12):48-53.
Wang P,Jiang Z,Ji W,et al.2016.Heterogeneity of intergranular,intraparticle and organic pores in Longmaxi shale in Sichuan Basin,South China:Evidence from SEM digital images and fractal and multifractal geometries[J].Marine&Petroleum Geology,72:122-138.
Wei Y L,Yang C H,Guo Y T,et al.2015.Experimental research on deformation and fracture characteristics of shale under cyclic loading[J].Chinese Journal of Geotechnical Engineering,37(12):2262-2271.
Yang F,Ning Z F,Kong D T,et al.2013.Pore structure of shales from high pressure mercury injection and nitrogen adsorption method[J].Natural Gas Geoscience,24(3):450-455.
Yang R,He S,Yi J,et al.2016.Nano-scale pore structure and fractal dimension of organic-rich Wufeng-Longmaxi shale from Jiaoshiba area,Sichuan Basin:Investigations using FE-SEM,gas adsorption and helium pycnometry[J].Marine&Petroleum Geology,70:27-45.
Zeng W,Zhang J,Ding W,et al.2013.Fracture development in Paleozoic shale of Chongqing area(South China).Part one:Fracture characteristics and comparative analysis of main controlling factors[J].Journal of Asian Earth Sciences,75(8):251-266.
Zhang P,Li S X,Zhang Z F.2011.General relationship between strength and hardness[J].Materials Science and Engineering:A,529(1):62-73.
Zhou S,Yan G,Xue H,et al.2016.2D and 3D nanopore characterization of gas shale in Longmaxi formation based on FIB-SEM[J].Marine&Petroleum Geology,73:174-180.
陈吉,肖贤明.2013.南方古生界3套富有机质页岩矿物组成与脆性分析[J].煤炭学报,38(5):822-826.
陈尚斌,朱炎铭,王红岩,等.2011.四川盆地南缘下志留统龙马溪组页岩气储层矿物成分特征及意义[J].石油学报,32(5):775-782.
刁海燕.2013.泥页岩储层岩石力学特性及脆性评价[J].岩石学报,29(9):3300-3306.
郭旭升,李宇平,刘若冰,等.2014.四川盆地焦石坝地区龙马溪组页岩微观孔隙结构特征及其控制因素[J].天然气工业,34(6):9-16.
侯振坤,杨春和,王磊,等.2016.大尺寸真三轴页岩水平井水力压裂物理模拟试验与裂缝延伸规律分析[J].岩土力学,37(2):407-414.
李霞颖,雷兴林,李琦,等.2015.油气田典型岩石三轴压缩变形破坏与声发射活动特征---四川盆地震旦系白云岩及页岩的破坏过程[J].地球物理学报,58(3):982-992.
时贤,程远方,蒋恕,等.2014.页岩微观结构及岩石力学特征实验研究[J].岩石力学与工程学报,33(S2):3439-3445.
王鹏,纪友亮,潘仁芳,等.2013.页岩脆性的综合评价方法---以四川盆地W区下志留统龙马溪组为例[J].天然气工业,(12):48-53.
魏元龙,杨春和,郭印同,等.2015.三轴循环荷载下页岩变形及破坏特征试验研究[J].岩土工程学报,37(12):2262-2271.
杨峰,宁正福,孔德涛,等.2013.高压压汞法和氮气吸附法分析页岩孔隙结构[J].天然气地球科学,24(3):450-455.