安棚深层系致密砂岩孔隙结构与渗透性关系的核磁共振试验研究
|
摘要
安棚深层系砂岩储层为特低孔特低渗透储层,发育微纳米级孔喉,储层物性规律性差,流体渗流特征复杂,储层定位和评价难度大。对目标层系砂岩进行饱和水核磁共振测量,并将T_2谱与其压汞曲线对比分析,应用最小二乘法拟合得出T_2弛豫时间与孔喉半径的转换参数,求得目标层系的岩心核磁孔喉分布及核磁孔喉参数,并结合核磁T_2分布与分形理论,计算了核磁孔喉分形维数,分析了各孔喉参数与渗透率的关系。结果表明,目标层系的孔喉分布呈双峰特征,相比压汞孔喉分布,核磁共振测量能获取更全面的孔喉信息;渗透率大于1×10~(-3)μm~2时孔喉半径主要分布在0.1~10μm的范围内,渗透率小于1×10~(-3)μm~2时孔喉半径主要分布在0.001~0.1μm的范围内;核磁T_2分布在一定的T_2区间内表现出分形特征;分形维数、核磁主流喉道半径、平均孔喉半径及中值半径均与储层的渗透率呈幂函数关系。
The sandstone reservoir in the deep series of strata in Anpeng area is considered as ultra-low porosity and permeability reservoir with nanometer and micrometer pores,the regularity of reservoir physic properties is poor,the flow characteristics of the fluid are complex,and the classification and evaluation of the reservoir are difficult.Nuclear magnetic resonance( NMR) measurements were performed on the saturated water cores. By comparing the T_2 spectrum with mercury intrusion curve,the conversion coefficients of T_2 relaxation time and throat radius were obtained by the least squares method and the pore-throat size distributions of cores were obtained. Based on NMR T_2 distribution and fractal theory,the fractal dimension of pore-throat is calculated and the relationship between porethroat parameters and permeability is analyzed. The results showed that the pore-throat size distributions show bimodal characteristics,compared with the distribution of pore-throat size obtained by mercury intrusion,the NMR measurements can obtain the pore structure more comprehensively. The pore-throat radius is mainly distributed in the range of 0. 1 ~ 10 μm and range of 0. 001 ~ 0. 1 μm when the permeability is more than 1 × 10~(-3)μm~2 and less than 1 × 10~(-3)μm~2 respectively. NMR T_2 distribution shows fractal characteristics in a certain T_2 interval,and the fractal dimension,the mainstream throat radius,the average pore-throat radius and the median radius are all related to the permeability of the reservoir in the form of a power function.
The sandstone reservoir in the deep series of strata in Anpeng area is considered as ultra-low porosity and permeability reservoir with nanometer and micrometer pores,the regularity of reservoir physic properties is poor,the flow characteristics of the fluid are complex,and the classification and evaluation of the reservoir are difficult.Nuclear magnetic resonance( NMR) measurements were performed on the saturated water cores. By comparing the T_2 spectrum with mercury intrusion curve,the conversion coefficients of T_2 relaxation time and throat radius were obtained by the least squares method and the pore-throat size distributions of cores were obtained. Based on NMR T_2 distribution and fractal theory,the fractal dimension of pore-throat is calculated and the relationship between porethroat parameters and permeability is analyzed. The results showed that the pore-throat size distributions show bimodal characteristics,compared with the distribution of pore-throat size obtained by mercury intrusion,the NMR measurements can obtain the pore structure more comprehensively. The pore-throat radius is mainly distributed in the range of 0. 1 ~ 10 μm and range of 0. 001 ~ 0. 1 μm when the permeability is more than 1 × 10~(-3)μm~2 and less than 1 × 10~(-3)μm~2 respectively. NMR T_2 distribution shows fractal characteristics in a certain T_2 interval,and the fractal dimension,the mainstream throat radius,the average pore-throat radius and the median radius are all related to the permeability of the reservoir in the form of a power function.
引文
1王学武,杨正明,李海波,等.核磁共振研究低渗透储层孔隙结构方法.西南石油大学学报(自然科学版),2010;32(2):69-72Wang Xuewu,Yang Zhengming,Li Haibo,et al.Experimental study on pore structure of low permeability core with NMR spectra.Journal of Southwest Petroleum University(Science&Technology Edition),2010;32(2):69-72
2张雁,王贺军,赵明.榆树林油田低渗储层微观特征及剩余油分布.科学技术与工程,2011;11(11):2473-2478Zhang Yan,Wang Hejun,Zhao Ming.Microscopic characteristics and residual oil distribution of low permeability reservoirs in Yushulin oil field.Science Technology and Engineering,2011;11(11):2473-2478
3赵清民,吕成远,孙侃,等.特低渗储层孔隙结构对CO2驱特征影响.科学技术与工程,2013;13(32):9498-9501Zhao Qingmin,LüChengyuan,Sun Kan,et al.The effect of pore structure on CO2flooding performance in ultra-low permeability reservoir.Science Technology and Engineering,2013;13(32):9498-9501
4赵跃华,李显路,张燕.安棚深层系储层特征及裂缝分布规律.大庆石油地质与开发,1999;18(6):9-11Zhao Yuehua,Li Xianlu,Zhang Yan.Characteristics of Anpeng deep series of strata and rule of fractures distribution.Petroleum Geology&Oilfield Development in Daqing,1999;18(6):9-11
5孙风华,陈祥,王振平.泌阳凹陷安棚深层系成岩作用与成岩阶段划分.西安石油大学学报(自然科学版),2004;19(1):24-27Sun Fenghua,Chen Xiang,Wang Zhenping.Diageneses and division of diagenetic stage of deep strata series in Anpeng area,Biyang Sag.Journal of Xi'an Shiyou University(Natural Science Edition),2004;19(1):24-27
6刘东升.致密砂岩储层分类评价方法在安棚深层系的应用.石油地质与工程,2014;28(6):48-50Liu Dongsheng.Application of tight sandstone reservoir classification evaluation methods in the Anpeng deep layer.Petroleum Geology and Engineering,2014;28(6):48-50
7刘峥君,黎明,周永强,等.安棚深层系致密储层渗流特征及产能预测.科学技术与工程,2016;16(25):243-248Liu Zhengjun,Li Ming,Zhou Yongqiang,et al.Productivity prediction of fractured wells and characteristic in tight oil reservoir of the deep layer of Anpeng.Science Technology and Engineering,2016;16(25):243-248
8李艳,范宜仁,邓少贵,等.核磁共振岩心实验研究储层孔隙结构.勘探地球物理进展,2008;31(2):129-132Li Yan,Fan Yiren,Deng Shaogui,et al.Experimental study of pore structure with nuclear magnetic resonance.Progress in Exploration Geophysics,2008;31(2):129-132
9李扬,张凤生,李建玉,等.川中大安寨段致密灰岩储层核磁共振T2谱特征与解析.油气地质与采收率,2017;24(1):11-18Li Yang,Zhang Fengsheng,Li Jianyu,et al.Characterization and evaluation of NMR T2spectrum of the tight limestone reservoir in the Daanzhai formation,Central Sichuan Basin.Petroleum Geology and Recovery Efficiency,2017;24(1):11-18
10蒲万芬,王崇阳,李一波,等.致密油储层CO2驱核磁共振实验研究.科学技术与工程,2017;17(7):30-34Pu Wanfen,Wang Chongyang,Li Yibo,et al.Nuclear magnetic resonance(NMR)experimental study of CO2flooding in tight reservoir.Science Technology and Engineering,2017;17(7):30-34
11姚远,高圣平.储层孔隙敏感性伤害的核磁共振实验研究.科学技术与工程,2016;16(11):157-161Yao Yuan,Gao Shengping.Experimental research on sensitivity damage in reservoir pores using nuclear magnetic resonance.Science Technology and Engineering,2016;16(11):157-161
12刘晓鹏,胡晓新.近五年核磁共振测井在储集层孔隙结构评价中的若干进展.地球物理学进展,2009;24(6):2194-2201Liu Xiaopeng,Hu Xiaoxin.Progress of NMR log in evaluating reservoir pore structure in the last five years.Progress in Geophys,2009;24(6):2194-2201
13高辉,孙卫,田育红,等.核磁共振技术在特低渗砂岩微观孔隙结构评价中的应用.地球物理学进展,2011;26(1):294-299Gao Hui,Sun Wei,Tian Yuhong,et al.Application of NMR technique in evaluation of micro-pore structure in extra-low permeability sandstone.Progress in Geophys,2011;26(1):294-299
14申本科,欧朝阳,史丹妮,等.砂砾岩储层有效厚度的划分与评价---以中国东部某盆地D凹陷S块沙四段为例.地球物理学进展,2015;30(5):2212-2218Shen Benke,Ou Chaoyang,Shi Danni,et al.Dividing and evaluating of sandy conglomerate reservoir-For example of SHA-4 segment of block S of D depression in China Eastern X B.Progress in Geophys,2015;30(5):2212-2218
15金武军,李军,武清钊,等.页岩气储层渗透率测井评价方法研究.地球物理学进展,2017;32(1):177-182Jin Wujun,Li Jun,Wu Qingzhao,et al.Study on well logging evaluation method of gas shale permeability.Progress in Geophys,2017;32(1):177-182
16李新,刘鹏,罗燕颖,等.页岩气储层岩心孔隙度测量影响因素分析.地球物理学进展,2015;30(5):2181-2187Li Xin,Liu Peng,Luo Yanying,et al.Analysis of influencing factors in porosity measurement of shale gas reservoir core.Progress in Geophys,2015;30(5):2181-2187
17房涛,张立宽,刘乃贵,等.核磁共振技术定量表征致密砂岩气储层孔隙结构---以临清坳陷东部石炭系-二叠系致密砂岩储层为例.石油学报,2017;38(8):902-915Fang Tao,Zhang Likuan,Liu Naigui,et al.Quantitative characterization of pore structure of tight gas sandstone reservoir by NMR T2spectrum technology:A case of Carboniferous-Permian tight sandstone reservoir in Linqing depression.Acta Petrolei Sinica,2017;38(8):902-915
18代全齐,罗群,张晨,等.基于核磁共振新参数的致密油砂岩储层孔隙结构特征---以鄂尔多斯盆地延长组7段为例.石油学报,2016;37(7):887-897Dai Quanqi,Luo Qun,Zhang Chen,et al.Pore structure characteristics of tight-oil sandstone reservoir base on a new parameter measured by NMR experiment:A case study of seventh member in Yanchang Formation,Ordos Basin.Acta Petrolei Sinica,2016;37(7):887-897
19张宸恺,沈金松,樊震.应用分形理论研究鄂尔多斯MHM油田低孔渗储层孔隙结构.石油与天然气地质,2007;28(1):110-115Zhang Chenkai,Shen Jinsong,Fan Zhen.Pore structure study of low porosity and permeability reservoirs in MHM oilfield of Ordos Basin with fractal theory.Oil&Gas Geology,2007;28(1):110-115
20沈金松,张宸恺.应用分形理论研究鄂尔多斯ZJ油田长6段储层孔隙结构的非均质性.西安石油大学学报(自然科学版),2008;23(6):19-23Shen Jinsong,Zhang Chenkai.Study on the heterogeneity of the pore structure of Chang 6 reservoir in ZJ oilfield,Ordos Basin using fractal theory.Journal of Xi'an Shiyou University(Natural Science Edition),2008;23(6):19-23
21吴浩,刘锐娥,纪友亮,等.致密气储层孔喉分形特征及其与渗流的关系-以鄂尔多斯盆地下石盒子组盒8段为例.沉积学报,2017;35(1):151-162Wu Hao,Liu Ruie,Ji Youliang,et al.Fractal characteristics of pore-throat of tight gas reservoirs and its relation with percolation:a case from He 8 member of permian Xiashihezi formation in Ordos Basin.Acta Sedimentologica Sinica,2017;35(1):151-162
22时宇,齐亚东,杨正明,等.基于恒速压汞法的低渗透储层分形研究.油气地质与采收率,2009;16(2):88-90Shi Yu,Qi Yadong,Yang Zhengming et al.Fractal study of low permeability reservoir based on constant-rate mercury injection.Petroleum Geology and Recovery Efficiency,2009;16(2):88-90
23朱卫红,吴胜和,陈阳阳,等.裂缝性致密砂岩储集层孔隙结构分形特征研究.2015油气田勘探与开发国际会议论文集.西安:陕西石油学会,2015:1026-1034Zhu Weihong,Wu Shenghe,Chen Yangyang,et al.Method for calculating the fractal dimension of the pore structure of fractured tight sandstone gas reservoirs.The Proceedings of 2015 International Field Exploration and Development Conference.Xi'an:Shaanxi Petroleum Society,2015:1026-1034
24罗少成,成志刚,林伟川,等.基于核磁共振测井的致密砂岩储层孔喉空间有效性定量评.油气地质与采收率,2015;22(3):16-21Luo Shaocheng,Cheng Zhigang,Lin Weichuan,et al.Quantitative evaluation of the effectiveness of pore-throat space in tight sand stone reservoirs based on nuclear magnetic resonance log.Petroleum Geology and Recovery Efficiency,2015;22(3):16-21
25肖立志.核磁共振成像测井与岩石核磁共振及其应用.北京:科学出版社,1998Xiao Lizhi.Nuclear magnetic resonance imaging logging and rock's magnetic resonance and its application.Beijing:Science Press,1998
26肖立志.核磁共振成像在EOR研究中的应用.石油学报,1995;16(3):106-110Xiao Lizhi.A study on the application of NMR imaging to EOR.Acta Petrolei Sinica,1995;16(3):106-110
27宁传祥,姜振学,苏思远,等.泥页岩核磁共振T2谱换算孔隙半径方法.科学技术与工程,2016;16(27):14-19Ning Chuanxiang,Jiang Zhenxue,Su Siyuan,et al.Method for calculating pore radius distribution in shale reservoirs from NMR T2spectra.Science Technology and Engineering,2016;16(27):14-19
28 Mao Z Q,He Y D,Ren X J.An improved method of using NMR T2distribution to evaluate pore size distribution.Chinese Journal of Geophysics,2005;48(2):412-418
29李爱芬,任晓霞,王桂娟,等.核磁共振研究致密砂岩孔隙结构的方法及应用.中国石油大学学报(自然科学版),2015;39(6):92-98Li Aifen,Ren Xiaoxia,Wang Guijuan,et al.Characterization of pore structure of low permeability reservoirs using a nuclear magnetic resonance method.Journal of China University of Petroleum(Natural Science Edition),2015;39(6):92-98
30 Mandelbrot B B.The fractal geometry of nature.New York:W HFreeman and Company,1983
31 Li S G.Fractal geomertry.Beijing:Higher Education Press,2004
2张雁,王贺军,赵明.榆树林油田低渗储层微观特征及剩余油分布.科学技术与工程,2011;11(11):2473-2478Zhang Yan,Wang Hejun,Zhao Ming.Microscopic characteristics and residual oil distribution of low permeability reservoirs in Yushulin oil field.Science Technology and Engineering,2011;11(11):2473-2478
3赵清民,吕成远,孙侃,等.特低渗储层孔隙结构对CO2驱特征影响.科学技术与工程,2013;13(32):9498-9501Zhao Qingmin,LüChengyuan,Sun Kan,et al.The effect of pore structure on CO2flooding performance in ultra-low permeability reservoir.Science Technology and Engineering,2013;13(32):9498-9501
4赵跃华,李显路,张燕.安棚深层系储层特征及裂缝分布规律.大庆石油地质与开发,1999;18(6):9-11Zhao Yuehua,Li Xianlu,Zhang Yan.Characteristics of Anpeng deep series of strata and rule of fractures distribution.Petroleum Geology&Oilfield Development in Daqing,1999;18(6):9-11
5孙风华,陈祥,王振平.泌阳凹陷安棚深层系成岩作用与成岩阶段划分.西安石油大学学报(自然科学版),2004;19(1):24-27Sun Fenghua,Chen Xiang,Wang Zhenping.Diageneses and division of diagenetic stage of deep strata series in Anpeng area,Biyang Sag.Journal of Xi'an Shiyou University(Natural Science Edition),2004;19(1):24-27
6刘东升.致密砂岩储层分类评价方法在安棚深层系的应用.石油地质与工程,2014;28(6):48-50Liu Dongsheng.Application of tight sandstone reservoir classification evaluation methods in the Anpeng deep layer.Petroleum Geology and Engineering,2014;28(6):48-50
7刘峥君,黎明,周永强,等.安棚深层系致密储层渗流特征及产能预测.科学技术与工程,2016;16(25):243-248Liu Zhengjun,Li Ming,Zhou Yongqiang,et al.Productivity prediction of fractured wells and characteristic in tight oil reservoir of the deep layer of Anpeng.Science Technology and Engineering,2016;16(25):243-248
8李艳,范宜仁,邓少贵,等.核磁共振岩心实验研究储层孔隙结构.勘探地球物理进展,2008;31(2):129-132Li Yan,Fan Yiren,Deng Shaogui,et al.Experimental study of pore structure with nuclear magnetic resonance.Progress in Exploration Geophysics,2008;31(2):129-132
9李扬,张凤生,李建玉,等.川中大安寨段致密灰岩储层核磁共振T2谱特征与解析.油气地质与采收率,2017;24(1):11-18Li Yang,Zhang Fengsheng,Li Jianyu,et al.Characterization and evaluation of NMR T2spectrum of the tight limestone reservoir in the Daanzhai formation,Central Sichuan Basin.Petroleum Geology and Recovery Efficiency,2017;24(1):11-18
10蒲万芬,王崇阳,李一波,等.致密油储层CO2驱核磁共振实验研究.科学技术与工程,2017;17(7):30-34Pu Wanfen,Wang Chongyang,Li Yibo,et al.Nuclear magnetic resonance(NMR)experimental study of CO2flooding in tight reservoir.Science Technology and Engineering,2017;17(7):30-34
11姚远,高圣平.储层孔隙敏感性伤害的核磁共振实验研究.科学技术与工程,2016;16(11):157-161Yao Yuan,Gao Shengping.Experimental research on sensitivity damage in reservoir pores using nuclear magnetic resonance.Science Technology and Engineering,2016;16(11):157-161
12刘晓鹏,胡晓新.近五年核磁共振测井在储集层孔隙结构评价中的若干进展.地球物理学进展,2009;24(6):2194-2201Liu Xiaopeng,Hu Xiaoxin.Progress of NMR log in evaluating reservoir pore structure in the last five years.Progress in Geophys,2009;24(6):2194-2201
13高辉,孙卫,田育红,等.核磁共振技术在特低渗砂岩微观孔隙结构评价中的应用.地球物理学进展,2011;26(1):294-299Gao Hui,Sun Wei,Tian Yuhong,et al.Application of NMR technique in evaluation of micro-pore structure in extra-low permeability sandstone.Progress in Geophys,2011;26(1):294-299
14申本科,欧朝阳,史丹妮,等.砂砾岩储层有效厚度的划分与评价---以中国东部某盆地D凹陷S块沙四段为例.地球物理学进展,2015;30(5):2212-2218Shen Benke,Ou Chaoyang,Shi Danni,et al.Dividing and evaluating of sandy conglomerate reservoir-For example of SHA-4 segment of block S of D depression in China Eastern X B.Progress in Geophys,2015;30(5):2212-2218
15金武军,李军,武清钊,等.页岩气储层渗透率测井评价方法研究.地球物理学进展,2017;32(1):177-182Jin Wujun,Li Jun,Wu Qingzhao,et al.Study on well logging evaluation method of gas shale permeability.Progress in Geophys,2017;32(1):177-182
16李新,刘鹏,罗燕颖,等.页岩气储层岩心孔隙度测量影响因素分析.地球物理学进展,2015;30(5):2181-2187Li Xin,Liu Peng,Luo Yanying,et al.Analysis of influencing factors in porosity measurement of shale gas reservoir core.Progress in Geophys,2015;30(5):2181-2187
17房涛,张立宽,刘乃贵,等.核磁共振技术定量表征致密砂岩气储层孔隙结构---以临清坳陷东部石炭系-二叠系致密砂岩储层为例.石油学报,2017;38(8):902-915Fang Tao,Zhang Likuan,Liu Naigui,et al.Quantitative characterization of pore structure of tight gas sandstone reservoir by NMR T2spectrum technology:A case of Carboniferous-Permian tight sandstone reservoir in Linqing depression.Acta Petrolei Sinica,2017;38(8):902-915
18代全齐,罗群,张晨,等.基于核磁共振新参数的致密油砂岩储层孔隙结构特征---以鄂尔多斯盆地延长组7段为例.石油学报,2016;37(7):887-897Dai Quanqi,Luo Qun,Zhang Chen,et al.Pore structure characteristics of tight-oil sandstone reservoir base on a new parameter measured by NMR experiment:A case study of seventh member in Yanchang Formation,Ordos Basin.Acta Petrolei Sinica,2016;37(7):887-897
19张宸恺,沈金松,樊震.应用分形理论研究鄂尔多斯MHM油田低孔渗储层孔隙结构.石油与天然气地质,2007;28(1):110-115Zhang Chenkai,Shen Jinsong,Fan Zhen.Pore structure study of low porosity and permeability reservoirs in MHM oilfield of Ordos Basin with fractal theory.Oil&Gas Geology,2007;28(1):110-115
20沈金松,张宸恺.应用分形理论研究鄂尔多斯ZJ油田长6段储层孔隙结构的非均质性.西安石油大学学报(自然科学版),2008;23(6):19-23Shen Jinsong,Zhang Chenkai.Study on the heterogeneity of the pore structure of Chang 6 reservoir in ZJ oilfield,Ordos Basin using fractal theory.Journal of Xi'an Shiyou University(Natural Science Edition),2008;23(6):19-23
21吴浩,刘锐娥,纪友亮,等.致密气储层孔喉分形特征及其与渗流的关系-以鄂尔多斯盆地下石盒子组盒8段为例.沉积学报,2017;35(1):151-162Wu Hao,Liu Ruie,Ji Youliang,et al.Fractal characteristics of pore-throat of tight gas reservoirs and its relation with percolation:a case from He 8 member of permian Xiashihezi formation in Ordos Basin.Acta Sedimentologica Sinica,2017;35(1):151-162
22时宇,齐亚东,杨正明,等.基于恒速压汞法的低渗透储层分形研究.油气地质与采收率,2009;16(2):88-90Shi Yu,Qi Yadong,Yang Zhengming et al.Fractal study of low permeability reservoir based on constant-rate mercury injection.Petroleum Geology and Recovery Efficiency,2009;16(2):88-90
23朱卫红,吴胜和,陈阳阳,等.裂缝性致密砂岩储集层孔隙结构分形特征研究.2015油气田勘探与开发国际会议论文集.西安:陕西石油学会,2015:1026-1034Zhu Weihong,Wu Shenghe,Chen Yangyang,et al.Method for calculating the fractal dimension of the pore structure of fractured tight sandstone gas reservoirs.The Proceedings of 2015 International Field Exploration and Development Conference.Xi'an:Shaanxi Petroleum Society,2015:1026-1034
24罗少成,成志刚,林伟川,等.基于核磁共振测井的致密砂岩储层孔喉空间有效性定量评.油气地质与采收率,2015;22(3):16-21Luo Shaocheng,Cheng Zhigang,Lin Weichuan,et al.Quantitative evaluation of the effectiveness of pore-throat space in tight sand stone reservoirs based on nuclear magnetic resonance log.Petroleum Geology and Recovery Efficiency,2015;22(3):16-21
25肖立志.核磁共振成像测井与岩石核磁共振及其应用.北京:科学出版社,1998Xiao Lizhi.Nuclear magnetic resonance imaging logging and rock's magnetic resonance and its application.Beijing:Science Press,1998
26肖立志.核磁共振成像在EOR研究中的应用.石油学报,1995;16(3):106-110Xiao Lizhi.A study on the application of NMR imaging to EOR.Acta Petrolei Sinica,1995;16(3):106-110
27宁传祥,姜振学,苏思远,等.泥页岩核磁共振T2谱换算孔隙半径方法.科学技术与工程,2016;16(27):14-19Ning Chuanxiang,Jiang Zhenxue,Su Siyuan,et al.Method for calculating pore radius distribution in shale reservoirs from NMR T2spectra.Science Technology and Engineering,2016;16(27):14-19
28 Mao Z Q,He Y D,Ren X J.An improved method of using NMR T2distribution to evaluate pore size distribution.Chinese Journal of Geophysics,2005;48(2):412-418
29李爱芬,任晓霞,王桂娟,等.核磁共振研究致密砂岩孔隙结构的方法及应用.中国石油大学学报(自然科学版),2015;39(6):92-98Li Aifen,Ren Xiaoxia,Wang Guijuan,et al.Characterization of pore structure of low permeability reservoirs using a nuclear magnetic resonance method.Journal of China University of Petroleum(Natural Science Edition),2015;39(6):92-98
30 Mandelbrot B B.The fractal geometry of nature.New York:W HFreeman and Company,1983
31 Li S G.Fractal geomertry.Beijing:Higher Education Press,2004