基于压汞分形的高变质石煤孔渗特征分析
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摘要
研究石煤(腐泥煤)的孔渗特征,对于深入了解页岩气的吸附/解吸特征具有重要意义。基于分形几何原理,推导出煤岩不同类型孔隙和毛细管压力曲线的分形几何模型,并将孔隙分形维数分为渗透分维数和扩散分维数分别计算。根据压汞实验数据分析,利用双对数图计算了安康地区石煤孔隙结构的分形维数。研究结果表明:石煤渗透分维数Ds介于2.524-2.917,其与挥发分产率、水分含量、灰分产率和迂曲度呈正相关关系,与变质程度及平均孔径呈负相关关系;扩散分维数Dk介于2.488-2.931,其与变质程度、挥发分产率、水分含量和平均孔径呈正相关关系,与灰分产率和迂曲度呈负相关关系;在物性方面,渗透分维数随孔隙度增大而减小,渗透性的分形表征与扩散分维数呈负相关关系,这说明渗透孔越不均一,煤岩孔隙度就越大,而扩散孔的均一化程度可以为评价石煤储层物性提供重要依据。
The study of pore penmeability characteristics of stone coal(sapropel coal)has great significance for deepened understanding of adsorption and desorption of shale gas.On the basis of the principle of fractal geometry,the fractal models for describing the different types of pore size and capillary pressure curve were developed and fractal dimension was divided into the penetration fractal dimension and the proliferation fractal dimension.According to the capillary pressure data,the fraction dimension is calculated on a log-log plot of intrusion volume versus pressure.The results show that the penetration fractal dimension(Ds) is from 2.524 to 2.931,and has positive relationship with volatile matter ratio,moisture ratio,ash content and tortuosity,while negative relationship with metamorphic grade and mean pore diameter.The proliferation fractal dimension(Dk) is from 2.400 to 2.934,and has positive relationship with metamorphic grade,volatile matter ratio,moisture ratio and mean pore diameter,and negative relationship with ash content and tortuosity.In the respect of physical properties of bone coal,the penetration fractal dimension increases with porosity,permeability and proliferation fractal dimension is negatively correlated.This shows that the more heterogeneous penetration hole,the greater the porosity of coal,and the degree of uniformity of the diffusing pore is important to the permeability transformation in reservoir.
The study of pore penmeability characteristics of stone coal(sapropel coal)has great significance for deepened understanding of adsorption and desorption of shale gas.On the basis of the principle of fractal geometry,the fractal models for describing the different types of pore size and capillary pressure curve were developed and fractal dimension was divided into the penetration fractal dimension and the proliferation fractal dimension.According to the capillary pressure data,the fraction dimension is calculated on a log-log plot of intrusion volume versus pressure.The results show that the penetration fractal dimension(Ds) is from 2.524 to 2.931,and has positive relationship with volatile matter ratio,moisture ratio,ash content and tortuosity,while negative relationship with metamorphic grade and mean pore diameter.The proliferation fractal dimension(Dk) is from 2.400 to 2.934,and has positive relationship with metamorphic grade,volatile matter ratio,moisture ratio and mean pore diameter,and negative relationship with ash content and tortuosity.In the respect of physical properties of bone coal,the penetration fractal dimension increases with porosity,permeability and proliferation fractal dimension is negatively correlated.This shows that the more heterogeneous penetration hole,the greater the porosity of coal,and the degree of uniformity of the diffusing pore is important to the permeability transformation in reservoir.
引文
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[2]李新景,胡素云,程克明.北美裂缝性页岩气勘探开发的启示[J].石油勘探与开发,2007,34(4):392-400.
[3]师永明,张玉广,何勇,等.利用毛管压力曲线分形方法研究流动单元[J].地学前缘,2006,13(3):129-134.
[4]傅雪海,秦勇,张万红,等.基于煤层气运移的煤孔隙分形分类及自然分类研究[J].科学通报,2005,50(增刊):51-55.
[5]马新仿,张士诚,郎兆新.用分段回归法孔隙结构的分形维数[J].石油大学学报(自然科学版),2004,28(6):56-60.
[6]胡宝林,张志龙,车遥,等.鄂尔多斯盆地煤储层孔隙分形特征研究[J].淮南工业学院学报,2002,22(4):1-4.
[7]赵爱红,廖毅,唐修义.煤的孔隙结构分形定量研究[J].煤炭学报,1998,23(4):439-442.
[8]YAO Yanbin,LIU Dameng,TANG Dazhen,et al.Fractalcharacterization of seepage-pores of coals from China:an investi-gation to permeability of coals[C]//12thConference of Int.Associa-tion for Math-ematical Geology.Beijing:State Key LaboratoryGeological Processes&Mineral Resources,2007:415-420.
[9]张松航,唐书恒,汤达祯,等.鄂尔多斯盆地东缘煤储层渗流孔隙分形特征[J].中国矿业大学学报,2009,38(5):713-718.
[10]MANDEBROT B B.The Fractual Geometry Nature[M].NewYork:W.H.Fremen,1982.
[11]FALLICO C,TARQUIS A M.Scaling analysis of water retentioncurves for unsaturated sandy loam soils by using fractal geome-try[J].European Journal of soil science,2010,61(3):425-436.
[12]ANGULO R F,ALVARADO V,GONZALEZ H.Fractal Di-mensions from Mercury Intrusion Capillary Tests[C].II LAPEC,Venezuela,1992:255-263.
[13]BERTEIA A,Nicolella C.A comparative study and an extendedtheory of percolation for random packings of rigid spheres[J].Powder Technology,2011,213:100-108.
[14]陈颙,陈凌.分形几何学[M].北京:地震出版社,2005:71-73.
[15]FRIESEN W L,MIKULA R J.Fractal dimensions of coal parti-cles[J].Colloid and Interface Science,1987,120(1):263-267.
[16]王祥,刘玉华,张敏,等.页岩气形成条件及成藏影响因素研究[J].天然气地球科学,2010,21(2):350-356.
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