黔西地区煤样孔隙综合分形特征及对孔渗性的影响

Pore integrated fractal characteristics of coal sample in western Guizhou and its impact to porosity and permeability

为了定量描述煤储层孔隙结构的复杂程度,基于压汞试验测试结果,运用分形理论,对黔西地区不同煤阶的32个煤样进行了分形特征研究,并探讨了分形几何参数与煤储层孔渗性的关系。结果表明:煤储层孔隙分形维数可分为渗流分形维数和扩散分形维数,利用不同分形段的孔隙体积比作为权值,通过加权求和方法可得到综合分形维数;渗流分形维数随变质程度增加而减小,扩散分形维数和综合分形维数均随变质程度增加而增大;分形界限、扩散孔隙体积分数及总孔体积都与综合分形维数、扩散分形维数具有较好的相关性,而且3个指标参数与综合分形维数的相关系数均高于与扩散分形维数的相关系数;综合分形维数、分形界限及扩散孔隙体积分数与煤储层孔隙度之间为负幂指数相关关系,总孔体积与煤储层孔隙度为线性正相关关系,与渗流分形维数和扩散分形维数相比,综合分形维数更有利于表征煤储层渗透性。

Based on a mercury injection test and fractal theory,a total of 32 coal samples from western Guizhou with different ranks were studied on their fractal characteristics in order to quantitatively describe the complexity of pore structure.The relationship between fractal geometry parameters,porosity and permeability of coal reservoir was also discussed.The result shows that the pore fractal dimension in this area could be divided into penetration fractal dimension and proliferation fractal dimension.In addition,by using the pore volume ration as weights and the fractal dimension of each diameter section weighted sum,the integrated fractal dimension could be calculated.At the same time,the penetration fractal dimension decreased with the increase of coal seam metamorphism,while the proliferation fractal dimension and integrated fractal dimension increased with the increase of coal seam metamorphism.The fractal boundary,proliferation pore volume fraction and total pore volume had a good correlation with the integrated fractal dimension and proliferation fractal dimension.Moreover,the correlation coefficient between integrated fractal dimension and anterior three parameters was higher than that proliferation fractal dimension and three parameters.The integrated fractal dimension,fractal boundary and proliferation pore volume fraction had a negative power exponent relationship with porosity,while a clear linear positive relationship was shown between total pore volume and porosity.Compared with penetration fractal dimension and proliferation fractal dimension,the integrated fractal dimension is more effective to explain coal reservoir permeability.