基于测井曲线分形维的碳酸盐岩孔隙结构分类方法

Classification method of carbonate pore structure based on fractal dimension of well logging curve

非均质储层的孔隙结构与物性、渗流、电性等特征密切相关,是影响储层品质及流体性质的重要因素.利用常规测井曲线实现全井段孔隙结构定量评价对于储层非均质性评价具有重要意义.首先根据岩心压汞资料对孔隙结构进行分类,依据分形理论求取不同测井曲线的分形维数,通过对比选取反应孔隙大小的孔隙度测井曲线盒维数和反应孔隙连通程度的电阻率曲线R/S维数来对孔隙结构进行分类评价,绘制孔隙度曲线加权盒维数和电阻率曲线加权R/S维数交会图,确定每类孔隙结构分类标准,最后利用分形维数范围对全井段孔隙结构进行分类.研究表明,不同测井曲线反应的岩石物理信息不同,其分形维不一定相同.地层非均质性越强,不同测量原理的曲线计算的分形维差别越大;通过提取反应不同测井曲线变化复杂程度的维度信息,建立交会图识别孔隙结构类型,充分考虑了孔隙大小和连通程度,避免了单一分形维无法完全反映曲线的变化程度,避开了流体等信息对测井曲线的影响,提取的参数仅反应岩石非均质性强度,有利于解决油气勘探中非均质性地层孔隙结构精细定量评价问题.

The pore structure of heterogeneous reservoir is closely related to physical properties,seepage and electrical properties,which is an important factor affected reservoir quality and fluid properties.It is of great significance for reservoir heterogeneity evaluation to realize pore structure quantitative evaluation by using conventional logging curve.Firstly,the pore structure is classified according to the mercury injection data.Then the fractal dimension of different logging curves were calculated based on the fractal theory.We selected the box dimension of three porosity curves(acoustic wave,neutron,density)and the R/S dimension of resistivity curve to classified and evaluated the pore structure.Then the crossplot of porosity box dimension and resistivity R/S dimension is made to determine the fractal dimension range of each kind of pore structure.Finally,the fractal dimension range is used to classify the pore structure of the whole well section.Research shows that,different logging curves reflect different physical information of rocks,and their fractal dimensions are not necessarily the same.The stronger the heterogeneity is,the greater the difference of fractal dimension is.By extracting the dimensional information of the complexity of different logging curves,the crossplot is established to identify the type of pore structure,which fully considers the pore size and connectivity,and avoids that the single fractal dimension can not fully reflect the change degree of the curve.The influence of fluid and other information on logging curve is avoided,and the extracted parameters only reflect the strength of rock heterogeneity,which is helpful to solve the problem of fine quantitative evaluation of pore structure of heterogeneous formation in oil and gas exploration.So as to realize the purpose of using the fractal dimension of conventional logging data to quickly classify and evaluate the pore structure.