基于地层孔隙结构的饱和度评价方法

A saturation evaluating method based on pore structure

油气勘探开发中阿尔奇公式是评价油气含量的经典模型,该模型适用于粒间孔隙的纯砂岩地层.然而实际油气评价中更多时候是以复杂孔隙结构地层为对象,复杂孔隙结构地层岩电关系却呈现出非阿尔奇特性,这意味着利用阿尔奇公式求取这类储层饱和度的可靠性大大降低.针对以上问题,采用变m、n指数和根据孔隙结构分类建立饱和度模型的方法一定程度上满足了此类地层饱和度评价的要求.但以上方法具有很强的区域性和经验性,没有从根本上解决复杂孔隙结构地层饱和度的准确评价问题.等效岩石组分模型将岩石等效为规则的圆柱体,由串联孔隙体积、并联孔隙体积和骨架体积构成,由许多这样大小不一的孔隙分量并联/串联构成整个岩石的导电体系,并引入孔隙结构系数表示不同孔隙的体积比,精确地描述了由复杂孔隙结构引起的非阿尔奇特性.其应用瓶颈是孔隙结构系数、饱和度因子等关键参数的确定方法.本文以等效岩石组分模型为基础。利用核磁测井资料和球管模型确定孔隙结构系数,根据孔隙结构寻优路径对地层进行分类,以岩电实验数据为基础利用阻尼最小二乘法分类确定模型参数,用等效岩石组分模型迭代计算地层饱和度,从而配套形成基于孔隙结构的饱和度评价方法.岩心实验数据分析和实际应用效果表明基于孔隙结构的饱和度模型与阿尔奇公式相比在复杂孔隙结构地层饱和度评价中具有优越性,在复杂孔隙结构地层含油气饱和度评价中具有良好的应用前景.

Archie＇s formula is the classical theory in evaluating the saturation in oil-gas exploration and development, it applies to pure sand formation with inter granular pore. But in practice, the litho-electric property of the reservoirs with complicated pore structures shows non-Archie phenomenon, which indicates the reduced reliability of Arehie＇ s formulation in calculating the saturation. To solve the problem, some methods have been proposed such as variable m, n parameters method and constructing saturation models based on the classification of pore structures. But these methods depend on regional experiences seriously, and cannot radically solve the problem of accuracy of saturation evaluation of reservoirs with complicated pore structures. The Equivalent Rock Element Model divide the pore structure into two orthogonal components based on the rock conductive mechanisrru One is oriented along electrical potential gradient and the other is perpendicular to the gradient. The pore structure coefficient is also introduced to describe the volume ratio of different pores in the model. So the model can accurately describe the non-Archie character of reservoirs with complicated pore structures. However this model has the restriction on determining some key parameters, such as pore structure coefficient, saturation factor and so on. In this paper, we base on the equivalent rock element model and firstly determine the pore structure coefficient from NMR logging data and sphere-cylinder mode, then we classify the reservoirs according to the optimal path of pore structure and determine model parameters on the basis of rock-electric experiment data with the damped least square method. After that, the saturation is determined by iterative calculation according to the equivalent rock element model. Finally, we propose a set of evaluation method for oil saturation. Core experiment data analysis and practical application results show that the saturation model based on pore structure can achieve better effect than Archie＇ s formulation in saturation evaluation of reservoirs with complex pore structures. So this method has good prospect in hydrocarbon saturation evaluation of these formations.