基于有效介质与等效岩石元素理论的特低渗透率储层饱和度模型

Saturation Model for Ultra-low Permeability Reservoirs Based on the Effective Medium Conduction Theory and Equivalent Rock Element Theory

清水洼陷沙三段储层属于特低渗透率储层,具有含泥质、微孔隙发育、束缚水饱和度较高、孔隙结构复杂的特征。建立该区块饱和度模型时应考虑这些因素对岩石导电性的影响。将含泥特低渗透储层等效成孔隙大小和形状及所含流体性质和含量不变的纯岩石,利用等效岩石元素理论描述孔腔和喉道比对岩石导电性的影响,利用有效介质对称导电理论描述孔隙结构对岩石导电性的影响,分别建立等效纯岩石的导电方程,并联立求解得出等效混合流体介质电导率表达式;再利用有效介质对称导电理论描述泥质附加导电对岩石导电性的影响,将求得的等效混合流体介质电导率代入该方程中,从而建立基于等效岩石元素理论和有效介质对称导电理论的含泥特低渗透储层导电模型。利用清水洼陷沙三段储层的岩电实验测量数据对该模型进行精度分析,测量岩样电导率值与计算电导率值平均相对误差很小,说明提出的模型能很好地描述特低渗透储层岩石的导电规律。利用建立的模型及确定的模型参数值处理了清水洼陷沙三段储层实际井资料,结果表明,所建立的模型适用于清水洼陷沙三段特低渗透泥质砂岩储层评价。

Reservoirs in ES3 Formation in Qingshui sub-sag have ultra-low permeability, shalebearing, more microscopic capillary pores, high irreducible water saturation and complex pore structure. Therefore it is necessary to take the influence of these factors on sand conductivity into account when establishing the saturation model for reservoirs. Firstly, shale-bearing and ultra- low permeability reservoirs are considered equivalently as clean sands which pore size, shape and fluid property, content are unchanged. The equivalent rock element theory is used to describe the influence of pore-throat ratio on sand conductivity, and the effective medium conduction theory is used to describe the influence of pore structure on sand conductivity. The conductivity equations of the equivalent clean sands are established respectively. Conductivity expression of equivalent mixed fluid is derived from the two equations. Secondly, the effective medium conduction theory is used to describe the influence of shale excess conductivity on shale-bearing and ultra-low sand conductivity. After substituting conductivity expression of equivalent mixed fluid into this equation, a conductivity model for shale-bearing and ultra-low permeability sand reservoirs is established based on equivalent rock element theory and effective medium conduction theory. Accuracy analysis of this model is done with experimental core data in ES3 Formation in Qingshui sub-sag. The average relative error of the measured conductivity and calculated conductivity of rock samples is very low. It shows that the proposed model can describe the conductivity law of shale-bearing and ultra-low permeability reservoirs perfectly. The log data in ES3 Formation in Qingshui sub-sag are processed and interpreted with the proposed model and model parameters determined from the optimization technology. The results show that the model can be applied in the evaluation of ultra-low permeability and shale-bearing sand reservoirs in ES3 Formation in Qingshui sub-sag.