联合核磁共振测井与Thomeer模型评价碳酸盐岩储层饱和度

Evaluation of the saturation of carbonate reservoirs by combining the nuclear magnetic resonance logging and the Thomeer model

碳酸盐岩储层孔隙类型多样、孔隙结构复杂,传统的饱和度评价模型无法表征岩石的微观结构,给饱和度评价工作带来了极大的困难。针对该问题,本文以毛管压力曲线资料与核磁共振测井资料为基础,提出了结合核磁共振测井的Thomeer饱和度模型。分析压汞资料的孔隙系统结构信息,利用Thomeer函数拟合得到多孔隙类型的毛管压力曲线分布,将复杂的孔隙结构表征为多条Thomeer曲线的共同作用。核磁共振测井是唯一能够连续定量表征储层孔隙结构特征的测井方法,利用核磁共振横向弛豫时间谱参数T2算术平均值(T2LM)与核磁孔隙度(MPHS),结合R35岩石物理分类计算Thomeer参数B_(v)、P_(d)、G和最大孔喉直径模态元素Porositon,构建复杂孔隙结构碳酸盐岩的饱和度评价模型,该模型解决了实验手段无法开展连续地层孔隙结构评价研究的问题。将该模型应用到中东X油田复杂孔隙结构碳酸盐岩储层进行饱和度评价,与J函数模型、阿尔奇公式进行对比。结果表明该联合模型方法相比于J函数模型与阿尔奇公式,相对误差分别从0.496、0.442降低到0.272,且能较好地表征变化趋势,无论是在高饱和度储层还是低饱和度储层,都取得了较好的应用效果。该模型可以最大程度上避免复杂孔隙碳酸盐岩储层带来的影响,提高饱和度评价精度。

Carbonate reservoirs have various pores and complex pore structures.However,the microstructure of rocks cannot be characterized using conventional saturation evaluation models,making it extremely difficult to perform the saturation evaluation of carbonate reservoirs.Given this,this study proposed a Thomeer saturation model combined with the nuclear magnetic resonance(NMR)logging based on the data of capillary pressure curves and NMR logging.Specifically,information about the structure of the pore system in the mercury injection data was analyzed,and then the capillary pressure curves of multiple pore types were obtained through fitting using the Thomeer function.Finally,the complex pore structure was characterized using multiple Thomeer curves.The NMR logging is the only logging method that can continuously and quantitatively characterize the pore structure of reservoirs.The Thomeer parameters B v,P d,and G and the modal element Porositon of the maximum pore throat diameter were calculated using the logarithmic mean of T2 transverse relaxation time for NMR(T2LM)and the NMR total porosity(MPHS),as well as the classification of pore throat R35.Accordingly,the saturation evaluation model for carbonates reservoirs with complex pore structures was constructed.This model allows for the continuous evaluation of formation pore structure that cannot be achieved using experimental methods.This model was applied to the saturation evaluation of the carbonate reservoirs with complex pore structures in oilfield X in the Middle East.By comparison with the J function model and Archie's formula,this model decreased the relative error from 0.496 and 0.442,respectively to 0.272,better characterized the variation trend,and achieved encouraging application effects regardless of the saturation of reservoirs.Therefore,this model can minimize the impacts of carbonate reservoirs with complex pore structures and improve the precision of the reservoir saturation evaluation.