稠油储层核磁共振孔隙度校正方法

Correction for the Nuclear Magnetic Resonance Porosity in Heavy Oil-bearing Reservoirs

受原油粘度的影响,利用核磁共振(NMR)测井获取的稠油储层的测井NMR孔隙度远低于地层的真实孔隙度,给稠油储层评价和NMR测井技术的应用带来极大挑战.为提高稠油储层孔隙度计算精度,必须对测井NMR孔隙度进行稠油校正.本研究选取我国南海东部盆地某油田韩江组10块代表性岩心样品,分别开展了原始状态、饱含稠油、残余油和饱含水状态的NMR实验.研究了孔隙含油相对体积对岩心NMR孔隙度的影响,并建立了基于地层深测向电阻率分类的岩心NMR孔隙度校正模型.将基于实验结果建立的岩心NMR孔隙度校正模型推广到实际地层,对目标区域A14井稠油储层实测测井NMR孔隙度进行处理的结果表明:本文提出的方法能够有效地校正孔隙含稠油对实测测井NMR孔隙度的影响,得到地层的真实孔隙度;校正前、后的稠油储层测井NMR孔隙度与常规气驱法测量的岩心孔隙度之间的相对误差由11.19%降低到4.84%.

The porosity acquired from nuclear magnetic resonance(NMR)logging is lower than the true value in heavy oil-bearing reservoirs due to the viscosity of heavy oil,which is a great challenge in heavy oil-bearing characterization and NMR logging.To improve the porosity prediction accuracy,the effect of heavy oil should be first corrected.In this study,10 typical core samples,which were drilled from the Hanjiang Formation of eastern South China Sea Basin,were chosen for the laboratory NMR experimental measurements under four conditions.These four conditions were initial condition,heavy oil saturated condition,residual oil condition and water saturated condition.The effects of heavy-oil volume on NMR porosity were analyzed,and a method to estimate true NMR porosity based on formation resistivity classification was established.The method was applied in our target well A14,and the true formation porosity was predicted from field NMR logging.The result showed that,the average relative error between NMR porosity and convention core derived porosity was improved from 11.19%to 4.84%by oil viscosity correct using this method.Thus the proposed method is able to effectively correct the effect of oil viscosity on NMR porosity.