Interpretation method of nuclear magnetic resonance dual-TW logging in oil-wet tight sandstone reservoirs

油润湿致密砂岩核磁共振双TW测井解释方法与流体识别

Fluid typing from nuclear magnetic resonance(NMR)logging in oil-wet tight sandstone reservoirs is proving to be diffi cult;thus,research into the NMR logging response mechanism and analysis methods is critical.The NMR response mechanism and theoretical method were investigated based on the oil-water distribution in the pores under oil-wet conditions.The data processing method is studied based on NMR dual-TW activation principle,and the equations of macroscopic magnetization vector,fl uid volume,and relaxation parameters are derived,which is a nonlinear inversion problem.The simulated annealing algorithm is used,and the fl uid relaxation parameters,oil volume,and water volume of the fl ushing zone are calculated.An ideal reservoir model is set up,and simulation results indicate that the above-mentioned NMR relaxation theory and algorithms are valid.A case study is conducted in Huanjiang Oilfi eld in the Ordos Basin,China.The calculated oil saturation of the fl ushing zone is consistent with the oil saturation calculated using the Archie formula,and the test results indicated that the new method is applicable.Moreover,the fl uid-typing cross-plot combined with oil test data is constructed on the basis of the saturation of the fl ushing zone,improving the accuracy of fl uid identifi cation.

在油湿条件下致密砂岩储层的核磁共振测井流体识别面临挑战,迫切需要开展测井响应机理和分析方法研究。基于油湿条件下油水分布特征,研究了核磁共振响应机理和理论方法,推导出了核磁共振双TW测井响应方程。根据核磁共振双TW观测原理,研究了双TW测井的数据处理方法,推导宏观磁化矢量与流体体积和弛豫参数的公式。采用模拟退火算法解决非线性反演,实现了冲洗带流体弛豫参数、含油体积与含水体积等。设置理想模型,基于数值模拟对上述理论和算法进行了正确性检验。在鄂尔多斯环江油田进行了实例应用,核磁计算的冲洗带含油饱和度与Archie公式计的含油饱和度以及测试结果是一致的,表明新方法是适用的。而且,基于冲洗带饱和度构建流体识别图版,提高了流体识别的精度。