Effect of high-salinity drilling fluids on nuclear magnetic resonance logging and its countermeasures

As the exploration of Bohai Oilfield moves into the middle-deep formations, high-salinity drilling fluids are often adopted in order to reduce the effect of formation caving and formation pressure on well drilling and test, but their adoption deteriorates the quality of nuclear magnetic resonance logging (NMR logging).In this paper, BZ19-6 Oilfield was taken as an example to solve this problem.Based on the logging data of Well A, the influential laws of high-salinity drilling fluids were investigated focusing on the principle and quality control of NMR logging.It is indicated that the main reason for the deterioration of logging quality is the reduction of drilling fluid's resistivity, which leads to the decrease of NMR logging gain, the reduction of instrumental stability and the increase of logging signal attenuation.The countermeasure is to inject the sealing slurry of high sealing and lubricating capacity into the open hole section before the logging operation.It is practically proved that this coping method can eliminate the effect of high-salinity drilling fluids on NMR logging effectively and improve the NMR logging quality in the operation zones (e.g.Well B) of BZ19-6 Oilfield significantly with the operation success rate of 100%.The research results provide the technical foundation for the exploration of middle-deep formations in Bohai Oilfield.