高矿化度钻井液对核磁共振测井的影响及对策

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

随着渤海油田的勘探步入中深部地层,为了降低地层垮塌及地层压力对钻井和试油的影响,往往采用高矿化度的钻井液,易造成核磁共振测井作业质量下降。为解决该问题,针对渤中19-6油田,围绕核磁共振测井原理和质量控制,基于A井测井资料,展开高矿化度钻井液影响规律研究。研究结果表明,导致测井质量下降的主要原因是钻井液电阻率降低,引起核磁共振测井增益减小,仪器工作稳定性降低,测井信号衰弱增大;应对方法是在测井作业前,裸眼段内垫入高封堵、高润滑封闭浆。实践证明,该方法能够有效消除高矿化度钻井液对核磁共振测井的影响,显著提高渤中19-6油田B井等作业区中核磁共振测井作业质量,作业成功率100%,为渤海油田勘探步入中深部地层提供技术经验。

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.