基于核磁共振实验的油基钻井液侵入分析

Invasion Analysis of Oil-Based Drilling Fluid Based on NMR Experiment

为了厘清准噶尔盆地南缘深层、超深层油基钻井液侵入特性及对核磁共振测井的影响,针对岩性、物性、钻井液侵入时间、钻井液成分、钻井液油水比、流体性质、温度等影响因素进行油基钻井液核磁共振实验分析研究。实验结果表明,油基钻井液侵入方式为驱替和渗吸两种方式。明确了油基钻井液滤液与基液的核磁共振T_(2)谱谱峰位置均为400ms,表明油基钻井液侵入地层的滤液为其基液;其核磁共振T_(2)谱特征不受油基钻井液油水比影响,受黏度控制;核磁共振T_(2)谱谱峰形态受流体性质、渗透率双重影响,不受岩性和孔隙度影响。油基钻井液不会影响核磁共振总孔隙度,但会导致可动孔隙发生改变,造成可动孔隙度增大的假象,其变化程度主要受渗透率和侵入时间双重控制。实验结果为油基钻井液侵入特性认识、核磁共振孔隙度校正奠定了基础。

In order to clarify the intrusion characteristics of deep and ultra-deep oil-based drilling fluids in the southern margin of Junggar basin and its influence on nuclear magnetic resonance(NMR) logging,NMR experiments are conducted to analyze the influencing factors such as lithology,physical properties,drilling fluid intrusion time,drilling fluid composition,drilling fluid oil-water ratio,fluid properties and temperature.The experimental results show that the invasion modes of oil-based drilling fluid are displacement and imbibition.The NMR T_(2) spectra of the filtrate and the base fluid are both 400 ms,indicating that the filtrate of the oil base drilling fluid invading the formation is its base fluid.The NMR T_(2) spectral characteristics are not affected by the oil-water ratio of oil-based drilling fluid,but are controlled by the viscosity.NMR peak morphology is influenced by fluid properties and permeability,but not by lithology and porosity.Oil-based drilling fluid does not affect the total NMR porosity,but causes changes in the mobile porosity,resulting in the illusion of increasing the mobile porosity.The degree of change is mainly controlled by permeability and invasion time.The experimental results lay a foundation for understanding the invasion characteristics of oil-based drilling fluid and nuclear magnetic resonance porosity correction.