油基钻井液条件下油层的NMR判识方法

油基钻井液具有润滑性好、抑制性强等特点，有利于井壁稳定和油气层保护，在非常规油气水平井及深井、超深井中广泛使用．但是，油基钻井液具有较强的荧光背景和全烃基值，岩屑难以洗出本色，地层油与钻井液的基础油融合，给油层的识别和评价带来了严重影响．为此，创新采用高分辨率低场核磁共振技术随钻监测钻井液含油率及含油性的变化．室内实验结果表明，油基钻井液不同于混油钻井液，后者属于水包油体系，钻遇油层后，在钻井液T₂谱上出现新峰；而前者属于油包水体系，钻遇油层后，在钻井液T₂谱上不出现新峰，但可通过含油性的变化识别重质油层，通过含油率的变化识别轻-中质油层，并在S903H井全油基钻井液及极端的地质条件下取得了较好的应用效果，证明了钻井液核磁共振是油基钻井液条件下一项有效的油层识别技术．

Oil Layer Identification by NMR with the Use of Oil-Based Drilling Fluid

Oil-based drilling fluids show advantages such as high shale inhibition and good lubrication, and are beneficial for borehole stability and protecting the oil layers in unconventional horizontal and deep wells. However, oil-based drilling fluids often have strong fluorescent signals and high total hydrocarbon ratio, such that it is difficult to wash the rock debris clean when these fluids are used, resulting in contamination of oil in the layer and making identification and evaluation of oil layers problematic. In this work, high-resolution low-field NMR while drilling was used to monitor the oil content in drilling fluids.The results showed that oil-based drilling fluids had different NMR characteristics from mixed drilling fluids. The latter is an oil-in-water system, such that the new peaks would arise in theT2 spectrum when drilling into oil layer. The former is a water-in-oil system, and no new peaks would arise in theT2 spectrum when drilling into the oil layer. Under such circumstance, however, heavy oil could be identified via oil characterization, and middle and light oil could be determined by analyzing oil content in the oil layer. This method proposed was applied in Well S903H with complex geology and the use of oil-based drilling fluid. It was proved that drilling fluid NMR technique an effective method for identifying oil layers.