采用低场核磁共振技术,针对油基钻井液油包水型乳状液乳滴的稳定性进行研究.引入弛豫试剂MnCl2?4H2O对W/Q型乳状液的T2分布曲线进行定性分析,位于10~1 000 ms之间的弛豫峰对应于中度可自由移动水和白油弛豫峰的叠合峰,定义为乳状液弛豫峰;1 000 ~10 000 ms之间的峰为高度可自由移动水的弛豫峰.基于此,以弛豫峰峰形为定性指标,弛豫峰面积比率和弛豫峰间距为定量指标,针对弛豫试剂、油水比和老化温度等因素对乳状液横向弛豫时间T2分布曲线的影响进行了分析,进而深入研究了其对油基钻井液乳状液乳滴稳定性的影响.还将低场核磁共振分析技术运用于油基钻井液乳状液体系相对含油率的测量.结果表明,低场核磁共振是一种高效、快捷、准确反映油基钻井液乳状液稳定性的分析测试技术,同时,还可用于油基钻井液乳状液或原油相对含油率的测量.%The stability of water-in-oil emulsion in oil-based drilling fluid was investigated by low field NMR(low field nuclear magnetic resonance).Firstly,the transverse relaxation time T2 of white oil and pure water were obtained by the CMPG pulse sequence,then,a further qualitative analysis on the T2 distribution curve of water in oil emulsion was conducted by introducing the relaxation reagent MnCl2?4H2O,the relaxation peak located between 10 ms and 1 000 ms corresponded to the overlapping peaks of moderate movable free water and white oil,which was defined as emulsion relaxation peak.The relaxation peak located between 1 000 ms and 10 000 ms corresponded to that of the high degree movable free water.Thus,in this paper,the relaxation peak area ratio and relaxation peak spacing were selected as quantitative indicators to investigate the influences of relaxation reagent,oil to water ratio and aging time on the transverse relaxation time T2 distribution curve of emulsion.In addition,low field NMR was also used to test the relative oil content in oil-based drilling fluids emulsion.Experimental results showed that the low field NMR is an efficient,fast and accurate analysis technique to reflect the stability of oil-based drilling fluids emulsion,and it also could be used to test the relative oil content in oil-based drilling fluids emulsion or crude oil efficiently and accurately.
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