试油过程中取水样的时机选择

TIMING SELECTION OF WATER SAMPLING DURING PRODUCTION TEST

准噶尔盆地东部地区至1998年底，共有水分析资料1385个，其中在钻井试油时所取的水样为1348个，经反复精选，可靠的、有代表性的水分析资料有225个，仅占全部水分析资料的16．69％．水样的可利用率太低，是由于试油时取水样的时机不当。按以往规范，用硝酸银（AgNO3）试剂滴定水样中的氯离子（Cl－）的方法效果不好，有三分之二以上的水样还是受到泥浆水不同程度的污染，不仅浪费人力、物力、财力，而且资料失真，对井下地质得出错误看法，给油气勘探造成负面影响。现提出改用石蕊试纸随试油抽水过程测定水样的pH值，当pH值由大变小，至pH值小于7．5时，是泥浆污染已经消除的最佳时机。石蕊试纸测定水样的pH值法比硝酸银滴定水样的Cl－法，设备更简单，成本更低。

1385 water samples had been collected by the end of 1998 in eastem Junggar basin. Among these, 1348 samples were taken during production test, and orily 225 twical sarnples picked out, accounting for 16.69% of total samples. It seems to me that such low utilization rate is caused by inappropriate tindng of water sampling during production test. According to convenhonal code, AgNO3, reagent was used to titrate Cl- ion in the sample.Because over two-thirds of samples were contaminated by the drilling mud, the result may be distorted. The author proposed to use litmus paper to measure pH value of water sample taken during production test. When pH value decrease to below 7.5, it is the optimum timing for sampling because mud contandnation elindnated at this point. The latter has a simpler insmiment and lower cost than the former,