| Summary: | Formation sampling while drilling (FSWD) is one of the most advanced formation sampling techniques in the world. It is characterized by short operation time, shallow mud invasion, and the obtained formation data is closer to the real situation of the reservoir. During the sampling process, the first fluid that the suction probe on the borehole wall inhales is basically drilling mud filtrate. With the increase of suction time, it gradually mixes into the formation fluid, and finally the formation fluid is infinitely close to 100%. At this time, it is very important to judge the starting time of sampling. If the sampling time is too early, the percentage of samples contaminated by drilling filtrate will be higher, which can not meet the requirement of fidelity. If the sampling time is too late, the drilling fluid will stop circulating for too long, which will cause sticking. In this paper, the prediction method of sampling time is to simulate the permeability of drilling fluid to formation under certain formation parameters and drilling conditions. Based on the simulated permeability results, the suction model of sampling tool is established to simulate the pumping situation, and the variation of the content of drilling filtrate in the pumped fluid with the suction time is obtained, that is, the relationship between the contamination rate of formation fluid and the suction time, This method is of great significance to the field application of fluid sampling tools while drilling.
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