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Abstract
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.
Highlights
It is very important to obtain geological parameters such as fluid type and property by collecting representative formation fluid samples, which is of great significance to accurately determine the oil-gas situation of reservoir and reasonably formulate medium and long-term development plan of oil and gas field [1,2]
There are two main ways to obtain formation fluid: wireline formation sampling and formation sampling while drilling(FSWD)
Due to the sampling after drilling, the formation is opened for a long time, and the formation near the wellbore is seriously polluted by mud filtrate, so it is difficult to obtain the real composition data of formation fluid [3]
Summary
It is very important to obtain geological parameters such as fluid type and property by collecting representative formation fluid samples, which is of great significance to accurately determine the oil-gas situation of reservoir and reasonably formulate medium and long-term development plan of oil and gas field [1,2]. Wireline formation sampling technology has been developed for a long time and the technology is mature now. Due to the sampling after drilling, the formation is opened for a long time, and the formation near the wellbore is seriously polluted by mud filtrate, so it is difficult to obtain the real composition data of formation fluid [3]. FSWD is developed on the basis of wireline formation sampling, formation pressure testing while drilling, and formation fluid analysis technology. It can quickly collect low pollution or non pollution formation fluid when the oil and gas reservoir is just opened. In China, CNOOC oilfield services [14,15] and PetroChina Daqing drilling engineering company[16] have made corresponding attempts in pressure and temperature measurement while drilling, but generally speaking, they are still in the stage of importing and imitating corresponding foreign instruments, and there are still some deficiencies in technical level, technical indicators and field application, especially in the absence of downhole opto-fluid analyzers, sampling time prediction is blank
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