气体钻井技术不但具有避免井漏、泥页岩水化膨胀和储层污染等问题的优点,而且能够大幅度提高钻井速度,提高钻井速度4~8倍,有利于及时发现和有效保护储层及提高油气采收率和单井产量,特别对坚硬地层、致密储层勘探有着重要的意义.但是气体携屑困难、井眼堵塞等问题一直是阻碍该钻井方式推广的瓶颈问题,解决这些问题的关键技术之一就是最小注气量的确定.目前多数文献是用地层温度代替环空温度来进行最小注气量计算,但由于气体的PVT效应,温度受压力流速影响较大,若用地层温度代替环空温度存在较大误差.同时,以往最小注气量计算方法均将关键点设置为钻铤顶部,然而本研究中发现井筒内气体的携岩动能并非一定在钻铤顶部最小,井身结构和钻具组合对关键点位置的影响较大.应用温度-压力耦合计算方式,确定的气体钻井最小注气量与现场施工更加接近,在给定工况下,最小注气量误差在0.4%左右.%Gas drilling technology not only has the advantages of avoiding the leakage of the well, the expansion of the mud shale and the pollution of the reservoir, but also can greatly improve the drilling speed, it is also beneficial to the timely detection and effective protection of reservoir and improve the recovery of oil and gas and the yield of single well. However, the difficulty for the chip carrying, the hole blocked hinder the development of this drilling technology. The key point to solve these problems is to determine the minimum air rate in gas drilling. At present, the formation temperature is always used to replace the annulus temperature to calculate the minimum air rate, but because of PVT effect of the gas, there will be a big error. Meanwhile, the traditional method of calculation takes the top of drill collar as the "key point", the minimum rock carrying shaft gas kinetic energy is not necessary in the top of the drill collar, the"key point" is influenced by the well structure and drilling tool combination. In this paper, the temperature and pressure coupling calculation method was used to calculate the gas drilling minimum gas injection rate, calculated result was closer to the construction site condition; Under the given conditions, the minimum gas injection error was about 0.4%.
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