根据欠平衡原理和小井眼环空压耗模型,提出一种适合小井眼欠平衡工况的钻井液密度计算方法,主要包括三个步骤:负压值确定、环空压耗计算和密度优化。应用该模型编制的软件对某井进行环空压耗计算,相对误差小于15%;结合现场数据验证,计算的钻井液密度符合现场施工要求。 According to the principle of underbalance and the annulus pressure depletion model of slim hole, a method for calculating the density of drilling fluid suitable for the underbalanced condition of slimhole is proposed. The method mainly includes three steps: negative pressure value calculation, annular pressure loss calculation and density optimization. The software of this model was used to calculate the annulus pressure loss of a well, the relative error was less than 15%. According to the field data, the calculated drilling fluid density was in accordance with the site construction requirements.