充气钻井液的影响因素分析

井底压力的控制是充气钻井、井底欠平衡和防止井壁坍塌的关键，对其控制因素的研究和分析具有重要的现实意义。为此，利用Mukherjee和Brill的倾斜管两相流方法，建立了求解井底压力的数值模型。利用四阶龙格库塔算法，提出了该数值模型的求解方法，给出了求解的计算流程图。分析得出影响充气钻井液井底压力的主要控制因素为注气量、钻井液排量、井斜角以及钻井液黏度，通过编写的软件对4个主要控制因素进行了敏感性分析。随着注气量的增加井底压力逐渐降低，但当增加到某极限值后井底压力反而会增加；随着钻井液排量的增加，井底压力逐渐增加；井底压力随井斜角的增加而减小；随着黏度的增加井底压力增加。

EFFECT ANALYSIS ON CBM AERATED DRILLING FLUID

The key to aerated drilling, downhole underbalance and borehole wall sloughing prevention is to control bottom pressure, so study and research on its controlling factors is of importance. The numerical model to calculate well bottom pressure is established through inclined two phase flow method by Mukherjee and Brill. The solution to this numerical model is got by fourth order Runge Kutta algorithm and its calculating flow diagram is given. It is shown that the main controlling factors on wellbottom pressure of drilling fluid is the gas injection volume, drilling fluid discharging volume, deviation angle and drilling fluid viscosity according to the analysis. The sensitivity analysis of these factors is taken through the software. With the increase of gas injecting volume, the wellbottom pressure increasingly decreases till up to an extreme, it rises up instead; with the increase of drilling fluid volume, the wellbottom pressure increasingly rises up; with the increase of deviation angle, the wellbottom pressure drops down; with the increase of wellbottom viscosity, the wellbottom pressure rises.