煤层气水平井煤层段井壁破裂压力预测——以沁水盆地樊庄3号煤层为例

针对煤层气井井壁破裂问题,应用岩石力学分析方法,从井壁应力分布入手,根据任意斜井井壁力学模型,结合最大拉应力理论,建立了水平井煤层段井壁临界破裂压力计算公式,并对沁水盆地樊庄3号煤层水平井煤层段井壁临界破裂压力进行了预测。结果显示:樊庄3号煤层水平井在钻井过程中(为防止地层被压开),钻井液密度应控制在3.28 g/cm3以内;水平井压裂时最小破裂压力梯度为3.22 MPa/hm。 

Prediction of fracture pressure at coal segment of CBM horizontal wells:with seam No.3 in Fanzhuang in Qinshui basin as an example

In order to solve the wellbore fracture problems of coal bed methane (CBM) wells, a formula based on the mechanical methods and the maximum normal stress theory for calculating the collapse pressure for the horizontal wells was established to calculate the critical fracturing pressure of the horizontal wellbore. The formula was used to forecast the critical fracturing pressure for the horizontal well in Qinshui Fanzhuang 3#CBM field. The results show that the drilling fluid density should be controlled within the 3.28 g/cm3 in drilling process of horizontal wells to prevent formation from being pushed open; and the minimum fracture gradient in fracturing horizontal well is 3.22 MPa/hm.