川东北元坝地区元坝11井地应力建模和井壁稳定性分析

 川东北元坝地区由于地质条件复杂,多次发生井漏、坍塌、溢流等复杂井况与事故,严重影响施工周期.本文利用GMI井壁稳定性软件,依据元坝11井钻井、测井及地质资料,计算了元坝11井的岩石力学参数,并依据岩石力学实验数据,实现了杨氏模量及泊松比的动静态转化.进一步,利用压裂资料及井眼崩落法则约束最小、最大主应力,计算了最大、最小主应力.建立了元坝11井的孔隙压力、坍塌压力及破裂压力三压力剖面,预测了泥浆密度窗口,分析了元坝11井的井壁稳定性.结果表明,元坝地区陆相地层自下沙溪庙组至须家河组坍塌压力变化较大,导致泥浆密度窗口缩小,并且钻井过程中选取泥浆密度不合适,地层多为砂泥岩薄互层,导致层段多次发生复杂情况,井眼扩径明显;海相地层变化相对较小,泥浆密度窗口较大,井壁相对稳定.

Stress Modeling and Well Stability of Well Yuanba11 in Yuanba Area in Northeastern Sichuan Basin

In Yuanba area of northwestern Sichuan Basin, due to complex geological conditions, many complicated downhole accidents occur, such as the well leakage, the borehole collapse and the overflow, which would affect the drilling schedules. Using the GMI well stability software, based on the drilling data, the well logging and the geological information in Well Yuanba11, the mechanical parameters were calculated. Combined with the experiment data, the Young's modulus and Poisson's ratio were converted from dynamic values to static ones. In addition, the minimum and the maximum horizontal stresses were constrained and computed by the fracture information and the wellbore breakout method. Based on above results, the three pressure section, the well stability analysis and the mud scope were investigated, to provide a basis for the drilling design. The results indicate that in Jianmenguan Formation of terrestrial layer, the strata is characterized by fractures and well water permeability, where the fluid would easily be lost. Then in the air drilling section, due to the high and variable collapse pressure, the air drilling is not suitable. After the routine drilling replaces the air drilling, the mud density is lower and near to the pore pressure and the collapse pressure, which would lead to unstable borehole. So, many complicated downhole accidents would occur. While drilling in the depth of 4000m, the mud density is increased so that the complicated situations are mitigated. But in Xujiahe Formation, owing to the low mud density, the pore pressure is so high that the overflow would occur. In the marine section, the mud weight is higher, and actually, the formation pressure is lower. Therefore, the plastic flow of the salt layer would occur and sometimes the stickings may occur, which are distributed in Jialijiang Formation and Changxin Formation.