孔隙压力变化对水平井井壁围岩应力的影响

Influence of pore pressure change on borehole surrounding rock stress of horizontal wells

针对水平井井壁围岩应力随井壁渗流压力变化的问题,考虑井内流体渗滤造成井壁岩石孔隙压力和孔隙度变化,推导孔隙度与井内流体压力和渗滤半径的理论关系,建立考虑孔隙压力变化的井壁围岩应力计算模型。应用模型计算表明:孔隙压力变化对井壁上径向、周向和轴向应力大小影响明显,渗滤带内随着距井眼中心距离增加,孔隙压力逐渐趋于地层初始压力,考虑和不考虑孔隙压力变化计算得到的径向、周向和轴向应力差值逐渐减小,在渗滤边界处考虑和不考虑孔隙压力变化计算得到的各向应力数值相等。

In view of the problem that borehole surrounding rock stress changes with well -wall seepage pressure in the horizontal well ,we took changes of the pore pressure and porosity caused by borehole fluid percolation into consideration ,de- duced a theoretical relationship among porosity,borehole fluid pressure, and percolation radius,and established a calculating model for sidewall surrounding rock stress considering the pore pressure change. Calculation results show that the pore pres- sure change has obvious effect on the radial, circumferential and axial stress of the sidewall. In the percolation region ,with the increase of distance from the center of the borehole ,the formation pore pressure approaches to original formation pressure, and difference value between radial stress, circumferential and axial stress with and without pore pressure change gradually de- creases. And stress values in all direction with and without pore pressure change are equal at the percolation border.