Effects of fluid seepage on wellbore stability of horizontal wells drilled underbalanced

Analysis of wellbore circumferential stresses shows that variation trends of radial stress and tangential stress are the same whether fluid seepage is considered or not, and that the minimum radial stress and the maximum tangential stress are reached at the wellbore wall. However, values of radial stress and tangential stress are greater when fluid seepage is considered. The effects from fluid seepage intensify with the decrease of effective fluid column pressure and diminish with the increase of radial distance. Meanwhile, sensitivity analysis has found that the borehole radius is an influencing factor and that pore pressure, cohesion strength and internal friction angle have certain impact on wellbore stability in both models.