Wellbore Strengthening: The Less-Studied Properties of Lost-Circulation Materials

Abstract

Abstract Lost circulation is one of the major issues that lead to unwanted non-productive time (NPT) while drilling with a narrow mud weight window and it requires engineered solutions to address the problem. In several instances in the past, wellbore strengthening was achieved by treating the drilling fluid with lost circulation material (LCM), utilizing Stress Caging or Wellbore Strengthening theory. Small fractures were propped and sealed with a proper size distribution of particles that isolates the fracture tip from fluid pressure and controls the fracture propagation, effectively increasing the near wellbore hoop stress. Laboratory data and field experience indicate limited success may occur if a single material such as sized calcium carbonate is used alone for wellbore strengthening. This is possibly due to size reduction that may occur while drilling or due to fracture closure stresses (FCS) acting on the particles. However, using calcium carbonate in conjunction with resilient graphitic carbon (RGC) material has shown to be effective in increasing the formation integrity. The effect of mechanical properties of LCMs on wellbore strengthening has been investigated using compression/crush tests at different confining pressures simulating a wide range of FCS. Crush test demonstrated compaction and significant crushing of the ground marble and ground nut shells at high confining pressure (~ 5000 Psi). Considerable improvement in the crushing resistance and resiliency of these materials was observed with small additions of RGC. Knowledge of deformation and failure behavior of different LCM materials may result in better design. In this paper recommendations are made on different combinations of LCM that may be used more effectively to provide wellbore strengthening.