Numeric Simulation of Factors Affecting the Strengthening of Borehole Wall

Borehole wall strengthening, as an early-stage borehole wall plugging technology, has been widely applied and developed in recent years, while the influencing factors and mechanism of the technology is still not revealed yet. In a study conducted to analyze the influencing factors and the mechanism of the borehole wall strengthening technology, a finite element model of porous media was established, and the anisotropic properties, location of bridging, rate of mud losses, and the pressure at the rear-end of the fracture were studied for their effects on the strengthening of borehole wall. It was shown in laboratory simulation that rigid plugging material, by mitigating the deformation caused by the pressure reduction at the rear-end of fractures, and transmitting the deformation to around the wellbore, increased the circumferential stress around the wellbore near the fractures after being bridged, thereby causing the fractures to close. It was found that the less the anisotropy of the formation stresses, the more remarkable the tendency of the fractures to close. Also found was that the higher the rate of mud loss, the more beneficial it was for the particles to bridge, and the better for the strengthening of borehole wall. In bridging, the nearer was the location of bridging to the mouth of the fractures, the closer was the pressure at the rear-end of the bridging location to the formation pore pressure, and it was more beneficial to the closure of fractures and to the inhibition of the development of the fracture tips.