井壁强化作用影响因素的数值模拟

近年来，井壁强化等先期封堵技术逐渐得到了应用和发展，但其相关影响因素及作用机理还未得到深入揭示。通过建立多孔弹性介质的有限元模型，考虑地应力各向异性、架桥位置、漏失速率及裂缝后端压力等因素的影响，对井壁强化机理及相关影响因素进行了分析。模拟结果表明，刚性封堵材料通过减缓裂缝后端由于压力下降所产生的形变，并将该形变向井壁周围传递，使架桥后裂缝附近的井壁周向应力增加，从而导致裂缝趋于闭合；地应力各向异性越小，裂缝闭合趋势越明显；漏失速率越大，越有利于封堵颗粒的快速架桥，井壁强化效果越好；封堵材料架桥时，架桥位置距离裂缝端口越近，架桥位置后端压力越接近地层孔隙压力，越有利于裂缝的闭合及抑制裂缝尖端的扩展。 

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.