漏失裂缝内封堵层演化规律及颗粒特征行为的可视化实验研究OA北大核心

Mud losses into fractures is one of the most difficult problems encountered in drilling unstable formations.Particle bridging is the most effective method of controlling mud losses into fractures.In traditional fracture experimental apparatus how the plugging layers are formed inside the fractures by the flow of particles is still not clearly understood,and this restricts the scientific build-up of a lost circulation slurry.To investigate the characteristic behavior of particles and the dynamic evolution of plugging layers inside fractures,a wellbore-fracture visualization experimental device is set up,and is used to systematically study the behavioral characteristics of the particles,the pattern in which the plugging layers are formed as well as the influencing mechanisms of the formation of the plugging layers under the effects of key factors such as particle size,particle concentration,flowrate of the particle slurry pumped into the fractures and the viscosity of the carrying fluid etc.The experimental results show that the plugging process taking place inside the fractures can be divided into four stages in each of which co-exist the mixing of the particles and the change of the characteristic behavior of the particles.The position at which a plugging layer is set up is highly sensitive to the size distribution of the particles,the concentration of the particles affects the time required for the fractures to be plugged,the structure of the plugging layers is easily altered by the viscosity of the carrying fluid,and too high a pump rate may damage the plugging structure previously formed.