Constructing a Tough Shield around the Wellbore by Stabilizing the Multi-Scale Structure of Granular Plugging Zone in Deep Fractured Reservoirs

Fracture plugging zone with low strength is one of the key reasons for plugging failure in deep fractured reservoirs. Forming a high-strength plugging zone is a key engineering problem to be solved in wellbore strengthening. In this chapter, wellbore strengthening mechanisms of plugging zone for wellbore strengthening in deep fractured reservoirs are revealed from a relationship between mechanical structure and strength standpoint. Physical granular bridging materials dislocation and crushing under pressure fluctuation induce the strong force chains network failure, which leads to macroscale friction or shear failure of plugging zone. The main methods to improve microscale materials stability are to increase friction resistance, exert embedding effect, and strengthen bonding effect. Factors, which strengthen the meso-structure stability, include increasing shear strength and proportion of strong force chains. Key measures to strengthen the macrostructure stability of plugging zone are by improving its compactness, controlling its length, and ensuring the stability timeliness.