Theoretical and Experimental Analysis on Wellbore Enhancement in Fractured Formation through Tight Fracture Plugging by Drilling Fluid

Abstract

With the aim to prevent lost circulation and wellbore instability in drilling, this paper probes deep into the wellbore enhancement mechanism and tight fracture plugging (TFP), and simulates the performance of different drilling fluids. First, the wellbore enhancement mechanism of stress cage technique, which improves wellbore pressure (WP) containment, was investigated through ABAQUS finite-element modeling. It was found that WP containment could be enhanced by improving the drilling fluid plugging or propping of existing or new fractures, which curbs fracture propagation and increases hoop stress of the wellbore. Moreover, a physical model of the TFP zone was established, revealing the microscale plugging mechanism. On this basis, the author put forward a way to optimize the TFP drilling fluid and thus the WP containment: creating a TFP zones with a strong force chain network from the rigid and resilient particles of reasonable type and size distribution and fibers. In addition, a novel simulation device was designed to evaluate and simulate the dynamic plugging features of drilling fluid, and used to optimize the enhanced TFP formulas for drilling fluid at wedge fractures of different widths. The optimized formulas can improve the loss-prevention of drilling fluid and significantly boost the WP containment in subsurface formation.