Lost circulation and filter cake evolution: Impact of dynamic wellbore conditions and wellbore strengthening implications

Abstract

Lost circulation events and mud filtration in drilling operations have been investigated over the years because they lead to non-drilling time (NDT) and increase the overall well cost. Solutions have been offered from the addition of fluid loss control additives, the use of lost circulation materials (LCM), advanced pills, to novel solutions and technologies such as wellbore strengthening, casing while drilling (CwD), and managed pressure drilling (MPD). However, lithology complexities, geothermal and geochemical effects, and wellbore drilling dynamics continue to push the boundaries to enhance available preventative and mitigation strategies.In this study, pore and fracture-scale mud invasions are investigated and the results are used in characterizing filter cake wellbore strengthening. The methods used have been described in detail in the paper. The theoretical and experimental investigations revealed that wellbore temperature, drill string rotary speed, fracture width, rock permeability and porosity, LCM type, and LCM concentration are critical factors influencing filter cake evolution. SEM image and elemental maps of selected samples showed near-wellbore pore plugging by granular LCM. More than a 50% reduction in losses through a 2000 μm fracture width was recorded and concentration thresholds were established for the granular and fibrous LCM's, based on dynamic wellbore conditions. The numerical results showed that the rock permeability and filter cake permeability profiles largely control the changes in a wellbore hoop stress profile. This integrated approach will provide extensive details which will help inform decision making and select critical parameters for drilling different lithologies, loss prone zones, and achieving wellbore strengthening.