Abstract
Wellbore strengthening (WBS) has proven to be an effective method for expanding the pressure windows of drilling operations. Recent research on WBS disclosed the critical role of filtercake in sealing microfractures during the initial stages of fracture initiation and propagation. In this study, a new parameter — “filtercake rupture resistance” — is proposed to simplify the quantitation of the filtercake’s potential to withstand pressure over a small fracture. A modified permeability plugging apparatus (PPA) was used to experimentally simulate the processes of filtercake rupture over a fracture on the wellbore wall and fracture sealing. The effects of filtercake thickness (permeability), filtercake yield strength in shear, and concentration of bentonite and a fine fibrous LCM on filtercake rupture resistance were investigated, along with the effects of these parameters on the effectiveness of filtercake in reducing fracture sealing time. Pressure spikes and fluctuations were observed when applying differential pressure across the filtercakes after formation of the cake. Filtercake of lower permeability and higher shear yield strength produce greater filtercake rupture resistance and shorter fracture sealing time. These results can be used to guide drilling fluids design for improved control of fluid loss.
