Microscopic flow study of model drilling fluid viscoelasticity on hole cleaning

One of the technical challenges in directional drilling is transporting drilled cuttings to the surface, because of the narrow settling clearance for the cuttings on the low side of the bore hole. Drilling fluid rheology is one of the factors determining the presence and size of the cuttings bed formed on the low side. Microscopic studies were carried out to compare the efficiency of purely viscous and viscoelastic rheology models to predict velocities of this cuttings transport process. Video microscopy, digital image processing and finite element analysis techniques were combined to study the effect of fluid rheology on the movement and resuspension of a model particle bed under well defined shearing flow conditions. The studies demonstrated that fluid material properties such as apparent viscosity, plastic viscosity (PV), yield point (YP) and gel-strength estimated from purely viscous fluid rheological models had limitations in predicting particle mobilization velocities and settling times.