Effect of cuttings on annular pressure loss

Accurate measurements of pressure loss in the annulus are critical in order to optimize drilling operations and to ensure a safe drilling environment. Monitoring Equivalent Circulating Density (ECD) is essential because it ensures that the applied dynamic fluid pressure is within the drilling margin. The presence of drill-cuttings in the annulus increases the ECD by increasing the effective density and rheology of the drilling fluid in the annulus. However, existing ECD models do not consider the effect of cuttings on drilling fluid even though one of the drilling fluids' primary functions is to carry cuttings from bottom-hole to the surface. This study proposes a modified pressure loss equation for Yield Power Law fluids that takes into consideration the effect of cuttings within the annular mud flow. The proposed equation is then evaluated against experiments that measure pressure gradients for fluids with solid particles. The accuracy of the modified pressure equation is significantly high when compared with actual experimental results. The objective of this work was to develop a model that couples the proposed modified pressure gradient equation with a cuttings transport model to predict the ECD for vertical wells. Additionally, the model provides a cuttings concentration map that illustrates the cuttings distribution vs. depth to highlight any problematic zones. Different drilling scenarios are presented in the results and discussions section to emphasize the effect of drilling rate of penetration (ROP) and flowrate on the cuttings concentration; as a result, on the annular pressure loss and ECD. The model also provides analyses on the bottoms-up time and on the volume of cuttings that reach the surface and highlights the effect of cuttings size on ECD and bottoms-up timePetroleum and Geosystems Engineerin