Mud loss into a single fracture during drilling of petroleum wells: modelling approach

Drilling in fractured zones in petroleum reservoirs often brings about severe mud loss problems. Understanding mud loss mechanics is vital for the development of troubleshooting techniques. It is equally important for the development of innovative methods of formation characterization based on drilling data measurements. A coupled one-dimensional model of mud loss into a single horizontal fracture intersected while drilling is developed. The model is computed with a finite difference scheme, yielding mud loss versus time curves strongly resembling the ones measured during drilling operations. Effects of different factors on mud loss dynamics are studied using the model; primarily those of initial fracture aperture, formation pressure, mud viscosity, well pressure, fracture inclination and permeability of fracture walls. Even with the simplifying assumptions made, the model is shown to be capable of adequately characterizing mud loss dynamics. Directions for further improvement and refinement of the model are outlined.