Modeling of yield-power-law drilling fluid losses in naturally fractured formations

Significant fluid loss while drilling through fractured formations is a major problem for drilling operations. From field experience we know that the type and rheological parameters of the drilling fluid have a strong impact on the rate and volume of losses. The industry has recently started to monitor mud loses in order to identify and characterize the fractures. The methodologies to characterize the geometry and conductivity of the fractures by quantitative analysis of field measurements are mainly based on mathematical models that describe the physical phenomena and the mechanisms under which flow within the fractures take place.;In this study, mathematical models for flow of Yield-Power-Law (Herschel-Bulkley) fluids in fractures are presented. The governing equations are derived using the principles of conservation of mass and linear momentum for radial flow in a fracture. Results show how the rheological properties of drilling fluid such as yield stress and flow behavior index (shear-thinning/thickening effect) of the fluid, significantly influence mud losses in fractured formations. Therefore, mud losses in fractures can be minimized by properly optimizing the rheological properties of the drilling fluid.;The model is improved by including the effect of formation fluid and fluid leak-off from the fracture wall into the primary porosity formation. Fracture ballooning due to deformation (opening/closing) of natural fractures is studied to avoid confusing this phenomenon with conventional losses or formation kick.;Using the provided models, quantitative analysis of losses that take into account fluid rheology in order to characterize the fracture can be achieved. One can obtain the hydraulic aperture of conductive fractures by continuously monitoring mud losses and fitting field records of mud losses to the model. For general applications, type-curves are provided that describe drilling fluid loss of Yield-Power-Law fluids into fractures. Newtonian, Bingham Plastic and Power Law fluids are special cases. The proposed model is very useful not only for drilling applications but also for well completion design and characterization of fractured reservoirs.;Field data measurements are used to demonstrate the practical application of the proposed technique. The numerical solution is also compared with experimental data obtained from radial flow between two parallel disks. Good agreement between the model, field data and experimental results confirm the validity and applicability of the model.