Publication

Abstract : Drilling through naturally fractured formations results in multiple complications; fracture ballooning and loss circulation are predominant among them that requires more understanding of the process. In order to better understand the mechanism behind fluid loss into the natural fractures a new model has been developed which addresses the shortcomings of pre-existing models.The paper presents a new comprehensive analytical model; represented by partial differential equation that can be used for various fluid rheologies and thus, eliminating the need for different models for different fluids. The model also takes into consideration of fracture deformation with constant and variable leak off rates into the formation. The proposed model was validated by reducing it to the preexisting models by incorporating their assumptions into it. The model has also been validated using synthetic as well as multiple field data. Sensitivity analyses were performed to determine the effects of fracture normal stiffness, leak off rate, mud-yield stress, aperture and other parameters on fluid losses. The new model presented demonstrates that fracture deformation and leak off pressure play important roles in the determination of fluid loss into the formation. The results have shown that by neglecting the fracture deformation or leak off results in the under estimation of fluid losses. It has also been found that the fluid Yield stress plays an important role in preventing fluid loss into the formation. Sensitivity analysis shows that once the pressure potential falls below the yield stress value, the fluid migration into the fracture is stopped.The novelty of the proposed model lies in the fact that it can be used for different drilling fluids and also more generic. It takes into account fracture deformation and leak-off into the formation which lead to more accurate estimation of fluid losses than the existing models.