Effects of fluid flow in triple porosity medium on fracture width and its propagation during lost circulation control

Abstract

During oil and gas well construction, lost circulation is one of the major challenges, and to migrate the problem, lost circulation materials (LCMs) should be used to resist fracture reopening with the hypothesis of fracture tip isolation. A triple porosity medium Darcy flowing model was developed to capture pressure distribution along the fracture surface, coupled with a dislocation-based fracture mechanics model to calculate fracture width and assess its propagation. In the model, mud cake on wellbore and fracture surface was considered as the third type of pore medium. The rest dual pore medium models incorporate the fluid flow through LCMs within fracture and the fluid leakoff from fracture into matrix. Sensitivity analyses of the key parameters, such as triple pore medium permeability, viscosity, wellbore pressure, plugging location are implemented, and the results emphasize that fracturing resistance effect of LCMs was controlled not only by the fluid flow within fractures, but also by the flow through mud cake on wellbore into matrix. To inhibit fracture reopening, in high permeability formations, both reduction of mud cake permeability and LCMs permeability were required while in lower permeability formations, fluid flow within fractures dominates and should be minimized. Besides, tip isolation can be achieved by extending sealing fracture length. However, high wellbore pressure or long operation time will result in elevated distances and unallowable fluid loss. Then, wellbore pressure must be reduced to cure the lost circulation. More viscosity of the fluid and total integrity plugging of LCMs are another major factor extending the time for pressure transfer to fracture tip, resisting unexpected fracture propagation. The method proposed in this study clarifies that tip isolation can be realized by fracture plugging and reduction of fluid filtration from the wellbore to matrix. Moreover, operational insights on LCMs design can also be derived.