Modeling and Experimental Study of Fracture-Based Wellbore Strengthenin

While drilling through depleted or partially depleted reservoirs, one may encounter a series of problems (e.g., lost circulation, wellbore instability, non-productive time, etc.) due to narrow mud weight window. Fracture-based wellbore strengthening techniques used in the industry effectively increase fracture reopening pressure (FROP) and ultimately reduce the cost of associated problems. However, traditional analytical and numerical studies using these techniques do not consider the time effect and usually ignore the fluid dynamics. Thus, these deficiencies may result in inaccurate wellbore strengthening operations if no proper fracture diagnostic techniques are available to acquire the real-time fracture geometry.;In this study, a quasi-static, dislocation-based fracture model is extended using fluid mass conservation with leak-off. A fixed dimensionless fracture coordinate system is employed and a numerical simulation procedure is developed. The fracture geometry, stress intensity factor, and FROP are verified with static solutions. Then, simulation results are compared with large leak-off solutions of Perkins-Kern-Nordgren (PKN) fracture model, which shows that the PKN model overestimates the fracture mouth width, fracture length, and wellbore pressure. Thus, the PKN model is not appropriate for wellbore strengthening applications. The presence of the wellbore in wellbore strengthening fracturing can generate near-wellbore effects that cannot be disregarded. Further investigation reveals that the FROP may be significantly affected by the fracture plug width. Finally, the proposed model qualitatively characterizes the influence of some controllable parameters (e.g., fluid properties, wellbore conditions, and wellbore strengthening materials (WSM) properties) on fracture propagation and FROP.;A large-scale true triaxial cell is constructed to conduct the experimental study. It overcomes several disadvantages (i.e., no horizontal stress anisotropy and no fracture arrest) of previous facilities. Several preliminary and formal experiments are performed. The WSM are composed of drilled cuttings and Chevron Loss Prevention Material (LPM). Cubical Berea sandstones (size is 12 in.;3)are used in the experiments. Bi-wing fractures are generated. The FROP exceeds (and almost doubled) the original formation breakdown pressure (FBP), which indicates the wellbore strengthening effects after plugging of WSM.;The proposed numerical model is useful for design of wellbore strengthening applications, especially for intentionally induced fractures (i.e., near-wellbore fracturing). Particle size distribution (PSD) of WSM can be designed on the basis of simulated fracture geometry. No complex model mesh generation or assignment of boundary conditions are needed, which are commonly used in finite element simulation or other numerical methods. The proposed model can also be used to optimize wellbore strengthening operations by performing sensitivity analysis.