Cernent sheath integrity during hydraulic fracturing: An integrated modeling approach

Recent arguments about the possibility of underground water pollution in particular regions have raised significant concerns regarding wellbore integrity during hydraulic fracturing in shallow formations. In this paper, we take a look at the containment of annulus cracks that might develop during hydraulic fracturing treatments. Wellbore integrity is highly dependent on the integrity of the bonding between the cement and the formation as well as the bonding between casing and cement. Cement heterogeneity resulted from unsmooth borehole surfaces, complex geological conditions, mud cakes, and cement contamination. Excessive fluid pressure during hydraulic fracturing could provide the driving force not only for initiation and propagation of fractures in longitudinal and transverse directions, but also in cases of low confining pressure, it may lead to fracture propagation around the casing, i.e. annulus cracks. A coupled three-dimensional poroelastic model with embedded cohesive zones is used to simulate different fracture propagation scenarios that may occur in vertical and horizontal wells during hydraulic fracturing stimulations. The cohesive layer theory is utilized to model initiation and propagation of transverse, longitudinal and delamination fractures. Using the numerical analysis provided in this paper, few hydraulic fracturing cases were simulated by taking the advantage of the treatment pressure data and petrophysical logs, and the results were compared with the post-treatment radioactive tracer logs available for these wells.