The fast growth of shale gas development through horizontal drilling and hydraulic fracturing has expanded the extraction of hydrocarbon resources in countries such as the United States, China, and Argentina. Even though the technology of fracturing low permeable shale can be replicated in different reservoirs, factors such as flow regime, high horizontal stress anisotropy, formation temperature and quantity of natural fractures will dictate several changes and considerations in the completion design.
High rates and pressures applied during hydraulic fracturing in a long horizontal section could induce wellbore integrity issues. This work will focus on researching how the integrity of the cement and casing is affected during these operations. A finite element analysis (FEA) was performed in order to study the stress concentration in casing and cement. The yield criterion of equivalent von Mises stress was applied in order to verify if the stresses were exceeding the casing yield strength and the cement compressive strength. The majority of the input parameters were based on a real case of casing deformation during hydraulic fracturing in a shale gas play in China.
The effect of wellbore centralization in wellbore integrity was the main parameter modeled in this work. It was demonstrated that a poor centralization that contributes to the formation of drilling fluid voids in the cement will induce casing failure during hydraulic fracturing operations. The equivalent maximum stress can increase from three to four times in casing and cement from a concentric case to an eccentric case in a cement sheath with voids. Boundary conditions were also studied in order to evaluate if the stress impact on the casing and cement are different and significant
