Coupling Effect of Transient Temperature-Pressure on Casing String During Volume Fracturing in Shale Gas Wells

Casing deformation has been found to be a very significant issue in the development process of shale gas in China, while the coupling effect of transient temperature-pressure has a significant impact on casing stress, and worthy of study. This paper presented a new numerical investigation to understand the coupling effect of transient temperature-pressure on casing string during volume fracturing. A wellbore temperature model was established to obtain the required input parameters of dynamic temperature boundary. The numerical model considers the coupling effect of transient temperature-pressure and the various cement sheath shapes. The results showed that the temperature of casing changed drastically during fracturing. Under the influence of the coupling effect of transient temperature-pressure, (a) when the cement sheath shape was integrity, the casing stress increased greatly and showed dynamic changes: first increased and then decreased, (b) when there was deficiency in cement sheath, with the increase of the eccentric distance or deficiency angle, the casing stress increased aggravating risk of casing deformation. Rotating the casing string during the cementing process to avoid the deficiency in cement sheath or using warm fracturing fluids to minimize the influence of the coupling effect of transient temperature-pressure are possible innovative strategies to solve these difficult problems.