The influence on casing stress for shale gas fracturing wells considering thermo-pressure coupling effect

Abstract

During the hydraulic fracturing process for shale gas wells, the fracturing fluid is injected into the wellbore with large pump rate. The bottom-hole temperature will decrease sharply, which increasing the risk of casing failure. Based on the actual data of shale gas wells, the influence of rheological parameters of fracturing fluid on heat transfer coefficient is analyzed. A transient thermo-pressure coupling model of casingcement sheath-formation combination is established. Sensitivity analysis is conducted for different pump rates, pressures and injection temperatures. The results indicate that: i. The rheological parameters of fracturing fluid can affect the heat transfer coefficient between the fluid and borehole wall, which in turn affects the temperature distribution at the bottom of the wellbore. ii. The increasing of pump rate will drastically reduce the bottom-hole temperature, then thermal stress generating on the casing. iii. The higher the original reservoir temperature, the greater the influence of the temperature. iv. The casing stress decreases then increases with the increasing of fracturing pressure. Therefore, the rheological parameters of fracturing fluid should be chosen reasonably to reduce the heat transfer coefficient. What is more, it is crucial to choose the appropriate fracturing pump rate, fracturing pressure and injection temperature, as far as possible to reduce the bottom-hole temperature difference, which avoiding excessive casing stress to enhance the casing safety for fracturing shale gas wells.

Integrity Evaluation of Cement Ring during Fracturing and Flowback of Horizontal Well in Jimsar Shale Oil

“…The annular cement ring has no gap, the volume of cement does not change during setting, and the casing/cement ring and cement ring/formation interface bond well before the wellbore load is applied. The casing/cement ring/formation complex keeps balance under wellbore load; after the cement slurry is completely set into the cement ring, the in situ stress is completely loaded on the cement ring [5][6][7][8][9][10][11].…”

“…Zhang et al [2] analyzed the influence of cement sheath elastic parameters on the integrity of casing cement sheath formation combination. Guo and Li [8] deduced the stress analytical solution of the combination based on the interface stress and displacement continuity conditions and studied the effects of cement sheath elastic modulus, Poisson's ratio, and thickness on casing stress. However, for horizontal well reservoirs, there is still a lack of in-depth research on the impact of periodic load during fracturing and flowback on the interface sealing of cement sheath and the specific requirements of mechanical properties of cement paste.…”

Analysis of casing stress during multistage fracturing of shale gas horizontal wells considering thermo‐hydro‐mechanical coupling

“…Zhu and Chen 24 used a hydromechanical coupling calculation method for porous media and established a three‐dimensional FEM to simulate the formation deformation. Guo et al 25 established a thermopressure coupling model of the CCF during shale fracturing, and focused on the influences of pumping rate, injection temperature, and fracture pressure on casing stress.…”