Cyclic Loading of Fiber-Containing Cement Sheaths in HPHT Conditions

A Chandler 7600 Ultra HPHT Viscometer was setup to imitate well bore conditions of high pressure, high temperature wells, and the research objective was to investigate the reaction of Class H cement with 35% silica and 0.5% nylon fiber to cyclic loading. This experimental setup facilitated the cyclic loading of the cement sheath by maintaining a constant confining pressure while the casing pressure was cycled. The fatigue endurance limit was found for 1,000 psi and 2,000 psi cyclic pressure differentials for the Class H with added fiber and the results were compared with that of Class H cement without fiber. At 1,000 psi pressure differentials, the cement with fiber remained intact until 15 cycles, whereas the cement without fiber failed at 14 cycles. At 2,000 psi pressure differentials the cement without nylon failed at 14 cycles, whereas the cement without nylon fiber failed at 13 cycles. These results clearly show that the cement with 0.5% nylon maintained integrity for one cycle longer for both 1,000 and 2,000 psi differentials tests when compared to the same cement without nylon fiber. The cement with added nylon therefore exhibits an increased tolerance to cyclic loading.