| dc.description.abstract | Chances of cement sheath failure increase considerably when the application involves deep, high pressure/ high temperature (HPHT) wells. Such failures occur as a result of temperature and pressure-induced stresses created by well events such as hydraulic fracturing, well testing, enhanced oil recovery, completion, production, and work over, or other remedial treatments. These would impose huge operational costs and in some circumstances lead to loss of production. Analytical and FEA modeling research has been done in the past but fewer experimental studies focused on finding the fatigue endurance cycles of oil well cements under HPHT conditions.
Abundant unconventional resources, producing from deeper horizons, numerous frac jobs in the US, and safety significance were the prime motivations for creating a new testing procedure for evaluating cement integrity under HPHT conditions. A novel HPHT cell was manufactured and mounted on a Chandler 7600, an extreme HPHT Rheometer. Cylindrical cement samples were cured and tested at constant confining pressure while the casing pressure varied cyclically. These samples failed after a certain number of cycles when reaching their fatigue endurance limit or if they had inconsistent chemistry to withstand the HPHT conditions.
This research explains a method for cement integrity evaluation and identifies the fatigue failure cycles for 1,000 psi, 2,000 psi and 5,000 psi pressure differentials between the confining pressure and maximum casing pressure. Class H cement and class H plus 35% silica were used in these experiments and cement failures such as radial cracking, debonding and disking were observed. | en |
