Cement failure probability under HPHT conditions supported by long term lab studies and field cases
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Cement durability is very important to maintain proper well isolation and stability under HPHT conditions. In the process of well completion and production, pressure decline and temperature variation with time can contribute to cement failure and wellbore stability issues. However, there is no available investigation in the durability and comparison of different types of cement at higher temperature and at different operational scenarios. Three different types of cement (72 pcf, 101 pcf and 118 pcf) commonly used in the Middle East were cured and tested at 300F in the study. The tests included one year mechanical properties measurement such as compressive strength development, Young's modulus and Poisson's ratio. Finite element method was used to analyze the failure probability of HPHT wells over with time. At the variation of bottom hole pressure and temperature, the casing, cement, and formation system failure probability was studied for these types of cement. The results show that the pressure variation has more effect on the wellbore stability than the temperature variation for HPHT wells. Low density cement can improve the wellbore stability issues due to the cement elastic behavior. This paper introduces the operational envelope for every type of cement investigated in order to achieve successful operations based on field conditions. Field cases were discussed to validate the results of this investigation. Copyright 2012, Society of Petroleum Engineers.
