Casing Thermal Stress and Wellhead Growth Behavior Analysis

Abstract In high-temperature wells or in high-temperature gas injection wells, casing thermal stress is an important issue that should be considered in well design. Stresses introduced by well temperature changes could be severe and critical, resulting in catastrophic well integrity failure and surface equipment damage if not properly identified. The problem can be more severe when a high-temperature well is constructed in a cold environment; the temperature increase from the equipment's as-installed condition to operation conditions would be even higher. A deepwater well or arctic area well installed in winter needs special consideration for thermal stress. A field example in this paper demonstrates a near miss catastrophic well integrity failure. The incident will be analyzed by using a multistring well thermal growth model to calculate casing thermal stress and wellhead growth. Casing thermal growth and stress is sensitive to the length of free moving casing sections. In this paper casing thermal behavior and wellhead movement will be discussed by analyzing different casing string top of cement (TOC) depths. This paper demonstrates how to minimize thermal force and reduce wellhead thermal growth by optimizing the casing cement level. At given conditions, adjusting surface tension during casing installation can also help counterbalance thermal force. It is important to understand the thermal forces and behavior of all casing strings in a well during its operational life.