Enhancing Zonal Isolation With Expandable Cement System for Gas Field

Abstract

Abstract HPHT well subjects zonal isolation and long term cement integrity into critical factor to achieve long term production life. Repeated cycles of high differential pressure and temperature tend to break bonding between cement, casing and formation. Microannulus as consequence of debonding will provide space. At gas wells, it will provide space for gas migration which may lead to sustained casing pressure. Providing zonal isolation is also important to ensure there will be no communication between two different formations or reservoirs This paper discusses the design, execution and evaluation of cement technology implemented at 9 5/8-in HPHT intermediate liner. Special softwares were used to simulate gas migration risk and stress analysis to cement sheath. High risk gas migration and microannulus were expected based on sofware results. An expandable cement system was identified as a solution and deployed successfully. In order to achieve better understanding of behaviour of cement slurry at field application, laboratory experiments were performed. To achieve long term cement integrity, it is not only about design of cement slurry, mud removal is one of the key factor need to be considered. Best practices were perfomed to achieve the highest mud removal efficiency. Expansion test was perfomed by using pressure curing chamber at 247°F. Expansion was detected for six days simulation which was considered as enough based on stress analysis simulation of compression, traction and microannulus cement sheath performed. It was indicated that expandable cement managed to eliminate microannulus which was created by pressure and temperature changes. Evaluation was performed by locating pressure sensor at the A annulus of 9 5/8-in liner and 13 3/8-in casing. The sensor indicated zero pressure at the annulus while drilling next two more section and during the production life of the well