Mechanism of pressure management by injecting nitrogen in casing annulus of deepwater wells》.pdfVIP

PETROLEUM EXPLORATION AND DEVELOPMENT Volume 42, Issue 3, June 2015 Online English edition of the Chinese language journal Cite this article as: PETROL. EXPLOR. DEVELOP., 2015, 42(3): 422–426. RESEARCH PAPER Mechanism of pressure management by injecting nitrogen in casing annulus of deepwater wells 1, 1 2 2 3 3 1 ZHOU Bo *, YANG Jin , LIU Zhengli , LUO Junfeng , HUANG Xiaolong , ZHOU Rongxin , SONG Yu 1. Ministry of Education Key Laboratory of Petroleum Engineering, China University of Petroleum, Beijing 102249, China; 2. Shenzhen Company of CNOOC, Shenzhen 518067, China; 3. CNOOC Energy Technology Services Limited, Tanggu 518000, China Abstract: The influence factors of annular pressure buildup are analyzed, and the temperature and pressure characteristics of annulus trap medium are simulated for deepwater wells. The method of pressure management by injecting nitrogen in casing annulus is proposed based the experiment result. Limited by the well structure and subsea system, long casing annulus exists between technical casing and production casing and it is filled with water-based, synthetic based or oil-based drilling fluid. In the process of oil/gas test and production, the temperature of the trapped fluid rises significantly under the influence of the well-bore fluid and the trap pressure buildup appears be- cause of liquid heat expansion. Experiments show that isothermal compressibility coefficient and thermal expansion coefficient are the key influencing factors for annulus pressure buildup. Trap pressure is very sensitive to the type of trapped medium (liquid, gas). Injecting 5%−20% volume fraction of nitrogen into the annulus can effectively control the annulus