Title: Hydrate risks and prevention solutions for a high pressure gas field offshore in South China Sea

Authors: Liang Zhang; Anyuan Huang; Wei Wang; Shaoran Ren; Shukai Jin; Dake Fang

Addresses: College of Petroleum Engineering, China University of Petroleum (Huadong), Qingdao 266580, China ' Gudao Branch Com. of Shengli Oilfeild, Sinopec, Dongying 257000, China ' Dongxin Branch Com. of Shengli Oilfeild, Sinopec, Dongying 257000, China ' College of Petroleum Engineering, China University of Petroleum (Huadong), Qingdao 266580, China ' Zhanjiang Branch Com. of CNOOC, Zhanjiang 524057, China ' Zhanjiang Branch Com. of CNOOC, Zhanjiang 524057, China

Abstract: YC13-4 gas field is located in the west of the South China Sea, where the seawater depth is around 90 m, and the average surface temperature is 26.2°C, while the minimum temperature at seabed is 18.9°C. Subsea wellheads are designed for gas production. In this paper, the risks of hydrate formation during drilling, well testing and gas production are analysed under different operation conditions. The results show that most hydrate problems will occur during shutdown and restart operations, and the degree of hydrate occurrence is slight to medium, which poses difficult tasks for choosing safe, reliable and economic methods to mitigate the hydrate problems. Various solutions for hydrate control in different processes are considered, including filling the wellbore with drilling/completion fluids or seawater for pressure control during shutdowns, and injection of methanol into wellbore and subsea pipeline during production. A simple and economic method using down-hole chokes to reduce gas pressure before it enters the hydrate stability zone is introduced, and the placement depth of the down-hole choke is determined. [Received: September 5, 2012; Accepted: March 6, 2013]

Keywords: gas hydrate; hydrate prevention; offshore gas reservoirs; down-hole choking; South China Sea; hydrate formation risk; hydrate occurrence; hydrate control; pressure control; methanol injection; gas pressure reduction.

DOI: 10.1504/IJOGCT.2013.056827

International Journal of Oil, Gas and Coal Technology, 2013 Vol.6 No.6, pp.613 - 623

Received: 07 Sep 2012
Accepted: 06 Mar 2013

Published online: 29 Jan 2014 *

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