Challenges and Solutions for Deepwater Drilling in the South China Sea
Authors: Xu Liangbin , Zhou Jianliang , LIU Zhengli , Jiang Shiquan 
Published: May 2013

In the mid 2012, three deep water exploration wells have been accomplished in the South China Sea by CNOOC as the operator employing the deep water drilling unit HYSY981, which symbolizes the epoch of deep water drilling of CNOOC. By reviewing the history of deep water drilling implemented by CNOOC and its partners, this paper put forward the key challenges of deep water drilling in South China Sea, such as typhoon, soliton, gas hydrates and so on. Potential solutions to these challenges are discussed in the paper, aiming at drilling safety. Firstly, this paper focuses on the strategy of the typhoon resistance for the new building deep water drilling unit (DWDU) HYSY981. On which the preliminary research results are given in the paper. The typhoon resistance solution is drawn up in combination with the platform dynamic analysis and operational mode that have been performed to demonstrate its feasibility. Secondly, the paper shows solutions to the soliton for deep water drilling in the South China Sea. And finally, the recommendation to deal with the risk of hydrate formation in deep water drilling is summarized.

1 Introduction

The construction of deep water semi-submersible drilling unit HYSY981, which was sponsored by CNOOC, begun from April 28th, 2008 and was finished on February 26th, 2010. The drilling unit HYSY981 is the first sixth generation semi-submersible drilling unit in China, which is designed and constructed independently by CNOOC. For HYSY981, the operating water depth beyond 3000m, the deck area is 114m length and 89m width. General 3rd dynamic position system is deployed on the drilling unit, while the unit itself can be positioned by anchoring when it is operated in waters less than 1500m deep. The drilling unit was designed to be able to maintain position in the occurrence of a-200years-return typhoon condition.[1]

The drilling unit HYSY981 carried out the first well drilling operation on March 6th, 2012 at the LH29–2–1 location. And until August 8th, 2012, the drilling unit has finished drilling and completion operation of three wells, which are LH29–2–1(754m water depth), LW6–1–1(1495m WD), and BY13–2–1(688m WD). During the process of drilling operations at these well locations, HYSY981 experienced four typhoons and twelve solitons. While taking reasonable measures to deal with these threats, the operator CNOOC has summarized experience of dealing with various deep water drilling problems, which forms recommendation for consequential deep water drilling operation of HYSY981 drilling unit in South China Sea.

From 2006 on, CNOOC and its partners such as Husky and Devon, has finished drilling and completion operations of 32 wells, including LW3–1–1, BY6–1–1, LW3–1–2, LH29–1–1, LH34–2–1 and LW3–1–10. During these operations period, there are 56 accidents, 20 of which cost NPT more than 100hrs. Figure.1 shows that weather influence and BOP accident are two main factors influencing South China Sea deep water drilling. Severe weather conditions seriously affect drilling operations. When Husky carried out drilling operation at LH34–2–1 location, typhoon " Koppu" attacked the drilling unit HYSY981, with the drilling riser & LMRP hanged on rotary table, the drilling unit was push to shallow water district, the LMRP collided with seafloor, which resulted in the damage of riser joint, telescopic joint and tensioner. More than 50 regular work days and 50 million dollars were lost. [2]

By reviewing the history of deep water drilling implemented by CNOOC and its partners in the South China Sea, this paper presents the key challenges to deep water drilling, such as typhoon, soliton, gas hydrates and so on, which are unique in the South China Sea. Firstly, proposed strategy solutions of the typhoon resistance for HYSY981 to these challenges are discussed in the paper, and these solutions should be draw up in combination with the platform structural analysis and operational mode.