National Gas Hydrate Program Expedition 02 (NGHP-02) was conducted from 3-March-2015 to 28- July-2015 off the eastern coast of India. The primary goal of this expedition was to explore for highly saturated gas hydrate occurrences in sand reservoirs that would become targets for future production tests. The first two months of the expedition were dedicated to logging-while-drilling (LWD) operations, and the next three months were dedicated to coring operations. With a total of five months of continuous field operations, the expedition was the most comprehensive dedicated gas hydrate investigations taken by India.
NGHP-02 has fulfilled the objective of discovering gas hydrates in sand reservoir, explore presence of free gas below gas hydrate stability zone and the identification of sites for pilot production testing for NGHP Expedition-03. The objective of this paper is to highlight challenges faced during drilling for Coring/ Logging/ Modular Formation Dynamic Tester (MDT) operations in NGHP-02 and potential risk associated with drilling gas hydrate in Krishna Godavari (KG) offshore of India for pilot production testing. The paper will also thrust on suitable well design, optimum drilling parameters, and ways to mitigate well control issues associated with drilling.
Operational complexities of NGHP-02 are minutely analysed and discussed in this paper. During drilling of well for gas hydrates in NGHP-02 expedition, the problems observed were gas plume below seafloor, drill pipe stuck in thick sand layer due to wellbore instability, difficulty in lowering logging & MDT tool in gas hydrate zone, wire line logging tool stuck inside drill pipe while pulling out logging tool. To overcome drilling hazards, feasibility study of suitable drilling technology like managed pressure drilling, casing while drilling, proper well design considering all the potential hazards to drill the well safely are discussed in detail.