OS3B-2:INTRODUCTION TO GMGS2 GAS HYDRATE DRILLING EXPEDITION: OVERVIEW

Guangxue ZHANG¹, Shengxiong YANG¹, Ming ZHANG¹, Jinqiang LIANG¹, Jingan LU¹

Peter SCHULTHEISS², Melanie HOLLAND², Xin SU³

1. Guangzhou Marine Geological Survey, China; 2. Geotek Ltd, UK; 3. China University of Geosciences, China

GMGS2 expedition was conducted from May 28^th to September 8^th,2013 and lasted for 104 days. The drilling sites are located on the east of North Slope of South China Sea. Totally 13 sites were drilled which distributed on about 326 km² sea area. 10 of these sites were logged through Schlumberger LWD tools whereas the other 3 sites is logged by wireline logging tools. Obvious anomalies from the resistivity and sonic curves of 7 pilot holes are found with the features which show clearly the existence of gas hydrates. The depth of gas hydrate bearing layers are generally below 220mbsf with the lower depth of about 9~23mbsf. ROV video recorded large amount of gas hydrate flecks just flowing out of the borehole when the bit drilled through the massive hydrate layer. 5 sites were cored and sampled and geochemical, MSCL, PCATS analysis were performed onboard the vessel. Massive, nodule, nugget and disseminated gas hydrate morphology samples had been recovered. In site analyses indicated that the saturation of disseminated gas hydrate bearing formation is up to 50%. Gas sample analyses including headspace gas ,void gas ,hydrate gas and pressure depressurization experiments confirms that the methane was the dominant hydrocarbon gas component. It is concluded that hydrate model in the drilling area is structure I.