Controlled Source Electromagnetic (CSEM) Study in West Svalbard Margin for Arctic Gas Hydrate Quantification

Bedanta Goswami

The energy potential of hydrates in West Svalbard continental margin deposits are yet to be assessed. Although a large number of geophysical datasets have been available for a number of years in this area, an integrated effort to quantify methane hydrates in this area is relatively new. In addition to unconventional resource potential, hydrate in West Svalbard margin is important for global climate considerations. About 250 plumes of methane bubbles from the seabed were observed during a 2008 research cruise just beyond the shelf edge of the continental margin. This coincides with recent warming of West Spitsbergen current by about 1C (in past three decades) that could have destabilized shallow hydrates around the observed plume area (Westbrook et al 2009). ). The landward edge of hydrate stability zone is likely to have shifted down slope, creating pockets of free gas, which are released through the seabed gas seeps. Resistivity changes observed in marine controlled source electromagnetic (CSEM) data should provide better constraints on concentrations of hydrate and free gas within the continental slope sediments. During cruise JCR269B in summer 2012, a 20-km-long east-west trending CSEM profile was acquired using a deep towed electromagnetic source (DASI), which transmitted a 100A square wave signal at 1Hz using a 100m long dipole antenna. The 1Hz fundamental frequency and higher order odd harmonics of the transmitted signal were logged using 14 ocean-bottom electric-field receivers (OBE’s) which were accurately placed on the seafloor using a remotely operated vehicle to record low frequency component of the transmitted signal. A deep-towed electric field receiver (VULCAN) was towed 300m behind the source to capture additional higher frequency information about shallow changes in resistivity, which OBEs may fail to record. The profile extends from the edge of observed seismic BSR at 900m through the continental slope up to the edge of observed plume locations at water depths of 350m. The profile provides resistivity information about the hydrate bearing sediments to the west and the free gas bearing sediments near the shelf break to the east. Measurements from the 14 OBE’s show higher resistivity (than background) at the edge of the predicted BSR to the west and free gas zone to the east. These are initial observations, which, in combination with the co-located seismic data, should lead to better constraints on the distribution and concentration of gas hydrate.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013