Exploration for Methane Hydrates with 3-D Vertical Seismic Profile (VSP) Technology, Alaska North Slope

Donn McGuire¹ and Steve Runyon^2
1 Anadarko Petroleum Corp, The Woodlands, TX
² Swift Energy, The Woodlands, TX

In the winter seasons of 2003 and 2004, Anadarko Petroleum, Maurer Technology and Noble Drilling, in a cooperative effort with the U.S. Department of Energy Department of Energy's Office of Fossil Energy (contract DE-FC26-01NT41331), drilled an exploratory well on the Alaska North Slope to investigate the occurrence, subsurface distribution and produceability of methane hydrates.

A 3D VSP survey was recorded in February 2004 using high frequency seismic data to identify, calibrate and delineate lateral variations in the subsurface within the hydrate stability zone (HSZ). The VSP consisted of 1185 surface source points and 80 levels of 3 component geophones at 25 foot intervals in the wellbore, resulting in a 3D survey of over 284,000 traces. Surface vibrators were used to create input signals with a frequency range from 8 to 220 Hz. at each surface position.

The VSP data processing produced dominant frequencies of 120-130 Hz and good quality, laterally-consistent reflection events were imaged. The lateral and vertical sampling density was superior to surface seismic data for delineating thin, fluvial-deltaic reservoir facies.

The processed VSP seismic data were correlated with the well log and core data to provide an integrated characterization of the Ugnu and West Sak sands within the HSZ. Although methane hydrates were not encountered in the wellbore, lateral variations in amplitude and reflectivity of the 3D VSP data were identified and investigated for evidence of changes in lithology or in hydrate/free-gas pore content. The VSP data suggest methane hydrates exist in close proximity to the well location.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005