INTEGRATION OF VSP SEISMIC DATA WITH CORE AND WELL LOG DATA TO INVESTIGATE LATERAL VARIATIONS OF POTENTIAL HYDRATE-BEARING SANDS, ALASKA NORTH SLOPE
Donn McGuire1, Steve Runyon2, Tom
Williams2, and Richard Sigal3
1 Anadarko Petroleum Corp., The Woodlands, TX
2 Maurer Engineering, Sugar Land, TX
3 University of Oklahoma, Norman
, OK
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. The well was continuously cored from surface to total depth in order to sample the entire thickness of the permafrost and hydrate stability zone. An on-site mobile core laboratory was designed and fabricated to measure rock properties at the well site in nearly in-situ conditions. Geophysical measurements of the core included compressional and shear velocities and density.
A 3D VSP survey was recorded in February 2004 for the purpose of using high frequency seismic data to identify 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 results of the VSP processing indicated useable frequencies (less than -30 dB down from maximum) over 200 Hz were retained, and good quality, laterally consistent reflection events were imaged.
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. 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.