Gas hydrate physical properties imaging by multi-attribute analysis - Blake Ridge BSR case history

We analysed the bottom simulating reflector (BSR) of the Blake Ridge, by us ing the 'multi-attribute' analysis. This technique allows prediction of pet rophysical/geological parameters along seismic lines (velocity, porosity, d ensity, resistivity etc.) starting from log data. Seismic attributes can be thought of as all parameters derived from seismics, by assuming that a sei smic trace is the real component of a complex one. The first attributes tha t can be calculated are the instantaneous amplitude, the instantaneous phas e and the instantaneous frequency. All the other attributes that will be co nsidered are derived from the previous ones. The algorithm that allows the correlation between logs and seismics is the generalised multiple linear re gression. This equation is solved by a least squares approach, called 'trai ning phase', which effectively consists of training the seismics to predict the reservoir parameter of interest at the tie locations. The resulting fu nction is then applied to the seismic profile, generating a target log pred icted section. We obtained five sections (VSP and P-wave velocity, density, porosity and resistivity), each of them representing the distribution of t he corresponding property along the profile; they permitted better characte risation of the nature of the BSR present in the Blake Ridge area. The obta ined-velocity section was finally translated in terms of gas hydrate and fr ee gas distribution by using theoretical approach. (C) 2001 Elsevier Scienc e BN. All rights reserved.