AVO INVERSION OF TROLL FIELD DATA

A stratigraphic elastic inversion scheme has been applied to a data se t from the Troll East Field, offshore Norway The objective of the pres ent work is to obtain estimates of the P- and S-wave velocities and de nsities of the subsurface. The inversion is carried out on tau - p tra nsformed common depth-point (CMP) gathers. The forward modeling is per formed by convolving a wavelet with the reflectivity that includes wat er-bottom multiples, transmission effects, and absorption and array ef fects. A damped Gauss-Newton algorithm is used to minimize a least-squ ares misfit function. Inversion results show good correlation between the estimated V-P/V-S ratios and the lithologies in the wells. The VP/ VS ratio is estimated to 2.1-3.0 for shale and 1.6-2.0 for sandstones. In the reservoir, the V-P/V-S ratio is estimated to 1.55 in the gas s and and to 1.62 below fluid contact.