COMPENSATING FOR SEISMIC ABSORPTION FOR ORTHOGONAL SHOOTING FIELD DATA: A CASE STUDY ON NW TUNU AREA, INDONESIA

摘要

Seismic data may suffer in quality because of surface/subsurface absorption of reflected waves creating dimming effects on seismic images. The dim zones often lead to mis-interpretation of geological structures and AVO attributes. Q-PSDM is a new technique to resolve the absorption effect through ray tracing thereby making the stacks and gathers having more reliable amplitudes. Moreover, Q-PSDM also corrects for phase distortions caused by the absorption. The process involves detailed velocity modeling and fine grid Q-model with resultant computationally intensive processing. This paper discusses the Q-PSDM methodology and processing applied to a portion of Northwest Tunu Area Mahakam Block. The purpose was to compensate for the amplitude loss and phase distortions caused by surface/subsurface anomalies. Field data were acquired using orthogonal (cross-spread) shooting with shot line and receiver line spacing being 200m each. The cross-spread shooting generates data spanning all 0-360 degree azimuths. The data is regularized into four 45° azimuths to estimate and understand the absorption (Q) and velocity variations in various directions. A fine grid of 50x50x20m was used to estimate the Q-model and velocity model. After modeling, the data were migrated in four individual azimuths all the way through post-migration processing. The final Q-PSDM results were compared with those of time processing (PSTM) referenced as base case initial processing. The results of Q-PSDM are encouraging in terms of amplitude compensation in dim zones on gathers and stacks. The results provided reliable AVO response to further evaluate potential drilling locations.