Towards a Comprehensive Workflow for Shallow Gas Corrections on Seismic Data

Shallow gas effects have been observed in many fields in Offshore Malaysia and in the Malay Basin in particular. Such effects have led to higher uncertainties in defining the field’s structure and consequently estimating Gross Bulk Volume (GBV) with direct impact on volumetric assessment. It is estimated that about 50% of the oil and gas fields in Offshore Malaysia are affected by shallow gas. This paper will discuss the different methods used in assessing and correcting the push down effects in travel time and the recovery of the seismic amplitudes as caused by shallow gas. An overall workflow and an assessment scheme have also been established to frame the setting and approach used in the interpretation and correction of shallow gas effects. This paper will propose an integrated solution for the travel time delay (sag) that conventional 3D streamer seismic data is substantially suppressed by under shallow gas. Multicomponent OBC seismic data has added crucial value in this topic of shallow gas effects on seismic amplitude loss (wipeout) where it was not at all possible to produce or deliver attribute or property maps from seismic amplitudes, to include as an input to the reservoir modeling studies and projects.