2D SEISMIC FORWARD MODELING OF SUBSURFACE WITH SHALLOW GAS CLOUD: A CASE STUDY FROM MALAY BASIN OFFSHORE

Poor quality of seismic data in the shallow gas cloud environment seems like a real
challenge for seismic processing and imaging. Amplitude loss and sagging effect in
the subsurface underneath the shallow gas cloud area are difficult to be handled
during processing without understanding the factor that caused the real effect. Seismic
forward modeling is capable to conduct a defined acquisition with different sourcereceiver
geometry in a survey area using geophysical software instead of real
acquisition with a fully crewed seismic vessel. The project will focus on the effect
created by the shallow gas cloud in 2D seismic forward modeling based on real
seismic and well log data taken from the study area in Malay Basin offshore.
Synthetic seismic is generated by 2D acoustic modeling with the input of P-wave
velocity, formation density and Q-value. The result of post-stack time migrated
synthetic seismic is later on be compared with real seismic data at the similar study
area in order to justify the anomalies present underneath shallow gas. It is justified the
amplitude loss underneath the gas cloud area is influenced by the lowest Q-value of
shallow gas model which has caused greater attenuation effect of seismic wave when
passing through the shallow gas cloud area. Thus, detail seismic processing workflow
including Q-compensation is necessary and is suggested for future works in order to
compensate this effect.