Publications

Time-lapse seismic monitoring is an important technology for reservoir management, especially for Enhanced Hydrocarbon Recovery (EHR). A time-lapse feasibility seismic study is needed before performing the project survey in Tetra Field. Tetra Field is located in the Eastern ‘arm’ of Sulawesi. The reservoir target is upper Miocene carbonate build-up of Mantawa Member Formation. We developed new paradigm using gradual assumption of water saturation change and avoided the constant assumption of water saturation change during the natural flow production. With the gradual assumption, we modeled the water drive during the production stages for two scenarios, first is when the lower part of carbonate reservoir has gas residual 20% and the second one is when there is no residual gas. The fluid substitution via Gassmann’s equation is used to create the scenarios and shows a significant change to zero-offset reflectivity (the intercept) but only minor changes to the AVO gradient.The change in seismic response is caused mainly by the density change during the fluid injection. At Top Mantawa Member (top of target interval), greater decrease of amplitude by 47% was obtained from the change in water saturation of 22% to 100%. At Top 1st GWC (base of target interval), there is a change of amplitude polarity where the water saturation changes from 22% to100%. The effect of seismic response changes significantly when the water saturation obtained exceeded 80% because the acoustic impedance difference of water saturation from 80% to 100% is greater than from the change of water saturation from 22% to 80%. From the time-lapse feasibility analysis study, the amplitude changes are big enough for considering that time-lapse seismic survey is feasible to do in Tetra Field.