Publications

Gas accumulation is extensively occurred in Sunda Basin. Most potential gas reserve is found around depocenter of the basin. But the gas reservoir is complicated by coexisting of gas sands, wet sands, shale and coal, which have quite close acoustic impedance. Of these, the coal bed is one that has very close acoustic impedance and similar AVO to the surrounded gas sands. Thus, detecting gas and proposing exploration wells in Banuwati-Mila gas fields are challenges to G&G work. Traditional AVO involves computation of the AVO intercept and gradient from a linear fit of P-wave reflection amplitude to the sine square of the angleof-incidence. Rock physics and fluid replacement modeling of Banuwati-02 and Mila-02 show class 3 AVO anomaly and seismic CDP data sets also have some AVO response. It is concluded that traditional AVO and its cross-plotting analysis of intercept and gradient could describe detail characteristics of Banuwati-Mila Upper Gita sandstone that would be crucial for understanding the gas sandstone reservoir and for optimizing well location and reducing drilling risk. Coal bed influences could be removed by much strong attenuation gradients. Gas sand thickness was mapped out by combining traditional AVO cross-plotting analysis and attenuation gradient. The map can indicate much potential area, and further optimize Mila-03 well location. Post-drilling of Mila-03, which encountered total 70 feet net gas pay in Upper Gita, proved the study results. Based on rock physics and fluid replacement modeling, traditional AVO cross-plotting analysis still has good effects in the Sunda basin. Integrated with attenuation gradient analysis, the gas sand characters and distribution could be delineated quantitatively or semi-quantitatively.