Evaluating Potential Reservoirs in the Gumai Formation at West Air Komering Area with MultiInversions Method
Abstract
The Gumai Formation is often regarded as a regional seal to the prolific Baturaja and Talang Akar Formations. However, new discoveries were found in the Gumai Formation that makes it an interesting intra-field exploration target. Therefore, this paper aims to compare the result of seismic inversion methods, their effects on the distribution of lithology and porosity within the Gumai Formation in West Air Komering Area and see how they impact the prospectivity evaluation in the later stage.
The principle of seismic inversion is to transform seismic reflection amplitudes into impedance values that can be used as a guidance to distribute porosity, lithology, and fluid saturation. However, different inversion methods may induce non-unique AI results, especially when dealing with low-contrasts lithologies within the Gumai Formation. Therefore, a comparative study between several inversion methods is necessary to cross correlate between the results. Several deterministic inversion methods were chosen comprises Model-Based Inversion (MBI), Fast Track “Colored” Inversion (CI), and Linier programming SparseSpike (LPSS) Inversion. The inversion results were then calibrated with the well data and subsequently used as input to the 3D static model to evaluate possible in-place volumes estimates after.
Results from LPSS and MBI shows many similarities whilst CI produced different result particularly in the southwestern part of the studied area. Despite many similarities, LPSS shows a blockier impedance compared to MBI. Overall, a high impedance anomaly in all inversion results indicates shaly sandstones. In general, the accumulation of shaly sandstones and relatively high porosity are observed in northeastern part of this area. There is a quite large range between the calculated volumetrics when each inversion result was used as input for the 3D property modelling.
This paper demonstrates a multi-scenario geophysical approach in evaluating intra-field potential which applicable to similar fields. By using multi-scenario method, risks and interpretation uncertainties are well captured. This will enable a better investment decision that also comply with the latest regulations from Indonesian Government.
