Publications

Gas production from the Tunu Shallow Zone has reached 250 MMScfd (30% of current Tunu production), incrementing the potential of the field and enabling a major new development of over 120 wells in the last 5 years at the Mahakam PSC. The shallow gas reservoirs are scattered all over the field and present a limited extension and patchy occurrences. The use of seismic is of prime importance to assess and locate the development wells, and is an integral part of the continuous effort to fight the general field decline. Pre-Stack Simultaneous seismic inversion was performed on the 3D PSDM data covering the Tunu field. Litho-seismic classification was computed using the inverted P-Impedance (IP) and Poisson Ratio (PR) in order to predict gas sand probabilities. At Tunu Shallow Zone, gas-bearing sand has very distinctive petroelastic properties compared to other facies. This discrepancy can be predicted using sonic logs and pre-stack seismic inversion. At this interval, P-Impedance and Poisson ratio show low values and form a discriminating parameter. In this study, the Poisson ratio is the key to detect the gas-bearing sands. The sensitivity of seismic-fluid detection depends on the ratio of porosity to pore space modulus. The low Poisson ratio indicates that seismic-fluid sensitivity is higher. Even though a coal layer could show similar IP value, the PR of the gas-bearing sand is still much lower. Results of the study have improved the prediction of the gas-bearing sand within Tunu Shallow Zone. The predicted gas-bearing sands show a good correlation at the existing wells. The results have been integrated to the methodology in order to de-risk and optimize the targets for the future wells.