Integrated Subsurface Study to Convert Upside Intrabeta Subzone Stakes into Additional Main Targets in Tunu Gas Field, Mahakam Delta, Indonesia
Authors: Gumilar Dwiki Drajat , Pribadi Riksa , Fadlan Dhanny , Afdhal Ramsyi Faiz , Ashfahani Adnan Syarafi , Akbar Edieth 
Published: October 2021

"Intrabeta" is a subzone located in the upper part of Tunu Main Zone between MF3-MF6 regional stratigraphic marker. Total cumulative production from this subzone is at 51 Bcf of gas and 4.96 MMBbl of oil. This interval is situated between Tunu Shallow Zone and Tunu Main Zone, which are the main producing intervals of Tunu Field, a giant mature gas field in Mahakam Delta, Indonesia. With Intrabeta reservoir depositional context more dominated by channel facies and more varied production fluid properties, the development of Intrabeta subzone became more challenging and previously classified as upsides. As Tunu Field is getting more matured, the challenge to deliver infill wells that economically profitable become more arduous. Thus, all attempts to give additional value to the future infill wells should be properly assessed. This paper aims to provide a comprehensive summary of how strategic collaboration between static and dynamic synthesis of Intrabeta subzone has given additional contribution in Tunu Field continuous value creation process.

The method started by conducting an extensive post-mortem review on all perforated reservoirs in Intrabeta subzone. Insights from the perforated reservoirs that comprise of production behavior, perforation success ratio, cumulative hydrocarbon production and updated portfolio are then utilized to provide initial prolific area map for future candidates maturation. Data coming from the dynamic analysis were then combined with static depositional analysis on how the hydrocarbon was distributed in Tunu Intrabeta subzone. A new structural map that has been corrected from seismic push-down effect due to shallow gas presence above Intrabeta interval was then utilized to map the structurally promising area. Deterministic channel boundaries and possible sweet spots are then identified and ranked based on the development confidence level.

Four wells with additional stakes from Intrabeta subzone have been proposed and drilled in Tunu Main Zone. All wells have successfully found the targeted Intrabeta targets with various post-mortem findings. While in some wells significantly better post-drilling results were encountered, in other cases slightly lower results were found due to static channel development and fluid dynamic uncertainties. All the lesson learned gathered from the pilot wells provide valuable insights on future improvement toward better and more robust Intrabeta candidate maturation methodology.

The insights gained from this study have given essential understanding of Tunu Intrabeta subzone characteristics and possible future potentials. Furthermore, this paper provides a comprehensive summary, systematical approach and lesson learned in enhancing previously upside potential of Intrabeta subzone in Tunu Main Zone to compelling additional targets in Tunu Main Zone future wells as part of the continuous value creation process in a giant mature gas field.