Publications

The Singa-1 well was drilled as a wildcat exploration well to test a Batu Raja Formation prospect within the South Palembang Sub-basin of the South Sumatra Basin. The prospect was interpreted to be a deeply buried reef (overlain by overpressured Gumai Formation shaks. The depth to target was prognosed to be around 12,000 ft TVDSS, over 3,000 ft deeper than any previously drilled Batu Raja targets in the area.High temperatures and pressures were anticipated prior to drilling. To safely achieve the well's objectives, casing had to be set as close as possible to the top of the carbonate to avoid potential drilling hazards. Due to the lack of offset wells to a comparable depth, pre-drill depth estimates were based on seismic stack.ing velocities only. As these estimates were not accurate enough for picking final casing points, both a conventional look-ahead VSP (vertical seismic profile) and a SWD (seismic-while-drilling) technique were employed during drilling to accurately predict the top of the reservoir.During operations it was found that both techniques had limitations but in combination were critical to the successful drilling of the well. Trace inversion of the conventional VSP data provided the initial depth estimates to the target. Using the SWD technique it was possible to continuously observe the changing velocities in the Gumai Formation shales. These velocities were then used to update the VSP inversion improving the accuracy and reliability of the depth estimates. The casing point was picked within the tolerances set out at the beginning of the well and led to the safe and successful drilling of the Singa-1 discovery well.