Publications

The Tangguh Gas Fields in Eastern Indonesia are covered by a variety of 3D seismic datasets, including several reprocessing of 1997 vintage towed-streamer acquisition. 2011 Controlled Beam Migration (CBM) reprocessing of this data resulted in an alternative structural map to the existing Post-stack Time Migration at several fields. This paper studies the impact of depth uncertainty on proposed appraisal well planning. The ability of CBM to handle multiple ray paths was judged to be a major source of excellent image improvement. On the 2011 dataset, overall S/N ratios and reflector continuity were much superior and faults were more obvious and easier to pick. An accurate velocity model is the key to getting a good image and accurate depth prediction. Depth uncertainty resulting from velocities is critical to assess when planning a well. A well was thought to be required then on the flank of a Tangguh Field to confirm the structure, recover a gas sample and confirm the gas water contact. The well location was originally selected on the old structural mapping, but the new CBM structure map was 165ft shallower. A thorough investigation was done to justify which map was most reliable and to ensure whether the location needed to be moved in order to not jeopardize the well objectives. A simple and efficient way to capture and communicate this depth uncertainty to drillers was developed.