Publications

Tangguh Phase 1 (first gas in 2009) consisted of two offshore platforms accessing the giant Jurassic Vorwata gas field, delivering gas to a two-train LNG plant. Phase 2 was sanctioned in 2016 to develop smaller Tangguh fields and supply a third LNG train. Drilling the thick karstified Eocene-Miocene overburden (usually on total losses) has the operational challenge of potentially drilling into large karstified fault zones and caves. This can result in stuck pipe and expensive sidetracks. The mitigation is to map the caves on seismic to avoid in well planning, but this can only be done on high-quality data. Phase 2 activity is concentrated in areas where the historical towed-streamer and sparse OBC seismic image is poor due to shallow carbonates, pervasive faulting and shallow gas. New high-density Ocean Bottom Node (HD OBN) seismic was commissioned to better illuminate the overburden and enhance reservoir characterization. A 730 km2 survey was acquired by BGP in 2017/18 using 8600 nodes. Up to three source vessels were used to speed-up operations using BP; Independent Simultaneous Source (ISS�) technology. Maximum offsets of 20km were recorded to provide diving waves needed for detailed velocity inversion. The dense wide-azimuth design resulted in a high fold of over 1500 (critical to improve signal-to-noise and resolution beneath the complex overburden and through the scattering and highly attenuating karst layers). The data was processed to technical limit by CGG including deblending, Full Waveform Inversion (FWI), anisotropic depth migration and converted wave processing. The high trace density and sampling allowed quality P-only fast-track products to be produced quickly (4 months after last shot), which had a high impact on well-planning. Final products (PZ and PS volumes) are delivering a step-change in image quality - highlighting zones of structural complexity and intense karstification and providing more reliable reservoir mapping.