Exploring the “undeformed” Bengal Fan and what lies below in the deepwater Rakhine Basin

Abstract

Ophir Energy and partner Parami Energy signed the deepwater AD-3 PSC in December 2014 and quickly covered the block with 10,000 square kilometres of broadband 3D seismic data. The time-processed seismic products greatly improved our understanding of both the structure and stratigraphy of the “undeformed” Bengal Fan west of the Rakhine deformation front. This permitted the joint venture partners to consider drilling an exploration well ahead of their PSC commitments. However, plans changed when it became evident that some of the best prospectivity was located in areas where shallow gas and Mass Transport Complexes were inducing large anomalies on the time structure of the data and attenuating important amplitude information through absorption (Q). As the exact causes of the image degradation were not clear a test swath of data was pre-stack depth migrated and the imaging uplift was sufficient for Ophir to approach processing contractors to investigate both optimal amplitude recovering and amplitude preserving depth solutions. A full-block depth processing scheme was subsequently designed which included volumetric Q tomography to produce a geologically intuitive interval Q model as input to a Q compensating Kirchhoff pre-stack depth migration. This talk will present the geology of the block, its exploration challenges and discuss how the various 3D seismic datasets have provided new insights into our understanding of the basin. Having deep (12 kilometre) and high quality 3D seismic data available over a large area has helped the joint venture develop a consistent geological model at the scale of this tectonically active margin. The new imaging of the basement has brought a few unexpected surprises regarding the nature of the crust and its early history before it was covered in Neogene times by a thick deepwater sediment fan sourced from the Bengal Delta. The seismic data shows evidence of a prolific biogenic gas charge as well as the potential for a deeper thermogenic petroleum system with basement highs providing a focus for migration within the Neogene channel systems. The Neogene prospectivity can now be further de-risked by pre-stack amplitude analysis and by interrogating the pre-stack depth migration velocity field which wasn’t possible using the time processed products.

AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018