Western offshore Myanmar: New insights on the Ayeyarwady River as the fairway for Pliocene-Pleistocene sandstone

Until 2012, the western Myanmar waters area was deemed unattractive for hydrocarbon exploration due to the apparent absence of a nearby large river system; hence, there was a perceived low chance of finding reservoirs. This paradigm underwent a transformative shift during the last decade, with successful hydrocarbon exploration in offshore block A-6. This tract straddles the convergent zone between the Indian plate in deep water and the Myanmar platelets in shallow water. The Pyi Thar-ST1 gas discovery, drilled in shallow water in 2012, and the ultradeep-water gas discovery wells of Shwe Yee Htun-1 and Pyi Thit-1 (tested) between 2015 and 2018 have revealed a new hydrocarbon play, including a new reservoir fairway. Our integrated interpretation of two- and three-dimensional seismic data, well logs, petrography, heavy-mineral analysis, U-Pb zircon age dating, and regional geologic context indicates that a Pliocene-Pleistocene fan system received sediment from the proto-Ayeyarwady-Chindwin river, which flowed east to west through a wide breach in the unstable continental slope of block A-6 during the Late Miocene. This depositional system formed the Pliocene-Pleistocene Western Ayeyarwady fan (WAF), which includes gas-bearing sandstone within levee-channel complex systems. This paper further shows how the WAF system was isolated from the sediment supply of the Ayeyarwady River and its delta system by a Late Pleistocene uplift, resulting in its present position.