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Carbonate play in the Offshore Papuan Plateau, PNG


Offshore PNG is a core exploration area for Total. The most significant play concept in the Offshore Papuan Plateau (OPP) is early Paleogene, isolated, Carbonate Platforms, which have been interpreted on modern, broadband 2D seismic data recently acquired during 2016 and 2017. The OPP forms part of the northern margin of the Coral Sea Basin, separated from the conjugate Queensland Plateau during the opening of the Coral Sea (62 to 52 Ma). The isolated carbonate platforms are often located on positive gravity anomalies associated with basement highs. Little is known about the stratigraphy due to an absence of well control. However, information from regional DSDP wells provides some stratigraphic control. These data suggest different unconformities at wells in the Cenozoic section with the two main unconformities at the Late Eocene to Oligocene (6-16 Ma duration) and from Late Miocene to mid-Pliocene (7.7 Ma duration). Based on the above and seismic interpretation, three main sedimentary sequences are identified: The Mesozoic syn-rift (Sequence 1); The break-up (BU) to mid-Miocene series including an inferred carbonate series (Sequence 2); and The Miocene to Pliocene foreland basin series (Sequence 3). The calibration points for the dating of these sequences are represented by the chrons of the Coral Sea oceanic crust and DSDP 287/210 control. The sedimentary pattern encapsulating the carbonates (Sequence 2) downlap onto the oceanic crust and thus provide a theoretical age of Early Paleogene for the carbonates, during a period of Coral Sea rifting and propagation of the oceanic crust north-westwards, south of the license area. In addition, Late Cretaceous and Eocene outcrops are referenced in the geological map of the adjacent SE PNG along with outcrop studies that support this proposed stratigraphy. From dense 2D seismic data acquired, three seismic facies were observed within the interpreted carbonate interval (Sequence 2): (1) Faint laminated, low amplitude, corresponding to inner platform, shallow-water facies; (2) High negative amplitude, corresponding to transitional or slope facies; Layered, and (3) Alternating low and high amplitude and corresponding to outer-platform or ramp facies or detrital wedges. In conclusion, the carbonate facies predicted are located on paleo-highs and form ‘isolated carbonate platforms’ which are associated with the rifting phase of the Coral Sea. Lateral time equivalent deposition is interpreted to be outer-shelf deposits. Younger carbonates located laterally and lapping on the previous isolated platform are probably more representative of carbonate ramps. During the deposition of these ramps, the previously isolated platforms, located on top of the horsts, may have undergone exposure and subsequent karstification processes. Paleogene and Neogene carbonate outcrops have been studied and used to help the interpretation of the carbonate morphologies observed on seismic.