Papua New Guinea has become one of the world’s most exciting exploration regions, with significant petroleum potential in the Gulf of Papua and its Northern Basins. Modern seismic data has enabled deeper imaging of distinctive tectonic packages and basement which has been utilised in the studies leading to the identification of several play types that have not been previously recognized. The Gulf of Papua is an incredibly large area covering over 187,000 sqkm, with only 27 offshore exploration wells drilled, restricted to the Fly River Platform and the nearshore Aure Fold Thrust Belt areas.

The deepwater offshore Gulf has been largely ignored by industry due to paradigms around the extent of oceanic crust, presence of source and reservoir facies. An extensive regional dataset was acquired by Searcher Seismic in the Gulf between 2006 and 2018.  The Searcher Database includes 76,361km 2D data, 1,795 km² 3D data, gulf-wide shipborne gravity and magnetics data, transition zone gravity and magnetics, 75 seabed cores, 37 heatflow observation points, five dredge samples, and a full satellite slick database. All of these datasets were made available to Discover Geoscience to carry out a detailed geological and geophysical review of offshore Gulf of Papua and develop a deep understanding of the hydrocarbon prospectivity of the Gulf of Papua.

Exploratory drilling to date has focussed on the Fly River Platform and the Aure Fold Thrust Belt, with other areas of the gulf, including the Moresby Trough, Eastern Plateau, Offshore Papuan Plateau and the Coral Sea, remaining completely unexplored. The traditional play types targeted by oil and gas companies in the Gulf of Papua to date include Miocene platform carbonates and pinnacle reefs, basement related horst blocks and Pliocene basin floor fans.

Discover carried out regional seismic facies mapping as a tool for development of paleogeography maps and numerous additional play types have been identified away from the drilled nearshore and onshore areas.

Utilizing Searcher’s seismic data, Discover were able to image up to 35km depth and map a likely Moho depth horizon. The data also illuminates a distinctive Coral Sea oceanic crustal character which was mapped and compared to the areas of attenuated continental crust. It was found that the actual extent of the true oceanic crust is likely much more restricted than previous publications would suggest, with most of the Gulf and Offshore Papuan Plateau areas being underlain by attenuated continental crust. This has significant implications not only for heat flow modelling but also for the interpretation of the stratigraphy preserved between the basement and the Base Tertiary Unconformity.

Reprocessing of the PPL379 3D seismic survey has resulted in a new deeper interpretation of the basement depth which leads to interpretation of a thick section of Mesozoic fluvio-deltaic to shallow marine sediments sitting below the Base Tertiary Unconformity, known to contain source rocks in the nearshore and onshore areas.

An extensive 1D basin modelling study was conducted across the Gulf of Papua. Burial history models were constructed based on crustal thinning history and sedimentation rates determined from structural, well and seismic data. Nine pseudo well models were thermally calibrated against present day temperature and vitrinite maturity data from six calibration wells. Results of the 1D Basin modelling indicate that Mesozoic source rocks in grabens across the Gulf of Papua began expulsion in the Early Cretaceous and suffered a hiatus during the Late Cretaceous and Tertiary uplift and erosional events, before becoming buried once again to maximum depth at present day. This modelling suggests that there is currently an active charge system throughout the grabens across the Gulf of Papua. This conclusion is supported by the seabed coring, seep and slick data and heatflow survey results.

The Gulf of Papua has been largely ignored by industry to date due to previously entrenched paradigms of thin, cold Tertiary stratigraphy overlying oceanic crust. The results of Searcher Seismic’s Geoscience program in the Gulf of Papua all point to a prospective basin with Northwest Shelf of Australia style stratigraphy, present day hydrocarbon charge and multiple play types.

The Gulf of Papua Prospectivity Study consists of five sections; Sequence Stratigraphic Framework, Tectonostratigraphic Elements, Facies and EOD Mapping, Charge Modelling and Play Concepts & Leads Inventory.

The Sequence Stratigraphic Framework consists of sixteen representative wells which have been reviewed for biostratigraphy, lithology, log character, hydrocarbon shows, trap configuration, rates of deposition and likely reason for failure. The post well analysis led to the development of a chronostratigraphy of the Gulf as well as, with the assistance of the seismic data, a detailed sequence stratigraphic framework.

A tectonostratigraphic elements map of the Gulf of Papua has been created in order to accurately define the individual provinces and sub-provinces of the Gulf. This map was created by mapping approximately 10,000 faults and then condensing those into the major fault, horst and graben trends. Sub basin areas have also been modelled showing varying maturities, volumes and timing of charge expulsion.

A modified Ramsayer method of seismic facies mapping was employed to each of the key chronostratigraphic packages across the Gulf of Papua. The facies mapping was combined with well analysis to produce Environment of Deposition Maps across five key chronostratigraphic intervals.

An extensive 1D Basin Modelling study was conducted across the Gulf of Papua. The modelling provided a crustal heatflow model, maturity and burial history through time, as well as source rock modelling, expulsion curves and generated hydrocarbon volumes.

A great number of play concepts and new play types have been identified as well as an extensive inventory of leads have developed across the area.

The Gulf of Papua study has identified multiple reservoir seal pairs, play types and leads across all areas of the gulf. Basin modelling shows good potential for large volumes of hydrocarbons to have been generated and expelled across most of the vast Gulf of Papua.

The Gulf of Papua Perspectivity Study is available alongside the underlying Gulf of Papua Seismic database.