Exploration Insights February 2020

14 | Halliburton Landmark Exploration Insights | 15 S N Papua New Guinea Onshore Torres Basin Proposed Mailu well Coral Sea 0 (not to scale) Depth (km) 0 cene Paleo rmity nfo Unco 3 R 3 R © 2020 Halliburton Hyper Extended Zone S S 6 9 50 km S S Recently Extinct Subducting Slab MOHO 20 40 Possible Kitchen Area Ambiguous Lower Crust Oceanic Crust 6 Mantle © 2020 Halliburton 9 20 40 Cenozoic Foreland and Thrust Belt Sequence Eocene to Miocene Carbonates Mantle S Probable Source Rocks Jurassic Rift Sequences ? Igneous Continental Crust R Probable Reservoirs Cretaceous Rift Sequences Oceanic Crust Figure 2> A schematic interpretation of the structure of the Papuan Plateau and the petroleum systems elements of the Mailu prospect. Neftex ® Insights subscribers can access greater detail in the Papuan Plateau Play Cross Section. Partially based on a Searcher seismic line within Amiribesheli et al. (2018). PETROLEUM SYSTEMS MODELS AND THEIR RELATIONSHIP TO TECTONICS Sediment thicknesses in the immediate vicinity of the Mailu platform appear to be limited, and potential kitchens are, thus, located to the north and in the onshore (Figure 2), where the Cenozoic sequence thickens towards a Miocene thrust belt. Given the lack of stratigraphic control and the uncertainties in the tectonic history, a wide range of interpretations is possible regarding the various elements of a petroleum system in this area. Key uncertainties include: 1. Is there a significant sedimentary sequence preserved onshore below the thrust belt? What is the stratigraphy of that sub-thrust sequence? Could it contain the margins of a consumed Cretaceous back-arc basin? 2. What source rocks are likely to be present in the region? Is the Jurassic preserved below the interpreted Cretaceous rifts and does it contain similar source rocks to those observed in the Papuan foreland and in the Gulf of Papua? 3. What kerogen types are likely to be present in such source rocks? The Jurassic source rocks in the Papuan Foreland appear to vary between clearly gas-prone Type III material and oil-prone cannel coals (Wood, 2010). Could a Cretaceous sequence contain more oil- prone material? 4. What is the present-day heat flow in the region, and what are the depths of hydrocarbon windows? Present day, heat flow could range from around 45 mW/m 2 , typical of the Papuan Foreland (Wood, 2010), to much higher figures compatible with the recent arc volcanic activity in the near onshore. Heat flows of around 65 mW/m 2 have been calculated for a few deep-water cores in the Coral Sea (Piggott and Bettis, 1996). 5. What heat flow and level of erosion are associated with the Paleocene Figure 3> Example of a Petroleum Systems Events Chart produced automatically within Permedia ® petroleum systems modeling software for a specific tectonic and heat flow history, and for a Jurassic Type III source rock. Thermal history and modeled Jurassic maturity are plotted against other petroleum systems elements of the Mailu prospect. Multiple simulations like this have been run. unconformity? What impact might these have on the risk of oil and gas having generated prior to the development of a trap and seal at Mailu? 6. Is biogenic gas a viable alternative petroleum system in the offshore region? 1D basin modeling studies often depend on identifying and analyzing a single, most likely interpretation. The levels of uncertainty here clearly make such an approach inappropriate, as any single combination of interpretations on each of the above uncertainties is almost certain to be wrong. Using the Neftex Insights regional database of public domain literature, GDE maps, chronostratigraphic charts, and plate reconstructions, we were able to constrain a range of outcomes on each of these key uncertainties and translate them into sensitivity analyses within Permedia petroleum systems modeling software. The parameters that we were able to vary included: 1) stratigraphic interpretations and depths, 2) heat flow histories, 3) kerogen types, and 4) levels of erosion on key unconformities. Several models were initially run for a calibration well in the Gulf of Papua, which provided constraints on thermal history and levels of erosion. Subsequently, two pseudo-wells were analyzed within, or representative of, the migration catchment of the Mailu prospect (Figure 1). Each sensitivity run was automatically converted within Permedia petroleum systems modeling software to a Petroleum Systems Events Chart (Figure 3). This enabled generation profiles for the candidate source rocks to be plotted against other key elements, such as the deposition of the Mailu carbonate and the development of a trap and seal over it. The full results of this study are available to Neftex Advanced Insights subscribers here. The proportion of simulated scenarios that are likely to provide an effective petroleum system was translated into exploration risk. Our analyses showed that the Mailu prospect requires long- distance migration from below the onshore thrust belt, with the most likely charge coming from Jurassic source rocks, which may largely be gas- prone and gas-mature, as illustrated in Figure 3. A higher risk model, suggested by elements of the complex tectonic history, invokes the presence of a Cretaceous oil-prone source rocks below the thrust belt, which is unproven in Papua New Guinea to date. Sedimentation rates in the region are outside the observed global range of significant biogenic systems, as documented in the May 2019 edition of the Exploration Insights magazine. SUMMARY At present, exploration in this region of Papua New Guinea carries a high degree of uncertainty and there is little doubt that Mailu is a high risk well, though one with the potential to open up a large new petroleum system. A failure at this location would not write-off remaining prospectivity, but in view of the dependency on long-distance migration, could restrict it to regions closer to the shoreline and to the likely

Exploration Insights February 2020 | Page 14