Exploration Insights February 2020

12 | Halliburton Landmark Exploration Insights | 13 PUK PUK Weimang Langia Manta Koko KIMU Papuan Thrust Belt IEHI BARIKEWA Papuan Foreland B B B B URAMU B B B B B Dibiri B B B BB ! ( B B B B B B Pasca B Flinders B B B BB Gulf of B Papua B PANDORA B B 6 Legend ! ( 1D Model Locations km ! ( by: Duncan Macgregor © 2020 Halliburton TRICERATOPS Subu-1 Elk/Antelope Raptor The Mailu Prospect, Papua New Guinea: Opportunity and Uncertainty in a New Frontier KURU B Torres Sub-Thrust 3 k m Mailu Flank Pseudo ! ( " Mailu (approx. location) PPL589 Papuan Plateau m 3 k Neftex ® Play Cross Section PPL576 Neftex ® Seismic Showcase Line " Mailu well location Block outlines 0 65 130 195 260 Kilometers Figure 1> Map showing the location of the Mailu prospect, and Neftex ® Insights products, including 1D models. Contours are sedimentary isopach from Swift (2012). New Neftex ® Insights products have been prepared for offshore Papua New Guinea to evaluate the prospectivity associated with undrilled frontier basins in the Papuan Plateau/Coral Sea region. A high profile deep-water well in this region, on the Mailu prospect (Figure 1), may be drilled by Total in 2020 (Shakerley et al., 2019). As part of our assessments, we have recently revised our most relevant gross depositional environment (GDE) maps, interpreted public domain seismic data in a Seismic Showcase, and undertaken 1D modeling at potential kitchen locations in the region (Figure 1). This work has had to deal with a high degree of uncertainty due to a lack of local well control, and the impact of a complex tectonic setting and history. This article illustrates how the Neftex portfolio, integrated with Permedia ® petroleum systems modeling software, can be used to develop and risk charge models for a prospect within an area of poor data control and high uncertainty. Exploration in Papua New Guinea has historically been concentrated in the onshore Papuan Fold Belt, with most wells having targeted Cretaceous sandstone reservoirs charged from Jurassic source rocks. More recently, Miocene carbonate reservoirs have been found to contain significant volumes of gas, the most important of these being the Elk and Antelope fields, first drilled in 2006. The Papuan Plateau area, by contrast, is undrilled. In addition to Total’s plans for the Mailu well, Larus Energy has acquired the license for the adjacent shallower block, PPL579, and is thought to be focusing on offshore carbonate prospects. THE MAILU PROSPECT A seismic line passing close to the Mailu prospect has been analyzed by Neftex in a recent Seismic Showcase section, available to subscribers to the Australia-New Zealand region. Additional sections can be viewed in various investors’ presentations (e.g. Swift, 2019). The prospect (Figure 1) lies in approximately 2,000 m of water. The objective, predicted by us to be a composite Eocene to Miocene carbonate platform, is at a depth of circa 3,500–4,000 m below sea level. The prospect is reported to be targeting potential resources in excess of 500 MMBOE — i.e. 3 Tcf if gas, (McLachlan, 2017). Total (Shakerley et al., 2019) has delayed the well several times, but it is now, reportedly, scheduled to be drilled in 2020. TECTONIC SETTING The commonly accepted model for the tectonostratigraphic evolution of the Papuan Plateau comprises two rift cycles — Early to Middle Jurassic, and Late Cretaceous to Paleocene — each followed by a post-rift phase (Figure 2) (Swift, 2012; Bulois et al., 2018). The stratigraphy of the first rift phase, often termed the ‘Gondwana’ phase, is extensive along the northern Australasian plate margin. It contains the main source rocks of the region, which comprise a coaly section overlain by thick intervals of low organic content mudrocks. This coaly section contains gas-prone Type III kerogen with subordinate amounts of oil-prone Type II kerogen (Wood, 2010; see also the Neftex Organic Geochemistry offering). The second phase of rifting in the Cretaceous culminated in the opening of the Coral Sea ocean in the Paleocene and is, therefore, often termed the ‘Coral Sea’ phase of rifting. The Paleocene appears to have been tectonically active, encompassing: major crustal movements on the Papuan Plateau; a period of uplift and erosion, even affecting regions now in very deep water; and ophiolite obduction onshore. Rifting was followed by a compressional phase from the Early Oligocene onwards, with the progressive development of a thrust belt and adjoining asymmetric foreland basin, informally termed the ‘Torres Basin’ (Swift, 2012). Total (Shakerley et al., 2019) has recently revised this model for the Albian to Paleocene, invoking two discrete phases of Cretaceous rifting: the first associated with proposed ‘Emo’ back arc spreading to the north; and the second culminating in the Coral Sea spreading. This refined model has positive implications for the development of Cretaceous source rock prone intervals in the section below the current thrust belt, as it suggests the existence of a restricted back-arc basin. The unconformity marking the onset of Coral Sea spreading is interpreted by Total (Shakerley et al., 2019) to be associated with large-scale uplift, driven by the flow of a ductile lower crust (Figure 2) from south to north, as interpreted on some high-quality, deep seismic acquired by Searcher (Amiribesheli et al., 2018). The concept that the development of this break-up unconformity, which extends across Papua New Guinea, was driven by deep crustal movements may also be applicable to other regions of the world, such as the Aptian unconformity in the South Atlantic. It can be noted that over much of the Gulf of Papua, to the west of this area of interest, Jurassic source rocks are thought to have generated prior to the uplift, and a possible heating episode associated with this unconformity.

Exploration Insights February 2020 | Page 12