Publications

Cenozoic aggraded platforms make up the reservoir component of some of the most prolific hydrocarbon plays in SE Asia. The plays are characterised by carbonate buildups that are today found in basins ranging from onshore to deepwater. Examples include the major oil and gas provinces of East Java, Natuna and North Sumatra. These plays have variable exploration maturity and are underexplored where the buildups lie in deepwater Neogene basins because the play is very difficult to derisk without drilling. This paper represents a discussion around pre-cursor tectonic and depositional settings for platform development, building on a scheme published by Bosence (2005) but applying it to associated Cenozoic petroleum systems. The scheme maps reasonably well on to Cenozoic build-up plays in SE Asia and can be used to help identify and de-risk future potential in the region.Views of carbonate platform development were dominated in the latter part of the last century by supply (carbonate factories) and accommodation space (sequence stratigraphy) [eg. Schlager, 1992]. The scheme proposed by Bosence (2005) turns attention instead to platform morphology, platform development through time as a function of anisotropic fluctuations in growth substrate. Differences in substrate stability and subsidence profiles are attributed to tectonic settings within basins. Tectonic setting, palaeo-climate, eustacy and proximity to landmasses influence how platforms prograde, aggrade and eventually drown. They also set the scene for the preservation of source rock, seal (versus thieving), burial and charge focus. By changing the emphasis to platform morphology, we can use tectonic setting as a global proxy for the prediction of morphological types, which are associated with variations in reservoir characterisation by analogue (Bosence 2005). Whereas both the aggradational architecture and reservoir characterization of the build-ups are crucial to de-risking potential well performance, an attempt is made here to characterise all play components as a function of the platform morphology to broaden the play understanding.Tectonic processes plays an important role in generating suitable settings for both initial carbonate growth and subsequent aggradational deposition. Continental margins undergoing thermal subsidence are ideally suited for long-term aggradational platform growth. Such settings are capable of generating architectural build-ups in excess of 1 km vertical relief and are typically located in present-day deepwater. Back-arc rifted basins with access to post-rift marine influences are also important in SE Asia, with lesser components of foreland basins, convergent margins, strike-slip settings and volcanic ridges. Tectonic setting, therefore, as well as palaeo-latitude can be used as global proxies to help identify and understand basins with very limited sub-surface data.The keys to unlocking the hydrocarbon potential in these plays are (i) understanding the petroleum system and risks, (ii) acquiring a detailed knowledge of the aggradational architecture of the buildup, (iii) knowledge of build-up age, burial history and reservoir characteristics and, not least, (iv) commercial prudence. Risks include an impoverished petroleum system [i.e. lean source rocks and/or bad charge-timing with respect to seal development], poor reservoir or permeability development, retention failure, high risk of CO2 contamination, and the current high-cost of development rendering exploration noncommercial. The rewards however may be significant in that trap sizes are usually large and reservoir risk is relatively low or reducible for frontier exploration. In an arena where new reserves addition has fast become the main focus for exploration, these plays remain one of the few in SE Asia that may still have the running room to deliver significant portfolio volume growth.The classification scheme described by Bosence (2005) is conditioned by Cenozoic and modern analogues. When applied to hydrocarbon plays, the scheme becomes heavily weighted towards passive margin or rifted back-arc settings. This is partly because platform aggradation associated with subsidence better suits extensional tectonics and partly because we have had more exploration success in these settings. Fault block platforms are considered the most attractive because as a play concept, it is both substantially material and still emerging. Subsiding margin platforms as a shelf edge play is heavily explored and fundamentally flawed in some respects. Subside the entire shelf and the game changes, perhaps completely, although it does have a charge challenge that has yet to be resolved. The largest potential play types are so-called offshore carbonate banks. Despite the super major potential, charge risks are considerable, with huge investment exposure, making it slip to third in the overall ranking. The remaining platforms (volcanic ridge, foreland margin, delta top and thrust top) remain poorly constrained by material value as yet, as they are under-explored. Their commercial value lies in how these integrate in to regional portfolios and whether the remaining running room suits your risk profile for volume growth.