The Sunrise and Troubadour fields form a complex of giant gas-condensate accumulations located in the Timor Sea some 450 km northwest of Darwin. Left unappraised for almost a quarter of a century since discovery, recently renewed attention has brought these stranded hydrocarbon accumulations to the point of comm-ercialisation.A focussed appraisal program during 1997–1999 driven by expectations of growth in LNG and domestic gas markets, involved the acquisition and processing of an extensive grid of modern 2D seismic and the drilling, coring and testing of three wells. The aim of this program was to quantify better both in-place hydrocarbon volumes (reservoir properties and their distribution) and hydrocarbon recovery efficiency (gas quality and deliverability). Maximum value has been extracted from these data via a combination of deterministic and probabilistic methods, and the integration of analyses across all disciplines.This paper provides an overview of these efforts, describes the fields and details major subsurface uncertainties. Key aspects are:3D, object-based geological modelling of the reservoir, covering the spectrum of plausible sedimentological interpretations.Convolution of rock properties, derived from seismic (AVO) inversion, with 3D geological model realisations to define reservoir properties in inter-well areas.Incorporation of faults (both seismically mapped and probabilistically modelled sub-seismic faults) into both the static 3D reservoir models and the dynamic reservoir simulations.Interpretation of a tilted gas-water contact apparently arising from flow of water in the Plover aquifer away from active tectonism to the north.Extensive gas and condensate fluid analysis and modelling.Scenario-based approach to dynamic modelling.In summary, acquisition of an extensive suite of quality data during the past two-three years coupled with novel, integrated, state-of-the-art analysis of the subsurface has led to a major increase in estimates of potentially recoverable gas and condensate. Improved volumetric confidence in conjunction with both traditional and innovative engineering design (e.g. Floating Liquefied Natural Gas technology) has made viable a range of possible commercial developments from 2005 onwards.

Summary Value-of-information (VOI) analysis is a powerful tool for short-term rationalization of data-acquisition costs. Even more, the longer-term added value of proper VOI analysis lies in the process of constructing the analysis and in the insight it gives into risk and opportunity management. A rigorous VOI analysis generally spans the full life cycle of E&P and, as such, requires input from a multidisciplinary team. A thorough examination of where data add value leads to value optimization and creation. To unlock this value, implementation of a rigorous, easy-to-use method is critical. Such an implementation has progressed in Woodside and has already led to a shift in mindset. VOI analyses are regarded not as cumbersome and fuzzy, but increasingly as an essential part of data acquisition and data analysis. As a result, sizeable reductions in well-data-acquisition costs have been achieved and data acquisition and analysis has become more focused. Introduction Data acquisition lies at the root of the E&P business. Data acquired as operator, partner, or otherwise form the basis for investment decisions and future growth as a company. Data acquisition, however, generally is costly. How costly became very clear in early 1999 when the oil price hovered around U.S. $10. In such an environment, all expenditure is challenged, and that challenge process has not disappeared with the subsequent rise in oil prices. The cost of data acquisition should be justified by the value of the data to the business. A VOI analysis is a means for such a justification. A VOI analysis essentially is an expected-monetary-value (EMV) calculation. It analyzes the expected benefit of a series of actions and outcomes under two assumptions: with or without the proposed data being available. The difference in EMV between the scenario with data acquisition and the scenario without is then the value of the data acquired. Typically, when this value is not enough to cover the cost of data acquisition (or is even negative), it is seen as a good reason not to acquire the data. However, VOI means more than cost reduction. Certainly, short-term cost reductions can be realized by reduction of data acquisition where this acquisition cannot be justified. The true power of the VOI analyses lies in better value, risk, and opportunity management.Value Assurance. If the value of data acquisition is known, it sets an immediate target for realizing this value once the data are acquired. This provides a focus on both value and cost.Value Creation. Sensitivity analyses of the VOI calculation identify the key risks and probabilities that may be managed to enhance value. This is particularly powerful when applied to portfolio management, opening the way to new opportunities and business growth. This powerful aspect of VOI analyses is rarely applied in practice. VOI analysis has the image of being good in theory but rather unfruitful in practice. It is perceived to be too complicated, too fuzzy, and too much work and to have too many parameters and too many assumptions. One can justify anything just by tweaking the parameters correctly. These are ingrained but incorrect perceptions, really based only on lack of knowledge, lack of tools, and perhaps poor experiences in the past. At the heart of the problem is the fact that monetary return on the investment of data acquisition is usually several years in the future.A 3D-seismic survey might pay off in terms of optimal positioning of development wells, enhancing recovery per well, and reducing unit cost per barrel.A full-diameter core over the reservoir might pay off in terms of a better understanding of the environment of deposition, leading to an optimized development scheme.Sidewall cores in an exploration well might pay off in terms of opening a new play, with a corresponding discovery and development in the future. The longer the time frame between data acquisition and payback (typically in the form of a development), the more difficult the VOI analysis is. A good analysis requires a full life-cycle approach and thus input from a multidisciplinary team—geoscientists, petroleum engineers, surface engineers, economists, and sometimes marketers and public relations officers. Similarly, data acquisition in a late phase of development might be very easy to justify because of a direct visible impact. But at the same time, there is often little room for change late in the development of a field and the value of the data is therefore limited. If new data cannot impact decisions, then those data have no value. Generally, early in the exploration phase of an area, data are valuable because so many options for development are still open.

The Sunrise-Troubadour giant gas-condensate fields lie on a massive, broad, low-relief structure 75km long and 50km wide. The fields have a gross reservoir thickness of 80m. They are located on the north western boundary of the Australian Plate and form the basis of a proposed green-field LNG project and an Australian domestic gas development. Statistical volumetric analysis has shown that reservoir quality, distribution and Net-To-Gross ratio (NTG) are the main static uncertainties affecting Gas-Initially-In-Place (GIIP). These parameters are a function of the environment of deposition of the reservoir interval. The low average NTG in some wells (as low as 30%) indicates potential for depositional heterogeneity which can impact dynamic fluid flow through the reservoir. Depositional modelling has therefore been a major focus for field evaluation and appraisal. The reservoir interval was deposited in a marginal marine setting on a slowly subsiding, broad, low-relief shelf. The overall retrogradational character of the reservoir interval is illustrated by the upward increase in the open marine character of the interbedded shales. There are two major relative sea level falls interpreted which resulted in the deposition of incised-valley and sharp-based, forced regressive shoreface deposits. These sandbodies form the major reservoir units in the fields. Highstand and transgressive deposits are characterised by relatively thin and discontinuous sandbodies. In order to fully capture the depositional uncertainty inherent in a field of this scale which only has limited well control (six wells), three groups consisting of sedimentologists, stratigraphers and biostratigraphers have independently interpreted the core and wireline data. The result was three different depositional interpretations. From these interpretations a most likely depositional model was developed. Low and high case 3-D depositional models were generated by varying NTG and sandbody correlatibility and geometries. The adjustment of these parameters reflected the range of depositional interpretations from the three individual expert groups. These models form the basis of multi-scenario reservoir simulation studies which indicate that development options for these fields are technically robust for the range of perceived subsurface scenarios. Introduction The Sunrise-Troubadour gas-condensate fields are located 450 km northwest of Darwin on the edge of the Australian continental shelf and 50 km from the adjacent Timor Trench (Fig. 1). Together they hold in-place volumes ranging from (P90 to P10) 11.6 to 24 Tcf gas and 510 to 1055 million bbls condensate. The fields have a combined areal closure of 1000 square kilometres with a maximum vertical closure of only 180 metres. The main reservoir interval is the Bathonian Upper Plover Formation.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractValue-of-Information analyses are a powerful tool for shortterm rationalisation of data acquisition costs. But even more so the longer-term added value of proper VOI analyses lies in the process of constructing the analysis, and in the insight it gives into risk and opportunity management. A rigorous VOI analysis generally spans the full life cycle of E&P, and as such requires input from a multi-disciplinary team. A thorough scrutiny about where data adds value will lead to value optimisation and creation.In order to unlock this value, implementation of a rigorous and easy-to-use methodology is critical. Such an implementation has progressed in Woodside, and has already led to a shift in mindset. VOI analyses are less regarded as cumbersome and fuzzy, but more and more as an essential part of data acquisition and data analysis. As a result, sizeable reductions in well data acquisition costs have been achieved, and data acquisition and analysis has become more focused.

No abstract