EAGE Workshop on Petroleum Play Assessment

Stratigraphic forward models encode what we know about dynamic stratigraphy in the form of a numerical model that can make various types of predictions of stratal geometries and facies distributions. Unfortunately, limited knowledge of the physical laws that govern various stratigraphic processes, incomplete knowledge of initial conditions, and limited computational power mean that such models have only limited predictive power typically better applied to issues such as reservoir presence rather than reservoir quality of detailed structure. Consequently, current examples of stratigraphic forward models are best used for exploration scale subsurface prediction using a multiple scenario probabilistic approach that is particularly well suited to play assessment and play fairway mapping. Multiple scenario modelling using the new Move sediment modelling tool is a fast and efficient way of identifying a range of statistically likely (but uncertain) deposit distributions and architectures. Application of conditional frequency mapping to these allows play fairway analysis to better accommodate this uncertainty, and hence lead to better play assessment.

For frontier basins, the development of petroleum play concepts and the construction of play fairway maps are difficult. In particular, the presence and potential extent of source rocks and reservoirs represents some of the main uncertainties. To provide an objective, process based, predictive methodology focused on these problems, global plate reconstructions were used as the basis for palaeogeographic mapping. These maps are underpinned by data and were coupled with state-of-the-art palaeo-Earth systems models (HadCM3 palaeoclimate model). Detailed palaeotectonics and palaeoenvironments maps were prepared and a new method relating topography and bathymetry to plate tectonic environments was used as the basis for palaeo digital elevation models (DEMs). These were gridded in GIS and used to provide the topographic and bathymetric boundary conditions for coupled ocean-atmosphere general circulation models. The compilation of the base maps was based on a global database of palaeoenvironmental and lithofacies data. These data include climate proxies that were used to test the veracity of the modelling results. This work is used to provide an understanding of the geohistory of the North Atlantic. It also provides key petroleum play concepts and unique, innovative methods to produce improved play fairway maps for North Atlantic margin basins.

This paper reviews alternative approaches to play assessment. The review covers both discrete (conventional) and continuous (unconventional) plays. There is a significant literature on the former topic (and also a range of more or less well established methods/approaches). For continuous resources we are looking at an emerging field that can benefit from a systematic review -- in order to be able to both adopt and adapt from assessment of discrete resources. The main body of the paper provides a review of alternative play assessment methods. The review concludes with a summary overview of key differences and similarities between the approaches used for assessing respectively discrete and continuous resources. Some of the key dimensions considered are interpretation of shared play risks and conditional risks, how to model recovery, the key inputs from analogs and the role of the assessment unit.

As industry has returned to basic exploration principles, play mapping is again a standard part of the exploration process. Many different methods are now employed for estimating and conveying the chance of geologic success for plays, or play segments, in map form.

The use of ArcGIS has enabled increasingly complex and diverse exploration data sets to be amalgamated, integrated and assessed in a user-friendly and relatively inexpensive environment. The Tellus™ global play fairways and petroleum systems database provides a unique platform for analysis of past exploration success and analysis of the future hydrocarbon potential of individual plays and stacked plays in single basins and across geographical regions. Common risk segment (CRS) maps for the main petroleum plays in a number of basins across the globe have been created by quantifying exploration risk for the Reservoir, Hydrocarbon Charge, Trap and Seal and Timing and hydrocarbon preservation: In addition to the geological issues outlined above, the exploration of a play or series of stacked plays in a basin or region are also at the mercy of geopolitical issues in the form of government policy (licensing rounds and available acreage), oil prices and exploration budgets. The spatial development of hydrocarbon discoveries in the basin (stacked plays) or in individual plays can be plotted using a simple algorithm in ArcGIS to display the fields discovered by decade or on smaller, user-defined time intervals.

This paper introduces a workflow and combination of techniques that proved to be a successful approach for de-risking the Messinian stratigraphic play. The key was to add confidence to the interpretation of seismic AVO anomalies in the Messinian section, as well as to the predicted depositional environment and reservoir facies away from well control. Detailed Seismic Sequence Stratigraphy, guided by wire line log interpretation and analysis of core data from nearby wells, was the foundation in developing the geological model for the stratigraphic play. As a result of this work, a seismic AVO anomaly at Messinian level, not associated with structural closure, was drilled and proved a success. The well penetrated the predicted sand facies with high gas saturation, and flowed gas at commercial rates in the well test. The new proven Messinian stratigraphic play de-risked many similar mapped prospects with significant

Nowadays majority of successful oil and gas discoveries are a result of the sophisticated studies combined with the most recent exploration techniques applied on variety of depositional complexes. One of the proven methods that largely decrease uncertainties in hydrocarbon exploration is numerical petroleum system modeling. By using different petroleum system modeling tools like 1D, 2D & 3D modeling here we investigate complex petroleum system of the southern Russia (Sea of Azov). The subsequent numerical models highlighted a new hydrocarbon system nested within the poorly explored transitional complex of the Sea of Azov.

This talk presents results from two studies undertaken at Exprodat, using geographic information system (GIS) software - used increasingly in this area in recent years with much success. Many companies only use GIS as a simple data integration and visualisation tool, and don’t exploit the spatial analysis capabilities which can be used to support the interpretation of large volumes of data and develop quantitative play analysis models.

Unconventional plays require a unique rationale to address geologic uncertainty, deliverability and commerciality that differs from the approach that is commonly applied to conventional plays. As the presence of hydrocarbons is commonly known to exist as a resource before wells specific to the play are drilled, operators can wrongly assume a certainty of geologic conditions and commercial outcome. Initial wells for unconventional plays should be drilled to measure reservoir characteristics to determine if the play should advance to testing for deliverability. Once deliverability is established then typically a commercial pilot program is initiated and if this is encouraging a full stage commercial development follows.

The Dead Sea Transform pull apart Hula Basin in Northern Israel forms a unique geological setting that was characterized in the Tertiary and Quaternary by continued subsidence, limited draining of the valley floor and wet conditions. These are ideal for the development of peat soils and their rapid burial, which resulted in the formation of coal beds. Gas produced in these beds accumulated in porous rocks above them or but primarily within the coal layers themselves ("Coalbed methane play" or CBM). The CBM is a relatively clean form of gas that is absorbed and trapped to the crystal structure of the source rock itself, the coal. The gas migrates within the coal layer in a liquid state dissolved in groundwater, and only minimal reduction of the hydrostatic pressure by pumping the water out allows its effective extraction. Over 40 wells in the Hula Valley targeted the porous and the CBM plays, with four of them producing coalbed gas in various quantities. Independent reserve estimation shows the existence of commercial quantities of gas in this play. Environmental and other strategic consideration may promote the development of the play into full scale production.

OMV New Zealand, on behalf of Joint Venture partners PTTEP New Zealand Ltd and Mitsui E&P Australia Pty Ltd, has undertaken a comprehensive four year evaluation of the petroleum potential of New Zealand’s Great South Basin. The Great South Basin (GSB) lies offshore, adjacent to the southeast coast of the South Island of New Zealand (Figure 1). The basin is the largest in the southern New Zealand region, covering an area of approximately 120,000 km2. Water depths range from 100 to 1,500 m, however 80% of the permit area lies in water depths greater than 200 m. Logistics, the amount and quality of available technical data, and environmental considerations are all major factors in exploring large and remote frontier basins. Determining the scope, method and application of projects at the beginning of the evaluation via both sequential and parallel work programmes proved vital in completing a thorough assessment of the basin in the relatively short amount of time available.

Petroleum system modeling is a vital component of exploration that contributes to volumetric and risk assessment at basin, play, and prospect scales. It can be applied during all stages of exploration, from regional charge evaluations for frontier basins with little or no well control to complex charge evaluations for individual prospects or fields within thoroughly explored areas. This paper presents integrated workflows that capture the results from basin and petroleum system analysis and populate play and prospect databases with information on potential hydrocarbon accumulations,including volumetric dependency among accumulations as well as leak connections among hydrocarbon pools. Alternative scenarios for the evolution of the petroleum system are used for capturing prospect risk and hydrocarbon entrapment uncertainty. Adding this stochastic dimension to the play and prospect databases provides a more robust understanding of the full range of possible outcomes that if used properly may provide significant competitive advantage.