ALBERT

Description: Sedimentary basins can be classified according to their structural genesis and evolutionary history and comprise tectonic and sedimentary cycles and stages, to which common elements of petroleum systems and plays may be linked. We describe a new method that allows easier and more efficient comparisons between petroliferous sedimentary basins with similar geologic characteristics. Using this method, we can make predictions of potential petroleum systems and plays occurring in underexplored basins or regions. In this article, the methodology is applied to the well-explored Gabon coastal basin (west African margin) and the conjugate Almada-Camamu Basin (Brazilian margin), which is a frontier basin. The two basins experienced a similar tectonostratigraphic evolution and share many similarities. We propose that petroleum systems and plays identified in the Gabon coastal basin might potentially also be present in the Almada-Camamu Basin. These could include a second lacustrine synrift petroleum system, as well as a fluviomarine transitional petroleum system. Potential, but not yet proven, reservoirs in the Almada-Camamu Basin include coarse sandstones surrounding basement highs within the synrift, synrift lacustrine carbonates, fluviomarine sandstones at the base of the transitional cycle, and early postrift ramp carbonates. The methodology and newly developed figures are particularly useful to obtain a first impression of the tectonostratigraphy, likely petroleum system and play development, and exploration history of potentially analogous basins. Furthermore, the approach allows for the recognition of important differences, raising questions that can be answered by more direct techniques.

Description: Among the oil and gas exploration community, the “play” has an almost mythical status—the successful play is the thing of which legends are made, and playmakers are regarded as heroes of the industry. But what is the play exactly and why do we need it? Curiously, considering the long period it has been in daily use, it has never really been unambiguously defined and, as a result, it has come to be used differently for different purposes. Although the term is in common use, in practice, its imprecision commonly leads us to simply ignore its significance as a concept in our rush to concentrate on prospect definition. These questions arise: Do we really need the play, and can we gain by defining it more precisely? I strongly believe that the play concept is such a valuable one that it should be central to exploration decision making; clustering petroleum accumulations into natural families helps us manage the risks inherent in new and existing venture evaluation. However, I believe that plays can best help us in this way if they comprise meaningful natural groups that we can use both for reliable analog comparison and in meaningful statistical analysis. In this review, I propose a three-tier hierarchic framework for play definition based on (1) the petroleum charge system, (2) the reservoir-seal formation pair or lithofacies, and (3) the trap type. These tiers can be related to the geodynamic, sedimentary, and tectonic events that drive phases in basin evolution, thus placing the concept directly in its geologic context. Harry Doust is a retired explorationist, currently serving as professor of regional and petroleum geology at the Vrije University of Amsterdam, where he teaches Master of Science classes and supervises students. His main research interest lies in the study of whether and under what conditions standard phases in the evolution of petroliferous sedimentary basins can be recognized. From this basis, he investigates the relationship between basin evolution and the occurrence of common petroleum system and play types. Before his retirement, Harry spent more than 30 yr working with Shell International in and on many parts of the world, particularly in the evaluation of new ventures. He has published widely on regional exploration evaluations.