QUANTITATIVE BASIN ANALYSIS
Innovative solutions for complex exploration problems
Over the last few years, there have been significant advances in our ability to describe and quantify the physical processes responsible for the development of sedimentary basins and how these processes operate over a wide range of spatial and temporal scales. This quantification offers the ability to investigate the interaction between tectonic, erosional, and sedimentary processes and how they determine basin architecture, sedimentary facies, and the stratigraphic stacking patterns that characterize basin systems. Karner and Driscoll have combined quantitative and isostatic basin modeling techniques with the principles of seismic sequence stratigraphy. The resulting technique employs both two-dimensional and three-dimensional kinematic and flexural models for the deformation of the lithosphere and sediment transport mechanisms. The elements of quantitative basin analysis are described in this document Quantitative Basin Analysis (QBA*) and provide a quantitative understanding of the interplay between tectonic deformation of the lithosphere, basin architecture, and the infill stratigraphy of the basin. In particular, the three-dimensional QBA approach determines the spatial distribution of rift flank and basin topography. With these topographic surfaces defined, it becomes possible to predict the development of river drainage systems and the preferred input sites of clastics to the evolving basin system. A rationale for describing sand/shale distribution within a developing basin implies that source and reservoir distribution and quality can also be estimated in addition to defining migration pathways. The results of QBA can be applied to exploration problems in five main ways:
Examples of modeling petroleum systems, based on QBA Group studies over the last few years, include the eastern Brazilian margin, Somalian Nogal basin, Albertine rift system of east Africa, the Canadian Jeanne D'Arc basin, the Northwest Australian shelf, the Chad and western Algerian basins, West of Shetlands margin, the Hebridean and eastern and western Rockall margins, and the West African continental margin. This broad experience base is providing important constraints and analogues for the investigation of new, frontier and mature hydrocarbon producing areas and systems.
Perhaps the most critical new research result for passive margin development centers around the recognition and ramifications of ductile extension of the lower plate as break-up is approached (also termed vertical extensional strain partitioning). Originally mapped and defined in our northwest Australian work, the same process appears to dominate the late-rift stage development of many passive continental margins, including the West Shetland, Eastern Brazilian and West African margins. A direct consequence of this extensional partitioning is the increased input of heat in those areas dominated by ductile extension, the distribution and amplitude of which is governed by the distribution and amplitude of lower plate extension. Predicted heat flows are extremely high at the end of rifting. These results should have a dramatic impact on deepwater play concepts of these margins.
An important element of QBA is in defining the structural framework of a region containing the various basin systems to be analyzed. Critical in defining the structural framework has been the role of the crustal Bouguer gravity anomaly, constructed by determining the Bouguer gravity anomaly of the region and subtracting a least-squares bicubic trend surface approximating the Moho topography. The crustal Bouguer gravity, because it highlights density contrasts within the crust, tends to accentuate sedimentary basins and flexurally compensated features such as rift flanks. The crustal Bouguer gravity is proving to be a valuable and powerful asset in helping to map the the three-dimensional architecture of rift basin systems, especially for exploration frontier regions.
2. Driscoll, N.W., and G.D. Karner, 1998. Lower crustal extension across the northern Carnarvon basin, Australia: Evidence for an eastward dipping detachment. J. Geophys. Res., 103, 4975-4992.
3. Karner, G.D., and N.W. Driscoll, 1999. Tectonic and stratigraphic development of the West African and eastern Brazilian Margins: Insights from quantitative basin modeling. In: "Oil & Gas habitats of the South Atlantic". Spec. Publ. Geol. Soc. Lond., 153, 11-40.
4. Karner, G.D., and N.W. Driscoll, 1999. Style, timing, and distribution of tectonic deformation across the Exmouth Plateau, northwest Australia, determined from stratal architecture and quantitative basin modelling. In: "Continental Tectonics", Spec. Publ. Geol. Soc. Lond., 164, 271-311.
5. Karner, G.D., 2000. Rifts of the Campos and Santos basins, southeastern Brazil: Distribution and timing. In: "Petroleum Systems of South Atlantic Margins", M. Mello and B. Katz (Eds.), Am. Assoc. Petrol. Geol. Mem. 73, 301-316.
6. Karner, G.D., N.W. Driscoll and D.H.N. Barker, 2003. Synrift subsidence across the West African continental margin: The role of lower plate ductile extension In: "Petroleum Geology of Africa: New Themes and Developing Technologies", Arthur, T.J, MacGregor, D.S., and Cameron, N.R. (Eds.), Spec. Publ. Geol. Soc. Lond., 207, 105-125.