NOVA SCOTIA CANADA: THE NEXT PLAY

Three studies answer industry questions on reservoir and petroleum systems

Research set to be completed in 2010 to offer many insights into offshore, with deliverables in 2008, 2009 and 2010

As a result of the latest drilling of modern deepwater wells, the main exploration question is “What is the volume and the location of the thickest sand transferred from the Cretaceous deltas on the Shelf to the Deepwater Slope.” The study of river sources and the transfer of sands to the deepwater, Scotian Basin project by Dr. Georgia Pe-Piper, professor of geology at Saint Mary’s University, will attempt to answer these questions.

In modern systems, turbidity currents form off deltas either by direct hyperpyenal flow of rivers or by slumping of prodelta sands, with turbidity current type controlling the location and style of the deepwater sands. Recent work shows that the Scotian Basin was supplied by several small mountainous rivers, but that only some sandy deltas extended to the continental shelf.

Composition of deltaic sandstones and shales will be analyzed to identify source areas for the rivers that deposited the deltas, and to identify where one river delta ended and began. The techniques used will include chemical fingerprinting of detrital minerals and lithic clasts, geochronology of monazite and zireon, the internal structure of zircon and quartz by cathodoluminescence and bulk geochemical composition of the sediment.

The channel sandstone grain size, paleoclimate and channel size will be evaluated to determine the best modern analogs for the Scotian Basin rivers. Conventional core will also be examined to record prodeltaic slumping and turbidity currents. Deepwater seismic data will be examined to validate and refine the predictions of the areas of greatest probability to find deepwater sands.

This study will provide a modern conceptual framework for the depositional systems that resulted in deepwater sandstone reservoirs offshore Nova Scotia. It will assist industry in better defining exploration targets by understanding where the thickest sands may be located and where the best reservoir quality may have developed.

Reservoir distribution is the greatest risk facing development of the deepwater offshore Nova Scotia. Dr. Grant Wach, Professor of Petroleum Geology at Dalhousie University, will be examining this occurrence in his study Reservoir distribution and characterization: Scotian Shelf to slope linked depositional systems.

Specifically, with Marathon’s Annapolis well encountering limited hydrocarbon-bearing sands, they had proof an active petroleum system existed. But a further delineation well (Crimson) was unsuccessful, failing to provide a better understanding of the reservoir distribution in the deepwater region. Sediment delivery to continental margins is highly dependent on sea level changes and processes associated with these changes. Conceptual models for marine clastic passive margin settings have underestimated the role of shelf-slope interplay and slope processes in delivering potential reservoir rock to the continental margin.

Understanding the linkages between shelf sediment capture/delivery systems, the role of shelf margin deltas, sea level and slope processes is critical to detecting reservoir rock distribution in deep and ultra-deep water. The Scotian Slope demonstrates a history of canyon and channel cut-and-fill and sediment transport linked to a variety of relative sea level stands in combination with seismicity and other causative factors.

This study proposes to address the stratigraphic framework and reservoir distribution and quality through the development of a sequence stratigraphic framework, paleogeographic models, and an improved understanding through analogue studies for linked depositional systems between the shelf and slope along the passive continental margin setting.

Data used in this study will be a combination of well and core data, conventional 2D and 3D and high-resolution seismic data, which is available over a variety of settings on the Scotian Shelf and Slope, allowing detailed analysis of deepwater sedimentation patterns in canyon, channel, non-channel and fan environments using Neogene to recent sedimentary sections.

As well, extensive multibeam seafloor topographic data, in combination with ultra-high resolution seismic data, will be used to allow an evaluation of Late Pleiscene and Holocene sedimentation patterns, including the latest transition from low-stand to high-stand systems and changes in sedimentation rates.

The results of recent wells and petroleum system models constructed along several seismic lines postulate a significant variation in the regional heat flow along the margin that coincides with previously defined variations in salt structures.

The study Analysis of petroleum systems on the Scotian Slope using thermal and seismic techniques by Dr. Keith Louden, Professor of Oceanography, Dalhousie University, will see new heat flow observations undertaken on four to six profiles to study regions surrounding salt structures and a recently-imaged zone of early rifting sediments. Heat flows from two regions will be contrasted; one with lower heat flow and autochthonous salt structures (diapirs) and the other with expected higher heat flow that is dominated by allochthonous salt structures (salt canopies).

New 2D petroleum system models will be undertaken along these profiles that will provide semi-qualitative assessments of maturation, burial history, hydrocarbon migration through time, hydrocarbon phase and saturation, pressure and migration in relation to emplacement of fault histories and salt tectonics, and reservoir temperature and heat flow through time. The new heat flow observations and better definition of deeper structures on the seismic section will place important constraints on the model parameters. Each seismic profile uses recent high-quality pre-stack migrated seismic data, which has greatly improved the definition of the salt and subsalt structures.

Included in this study, the deep high-quality NovaSpan data will be used to more precisely define the velocity profile of the deepwater sediments. The Nova Span data, along with multi-component ocean bottom seismometer data, will also better characterize the physical properties of the sediments, including characterization of potential reservoir sands. Since the area contains a variety of reflector patterns, and standard approaches to velocity modeling and attribute analysis have been unsuccessful, full waveform 2D modeling will be investigated.

Inversion of the NovaSpan dataset will also be attempted due to the wide aperture and dense coverage of the dataset. This, combined with the ocean bottom seismometer data, will provide opportunity to develop models for both P and S waves. Results from the Torbrook and Annapolis wells will benchmark the results comparing regions with and without sand.