STREAMLINE BASED SIMULATION OF CO 2 INJECTION IN SALINE AQUIFERS

ABSTRACT Design and implementation of CO 2 sequestration projects in saline aquifers require, in part, a solid understanding of the key physical mechanisms that determine distribution of the injected CO 2 within the target aquifer. This understanding then forms the basis for model formulation and development of simulation techniques appropriate for resolving the essential physics. In addition, a significant level of uncertainty exists as to the spatial distribution of rock properties. This, in turn, calls for development of simulation tools that are accurate and computationally efficient enough that repeated simulations can be performed to assess uncertainties in predicted movement of the injected CO 2 . In this paper we address the question of how to simulate accurately and efficiently the injection phase of CO 2 storage in saline aquifers at field scale. In these flow settings, we seek to resolve the permeability heterogeneity of a given aquifer as well as to represent adequately the interplay of gravity, capillary and viscous forces. We demonstrate that compositional streamline simulation is an accurate and efficient method for predicting the movement of CO 2 in aquifers during the injection period. We describe how to handle the compositional effects (solubility of CO 2 in brine) in a very efficient manner based on look-up tables and explicit calculation of phase distributions and compositions, followed by evaluation of transport properties. The streamline approach is compared to conventional finite difference simulation tools

Population genomics of the Viking world.

The maritime expansion of Scandinavian populations during the Viking Age (about AD 750-1050) was a far-flung transformation in world history1,2. Here we sequenced the genomes of 442 humans from archaeological sites across Europe and Greenland (to a median depth of about 1×) to understand the global influence of this expansion. We find the Viking period involved gene flow into Scandinavia from the south and east. We observe genetic structure within Scandinavia, with diversity hotspots in the south and restricted gene flow within Scandinavia. We find evidence for a major influx of Danish ancestry into England; a Swedish influx into the Baltic; and Norwegian influx into Ireland, Iceland and Greenland. Additionally, we see substantial ancestry from elsewhere in Europe entering Scandinavia during the Viking Age. Our ancient DNA analysis also revealed that a Viking expedition included close family members. By comparing with modern populations, we find that pigmentation-associated loci have undergone strong population differentiation during the past millennium, and trace positively selected loci-including the lactase-persistence allele of LCT and alleles of ANKA that are associated with the immune response-in detail. We conclude that the Viking diaspora was characterized by substantial transregional engagement: distinct populations influenced the genomic makeup of different regions of Europe, and Scandinavia experienced increased contact with the rest of the continent