Multiscale Parameterization of Petrophysical Properties for Efficient History-Matching

The prediction of fluid flows within hydrocarbon reservoirs requires the characterization of petrophysical properties. Such characterization is performed on the basis of geostatistics and history-matching; in short, a reservoir model is first randomly drawn, and then sequentially adjusted until it reproduces the available dynamic data. Two main concerns typical of the problem under consideration are the heterogeneity of rocks occurring at all scales and the use of data of distinct resolution levels. Therefore, referring to sequential Gaussian simulation, this paper proposes a new stochastic simulation method able to handle several scales for both continuous or discrete random fields. This method adds flexibility to history-matching as it boils down to the multiscale parameterization of reservoir models. In other words, reservoir models can be updated at either coarse or fine scales, or both. Parameterization adapts to the available data; the coarser the scale targeted, the smaller the number of unknown parameters, and the more efficient the history-matching process. This paper focuses on the use of variational optimization techniques driven by the gradual deformation method to vary reservoir models. Other data assimilation methods and perturbation processes could have been envisioned as well. Last, a numerical application case is presented in order to highlight the advantages of the proposed method for conditioning permeability models to dynamic data. For simplicity, we focus on two-scale processes. The coarse scale describes the variations in the trend while the fine scale characterizes local variations around the trend. The relationships between data resolution and parameterization are investigated.     

The geoarchaeology and traditional knowledge of winter sod houses in eastern Hudson Bay,Canadian Low Arctic

A multidisciplinary study was undertaken at the Qijurittuq Site (IbGk‐3) on Drayton Island in Low‐Arctic Quebec (Canada) to document the relationships between climatic, environmental, and cultural changes and the choice of Thule/Inuit dwelling style in the eastern Arctic. Several marine terraces were ¹⁴C‐dated with shells in order to reconstruct the area's uplift (glacioisostatic rebound) curve. Plant macrofossil analysis of peat was conducted to reconstruct past vegetation and, indirectly, past climate. Archaeological surveys and excavations characterized the structure of subterranean sod houses at the Qijurittuq Site and were supplemented with open interviews with Inuit elders for a better understanding of site location and the use of household space. The sites selected for habitation were well‐drained sandy marine terraces in a valley sheltered from prevailing winds. Sod houses were in turn made possible by the abundance of driftwood on the island and the presence of nearby peatland. Thule/Inuit people used semi‐subterranean houses rather than igloos at the Qijurittuq Site during the dry, cold conditions toward the end of the Little Ice Age. Stable environmental conditions and food supply during winter possibly explain the use of those semipermanent houses on Drayton Island. However, it does not exclude the use of igloos during short expeditions on ice. © 2011 Wiley Periodicals, Inc.     

Genotyping of Rhodopirellula baltica organisms using multispacer sequence typing

Rhodopirellula baltica is a ubiquitous Planctomycetes organism isolated from marine environments worldwide. Multilocus sequence analysis (MLSA) has been the only method used to assess the diversity of R. baltica organisms. Here, we developed multispacer sequence typing (MST) genotyping and applied it to four R. baltica isolates from the French Mediterranean Sea and R. baltica DSM10527^T type strain. While MLSA yielded interpretable sequences for two of nine genes in three R. baltica isolates, MST based on sequencing two intergenic spacers yielded an unambiguous, strain‐specific profile for each one of the four R. baltica isolates under investigation. We propose that MST could be used as an alternative R. baltica genotyping method to assess the diversity of these Planctomycetes organisms.     

The Colônia structure,São Paulo,Brazil

Abstract– The near‐circular Colônia structure, located in the southern suburbs of the mega‐city of São Paulo, Brazil, has attracted the attention of geoscientists for several decades due to its anomalous character and the complete absence of any plausible endogenous geologic explanation for its formation. Origin by impact cratering has been suggested repeatedly since the 1960s, but no direct evidence for this has been presented to date. New seismic data have been recently acquired at Colônia, providing new insights into the characteristics and possible layering of infill of the structure, as well as into the depth to the underlying basement. We review the current knowledge about the Colônia structure, present the new seismic data, and discuss the existing—as yet still indirect—evidence for a possible origin by an impact. The new data suggest the existence of a sedimentary fill of approximately 275 m thickness and also the presence of two intermediate zones between sediment and basement: an upper zone that is approximately 65 m thick and can be interpreted as a possible crater‐fill breccia, whereas the other zone possibly represents fractured/brecciated basement, with a thickness of approximately 50 m. Although this depth to basement seems to be inconsistent with the expected geometry of a simple, bowl‐shape impact structure of such diameter, there are a number of still unconstrained parameters that could explain this, such as projectile nature, size and velocity, impact angle, and particularly the current erosion depth.     

Comparison of numerical methods for simulating strongly nonlinear and heterogeneous reactive transport problems—the MoMaS benchmark case

Although multicomponent reactive transport modeling is gaining wider application in various geoscience fields, it continues to present significant mathematical and computational challenges. There is a need to solve and compare the solutions to complex benchmark problems, using a variety of codes, because such intercomparisons can reveal promising numerical solution approaches and increase confidence in the application of reactive transport codes. In this contribution, the results and performance of five current reactive transport codes are compared for the 1D and 2D subproblems of the so-called easy test case of the MoMaS benchmark (Carrayrou et al., Comput Geosci, 2009, this issue). This benchmark presents a simple fictitious reactive transport problem that highlights the main numerical difficulties encountered in real reactive transport problems. As a group, the codes include iterative and noniterative operator splitting and global implicit solution approaches. The 1D easy advective and 1D easy diffusive scenarios were solved using all codes, and, in general, there was a good agreement, with solution discrepancies limited to regions with rapid concentration changes. Computational demands were typically consistent with what was expected for the various solution approaches. The differences between solutions given by the three codes solving the 2D problem are more important. The very high computing effort required by the 2D problem illustrates the importance of parallel computations. The most important outcome of the benchmark exercise is that all codes are able to generate comparable results for problems of significant complexity and computational difficulty.     

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