Production of gas out of low permeability shale packages is very recent in the Western Canadian Sedimentary Basin (WCSB). The process of gas release and production from shale gas sediments is not well understood. Because of adsorptive capacity of certain shale constituents, including organic carbon content, coalbed methane models are sometimes being applied to model and simulate tight shale gas production behaviour. Alternatively, conventional Darcy flow models are sometimes applied to tight shale gas. However, neither of these approaches takes into account the differences in transport mechanisms in shale due to additional nanopore networks. Hence, the application of existing models for shale results in erroneous evaluation and predictions. Our analysis shows that a combination of a nanopore network connected to a micrometre pore network controls the gas flow in shale. Mathematical modelling of gas flow in nanopores is difficult since the standard assumption of no-slip boundary conditions in the Navier-Stokes equation breaks down at the nanometre scale, while the computational times of applicable molecular-dynamics (MD) codes become exorbitant. We found that the gas flow in nanopores of the shale can be modeled with a diffusive transport regime with a constant diffusion coefficient and negligible viscous effects. The obtained diffusion coefficient is consistent with the Knudsen diffusivity which supports the slip boundary condition at the nanopore surfaces. This model can be used for shale gas evaluation and production optimization. Introduction Shale gas is a type of reservoir classified under the Unconventional Gas heading. These ‘difficult to produce’ reservoirs will play an increasingly important role in Canadian gas production because they are showing the potential to offset declining conventional gas production. Quite simply, shale gas is natural gas produced from shale sequences. Gas shales are predominantly lithified clays with organic material and detrital minerals present in varying amounts. Organic matter is an integral constituent of a productive shale gas reservoir. In addition, these fine-grained rocks are microporous, causing low permeabilities. While shale gas production has had a long history in the United States, dating back about 80 years, it is still at the very early stages of commercial production in Canada. Very little public data exists on shale gas production, yet industry interest is on the rise. A variety of estimates indicate that between 550 and 860 trillion cubic feet of gas-in-place could exist in potential shale gas formations in Western Canada(1,2). But shales can be difficult to evaluate using conventional laboratory techniques. Much of this has to do with resident clays that can have bound water either as part of their matrix or loosely bound in the interlayers in amounts of 75 to 80%. Another challenge can be the accurate measurement of in situ permeabilities, which are on the nanoscale. Core samples have often been subjected to coring induced or stress release fractures, resulting in greatly overstated permeability measurements. While some shales in Western Canada are, at this early stage, showing the proper geochemical and reservoir properties to support gas production, new techniques need to be developed to more accurately understand shale properties and their productive potential.

A combined continental‐oceanic magnetotelluric (MT) transect of the southern Appalachians orogenic belt has been completed that spans nearly 600 km on land and extends over 1000 km offshore beneath the Atlantic Ocean (Figure 1). The study is revealing the long‐term changes in the lithosphere that occur as active subduction regimes degenerate to fossil regimes, and tests the degree to which the latter are modified by subsequent extension. The electrical resistivity structure of active subduction has been examined by several researchers in recent years [Wannamaker and Hohmann, 1991; Jones, 1993], but here is the first thorough examination of a currently passive, former convergent margin.

Abstract. Fluxgate magnetometers are an important tool in geophysics and space physics but are typically sensitive to variations in sensor temperature. Changes in instrumental gain with temperature, thermal gain dependence, are thought to be predominantly due to changes in the geometry of the wire coils that sense the magnetic field and/or provide magnetic feedback. Scientific fluxgate magnetometers typically employ some form of temperature compensation and support and constrain wire sense coils with bobbins constructed from materials such as MACOR machinable ceramic (Corning Inc.) which are selected for their ultra-low thermal deformation rather than for robustness, cost, or ease of manufacturing. We present laboratory results comparing the performance of six geometrically and electrically matched fluxgate sensors in which the material used to support the windings and for the base of the sensor is varied. We use a novel, lowcost thermal calibration procedure based on a controlled sinusoidal magnetic source and quantitative spectral analysis to measure the thermal gain dependence of fluxgate magnetometer sensors at the ppm • C −1 level in a typical magnetically noisy university laboratory environment. We compare the thermal gain dependence of sensors built from MA-COR, polyetheretherketone (PEEK) engineering plastic (virgin, 30 % glass filled and 30 % carbon filled), and acetal to examine the trade between the thermal properties of the material, the impact on the thermal gain dependence of the fluxgate, and the cost and ease of manufacture. We find that thermal gain dependence of the sensor varies as one half of the material properties of the bobbin supporting the wire sense coils rather than being directly related as has been historically thought. An experimental sensor constructed from 30 % glass-filled PEEK (21.6 ppm • C −1 ) had a thermal gain dependence within 5 ppm • C −1 of a traditional sensor constructed from MACOR ceramic (8.1 ppm • C −1 ). If a modest increase in thermal dependence can be tolerated or compensated, then 30 % glass-filled PEEK is a good candidate for future fluxgate sensors as it is more economical, easier to machine, lighter, and more robust than MACOR.

Erebus volcano, Antarctica, with its persistent phonolite lava lake, is a classic example of an evolved, CO2-rich rift volcano. Seismic studies provide limited images of the magmatic system. Here we show using magnetotelluric data that a steep, melt-related conduit of low electrical resistivity originating in the upper mantle undergoes pronounced lateral re-orientation in the deep crust before reaching shallower magmatic storage and the summit lava lake. The lateral turn represents a structural fault-valve controlling episodic flow of magma and CO2 vapour, which replenish and heat the high level phonolite differentiation zone. This magmatic valve lies within an inferred, east-west structural trend forming part of an accommodation zone across the southern termination of the Terror Rift, providing a dilatant magma pathway. Unlike H2O-rich subduction arc volcanoes, CO2-dominated Erebus geophysically shows continuous magmatic structure to shallow crustal depths of < 1 km, as the melt does not experience decompression-related volatile supersaturation and viscous stalling.

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