Physical properties of carbonate fault rocks,fucino basin (Central Italy): implications for fault seal in platform carbonates

We documented the porosity, permeability, pore geometry, pore type, textural anisotropy, and capillary pressure of carbonate rock samples collected along basin‐bounding normal faults in central Italy. The study samples consist of one Mesozoic platform carbonate host rock with low porosity and permeability, four fractured host rocks of the damage zones, and four fault rocks of the fault cores. The four fractured samples have high secondary porosity, due to elongated, connected, soft pores that provide fluid pathways in the damage zone. We modeled this zone as an elastic cracked medium, and used the Budiansky–O'Connell correlation to compute its permeability from the measured elastic moduli. This correlation can be applied only to fractured rocks with large secondary porosity and high‐aspect ratio pores. The four fault rock samples are made up of survivor clasts embedded in fine carbonate matrices and cements with sub‐spherical, stiff pores. The low porosity and permeability of these rocks, and their high values of capillary pressure, are consistent with the fault core sealing as much as 77 and 140 m of gas and oil columns, respectively. We modeled the fault core as a granular medium, and used the Kozeny–Carmen correlation, assigning the value of 5 to the Kozeny constant, to compute its permeability from the measured porosities and pore radii. The permeability structure of the normal faults is composed of two main units with unique hydraulic characteristics: a granular fault core that acts as a seal to cross‐fault fluid flow, and an elastic cracked damage zone that surrounds the core and forms a conduit for fluid flow. Transient pathways for along‐fault fluid flow may form in the fault core during seismic faulting due to the formation of opening‐mode fractures within the cemented fault rocks.     

Measurements of gas permeability and diffusivity of tight reservoir rocks: different approaches and their applications

Permeability and diffusivity are critical parameters of tight reservoir rocks that determine their viability for commercial development. Current methods for measuring permeability and/or diffusivity may lead to erroneous results when applied to very tight rocks including gas shales, coal, and tight gas sands, as well as rocks considered as seals for nuclear waste repositories and strata for geological sequestration of CO₂. The use of He as routinely applied to measure porosity, permeability, and diffusivity may result in non-systematic errors because of the molecular sieving effect of the fine pore structure to larger molecules such as reservoir gases. Utilizing gases with larger adsorption potentials than He, such as N₂, and including all reservoir gases to measure porosity or permeability of rocks with high surface area is a viable alternative, but requires correcting for adsorption in the analyses. This study expands several approaches to measure permeability and diffusivity with considerations for gas adsorption, which has not been explicitly considered in previous studies. We present new models that explicitly correct for adsorption during pulse-decay measurements of core under reservoir conditions, as well as on crushed samples used to approximate permeability or diffusivity. We also present a method to determine permeability or diffusivity from on-site drill-core desorption test data as carried out to determine gas in place in coals or gas shales. Our new approach utilizes late-time data from experimental pressure-decay tests, which we show to be more reliable and theoretically (and practically) accurate than the early-time approach commonly used to estimate gas-transport properties.     

Massive dolomitization of a Messinian reef in the Great Bahama Bank: a numerical modelling evaluation of Kohout geothermal convection

The hypothesis that Kohout thermal convection may have induced the massive dolomitization of the 60 m thick lowest more reefal unit in well Unda [top of Great Bahama Bank (GBB)] is evaluated through numerical modelling. A two‐dimensional (2‐D) section, including lithological and petrophysical data, together with datings for the sediments of the GBB, was used in the basin model TEMISPACK to reconstruct the history of the whole platform, with a focus on the reef unit. Simulations showed that during high sea‐level periods, Kohout convection is a valid mechanism in the settings of the GBB, although the convection cell remains flat in most cases because of high permeability anisotropy. This mechanism induces rapid fluid flow in the superficial as well as in the deeper parts of the platform, with velocities of at least two orders of magnitude higher than with compaction alone. Lithology appears as a strong control of fluid circulations at the margin scale through the permeability anisotropy, for which a critical value lies between values of 10 and 100. The reefal unit in Unda is part of a larger area determined by the lithologic distribution, in which flow velocities are significantly higher than in the rest of the platform. These velocities are high enough to bring the magnesium necessary to precipitate the observed amounts of dolomite, within durations in agreement with the available time of post‐reef deposition high sea level(s). However, neither fluid flow pattern nor flow velocities are able to explain the preferential massive dolomitization of the lower reef unit and the complete absence of dolomite in the upper one.     

油气地缘经济与中国油气安全

本文从地缘政治观念向地缘经济观念发展的观点出发,通过对全球油气中心随时空转移和变化的分析,着重阐述了冷战以后全球形成的\"石油心脏地带\"和\"内需求月形地带\"及\"外需求月形地块\"的油气地缘经济格局以及有关国家围绕争夺中亚油气资源和跨国运输通道构成的内外两个三角之间的油气地缘战略竞赛,在此基础上讨论了中国油气安全所面临的处境与应采取的对策。     

China's "Dash for Gas": Challenges and Potential Impacts on Global Markets

Two UK-based researchers examine the significant recent growth in China's demand for natural gas, a fuel not long ago considered of marginal importance but now viewed as critical for the country's future economic growth. Based on a range of databases as well as industry and media reports, the authors demonstrate how rapid demand growth since 2005 has transformed China from a minor, self-sufficient gas producer to a major buyer on international gas markets. They also analyze projections for future demand growth (25 years), showing China's demand for gas will grow faster that anywhere else in the world, and explore the potential for development of China's substantial domestic gas reserves to mitigate import demand over the short to medium term. The study concludes with an assessment of China's potential impact on global gas markets over short, intermediate, and long time horizons.     

Chlorine stable isotope ratios as tracer for pore‐water advection rates in a submarine gas‐hydrate field: implication for hydrate concentration

At Ocean Drilling Program Site 997 in Blake Ridge gas‐hydrate field in West Atlantic, pore‐water studies revealed a pronounced downward depletion of the heavy chlorine isotope to nearly ?4‰δ³⁷Cl at approximately 750 m below sea floor (mbsf) associated with a 10% downward chlorinity decrease. This is one of the stronger ³⁷Cl depletions hitherto reported for marine pore waters. Chlorinity reductions in hydrate‐bearing sediments commonly result from fresh‐water release by hydrate melting. However, in situ measurements at Site 997 suggest that >50% of the chlorinity reduction occurred prior to hydrate dissociation. Modeling the chlorinity profile shows that advection of a strongly ³⁷Cl‐depleted, low‐chlorinity water (506 mm ) from below the drilled sequence can explain the reduction prior to sampling. Fitting the model to the δ³⁷Cl curve yielded an advection rate of 0.18 mm year^?1. Diffusive mixing with near‐0‰‐δ³⁷Cl paleo‐seawater with maximum chlorinity at shallow subsurface depths (561 mm at approximately 20 mbsf) produced the smooth, steady trend. Separating that part of the freshening caused by advection and diffusion from that due to hydrate dissociation allowed estimation of average hydrate concentrations of 3.8% of the pore space (up to 24.5% in hydrate‐rich layers; near‐100% in rare massive hydrate layers). The deep‐seated source of the ³⁷Cl‐depleted, low‐chlorinity water remains unknown and might be located below the sedimentary section in the oceanic basement.     

Russia's Energy Policy: A Divergent View

A noted American analyst of Russian, Central Asian, and Transcaucasian oil and gas industries and markets offers his own perspective on issues raised in the preceding paper on Russia's energy policy (Milov et al., 2006). While generally concurring that Russia indeed pursues an ad hoc (rather than systemic) energy policy, he expresses divergent views on the role of government-regulated versus market-based pricing in final and primary energy use, reasons for the intense flows of oil and gas to Europe, the role of pipelines in determining oil export allocations, and the contribution of regional monopolies and refining capacity to domestic oil product prices. Journal of Economic Literature, Classification Numbers: L71, O13, Q40, Q48. 20 references.     

The New Economics of North American Arctic Oil

Over the past five years there has been a remarkable resurgence in oil and gas exploration in the North American Arctic. From completed disinterest only a half a decade ago the region has attracted billions of dollars in new investments from a host of different international oil companies. Unlike the past booms in the region, which inevitably ended in busts, this new wave of development is different. This article examines the changes in both the Arctic itself as well as the global energy environment and concludes that the North American Arctic will see slow bust sustained development over the coming decades, ultimately becoming one of the last great oil producing regions in the world.     

Mechanisms of strain-rate- and reaction-dependent permeability in the mid-crust of the Southern Alps: insight from three-dimensional mechanical models

We used three-dimensional mechanical modelling to explore the interplay of rheology, modes of permeability creation and fluid flow in the mid-crust of an oblique orogen. We used the central Southern Alps and the Otago Schist of New Zealand to constrain our models. We also compared our models with the magnetotelluric survey along the Rangitata–Whataroa rivers that imaged a U-shaped zone of high conductivity, interpreted as interconnected fluids, beneath the central Southern Alps. Modelling was carried out using the numerical code FLAC^3D. We used a number of simple assumptions: an initially homogeneous starting material, deformation boundary conditions based on the tectonics of the South Island, the capability of the modelled material to develop an anisotropic permeability structure, strain rate and reaction-induced permeability increases, initial saturation and lithostatic pore pressures as a basis for our models. The initial isotropic permeability was 10⁻¹⁸ m². We modelled two possible mechanisms of permeability increase: (i) strain-rate dependent and (ii) reaction dependent. For a strong mid-crust, the models showed enhanced permeability and hence fluid interconnectivity in a symmetric region beneath the model main divide, both ends were turned up towards the brittle–ductile transition and fluid flow was the greatest in the across strike direction. For a weak mid-crust, the region of enhanced permeability was asymmetric and turned up towards the brittle–ductile regime close to the Alpine Fault. The strong mid-crust model reproduces the features that are common to all interpretations of the MT soundings and is our preferred model for the central Southern Alps.     

Structural controls on hydrothermal flow in a segmented rift system, Taupo Volcanic Zone, New Zealand

Vigorous hydrothermal convection transfers 10 times the average continental heat flow through the central Taupo Volcanic Zone (TVZ), a region of active extension (approximately 8 mm year^?1) and productive rhyolitic volcanism. Over 20 high‐temperature (>250°C) geothermal fields occur within Quaternary pyroclastic basins, with convective circulation to depths of 7–8 km presumably extending through basement rocks. Parallel‐striking normal faults, fractures and dikes dissect the convective regime, interacting with fluids to either enhance or restrict flow according to the relative permeability of structure and host rock. In the basement, high bulk permeability is maintained by focussed flow through faults and associated fractures well oriented for reactivation in the prevailing stress field. In contrast, distributed flow through fault‐bounded compartments prevails within Quaternary basins, masking any signal of deeper structural control. Exceptions occur where more competent rocks are exposed at the surface. As in narrow magmatic rifts elsewhere, the extensional fabric is partitioned into discrete rift segments linked along strike by accommodation zones. Eighty per cent of TVZ geothermal fields correlate spatially with rift architecture, with 60% located in accommodation zones. We suggest that segmented rift fabrics generate bulk permeability anisotropy that is to some extent predictable, with rift segments characterized by enhanced axial flow, and accommodation zones characterized by locally enhanced vertical permeability that is tectonically maintained. This provides a plausible explanation for the common occurrence of geothermal fields within accommodation zones and their notable absence within densely faulted rift segments. Maintenance of structural permeability in zones of active hydrothermal precipitation necessarily requires repeated brittle failure. Geothermal plumes therefore exploit tectonically maintained permeability within accommodation zones, with rift segments functioning mostly as drawdown regions. The influence of rift architecture on flow paths has important implications for geothermal extraction and epithermal mineral exploration within the TVZ and other structurally segmented hydrothermal systems, both active and extinct.     

Russia’s energy relations with China: passing the strategic threshold?

This article examines Russian energy policies toward China over the past decade as reluctant engagement changed into a priority energy partnership. From 2008 to 2016 Russian and Chinese companies signed several major oil and gas agreements, a period in which Moscow reassessed China as a future energy consumer and lifted bilateral cooperation to a new level. The article utilizes the strategic partnership concept as an analytical framework and finds traditional realist concepts and hedging inadequate for this particular case. The study illuminates Russian geopolitical considerations and acceptance of vulnerability, which combined make long-term Russian energy policies more China dependent. Officially, Russia seeks diversification among Asian energy buyers, but its focus has increasingly been on China. Western sanctions imposed in 2014 for Russia’s role in Ukraine accelerated this trend. Moscow’s energy policies toward Beijing with its pipelines and long-term agreements are permanent arrangements that resemble strategic partnership policies. China is eager to increase energy relations with Russian companies, but Beijing also ensures that it does not become too dependent on one supplier. Russian concern over its increased dependence on China in the East is deemed secondary to expanding Russia’s customer base beyond the still-dominant European market.     

Transfer of hydrocarbons from natural seeps to the water column and atmosphere

Results from surface geochemical prospecting, seismic exploration and satellite remote sensing have documented oil and gas seeps in marine basins around the world. Seeps are a dynamic component of the carbon cycle and can be important indicators for economically significant hydrocarbon deposits. The northern Gulf of Mexico contains hundreds of active seeps that can be studied experimentally with the use of submarines and Remotely Operated Vehicles (ROV). Hydrocarbon flux through surface sediments profoundly alters benthic ecology and seafloor geology at seeps. In water depths of 500–2000 m, rapid gas flux results in shallow, metastable deposits of gas hydrate, which reduce sediment porosity and affect seepage rates. This paper details the processes that occur during the final, brief transition — as oil and gas escape from the seafloor, rise through the water and dissolve, are consumed by microbial processes, or disperse into the atmosphere. The geology of the upper sediment column determines whether discharge is rapid and episodic, as occurs in mud volcanoes, or more gradual and steady, as occurs where the seep orifice is plugged with gas hydrate. In both cases, seep oil and gas appear to rise through the water in close proximity instead of separating. Chemical alteration of the oil is relatively minor during transit through the water column, but once at the sea surface its more volatile components rapidly evaporate. Gas bubbles rapidly dissolve as they rise, although observations suggest that oil coatings on the bubbles inhibit dissolution. At the sea surface, the floating oil forms slicks, detectable by remote sensing, whose origins are laterally within ～1000 m of the seafloor vent. This contradicts the much larger distance predicted if oil drops rise through a 500 m water column at an expected rate of ～0.01 m s^?1 while subjected to lateral currents of ～0.2 m s^?1 or greater. It indicates that oil rises with the gas bubbles at speeds of ～0.15 m s^?1 all the way to the surface.     

Observations on the Influence of High Oil Prices on Russia's GDP Growth

A noted economist and observer of post-Soviet affairs presents a study probing the influence of high oil prices on Russia's GDP growth. The paper analyzes the contributions to the country's GDP by sectors of origin and final use, and pays special attention to the influence of trade margins produced by oil and gas but recorded and placed by Goskomstat Rossii in Russia's trade sector. The author's interpretation of statistical data released by Goskomstat Rossii as well as by Russian customs authorities enables him to conclude that the present-day economic boom in Russia can be characterized as consumption-led growth fueled by oil and gas export revenues. Journal of Economic Literature, Classification Numbers: C67, C82, E23, L71, Q43. 2 figures, 10 tables, 20 references.     

The Booming Russo-Japanese Economic Relations

A noted Japanese economist analyzes the history, present status, and future prospects for Russo-Japanese economic relations. The author demonstrates that the boom in trade between the two countries in the 2000s is unprecedented, ending the stagnation in bilateral trade that began in the early 1980s, when the era of large-scale Siberian resource development projects came to an end. He argues that underlying the current boom is an eastward shift in the Russian economy, characterized by its energy and investment policies as well as foreign economic relations. The paper considers in detail two important factors supporting this boom: (1) Japan’s exports of automobiles to Russia; and (2) Russia’s exports of oil and gas to Japan. He concludes with a guardedly optimistic prognosis suggesting growth in the bilateral economic relations on the grounds of the continuing eastward shift of the Russian economy and a marked correspondence between the demand and supply of the two countries. Journal of Economic Literature, Classification Numbers: F140, O520, P280, Q430. 7 figures, 4 tables, 50 references.