Determining effective wellbore permeability from a field pressure test: a numerical analysis of detection limits

We propose a simple pressure test that can be used in the field to determine the effective permeability of existing wellbores. Such tests are motivated by the need to understand and quantify leakage risks associated with geological storage of CO₂ in mature sedimentary basins. If CO₂ is injected into a deep geological formation, and the resulting CO₂ plume encounters a wellbore, leakage may occur through various pathways in the “disturbed zone” surrounding the well casing. The effective permeability of this composite zone, on the outside of the well casing, is an important parameter for models of leakage. However, the data that exist on this key parameter do not exist in the open literature, and therefore specific field tests need to be done in order to reduce the uncertainty inherent in the leakage estimates. The test designed and analyzed herein is designed to measure effective wellbore permeability within a low-permeability caprock, bounded above and below by permeable reservoirs, by pressurizing the reservoir below and measuring the response in the reservoir above. Alternatively, a modified test can be performed within the caprock without directly contacting the reservoirs above and below. We use numerical simulation to relate pressure response to effective well permeability and then evaluate the range of detection of the effective permeability based on instrument measurement error and limits on fracture pressure. These results can guide field experiments associated with site characterization and leakage analysis.     

Conditions of Quaternary magmatism at Spitsbergen Island

Petrological and geochemical data obtained on the Quaternary lavas of volcanoes at Spitsbergen Island indicate that the rocks were produced via the deep-seated crystallization of parental alkaline magmas at 8–10 kbar. The character of clinopyroxene enrichment in incompatible elements indicates that the mineral crystallized from more enriched melts than those inferred from the composition of the host lavas. These melts were close to the parental melts previously found as veinlets in mantle hyperbasite xenoliths in the lavas. According to the character of their enrichment in Pb and Sr radiogenic isotopes and depletion in Nd, the basalts from Spitsbergen Island define a single trend with the weakly enriched tholeiites of the Knipovich Ridge, a fact suggesting the closeness of the enriched sources beneath the continental margin of Spitsbergen and beneath the spreading zone. Magmatic activity at Spitsbergen was related to the evolution of the Norwegian-Greenland basin, which evolved in pulses according to the shift of the spreading axes. The most significant of the latter events took place in the Neogene, when the Knipovich Ridge obtained its modern position near the western boundary of Spitsbergen. Early in the course of the evolution, the emplacement of alkaline melts generated at Spitsbergen into the oceanic mantle could form the enriched mantle, which was later involved in the melting process beneath the spreading zone.     

Numerical simulation of a stratigraphic model

A multi-lithology diffusive stratigraphic model is considered, which simulates at large scales in space and time the infill of sedimentary basins governed by the interaction between tectonics displacements, eustatic variations, sediment supply, and sediment transport laws. The model accounts for the mass conservation of each sediment lithology resulting in a mixed parabolic, hyperbolic system of partial differential equations (PDEs) for the lithology concentrations and the sediment thickness. It also takes into account a limit on the rock alteration velocity modeled as a unilaterality constraint. To obtain a robust, fast, and accurate simulation, fully and semi-implicit finite volume discre tization schemes are derived for which the existence of stable solutions is proved. Then, the set of nonlinear equations is solved using a Newton algorithm adapted to the unilaterality constraint, and preconditioning strategies are defined for the solution of the linear system at each Newton iteration. They are based on an algebraic approximate decoupling of the sediment thickness and the concentration variables as well as on a proper preconditioning of each variable. These algorithms are studied and compared in terms of robustness, scalability, and efficiency on two real basin test cases.     

Spectroscopic monitoring of SS 433: A search for long-term variations of kinematic model parameters

Between 1994 and 2006, we obtained uniform spectroscopic observations of SS 433 in the region of Hα. We determined Doppler shifts of the moving emission lines, Hα ₊ and Hα _?, and studied various irregularities in the profiles for the moving emission lines. The total number of Doppler shifts measured in these 13 years is 488 for Hα _? and 389 for Hα ₊. We have also used published data to study possible long-term variations of the SS 433 system, based on 755 Doppler shifts for Hα _? and 630 for Hα ₊ obtained over 28 years. We have derived improved kinematic model parameters for the precessing relativistic jets of S S 433 using five-and eight-parameter models. On average, the precession period was stable during the 28 years of observations (60 precession cycles), at 162.250^d ± 0.003^d. Phase jumps of the precession period and random variations of its length with amplitudes of ≈6% and ≈1%, respectively, were observed, but no secular changes in the precession period were detected. The nutation period, P _nut = 6.2876^d ± 0.00035^d, and its phase were stable during 28 years (more than 1600 nutation cycles). We find no secular variations of the nutation cycle. The ejection speed of the relativistic jets, v, was, on average, constant during the 28 years, β = v/c = 0.2561 ± 0.0157. No secular variation of β is detected. In general, S S 433 demonstrates remarkably stable long-term characteristics of its precession and nutation, as well as of the central “engine” near the relativistic object that collimates the plasma in the jets and accelerates it to v = 0.2561c. Our results support a model with a “slaved” accretion disk in S S 433, which follows the precession of the optical star’s rotation axis.     

The Seyfert 1 galaxy Ark 120. Spectral variability in 1992–2005

We have studied the variability of the Hβ line and the adjacent continuum in the spectrum of the Seyfert galaxy Ark 120, based on spectral observations of the galaxy’s nucleus obtained in the Crimea in 1992–2005, supplemented by published data for 1988–1996. Irregular variability on various timescales (years to days) can be accompanied by periodic brightness variations in both the continuum and the Hβ line, with a period of P ～ 430 days and an amplitude of Δm ～ 0.2 ^m in the continuum, which were traced for more than 13 cycles. In total, in 1988–2005, the flux variations in the line lag those in the continuum by 55 ± 9 days if calculated from the peak of the cross correlation function, or by 72 ± 7 days, if calculated from the centroid of the CCF. The delay is correlated with the continuum brightness, increasing when the continuum flux increases. The Hβ line profiles indicate both a high degree of diversity and the presence of features that recur after various extended time intervals. Analysis of the evolution of the differences between each individual normalized line profile and the mean normalized profile indicates systematic motion of excesses relative to the average profile from negative to positive radial velocities. In contrast, parts of the Hβ line with low radiation relative to the mean normalized profile evolve in the opposite direction (from the red to the blue Hβ wing). This pattern is also typical for the rotating broad-line region, if this region has the form of a disk. The rotation period exceeds 9000–10000 days, or 25–27 years. The size of the broad-line region calculated form this period corresponds to a reverberation time of no fewer than 30 days, consistent with the results of cross-correlation analysis.     

Paleogeographic regionalization of Triassic seas based on conodontophorids

Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic     

Spatial Heterogeneity Created by Burrowing Crabs Affects Human Impact on Migratory Shorebirds

We show that, as previously described, there are conflicts between areas used by people and shorebirds. However, we propose that burrowing organisms add complexity to the shorebird–human interaction that should be taken into account for management and conservation. This is because SW Atlantic mudflats are dominated by high densities (up to 60 crabs m⁻²) of a strong bioturbator, the burrowing crab Neohelice granulata (=Chasmagnathus granulatus). These crabs affect the habitat use and foraging performance of shorebird species. The two-banded plover Charadrius falklandicus feed more in burrow areas whereas the yellowlegs Tringa spp. and the white-rumped sandpiper Calidris fuscicollis tend to avoid burrow areas. We evaluated the effect of human recreational activities on shorebirds, taking into account shorebird–crab interaction, during shorebird migratory periods (November to April) of 2001, 2002, and 2003. This study was performed at the Mar Chiquita coastal lagoon (37° 40′ S, Argentina). Results showed that people only rarely used the extensive soft bottom intertidals dominated by burrowing assemblages of N. granulata because the soft sediments make walking difficult. Therefore, human impact is reduced for the two-banded plover. However, for several migratory shorebirds that also avoid burrow areas, these areas act as suboptimal alternative areas when human impact is important in their preferred habitats. When human activity is low, shorebirds remain foraging in the area but they decrease their feeding intakes. The extensions of burrow areas differ among estuaries and are likely to generate between-estuaries differences as stopover sites for shorebirds. Also, other species that form large burrowing assemblages can have a similar impact on shorebird–human interactions.     

Water and Boating Activity as Dispersal Vectors for <Emphasis Type="Italic">Schinus terebinthifolius</Emphasis> (Brazilian pepper) Seeds in Freshwater and Estuarine Habitats

Schinus terebinthifolius (Brazilian pepper), a native of South America, is currently naturalized in 20 countries worldwide and can alter native systems by displacing flora and forming monotypic stands. The primary described mechanism of seed dispersal is through consumption of fruits by birds and mammals. We evaluated an alternative dispersal method by evaluating the potential for S. terebinthifolius growing in freshwater and estuarine environments to disperse via water currents. Specifically, we: (1) determined the duration fruits remained buoyant in three salinities, (2) estimated the viability of seeds after 7 days in water, (3) estimated the dispersal rate of floating solitary fruits, and (4) examined the role of boat wakes in moving seeds above mean high water at the shoreline. The length of time fruits floated in 0 ppt water (4.9 days) was significantly less than 15 ppt saltwater (6.2 days), and 30 ppt saltwater (6.9 days). After 7 days, over 13% of seeds remained viable in 0 ppt, 15 ppt, and 30 ppt water. By combining mean dispersal rates and the mean number of days fruits floated, we calculated individual fruits could be transported 16.9 km in 0 ppt and over 22 km in 15 and 30 ppt water. To increase germination, seeds must be stranded above the intertidal zone. Wind wakes alone never achieved this result; however, boat wakes plus wind wakes significantly increased the movement of fruits above the intertidal region into drier soils. The use of both vertebrate dispersal vectors and water dispersal may potentially increase the rate of invasion, establishment, and survival of S. terebinthifolius in freshwater and estuarine environments.