Relationships among some locally conservative discretization methods which handle discontinuous coefficients

This paper presents the relationships between some numerical methods suitable for a heterogeneous elliptic equation with application to reservoir simulation. The methods discussed are the classical mixed finite element method (MFEM), the control-volume mixed finite element method (CVMFEM), the support operators method (SOM), the enhanced cell-centered finite difference method (ECCFDM), and the multi-point flux-approximation (MPFA) control-volume method. These methods are all locally mass conservative, and handle general irregular grids with anisotropic and heterogeneous discontinuous permeability. In addition to this, the methods have a common weak continuity in the pressure across the edges, which in some cases corresponds to Lagrange multipliers. It seems that this last property is an essential common quality for these methods. T.F. Russell: Partially supported by the National Science Foundation Grant Nos. DMS-0084438 and DMS-0222300.     

New data on the structure of the sedimentary section on the Ita Mai Tai Guyot (Magellan Seamounts,Pacific Ocean)

The geological-prospecting investigations carried out by scientists from the Yuzhmorgeologiya State Scientific Center in the eastern segment of the Magellan Seamounts of the Pacific during the cruise of the R/V Gelendzhik in 2003–2010 brought new data on the topography of the Ita Mai Tai Guyot and its Lower Cretaceous-Pleistocene sedimentary section. The guyot is characterized by its complex irregular morphology with angular outlines being complicated by numerous relief mesoforms: spurs, scarps, and volcanic cones and domes. It is shown that the sedimentary cover was formed during a long period. The analysis of the organic macro- and microfaunal remains from the sedimentary rocks made it possible to define transgressive phases in the guyot’s development: the Albian-Cenomanian, the Late Campanian-Maastrichtian, and the late Paleocene-early Eocene. The oolitic limestone sequence recovered by DSDP Hole 202 is determined to be the Albian in age. Based on the original and published data, the geological development of the guyot was analyzed in comparison with other similar structures of the Magellan Seamounts.     

Computing derivative information of sequentially coupled subsurface models

A generic framework for the computation of derivative information required for gradient-based optimization using sequentially coupled subsurface simulation models is presented. The proposed approach allows for the computation of any derivative information with no modification of the mathematical framework. It only requires the forward model Jacobians and the objective function to be appropriately defined. The flexibility of the framework is demonstrated by its application in different reservoir management studies. The performance of the gradient computation strategy is demonstrated in a synthetic water-flooding model, where the forward model is constructed based on a sequentially coupled flow-transport system. The methodology is illustrated for a synthetic model, with different types of applications of data assimilation and life-cycle optimization. Results are compared with the classical fully coupled (FIM) forward simulation. Based on the presented numerical examples, it is demonstrated how, without any modifications of the basic framework, the solution of gradient-based optimization models can be obtained for any given set of coupled equations. The sequential derivative computation methods deliver similar results compared to FIM methods, while being computationally more efficient.     

An ichnofossil assemblage from the fluvial deposits of the Upper Pliocene–Pleistocene Pinjor Formation (Siwalik Group), northwestern Himalayas,India: Palaeoenvironmental implications

Continental (fluvial) strata of the Pinjor Formation (Siwalik Group), northwestern Himalayas, India, contain an invertebrate trace fossil assemblage containing Planolites beverleyensis, Palaeophycus isp., Scoyenia gracilis, Taenidium barretti and other undifferentiated traces. The traces are found in an \(\sim \)26 m thick interval of alternating pinkish red siltstone, which is intercalated with mudstone, and thickly-bedded buff and greenish coloured sandstone. These sediments are interpreted as the deposits of floodplains and channel-bars of fluvial environments and low-energy overbank floodplain deposits. The trace fossils studied here are the first well documented ichnofossil assemblage from the vast, late Cenozoic Siwalik depositional system. They are not only of palaeoenvironmental significance, but they add to the growing ichnofossil database in facies of fluvial origin and should be an impetus to further ichnological studies of the Siwalik Group.     

Determination of Selenium in Thirty-Two Geochemical Reference Materials by Continuous - Flow Hydride Generation Atomic Absorption Spectrophotometry

A continuous-flow hydride atomic absorption spectrophotometric method has been applied to 32 geochemical reference materials for the determination of selenium. The sample is decomposed with a mixture of nitric, perchloric and hydrofluoric acids. Selenium values obtained in this study are in general agreement with literature values and provide additional certification for these reference materials. The precision of the method is generally better than 5% relative standard deviation. The lower limit of determination of selenium in the sample is 12 ppb.     

Organic geochemistry and pore water chemistry of sediments from Mangrove Lake,Bermuda

Mangrove Lake, Bermuda, is a small coastal, brackish-water lake that has accumulated 14 m of banded, gelatinous, sapropelic sediments in less than 10⁴ yr. Stratigraphic evidence indicates that Mangrove Lake's sedimentary environment has undergone three major depositional changes (peat, freshwater gel, brackish-water gel) as a result of sea level changes. The deposits were examined geochemically in an effort to delineate sedimentological and diagenetic changes. Gas and pore water studies include measurements of sulfides, ammonia, methane, nitrogen gas, calcium, magnesium, chloride, alkalinity, and pH. Results indicate that sulfate reduction is complete, and some evidence is presented for bacterial denitrification and metal sulfide precipitation. The organic-rich sapropel is predominantly algal in origin, composed mostly of carbohydrates and insoluble macromolecular organic matter called humin with minor amounts of proteins, lipids, and humic acids. Carbohydrates and proteins undergo hydrolysis with depth in the marine sapropel but tend to be preserved in the freshwater sapropel. The humin, which has a predominantly aliphatic structure, increases linearly with depth and composes the greatest fraction of the organic matter. Humic acids are minor components and are more like polysaccharides than typical marine humic acids. Fatty acid distributions reveal that the lipids are of an algal and/or terrestrial plant source. Normal alkanes with a total concentration of 75 ppm exhibit two distribution maxima. One is centered about n-C₂₂ with no odd/even predominance, suggestive of a degraded algal source. The other is centered at n-C₃₁ with a distinct odd/even predominance indicative of a vascular plant origin. Stratigraphic changes in the sediment correlate to observed changes in the gas and pore water chemistry and the organic geochemistry.     

pp′-DDT adsorption to suspended particulate matter in sea water

A procedure was devised to study pp′-DDT [2,2-bis($\text{p-}\text{chlorophenyl}$)-1,1,1-trichloroethane] adsorption and desorption to suspended particulates in aqueous solutions. DDT adsorption to a marine sediment, sediment fractions, clay and humic acid suspended in sea water was investigated and the humic fraction was found to have a greater adsorbing capacity than the clay or sediment. Removal of the humic fraction from sediment reduced the adsorption capacity to less than 60 per cent of the original sediment sample. It was concluded that suspended humic particulates may be important agents for transporting chlorinated hydrocarbons through the water column and for concentrating them in sediments and in detritus-feeding organisms.     

Hydration, 18O enrichment and oxidation during ocean floor hydrothermal metamorphism of ophiolitic metabasic rocks from E. Liguria,Italy

During ocean-floor hydrothermal metamorphism of a 225 m thick allochthonous Jurassic sequence of ophiolitic pillow lavas and underlying material in E. Liguria, Italy, the rocks were hydrated, enriched in ¹⁸O and oxidised. H₂O⁺ contents increased from ~0.3 to 3.8 wt.%, δ¹⁸O values increased from ~ +6‰ to values as high as +13.2‰, and ($\text{Fe}{}_2\text{O}{}_3\text{FeO}$1) increased from 0.18 to ratios as high as 1.0. Both δ¹⁸O values and oxidation ratios decrease in the original direction of increasing depth. Pillow margins are consistently more enriched in ¹⁸O and are more oxidised than cores.These observations are qualitatively interpreted in terms of a non-isothermal, heterogeneous reaction model of interaction of basalt with oxygen-bearing sea water during flow through the packed bed of pillows. Fluid flow approximated undirectional downward motion, and occurred in the recharge part of a cycle of single pass convection. Mass transfer through the pile was by flow (infiltration metasomatism), whereas intra-pillow mass transfer was diffusional. Oxygen isotope exchange and oxidation did not occur under conditions of perfect incremental equilibrium. An integrated bulk volumetric water/rock ratio of ~2 × 10³:1 is estimated from the oxidation profile.     

Decomposition of alkyl dixanthogens in aqueous solutions

Alkyl dixanthogens, (ROCSS)₂, decompose in aqueous solution in the presence of nucleophiles in many ways.It is proposed here that in alkaline solution the principal methods of decomposition of ethyl dixanthogen are by simultaneous attack of OH^? ions on the sulphur-sulphur bond to give products which include xanthate ion (ROCSS^?) and peroxide (H₂O₂) and on the carbon-sulphur bond to give products which include monothiocarbonate ion (ROSCO^?), sulphide ion (S^2?), and sulphur (S⁰). Above pH 12 reaction is complete in a few minutes, and more monothiocarbonate than xanthate is formed. At pH 9 the reaction takes over 20 h and more xanthate than monothiocarbonate is formed.The primary products react further to give various ions which depend in part on the pH of the system. In alkaline solution some of the xanthate and peroxide react to give perxanthate (ROCSSO^?). In acid solution both xanthate and monothiocarbonate decompose rapidly; CS₂ is formed from xanthate and OCS from monothiocarbonate.In the presence of other nucleophiles at pH 9.2, dissolved dixanthogen decomposes much more quickly than with OH^? alone, and other reactions occur. With thiosulphate a higher proportion of xanthate is formed together with some xanthyl thiosulphate and monothiocarbonate but no perxanthate. With sulphite (in the absence of oxygen) or cyanide the products include xanthate and monothiocarbonate but no perxanthate. With sulphite in the presence of oxygen, perxanthate is also formed.Suspensions of dixanthogens react slowly but in a similar fashion to dissolved dixanthogens.Longer-chain dixanthogens are much less soluble than ethyl dixanthogen but, in general, react in a similar way. Higher temperatures increase the rate of decomposition by OH^?.This work has various implications in operating plants.     

Experimental investigations of low-Ca pyroxene stability and olivine-pyroxene-liquid equilibria at 1-atm in natural basaltic and andesitic liquids

This paper reports experiments carried out at 1-atm under conditions of controlled oxygen fugacity, using natural andesites and andesite mixed with augite+synthetic pigeonite or augite+orthopyroxene. The experimental results are used (1) to investigate the controls of Mg^# (Mg/[Mg+Fe²⁺]) and temperature on low-Ca pyroxene stability (pigeonite vs orthopyroxene), (2) to quantify the effects of variations in bulk composition on the position of multiple saturation boundaries in mineral component projection schemes and (3) to develop a thermodynamic model for silica activity for melts saturated with olivine and pyroxene. Over the Mg^# range of 0.80–0.30 the minimum temperature of pigeonite stability in natural compositions is equivalent to the Lindsley (1983) boundary determined for pure Ca-Mg-Fe pigeonites. For the low variance, 5-phase assemblage oliv-aug-low-Ca pyroxene-plag-liquid, expressions involving liquid (Na₂O+K₂O)/(Na₂O+K₂O+CaO),Mg^# and TiO₂ content predict temperature and the movement of multiple saturation boundaries in pseudoternary projections in response to changing melt composition. The equilibrium for the low pressure melting of low-Ca pyroxene to olivine+liquid is formulated as a geothermometer and monitor of silica activity. Equilibrium constants estimated from thermochemical data and activities calculated for experimentally produced olivine and pyroxenes are used to develop a model for silica activity in liquid.