88 results found
Stolum HH, Smalley PC, 1992, Deterministic method for assessing reservoir communication based on strontium fingerprinting, Pages: 451-464
Incomplete or ambiguous knowledge about communication is an important area of uncertainty in reservoir simulation. We document several cases in which a new quantitative and deterministic method, strontium fingerprinting, can be used to give exact predictions of reservoir communication and flow units. In all cases, the isotopic composition of strontium (87Sr/86Sr) dissolved in the formation water was used to monitor compositional variability of formation water. This natural isotopic tracer is particularly useful as it can be measured simply from conventional core samples by extracting residual salts which have precipitated in the pore spaces as a result of formation water evaporation during storage. We have termed this technique `Residual Salt Analysis' (RSA). It enables detailed sampling in any part of a well for which there is core available. So far, RSA data have tended to yield rather ambiguous predictions. A quantitative method for treating the data has been lacking, as well as an empirical foundation of interpretations. However, we have tested the following hypotheses with empirical data: Intrafield variability of formation water chemistry may be closely correlated with reservoir compartmentalization. If two reservoir units are in good flow communication, their formation waters are likely to have been homogenized by flow and diffusion. On the other hand, a lack of flow communication will inhibit water mixing and thus preserve variations in water compositions. Thus, whatever the cause of intra-field variations in water composition, two reservoir units that have a similar water chemistry are more likely to be in good flow communication than two units with different water compositions. The Sr-ratio values obtained from five wells (n = 117) show a natural tendency to clustering. This contrasts with, for instance, a statistical normal distribution of the data. Moreover, data from distinct reservoir units in different wells are aggregated as distinct clusters in near
Smalley PC, England WA, 1992, Assessing reservoir compartmentalization during field appraisal: How geochemistry can help, Pages: 423-431
This paper describes how deterministic information about reservoir compartmentalization can be derived from the study of variations in reservoir fluid composition (oil and water). Oil compositional differences (e.g. PVT data, GC fingerprints) between-well, especially those that relate to changes in density, are useful indicators of reservoir compartmentalization. Such differences would be rapidly mixed by density-driven convection; their preservation indicates a barrier to fluid flow. Where suitable samples are available (e.g. core extracts, multiple DSTs), oil variations within-well would help identify barriers to vertical flow. Water variations are particularly useful if examined on the intra-well scale, e.g. by using residual salt analysis of strontium isotopes (sensitive indicators of water composition) from core samples. Sr variations in water and oil legs reflect the ability of waters to mix and the detailed oil-filling history. Both help identify barriers to vertical fluid flow. The integration of such deterministic data with other measurements (e.g. pressure, sequence stratigraphy), and with stochastic modelling, will provide the ultimate reservoir description.
SMALLEY PC, LONOY A, RAHEIM A, 1992, SPATIAL SR-87/SR-86 VARIATIONS IN FORMATION WATER AND CALCITE FROM THE EKOFISK CHALK OIL-FIELD - IMPLICATIONS FOR RESERVOIR CONNECTIVITY AND FLUID COMPOSITION, APPLIED GEOCHEMISTRY, Vol: 7, Pages: 341-350, ISSN: 0883-2927
SMALLEY PC, MAILE CN, COLEMAN ML, et al., 1992, LASSIE (LASER ABLATION SAMPLER FOR STABLE ISOTOPE EXTRACTION) APPLIED TO CARBONATE MINERALS, CHEMICAL GEOLOGY, Vol: 101, Pages: 43-52, ISSN: 0009-2541
SMALLEY PC, FIELD D, 1991, REE, TH, HF, TA IN BAMBLE GABBROS (SOUTHERN NORWAY) AND THEIR AMPHIBOLITIZED EQUIVALENTS - IMPLICATIONS FOR GABBRO TECTONIC SETTING, PRECAMBRIAN RESEARCH, Vol: 53, Pages: 233-242, ISSN: 0301-9268
DICKSON JAD, SMALLEY PC, KIRKLAND BL, 1991, CARBON AND OXYGEN ISOTOPES IN PENNSYLVANIAN BIOGENIC AND ABIOGENIC ARAGONITE (OTERO COUNTY, NEW-MEXICO) - A LASER MICROPROBE STUDY, GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 55, Pages: 2607-2613, ISSN: 0016-7037
DICKSON JAD, 1990, INTRACRYSTALLINE CARBON AND OXYGEN ISOTOPE VARIATIONS IN CALCITE REVEALED BY LASER MICROSAMPLING, GEOLOGY, Vol: 18, Pages: 809-811, ISSN: 0091-7613
Dickson JAD, Smalley PC, Raheim A, et al., 1990, Intracrystalline carbon and oxygen isotope variations in calcite revealed by laser microsampling, Geology, Vol: 18, Pages: 809-811, ISSN: 0091-7613
Vugs in lower Carboniferous limestone from Abercriban, southern Wales, are filled with calcite crystals displaying chemical growth zonation. Nine samples, physically separated from individual growth zones amalgamated from different crystals and analyzed by using standard acid digestion techniques, yielded ranges in δ 13 C and δ 18 O of +0.4‰ to -2.6‰ and -6.3‰ to -9.0‰, respectively. There is a general trend toward lighter carbon- and oxygen-isotope compositions in the younger zones. Thirty laser-ablation analyses of individual ~30-μm-wide zones from the same material revealed a much wider variation in δ 13 C and δ 18 O (+3.8‰ to -3.0‰ and -3.1‰ to -11.0‰), though with similar mean compositions. Significant jumps in isotopic composition were revealed between consecutive growth zones. The high spatial resolution of laser sampling has identified a fine-scale isotopic zonation that has hitherto gone undetected. This zonation suggests that calcite precipitation may be punctuated (or even driven) by changes in nature of pore water and sources of solutes. -from Authors
Egeberg PK, Aagaard P, Smalley PC, 1990, Major element and oxygen isotope studies of interstitial waters: ODP Leg 113
Alteration of calc-alkalic volcanic material dispersed in the sediment is an important process. A diagenetic reaction is constructed that involves transformation of volcanic glass into smectite, zeolite (represented by phillipsite), chert, and iron sulfide. Mass balance is obtained without having to invoke unreasonable large amounts of volcanic matter or interactions between seawater and basement. -from Authors
Egeberg PK, Smalley PC, Aagaard P, 1990, Strontium isotope geochemistry of Leg 113 interstitial waters and carbonates
The concentration of dissolved Sr and the distribution of 87Sr/86Sr isotope ratios in Leg 113 interstitial waters may be interpreted in terms of mixing of Sr from four different reservoirs: indigenous seawater, marine carbonate minerals, and basaltic and siliceous detrital material. The input to the pore water from these reservoirs is determined by the reactivity of the reservoir rather than its size. -from Authors
SMALLEY PC, STIJFHOORN DE, RAHEIM A, et al., 1989, THE LASER MICROPROBE AND ITS APPLICATION TO THE STUDY OF C AND O ISOTOPES IN CALCITE AND ARAGONITE, SEDIMENTARY GEOLOGY, Vol: 65, Pages: 211-221, ISSN: 0037-0738
RUNDBERG Y, SMALLEY PC, 1989, HIGH-RESOLUTION DATING OF CENOZOIC SEDIMENTS FROM NORTHERN NORTH-SEA USING SR-87 SR-86 STRATIGRAPHY, AAPG BULLETIN-AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS, Vol: 73, Pages: 298-308, ISSN: 0149-1423
Smalley PC, Raheim A, Rundberg Y, et al., 1989, Strontium-isotope stratigraphy: applications in basin modelling and reservoir correlation
The 87Sr/86Sr isotope ratio is homogeneous in sea water at any one time, but has fluctuated during geological time along the path which can be reconstructed by the Sr-isotopic analysis of marine precipitates (eg carbonate or phosphate fossils) of known age. The resultant "seawater curve' can be used as a relative dating tool by analysing carbonate/phosphate fossils from a marine sediment, locating its position on the curve and reading off the corresponding age. Such ages are independent of biofacies or faunal provincialism. A study of Cenozoic sediments from the northern North Sea produced ages on submilligram samples of bioclastic carbonate with precisions of ±0.5-3.0 Ma. When integrated with seismic studies, the results placed important sequence boundaries at approximately 35 Ma, 34-30 Ma and 22 Ma. These boundaries represent hiatuses of various durations. The data illustrate the important potential of Sr-isotope stratigraphy for the production of precise burial histories, which possess the distinct advantage of being based upon dates calculated by an objective numerical method with quantifiable uncertainties. The high quality and resolution of dating and correlation using Sr-isotope stratigraphy, combined with the simplicity and cost-effectiveness of the method, and the increasing availability of access to the analytical instrumentation, suggest that Sr-isotope stratigraphy is set to become a routine technique for basin analysis and correlation in reservoirs. -from Authors
Smalley PC, Qvale G, Qvale H, 1989, Some ages from Leg 104 Site 642 obtained by Rb-Sr glauconite dating and Sr isotope stratigraphy
We have attempted to date several samples from Site 642 using a combination of Sr isotope stratigraphy and Rb-Sr dating of glauconite. A carbonate shell fragment gives a Sr isotope stratigraphy date of 17.3±1.0 Ma, which agrees well with available biostratigraphic and paleomagnetic data. Glauconites from a nearby sample give a similar date. One carbonate shell fragment and two fish teeth samples give concordant Sr isotope stratigraphy ages of about 37 Ma (latest Eocene). Rb-Sr glauconite analyses from one of the samples, while showing some substrate contamination, also support an Eocene age. As specific reworking of fish teeth and carbonate macrofossils (and also glauconite) from 37 Ma-old sediments into three different samples is most unlikely, we view the 37-Ma date as the depositional age of the core. -from Authors
Aagaard P, Egeberg PK, Smalley PC, 1989, Diagenetic reactions in Leg 104 sediments inferred from isotope and major element chemistry of interstitial waters
The variations in major elements and isotope composition (87Sr/86Sr, δ18O, δD) of interstitial waters in Leg 104 sediments is most probably caused by the alteration of volcanic matter. A reaction scheme where volcanic glass reacts with pore-water magnesium and potassium to form trioctahedral smectite, phillipsite, and chert is proposed. Model calculations demonstrate that the pore waters may evolve their negative δ18O signatures without recourse to unreasonably large amounts of volcanic detritus or external sources. -Authors
SMALLEY PC, BLOMQVIST R, RAHEIM A, 1988, SR ISOTOPIC EVIDENCE FOR DISCRETE SALINE COMPONENTS IN STRATIFIED GROUND WATERS FROM CRYSTALLINE BEDROCK, OUTOKUMPU, FINLAND, GEOLOGY, Vol: 16, Pages: 354-357, ISSN: 0091-7613
Smalley PC, Råheim A, Dickson JAD, et al., 1988, <sup>87</sup>Sr/<sup>86</sup>Sr in waters from the Lincolnshire Limestone aquifer, England, and the potential of natural strontium isotopes as a tracer for a secondary recovery seawater injection process in oilfields, Applied Geochemistry, Vol: 3, Pages: 591-600, ISSN: 0883-2927
The Sr isotope composition of formation waters is a sensitive indicator of diagenetic processes in the host sediments, mixing processes between different bodies of water, and the connectivity of hydrological systems. The 87Sr/86Sr ratio of present seawater is constant worldwife, while formation waters in hydrocarbon reservoirs have various values, depending on the aforementioned effects, in most cases different from modern seawater. This forms the basis of a natural tracer technique for seawater injection projects, involving characterization of the 87Sr/86Sr ratios and Sr contents of formation waters in the reservoir before injection commences, followed by monitoring of these parameters in the produced water as injection proceeds. This method is best suited to reservoirs in which the formation waters have low Sr concentrations and 87Sr/86Sr ratios much higher or lower than seawater. Available data for reservoir formation waters suggest that breakthrough recognition could be expected at <10% seawater in many sandstone reservoirs, while the method would be less sensitive in carbonate reservoir or situations where the formation waters had interacted with evaporites, as the associated waters tend to have high Sr contents. In heterogeneous but well-mapped reservoirs, it may be possible to obtain information about flow paths/mechanisms before breakthrough. Combination with other chemical and isotopic tracers creates a very powerful tool, the Sr method acting as a safeguard should the batch of water containing the conventional tracers be overtaken by subsequently injected seawater. The Sr method could also be used for injection projects that were begun without the addition of tracers. A natural analogue of a water injection process is found in the Jurassic Lincolnshire Limestone aquifer in England, where rapidly moving fresh meteoric water mixes progressively with an older saline formation water. The 87Sr/86Sr data enable quantitative modelling of this mixing process. T
SMALLEY PC, FIELD D, RAHEIM A, 1988, RB-SR SYSTEMATICS OF A GARDAR-AGE LAYERED ALKALINE MONZONITE SUITE IN SOUTHERN-NORWAY, JOURNAL OF GEOLOGY, Vol: 96, Pages: 17-29, ISSN: 0022-1376
EMERY D, DICKSON JAD, SMALLEY PC, 1987, THE STRONTIUM ISOTOPIC COMPOSITION AND ORIGIN OF BURIAL CEMENTS IN THE LINCOLNSHIRE-LIMESTONE (BAJOCIAN) OF CENTRAL LINCOLNSHIRE, ENGLAND, SEDIMENTOLOGY, Vol: 34, Pages: 795-806, ISSN: 0037-0746
SMALLEY PC, FORSBERG A, RAHEIM A, 1987, RB-SR DATING OF FLUID MIGRATION IN HYDROCARBON SOURCE ROCKS, CHEMICAL GEOLOGY, Vol: 65, Pages: 223-233, ISSN: 0009-2541
SMALLEY PC, NORDAA A, RAHEIM A, 1986, GEOCHRONOLOGY AND PALEOTHERMOMETRY OF NEOGENE SEDIMENTS FROM THE VORING PLATEAU USING SR, C AND O ISOTOPES, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 78, Pages: 368-378, ISSN: 0012-821X
LAMB RC, SMALLEY PC, FIELD D, 1986, P-T CONDITIONS FOR THE ARENDAL GRANULITES, SOUTHERN-NORWAY - IMPLICATIONS FOR THE ROLES OF P, T AND CO2 IN DEEP CRUSTAL LILE-DEPLETION, JOURNAL OF METAMORPHIC GEOLOGY, Vol: 4, Pages: 143-160, ISSN: 0263-4929
Field D, Smalley PC, Lamb RC, et al., 1985, Geochemical evolution of the 1.6-1.5 Ga-old amphibolite-granulite facies terrain, Bamble sector, Norway: dispelling the myth of Grenvillian high-grade reworking.
The quartzofeldspathic charnockitic orthogneisses in the coastal regions of the Bamble sector are highly fractionated in K, Rb and other LIL elements. This fractionation is related to the imposition of the granulite-facies assemblages, and thus to the single high-grade metamorphic event that can be recognized in these rocks. Rb/Sr isotopic studies restrict this event to the pre-Grenvillian; it occurred some 1540 m.y. ago, the age confirmed by newly presented data. In this area the Sveconorwegian cycle (1200-900 m.y.) is represented only by intrusive event(s). Associated low-T hydrous fluids were introduced, causing low-grade mineralogical alterations in the pre-existing gneisses and which disturbed, and sometimes reset, the Rb/Sr isotopic systems. There was no regional Grenvillian high-grade reworking in the sector.-J.M.H.
Smalley PC, Field D, 1985, Geochemical constraints on the evolution of the Proterozoic continental crust in southern Norway (Telemark sector).
This crust consists of supracrustal gneisses and several later plutonic suites intruded between 1600-1250 m.y. ago. In age order these are: metabasites and tonalites; granites; and charnockite-alkaline complexes. The metabasites and tonalites are calcic to calc-alkaline with MORB-like HFSE (P, Zr, T, HREE, Y) abundances, but enriched in LIL elements and deficient in Ta and Nb relative to other incompatible elements. The later plutonic rocks become progressively more alkaline, with higher Fe/Mg ratios, and are highly-enriched in LILE and HFSE; Nb-deficiencies are less pronounced. The chemical evolution is similar to that observed in modern cordilleran orogens, in the transition from island and primitive continental arcs to mature continental and back-arc-anorogenic environments, and is interpreted in terms of variation in sub-crustal source composition. The earliest rocks were derived from previously-depleted mantle which had experienced subduction-related enrichment in LILE via hydrous fluids originating in the subducted slab at the time of, or shortly before, magma generation. The later rocks have an increasing component derived from a within-plate mantle type, which had been modified by the introduction of non-subduction-related CO2-rich LILE- and HFSE-bearing fluids or partial melts.-J.M.H.
Smalley PC, Field D, 1985, Geochemical constraints on the evolution of the Proterozoic continental crust in southern Norway (Telemark sector).
The Proterozoic continental crust of the Telemark sector consists of supracrustal gneisses and several later plutonic suites intruded between 1.6 and 1.25 Ga ago. The chemical evolution is similar to that observed in modern cordilleran orogens, in the transition from island and primitive continental arcs to mature continental and back arc-anorogenic environments, and is interpreted in terms of variation in sub-crustal source composition. The earliest rocks were derived from previously depleted mantle which had experienced subduction-related enrichment in LILE via hydrous fluids originating in the subducted slab at the time of, or shortly before, magma generation. The later rocks have an increasing component derived from a within-plate mantle type, which had been modified by the introduction of non-subduction-related CO2 - rich LILE- and HFSE- bearing fluids or partial melts. These geochemical signatures developed during accretion of the Proterozoic south Norwegian crust above a W-migrating, E-dipping subduction zone. -from Authors
SMALLEY PC, FIELD D, RAHEIM A, 1983, RESETTING OF RB-SR WHOLE-ROCK ISOCHRONS DURING SVECONORWEGIAN LOW-GRADE EVENTS IN THE GJERSTAD AUGEN GNEISS, TELEMARK, SOUTHERN-NORWAY, ISOTOPE GEOSCIENCE, Vol: 1, Pages: 269-282, ISSN: 0167-6695
SMALLEY PC, FIELD D, LAMB RC, et al., 1983, RARE-EARTH, TH-HF-TA AND LARGE-ION LITHOPHILE ELEMENT VARIATIONS IN METABASITES FROM THE PROTEROZOIC AMPHIBOLITE-GRANULITE TRANSITION ZONE AT ARENDAL, SOUTH-NORWAY, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 63, Pages: 446-458, ISSN: 0012-821X
Smalley PC, Field D, Råheim A, 1983, Resetting of Rb−Sr whole-rock isochrons during Sveconorwegian low-grade events in the Gjerstad augen gneiss, Telemark, southern Norway, Chemical Geology, Vol: 41, Pages: 269-282, ISSN: 0009-2541
The Gjerstad augen gneiss comprises a single igneous body that shows intrusive relationships to the surrounding older Telemark gneisses. The formation of the gneissic structure and augen texture was due to mylonitic deformation along a major shear zone, the Porsgrunn—Kristiansand fault zone. The augen gneiss can be divided petro-graphically into green, grey (both pyroxene-bearing) and pink types. Samples from three locations were analysed isotopically. Two distinct (at 2σ level) groups of ages were obtained which are interpreted as: (a) (~ 1250 Ma) cooling after high-temperature deformation and formation of retrogressive corona structures; (b) (~ 1080 Ma) resetting of whole-rock systems during low-grade mineral alteration by hydrous fluids. At ~ 900 Ma, there was further isotopic disturbance during low-grade alteration related to the intrusion of pegmatite veins. The significant age differences are not related to colour (= grade) of samples, and significantly different ages have been found in the same rock body within a single locality. As the Gjerstad augen gneiss was intruded before ~ 1250 Ma into a previously existing gneissic terrain, the gneiss-forming event and associated upper amphibolite facies metamorphism in the Gjerstad region is constrained to be pre ~ 1250 Ma, i.e. Pre-Sveco-norwegian. © 1983, Elsevier Science Publishers B.V.. All rights reserved.
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