bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morgan pressure cycling in-situ combustion project: performance and modelling
Authors: Marjerrison D. M. , Fassihi M. R. 
Published: April 2008

Abstract

Amoco Canada has been operating a pressure cycling fireflood at Morgan, in the Lloydminster area of Alberta, Canada, since the mid-1980s. A pressure cycle consists of air injection into a central injector accompanied by production from its surrounding producers. The reservoir contains a 12° API heavy crude and the wells are laid out in 30 acre (12 ha), seven-spot patterns. The rapid drop in crude oil prices in 1986 led to the successful development and implementation of an innovative pressure cycling-combustion process. This paper looks at the performance of the project and the numerical modelling done to history-match the results. The numerical modelling effort was undertaken to explain the high oil rates (individual wells at 120 STB/D = 19 m
3
/D) and the extraordinarily low injected air to produced oil ratio (AOR) of less than 2 MSCF/STB (355 m
3
/m
3
). Mechanisms incorporated in the numerous model include: (1) a high-speed channel from the injector to the producer, (2) combustion gas entrainment by the oil phase and (3) oil upgrading. The physics involved with these mechanisms are explained and the model results are compared with the actual field data. Also, model sensitivity to variations in the assumptions regarding the mechanisms are discussed.
Cyclostratigraphy and correlation of the Cenomanian Stage in Western Europe
Authors: Gale A. S. 
Published: April 2008

Abstract

Basinal successions of Cenomanian age in Western Europe are dominated by pelagic and hemipelagic sediments, and display conspicuous primary bedding cyclicity (couplets) which is attributed to climatically-controlled variations in carbonate productivity. Within single basins individual rhythmic couplets are widely identifiable and enable basin-wide decimetre-scale correlation. A high resolution ammonite biostratigraphy (aided by inoceramid bivalves) is used to correlate successions in separate basins, and allows a comparison of couplet numbers to be made. Couplet numbers are similar across Western Europe, in spite of an order of magnitude thickness variation, and the carbonate: clay ratios of beds and groups of beds are persistent and diagnostic of particular levels. Additionally, beds with distinctive ichnofabrics (e.g. abundant dark
Chondrites
) are regionally extensive in the basins of northern Europe. It has proved possible to construct a composite cyclostratigraphy for the Cenomanian, graduated by 212 precession units (mode at 21 ka), which indicate a duration for the stage of 4.45 Ma. Corroboration of this cyclochronology comes from radiometric dating; the Middle Cenomanian basal
A. rhotomagense
Zone to the Upper Cenomanian basal
N. juddii
Zone contain 107 precession couplets in Western Europe, giving a duration 2.24 Ma. The equivalent biostratigraphic interval in the Western Interior Basin of the USA recently yielded Ar-Ar dates of 2.2 Ma from sanidines in bentonites The dominance of the precession cycle in the mid-Cretaceous is in keeping with results from climate sensitivity modelling.
Geochemical constraints from formation water analyses from the North Sea and the Gulf Coast Basins on quartz, feldspar and illite precipitation in reservoir rocks
Authors: Bjørlykke Knut , Aagaard Per , Egeberg Per K. , Simmons Scott P. 
Published: April 2008

Abstract
Formation water analyses from North Sea and Gulf Coast Basin reservoirs provide important constraints on burial diagenetic processes. Thermodynamic calculations show that aluminium solubilities are low (< 1 ppm at 130°C) even in the presence of organic acids. Illite therefore forms mainly at the expense of dissolving aluminous minerals such as smectite and kaolinite. The potassium values of the formation waters are always lower than K-feldspar saturation during burial diagenesis (> 1.5 km burial depth), suggesting that K-feldspar is continually being dissolved. The potassium concentrations indicate, in most cases, super-saturation with respect to illite. This is evidence that the failure of illite to form is probably because aluminium is not available. In the North Sea Basin, potassium concentrations approach equilibrium with kaolinite and illite at higher temperatures (140°C), indicating that illitization at that point keeps up with K-feldspar dissolution. In the subsiding parts of the Gulf Coast Basin, where kaolinite and smectite are being heated, the potassium values are clearly lower than in the uplifted (cooling) parts of the basin where illite is not forming. This suggests that the potassium concentrations are to a large extent controlled by the rate of illite precipitation, which again depends on the availability of aluminium from dissolving Al-minerals. There is considerable evidence that both illitization and quartz cementation may continue in the water-saturated parts of the pore after oil emplacement. This is also consistent with an almost closed-system burial diagenesis. The primary mineralogical composition of the sediments and early diagenetic processes strongly influence deeper burial diagenesis and in particular the precipitation of illite.
Compositional heterogeneities in oilfield formation waters: identifying them, using them
Authors: Smalley P. C. , Dodd T. A. , Stockden I. L. , Råheim A. , Mearns E. W. 
Published: April 2008

Abstract

Two new techniques are now available for gaining information on formation water composition from core samples: core centrifugation, in which preserved core samples, complete with their preserved fluid content, are ultracentrifuged to extract the oil and water; and residual salt analysis (RSA), where salts are redissolved from unpreserved dry core and parameters such as
87
Sr/
86
Sr are measured in the leachate. These methods are described and details given on the quality control measures that are crucial in order to avoid artefacts of core contamination by drilling fluids. Such methods have allowed formation-water compositional data to be obtained at the sub-metre scale, in some cases revealing significant small-scale variations (gradients and steps) in formation-water chemistry.

Resistivity (related to salinity) variations are important for interpretation of water saturation from electrical resistivity logs, which in turn affects the estimate of the total amount of oil contained in the field. In the Machar chalk-reservoired oilfield, formation-water data derived by RSA and core centrifugation both indicate variations in salinity (TDS 140 000–220 000 ppm) that significantly affect resistivity. In some oilfields, assumption of a single resistivity value for the whole field could thus lead to errors in petroleum reserves estimation.
Step changes in formation-water composition can be used as indicators of reservoir fluid compartmentalization, important for field development strategy. Examples are given of cases where RSA variations have been used to distinguish between laterally restricted and laterally extensive shales, both in the oil and water legs. Analysis of water compositional variation forms a valuable addition to the range of tools available for assessing reservoir compartmentalization during reservoir appraisal. This is because natural variations in fluid compositions provide quasi-dynamic data (i.e. how fluids have moved slowly during geological time), from which inferences can be made about more rapid fluid-flow patterns under dynamic (oil production) conditions.
Characterization of high molecular weight hydrocarbons (>C
40
) in oils and reservoir rocks
Authors: Philp R. P. , Bishop A. N. , Del Rio J.-C. , Allen J. 
Published: April 2008

Abstract

The presence of high molecular weight hydrocarbons in crude oils has been known for some time, particularly in view of their ability to precipitate and form barriers and blockages in pipelines. Recent advances in analytical technology have led to the development of capillary columns for gas chromatography capable of withstanding high temperatures (350 to 450°C), which allow the characterization of hydrocarbons with carbon numbers as great as C100 and above. Consequently, the individual high molecular weight hydrocarbon compounds in oils and waxes can now be identified. In the present paper, results are presented from high temperature gas chromatographic analyses of naturally occurring waxes. These clearly show the presence of significant concentrations of hydrocarbons with carbon numbers in excess of C
40
in many of these samples. In order to assist in the quantification of these high molecular weight hydrocarbons, we have also assessed the potential of thermal microdistillation coupled with a field ionization detector, to obtain more accurate molecular weight distributions in wax samples. This is based on the concept that high temperature gas chromatography has an upper carbon number limit in the range C
100
to C
120
. Thermal distillation may provide the ability to exceed that limit and determine the presence of compounds above C
120
. More detailed characterization of the wax fractions on a molecular level has the potential to provide clues as to the composition and origin of the residual components left in a petroleum reservoir at the end of its production history. A better understanding of the nature of this material will lead to improved secondary and tertiary recovery mechanisms, and other enhanced oil recovery procedures.
Overview of the geochemistry of some tar mats from the North Sea and USA: implications for tar-mat origin
Authors: Wilhelms A. , Larter S. R. 
Published: April 2008

Abstract
Tar mats and oil legs from several marine source-rock derived oil fields (Ula and Oseberg, North Sea and an unidentified North American example) have been geochemically characterized. Tar mats were derived from the same petroleum system as the oil-leg oils and are found in the most porous and permeable portions of the reservoir. It is possible to eliminate some potential tar-mat formation mechanisms using the data from case histories and subsurface asphaltene solubility characteristics. Adsorption of asphaltenes on reservoir clays and light to moderate levels of biodegradation can probably be eliminated as feasible tar-mat formation mechanisms. Thermal degradation of oil in the carrier and reservoir causing asphaltene precipitation may be a major contributing factor to formation of tar mats in the Ula Field, whereas increased gas solution in the oil leg may have contributed to deasphaltation in the Oseberg Field. Based on tentative mass-balance calculations, the extreme pressure dependence of asphaltene solubility in subsurface crude oils and the occurrence of tar mats in zones of elevated permeability, it is suggested that tar-mat formation is initiated during petroleum migration. While tentative, this model may provide a more generic initiation mechanism than others in the literature.
The filling and emptying of the Ula Oilfield: fluid inclusion constraints
Authors: Oxtoby Norman H. , Mitchell Alan W. , Gluyas Jon G. 
Published: April 2008

Abstract
The Norwegian sector Ula Field contains 430 million barrels of oil reserves trapped in a dip-closed Upper Jurassic sandstone reservoir and has multiple oil-water contacts (OWCs). Historically, the depth to the contacts has been the subject of some debate and development drilling has now proven the existence of at least six. The precise nature of some of these contacts remains uncertain because all were discovered after production start-up and determination of their origin is critical to future field development. The relationship of oil inclusion abundances to OWCs and rock properties (porosity, permeability) has been evaluated (a) to gain an insight into the filling history and mechanisms, and (b) to attempt to define pre-production OWCs. Oil inclusion abundances decrease with depth and towards present OWCs in Ula, but oil inclusions also occur below them. They indicate that Ula filled from the crest down, and that the filling was synchronous with cementation to at least 3500 metres subsea. Below this depth, cementation appears to have reduced permeability to such an extent prior to charge that the resulting filling geometry was irregular. Local abundance peaks within the oil column correlate with the tops of coarsening-upward cycles. Rare oil inclusions below the oil legs may represent either migration pathways updip from the source or invasion downdip from the main oil leg along higher permeability zones. Oil inclusions persist to greater depths in the east and south-east of the field which indicates that oil charged the field from these directions. A number of models explaining the variability of the OWCs have been ruled out by this work, thereby reducing the uncertainty in field development planning.
Migration of hydrocarbons in the Tampen Spur area, Norwegian North Sea: a reservoir geochemical evaluation
Authors: Horstad I. , Larter S. R. , Mills N. 
Published: April 2008

Abstract
This paper describes the application of reservoir geochemical protocols to a study of oil-field and regional petroleum compositional variations in the major fields in the Tampen Spur area. The Tampen Spur high is located in the middle of several oil-mature to gas-mature source-rock kitchens and most of the structures might receive petroleum from several different directions. Based on the definition of several different petroleum populations within the Tampen Spur area, we define five major petroleum charging systems. Correlating the petroleum population variations with geological information allows us to derive likely migration/fill scenarios for many of the oil-fields and requires us to invoke a new Upper Jurassic carrier system in parts of the area connecting Brent Group reservoirs across major faults. Based on this hypothesis, two exploration wells were drilled on structures to test this carrier and petroleum was found in one of the structures. An understanding of the migration pathways and petroleum drainage efficiency of the basins is of great economic interest, because most of the smaller substructures are marginally economic. Thus, it is important to provide an effective risk analysis and ranking of the satellite prospects prior to drilling. This study has demonstrated that filling and migration in a geological province are controlled by a series of complex processes and that the filling history of the structures within the Tampen Spur is more complicated than suggested earlier.
Modelling density-driven mixing rates in petroleum reservoirs on geological time-scales, with application to the detection of barriers in the Forties Field (UKCS)
Authors: England W. A. , Muggeridge A. H. , Clifford P. J. , Tang Z. 
Published: April 2008

Abstract
This paper discusses how to deduce the strength of intra-field barriers in reservoirs which have significant present-day differences in reservoir fluid density. The method combines a knowledge of the geological time available since filling, with estimates of the rate of density-driven mixing. If the observed density differences are inconsistent with a barrier-free reservoir model, we show how limits can be set on the strength of the barrier needed to account for any observed lack of mixing. A case history from the Forties Field is presented, illustrating these principles. It is shown that a transmissibility barrier of at least 1% must be included to account for the present-day lack in density equilibration between Forties and SE Forties. The results are validated against pressure decline data since production start-up. Two methods of estimating density-driven mixing rates are given. One is based on an analytical formula applicable to a rectangular geometry, and the other uses an unmodified black oil simulator. One significant result is the weak dependence of mixing rates on vertical permeability over a wide range of values, for many typical reservoir configurations. This implies that in many geological circumstances, subsurface density differences (coexisting at the same depth) can be used to infer the presence of intra-reservoir barriers.
Geological setting and ecology of the Broken Spur hydrothermal vent field: 29°10′N on the Mid-Atlantic Ridge
Authors: Murton Bramley J. , Van Dover Cindy , Southward Eve 
Published: April 2008

Abstract
Deep-towed sidescan sonar and manned submersible studies have shown that hydrothermal activity within the Broken Spur vent field, located at 29°10′N on the Mid-Atlantic Ridge, is controlled by a combination of recent volcanic and tectonic activity. Three sulphide mounds, with high-temperature fluid vents, and two weathered sulphide mounds, with low-temperature fluid seeps, are aligned across an axial summit graben that lies along the crest of a neovolcanic ridge within the axial valley floor. The largest high-temperature venting sulphide mound, which is up to 40 m high, lies in the centre of the graben. Two further, but smaller, high-temperature sulphide mounds are located to the east and west of the larger mound. All three high-temperature venting mounds lie on an axis that strikes 115°, orthogonal to the trend of the axial summit graben and neovolcanic ridge. These directions are similar to the strike of two sets of faults that locally intersect at the vent site and which probably control the location of hydrothermal emission. The fauna colonizing the vents are distinct, at least at a species level, from those found at other hydrothermal sites on the Mid-Atlantic Ridge. New species of bresiliid shrimp, and a new genus of brittle star have been found along with other fauna in an ecosystem that is otherwise similar to those found at high-temperature hydrothermal sites elsewhere on the Mid-Atlantic Ridge. However, the populations of the bresiliid shrimp at Broken Spur are significantly lower in abundance than those of the same genus found elsewhere. The size, shape and state of alteration of the sulphide mounds and the extent of their oxyhydroxide sediments and weathered sulphide talus aprons, suggests that hydrothermal activity at the Broken Spur vent field has been long-lived, probably for several thousand years. This is supported by the unique speciation of fauna present, which also suggests that the Broken Spur vent field is isolated (in terms of faunal accessibility) from other vent sites on the Mid-Atlantic Ridge. The low population of the shrimp, in an otherwise active and long-established hydrothermal habitat, suggests that the hydrothermal activity at Broken Spur is in a state of change and may have been recently rejuvenated.
Venting from the Mid-Atlantic Ridge at 37°17′N: the Lucky Strike hydrothermal site
Authors: Klinkhammer G. P. , Chin C. S. , Wilson C. , German C. R. 
Published: April 2008

Abstract
The Lucky Strike hydrothermal field on the Mid-Atlantic Ridge (MAR) at 37°17′N was discovered in 1992 during dredging operations carried out as part of the FARA Program (French-American Ridge Atlantic). The vent field at Lucky Strike lies in a depression between three cones that form the summit of an axial seamount. The summit rises 400 m above the rift valley floor to a water depth of 1570 m. Hydrothermal fluids stream from several vent complexes with exit temperatures up to 333°C. This paper presents the first observations of hydrothermal plumes in the water column over Lucky Strike, including anomalies in light scattering with a nephelometer and dissolved Mn with the zero-angle photon fibre optic spectrometer. Plumes at Lucky Strike are small compared with those at other MAR hydrothermal sites such as TAG (26°N) and MARK (23°N). These small plumes are consistent with the relatively low Fe and Mn concentrations found in associated vent waters. The Sr/Ca ratios of these fluids are low, suggesting that the basaltic substrate below Lucky Strike is highly altered, but rare earth element concentrations are also low, indicating reduced mobilization. These observations together with the low fluid temperatures are suggestive of an old and waning hydrothermal system with extensive zones of subfloor alteration.
Hydrothermal plumes at Broken Spur, 29°N Mid-Atlantic Ridge: chemical and physical characteristics
Authors: James R. H. , Elderfield H. , Rudnicki M. D. , German C. R. , Palmer M. R. , Chin C. , Greaves M. J. , Gurvich E. , Klinkhammer G. P. , Ludford E. , Mills R. A. , Thomson J. , Williams A. C. 
Published: April 2008

Abstract

Two distinct hydrothermal plumes have been identified and sampled in the vicinity of active hydrothermal vents recently discovered at a site named Broken Spur, 29°10.15′N 43°10.28′W, on the Mid-Atlantic Ridge. The northern plume (29°10.13′N 43°10.61′W) most closely associated with Broken Spur consists of a weak plume (heat flux
c.
5 MW), whereas plumes detected to the south (29°09.11′N 43°10.54′W) are much stronger (heat flux
c.
57 MW). The plumes are characterized by dissolved
222
Rn, Fe and Mn anomalies of up to 20 dpm/100 kg, 32 and 14 nmol/l, respectively, and enhanced concentrations of Fe, Mn, Cu, Zn, Cd, Co and Pb in the particulate phase. Comparison of Fe:Mn ratios in the plume (3.7) to Fe:Mn in vent fluids collected at Broken Spur (7.9) suggests that
c.
530f hydrothermal Fe is removed during plume evolution.
Mineralogy and sulphur isotope characteristics of a massive sulphide boulder, Galapagos Rift, 85°55′W
Authors: Knott Richard , Fallick Anthony E. , Rickard David , Bäcker Harald 
Published: April 2008

Abstract

The submarine hydrothermal sulphide deposits of the Galapagos Rift are characterized by being exceptionally Cu-rich. Fe- and Cu-Fe sulphides are extremely heterogeneous, display granular textures and evidence of open space growth. Core was examined from a 1.5 m diameter massive sulphide boulder collected by TV grab on the GARIMAS II cruise. The main growth stage is dominated by pyrite and chalcopyrite, forming granular aggregates from <1 mm to >5 cm. These sulphides have δ
34
S from +2.7 to + 5.5‰. The Fe-Cu sulphides are modified by minor seawater oxidation and a late stage marcasite-sphalerite-galena-barite assemblage. δ
34
S varies along the core in a systematic manner and there appears to be an isotopically heavy deviation from the modal +3.9‰. This is related to particular zones and suggests a second, isotopically distinct S source, which is interpreted to be a hydrothermal diagenetic solution derived from a shallow seawater-hydrothermal circulation system.
Distribution and transformation of Fe and Mn in hydrothermal plumes and sediments and the potential function of microbiocoenoses
Authors: Sudarikov S. M. , Davydov M. P. , Bazelyan V. L. , Tarasov V. G. 
Published: April 2008

Abstract
The spatial separation of suspended Fe and Mn in plumes, recorded at Mid-Atlantic Ridge (MAR) sites, some regions on the East Pacific Rise (EPR) and in the western Pacific, is reflected in the Fe and Mn distribution in metalliferous sediments of hydrothermal origin. Investigations at 21.5–23.5°S EPR show that at a downstream distance of 10 km from the vents the total Fe and Mn contents are lower than those on the flanks. Primary suspended Mn precipitates more than 20 km from the high-temperature vents, whereas the main suspended Fe precipitates within 10 km of the active vent area. In the vicinity of the vents a zone of ‘geochemical minimum’ was observed. Bacterial masses were observed in plumes and sediments in hydrothermal sites of the Pacific. Microbial coenoses were studied to show the increased activity of heterotrophic and Fe-Mn bacteria at several horizons of MAR hydrothermal plumes. Near-surface plumes studied in Matupi Harbour (New Britain) were characterized by both the separation of suspended Fe and Mn horizontally and a corresponding increased presence of micro-organisms. The activity of micro-organisms accompanied differentiation of the suspended and dissolved Mn at the periphery of the plume. Evidence suggests a significant role for bacteria in removing Mn from plumes in different regions of the ocean.