bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic stratigraphy of an accommodation-zone margin rift-lake delta, Lake Malawi, Africa
Authors: Scholz C. A. 
Published: April 2008

Abstract

The Ruhuhu River enters Lake Malawi adjacent to an accommodation zone, a major linkage region between two adjacent half-graben basins that switch dip-polarity along the axis of the Malawi Rift. A large drainage basin developed because of the drop in elevation of the rift shoulder at the accommodation zone. Single-channel digital seismic reflection data indicate that the Ruhuhu River delta’s offshore depositional slopes are steep (2–7°), and that subsurface reflections show a strongly divergent stratal character. Sets of prograding clinoforms are observed at various stratigraphic levels and are interpreted as sand-prone lowstand delta lobes. These prograding packages are 20–50 m thick, and typically cover an area of
c.
10 km
2
. Such accommodation zone delta margins are considered prospective areas for hydrocarbon exploration because of their enhanced structural closure, high input of coarse clastic material for reservoir facies and close proximity to organic-rich deep-water shales.
Environmental dust analysis in opencast mining areas
Authors: Merefield John , Stone Ian , Jarman Philip , Rees Geraint , Roberts Jo , Jones Jeff , Dean Andrew 
Published: April 2008

Abstract
An atmospheric dust database has been set up for the western end of the South Wales Coalfield. This, the first of its kind in the UK, comprises dust data from British Standard 1747 four-way directional gauges, a window ledge sampler and an experimental frisbee deposit gauge. X-Ray diffraction was used to characterize the dust on the basis of mineralogy. Scanning electron microscopy was used to examine particle size and shape and an energy dispersive X-ray analysis system was used to locate coal particles.
For 18 months, a total of 15 directional and three frisbee gauges were used to collect dust on and around the Ffos Las opencast coal site in South Wales, UK. Additionally, two more directional gauges have been installed in the Brecon Beacons and at Exeter in south-west England to provide data from outside the coal mining area.
Processed data from the X-ray diffractograms, along with the weather data from an onsite weather gauge, are input to a geographical information system (ArcInfo), where they can be manipulated statistically. Rose diagram plots for the area can thus be presented, giving the mineralogical contents of dust from the four directions of each sampling station, set in a spatial context. A series of these plots introduces the temporal element.
This new dust data technology already shows considerable potential for use in nuisance complaints, planning applications, site licence renewals and for the implementation of future European environmental protection legislation.
Controls of coalbed methane prospectivity in Great Britain
Authors: Baily H. E. , Glover B. W. , Holloway S. , Young S. R. 
Published: April 2008

Abstract

Only in the last few years has there been a significant increase in exploration for coalbed methane (CBM) in Great Britain. There are several geological controls on British CBM prospectivity which combine with socio-political constraints in limiting the direct transfer of experience and technology from the USA where, until recently, CBM development has been concentrated. In many parts of the world, the depth of burial and rank of coals may be used as approximate indicators of CBM potential. However, in most British coal-bearing basins, one of the most important factors controlling the amount of preserved adsorbed methane in coals appears to be the degree of syn- and post-depositional basin inversion. Although enough methane to saturate the coals was probably generated during the formation of the Late Carboniferous basins, extensive degasification took place during the end-Carboniferous Variscan orogeny. Subsequent Permo-Triassic and later reburial of coals seems to have been insufficient to replenish adsorbed methane over much of the CBM target areas of Great Britain. Those British coal-bearing basins which can be identified as having been originally deeply buried, only midly inverted during the Variscan orogeny and which have remained relatively deeply buried beneath Mesozoic cover until early Cenozoic times are likely to contain the most preserved adsorbed methane and consequently prove the best prospects. Identification of a consumer and an adequate infrastructure further limit the potential of CBM prospects. In addition, at present, geological factors such as
in situ
stress, Coal Measures sedimentology, coal cleat orientation, hydrogeology and hydrology, and planning and environmental issues are considered in more detail only at the well-siting stage. As a knowledge of British CBM grows, however, these factors will become more important in initial licence acquisition.
Pre-sedimentary palaeo-relief and compaction: controls on peat deposition and clastic sedimentation in the Radnice Member, Kladno Basin, Bohemia
Authors: Opluštil Stanislav , Vízdal Petr 
Published: April 2008

Abstract
Pre-sedimentary palaeo-topography was a major control on facies distribution during the deposition of the basal unit (the Radnice Member) in the Kladno Basin. The undisturbed accumulation of peat took place in calm valleys protected by surrounding ridges from the effect of fluvial dynamics, whereas in open depressions only thin or split coals occurred. Facies distribution and the thickness of deposits depend on the palaeo-relief which influenced compaction rates and peat bog development without a major role of local synsedimentary tectonism within the study area. Different positions of both the maximum thicknesses of the clastic interseam intervals and lines of splitting of the coals have been documented. The thickest coals (up to 7m) originated near the base of the Carboniferous deposits in the axes of depressions, either locked or protected by the adjacent ridges. They are underlain mostly by fine-grained sediments, responsible for an even compaction rate compensated by peat accumulation. Stratigraphically higher coals have maximum thicknesses of only 2.5 m at the depression margins or in shallow depressions. Towards the axes of the main depressions they are either split or thinner due to the rapid compaction rate of a thick sequence of fine-grained sediments and organic matter. Moreover, the drainage pattern changed as a result of the burial of relief. Owing to compaction, however, the river systems occupied routes along the palaeo-valley axes. No mineable coals occur in the area underlain by a thick sequence of coarse-grained sediments as a result of weak compaction.
Organic carbon as a palaeoenvironmental indicator in the marine realm
Authors: De Leeuw J. W. , Frewin N. L. , Van Bergen P. F. , Sinninghe Damsté J. S. , Collinson M. E. 
Published: April 2008

Abstract

Recent developments in biogeochemistry have made accessible all information currently known to be present in sedimentary organic compounds, i.e. the carbon skeleton structure, the positions of functional groups and stable carbon isotope ratios. This combined information has strengthened the applications of sedimentary organic compounds as biomarkers and palaeoenvironmental indicators. This review summarizes the most important biomarkers and their applications in reconstructing marine palaeoenvironments and processes. The marine environment is characterized by the combined presence of specific compounds, such as organic sulphur compounds, dinosteroids, 24-
n
-propylsteroids (even in trace amounts), high amounts of C
25
HBI hydrocarbons and the absence of long chain
n
-alkanes with odd over even predominance, bicadinanes and specific higher-plant triterpenoids (e.g. oleanane). Furthermore, palaeoenvironmental conditions, such as photic zone anoxia, hypersalinity, microbial sulphate-reducing activity, algal blooming, palaeo-upwelling and palaeo-surface seawater temperature are indicated by molecular and/or isotopic characteristics. Biomarkers from terrestrial sources are included because land-derived organic matter is an important contributor to coastal and shallow-marine environments. A short case study, within a Holocene terrestrial/marine setting (Florida Bay, USA), is also presented to illustrate the reconstruction of transgressive-regressive trends using selected organic compounds.
Application and analysis of a new method for calculating tensor permeability
Authors: King Michael J. 
Published: April 2008

Abstract
Geostatistical techniques generate multi-million gridblock reservoir descriptions which must be scaled up to coarser models before being utilized in standard reservoir simulators. When the underlying structure is cross-bedded, and the imposed pressure drop does not follow the layering, the effective permeability must be represented as a full tensor to capture the flow properties of the system. We present a novel method of computation for effective permeability, which preserves tensorial cross-flow effects while remaining compatible with standard (non-tensor) simulation. The resulting mixed finite element formulation, periodic boundary conditions and ‘self-consistent’ inlet and outlet pressures provide an unique non-linear scale-up computation. The method is applied to a synthetic data set drawn from a North Sea reservoir. For a typical value of Kv/Kh — about 5% — the cross-terms dominate over the diagonal in the computation of vertical permeability. In overall response, the use of the standard diagonal tensor and five-point finite difference scheme is in error by about 15%, and in error by a factor of 100% in the evaluation of Kv/Kh. The results are especially important in evaluating the productivity from horizontal wells, where vertical flow dominates.
Towards measurement of capillary pressure and relative permeability at representative wettability
Authors: Kokkedee J. A. , Boutkan V. K. 
Published: April 2008

Abstract
Equipment and experimental methods are presented for simultaneous measurement of capillary pressure and relative permeability, using a modification of the continuous injection method. Initial experiments on Berea core material using laboratory fluids showed that the reproducibility of the measured data is good. Capillary pressure and relative permeability curves measured by our new methods were consistent with previous results. Experiments with a dead reservoir crude demonstrated that wettability changes can be monitored as a function of time. This possibility will be used in future experiments to compare capillary pressure and relative permeability curves under reservoir conditions with those under less severe conditions.
SAGA injection: a new combination IOR process for stratified reservoirs
Authors: Hanssen Jan Erik , Surguchev Leonid M. , Svorstøl Idar , Blaker Tore 
Published: April 2008

Abstract
Specific features of North Sea sandstone reservoirs and reservoir fluids determine quite special conditions for water-alternating-gas (WAG) injection which must be taken into account when tuning WAG parameters for the particular stratification and anisotropy of a heterogeneous reservoir. Combining advantages of waterflooding and gas injection, WAG can be very effective in stratified reservoirs. Even so, gravity segregation and early breakthrough may cause poor sweep, especially in reservoirs with low restriction to the cross-flow within the layers and with low permeable layers underlying high permeable layers. The first part of this paper presents results of WAG prediction and process tuning for a reservoir of this class. The second part introduces a new process for selectively controlling injectant flow, surfactant-alternating-gas-ameliorated (or SAGA) injection, which may yield further improvement. In this process, a foaming surfactant added to part of a water half-cycle preferentially enters the swept region. Foam that is generated by gas/surfactant displacement in a subsequent gas half-cycle will block or reduce further entry of gas and water into the high permeable layer, diverting injectant to unswept layers as the reservoir is maintained on WAG flood. Analytical estimates and numerical simulations indicate positive effects of SAGA injection on oil recovery and GOR over WAG injection. Simulation results quantifying the effect of foam plugging, injection parameters and time factor on WAG performance are discussed. Experiments in a physical stratified reservoir model demonstrate the selective placement of foamer, foam-plug generation, and effectiveness of the combined action of WAG and foam. The visualization of physical model experiments is essential for demonstrating foam process mechanisms and is useful in illustrating segregation and viscous/gravity effects in SAGA injection.
Rapid evaluation of the impact of heterogeneity on miscible gas injection
Authors: King M. J. , Blunt M. J. , Mansfield M. , Christie M. A. 
Published: April 2008

Abstract
To predict and manage petroleum production there are two challenges: first, to generate and utilize tremendous detail in our reservoir description and second, to recognize that the majority of this detail is uncertain. Techniques, therefore, are needed to assess uncertainty while making predictions of oil, water, and gas production. We demonstrate that by using a mixture of old and new techniques (streamlines and fine grid simulation) we obtain the speed of the first while retaining the rigour and accuracy of the second. The method is applied to the rapid evaluation of the impact of reservoir heterogeneity on miscible gas injection.
A WAG injection pilot in the Lower Brent Formation at the Gullfaks Field
Authors: Dalen Vilgeir , Instefjord Rune , Kristensen Reidar 
Published: April 2008

Abstract
The Gullfaks Field is a large oilfield in the Norwegian Sector of the North Sea. The field is compartmentalized by a dense and complex fault pattern, and most of the oil is contained in poorly consolidated but high-quality reservoir sands. Production started in 1986, and waterflooding is the main recovery method. Water-alternating-gas (WAG) injection — or supplementary injection of gas in existing water injection wells — has been identified as a possible method for increasing and accelerating oil recovery from Gullfaks. To verify the potential of this technique, a WAG pilot was initiated in 1991. The target area for the gas was primarily one fault block where major water breakthrough had occurred. In this paper, relevant field observations are presented, and the effects of the WAG pilot injection on flow performance and recoveries are discussed on the basis of the field observations and a detailed, history-matched 3D simulation model for the pilot area. In the present case, the gas migrates rapidly towards the top of the formation and accumulates in secondary gas caps. Improved immiscible displacement of attic oil is the main benefit of gas injection in this case.
Improving oil recovery from Oseberg Gamma North using horizontal wells
Authors: Madsen T. , Lie O. , Velvin M. 
Published: April 2008

Abstract
The Oseberg Gamma North field is a small satellite to the Oseberg field. The reservoir is a tilted heterogeneous sand package with a thin oil zone between a gas cap and an aquifer. The field has been produced from one horizontal subsea well since October 1991. The main reason for the development is to supply gas for injection in the Oseberg field, but also to optimize oil recovery.
In planning the development of a small field like Gamma North, particular attention must be paid to existing uncertainties in geology and reservoir conditions, concept feasibility and cost. Our strategy at Oseberg Gamma North therefore emphasizes flexibility by allowing stepwise decisions to be made as more detailed reservoir information becomes available.
Effects of pore-scale displacement mechanisms and small-scale heterogeneities on oil recovery by surfactant flooding
Authors: Schilling Birgitte E. R. , Stensen Jan-Åge , Øren Pål-Eric 
Published: April 2008

Abstract
This paper describes the basic mechanisms by which waterflood residual oil is mobilized and recovered during tertiary surfactant flooding in strongly water-wet glass micromodels. Of the two models used, one displayed a uniform and the other one a more heterogeneous distribution of water flood residual oil. Mobilization of residual oil proceeds by an imbibition-drainage mechanism where a surfactant imbibition displacement is always associated with a corresponding oil-water displacement (drainage) process. The drainage results in reconnection of residual oil and leads to the formation of an oil bank whilst the imbibition process may lead to breakup and trapping of mobilized oil. Although the magnitude of the residual oil saturation was similar for both models, microscopic sweep and recovery efficiency are found to be significantly higher when the residual oil is uniformly distributed. For more heterogeneous distributions of residual oil, surfactant flow through low resistance water paths results in substantial dispersion and early surfactant breakthrough.
A preliminary evaluation of an LTPF process for Statfjord Field, Norway
Authors: Kalpakci B. , Arf T. G. , Grist D. M. , Hyde S. B. , Vikane O. , Espedal S. 
Published: April 2008

Abstract
A preliminary laboratory study was initiated in 1991 to assess the potential of Low Tension Polymer Flood (LTPF) in the Statfjord Field Upper Brent Formation. On the basis of phase behaviour and compatibility experiments, four formulations were identified for further evaluation and a live oil core flood test was conducted to assess the oil recovery potential of one formulation under reservoir conditions. Encouraged by the initial laboratory results, a three-step LTPF process design strategy was followed. A target area of the reservoir was identified, the performance of the waterflood in this area was history-matched using the LTPF simulator and a predictive simulation of several LTPF application strategies was performed.
The chemical flood simulator, BPOPE, was first employed to match the laboratory core flow test by incorporating the LTPF characteristics measured. Following this conditioning, it was then used to assess the application of LTPF in the formation selected. A variety of perforation strategies, LTPF slug sizes and operating conditions were tested, all with reservoir cooling due to the injection of cold sea water.
The modelling shows LTPF to be sensitive to slug size in particular, to surfactant phase behaviour and to adsorption loss levels. It was concluded that the LTPF process could be applied to the Tarbert formation, to yield additional recovery. However, an optimization is required to make the LTPF process attractive for implementation. This paper presents the essential phase behaviour data, the results of the live oil core flow test, and discussion of the computer simulation approach and the results.
Constraints for using high-frequency sedimentary cycles in cyclostratigraphy
Authors: Cotillon P. 
Published: April 2008

Abstract

High-frequency cycles can be used for setting accurate correlations within basins, between sites of the world-ocean or between two different continents. Besides, since Gilbert (1895,
Journal of Geology
,
3
, 121–127), the cycles forming marl-limestone couplets have been regarded as chronostratigraphic tools for estimating durations of some stages, formations and biostratigraphical units. But this use is dangerous if applied without caution. Firstly, the period of decimetric couplets can vary along sedimentary successions because it is negatively correlated to the sedimentation rate. Indeed, in a dilated and quickly deposited series, many low-order cycles, unapparent in slowly deposited sediments because of bioturbation, occur as centrimetric to decimetric units and can be gathered in groups differing from the 100 ka bundles. Examples from the Lower and Middle Cretaceous show that 21 ka cycles are well-expressed with sedimentation rates of 5–30 m Ma
−1
. Secondly, the recording of orbital cycles depends on the facies and on the characteristics of sedimentary fluxes. Thirdly, corrections must be done for the variation of some orbital frequencies with time.

In summary, facies suitable for cyclostratigraphic work show moderate sedimentation rate, homogeneous lithologies with a balance of limestone and marl and are related to high sea-level periods which coincide generally with regular fluxes.
Geochemical criteria for reservoir characterization
Authors: Anissimov Leonid 
Published: April 2008

Abstract
This paper shows how the basinal analysis of formation waters and petroleums may be used to deduce the general geological setting of the source-reservoir system. There are two extreme cases, principally depending on the relative volumes of the source and reservoir regions. If the source rock region dominates, a ‘closed’ system results. Otherwise, where the reservoir volume is large the system is ‘open’. The ‘reservoir’ may be thought of as including the ‘carrier bed’ if appropriate.

In the ‘closed’ system, for example the carbonate reefs of the Western Canada Basin, water-soluble products of petroleum generation (e.g. benzene and H
2
S) are preserved in the reservoir. There is insufficient water to remove these components by aqueous solution. The partial pressure of methane is expected to be the same in formation waters and petroleums, since they can equilibrate in a ‘closed’ system. In an ‘open’ system the volume of water in the ‘reservoir’ is large compared to the source. Water and petroleum expelled from the mature source rock kitchen cannot reach equilibrium with the vast volume of formation fluids. Regions which connect with local source kitchens are expected to experience alterations in salinity and dissolved organics. Concentrations of water-soluble components will therefore be reduced in petroleums.

Data from ‘open’ and ‘closed’ systems are presented from the Devonian of the Volga-Ural province. A reduction in water salnity below 3 km, near the source kitchen is attributed to expulsion of a low salinity water during oil generation. Related changes in aqueous benzene concentrations are also seen.
Diagenesis of the Rotliegend Sandstones in the V-Fields, southern North sea: a fluid inclusion study
Authors: McNeil B. , Shaw H. F. , Rankin A. H. 
Published: April 2008

Abstract

Illite, quartz, Fe-dolomite (with some dolomite), anhydrite and barite are the principal pore-filling cements in the analysed samples of the Rotliegend sandstones from the Vulcan, South Valiant and Vanguard Fields of the southern North Sea. Apart from illite, these cements also infill fractures cutting the Rotliegend sandstones, but in the fractures there is a predominance of anhydrite and barite whereas in the pore infills, quartz and Fe-dolomite predominate. The quartz, Fe-dolomite and sulphate cements have been studied using a variety of analytical techniques but with the emphasis on fluid inclusion microthermometry. The results indicate that fluids at temperatures of 70 to 125°C, with salinities of 17 to 24 eq. wt% NaCl and an overall composition of Na-Ca-Mg-K-Cl-SO
4
, were involved in authigenic mineral formation in pore spaces and fractures. Hydrocarbons were detected in the fluid inclusions hosted in the cements and indicate that cementation occurred in the presence predominantly of methane and only rarely liquid hydrocarbons. Relating the microthermometry homogenization/formation temperatures to the burial history, quartz cementation occurred mainly in the late Permian to late Cretaceous, Fe-dolomite during the Jurassic to mid-Cretaceous, and anhydrite and barite mainly in the mid-to late Cretaceous.