bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some examples and possible explanations for oil generation from coals and coaly sequences
Authors: Thompson S. , Cooper B. S. , Barnard P. C. 
Published: April 2008

Abstract
Coals and associated shales are important oil source rocks in certain deltaic environments, in which selective processes of degradation or reworking increase the content of hydrogen-rich kerogen. The formation of hydrogen-rich kerogen in a deltaic setting is either by preferential concentration of plant cuticles and spores after reworking of delta top freshwater peats, or, by accumulation of delta margin peats under saline conditions. In each case the source rocks and derived oils may be expected to show distinctive indicators of the depositional environment in the associated alkane content, sulphur content, biomarker and carbon isotope signatures.
Coals in the Oligo-Miocene Talang Akar Formation of South Sumatra and Northwest Java Basins contain perhydrous vitrinite and are the source of isotopically relatively light waxy oils which contain biomarkers derived from tree resins. Waxy oils are also produced in the Sunda Basin, between Sumatra and Java but in this case the upper (coaly) part of the Talang Akar Formation is immature and the oils are derived from algal kerogen in the older, lacustrine Banuwati Formation shales; these oils are distinguished by low contents of land plant biomarkers and by a markedly heavier carbon isotopic signature.
In the Western Desert of Egypt, coals of the mostly marine Jurassic Khatatba Formation have sourced oils with a relatively heavy isotopic signature. It is proposed that the isotopically heavy character of the coals and oils is due to a combination of microbial contribution, and raised salinity (and sulphate) levels due to marine influence.
In northern England, Namurian (Pendleian) marine shales are generally distal turbidites derived from pro-delta sediments but mostly without oil source potential. Rich oil source rocks occur as basinal shales at the extreme margins of or interdigitating with the turbidites or as condensed sequences on structural highs. They contain kerogen derived by reworking of peats of a deltaic-coastal plain environment, and may be correlated with many of the oil shows and produced oils of the area.
The examples demonstrate that the recognition of source rock facies aids exploration by guiding the prediction of the location and potential of oil-prone facies, but that this is only possible if all facets of oil and source rock geochemistry are integrated with a knowledge of sedimentary processes.
A maturity and palaeoenvironmental assessment of condensates and oils from the North Sumatra Basin, Indonesia
Authors: Matchette-Downes C. J. , Fallick A. E. , Karmajaya  , Rowland S. 
Published: April 2008

Abstract
Five light oils and condensates from the wells drilled in Lower to Upper Miocene reservoir rocks of the North Sumatra Basin were analysed by gas chromatography-mass spectrometry and stable isotope ratio mass spectrometry. In conjunction with data from over 1600 well and outcrop samples the results were used to describe the character of the presumed source rocks in terms of organic matter maturity and palaeoenvironment of deposition. The source rock character was further constrained by the maturity of the drilled sections, geothermal gradient observations and re-evaluation of the geology of the region.
Dominant lacustrine with subordinate ombrogenous raised peat bog palaeoenvironments of deposition are indicated. It is envisaged that raised mires fringed large lakes in the area. Tectonic disturbance probably caused periodic flooding of the swamps and ultimately a complete marine incursion occurred.
The oils and condensates are mature to extremely mature. Some oils are mixtures of oils of different maturities and discrete terrestrial sources.
The oil potential of Mid-Jurassic coals in northern Egypt
Authors: Bagge Mark A. , Keeley Martin L. 
Published: April 2008

Abstract
Geochemical analysis of selected coals indicates that some of the Jurassic coals in Egypt have oil-generating potential. Other coals have just gas potential, but may have already generated oils as they are now post-mature for oil generation. Petrographic analysis of the coals reveals a composition dominated by vitrinite, but with variable liptinite contents and the occurrence of fluorescent vitrinite in some coals. It is not clear which components of the coal are responsible for the oil potential; it is probable that liptinite, hydrogen-rich vitrinites and a fine-grained groundmass of algal origin all contribute. A combination of Rock-Eval Hydrogen Indices and pyrolysis-gc P2 fingerprints provides the best method for determination of the oil- or gas-prone nature of the coals.
Attempts at correlating oils to source rock extracts illustrate the problem of oil-source correlations involving a rapidly varying source rock environment. The bitumen extracts from the coals reveal variable characteristics which reflect facies variations in the coals. Several of the coals have unusual saturated hydrocarbon and biological marker distributions that are atypical of humic coals and give a poor correlation to the waxy oils from the Meleiha field. The best oil-source rock correlation is with a carbonaceous shale, not a coal, but it is likely the oils were derived from large volumes of source rock including coals and carbonaceous shales. As the coals have unusual extract characteristics, any oils derived from a more localized environment in the coal swamp may show very unusual geochemical characteristics, and would not be recognized immediately as being derived from terrestrial coals.
Coal and coal-bearing strata as oil-prone source rocks: current problems and future directions
Authors: Scott Andrew C. , Fleet Andrew J. 
Published: April 2008

Abstract
At present, the principal problems concerning coaly sequences as oil-prone source rocks are, still, how can we identify which coals expel oil (liquid-phase petroleum) and how do we predict the presence and distribution of such coals in the sub-surface? To tackle these problems four key areas of study need addressing. Firstly, the representatives of the database, on which our current empirical understanding is based, needs verification. Secondly, the nomenclature used to describe coals and related kerogens must be clearly integrated. Thirdly, the constituents of these coals and kerogens, their botanical precursor and their petroleum products need to be established. Finally, controls on oil migration out of coal-bearing sequences need elucidating. Ways of addressing these problems might include a multi-/interdisciplinary study, ‘bottom-up’ studies from plant constituents, and comparative migration studies based on suites of coals from different settings.
Tectonic control of the sedimentary record and stress-induced fluid flow: constraints from basin modelling
Authors: Van Balen R. , Cloetingh S. 
Published: April 2008

Abstract
Many basins show deviations from the simple subsidence pattern predicted by the stretching model for basin evolution. Incorporating finite strength of the lithosphere during rifting and stresses acting on the lithosphere during the post-rift phase of basin evolution can successfully explain these deviations. Finite strength of the lithosphere during rifting causes flexurally supported rift-shoulders. The erosion of these rift-shoulders induces both additional uplift at the basin margin and sediment loading-induced subsidence in the basin centre, causing tilting of syn-rift sediments. A ‘break-up’ unconformity results from the progressive diminishing of this tilting towards the end of the rifting period, separating the syn- and post-rift sediments. As the amount of erosion is primarily controlled by climatic conditions, basins having the same tectonic history but, for example, located at different lattitudes will not have developed the same pattern of stratigraphic fill. The same effect is expected if another mechanism causes the uplift of the basin margin, as, for example, a change in the level of intraplate stress.
Plate reorganizations are the main cause for changes in the level of intraplate stress. We demonstrate that the in-plane stress variations affect the fluid flow regime in rifted basins, with possible implications for the diagenesis of sediments, primary migration of hydrocarbons, faulting and localization of economic resources. Examples include the North Sea and Pannonian Basin. An increase in the level of compressive stress causes flank uplift and basin centre subsidence, inducing a contemporaneous increase of meteroic water influx and compaction-driven fluid overpressures. An increase in the level of tensile inplane stress induces the opposite effects.
Fluid flow and heat transport in the upper continental crust
Authors: Deming David 
Published: April 2008

AbstractThe upper 10–15km of the continental crust is saturated with aqueous brines and is sufficiently permeable to allow the circulation of these fluids. The most important driving forces for fluid flow in the continental crust are topography gradients, sediment compaction and diagenesis, and buoyancy forces. Topographically-driven flow is generally the most efficient mechanism for mass and heat transport, and therefore has recently been favoured in theories of the origin of Mississippi Valley-type lead-zinc deposits. The magnitude of heat transport by fluid movement in the crust has an exponential dependence upon the depth of circulation. In areas of the continental crust with appreciable topography gradients (c.0.01) and permeabilities greater thanc.10−17m2, the background thermal state will likely be appreciably perturbed by groundwater movement. Fluid circulation in the upper crust is both continuous and pervasive due to topography and fluid-density gradients. The old conception of the continental crust as an unchanging body of solid rock should be replaced by a paradigm that recognizes the continental crust as a two-component system; a solid framework which continuously evolves through thermal, chemical, and mechanical interaction with crustal fluids.
Fluid chemistry and hydrological regimes in geothermal systems: a possible link between gold-depositing and hydrocarbon-bearing aqueous systems
Authors: Nicholson Keith 
Published: April 2008

Abstract
Geothermal fluids form by the infiltration, heating and circulation of meteoric waters in the Earth’s crust. Rock-water reactions, boiling and condensation processes influence the chemistry of the fluids. The composition of geothermal fluids ranges from that of gold-depositing, dilute waters to saline, oil-field brines; as such they form a link between these two aqueous systems. Techniques developed to examine the processes active in geothermal systems may find valuable application in gold exploration and hydrocarbon reservoir modelling. The concept of hydrological regime is introduced and applied to recognising deposits of geothermal activity, the level of preservation and permeable, potentially gold-bearing zones in ancient epithermal systems. Mixing models, such as Cl-enthalpy plots, and geothermometry can aid identification of breakthrough of edge waters and casing damage. Differences in the equilibration time of geothermometers may enable the thermal profile or history of the reservoir to be developed. Statistical models enable major controls or sources of the solutes to be isolated, and aid in the correlation of formation waters between wells.
The role of geopressure zones in the formation of hydrothermal Pb-Zn Mississippi Valley type mineralization in sedimentary basins
Authors: Fowler Anthony D. 
Published: April 2008

Abstract

Geopressure zones immediately subjacent to platform carbonate rocks can be modelled to serve as proximal sources of hydrothermal fluids for epigenetic Pb-Zn deposits in sedimentary basins. In some geopressure zones of the Gulf of Mexico, geothermal gradients can be as high as 10°C 100 m
−1
. This arises because the water-saturated geopressured shale masses act as thermal insulators. Geopressure zones may have sufficient fluid pressure to rupture overlying strata, providing a vertical conduit for hot mineralized brine to migrate directly into carbonate host rocks.
The use of natural He, Ne and Ar isotopes to study hydrocarbon-related fluid provenance, migration and mass balance in sedimentary basins
Authors: Ballentine C.J. , O’nions R.K. 
Published: April 2008

Abstract
Hydrocarbon accumulations contain rare gases derived from the atmosphere, the crust and, in some cases, the mantle. The distinctive isotopic structure of these different rare gas components allows them to be resolved. The relative abundances of the He, Ne and Ar in the crustal, mantle and atmosphere-derived components provides information on the physical processes which have operated in the subsurface. When combined with mass balance considerations, which place constraints on the scale of fluid movements in sedimentary basins, the rare gases provide powerful constraints on fluid provenance and transport.
Results of case studies from two extensional basin systems, the Pannonian and Vienna basin, and the sub-Alpine loading basin of the Po, illustrate how the rare gases provide information about the extent of hydrocarbon-groundwater interaction, constrain the mechanism of hydrocarbon gas transport, and provide an insight into the behaviour of the fluid regimes in different types of sedimentary basin.
Some comments on the classification of resources and reserves
Authors: Armitage M. G. , Potts M. F. A. 
Published: April 2008

Abstract
Resource and reserve classification systems are used by stock markets, investors, mining companies etc. in order to make their decision making apparently more soundly based. In view of the subjectivity of geology and diversity of mining methods, in producing and adhering to such systems those charged with the responsibility of estimating reserves run the risk of inadvertently misleading these people and of risking their own integrity. This is not to say that we should not have classification systems at all, but more that they need to reflect the reality as much as the requirement. There are additional problems at present because of the number of classification systems currently in use and the widely different uses to which they are commonly put. The worldwide acceptance of a single terminology of resource and reserve classification would go some way to reducing these. Different classification systems may be required for different applications. In addition, a move to a more systematic quantitative assessment of confidence is proposed which may reduce some of the problems inherent in such an imprecise science.
INTMOV: a program for the interactive analysis of spatial data
Authors: Hatton W. 
Published: April 2008

Abstract
A set of programs have been developed to compute moving-windows statistics from spatial data, which are fully interactive, allowing the user to compute and display two plan views of the window statistics, the parent population histogram and the two histograms of the windows statistics all on one graphical display. Stationarity of a deposit can be checked instantly at differing window sizes with all the sample data or with partitioned subsets. Data can be read into the routine from a current exploration campaign or from working site-survey data, allowing comparisons between ‘projected’ and ‘ground’ truth. Screen and DXF file output of the local neighbourhood window statistics are plotted in a colour which corresponds to standard confidence bands of the parent or global distribution. Rapid identification of local anomalies is possible. Window statistics for all the neighbourhoods can be written to file at any subset number of the original sample number. Plots of the window means and standard deviations versus numbers of boreholes allow the exploration geologist to check stationarity in a retrospective way. The main aim in the development of these routines was to reduce the amount of user keystrokes needed to compute and display the maximum amount of neighbourhood information. The technique is demonstrated with examples from UK Coal Measures.
Quantifying differences between computer models of orebody shapes
Authors: Sides E. J. 
Published: April 2008

Abstract
Several different methods have been used for the representation of orebody shapes in computer systems including serial-slice, gridded seam, regular block, mathematical functions, solid geometry, and boundary representation models. The accuracy and precison of such models are affected by factors such as errors associated with the original data used, natural variations, errors in data capture and processing, etc.
In order to asses the relative importance of such factors it is necessary to quantify differences in accuracy and precision between different model structures. To meet this objective a new technique which relies on statistical study of a series of sample lines, intersecting two or more different orebody models, is proposed.
Application of this technique on orebody models at the Neves-Corvo copper-tin deposits in southern Portugal suggested that in certain circumstances regular block models can give very poor estimates of the total volume of materials of different geological types. In addition it was shown quantitatively that shape interpretations close to the plane of drill-sections are better, in terms of accuracy and precision, than interpretations for zones falling between the drill-section planes.
Computer modelling of dewatering a major open pit mine: case study from Nevada, USA
Authors: Cameron R. I. , Middlemis H. 
Published: April 2008

Abstract
Operations began in 1985 at Amax Gold Inc.’s Sleeper Mine in Nevada, and the major open pit has been one of the largest North American gold producers. The orebody in Tertiary volcanic rocks is overlain mainly by the Desert Valley basin fill gravels. Natural groundwater levels at the mine are around 10–15 m below surface, and dewatering has been a major activity since initial overburden stripping. With a final projected mine depth of 215 m, a properly designed and cost-effective dewatering scheme, fully integrated with the mine plan, was required. Field investigation and numerical computer modelling proceeded in parallel, the feedback between the two activities being essential to the optimization of the dewatering scheme.

The basis of effective dewatering has been the interception of groundwater in the overburden before it can reach the pit. This paper describes the groundwater model, based on the USGS
modflow
code, which was specifically designed to develop a wellfield design for optimum dewatering. The model enabled the determination of the most cost-effective wellfield configuration, pumping rate and distance from the pit. Subsequent field observations showed that real drawdowns were within 50f those predicted.

The interceptor model has also been used to investigate the dewatering rate and cost implications of expanding the pit in the direction of the wellfield; and the implications of power failure at the wellfield for determination of standby generating capacity.
Volcanism and sedimentation in a rifting island-arc terrain: an example from Tonga, SW Pacific
Authors: Clift Peter D. ,   ODP Leg 135 Scientific Party
Published: April 2008

Abstract
Scientific drilling of narrow sub-basins within the Lau back-arc basin system of the SW Pacific has recovered uppermost Miocene to Recent volcaniclastic sediment and pelagic nannofossil oozes. Pliocene sediment gravity flow and turbidite sands from the western Lau Basin indicate a local source for the sediment, probably intrabasinal seamount volcanoes active during the initial stages of arc rifting. Derivation of abundant material from either the remnant volcanic arc (Lau Ridge) or the new Tofua arc is ruled out by the rugged topography of the basin and the proximal nature of the facies. Sediments from the Tonga platform, adjacent to the present day Tofua arc, indicate a peak in volcanic activity prior to and during the generation of the first back-arc basin crust at 5.25 Ma. A 2.0 Ma hiatus in arc volcanism on the trench side of the basin after rifting was brought to an end by the foundation of the Tofua arc at 3.0 Ma (Late Pliocene). On the basis of the sedimentary, geochemical and seismic data it is suggested that basin rifting involved an initial stage of extension of the original island arc, accompanied by volcanism in the form of major seamount volcanoes within the basin. These produced volcanic ash by submarine eruption, which was then reworked into adjacent sub-basins by slumping, gravity flow or turbidity current. Basin opening proceeded with a trenchward migration of extension and volcanism with time. This system was disrupted by the southward propagation of the Eastern Lau Spreading Centre into the southern Lau Basin at 1.5–1.0 Ma. This resulted in extension and volcanism being concentrated along the median valley of the spreading centre and a cessation in explosive volcanism of wide compositional range. Sedimentation in the Lau Basin since that time has been principally pelagic with minor ash layers mostly derived from the Tofua arc.
Geochemistry of Lau Basin volcanic rocks: influence of ridge segmentation and arc proximity
Authors: Pearce Julian A. , Ernewein Michelle , Bloomer Sherman H. , Parson Lindsay M. , Murton Bramley J. , Johnson Lynn E. 
Published: April 2008

Abstract

Side-scan sonar imaging of the Central Lau Basin (SW Pacific) has revealed a Central Lau Spreading Centre (CLSC) propagating southwards at the expense of an Eastern Lau Spreading Centre (ELSC) with a small Intermediate Lau Spreading Centre (ILSC) forming a ‘relay’ between the two. Volcanic rocks sampled along these spreading centres, and from two adjacent seamounts, are glassy to fine-grained pillow lavas and sheet flows of basalts, ferrobasalts and andesites. The evolved rocks are mostly confined to the propagating tip of the CLSC and can be explained by a high rate of cooling relative to magma supply, as invoked for magma genesis at propagating ridges elsewhere. Compared with equivalent rocks from the eastern Pacific, the most evolved members of the CLSC suite require similarly high degrees (>90%) of fractional crystallization from their basaltic parents. Fractional crystallisation cannot, however, account for the compositional differences between CLSC and ELSC lavas. Whereas the composition of the CLSC lavas lies just within the compositional spectrum of typical N-MORB, the ELSC lavas are distinctly enriched in alkali and alkaline earth elements, reach oxide and apatite saturation at lower Fe, Ti and P concentrations and generally show greater vesicularity despite slightly greater depths of eruption, all indicative of a water-rich subduction component. They also have lower contents of Ni, Sc, Na and Fe and higher contents of Si at a given MgO concentration that indicate a more depleted and more hydrous mantle beneath the ELSC compared with the CLSC. These results provide further evidence that, beneath the Central Lau Basin, the source composition changes progressively from MORB-type to island arc tholeiite type as the subduction zone is approached, both eastwards from the CLSC to ELSC and southwards along the ELSC to the Valu Fa Ridge. They also indicate that the composition of the subduction component may vary systematically away from the arc, with Th, LREE, Ba, Rb and H (as H
2
O) all present close to the arc, only Ba, Rb and H
2
O present at intermediate distances and just H
2
O perceptible at the furthest distances.