Imperial College London

ProfessorAlFraser

Faculty of EngineeringDepartment of Earth Science & Engineering

Chair in Subsurface Geoscience
 
 
 
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Contact

 

+44 (0)20 7594 6530alastair.fraser

 
 
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Location

 

1.35Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

57 results found

Badejo SA, Muxworthy AR, Fraser A, Neumaier M, Perkins JR, Stevenson GR, Davey Ret al., 2021, Using magnetic techniques to calibrate hydrocarbon migration in petroleum systems modelling: A Case Study from the Lower Tertiary, UK Central North Sea, Geophysical Journal International, Vol: 227, Pages: 617-631, ISSN: 0956-540X

Magnetic minerals form or alter in the presence of hydrocarbons, making them a potential magnetic proxy for identifying hydrocarbon migration pathways. In this paper, we test this idea by magnetically measuring core samples from the Tay Fan in the Western Central Graben in the Central North Sea. In a companion paper, 3-D petroleum systems modelling has been carried out to forward model migration pathways within the Tay Fan. Rock magnetic experiments identified a range of magnetite, maghemite, iron sulphides, siderite, goethite and titanohematite, some of which are part of the background signal, and some due to the presence of hydrocarbons. Typical concentrations of the magnetic minerals were ∼10–200 ppm. Importantly, we have identified an increasing presence of authigenic iron sulphides (likely pyrite and greigite) along the identified lateral hydrocarbon migration pathway (east to west). This is likely caused by biodegradation resulting in the precipitation of iron sulphides, however, though less likely, it could alternatively be caused by mature oil generation, which subsequently travelled with the migrating oil to the traps in the west. These observations suggest mineral magnetic techniques could be a rapid alternative method for identifying the severity of biodegradation or oil maturity in core sample, which can then be used to calibrate petroleum systems models.

Journal article

Badejo S, Fraser A, Neumaier M, Muxworthy A, Perkins Jet al., 2021, 3D Petroleum Systems Modelling as an exploration tool in mature basins: A study from the Central North Sea, UK., Marine and Petroleum Geology, ISSN: 0264-8172

Journal article

Palci F, Fraser AJ, Neumaier M, Goode T, Parkin K, Wilson Tet al., 2020, Shale oil and gas resource evaluation through 3D basin and petroleum systems modelling: a case study from the East Midlands, onshore UK, Petroleum Geoscience, Vol: 26, Pages: 525-543, ISSN: 1354-0793

Technological advances in horizontal drilling and hydraulic fracturing have led to a re-evaluation of the UK Carboniferous sequences for shale oil and gas potential. In the Gainsborough Trough, hemipelagic mudstones known collectively as the Bowland Shale were deposited during the Pendleian Substage (Late Mississippian). In this study the interpretation of heritage 2D and recent 3D seismic data allowed the reconstruction of the tectonic evolution of the basin, which was simulated in a 3D basin and petroleum systems model. The model enabled the first prediction of generated, adsorbed, retained and expelled hydrocarbon volumes. Between 8 and 26 Bbbl of STOIIP, and between 11 and 38 tcf of GIIP have been estimated to lie within the Bowland Shale in the Gainsborough Trough. However, at the present time, there is considerable uncertainty concerning these in-place volumes, and no tests have proven the recoverability of oil and gas from the Bowland Shale in this area. Importantly, the Bowland Shale has been modelled as a single homogeneous layer, and the in situ volume numbers need to be corrected for a net to gross factor, once the criteria required for the definition for net reservoir in this formation are better understood.

Journal article

Badejo SA, Muxworthy A, Fraser A, Stevenson G, Zhao X, Jackson Met al., 2020, Identification of magnetic enhancement at hydrocarbon/water contacts, American Association of Petroleum Geologists (AAPG) Bulletin, ISSN: 0149-1423

Identifying the depths of the hydrocarbon-fluid contacts in a reservoir is important for determining hydrocarbon reserves and production planning. Using core samples from the Tay sandstone reservoir in the Central North Sea, we show that thereis a magnetic enhancement at the hydrocarbon-fluid contacts, that is detectable both through magnetic susceptibility measurements and magnetic hysteresis measurements. We observed this magnetic enhancement at both gas-oil and oil-water contacts, that have been independently identified using non-magnetic methods; we did not consider gas-water contacts in this study. We demonstrate that this magnetic enhancement is due to the precipitation of new nanometric iron oxide (magnetite) and iron sulphide (greigite)phases. The magnetic enhancement may be caused by diagenetic changes or preferential biodegradation at the top of the oil column during early filling and at the oil water contact. Our findings have the potential to be used to identify paleo-hydrocarbon-fluid contact in both structurally modified fields and failed wells. The technique can also be used to infer the fill history of a basin and calibrate petroleum systems models. Magnetic susceptibility measurements have the advantage that they can easily and quickly be measured in the field on whole core-material.

Journal article

Angus L, Hampson G, Palci F, Fraser Aet al., 2020, Characteristics and context of high-energy, tidally modulated, barred shoreface deposits: Kimmeridgian–Tithonian sandstones, Weald Basin, southern UK and northern France, Journal of Sedimentary Research, Vol: 90, Pages: 313-335, ISSN: 1527-1404

The influence of tides on the sedimentology of wave-dominated shorefaces has been emphasized in recent studies of modern shorelines and related facies models, but few ancient examples have been reported to date. Herein, we use a case study from the stratigraphic record to develop a revised facies model and predictive spatio-temporal framework for high-energy, tidally modulated, wave-dominated, barred shorefaces.Kimmeridgian–Tithonian shallow-marine sandstones in the Weald Basin (southern England and northern France) occur as a series of laterally extensive tongues that are 5–24 m thick. Each tongue coarsens upward in its lower part and fines upward in its upper part. The lower part of each upward-coarsening succession consists of variably stacked, hummocky cross-stratified, very fine- to fine-grained sandstone beds and mudstone interbeds that are moderately to intensely bioturbated by a mixed Skolithos and Cruziana ichnofacies. This lower part of the succession is interpreted to record deposition on the subtidal lower shoreface, between effective storm wave base and fairweather wave base. The upper part of each upward-coarsening succession comprises cross-bedded, medium- to coarse-grained sandstones that are pervasively intercalated with mudstone-draped, wave-rippled surfaces (including interference ripples) which mantle the erosional bases of trough cross-sets. Bioturbation is patchy, and constitutes a low-diversity Skolithos ichnofacies. Cross-bedded sandstones are arranged into cosets superimposed on steeply dipping (up to 10˚) clinoforms that dip offshore and alongshore, and extend through the succession. These deposits are interpreted to record shallow subtidal and intertidal bars on the upper shoreface, which likely contained laterally migrating rip channels or formed part of a spit. The lower, upward-coarsening part of each sandstone tongue represents an upward-shallowing, regressive shoreface succession in which the internal bedding of upper-shor

Journal article

Abubakar R, Muxworthy A, Fraser A, Sephton MA, Watson JS, Heslop D, Paterson G, Southern Pet al., 2020, Mapping hydrocarbon charge-points in the Wessex Basin using seismic, geochemistry and mineral magnetics, Marine and Petroleum Geology, Vol: 111, Pages: 510-528, ISSN: 1873-4073

This study reports a multidisciplinary approach to determining hydrocarbon charge-points and migration in the Wessex Basin, southern England. Geochemical analysis of reservoir core material (Bridport Sandstone and Inferior Oolite) using gas chromatography-mass spectrometry (GC-MS), suggests that the oil in the Wessex Basin is from a single source, and that small variations in environmentally sensitive biomarkers are likely due to small differences in maturity or depositional conditions during the formation of the oil over millions of years. Using seismic data, basin modelling revealed two potential hydrocarbon migration pathways from the hanging wall of the Purbeck fault into the Sherwood Sandstone reservoir at Wytch Farm. One of these potential pathways is represented by cores termed Creech and the other Bushey Farm. To try to distinguish between the two potential pathways, cores were studied using mineral magnetic techniques. The magnetic signature was characterised using low-temperature (<50 K) magnetic measurements; this is because much of the magnetic signature was dominated by nanoparticles < 30 nm, which are thermally activated at room temperature and magnetically “transparent”. Wells that contained considerable amounts of hydrocarbons were dominated by nanometric magnetite (<30 nm). Such particles are small enough to migrate with the oil, through pore spaces, which are of the order ~100 nm. Wells located at the fringes of large hydrocarbon accumulation had enhanced pyrrhotite-dominated magnetic signals. Of the two potential migration pathways, the mineral magnetic results suggest that the oil migrated through Creech rather than through Bushey Farm.

Journal article

Lodhia B, Roberts G, Fraser A, Jarvis J, Cowan R, Newton Ret al., 2019, Observation and simulation of solid sedimentary flux: examples from northwest Africa, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 20, Pages: 4613-4634, ISSN: 1525-2027

The sedimentary archive preserved at passive margins provides important clues about the evolution of continental topography. For example, histories of African uplift, erosion, and deposition of clastic sedimentary rock provide information about mantle convection. Furthermore, relating histories of uplift and erosion from regions where sediment is generated to measurements of efflux is important for understanding basin evolution and the distribution of natural resources. We focus on constraining Mesozoic to Recent solid sedimentary flux to northwest Africa's passive margin, which today is fed by rivers draining dynamically supported topography. Histories of sedimentary flux are calculated by mapping stratigraphy using seismic reflection and well data courtesy of Tullow Oil Plc and TGS. Stratigraphic ages, conversion from two‐way time to depth and compaction, are parameterized using biostratigraphic and check‐shot records from exploration, International Ocean Discovery Program and Deep Sea Drilling Project wells. Results indicate that Late Cretaceous to Oligocene (∼100–23 Ma) sedimentary flux decreased gradually. A slight increase in Neogene sedimentary flux is observed, which is concomitant with a change from carbonate to clastic sedimentation. Pliocene to Recent (∼5–0 Ma) flux increased by an order of magnitude. This history of sedimentary flux and facies change is similar to histories observed at other African deltas. To constrain sources of sedimentary flux, 14,700 longitudinal river profiles were inverted to calculate a history of continental uplift. These results were used to parameterize a simple “source‐to‐sink” model of fluvial erosion and sedimentary efflux. Results suggest that increased clastic flux to Africa's deltas from ∼30 Ma was driven by denudation induced by dynamic support.

Journal article

Fraser SI, Lentini MR, Fraser AJ, 2018, Introduction to the thematic set: Rifts III: catching the wave, PETROLEUM GEOSCIENCE, Vol: 24, Pages: 376-378, ISSN: 1354-0793

Journal article

Flesche H, Rutledal H, Fraser A, 2018, Evaluation of an IOR discovery at the Oseberg field in the North Sea using rock physics and seismic data analysis, Pages: 1764-1768

A significant IOR discovery was made in the Gamma Main Statfjord (GMS) structure within the Oseberg field in the North Sea. Rock physics and analysis of seismic inversion data was used to reduce uncertainty and to aid planning of production and injection wells.

Conference paper

Palci F, Fraser A, Neumaier M, Parkin K, Wilson T, Goode T, Yang Set al., 2018, The unconventional petroleum potential of the Gainsborough Trough, onshore UK. A petroleum systems modelling approach

The Gainsborough Trough is a well-studied sedimentary basin located in the East Midlands, onshore UK. The basin comprises Carboniferous sequences which have been important targets for conventional resources since the 1920s. The successful exploitation of unconventional resources in the US has led to the exploration and appraisal of shale oil and gas resources within the UK. In the Gainsborough Trough, type II marine shales known as the Bowland Shale, were deposited during the Pendleian sub stage (late Mississippian). In this study, a detailed interpretation of 2D and 3D seismic reflection data allows the construction of a sophisticated 3D basin and petroleum systems model. The model is calibrated by structural and stratigraphic data from well, outcrop and seismic datasets. The output of the model is an estimate of in-place volumes of shale oil and gas resources and associated unconventional hydrocarbon sweet spot maps. A total of 18 billion barrels of oil and 25 Tcf of gas have been estimated within the Bowland Shale Formation in the Gainsborough Trough. Additionally, the prediction of primary vs secondary gas generation was also possible.

Conference paper

Roberts GG, Lodhia B, Fraser A, Fishwick S, Goes S, Jarvis Jet al., 2018, Continental margin subsidence from shallow mantle convection: example from West Africa, Earth and Planetary Science Letters, Vol: 481, Pages: 350-361, ISSN: 0012-821X

Spatial and temporal evolution of the uppermost convecting mantle plays an important role in determining histories of magmatism, uplift, subsidence, erosion and deposition of sedimentary rock. Tomographic studies and mantle flow models suggest that changes in lithospheric thickness can focus convection and destabilize plates. Geologic observations that constrain the processes responsible for onset and evolution of shallow mantle convection are sparse. We integrate seismic, well, gravity, magmatic and tomographic information to determine the history of Neogene-Recent (<23 Ma) upper mantle convection from the Cape Verde swell to West Africa. Residual ocean-age depths of +2 km and oceanic heat flow anomalies of +16 ± 4 mW m−2 are centered on Cape Verde. Residual depths decrease eastward to zero at the fringe of the Mauritania basin. Backstripped wells and mapped seismic data show that 0.4–0.8 km of water-loaded subsidence occurred in a ∼500 × 500 km region centered on the Mauritania basin during the last 23 Ma. Conversion of shear wave velocities into temperature and simple isostatic calculations indicate that asthenospheric temperatures determine bathymetry from Cape Verde to West Africa. Calculated average excess temperatures beneath Cape Verde are View the MathML source °C providing ∼103 m of support. Beneath the Mauritania basin average excess temperatures are View the MathML source °C drawing down the lithosphere by ∼102 to 103 m. Up- and downwelling mantle has generated a bathymetric gradient of ∼1/300 at a wavelength of ∼103 km during the last ∼23 Ma. Our results suggest that asthenospheric flow away from upwelling mantle can generate downwelling beneath continental margins.

Journal article

Suleiman A, Magee C, Jackson CAL, Fraser Aet al., 2017, Igneous activity in the Bornu Basin, onshore NE Nigeria: implications for opening of the South Atlantic, Journal of the Geological Society, Vol: 174, Pages: 667-678, ISSN: 0016-7649

The structure of igneous plumbing systems in circum-South Atlantic, intra-continental rift basins, e.g., the West and Central African Rift Systems (WCARS), remains enigmatic due to poor subsurface data coverage and quality. How magmatism in these basins related to the opening of the South Atlantic is thus poorly understood. We integrate2D and 3D seismic reflection data (c. 27600 km2), data from 23 boreholes, and field observations from the Bornu Basin and Upper Benue Trough, onshore NE Nigeria to examine the timingand development of igneous bodies possibly related to opening of the South Atlantic. We identify numerous sills, which typically have saucer-shaped and en-echelon morphologies,and extrusive volcanic cones. The igneous rocks are alkali basalts and dolerites. Seismic-stratigraphic relationships indicate that emplacement occurred in the Early Cretaceous (Albian-to-Cenomanian; ca. 120 Ma),Late Cretaceous(Santonian-to-early Campanian; ca. 83 Ma), and Cenozoic (Miocene; ca. 22 Ma). Magmatism was broadly coeval with major plate boundary interactions, characterized by major azimuthal changes in fracture zones in the developing South Atlantic Ocean. The broad temporal correlation between intra-continental rift basin magmatism and plate boundary interactions suggests that periods of magma emplacement may have, in some way, been instigated by stress dissipation into intra-continental rift basins.

Journal article

Suleiman AA, Magee C, Jackson CA-L, Fraser AJet al., 2017, Igneous Activity in the Bornu Basin, Onshore NE Nigeria; Implications for Opening of the South Atlantic, Journal of the Geological Society, ISSN: 0016-7649

Journal article

Neumaier M, Ariyanto P, Fraser AJ, Aribi N, Smith S, Nollet Set al., 2017, The exceptional 4D oil charge history of the Wytch Farm Field (Wessex Basin, UK)

Previous published oil charge models of the Wytch Farm Field point to the importance of the paleo-structural configuration of the greater Wytch farm area, but remain simple and non-quantitative. They do not explain why the charge has been successful only for Wytch Farm and a series smaller satellite traps along a fill/spill chain to the west, but did not work elsewhere. Structural modeling and restoration, paleo-fault analysis and paleo-drainage area analysis were carried out to recreate a pre-inversion 3D structural configuration of the greater Wytch Farm area. In this restored space, corresponding to Cretaceous times, the oil kitchen and carriers beds of the hanging wall were modeled to be locally in contact with the footwall carrier beds and reservoirs. This past zonal juxtaposition along the fault system occurred at some specific locations only. Pre-inversion drainage area-based oil migration analysis and petroleum systems modeling were applied to investigate the duration of the localized "charge window", cross-fault charge amounts and rates. With this new quantitative 4D charge model for the greater Wytch Farm area, oil and gas discoveries, shows and seeps, the absence of charge in other structures, and the successful charge of the Wytch Farm oil field can be explained.

Conference paper

Neumaier M, Vaslin A, Jacolin JE, Kleine A, Palci F, Fraser A, Parkin K, Wilson Tet al., 2017, Well-based shale resource assessment using high resolution basin and petroleum systems modeling, Pages: 2992-3003

We present a resource assessment from the Upper Bowland Shale, East Midlands, onshore UK, based on coupled petrophysical interpretation and high resolution basin and petroleum systems modeling (BPSM). In most past BPSM studies, the source rock was typically treated as a single formation with bulk properties, and intra-formational heterogeneities within the bulk rock were not taken into account. In the presented study, we have used a high resolution stratigraphy and geochemical data for the definition of intra-shale sweetspots and a quantitative volumetric assessment of oil and gas retained within the shale. Since a large part of the assumed oil and gas kitchen is relatively flat-lying and the vertical heterogeneity is considered more important than the lateral variations in facies, 1D basin and petroleum systems modeling is performed at a representative well location (Scaftworth B2). Petrophysical logs are computed and calibrated to core and cuttings as applicable and used in the modeling. Integrating a 14 component source rock kinetic, processes such as hydrocarbon generation and adsorption, intra-formational migration and expulsion are simulated at a meter scale. As a result of the modeling, prospective layers can be identified based on modeled free-phase oil and gas saturation and volume, adsorbed amounts, detailed composition as well as fluid properties (e.g., density, viscosity, and oil GOR and API). Such vertical "sweetspot units" can be used to define the intervals prospective for horizontal drilling and hydraulic fracturing.

Conference paper

Allen H, Jackson CA-L, Fraser AJ, 2016, Gravity-driven deformation of a youthful saline giant: the interplay between gliding and spreading in the Messinian Basins of the Eastern Mediterranean, Petroleum Geoscience, Vol: 22, Pages: 340-356, ISSN: 1354-0793

The triggers and drivers for salt-related deformation on continental margins are intensely debated, reflecting uncertainties regarding the diagnostic value of certain structural styles, in addition to the fundamental mechanics associated with the two principal mechanisms (gliding and spreading). Determining the triggers and drivers for salt-related deformation is important because they provide insights into continent-scale geodynamic processes, the regional kinematics of gravity-driven deformation, and sediment dispersal and hydrocarbon prospectivity. The processes associated with and timing of deformation of Messinian salt in the offshore eastern Mediterranean are uncertain, thus is our understanding of the geodynamic evolution of this tectonically complex region. We here use an extensive 2D and 3D seismic reflection dataset to test models for the salt-tectonic development of Messinian salt. We contend that gliding and spreading were not mutually exclusive, but likely overlapped through time and space, showing a close relationship local and far-field tectonics (gliding), as well as differential overburden loading (spreading). We also argue that intrasalt strain and seismic-stratigraphic patterns can be explained by a model invoking a single, post-Messinian period of salt-related deformation, rather than a more complex model involving two separate, non-coaxial deformation events occurring during and after salt deposition.

Journal article

Albalushi A, Neumaier M, Fraser AJ, Jackson CA-Let al., 2016, The impact of the Messinian Salinity Crisis on the petroleum system of the Eastern Mediterranean: a critical assessment using 2D-petroleum system modelling, Petroleum Geoscience, Vol: 22, Pages: 357-379, ISSN: 1354-0793

The offshore Levant Basin demonstrates one of the most phenomenal natural examples of a working petroleum system associated with a relatively rapid unloading and loading cycle caused by the the Messinian Salinity Crisis (MSC). In this study, 2D basin and petroleum systems modelling suggests that the geologically instantaneous water unloading of c. 2070 m and subsequent rapid salt deposition and refill impacts the subsurface pore pressure and temperature in the underlying sediments. The pressure drop is modelled to be instantaneous, whereas the impact on temperature is more of a transient response. This has important consequences for the shallow sub-Messinian biogenic petroleum system, which is assumed to have experienced fluid brecciation associated with massive fluid escape events. Deeper Oligo-Miocene sediments are far less affected, thus indicating a "preservation window" for biogenic gas accumulations, which hosts the recent discoveries (Tamar, Leviathan, Aphrodite). Hydrocarbon accumulations of a "bubble point oil" composition are modelled to have experienced cap expansion during the drawdown, with the pressure drop being the primary control. This study suggests that seal-limited traps are expected to have undergone a catastrophic seal failure whereas the impact of the MSC is modelled to be less destructive for size-limited and particularly charge-limited traps.

Journal article

Mannie AS, Jackson CA-L, Hampson GJ, Fraser AJet al., 2016, Tectonic controls on the spatial distribution and stratigraphic architecture of a net-transgressive shallow-marine syn-rift succession in a salt-influenced rift basin: Middle-to-Upper Jurassic, Norwegian Central North Sea, Journal of the Geological Society, Vol: 173, Pages: 901-915, ISSN: 0016-7649

Syn-depositional deformation in salt-influenced rift basins is complex, being driven by a combination of normal faulting and the growth of salt structures such as diapirs. Due to a lack of data with which to simultaneously constrain basin structure and syn-rift stratigraphic architecture, we have a poor understanding of how these processes control shallow marine deposition in such settings. To improve our understanding we here use seismic reflection and borehole data from the Norwegian Central North Sea to investigate the role that syn-depositional fault growth and salt movement played in controlling the sub-regional stratigraphic architecture of a net-transgressive shallow-marine syn-rift succession (Middle-to-Late Jurassic). The rift-related structural framework, which is usually dominated by normal fault-bound horst and graben, is strongly modified where an Upper Permian salt layer (Zechstein Supergroup) is sufficiently thick and mobile to act as an intra-stratal detachment, giving rise to decoupled rift-related basement and cover structural styles. Furthermore, cover extension allows the salt to rise diapirically, resulting in the formation of large salt diapirs and supra-salt normal faults formed due to late-stage salt withdrawal and diapir collapse. Rift-related normal faulting and the growth of salt structures had a dual control on the depositional thickness and facies distribution within the net-transgressive, predominantly shallow-marine, Middle-to-Upper Jurassic syn-rift succession. The resulting facies architecture reflects a delicate balance between fault- and salt flow-driven accommodation creation and intra- and extra-basinal sediment supply. Where sediment supply and accumulation rate exceeded accommodation, little or no change in facies is observed across syn-depositional structures. In contrast, where accommodation outpaced sediment supply and accumulation rate, footwall-attached shorelines locally developed adjacent to large, thick-skinned normal f

Journal article

Badejo, Muxworthy AR, Fraser A, 2016, Application of magnetic techniques to lateral hydrocarbon migration - Lower Tertiary reservoir systems, UK North Sea (poster), Magnetic Interactions 2016

Conference paper

Abubakar R, Muxworthy AR, Sephton M, Fraser A, Watson J, Southern P, Heslop D, Paterson Get al., 2016, Mapping Petroleum Migration Pathways in Wessex Basin Using Magnetics and Seismic Mapping (poster), Magnetic Interactions 2016

Conference paper

Abbott SS, John CM, Fraser AJ, 2015, Detailed 3-D depositional architecture of Late Jurassic carbonate-anhydrite cycles (Brightling Mine, Weald Basin, UK), Marine and Petroleum Geology, Vol: 69, Pages: 74-93, ISSN: 1873-4073

Quantifying the geometries of evaporite deposits at a <1 km scale is critical in our understanding of similar ancient depositional systems, but is challenging given evaporite mineral dissolution at surface conditions. A high-resolution stratigraphic study of the basal Purbeck Beds in Brightling Mine, UK, provides insight into the three-dimensional architecture, lateral continuity and vertical heterogeneity within an evaporite seal. We conducted a field mapping study, combined with X-ray diffraction, petrographic microscopy, and δ13C and δ18O isotope analysis. The stratigraphic interval contains five facies. In stratigraphic order, these include supratidal porphyritic nodular evaporite, shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite, subtidal shale, and subtidal laminar marl, capped by nodular anhydrite. The interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal (tidal flat) facies and subtidal (shallow marine) facies laterally passed into the evaporative sabkha. The cycles are interpreted as meter-scale shoaling-upward sequences, likely controlled by localized high-frequency changes in relative sea level and/or sabkha hydrology. Spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam. The variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution, eolian processes, and coastal erosion. These observations indicate a similar mode of deposition to the modern-day sabkha of the Persian Gulf. We conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses, but largely continuous lateral bedding at an interwell-scale.

Journal article

Abubakar R, Muxworthy AR, Southern P, Watson JS, Fraser AJ, Almeida TP, Sephton MAet al., 2015, Formation of magnetic minerals in hydrocarbon-generation conditions, Marine and Petroleum Geology, ISSN: 1873-4073

In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields.

Journal article

Abubakar R, Muxworthy AR, Sephton M, Fraser A, Heslop D, Paterson G, Southern Pet al., 2015, Mapping Petroluem Migration Pathways Using Magnetics and Seismic Interpretations (poster), AGU Fall 2015

Conference paper

Smith DG, Bailey RJ, Burgess PM, Fraser AJet al., 2015, Strata and time: probing the gaps in our understanding, Conferene on Strata and Time - Probing the Gaps in Our Understanding, Publisher: GEOLOGICAL SOC PUBLISHING HOUSE, Pages: 1-10, ISSN: 0305-8719

Sedimentary strata are the paramount source of geohistorical information. The ‘frozenaccidents’ of individual deposits preserve evidence of past physical, chemical and biological processesat the Earth’s surface, while the spatial relationships between strata (especially superposition)yield successions of events through time. There is, however, no one-to-one relationshipbetween strata and time, and the interpretation of the stratigraphic record depends on an understandingof its limitations. Stratigraphic continuity and completeness are unattainable ideals, andit is the departures from those ideals – the often cryptic gaps in the record – that provide bothits characteristic texture and the principal challenge to its analysis. The existence of gaps isclearly demonstrated by consideration of accumulation rates, but identifying and quantifyingthem in the field is far more difficult, as is assessing their impact on the degree to which the stratigraphicrecord represents the environments and processes of the past. These issues can be tackled ina variety of ways, from empirical considerations based on classical field observations, to new waysof analysing data, to the generation and analysis of very large numbers of synthetic datasets. Therange of approaches to the fundamental questions of the relationship between strata and time continuesto expand and to challenge long-established practices and conventions.Superposed sedimentary strata are the most accessible routes into deep time, and acceptance oftheir historical significance was a major scientific breakthrough. Given that the study of strata hasbeen undertaken in something like its modern form for over two centuries, stratigraphy as a scientificdiscipline might be expected to have stabilized, as perhaps is indicated by stratigraphy textbookssuggesting that the subject is widely regarded as boring. Yet if there is a problem withstratigraphy, it is the converse: its development is increasingly

Conference paper

Wygrala BP, Neumaier M, Clayton C, Hantschel T, Kleine A, Al-Balushi A, Fraser A, Jackson Cet al., 2014, Sensitivity analysis of controlling factors in biogenically charged petroleum systems- A case study from the Levantine Basin

Conference paper

Maynard JR, Fraser AJ, Allen MB, Scott RA, Drachev Set al., 2010, Russia, FSU and the circum-arctic: The final frontier, Pages: 589-590, ISSN: 2047-9921

Sixteen papers representing the petroleum geology of the Arctic, Russia and former Soviet Union were presented over the first day and a half of PGC VII. The region is huge, diverse and has generated a great deal of excitement and outside investment in the industry over the 20 years since the collapse of the Soviet Union. The Arctic region in particular has significance as perhaps the last great frontier hydrocarbon province on Earth. The region is large, approximately 5000 km across a polar view north of the Arctic Circle (Fig. 1). Importantly, from an oil and gas exploration perspective, the Arctic Ocean has the most extensive continental shelf area of any ocean basin (c. 50% of offshore area). Much of this sits in the broad Russian offshore Arctic in water depths of less than 50 m. There are numerous sedimentary basins in the Arctic, some well known, but most poorly understood. Art Grantz (United States Geological Survey) and colleagues estimated resources at 114 × 109 barrels of undiscovered oil and 2000 × 1012 standard cubic feet (SCF) of natural gas. If the estimates are correct, these hydrocarbons would account for more than a fifth of the world's undiscovered resources. This great prize, in a world of diminishing reserves, has recently brought territorial issues into focus between the five countries with claims in the Arctic Ocean (Russia, Norway, Denmark, Canada and the USA). All of this is taking place against a backdrop of increasing concern for the fragile Arctic environment. © Petroleum Geology Conferences Ltd. Published by the Geological Society, London.

Conference paper

Fraser AJ, 2010, A regional overview of the exploration potential of the Middle East: A case study in the application of play fairway risk mapping techniques, Pages: 791-800, ISSN: 2047-9921

The Middle East is the world's most prolific petroleum province, containing the world's top five countries in terms of oil reserves and four of the top 10 oil producers. This success is largely due to the stacked nature of what are essentially very simple play systems with multiple carbonate platform and deltaic clastic reservoirs, widespread evaporitic seals, world class source rocks and the overprint of very large compressional anticlines in both fold belt and foreland settings. As with most working petroleum systems, all areas of the Middle East are not equally endowed with petroleum resources and future potential. Using an analysis of the prolific Upper Jurassic 'Arab' play fairway of the Middle East, the application of play fairway risk mapping techniques is demonstrated. © Petroleum Geology Conferences Ltd. Published by the Geological Society, London.

Conference paper

Fraser SI, Fraser AJ, Lentini MR, 2010, Rifts renaissance: stretching the crust and extending exploration frontiers, PETROLEUM GEOSCIENCE, Vol: 16, Pages: 187-188, ISSN: 1354-0793

Journal article

Sabato Ceraldi T, Ali HM, Green T, Benjamin K, Bourne M, Kamel M, Alexander J, Coterill K, Poole A, Fraser Aet al., 2010, Messinian facies and Oligo-miocene slumping in offshore sirt basin libya and sub-Messinian seismic imaging, Pages: 2649-2653

During the Messinian (6.3-5.6 Ma) the Gibraltar Straits temporarily closed as a result of the continued collision of Africa and Eurasia. The relict Mediterranean ocean basin quickly evaporated and the sea level fell dramatically. As a result an erosional and karst surface was formed which can be identified in both outcrops and seismic data in the Sirt basin. At the base of the slope, the erosional surface becomes a bright seismic event which marks the Messinian evaporate basin. Well data indicate that anhydrite and gypsum were deposited in a sabkha environment. The central part of the Sirt Basin became isolated between the karstified slope and the outer basin high. The interval is characterized by a seismic facies of laterally continuous bright events onlapping the erosional surface. This facies is interpreted as clastic deposits within a Late Messinian enclosed lake (Lake Sirt). There is a strong correlation between the seismic facies and seismic data quality. The areas with best data quality correspond to the mapped extent of Lake Sirt characterized by clastic sedimentation. The areas with the poorest data quality correspond to the parts of the basin with sabkha depositional environments and anhydrite, largely surrounding the lacustrine environments. © 2010, European Association of Geoscientists and Engineers.

Conference paper

Slack J, Bader A, Jones B, Afifi T, Fraser A, Sabato Ceraldi Tet al., 2009, Rertiary stratigraphy of the offshore sirt basin, Libya

The onshore Sirt Basin, Libya, is a prolific hydrocarbon basin, with reserves of approximately 50 billion barrels OE, however comparatively little exploration activity has occurred in the offshore extension of this rift basin. In advance of drilling deepwater exploration wells in the basin, this study has been undertaken to understand the Tertiary post-rift section. Regional seismic data was used to define 8 Tertiary sedimentary packages through the observation of stratal terminations and geometries that indicate a re-organisation of sedimentation. Biostratigraphy has been used to pick formation tops and tie these 8 seismically defined packages to eight offshore wells. This has allowed the development of a chronostratigraphy. During the Eocene there is a well developed carbonate margin however, at top Eocene there is a major change in sedimentation from carbonates to clastics, which subsequently infill the basin. This is coincident with a pulse of Syrian Arc inversion. This inversion appears to have continued through to the Early Oligocene and is postulated to have caused an initial phase of slumping. There is a dramatic second phase of slumping that is focussed on the NE basin margin and is likely to have a local tectonic cause. The Messinian event is represented as an erosional surface on the basin margins and lacustrine and evaporitic deposits in the basin centre. This is overlain by a very thin Plio-Pleistocene section.

Conference paper

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