44 results found
Marsh AI, Williams OBE, FREng LG, et al., 2021, A sensitivity study of the factors affecting the risks associated with the disposal of spent nuclear fuel in a geological disposal facility in a clay environment, Progress in Nuclear Energy, Vol: 140, Pages: 1-17, ISSN: 0149-1970
The disposal route for the UK's inventory of spent nuclear fuel has yet to be decided upon, however if the UK follows the approach taken by many nations, its spent nuclear fuel will be destined for geological disposal. This paper provides a simplified, approach to the calculation of radiological risk posed to members of the public, associated with the disposal of spent advanced gas-cooled reactor (AGR) nuclear fuel in a geological disposal facility (GDF) located in a hypothetical clay geological setting. Simulating the release of radionuclides at differing levels of complexity shall aid in the development of aspects of the design, construction, operation, decommissioning and post-closure phases of geological disposal and the development of a safety case for geological disposal. This paper presents a high-level, 1-D model built in GoldSim, to provide an initial indication of the radiological risks to the public, the nature of which would require further development into a complex total system model in order to facilitate risk evaluation supplementary to a safety case. The model was validated against benchmark calculations provided by Radioactive Waste Management Ltd. The base case calculations suggest that the predicted risks to the potential exposed groups are well below, approximately 2 orders, the recommended risk guidance level of 1 × 10−6 per year. A number of sensitivity studies were carried out to identify the importance of various factors that could influence the predicted risks. Sensitivity analysis indicated that the most influential sensitivities on the annual risk posed by geological disposal were the depth and rate at which spent nuclear fuel dissolved in contact with groundwater. The pathways available for groundwater flow to the biosphere were also noted to significantly alter the peak risk observed; crucially almost all sensitivities did not increase the peak risk to within 1 order of magnitude below the recommended risk guidance level. Va
Mider G, O'Connor W, Lawrence J, et al., 2021, An investigation into ground movement on the Ventnor landslide complex, UK using Persistent Scatterer Interferometry, Remote Sensing, ISSN: 2072-4292
Marsh AI, Williams LG, Lawrence JA, 2021, The important role and performance of engineered barriers in a UK geological disposal facility for higher activity radioactive waste, Progress in Nuclear Energy, Vol: 137, ISSN: 0149-1970
The effective management of radioactive waste is a necessary prerequisite to the use of nuclear energy. The UK's policy for the long-term management of higher activity radioactive waste (HAW), and potentially spent nuclear fuel (SNF), is disposal in a deep underground geological disposal facility (GDF). A GDF will isolate HAW from mankind until the radioactivity has decayed to levels where any risk to future generations is acceptably low. It is likely, therefore, that a GDF will need to safely contain radioactive materials for hundreds of thousands of years. The necessary isolation will be provided by a combination of natural (geological) and engineered barriers. A multi-layered engineered barrier system will provide the defence-in-depth that is required to give the public confidence in the long-term performance of the GDF. This paper identifies the significant role each engineered barrier or “layer” plays in ensuring that long-lived radionuclides remain isolated from the biosphere and receptors within the vicinity of a GDF. Receptors include human and animal populations, and the natural environment. The paper also explores the characteristics and performance of a number of suitable candidate materials for use in the UK GDF engineered barriers. An indication of the lifetime of potential barriers under conditions pertinent to each of the UKs proposed geological settings is given. As the performance of the engineered barriers will be vital to the GDF post-closure safety case, several areas for further work are proposed.
Edgar J, Ghail R, Lawrence J, et al., 2021, The impact of facies variability within the Harwich Formation on ground engineering in the London area, UK, Quarterly Journal of Engineering Geology and Hydrogeology, ISSN: 1470-9236
The Eocene Harwich Formation, underlying the Greater London (UK) area, presents many construction problems for design and location of tunnels, pipelines, and other engineering infrastructure projects. Variable deposits make up the sequence of the Harwich Formation. These include cemented fault zones, hard grounds, loose gravel and sand that, when unexpectedly encountered, can cause construction delays and increase costs. Here, we interpret borehole cores and logs, in-situ observations coupled with borehole derived samples, and calculate particle-size distributions to develop a general facies model that accounts for the lithological distribution within the Harwich Formation. This provides an improved geological framework for proposed subsurface construction that can reduce inherent engineering uncertainties, not only in the London region, but potentially in other similar geological environments.
Rashid F, Hussein D, Lawrence JA, et al., 2021, Fluid flow and permeability analysis of tight gas carbonate reservoir rocks using fractures and dynamic data, Journal of Natural Gas Science and Engineering, Vol: 90, Pages: 1-18, ISSN: 1875-5100
The porosity, permeability, rock material and fracture networks of the newly discovered tight carbonate reservoir rock, the Early Cretaceous Sarmord Formation in Zagros basin are examined. The methods used to investigate the formation are rock cores, micro-resistivity image logs, drill stem tests, drilling fluid data, petrophysical wireline data and drilled cutting samples.The analysed data show that the Sarmord Formation is characterized by extensive open and partially open macro-fractures formed by the local stress from fault and fold propagation. These fractures are sub-vertical with an average dip of 73°, fracture aperture of 0.44 mm and persistence (length) of 11.0 cm. The dominant strike of the fractures is NE-SW, parallel to the observed faults and perpendicular to the main Miran West structure.The vast majority of reservoir porosity was found to be in the rock matrix, with the fractures having very limited impact (average fracture porosity is 0.032%) on porosity. In contrast the fracture permeability averages 240 mD which is four orders of magnitude greater than the matrix permeability. As a result, the inter-connected fractures create effective fluid flow pathways and enhanced hydrocarbon migration perpendicular to the fold structure. Faulting associated with the field structure led to fault damaged zones which act as zones of inter-connected fractures with higher permeability and preferential fluid flow pathways. It is demonstrated that the fracture permeability is driven by the fracture aperture and spacing, whilst the fracture persistence has limited control on permeability.The findings of this study highlight that the importance of fractures and faults on reservoir's quality in tight gas bearing rocks. The network of inter-connected fractures, provide the fluid flow which control the permeability. In contrast the matrix controls the pore spaces and the hydrocarbon storage. This work emphasizes the importance of understanding the impact of structural
Mider G, Lawrence J, Mason P, et al., 2020, Monitoring Littoral Platform Downwearing using Differential SAR Interferometry, Remote Sensing, Vol: 12, ISSN: 2072-4292
A methodology for the remotely sensed monitoring, measurement and quantification of littoral zone platform downwearing has been developed and is demonstrated, using Persistent Scatterer Interferometric Synthetic Aperture Radar data and analysis. The research area is a 30 km section of coast in East Sussex, UK. This area combines a range of coastal environments and is characterised by the exposure of chalk along the cliffs and coastal platform. Persistent Scatterer Interferometry (PSI) has been employed, using 3.5 years of Sentinel-1 SAR data. The results demonstrate an average ground level change of −0.36 mm a−1 across the research area, caused by platform downwearing. Protected sections of coast are downwearing at an average of −0.33 mm a−1 compared to unprotected sections, which are downwearing more rapidly at an average rate of −1.10 mm a−1. The material properties of the chalk formations in the platform were considered, and in unprotected areas the weakest chalk types eroded at higher rates (−0.66 mm a−1) than the more resistant formations (−0.53 mm a−1). At a local scale, results were achieved in three studies to demonstrate variations between urban and rural environments. Individual persistent scatterer point values provided a near-continuous sequence of measurements, which allowed the effects of processes to be evaluated. The results of this investigation show an effective way of retrospective and ongoing monitoring of platform downwearing, erosion and other littoral zone processes, at regional, local and point-specific scales.
Morgan T, Ghail R, Lawrence J, 2020, Major faulting in London: evidence for inherited basement faults in the London Basin, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 54, Pages: 1-14, ISSN: 1470-9236
The near-surface of London is faulted, although the locations, architecture and tectonic origins of the faults are broadly unknown. This presents serious issues for geotechnical engineering in London and has implications for our structural understanding of the London Basin. The region is a product of Alpine compression, yet it is unclear whether these major faults are new Alpine shears or reactivated basement faults. We assess the plausibility of Alpine reactivation and inheritance of basement faults in London through three investigations: analysing structures in the near-surface; mechanically assessing the feasibility of basement fault reactivation under Alpine stress conditions; and comparing inheritance mechanisms with observations in London and the Thames Estuary. Three major en echelon fault sets are identified. These appear to have compartmentalized London's near-surface geology and are all interpreted to be products of Alpine reactivation of the underlying basement faults. Fault interaction and linkage is evidenced by complex zones of intense faulting identified by tunnelling projects. The role of new structural development in accommodating Alpine compression is considered to have been comparatively minor. The lack of major faulting in the basin's interior may reflect the competence of the underlying Anglo–Brabant Massif in restricting Alpine strains to its margins.
Scoular J, Ghail R, Lawrence J, et al., 2020, Retrospective InSAR analysis of East London during the construction of the Lee Tunnel, Remote Sensing, Vol: 12, Pages: 1-19, ISSN: 2072-4292
The Lee Tunnel was constructed as the first part of the Thames Tideway Improvement scheme, between 2010 and 2016. With tunnelling for the East section of the main Thames Tideway Tunnel, which joins the Lee Tunnel at Abbey Mills Pumping Station, beginning in early 2020, this paper investigates patterns of deformation in East London during construction of the Lee Tunnel. An unexpected geological feature, later identified as a drift filled hollow, was discovered during tunnelling. This study demonstrates that had eight years of ERS Persistent Scatterer Interferometry (PSI) data been analysed prior to tunnelling, the unusual pattern of displacement may have been recognised and further targeted borehole investigations taken place before the launch of the tunnel boring machine. Results also show how areas of different land use, including cemeteries and historic landfill, exhibit differences in settlement behaviour, compared with surrounding terraced housing. This research highlights the challenges in interpreting PSI results in an urban area with ongoing construction and the value of a long archive of data, which now spans almost three decades in London, that can be used to establish a baseline prior to construction.
Rashid F, Hussein D, Lawrence JA, et al., 2020, Characterization and impact on reservoir quality of fractures in the Cretaceous Qamchuqa Formation, Zagros folded belt, Marine and Petroleum Geology, Vol: 113, Pages: 1-22, ISSN: 0264-8172
Reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties, the tectonic origin of fractures, the relationship of fractures to other sedimentary features within the rockmass and diagenesis. In this study fracture analysis, porosity and permeability of the Qamchuqa Formation in the Miran West block of the Zagros folded belt in Kurdistan has been studied. This was undertaken using core analysis, micro-resistivity image logs, drill stem tests (DST), mud logging data, Repeat Formation Test (RFT), drilled cutting samples and wireline log data.The integrated analysis shows that the Qamchuqa Formation is characterized by heterogeneous sedimentary and tectonic features. The sedimentary features include burial stylolites, dissolution seams and some fractures which formed at early stages of burial and diagenesis (Phase 1). Open fractures, partially open mineralized fractures, veins and tectonic stylolites were formed by later tectonic activity (Phase 2).The finding of this study highlight that the fracture properties including aperture, length, frequency and origin, play an important role in controlling the reservoir's quality. The open fractures and partially open mineralized fractures enhance permeability providing an inter-connected fracture network, leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock. The fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix. In contrast, structures including stylolites, dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow.This work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs.
Scoular JM, Croft J, Ghail RC, et al., 2019, Limitations of persistent scatterer interferometry to measure small seasonal ground movements in an urban environment, Quarterly Journal of Engineering Geology and Hydrogeology, Vol: 53, Pages: 39-48, ISSN: 1470-9236
London Clay, which underlies the majority of Greater London, has a high shrink–swell potential that can result in damage to foundations and surface infrastructure due to seasonal expansion and contraction of the clay. Currently, surface movement as a result of shrink–swell is not monitored in London, meaning that the magnitude and cyclicity of these movements is poorly understood. Persistent Scatterer Interferometric (PSI) Synthetic Aperture Radar data provide high-precision line-of-sight displacement measurements at a high point density across urban areas, offering the possibility of routine shrink–swell monitoring across whole cities. To test this, PSI data derived from TerraSAR-X (TSX) observations for the period from May 2011 to April 2017 were analysed for shrink–swell patterns across three areas of London in Hammersmith, Muswell Hill and Islington. A consistent cyclicity and amplitude was detected at all sites and the number of cycles is comparable with those identified in rainfall data. The amplitude of these cycles is smaller than anticipated, most probably because of the resisting effect of roads and pavements. The Cranfield University Leakage Assessment from Corrosivity and Shrinkage (LEACS) database was used to subdivide the PSI data and the average velocity and amplitude of each class statistically tested for significant differences between classes. The results show that it is not possible to statistically isolate possible soil shrink–swell movement in TSX PSI data in London.
Aliyu MM, Shang J, Murphy W, et al., 2019, Assessing the uniaxial compressive strength of extremely hard cryptocrystalline flint, International Journal of Rock Mechanics and Mining Sciences, Vol: 113, Pages: 310-321, ISSN: 0020-7624
Cryptocrystalline flint is an extremely hard siliceous rock that is found in chalk formations. The chalk is frequently a prefered rock type, which in recent decades is often used as a host for underground rock caverns and tunnels in Europe and North America. A reliable estimation of the uniaxial compressive strength (UCS) of the extremely strong flint, with an average UCS of about 600 MPa will provide guidance for a proper engineering design, where flint is encountered, thereby avoiding project progress delay, litigation as well as economic consequences. Conventional UCS measurement using core samples is cumbersome for flint due to the extreme strength and hardness of the rock, for which the core sample preparation process is often extremely difficult. In this study, the UCS prediction models of flints collected from the North-West Europe were developed and the validity of the developed models was investigated. A series of laboratory index tests (comprising the three-point-bending, point load, ultrasonic velocity, density, Shore hardness and Cerchar Abrasivity tests) were perfomed. The index test results were correlated with the UCS values previously determined in the laboratory using both cylindrical and cuboidal specimens to develop the UCS prediction models. Regression analysis of the UCS and the index test results was then performed to evaluate for any potential correlations that can be applied to estimate the UCS of the cryptocrystalline flint. Intensive validity and comparison studies were performed to assess the performance of the proposed UCS prediction models. This study showed that UCS of the tested flint is linearly correlated with its point load strength index, tensile strength and compressional velocity, and is parabolically correlated with its density. The present study also demonstrated that only a couple of the previously developed empirical UCS models for estimating UCS are suitable for flint, which should be used with care.
Lawrence JA, Spence R, Mortimore RN, et al., 2018, Coastal cliff rock mass weakening of chalk and the impact of salt water, Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, Vol: 171, Pages: 545-555, ISSN: 1353-2618
The relationship between salt water and the strength of Chalk forming the coastal cliffs of northwest Europe was investigated. Uniaxial compressive strength (UCS) tests on core samples from three horizontal boreholes drilled at the base of Chalk cliffs in East Sussex, UK, showed the weakest Chalk to be near the cliff face. The UCS nearly doubled over the length of the 9 m deep boreholes. The UCS results were close to values expected for Chalk of this intact dry density for samples farthest from the cliff face. High chloride concentrations (salt water) of up to 69 000 mg/l were found to be associated with the lowest UCS values closest to the cliff face. Lower chloride concentrations, with values of 1850 mg/l or less and often with a non-marine origin, were found in the stronger core samples. It can be concluded that the Chalk coastal cliffs in the areas tested became weaker towards the cliff face. This can, in part, be linked to salt water weakening although it is likely that other factors are also contributing to this phenomenon.
Lawrence JA, Preene M, Lawrence U, et al., 2018, Engineering in Chalk, Publisher: ICE Publishing, ISBN: 978-07277-6407-2
Lawrence J, hussein D, Rashid F, et al., 2018, Developing pore size distribution models in heterogeneous carbonates using especially nuclear magnetic resonance, Engineering in Chalk
Agar S, Lawrence J, Ghail R, et al., 2018, PSInSAR remote sensing observations of deformation behaviour at Salisbury Plain, UK, Chalk 2018, Publisher: ICE Publishing, Pages: 269-274
PSInSAR is a radar remote sensing approach that offers measurements of ground deformation over large areas at sub-mm precision. The technique has significant potential for granting insight into ongoing geological processes. Data recovery in rural areas is challenging due to the highly inconsistent radar scattering behaviour exhibited by vegetated ground, and thus a rural area of the UK – Salisbury Plain - was used as a case study to examine the challenges and potential for PSInSAR techniques in rural areas. Results showed regional uplift of clay formations relative to the Chalk, which was attributed to clay shrink-swell correlated with seasonal increases in groundwater levels.
Lawrence J, mortimore R, Thrower A, 2018, Macro and micro fabrics in chalk identified using the Bushinsky Oil Technique: an updated method and new applications for an old experimental technique, Engineering in Chalk
Morgan T, Lawrence J, Ghail R, 2018, Fault damage zones: Implications for geotechnical engineering near faulting, 15th Young Geotechnical Engineer Symposium
Faulting not only produces a plane of weakness within the rockmass but can significantly weaken it locally by the development of a damage zone around the fault. The paper aims to highlight to the geotechnical community the potential impact of the fault damage zone by using GSI and Hoek-Brown assessments of the rockmass strength on a case study from Culver, SW England. Both assessments demonstrated that the rockmass within the damage zone is weaker than the unfaulted rock, weakening significantly towards the fault core.
Aliyu MM, Murphy W, Lawrence JA, et al., 2018, Impact of tectonic faults on the morphology and mechanical properties of grey flints, Pages: 515-520
Grey flints of different morphologies (tabular and nodular) located proximally and distally to large tectonic faults were investigated. Different positions to tectonic faults were considered to examine the influence of geological structures on mechanical properties of flints. Different morphologies were considered to investigate the variation in mechanical properties of flints with morphology. Uniaxial compressive strength, point load strength, tensile strength, density and deformability of grey flints were tested. The results show grey flints are stronger, denser and more rigid than similar flints from zones of tectonic disturbance and faulting, but do not show any trend between flint morphology and mechanical properties. Understanding field variables such as the influence of proximity to tectonic faults and the variation in mechanical properties of flint may provide important input for the successful design of engineering projects and the behaviour of chalk oil reserviours.
Asoms SG, Stavrou A, Lawrence JA, 2018, Developing a GIS based methodology for coastal chalk cliff retreat using multiple datasets, Pages: 369-374
Topographical mapping survey data which covered a period from 1951 to 2000 was used as the main data set to develop a cliff recession analysis of the coastal cliffs at Birling Gap, East Sussex, UK. This a portion of the coast is dominated by the Seven Sisters chalk coastal cliffs and Birling Gap is characterized by the presence of a palaeo-valley which formed during the Devensian glaciation. The entire area is subject to high rates of erosion and frequently cliff collapses at all scales. Using a GIS platform, a database was created geo-referencing this detailed cartographic historical record. The cartographic information was translated into spatial linear elements within the GIS; each linear element defining the position of the cliff at a specific period. A spatial and statistical analysis of the georeferenced information provided a complete and comprehensive analysis of the shoreline recession, allowing spatial and temporal correlation of the coastal erosion occurring at this location. The cartographic information was then enhanced by using more recent data sets, mainly obtained by aerial photos, which allowed the analysis to be extended into the 21st century. This methodology was developed to demonstrate how different data sets can efficiently and effectively be combined to provide end users with a single referenceable tool to holistically investigate the processes, causes and impact of coastal erosion.
Asoni SG, Stavrou A, Lawrence JA, 2018, Erosion of the chalk coastal cliffs at Birling Gap, Sussex, UK. Correlation between rate of coastal retreat, geotechnical rocks properties and precipitation, Pages: 361-367
Birling Gap forms part of the Seven Sister cliffs, East Sussex, UK. Geotechnically the area is characterized by the presence of a Devensian paleovalley developed in a shallow syncline within the Seaford Chalk Formation. It is a dynamic coast line which is subject to continual erosion. A detailed survey has been undertaken along the coast of Birling Gap from 1950 to 2000. Using these data, the spatial information is translated into geospatial elements of an ArcGIS platform. The geo-referencing process defines the position of the cliff in a specific period. Aerial photos and most recent mapping survey are used to extend and complete the temporal analysis to the 21 st century. The outputs show that mean rate of coast retreat is 0.54 m/y and circa 30 m of coast has been lost in the last 60 years. Analysing the pluviometry data, it is possible to establish a relation between peak precipitation and high rates of coastal retreat. Higher rates of retreat are measured on the central portion of the studied area which is characterized by the deeply weathered paleovalley, which differs geotechnically from the surrounding more competent, less weathered chalk. The study shows how an accurate mapping survey translated into a GIS database can be a useful tool to understand the temporal geodynamic and hydrodynamic evolution of coastal environments. This work quantifies rapid erosion along this part of our chalk coastline and identifies that erosion is higher during periods of prolonged increased precipitation.
Hadlow NW, Lawrence JA, Mortimore RN, 2018, Evaluation and prediction of anticipated depths of weathering (engineering rockhead) as a function of geomorphology in areas of chalk outcrop in southern England and northern France, Pages: 711-720
Conceptual models of weathering in areas of chalk outcrop in southern England indicate that the depth of weathering and engineering rockhead are variable with respect to geomorphology. This variation is typically demonstrated by the transition from interfluve to valley with the depth of weathering changing as result of elevation and aspect. Valley axes are shown to have the deepest weathering, inter-fluves the shallowest and valley slopes a transitional depth with slope gradients on north-west facing slopes generally greater than southeast facing slopes. The main processes considered to have formed the weathering profiles in the Chalk of southern England are periglacial processes associated with seasonal freeze-thaw and mass movement in the last ice-age. In this study, analysis of historical site investigation data, including geophysical surveys, has allowed these conceptual models to be reviewed. This analysis has suggested that two physical transitions occur within the near-surface chalk rock mass that relate to geomorphology. The first, and deepest, transition is considered to represent an opening of discontinuities in the rock mass as a consequence of relaxation in the near surface due to unloading. The second transition is considered to represent an increase in discontinuity frequency in the rock mass due to formation of new discontinuities which progressively intensifies towards the surface. The base of the second transition is generally considered to be engineering rockhead for most engineering situations. Using the data reviewed, a model was developed to estimate the approximate position of these transitions based on relative ground surface elevation within a geomorphological domain. This model may be used to estimate the depth of engineering rockhead based on topographical data, such as a digital terrain model (DTM), in the absence of site investigation data for a site. This has applications for preliminary design where piled foundations or shallow tunnelli
Mider G, Lawrence JA, 2018, Anisotropic permeability of chalk, Pages: 481-487
The consolidation history of chalk denotes that it has been subjected to different horizontal and vertical stresses throughout its geological history. A testing programme was developed to investigate whether this would mean that chalk exhibits anisotropic permeability. Three Southern Province Chalk formations in south east England were tested; West Melbury Marly Chalk, Seaford Chalk and Newhaven Chalk formations. All the specimens were collected in the field, orientations were recorded before the samples were cut and prepared for laboratory testing. The laboratory testing programme identified small anisotropics in permeability measurements in Seaford and Newhaven Chalk formations, and anisotropy in unconfined compressive strength measurements. Anisotropic permeability in the West Melbury Marly Chalk Formation is unresolved due to heterogeneity of the samples collected from the formation. All tested samples also had index properties measured, and they have also been presented in the paper. It can be concluded that vertical samples in the Seaford and Newhaven Chalk formations are more permeable and weaker than horizontally drilled samples.
, 2018, ENGINEERING IN CHALK., ISBN: 9780727764072
Hussein D, Collier R, Lawrence JA, et al., 2017, Stratigraphic correlation and paleoenvironmental analysis of the hydrocarbon-bearing Early Miocene Euphrates and Jeribe formations in the Zagros folded-thrust belt, Arabian Journal of Geosciences, Vol: 10, ISSN: 1866-7538
The Lower Miocene Euphrates and Jeribe formations are considered as the main targets of the Tertiary petroleum system in the western part of the Zagros Basin. The formations consist of carbonates with some evaporate intercalations of the Dhiban Formation. This study utilized data from a field investigation including newly described outcrop sections and newly discovered productive oil fields within the Kirkuk embayment zone of the Zagros fold and thrust belt such as Sarqala and Kurdamir wells. This work is the first to show a stratigraphic correlation and paleoenvironmental interpretation by investigating both well data and new outcrop data. Three depositional environments were identified, (1) an inner and outer ramp belts environment, (2) shoal environment, and (3) restricted lagoon environment. Within these 3 environments, 12 microfacies were identified, based on the distribution of fauna mainly benthonic foraminifera, rock textures, and sedimentary structures. The inferred shallow water depths and variable salinities in both the Euphrates Formation and Jeribe Formation carbonates are consistent with deposition on the inner ramp (restricted lagoon and shoal) environments. Those found in the Euphrates Formation constrained the depositional environment to the restricted lagoon and shoal environment, while the microfacies in the Jeribe Formation provided evidence for an inner ramp and middle to outer ramp belt environments. This study represents the first detailed research that focuses on the stratigraphic correlation and changes in carbonate facies with the main aim to provide a wider understanding of stratigraphy of these carbonate reservoirs throughout the northern part of Iraq.
Rashid F, Glover PWJ, Lorinczi P, et al., 2017, Microstructural controls on reservoir quality in tight oil carbonate reservoir rocks, Journal of Petroleum Science and Engineering, Vol: 156, Pages: 814-826, ISSN: 0920-4105
In carbonate reservoir rocks the complex interaction between the petrophysical properties corresponds to the various depositional microstructures which are modified by various diagenetic process es that ultimately define the reservoir quality, and pose challenges to the prediction of permeability. The permeability heterogeneity in the carbonate oil reservoirs of northern Iraq varies widely and is thought to be controlled by a number of different factors. In this work, controls of matrix permeability for the Cretaceous Kometan formation selected from five oil fields in Kirkuk embayment zone have been investigated. Helium porosity, helium pulse decay permeability, brine permeability, Nuclear Magnetic Resonance (NMR), Mercury Injection Capillary pressure (MICP), Scanning Electronic Microscopy (SEM), X-Ray diffraction (XRD), and photomicrography of thin section have been used to investigate the effect of microstructure on the variation of permeability in the Kometan Formation. The formation has porosities and permeabilities which range from 0.5 ± 0.5% to 29 ± 0.5% and from 0.65 ± 0.08 μD to 700 ± 0.08 μD respectively. Three types of pore systems have been investigated using pore type, pore size and pore-throat size as characterizing parameters. We have recognized three microstructural types: (i) matrix composed of nano-intercrystalline pores (pore diameter d p smaller than 1 μm and a nanoporous pore-throat size), (ii) matrix composed of micro-intercrystalline pores (1 < d p < 10 μm with a corresponding micron-scale pore-throat distribution), and (iii) meso-intragranular and moldic pores (d p > 10 μm) also with microporous pore-throat radii. The nano-intercrystalline pore system is common across northern Iraq and represents the effective pore system type in the reservoirs of the Kirkuk embayment zone. For these tight carbonate reservoirs, the mineralogy, especially of quartz and clay minerals (illite and smectite
The petrographic and mechanical properties of flints from the Burnham (North Landing, Yorkshire, UK), Seaford (East Sussex, UK, and Dieppe, France), and Lewes Nodular (Mesnil-Val, France) Chalk formations have been investigated. Microtexture and mineral composition of flints are studied to understand how the geological and petrophysical properties of the flint affect drilling responses to the rock and investigate any spatial variation. The flints are categorized based on physical observation into white crust and light brownish grey, dark brownish grey and grey flints. Scanning electron microscopy shows textural variation in the classes. The white crust, light brownish grey, brownish grey and grey flints from the Burnham Chalk Formation from North Landing contain more calcite and have coarser, more poorly cemented silica spherules in comparison with similar classes of flint from the Seaford and Lewes Chalk formations from the Anglo-Paris Basin. In these latter flints, the structure is dominated by massive quartz cement with trace calcite independent of location. Strength tests show that the grey flints from North Landing are weaker than equivalents from the Anglo-Paris Basin. It is suggested that variation in engineering properties between grey and the dark brownish grey flints is caused by mineral composition, microtexture, structure and the local or site geology of flint materials.
Aliyu MM, Murphy W, Collier R, et al., 2015, Classification of flints for drill wear potential, Future Developments of Rock Mechanics. EUROCK2015 & 64th Geomechanics Colloquium, Publisher: Austrian Society for Geomechanics, Pages: 309-314
The assessment of abrasiveness and hardness of rocks have been extensively coveredby previous researchers, with little attention to flints, which were only described as highly abrasive.However, analysis of flints has shown that abrasivity of flints varies. These parameters areimportant inputs for the prediction of drill bit wear rate and design of various parts ofdrilling/tunneling/mining equipment. In this paper, a classification of flints (sampled from theEnglish, French and Danish Chalk) which correlates with the abrasivity and hardness of flints isproposed. The results showed lighter/grey flints (with more calcite) have lower potential to causedrill bit wear as indicated by hardness and geotechnical wear indices than dark flints. This tends tosuggest that even small variations in the carbonate content results in significant variation inabrasivity and that colour can be used as an indication of the potential of flints to cause tool wear.
Stavrou A, Murphy W, Lawrence JA, 2015, Evaluating the influence of block size in cable bolt performance, Future Developments of Rock Mechanics. EUROCK2015 & 64th Geomechanics Colloquium, Publisher: Austrian Society for Geomechanics, Pages: 859-864
Rashid F, Glover PWJ, Lorinczi P, et al., 2015, Permeability prediction in tight carbonate rocks using capillary pressure measurements, Marine and Petroleum Geology, Vol: 68, Pages: 536-550, ISSN: 0264-8172
The prediction of permeability in tight carbonate reservoirs presents ever more of a challenge in the hydrocarbon industry today. It is the aim of this paper to ascertain which models have the capacity to predict permeability reliably in tight carbonates, and to develop a new one, if required. This paper presents (i) the results of laboratory Klinkenberg-corrected pulse decay measurements of carbonates with permeabilities in the range 65 nD to 0.7 mD, (ii) use of the data to assess the performance of 16 permeability prediction models, (iii) the development of an improved prediction model for tight carbonate rocks, and (iv) its validation using an independent data set. Initial measurements including porosity, permeability and mercury injection capillary pressure measurements (MICP) were carried out on a suite of samples of Kometan limestone from the Kurdistan region of Iraq. The prediction performance of sixteen different percolation-type and Poiseuille-type permeability prediction models were analysed with the measured data. Analysis of the eight best models is included in this paper and the analysis of the remainder is provided in supplementary material. Some of the models were developed especially for tight gas sands, while many were not. Critically, none were developed for tight gas carbonates. Predictably then, the best prediction was obtained from the generic model and the RGPZ models (R2 = 0.923, 0.920 and 0.915, respectively), with other models performing extremely badly. In an attempt to provide a better model for use with tight carbonates, we have developed a new model based on the RGPZ theoretical model by adding an empirical scaling parameter to account for the relationship between grain size and pore throat size in carbonates. The generic model, the new RGPZ Carbonate model and the two original RGPZ models have been tested against independent data from a suite of 42 samples of tight Solnhofen carbonates. All four models performed very creditably with the
Rashid F, Glover PWJ, Lorinczi P, et al., 2015, Porosity and permeability of tight carbonate reservoir rocks in the north of Iraq, Journal of Petroleum Science and Engineering, Vol: 133, Pages: 147-161, ISSN: 0920-4105
The distribution of reservoir quality in tight carbonates depends primarily upon how diagenetic processes have modified the rock microstructure, leading to significant heterogeneity and anisotropy. The size and connectivity of the pore network may be enhanced by dissolution or reduced by cementation and compaction. In this paper we have examined the factors which affect the distribution of porosity, permeability and reservoir quality in the Turonian-Campanian Kometan Formation, which is a prospective low permeability carbonate reservoir rock in northern Iraq. Our data includes regional stratigraphy, outcrop sections, well logs and core material from 8 wells as well as a large suite of laboratory petrophysical measurements. These data have allowed us to classify the Kometan Formation into three lithological units, two microfacies and three petrofacies. Petrofacies A is characterized by dense and compacted and cemented wackstone/packstone with nanometer size intercrystalline pores and stylolites and presents a poor reservoir quality (porosity range 0.005±0.01 to 0.099±0.01, permeability range 65nD-51μD). Occasional open fractures in Petrofacies A improve reservoir quality resulting in a 2-3 order of magnitude increase in permeability (up to 9.75mD). Petrofacies B is a dissolved wackstone/packstone that contains moldic and vuggy pores (porosity range 0.197±0.01 to 0.293±0.01; permeability range 0.087-4.1mD), with both presenting good reservoir quality, while Petrofacies C is a carbonate mudstone that has undergone dissolution and possibly some dolomitization (porosity range 0.123±0.01 to 0.255±0.01; permeability range 0.065-5mD). All three petrofacies can be distinguished from wireline log data using porosity and NMR measurements. A poroperm plot of all of the data is fitted by a power law of the form k(mD)=aϕ<sup>b</sup> with a=28.044 and b=2.6504 with coefficient of determination, R<sup>2</sup>=0.70
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