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  • JOURNAL ARTICLE
    Iglauer S, Paluszny A, Blunt MJ, Iglauer S, Paluszny A, Blunt MJ, Iglauer S, Paluszny A, Blunt MJ, Iglauer S, Paluszny A, Blunt MJet al., 2015,

    Simultaneous oil recovery and residual gas storage: A pore-level analysis using in situ X-ray micro-tomography (vol 103, pg 905, 2013)

    , FUEL, Vol: 139, Pages: 780-780, ISSN: 0016-2361
  • JOURNAL ARTICLE
    Al-Hadhrami MM, Alkindi AS, Muggeridge AH, Al-Hadhrami MM, Alkindi AS, Muggeridge AHet al., 2014,

    Experimental and numerical investigations into the effect of heterogeneities on the recovery of heavy oil by VAPour EXtraction (VAPEX)

    , FUEL, Vol: 135, Pages: 413-426, ISSN: 0016-2361
  • CONFERENCE PAPER
    Al-Shamma B, Gosselin O, King P, 2014,

    Parameterization using sensitivity methods for global history matching techniques

    , Pages: 887-891

    For any history-matching method, an efficient optimisation method is required, but more importantly an effective selection of parameters. The parameterisation assists in reducing a large number of possible parameters, in the absence of available data measurements, lowering also the number of altered parameters. This paper describes the implementation of flexible integrated parameterization and optimization methods, tested on the PUNQS3 synthetic model, an iterative series of parameterisation, as a pragmatic strategy, and a comparison between various parameterization methods: layer-based, gradient-based, median-based, and distribution-based. The chosen parameters are regions or zones where permeabilities and porosity are adjusted using a common multipliers. The selected parameters are then utilized as search parameters to minimize an objective function, which quantifies the mismatch between the observed and simulated production data, using a so-called global minimisation algorithm. Successive parameterizations can be used, as part of an iterative process, where the history match is improved by further parameterisation, based on the previous "best match". The optimisation techniques cannot perform well without a suitable and effective parameterisation method. This study shows a pragmatic combination of a global technique and various parameterisation methods. It emphasizes, that a low objective function can be far from the true models, and not predictive.

  • JOURNAL ARTICLE
    AlSofi AM, Blunt MJ, AlSofi AM, Blunt MJet al., 2014,

    Polymer flooding design and optimization under economic uncertainty

    , JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING, Vol: 124, Pages: 46-59, ISSN: 0920-4105
  • CONFERENCE PAPER
    Alkhatib A, King P, 2014,

    Enhanced decision making for chemical EOR processes under uncertainty - Applying the LSPC method

    The Least Squares Monte Carlo method is a decision evaluation method that can capture the value of flexibility of a process. This method was shown to provide us with some insight into the effect of uncertainty on decision making and to help us capture the upside potential or mitigate the downside effects for a chemical EOR process. The method is a stochastic approximate dynamic programming approach to decision making. It is based on a forward simulation coupled with a recursive algorithm which produces the near-optimal policy. It relies on Monte Carlo simulation to produce convergent results. This incurs a significant computational requirement when using this method to evaluate decisions for reservoir engineering problems because this requires running many reservoir simulations. The objective of this study was to enhance the performance of the Least Squares Monte Carlo method by improving the sampling method used to generate the technical uncertainties used in producing the production profiles. The probabilistic collocation method has been proven to be a robust and efficient uncertainty quantification method. It approximates the random input distributions using polynomial chaos expansions and produces a proxy polynomial for the output parameter requiring a limited number of model responses that is conditional on the number of random inputs and the order of the approximation desired. The resulting proxy can then be used to generate the different statistical moments with negligible computational requirement. By using the sampling methods of the probabilistic collocation method to approximate the sampling of the technical uncertainties, it is possible to significantly reduce the computational requirement of running the decision evaluation method. Thus we introduce the least square probabilistic collocation method. Both methods are then applied to chemical EOR problems using a number of stylized reservoir models. The technical uncertainties considered include the residu

  • JOURNAL ARTICLE
    Alkhatib A, King P, Alkhatib A, King P, Alkhatib A, King P, Alkhatib A, King Pet al., 2014,

    Robust quantification of parametric uncertainty for surfactant-polymer flooding

    , COMPUTATIONAL GEOSCIENCES, Vol: 18, Pages: 77-101, ISSN: 1420-0597

    Uncertainty in surfactant-polymer flooding is an important challenge to the wide-scale implementation of this process. Any successful design of this enhanced oil recovery process will necessitate a good understanding of uncertainty. Thus, it is essential to have the ability to quantify this uncertainty in an efficient manner. Monte Carlo simulation is the traditional uncertainty quantification approach that is used for quantifying parametric uncertainty. However, the convergence of Monte Carlo simulation is relatively low, requiring a large number of realizations to converge. This study proposes the use of the probabilistic collocation method in parametric uncertainty quantification for surfactant-polymer flooding using four synthetic reservoir models. Four sources of uncertainty were considered: the chemical flood residual oil saturation, surfactant and polymer adsorption, and the polymer viscosity multiplier. The output parameter approximated is the recovery factor. The output metrics were the input-output model response relationship, the probability density function, and the first two moments. These were compared with the results obtained from Monte Carlo simulation over a large number of realizations. Two methods for solving for the coefficients of the output parameter polynomial chaos expansion are compared: Gaussian quadrature and linear regression. The linear regression approach used two types of sampling: full-tensor product nodes and Chebyshev-derived nodes. In general, the probabilistic collocation method was applied successfully to quantify the uncertainty in the recovery factor. Applying the method using the Gaussian quadrature produced more accurate results compared with using the linear regression with full-tensor product nodes. Applying the method using the linear regression with Chebyshev derived sampling also performed relatively well. Possible enhancements to improve the performance of the probabilistic collocation method were discussed. These enha

  • JOURNAL ARTICLE
    Alkhatib A, King P, Alkhatib A, King P, Alkhatib A, King P, Alkhatib A, King Pet al., 2014,

    An approximate dynamic programming approachto decision making in the presence of uncertainty for surfactant-polymer flooding

    , COMPUTATIONAL GEOSCIENCES, Vol: 18, Pages: 243-263, ISSN: 1420-0597

    The least squares Monte Carlo method is a decision evaluation method that can capture the effect of uncertainty and the value of flexibility of a process. The method is a stochastic approximate dynamic programming approach to decision making. It is based on a forward simulation coupled with a recursive algorithm which produces the near-optimal policy. It relies on the Monte Carlo simulation to produce convergent results. This incurs a significant computational requirement when using this method to evaluate decisions for reservoir engineering problems because this requires running many reservoir simulations. The objective of this study was to enhance the performance of the least squares Monte Carlo method by improving the sampling method used to generate the technical uncertainties used in obtaining the production profiles. The probabilistic collocation method has been proven to be a robust and efficient uncertainty quantification method. By using the sampling methods of the probabilistic collocation method to approximate the sampling of the technical uncertainties, it is possible to significantly reduce the computational requirement of running the decision evaluation method. Thus, we introduce the least squares probabilistic collocation method. The decision evaluation considered a number of technical and economic uncertainties. Three reservoir case studies were used: a simple homogeneous model, the PUNQ-S3 model, and a modified portion of the SPE10 model. The results show that using the sampling techniques of the probabilistic collocation method produced relatively accurate responses compared with the original method. Different possible enhancements were discussed in order to practically adapt the least squares probabilistic collocation method to more realistic and complex reservoir models. Furthermore, it is desired to perform the method to evaluate high-dimensional decision scenarios for different chemical enhanced oil recovery processes using real reservoir data.

  • JOURNAL ARTICLE
    Amaechi B, Iglauer S, Pentland CH, Bijeljic B, Blunt MJ, Amaechi B, Iglauer S, Pentland CH, Bijeljic B, Blunt MJ, Amaechi B, Iglauer S, Pentland CH, Bijeljic B, Blunt MJet al., 2014,

    An Experimental Study of Three-Phase Trapping in Sand Packs

    , TRANSPORT IN POROUS MEDIA, Vol: 103, Pages: 421-436, ISSN: 0169-3913

    The trapped saturations of oil and gas are measured as functions of initial oil and gas saturation in water-wet sand packs. Analogue fluids-water, octane and air-are used at ambient conditions. Starting with a sand-pack column which has been saturated with brine, oil (octane) is injected with the column horizontal until irreducible water saturation is reached. The column is then positioned vertically and air is allowed to enter from the top of the column, while oil is allowed to drain under gravity for varying lengths of time. At this point, the column may be sliced and the fluids analyzed by gas chromatography to obtain the initial saturations. Alternatively, brine is injected through the bottom of the vertical column to trap oil and gas, before slicing the columns and measuring the trapped or residual saturations by gas chromatography and mass balance. The experiments show that in three-phase flow, the total trapped saturations of oil and gas are considerably higher than the trapped saturations reported in the literature for two-phase systems. It is found that the residual saturation of oil and gas combined could be as high as 23 %, as opposed to a maximum two-phase residual of only 14 %. For very high initial gas saturations, the residual gas saturation, up to 17 %, was also higher than for two-phase displacement. These observations are explained in terms of the competition between piston-like displacement and snap-off. It is also observed that less oil is always trapped in three-phase flow than in two-phase displacement, and the difference depends on the amount of gas present. For low and intermediate initial gas saturations, the trapped gas saturation rises linearly with initial saturation, followed by a constant residual, as seen in two-phase displacements. However, at very high initial gas saturations, the residual saturation rises again. © 2014 Springer Science+Business Media Dordrecht.

  • JOURNAL ARTICLE
    Amin SM, Weiss DJ, Blunt MJ, Mohd Amin S, Weiss DJ, Blunt MJ, Mohd Amin S, Weiss DJ, Blunt MJet al., 2014,

    Reactive transport modelling of geologic CO2 sequestration in saline aquifers: The influence of pure CO2 and of mixtures of CO2 with CH4 on the sealing capacity of cap rock at 37 degrees C and 100 bar

    , CHEMICAL GEOLOGY, Vol: 367, Pages: 39-50, ISSN: 0009-2541

    The costs of CO 2 separation for carbon capture and storage can be reduced through capturing less pure CO 2 . The presence of impurities such as methane (CH 4 ) in the CO 2 gas stream, however, affects the geochemical and geophysical processes in the subsurface. The dissolved CO 2 in the brine decreases the pH which dissolves minerals such as calcite and albite. The dissolution of these minerals increases the amount of Ca 2+ and Na + in the brine. The presence of these ions leads the precipitation of the secondary solid carbonates calcite and dawsonite. To test this process, we developed a kinetic batch and a one-dimensional reactive transport model using PHREEQC 2.15.0, to predict mineral alteration induced in the cap rock by penetration of brine containing dissolved CO 2 from the underlying aquifer over a period of 10,000years. The chemical composition of the Nordland shale formation water that overlies the Utsira sand in the Sleipner field was used as a model case in this study. The model was run for pure CO 2 and for mixtures with CH 4 (1-4 (w/w)%) in the injected gas stream at a temperature of 37°C and at a pressure of 100bar. The simulations suggest that a mixture of CO 2 and CH 4 suppresses an anticipated increase in the porosity of the cap rock. Thus, our results suggest that injection of a CO 2 -CH 4 mixture inhibits cap rock dissolution and helps maintain the sealing capacity of the cap rock, while reducing separation costs. © 2014 Elsevier B.V.

  • CONFERENCE PAPER
    Anastasaki E, Xiang J, Latham JP, 2014,

    BUILDING CONCRETE UNIT ARMOURED BREAKWATERS IN A NUMERICAL MODEL ENVIRONMENT - A NEW PLACEMENT TECHNIQUE

    , Coasts, Marine Structures and Breakwaters 2013: From Sea to Shore - Meeting the Challenges of the Sea
  • JOURNAL ARTICLE
    Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJet al., 2014,

    Pore-scale contact angle measurements at reservoir conditions using X-ray microtomography

    , ADVANCES IN WATER RESOURCES, Vol: 68, Pages: 24-31, ISSN: 0309-1708

    Contact angle is a principal control of the flow of multiple fluid phases through porous media; however its measurement on other than flat surfaces remains a challenge. A new method is presented for the measurement of the contact angle between immiscible fluids at the pore scale at reservoir conditions (10MPa and 50°C) inside a quarry limestone through the use of X-ray microtomography. It is applied to a super-critical CO 2 -brine-carbonate system by resampling the micro-CT data onto planes orthogonal to the contact lines, allowing for vectors to be traced along the grain surface and the CO 2 -brine interface. A distribution of contact angles ranging from 35° to 55° is observed, indicating that the CO 2 -brine-carbonate system is weakly water-wet. This range of contact angles can be understood as the result of contact angle hysteresis and surface heterogeneity on a range of length scales. Surface heterogeneity is examined by comparison of micro-CT results with optical thin sections and SEM images. © 2014 The Authors.

  • JOURNAL ARTICLE
    Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJet al., 2014,

    Pore-scale imaging of trapped supercritical carbon dioxide in sandstones and carbonates

    , INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL, Vol: 22, Pages: 1-14, ISSN: 1750-5836

    Geological carbon dioxide storage must be designed such that the CO 2 cannot escape from the rock formation into which it is injected, and often simple stratigraphic trapping is insufficient. CO 2 can be trapped in the pore space as droplets surrounded by water through capillary trapping. X-ray microtomography was used to image, at a resolution of 6.6μm, the pore-scale arrangement of these droplets in three carbonates and two sandstones. The pressures and temperatures in the pore space were representative of typical storage formations, while chemical equilibrium was maintained between the CO 2 , brine and rock phases to replicate conditions far away from the injection site. In each sample substantial amounts of CO 2 were trapped, with the efficiency of trapping being insensitive to pore-morphology and chemistry. Apart from in one extremely well connected sample, the size distribution of residual ganglia larger than 10 5 voxel 3 obey power law distributions with exponents broadly consistent with percolation theory over two orders of magnitude. This work shows that residual trapping can be used to locally immobilise CO 2 in a wide range of rock types. © 2014 The Authors.

  • JOURNAL ARTICLE
    Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJ, Andrew M, Bijeljic B, Blunt MJet al., 2014,

    Pore-by-pore capillary pressure measurements using X-ray microtomography at reservoir conditions: Curvature, snap-off, and remobilization of residual CO2

    , WATER RESOURCES RESEARCH, Vol: 50, Pages: 8760-8774, ISSN: 0043-1397

    © 2014. American Geophysical Union. All Rights Reserved. X-ray microtomography was used to image the shape and size of residual ganglia of supercritical CO 2 at resolutions of 3.5 and 2 μm and at representative subsurface conditions of temperature and pressure. The capillary pressure for each ganglion was found by measuring the curvature of the CO 2 -brine interface, while the pore structure was parameterized using distance maps of the pore space. The formation of the residual clusters by snap-off was examined by comparing the ganglion capillary pressure to local pore topography. The capillary pressure was found to be inversely proportional to the radius of the largest restriction (throat) surrounding the ganglion, which validates the imbibition mechanisms used in pore-network modeling. The potential mobilization of residual ganglia was assessed using a reformulation of both the capillary (N cmacro ) and Bond numbers (N bmacro ), rigorously based on a balance of pore-scale forces, with the majority of ganglia remobilized at N cmacro around 1. Buoyancy forces were found to be small in this system (N bmacro < < 1), meaning the gravitational remobilization of CO 2 after residual trapping would be extremely difficult.

  • CONFERENCE PAPER
    Andrew MG, Bijeljic B, Blunt MJ, 2014,

    Reservoir-condition pore-scale imaging -contact angle, wettability, dynamics and trapping

    , Pages: 2804-2808

    Firstly capillary trapping is examined in a range of five different rock types, including both carbonates and sandstones. Rocks are imaged both after drainage and imbibition, and in all cases between 65-70% of the CO2 in place after drainage was trapped. Trapped cluster size distributions are compared to rock connectivity as determined using pore network modelling. Better connected pore-spaces tend to have more large clusters relative to small clusters, and visa-versa. This is important as small clusters are more difficult to remobilise by viscous and gravitational forces. They also present a relatively larger surface area for reaction and mineralization. Secondarily wettability is analysed by measuring contact angle manually. In order to do this the contact line was found in 3D and the data set resampled onto planes perpendicular to the contact line at a particular point. Contact angles ranging from 35-55o were found, indicating that the super-critical CO2-brine-carbonate system is weakly water wet. The range in contact angles is interpreted as the result of contact angle hysteresis associated with surface heterogeneity. Finally the first images of CO2 drainage at reservoir conditions are also presented, imaged at Diamond Light Source, represented an unprecented depth of information about pore-scale flow processes.

  • CONFERENCE PAPER
    Bardy G, Biver P, Caumon G, Renard P, Corpel V, King PRet al., 2014,

    Proxy comparison for sorting models and assessing uncertainty on oil recovery profiles

    To study the impact of subsurface uncertainties on oil recovery, it is common to build a large set of models which cover these uncertainties. Despite increase of computational capabilities, as models become more complex, it is not possible to perform full physic flow simulation for all the generated models. This is why stochastic reservoir model sets are often decimated to assess the impact of static uncertainties on dynamic reservoir performance. This contribution will focus on the use of proxy to perform this data set reduction. A lot of different proxies have been developed, from the simplest to the more complicated so it is difficult to choose the good one according to a particular goal. We present different criteria to compare the proxy quality and their helps to assess uncertainties on oil recovery. A first criterion will be based on the relation which may exists between the model distances computed on the proxy responses and those compute on flow responses. Another criterion is the speed factor and simplification provide by the proxy compared to the full physic simulator. These two criteria are very simple and can be applied in an early time to avoid deploying time consuming proxies which won't provide accurate information. The last criterion presented here, is the confidence intervals which can be computed around probabilistic reservoir production forecasts computed on a small representative subset of model. Even if this criterion can be used only when the entire dataset has been simulated, it provides some quantification about a possible bias created by a proxy and the remaining uncertainties on oil recovery. We present here a comparison study between widely different proxy responses applied on a real dataset of that methodology. This will give us some keys to choose a proxy which is a good compromise between accuracy and easy to handle methodology.

  • JOURNAL ARTICLE
    Blumenfeld R, Edwards SF, Blumenfeld R, Edwards SF, Blumenfeld R, Edwards SFet al., 2014,

    Granular statistical mechanics - a personal perspective

    , EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, Vol: 223, Pages: 2189-2204, ISSN: 1951-6355

    © 2014, EDP Sciences and Springer. The science of granular matter has expanded from an activity for specialised engineering applications to a fundamental field in its own right. This has been accompanied by an explosion of research and literature, which cannot be reviewed in one paper. A key to progress in this field is the formulation of a statistical mechanical formalism that could help develop equations of state and constitutive relations. This paper aims at reviewing some milestones in this direction. An essential basic step toward the development of any static and quasi-static theory of granular matter is a systematic and useful method to quantify the grain-scale structure and we start with a review of such a method. We then review and discuss the ongoing attempt to construct a statistical mechanical theory of granular systems. Along the way, we will clarify a number of misconceptions in the field, as well as highlight several outstanding problems.

  • JOURNAL ARTICLE
    Boot-Handford ME, Abanades JC, Anthony EJ, Blunt MJ, Brandani S, Mac Dowell N, Fernandez JR, Ferrari M-C, Gross R, Hallett JP, Haszeldine RS, Heptonstall P, Lyngfelt A, Makuch Z, Mangano E, Porter RTJ, Pourkashanian M, Rochelle GT, Shah N, Yao JG, Fennell PS, Boot-Handford ME, Abanades JC, Anthony EJ, Blunt MJ, Brandani S, Mac Dowell N, Fernández JR, Ferrari MC, Gross R, Hallett JP, Haszeldine RS, Heptonstall P, Lyngfelt A, Makuch Z, Mangano E, Porter RTJ, Pourkashanian M, Rochelle GT, Shah N, Yao JG, Fennell PS, Boot-Handford ME, Abanades JC, Anthony EJ, Blunt MJ, Brandani S, Mac Dowell N, Fernández JR, Ferrari M-C, Gross R, Hallett JP, Haszeldine RS, Heptonstall P, Lyngfelt A, Makuch Z, Mangano E, Porter RTJ, Pourkashanian M, Rochelle GT, Shah N, Yao JG, Fennell PSet al., 2014,

    Carbon capture and storage update

    , ENERGY & ENVIRONMENTAL SCIENCE, Vol: 7, Pages: 130-189, ISSN: 1754-5692

    In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO < inf > 2 < /inf > from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO < inf > 2 < /inf > capture technologies, available in the short and long term, and their technological maturity, before discussing CO < inf > 2 < /inf > transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO < inf > 2 < /inf > from the air and CO < inf > 2 < /inf > reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS. © 2014 The Royal Society of Chemistry.

  • JOURNAL ARTICLE
    Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJ, Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJ, Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJ, Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJ, Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJ, Carriero A, Zimmermann EA, Paluszny A, Tang SY, Bale H, Busse B, Alliston T, Kazakia G, Ritchie RO, Shefelbine SJet al., 2014,

    How Tough Is Brittle Bone? Investigating Osteogenesis Imperfecta in Mouse Bone

    , Journal of Bone and Mineral Research, Vol: 29, Pages: 1392-1401, ISSN: 1523-4681

    The multiscale hierarchical structure of bone is naturally optimized to resist fractures. In osteogenesis imperfecta, or brittle bone disease, genetic mutations affect the quality and/or quantity of collagen, dramatically increasing bone fracture risk. Here we reveal how the collagen defect results in bone fragility in a mouse model of osteogenesis imperfecta (oim), which has homotrimeric α1(I) collagen. At the molecular level, we attribute the loss in toughness to a decrease in the stabilizing enzymatic cross-links and an increase in nonenzymatic cross-links, which may break prematurely, inhibiting plasticity. At the tissue level, high vascular canal density reduces the stable crack growth, and extensive woven bone limits the crack-deflection toughening during crack growth. This demonstrates how modifications at the bone molecular level have ramifications at larger length scales affecting the overall mechanical integrity of the bone; thus, treatment strategies have to address multiscale properties in order to regain bone toughness. In this regard, findings from the heterozygous oim bone, where defective as well as normal collagen are present, suggest that increasing the quantity of healthy collagen in these bones helps to recover toughness at the multiple length scales.

  • JOURNAL ARTICLE
    Ciotta F, Trusler JPM, Vesovic V, Ciotta F, Trusler JPM, Vesovic V, Ciotta F, Trusler JPM, Vesovic V, Ciotta F, Trusler JPM, Vesovic Vet al., 2014,

    Extended hard-sphere model for the viscosity of dense fluids

    , FLUID PHASE EQUILIBRIA, Vol: 363, Pages: 239-247, ISSN: 0378-3812

    An extended hard-sphere model is reported that may be applied to correlate and predict the viscosity of gases, liquids and supercritical fluids. The method is based on the hard-sphere model of Dymond and Assael and uses their roughness factors and molar core volumes to relate reduced viscosity to a universal function of reduced volume. The extended model behaves correctly in the limit of low densities and offers improved accuracy at high densities. The new universal reference function was determined from a large database of experimental viscosities for alkanes extending up to reduced densities of 0.84. It has been tested by correlating the viscosity of two high-viscosity liquids not used in the development of the universal function and has shown to perform satisfactorily up to reduced densities of approximately 0.9. © 2013 Elsevier B.V.

  • JOURNAL ARTICLE
    Dale A, John CM, Mozley PS, Smalley PC, Muggeridge AH, Dale A, John CM, Mozley PS, Smalley PC, Muggeridge AH, Dale A, John CM, Mozley PS, Smalley PC, Muggeridge AHet al., 2014,

    Time-capsule concretions: Unlocking burial diagenetic processes in the Mancos Shale using carbonate clumped isotopes

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 394, Pages: 30-37, ISSN: 0012-821X

    Septarian carbonate concretions contain carbonate precipitated during progressive growth of the concretion and subsequent fracture-filling. As such, they have been used to track variations in δ 13 C and δ 18 O of pore waters during diagenesis and to define diagenetic zones in clastic rocks. However, the δ 18 O value of the carbonate is dependent on precipitation temperature and the δ 18 O value of the pore fluid from which it precipitated. Interpretations must assume one of these parameters, both of which are highly variable through time in diagenetic settings. Carbonate clumped isotopes of the cement can provide independent estimates of temperature of precipitation, allowing the pore-water δ 18 O to be back-calculated. Here, we use this technique on carbonate concretions and fracture fills of the Upper Cretaceous Prairie Canyon Member, Mancos Shale, Colorado. We sampled concretions from two permeable horizons separated by a 5 m shale layer, with one permeable horizon containing concretions with septarian fractures. We show cores precipitated at cooler temperatures (31 °C, ~660 m burial depth) than the rims (68 °C (~1980 m burial depth) and relate that to the δ 13 C carbonate values to suggest the concretion core precipitated in the methanogenic zone, with increasing input from thermogenically produced CO 2 . The two concretion-bearing horizons have different back-calculated δ 18 O porewater values (mean -2.65‰ and 1.13‰ VSMOW) for cements formed at the same temperature and similar δ 13 C values, suggesting the shale layer present between the two horizons acted as a barrier to fluid mixing. Additionally, the δ 18 O carbonate of the septarian fractures (-13.8‰ VPBD) are due to precipitation at high temperatures (102 to 115 °C) from a fluid with a mean δ 18 O porewater of 0.32‰ (VSMOW). Therefore, we can tie in the cementation history of the formation to temporal an

  • JOURNAL ARTICLE
    Deveugle PEK, Jackson MD, Hampson GJ, Stewart J, Clough MD, Ehighebolo T, Farrell ME, Calvert CS, Miller JK, Deveugle PEK, Jackson MD, Hampson GJ, Stewart J, Clough MD, Ehighebolo T, Farrell ME, Calvert CS, Miller JKet al., 2014,

    A comparative study of reservoir modeling techniques and their impact on predicted performance of fluvial-dominated deltaic reservoirs

    , AAPG BULLETIN, Vol: 98, Pages: 729-763, ISSN: 0149-1423

    Multiple techniques are available to construct three-dimensional reservoir models. This study uses comparative analysis to test the impact of applying four commonly used stochastic modcling techniques to capture geologic heterogeneity and fluid-flow behavior in fluvial-dominated deltaic reservoirs of complex facies architecture: (1) sequential indicator simulation; (2) object-based modeling; (3) multiple-point statistics (MPS); and (4) spectral component geologic modeling. A reference for comparison is provided by a high-resolution model of an outcrop analog that captures facies architecture at the scale of parasequences, delta lobes, and fades-association belts. A sparse, pseudosubsurface data set extracted from the reference model is used to condition models constructed using each stochastic reservoir modeling technique. Models constructed using all four algorithms fail to match the facies-association proportions of the reference model because they are conditioned to well data that sample a small, unrepresentative volume of the reservoir. Simulated sweep efficiency is determined by the degree to which the modeling algorithms reproduce two aspects of fades architecture that control sand-body connectivity: (1) the abundance, continuity, and orientation of channelized fluvial sand bodies; and (2) the lateral continuity of barriers to vertical flow associated with flooding surfaces. The MPS algorithm performs best in this regard. However, the static and dynamic performance of the models (as measured against facies-association proportions, facies architecture, and recovery factor of the reference model) is more dependent on the quality and quantity of conditioning data and on the interpreted geologic scenario(s) implicit in the models than on the choice of modeling technique. Copyright ©2014. The American Association of Petroleum Geologists. All rights reserved.

  • JOURNAL ARTICLE
    Fitch PJR, Jackson MD, Hampson GJ, John CM, Fitch PJR, Jackson MD, Hampson GJ, John CM, Fitch PJR, Jackson MD, Hampson GJ, John CMet al., 2014,

    Interaction of stratigraphic and sedimentological heterogeneities with flow in carbonate ramp reservoirs: impact of fluid properties and production strategy

    , PETROLEUM GEOSCIENCE, Vol: 20, Pages: 7-26, ISSN: 1354-0793

    It is well known that heterogeneities in carbonate reservoirs impact fluid flow during production. However, few studies have examined the impact of the same heterogeneities on flow behaviour with different fluid properties and production scenarios. We use integrated flow simulation and experimental design techniques to investigate the relative, first-order impact of stratigraphic and sedimentological heterogeneities on simulated recovery in carbonate ramp reservoirs. Two production strategies are compared, which promote dominance of either horizontal or vertical flow. We find that the modelled geology is more important than the simulated fluid proper ties and production scenarios over the ranges tested. Of the heterogeneities modelled here, rock properties and stratigraphic heterogeneities that control reservoir architecture and the spatial distribution of environment of deposition (EOD) belts are important controls on recovery regardless of the production strategy. The presence of cemented hardground surfaces becomes the key control on oil recovery in displacements dominated by vertical flow. Permeability anisotropy is of low importance for all production strategies. The impacts of stratigraphic heterogeneities on recovery factor and water breakthrough are more strongly influenced by fluid properties and well spacing in displacements dominated by vertical flow. These results help to streamline the reservoir modelling process, by identifying key heterogeneities, and to optimize production strategies. © 2014 EAGE/The Geological Society of London.

  • JOURNAL ARTICLE
    Go J, Bortone I, Muggeridge A, Smalley C, Go J, Bortone I, Muggeridge A, Smalley C, Go J, Bortone I, Muggeridge A, Smalley C, Go J, Bortone I, Smalley PC, Muggeridge Aet al., 2014,

    Predicting Vertical Flow Barriers Using Tracer Diffusion in Partially Saturated, Layered Porous Media

    , TRANSPORT IN POROUS MEDIA, Vol: 105, Pages: 255-276, ISSN: 0169-3913

    © 2014, Springer Science+Business Media Dordrecht. Sudden changes in isotopic tracer concentration in pore waters have been interpreted as indicating barriers to vertical advective flow through porous rocks in the subsurface, e.g. step changes in 87 Sr/ 86 Sr ratio are often used in the oil and gas industry as a signature of reservoir compartmentalisation. This study shows that this is not necessarily the case. It can take millions of years for such step changes to equilibrate by diffusion if there is no flow resulting from pressure or density gradients even in high permeability, high porosity rocks, particularly if the water saturation is low. Changes in tracer concentration gradients can be good indicators of changes in porosity (or water saturation) between layers. In contrast changes in sorption without a change in porosity are almost impossible to identify. The time taken for concentration gradients to equilibrate is affected by the layer properties but can be quickly estimated from the harmonic average of the effective diffusion coefficient for each layer and a simple analytical expression for a homogeneous system. This was achieved by performing a sensitivity analysis on different layer properties (porosity contrast, saturation contrast, sorption contrast, thickness ratio) using existing analytical solutions for diffusion in layered systems.

  • JOURNAL ARTICLE
    Guadagnini A, Blunt MJ, Riva M, Bijeljic B, Guadagnini A, Blunt MJ, Riva M, Bijeljic B, Guadagnini A, Blunt MJ, Riva M, Bijeljic Bet al., 2014,

    Statistical Scaling of Geometric Characteristics in Millimeter Scale Natural Porous Media

    , TRANSPORT IN POROUS MEDIA, Vol: 101, Pages: 465-475, ISSN: 0169-3913

    We analyze statistical scaling of structural attributes of two millimeter scale rock samples, Estaillades limestone and Bentheimer sandstone. The two samples have different connected porosities and pore structures. The pore-space geometry of each sample is reconstructed via X-ray micro-tomography at micrometer resolution. Directional distributions of porosity and specific surface area (SSA), which are key Minkowski functionals (geometric observables) employed to describe the pore-space structure, are calculated from the images, and scaling of associated order-q sample structure functions of absolute incremental values is analyzed. Increments of porosity and SSA tend to be statistically dependent and persistent (tendency for large and small values to alternate mildly) in space. Structure functions scale as powers ξ(q) of directional separation distance or lag, s, over an intermediate range of s, displaying breakdown in power law scaling at large and small lags. Powers ξ(q) of porosity and SSA inferred from moment and extended self-similarity (ESS) analyses of limestone and sandstone data tend to be quasi-linear and nonlinear (concave) in q, respectively. We observe an anisotropic behavior for ξ(q), which appears to be mild for the porosity of the sandstone sample while it is marked for both porosity and SSA of the limestone rock sample. The documented nonlinear scaling behavior is amenable to analysis by viewing the variables as samples from sub-Gaussian random fields subordinated to truncated fractional Brownian motion or fractional Gaussian noise. © 2013 Springer Science+Business Media Dordrecht.

  • JOURNAL ARTICLE
    Hellmann R, Bich E, Vogel E, Vesovic V, Hellmann R, Bich E, Vogel E, Vesovic V, Hellmann R, Bich E, Vogel E, Vesovic V, Hellmann R, Bich E, Vogel E, Vesovic Vet al., 2014,

    Intermolecular potential energy surface and thermophysical properties of the CH4-N-2 system

    , JOURNAL OF CHEMICAL PHYSICS, Vol: 141, Pages: 224301-224301, ISSN: 0021-9606

    A five-dimensional potential energy surface (PES) for the interaction of a rigid methane molecule with a rigid nitrogen molecule was determined from quantum-chemical ab initio calculations. The counterpoise-corrected supermolecular approach at the CCSD(T) level of theory was utilized to compute a total of 743 points on the PES. The interaction energies were calculated using basis sets of up to quadruple-zeta quality with bond functions and were extrapolated to the complete basis set limit. An analytical site-site potential function with nine sites for methane and five sites for nitrogen was fitted to the interaction energies. The PES was validated by calculating the cross second virial coefficient as well as the shear viscosity and binary diffusion coefficient in the dilute-gas limit for CH4-N2 mixtures. An improved PES was obtained by adjusting a single parameter of the analytical potential function in such a way that quantitative agreement with the most accurate experimental values of the cross second virial coefficient was achieved. The transport property values obtained with the adjusted PES are in good agreement with the best experimental data.

  • JOURNAL ARTICLE
    Kang PK, de Anna P, Nunes JP, Bijeljic B, Blunt MJ, Juanes R, Kang PK, De Anna P, Nunes JP, Bijeljic B, Blunt MJ, Juanes R, Kang PK, de Anna P, Nunes JP, Bijeljic B, Blunt MJ, Juanes Ret al., 2014,

    Pore-scale intermittent velocity structure underpinning anomalous transport through 3-D porous media

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 41, Pages: 6184-6190, ISSN: 0094-8276

    © 2014. American Geophysical Union. We study the nature of non-Fickian particle transport in 3-D porous media by simulating fluid flow in the intricate pore space of real rock. We solve the full Navier-Stokes equations at the same resolution as the 3-D micro-CT (computed tomography) image of the rock sample and simulate particle transport along the streamlines of the velocity field. We find that transport at the pore scale is markedly anomalous: longitudinal spreading is superdiffusive, while transverse spreading is subdiffusive. We demonstrate that this anomalous behavior originates from the intermittent structure of the velocity field at the pore scale, which in turn emanates from the interplay between velocity heterogeneity and velocity correlation. Finally, we propose a continuous time random walk model that honors this intermittent structure at the pore scale and captures the anomalous 3-D transport behavior at the macroscale.

  • JOURNAL ARTICLE
    Lang PS, Paluszny A, Zimmerman RW, Lang PS, Paluszny A, Zimmerman RW, Lang PS, Paluszny A, Zimmerman RW, Lang PS, Paluszny A, Zimmerman RWet al., 2014,

    Permeability tensor of three-dimensional fractured porous rock and a comparison to tracemap predictions

    , JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 119, Pages: 6288-6307, ISSN: 2169-9313

    © 2014. American Geophysical Union. All Rights Reserved. The reduction from three- to two-dimensional analysis of the permeability of a fractured rock mass introduces errors in both the magnitude and direction of principal permeabilities. This error is numerically quantified for porous rock by comparing the equivalent permeability of three-dimensional fracture networks with the values computed on arbitrarily extracted planar trace maps. A method to compute the full permeability tensor of three-dimensional discrete fracture and matrix models is described. The method is based on the element-wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and is validated against analytical expressions for periodic anisotropic porous media. For isotropic networks of power law size-distributed fractures with length-correlated aperture, two-dimensional cut planes are shown to underestimate the magnitude of permeability by up to 3 orders of magnitude near the percolation threshold, approaching an average factor of deviation of 3 with increasing fracture density. At low-fracture densities, percolation may occur in three dimensions but not in any of the two-dimensional cut planes. Anisotropy of the equivalent permeability tensor varies accordingly and is more pronounced in two-dimensional extractions. These results confirm that two-dimensional analysis cannot be directly used as an approximation of three-dimensional equivalent permeability. However, an alternative expression of the excluded area relates trace map fracture density to an equivalent three-dimensional fracture density, yielding comparable minimum and maximum permeability. This formulation can be used to approximate three-dimensional flow properties in cases where only two-dimensional analysis is available.

  • JOURNAL ARTICLE
    Leal AMM, Blunt MJ, LaForce TC, Leal AMM, Blunt MJ, LaForce TCet al., 2014,

    Efficient chemical equilibrium calculations for geochemical speciation and reactive transport modelling

    , GEOCHIMICA ET COSMOCHIMICA ACTA, Vol: 131, Pages: 301-322, ISSN: 0016-7037
  • JOURNAL ARTICLE
    Lei Q, Latham J-P, Xiang J, Tsang C-F, Lang P, Guo L, Lei Q, Latham JP, Xiang J, Tsang CF, Lang P, Guo L, Lei Q, Latham J-P, Xiang J, Tsang C-F, Lang P, Guo L, Lei Q, Latham J-P, Xiang J, Tsang C-F, Lang P, Guo Let al., 2014,

    Effects of geomechanical changes on the validity of a discrete fracture network representation of a realistic two-dimensional fractured rock

    , INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, Vol: 70, Pages: 507-523, ISSN: 1365-1609

    This paper aims to examine the validity of the discrete fracture network (DFN) method in representing a realistic two-dimensional fractured rock in terms of their geomechanical response to in-situ stresses and hydraulic behaviour in a steady state fluid field. First, a real fracture network is extracted from the geological map of an actual rock outcrop, which is termed the analogue fracture network (AFN). Multiple DFN realisations are created using the statistics of the analogue pattern. A conductivity parameter that was found to have a linear relationship with the conductivity of 2D fracture networks is included to further enhance network similarity. A series of numerical experiments are designed with far-field stresses applied at a range of angles to the rock domains and their geomechanical response is modelled using the combined finite-discrete element method (FEMDEM). A geomechanical comparison between the AFN and its DFN equivalents is made based on phenomena such as heterogeneity of fracture-dependent stress contours, sliding between pre-existing fracture walls, coalescence of propagating fractures and variability of aperture distribution. Furthermore, an indirect hydro-mechanical (HM) coupling is applied and the hydraulic behaviour of the porous rock models is investigated using the hybrid finite element-finite volume method (FEFVM). A further comparison is conducted focusing on the hydraulic behaviour of the AFN and DFNs under the effects of geomechanical changes. The results show that although DFNs may represent an AFN quite well for fixed mechanical conditions, such a representation may not be dependable if mechanical changes occur. © 2014 Elsevier Ltd.

  • CONFERENCE PAPER
    Lei Q, Latham JP, Xiang J, Lang Pet al., 2014,

    Coupled FEMDEM-DFN model for characterising thestress-dependent permeability of an anisotropic fracture system

    , 1st International Conference on Discrete Fracture Network Engineering

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