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- Al-Marooqi, S.H, et al.
(författare)
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Pore-Scale modelling of NMR relaxation for the characterization of wettability
- 2006
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Ingår i: Journal of Petroleum Science and Engineering. - : Elsevier BV. - 0920-4105 .- 1873-4715. ; 52:1-4, s. 172-186
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Tidskriftsartikel (refereegranskat)abstract
- Several research groups are currently investigating the determination of wettability usingNMR relaxation times. Although correlations with traditional wettability indices have been presented with some success, further effort is needed to relate the wettability atpore-scale to a core-scale measurement of NMR response. For example, a qualitative method using the arithmetic mean of relaxation times at various saturations has been presented [Guan, H., Brougham, D., Sorbie, K.S., Packer, K.J., 2002. Wettability effects in a sandstone reservoir and outcrop cores from NMR relaxation time distributions. J. Petroleum Sci. and Eng. 34, 35-54] and a wettability index that quantifies the amount of surface area that is wetted either by oil or by water, by using the T2 peak at four different saturations has been proposed [Fleury, M., Deflandre, F., 2003. Quantitative evaluation of porous media wettability using NMR relaxometry. Mag. Reson. Imaging 21, 385-387]. Our group at the Imperial College have previously shown experimentally that the T2 distribution provides valuable information about wettability and overall fluid distribution within thepore-space, which is lost if only a single value from the T2 distribution is considered [Al-Mahrooqi, S.H., Grattoni, C.A., Moss, A.K., Jing, X.D., 2003. An investigation of the effect ofwettability on NMR characteristics of sandstone rock and fluid systems. J. Petroleum Sci. and Eng. 39, 389-398]. In this paper we use a simple pore-scale model to understand the effect of wetting and its relationship with NMR relaxation times. The model uses triangular capillary pores with a given pore size distribution. The oil/water distribution within thepores is obtained as a function of capillary pressure and wettability. At a given capillary pressure, the volumes and surface areas of water and oil are calculated for each individual pore. This allows us to calculate the theoretical T2 distribution for that pore size distribution as a function of wettability and saturation. We have used the model to study the T2 distribution for a range of wettabilities and saturations. Results from the model confirmed previous observations from experiments regarding the effect of wettability onNMR T2 distributions. Based on these qualitative results, an improved index for characterising wettability from the T2 distribution has been proposed. We tested the proposed index using NMR T2 data from synthetic and real sandstone core plugs with different wettabilities, ranging from strongly water-wet to strongly oil-wet. Comparison between the proposed index and wettability for the synthetic samples and Amott-Harvey index for core plugs show good correlation.
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- Carpenter, Stephen R., et al.
(författare)
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Accelerate Synthesis in Ecology and Environmental Sciences
- 2009
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Ingår i: BioScience. - : Oxford University Press (OUP). - 0006-3568 .- 1525-3244. ; 59:8, s. 699-701
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Tidskriftsartikel (refereegranskat)abstract
- Ecology is a leading discipline in the synthesis of diverse knowledge. Ecologists have had considerable experience in bringing together diverse, multinational data sets, disciplines, and cultural perspectives to address a wide range of issues in basic and applied science. Now is the time to build on this foundation and invest in ecological synthesis through new national or international programs. While synthesis takes place through many mechanisms, including individual efforts, working groups, and research networks, centers are extraordinarily effective institutional settings for advancing synthesis projects.
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- Ekneligoda, Thushan C., et al.
(författare)
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Boundary perturbation solution for nearly circular holes and rigid inclusions in an infinite elastic medium
- 2008
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Ingår i: Journal of applied mechanics. - : ASME International. - 0021-8936 .- 1528-9036. ; 75:1, s. 011015-
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Tidskriftsartikel (refereegranskat)abstract
- The boundary perturbation method is used to solve the problem of a nearly circular rigid inclusion in a two-dimensional elastic medium subjected to hydrostatic stress at infinity. The solution is taken to the fourth order in the small parameter epsilon that quantifies the magnitude of the variation of the radius of the inclusion. This result is then used to find the effective bulk modulus of a body that contains a dilute concentration of such inclusions. The corresponding results for a cavity are obtained by setting the Muskhelishvili coefficient K equal to -1, as specified by the Dundurs correspondence principle. The results for nearly circular pores can be expressed in terms of the pore compressibility. The pore compressibilities given by the perturbation solution are tested against numerical values obtained using the boundary element method, and are shown to have good accuracy over a substantial range of roughness values.
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- Ekneligoda, Thushan C., et al.
(författare)
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Shear compliance of two-dimensional pores possessing N-fold axis of rotational symmetry
- 2008
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Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 464:2091, s. 759-775
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Tidskriftsartikel (refereegranskat)abstract
- We use the complex variable method and conformal mapping to derive a closed-form expression for the shear compliance parameters of some two-dimensional pores in an elastic material. The pores have an N-fold axis of rotational symmetry and can be represented by at most three terms in the mapping function that conformally maps the exterior of the pore into the interior of the unit circle. We validate our results against the solutions of some special cases available in the literature, and against boundary-element calculations. By extrapolation of the results for pores obtained from two and three terms of the Schwarz-Christoffel mapping function for regular polygons, we find the shear compliance of a triangle, square, pentagon and hexagon. We explicitly verify the fact that the shear compliance of a symmetric pore is independent of the orientation of the pore relative to the applied shear, for all cases except pores of fourfold symmetry. We also show that pores having fourfold symmetry, or no symmetry, will have shear compliances that vary with cos 4 theta. An approximate scaling law for the shear compliance parameter, in terms of the ratio of perimeter squared to area, is proposed and tested.
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- Moreau, D., et al.
(författare)
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A two-time-scale dynamic-model approach for magnetic and kinetic profile control in advanced tokamak scenarios on JET
- 2008
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 48:10
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Tidskriftsartikel (refereegranskat)abstract
- Real-time simultaneous control of several radially distributed magnetic and kinetic plasma parameters is being investigated on JET, in view of developing integrated control of advanced tokamak scenarios. This paper describes the new model-based profile controller which has been implemented during the 2006-2007 experimental campaigns. The controller aims to use the combination of heating and current drive (H&CD) systems-and optionally the poloidal field (PF) system-in an optimal way to regulate the evolution of plasma parameter profiles such as the safety factor, q(x), and gyro-normalized temperature gradient,. rho*(Te)(x). In the first part of the paper, a technique for the experimental identification of a minimal dynamic plasma model is described, taking into account the physical structure and couplings of the transport equations, but making no quantitative assumptions on the transport coefficients or on their dependences. To cope with the high dimensionality of the state space and the large ratio between the time scales involved, the model identification procedure and the controller design both make use of the theory of singularly perturbed systems by means of a two-time-scale approximation. The second part of the paper provides the theoretical basis for the controller design. The profile controller is articulated around two composite feedback loops operating on the magnetic and kinetic time scales, respectively, and supplemented by a feedforward compensation of density variations. For any chosen set of target profiles, the closest self-consistent state achievable with the available actuators is uniquely defined. It is reached, with no steady state offset, through a near-optimal
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- Von Lensa, W., et al.
(författare)
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Red-impact : A European research programme to assess the impact of partitioning and transmutation on final nuclear waste disposal
- 2008
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Ingår i: Int. Congr. Adv. Nucl. Power Plants - ICAPP, "Nucl. Renaiss. Work". - 9781604238716 ; , s. 2564-2573
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Konferensbidrag (refereegranskat)abstract
- It is the objective of the EU-funded 'Red-Impact' project to analyse the impact of partitioning, transmutation and waste reduction technologies on the final nuclear waste disposal. The partnership of 25 organisations is originating from European nuclear industry, waste agencies, research centres and universities. The system studies focus on a realistic evolution of P&T technologies and advanced fuel cycles which can be deployed incrementally on an industrial scale as well as on future developments such as reactors of the third and fourth generation (Gen III & Gen IV) and Accelerator Driven Systems (ADS). A comprehensive inventory of all existing and foreseen nuclear fuel cycle facilities in Europe has been performed including a review on worldwide ongoing R&D programs on P&T. Thus, it was possible to select a set of three so-called "industrial scenarios", taking into account industrial feasibility of alternate strategies leading to increased actiniae burning and reduced actinide generation based on direct disposal (reference case) or MOXfuel for LWR and plutonium recycle in Sodium Fast Reactors (SFR). R&D needs for the development of processes and technologies have also been addressed. In addition, three 'innovative scenarios ' have been identified allowing multi-recycling of plutonium and minor actinides in SFR and Accelerator-Driven Systems (ADS) as well as GANEX or COEXprocess and PYRO reprocessing technologies. Waste streams have been calculated for all of these scenarios including the transition from the present situation towards new fuel cycle options. These data provide the input to specific analyses on the impact on geological disposal in different host formations such as granite, clay and salt. The results show that advanced fuel cycles influence the required size of the geological repository in case of disposal in clay, salt or hard rock formations. Recycling of all the actinides results in a reduction of the necessary gallery length (depending on geology and design) at least by a factor 3. If additionally cesium and strontium are extracted from the high-level waste for separate decay, the reduction factor will become 10 or more. In the frame of the project, the feasibility and the impact of the Cs or Sr separated management were not assessed or evaluated. Transmutation of the actinides fast neutron spectrum reactors (FR or ADS) results in a limited reduction of the maximum dose because the dose is essentially due to long-lived fission and activation products. On the other hand, reprocessing the spent fuel decreases the maximum dose at the storage with a factor 5 because a considerable fraction of the iodine is separated from the high level waste during reprocessing. The radiotoxicity in the high level waste or spent fuel as well as human intrusion doses after 500 years are drastically reduced by the transmutation of the actinides. Evaluating actinide minimization systems and industrialised P&T in general requires an assessment of relevant nuclear fuel cycles especially with regard to the economic, environmental and societal advantages/disadvantages (i.e. the sustainability of the fuel cycles). Thus, a set of indicators has been derived for each of these areas. The results are analysed using the multi-criterion analysis approach which allows the importance of each of the indicators to be specified.
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| 19. |
- Westlén, Daniel, et al.
(författare)
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Impact of P&T on geological repositories an overview of the euratom red impact project
- 2007
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Ingår i: GLOBAL 2007. - 0894480553 - 9780894480553 ; , s. 772-781
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Konferensbidrag (refereegranskat)abstract
- The European Commission project Red Impact is in a state of conclusion after three years. Within the project, the consequences of P&T on, mainly, geological disposal have been investigated. Six scenarios have been developed, including three considered to be deployable today, and three more advanced scenarios including P&T in different ways. The scenarios all have different strengths and weaknesses, which are discussed in the present paper.
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