Naturally Fractured Reservoirs (NFR's) have received little attention as potential CO2 storage sites. Two main facts deter from storage projects in fractured reservoirs: (1) CO2 tends to be nonwetting in target formations and capillary forces will keep CO2 in the fractures, which typically have low pore volume; and (2) the high conductivity of the fractures may lead to increased spatial spreading of the CO2 plume. Numerical simulations are a powerful tool to understand the physics behind brine‐CO2 flow in NFR's. Dual‐porosity models are typically used to simulate multiphase flow in fractured formations. However, existing dual‐porosity models are based on crude approximations of the matrix‐fracture fluid transfer processes and often fail to capture the dynamics of fluid exchange accurately. Therefore, more accurate transfer functions are needed in order to evaluate the CO2 transfer to the matrix. This work presents an assessment of CO2 storage potential in NFR's using dual‐porosity models. We investigate the impact of a system of fractures on storage in a saline aquifer, by analyzing the time scales of brine drainage by CO2 in the matrix blocks and the maximum CO2 that can be stored in the rock matrix. A new model to estimate drainage time scales is developed and used in a transfer function for dual‐porosity simulations. We then analyze how injection rates should be limited in order to avoid early spill of CO2 (lost control of the plume) on a conceptual anticline model. Numerical simulations on the anticline show that naturally fractured reservoirs may be used to store CO2.
The linear friction welding (LFW) process-of the type required for production of bladed discs for the next-generation aeroengines-was modeled using numerical methods developed previously. An elastic-viscoplastic material formulation was considered to allow for residual stress calculations to be included in the numerical solution. A study of the evolution of residual stress during the welding and cooling processes was made. It was evident that residual stresses arose primarily as a consequence of the cooling of the part after joining is completed. The sensitivity of predicted residual stress to the applied forge load was investigated and compared with measurements from X-ray diffraction methods. Only small changes in residual stress were predicted for large changes in forge load, supporting the hypothesis that the welding process is only of secondary importance to residual stress formation, after the cooling process. Finally, a sensitivity study was carried out investigating the accuracy of modeling the welding process with a simpler, viscoplastic material law, and only switching to the more computationally demanding elastic-viscoplastic law for the cooling modeling. Predictions suggested that this was a sufficient modeling method, given that stress during the welding stage is almost uncorrelated to that present once ambient temperature is reached.
Spontaneous countercurrent imbibition into a finite porous medium is an important physical mechanism for many applications, included but not limited to irrigation, CO 2 storage, and oil recovery. Symmetry considerations that are often valid in fractured porous media allow us to study the process in a onedimensional domain. In 1-D, for incompressible fluids and homogeneous rocks, the onset of imbibition can be captured by self-similar solutions and the imbibed volume scales with ffiffi t p . At later times, the imbibition rate decreases and the finite size of the medium has to be taken into account. This requires numerical solutions. Here we present a new approach to approximate the whole imbibition process semianalytically. The onset is captured by a semianalytical solution. We also provide an a priori estimate of the time until which the imbibed volume scales with ffiffi t p . This time is significantly longer than the time it takes until the imbibition front reaches the model boundary. The remainder of the imbibition process is obtained from a selfsimilarity solution. We test our approach against numerical solutions that employ parametrizations relevant for oil recovery and CO 2 sequestration. We show that this concept improves common first-order approaches that heavily underestimate early-time behavior and note that it can be readily included into dual-porosity models. Key Points: New physically based model for spontaneous imbibition Model captures transition from earlytime to late-time imbibition Model validated for different applications Correspondence to: R. March, rafael.march@pet.hw.ac.uk Citation: March, R., F. Doster, and S. Geiger (2016), Accurate early-time and latetime modeling of countercurrent spontaneous imbibition, Water Resour.
Geological reservoirs can be extensively fractured but the well-test signatures observed in the wells may not show a pressure transient response that is representative of naturally fractured reservoirs (NFRs): for example, one that indicates two distinct pore systems (i.e. the mobile fractures and immobile matrix). Yet, the production behaviour may still be influenced by these fractures. To improve the exploitation of hydrocarbons from NFRs, we therefore need to improve our understanding of fluid-flow behaviour in fractures. Multiple techniques are used to detect the presence and extent of fractures in a reservoir. Of particular interest to this work is the analysis of well-test data in order to interpret the flow behaviour in an NFR. An important concept for interpreting well-test data from an NFR is the theory of dual-porosity model. However, several studies pointed out that the dual-porosity model may not be appropriate for interpreting well tests from all fractured reservoirs. This paper therefore uses geological well-testing insights to explore the limitations of the characteristic flow behaviour inherent to the dual-porosity model in interpreting well-test data from Type II and III NFRs of Nelson's classification. To achieve this, we apply a geoengineering workflow with discrete fracture matrix (DFM) modelling techniques and unstructured-grid reservoir simulations to generate synthetic pressure transient data in both idealized fracture geometries and real fracture networks mapped in an outcrop of the Jandaira Formation. We also present key reservoir features that account for the classic V-shape pressure derivative response in NFRs. These include effects of fracture skin, a very tight matrix permeability and wells intersecting a minor, unconnected fracture close to a large fracture or fracture network. Our findings apply to both connected and disconnected fracture networks.
Claves para la intervención con menores acogidos en recursos residenciales, que presentan conductas problemáticas Keys for intervention in residential care centers with minors presenting problematic behaviors RAFAEL MARCH 1 RESUMEN Este artículo presenta a modo de reflexión, algunas claves útiles para intervenir sobre los problemas de conducta que padecen algunos de los niños acogidos en los Centros de protección a la Infancia. Así, se comienza acotando los conceptos de "trastorno de conducta" y "conducta problemática" para posteriormente realizar un análisis de los elementos que interactúan en el hogar, y llegar a plantear los tres niveles que comporta la intervención sobre este tipo de conductas: La prevención, el abordaje de las crisis y los programas especializados. El primero de ellos, núcleo de este trabajo, se basa en el establecimiento de un encuadre relacional y normativo, flexible, dinámico y consensuado para todo el personal del centro. ABSTRACTThis article presents in a reflexive way, some useful keys to intervene on behavior problems showed by some of the children in residential care centers. In the first part, the concepts of "behavior disorder" and "behavior problem" are defined, and later on the author performs an analysis of the elements that interact within the "dynamic" of the centers, and establishes the three levels which complete the intervention on these kind of misconduct: prevention, crisis approach and specialized programs. The first of these levels, developed in this article, is based on the establishment of a relational and normative setting, which must be flexible, dynamic, and has to be agreed by the whole of the center working staff.
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