Diagnosis of formation damage mechanism allows choosing the right damage removal technology during seawater injection and Produced Water Re-Injection (PWRI). Reliable prediction of injectivity decline is essential for planning of well stimulation, fracturing, etc. Usually the stabilisation of well injectivity index after decline is explained by erosion of external filter cake, or by warm holes or even by fracture opening. Nevertheless, the stabilisation is observed in corefloods, which evidences internal erosion. So, particle deposit erosion must be considered to interpret the injectivity stabilisation. The particle erosion was described by introduction of a new particle storage capacity function which is equal to maximum retained concentration versus dimensionless flow velocity. After the maximum is reached by the retained concentration, particle capture does not happen any more. The particle storage capacity function is a reological characteristic that closes system of governing equations. The coreflood by suspension with permeability stabilisation was performed with a constant injection rate. Pressure drop on the core and rate have been measured during the flooding. The analytical model developed allows to perfectly match the experimental impedance curve and calculate from it three injectivity damage parameters - filtration and formation damage coefficients, and also the maximum retention concentration. The obtained values of filtration and formation damage coefficients are in the usual variation range for these coefficients. Introduction of just one new parameter - maximum retained concentration - into a classical suspension filtration model allows for significant enrichment of the physics schema for suspension transport and retention. An analytical model of suspension coreflood with piecewise constant rate shows that after changing the flow velocity from some value and coming back to the same value, the impedance returns to the initial constant velocity curve. It takes some time after an abrupt flux decrease to stabilise the resistance growth rate, while the resistance growth rate stabilises immediately after abrupt flux increase. If flow regime changes from low velocity to high velocity, there appears a short particle pulse at the outlet; it does not happen when velocity changes from high value to low value. Introduction Well injectivity decline is a wide spread phenomenon in waterflood projects 1–5. It happens during seawater flooding, producer water re-injection and, generally speaking, during injection of any poor quality water. The phenomenon is attributed to capture of solid and liquid particles by rock from the injected water causing the permeability and, consequently, the injectivity decline 6,7. After some partial filling of the porous space by particles near to the reservoir inlet cross-section (in the near-wellbore vicinity), the formation of external filter cake on the wellbore wall starts 8–12. The cake build-up causes further injectivity decline. This decline takes place for sometime, and stabilises afterwards 1,13. Injectivity stabilisation was explained by several different physics mechanisms. Particle dislodging is one of them. F. Civan 14 and M. Sharma 15,16 model the equilibrium of a "last" deposited particle on the cake surface via force balance or force moment (torque) balance. The larger is the cake, the lower is the filtrate velocity, the lower is the viscous force sticking the particle to the cake surface. At some critical cake thickness, the drag force (the drag force moment) exceeds the friction force caused by the permeate force (the permeate force moment) and no particles deposit on the cake surface any more. Similar approach was developed for particle dislodging and cake erosion on membranes 17–24. Another explanation for well injectivity stabilisation are warmholes sporadically disturbing the cake continuity and resulting in simultaneous particle penetration into reservoir and filtration via external cake 25,26. Observing the complex physical model for cake build-up and stabilization tuned from injectivity history of several wells 27, Dr. Z. Khatib and Dr. P. van den Hoeg (Shell) speculated that probably the so called comprehensive model of injectivity impairment is too complex and involves too many different physics mechanisms 28,29. They also commented that some structural changes in situ porous media are responsible for injectivity index stabilisation.

Como aferir e monitorizar desigualdades sociais na sociedade portuguesa contemporânea, nomeadamente à escala regional? Os debates científicos contemporâneos apelam para que as problemáticas das desigualdades e do desenvolvimento se aproximem entre si. Este artigo pretende ser um contributo para a compreensão das relações entre estas problemáticas, considerando as desigualdades sociais do país, as suas assimetrias regionais e as desvantagens específicas dos territórios de baixa densidade. Para o efeito, analisamos como a demografia, a educação, o emprego, as classes sociais e a saúde estão associadas a desigualdades sociais entre as regiões do território nacional. Os resultados da pesquisa apontam para a persistência, na sociedade portuguesa, de processos de desenvolvimento desiguais à escala regional e no que diz respeito aos territórios de baixa densidade.

Este artigo centra-se na constatação de que a proporção de crianças (0-17 anos) entre os beneficiários do Rendimento Social de Inserção (RSI) está a descer consistentemente desde há alguns anos, em contraste com uma taxa de pobreza infantil persistentemente alta. Esta contradição é demonstrada através da exploração dos dados sobre o RSI cruzados com as estatísticas do INE referentes à pobreza infantil (ICOR-EU-SILC), medida com base na pobreza monetária. É desenvolvida uma hipótese para explicar esta contradição, assente nas transformações legais do RSI e na dificuldade do estado em desenvolver medidas de apoio social com impacto na pobreza infantil.

No abstract

A educação e formação de adultos não se restringe, hoje, a práticas educativas que se definem por relação a um qualquer sistema escolar (ou profissional). Ainda assim, e sendo a aprendizagem transversal às várias dimensões da vida humana e passível de acontecer em distintos contextos sociais, é legítimo que se questionem, por via de um inquérito, 32 adultos analfabetos ou com baixos índices de literacia sobre a perspectiva que perfilham quanto à organização escolar. Porque alguns deles experienciaram essa realidade e precocemente a abandonaram, porque outros têm familiares mais novos a frequentarem a escola, porque todos vivem num espaço/tempo onde tal instituição detém um papel de realce para cada um e para a comunidade. Além disso, com recurso à associação de palavras ou a respostas relativamente breves a partir de questões específicas, torna-se possível ler as representações construídas face ao assunto em discussão –o significado e importância da escola–, por indivíduos com idades compreendidas entre os 28 e os 69 anos, assumindo que as suas dificuldades de literacia serão mais um problema social do que uma deficiência individual.