Assessment of the Impact of Wax Deposition in a Pre-Salt Project

Despite pre-salt fields in Brazil usually having high production per well, one of the areas presents a reservoir with low permoporosity, which results in small flowrates with fluid temperatures during production below the one that is critical for wax deposition. The operations commonly used to remove the wax deposits are diesel soaking and pigging, which brings production losses and OPEX increase. Thus, the economic analysis should consider these events reducing the operational efficiency of production. To evaluate the production drop due to wax deposition, it was necessary to perform a loop test to determine the wax growth throughout time. With a multiphase simulator, it is possible to choose the deposition model and the diffusion coefficient that best fits the analyzed fluid. However, one of the limitations of this first analysis is the lack of data to determine the effect of the shear stripping, as the test is performed under a laminar flow. As this term plays an important role in wax growth, it was necessary to add to the simulation model the shear coefficient fitted from another pre-salt field. With this information, it will be possible to make a more reliable evaluation of the impact of wax deposition, increasing the confidence in the production curve, OPEX and NPV of the full field project. This paper shows the methodology that has been applied to evaluate the impact of wax deposition in pre-salt fields. It presents the deposition model, and its coefficients used to fit the multiphase transient models to a pre-salt field.

Deviations from classical droplet evaporation theory

In this article, we show that significant deviations from the classical quasi-steady models of droplet evaporation can arise solely due to transient effects in the gas phase. The problem of fully transient evaporation of a single droplet in an infinite atmosphere is solved in a generalized, dimensionless framework with explicitly stated assumptions. The differences between the classical quasi-steady and fully transient models are quantified for a wide range of the 10-dimensional input domain and a robust predictive tool to rapidly quantify this difference is reported. In extreme cases, the classical quasi-steady model can overpredict the droplet lifetime by 80%. This overprediction increases when the energy required to bring the droplet into equilibrium with its environment becomes small compared with the energy required to cool the space around the droplet and therefore establish the quasi-steady temperature field. In the general case, it is shown that two transient regimes emerge when a droplet is suddenly immersed into an atmosphere. Initially, the droplet vaporizes faster than classical models predict since the surrounding gas takes time to cool and to saturate with vapour. Towards the end of its life, the droplet vaporizes slower than expected since the region of cold vapour established in the early stages of evaporation remains and insulates the droplet.

Comparison of permafrost mean annual ground temperature derived from two different satellite-based schemes: land surface temperature based (ESA CCI+ Permafrost) versus surface status (Metop ASCAT)

<p>Different approaches exist for a satellite-based estimation of mean annual ground temperature (MAGT). Landsurface temperature can be ingested by transient models. Surface status information (frozen/unfrozen days) has been shown to be applicable for the estimation of ground temperature as well. Such approaches are based on an empirically defined relationship. Both approaches have been evaluated with in situ bore hole measurements, but not yet compared with each other.</p><p>A comparison between yearly arctic mean temperatures, derived from the advanced scatterometer (ASCAT) and data from ESA’s CCI+ Permafrost project was carried out. The used ASCAT record is available from 2008 (first full year) onwards while the latest CCI+ Permafrost data is available from 1997 to 2018. The ASCAT data was recorded by satellites whose measurements are only intermittently available as one flyover over the whole arctic north of 60°N takes two days on average. To fill in the missing values exponentially weighted moving averages (EWMA) were used. From the number of frozen days an expected average temperature was derived based on Kroisleitner et al. (2018).</p><p>The CCI+ Permafrost data incorporates modelled MAGT for depths between the surface down to a depth of 10 meters. These data points were extracted from the raster files (~1km resolution) and averaged over polygons representing an approximation of the ASCAT grid (footprint approximation). Single polygon areas range from 150-160 km². Only footprints for which data is available in both records (and thus permafrost presence) have been eventually compared.</p><p>The CCI+ Permafrost data shows an average surface temperature of -1.42 °C for the areas analyzed between 2008 and 2018 while the statistically padded ASCAT data suggests a mean temperature of -1.18 °C over the same time period. The ASCAT retrieval corresponds to a general MAGT whereas CCI+ Permafrost values are available for certain depths. Water fraction within ASCAT footprint also affect the quality of the derivation of frozen days. New calibration considering certain depths and water fraction is suggested.</p>

Heat Transfer Considerations on the Spontaneous Triggering of Vapor Explosions—A Review

Vapor explosions have been investigated both theoretically and experimentally for several decades, focusing either on the vapor film, or on mechanical aspects. Where the main interest for industry lies in the safety risks of such an event, fundamental research is focusing on all partial processes that occur during a vapor explosion. In this paper, vapor explosions are discussed from a heat transfer point of view. Generally accepted knowledge of heat transfer between hot surfaces and liquids is compared to early investigations regarding the origin of vapor explosions. Both steady state and transient models are discussed. The review of available literature suggests that vapor explosions trigger spontaneously by the collapse of the boiling film. Better understanding of the fundamental aspects of vapor explosions might give rise to future ideas on how to avoid them.

Endothelial S1P 1 Signaling Counteracts Infarct Expansion in Ischemic Stroke

Rationale: Cerebrovascular function is critical for brain health, and endogenous vascular-protective pathways may provide therapeutic targets for neurological disorders. Sphingosine 1-phosphate (S1P) signaling coordinates vascular functions in other organs, and S1P receptor-1 (S1P 1 ) modulators including fingolimod show promise for the treatment of ischemic and hemorrhagic stroke. However, S1P 1 also coordinates lymphocyte trafficking, and lymphocytes are currently viewed as the principal therapeutic target for S1P 1 modulation in stroke. Objective: To address roles and mechanisms of engagement of endothelial cell (EC) S1P 1 in the naïve and ischemic brain and its potential as a target for cerebrovascular therapy. Methods and Results: Using spatial modulation of S1P provision and signaling, we demonstrate a critical vascular protective role for endothelial S1P 1 in the mouse brain. With an S1P 1 signaling reporter, we reveal that abluminal polarization shields S1P 1 from circulating endogenous and synthetic ligands after maturation of the blood-neural barrier, restricting homeostatic signaling to a subset of arteriolar ECs. S1P 1 signaling sustains hallmark endothelial functions in the naïve brain, and expands during ischemia by engagement of cell-autonomous S1P provision. Disrupting this pathway by EC-selective deficiency in S1P production, export, or the S1P 1 receptor substantially exacerbates brain injury in permanent and transient models of ischemic stroke. By contrast, profound lymphopenia induced by loss of lymphocyte S1P 1 provides modest protection only in the context of reperfusion. In the ischemic brain, EC S1P 1 supports blood-brain barrier (BBB) function, microvascular patency, and the rerouting of blood to hypo-perfused brain tissue through collateral anastomoses. Selective S1P 1 agonism counteracts cortical infarct expansion after middle cerebral artery occlusion by engaging the endothelial receptor pool after BBB penetration. Conclusions: This study provides genetic evidence to support a pivotal role for the endothelium in maintaining perfusion and microvascular patency in the ischemic penumbra that is coordinated by S1P signaling and can be harnessed for neuroprotection with BBB-penetrating S1P 1 agonists.