Background: Surgical mortality data are collected routinely in high-income countries, yet virtually no low-or middle-income countries have outcome surveillance in place. The aim was prospectively to collect worldwide mortality data following emergency abdominal surgery, comparing findings across countries with a low, middle or high Human Development Index (HDI).Methods: This was a prospective, multicentre, cohort study. Self-selected hospitals performing emergency surgery submitted prespecified data for consecutive patients from at least one 2-week interval during July to December 2014. Postoperative mortality was analysed by hierarchical multivariable logistic regression.
Wind-formed ripples are distinctive features of many sandy aeolian environments, and their development and migration are basic responses to sand transport via saltation. Using data from the literature and from original field experiments, we presented empirical models linking dimensionless migration rates, urgd (ur is the ripple migration speed, g is the gravity acceleration, and d is the grain diameter) with dimensionless shear velocity, u*/u*t (u* is shear velocity and u*t is fluid threshold shear velocity). Data from previous studies provided 34 usable cases from four wind tunnel experiments and 93 cases from two field experiments. Original data comprising 68 cases were obtained from sites in Ceará, Brazil (26) and California, USA (42), using combinations of sonic anemometry, sand traps, photogrammetry, and laser distance sensors and particle counters. The results supported earlier findings of distinctively different relationships between urgd and u*/u*t for wind tunnel and field data. With our data, we could also estimate the contribution of creep transport associated with ripple migration to total transport rates. We calculated ripple-creep transport for 1 ≤ u*/u*t ≤ 2.5 and found that this accounted for about 3.6% (standard deviation = 2.3%) of total transport.
Summary An experimental investigation of volumetric sweep during fireflooding was conducted in three- dimensional (3D) scaled models. The effect of oxygen vs. air injection, water/oxygen ratios, injection rates, and crude-oil parameters on sweep efficiency and performance of the fireflood were evaluated. Results indicate that the sweep of a fireflood was similar for both oxygen and air combustion; water injection resulted in a small decrease in the sweep of the fireflood; wet combustion required less oxygen or air and increased the oil recovery and recovery rate; fireflooding a medium-gravity crude-oil reservoir resulted in a larger sweep than a heavy-oil reservoir; and (within the limited range of this study) higher injection rates improved the sweep efficiency. Introduction Fireflooding or in-situ combustion is an important enhanced recovery process that has been studied extensively the past 30 years. This process has been considered particularly applicable for in-situ exploitation of medium particularly applicable for in-situ exploitation of medium and heavy oil resources. Although many successful field projects have been reported in the literature, projects have been reported in the literature, considerable development may be required before fireflooding can be extensively applied in heavy-oil reservoirs on a commercial basis. Oxygen fireflooding and fire-water flooding are two process variations that could improve both the technical process variations that could improve both the technical performance and the economic feasibility of in-situ performance and the economic feasibility of in-situ combustion. Both variations have the potential for reducing the primary expense of oxygen injection and increasing the rate of recovery. Oxygen fireflooding involves the injection of pure oxygen or oxygen-enriched air instead of compressed air. Oxygen injection could be cheaper than air at high pressures and flow rates. There has been much speculation pressures and flow rates. There has been much speculation that the sweep efficiency could be improved with oxygen injection. The many possible technical and economic advantages of oxygen fireflooding and the potential hazards have been discussed in the literature. Combustion-tube tests comparing various oxygen concentrations have been reported. In addition, field experiments have been performed, and several additional projects are in progress. performed, and several additional projects are in progress. Fire-water flooding is a recovery technique in which water is injected simultaneously with air (or oxygen). Fire-water flooding can improve the fireflood performance by reducing the air requirement, by recovering some of the heat remaining behind the combustion front, and by improving the recovery as a result of a larger steam bank. Dry and wet fireflooding have been compared in laboratory combustion-tube tests and field pilots.
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