Typical urban flood flow features are usually computed using two-dimensional numerical models. How such modelling can be implemented in dense urban areas with obstacles is investigated. A strategy for representing the effect of urban obstacles in various flow conditions is defined. The comparison between the available laboratory measurements and the model results show that if the water depth is high enough and the flow remains subcritical, two-dimensional modelling with constant eddy viscosity provides the effect of the obstacles on the flow distribution accurately, even with a coarse mesh; moreover, an oversimplified representation of the sidewalks averaging the street cross section elevations seems sufficient. Oppositely, if the water depth is low and/or the flow becomes supercritical, the description of the flow is not relevant enough and it generates errors in the flow distribution at the crossroads.
Floods in dense urban areas propagatemainly through the streets, where the flow can be locally affected by elements of urban topography. This study aims at assessing the need of integrating detailed topography in numerical models when simulating urban floods. Acoustic Doppler Velocimetry and Large Scale Particle Image Velocimetry measurements in an experimental three branch junction representing a city crossroad are used to calibrate a numerical model solving the 2D shallow water equations. A constant eddy viscosity model proves to be accurate enough to calculate velocity fields, but such model requires a fine calibration against experimental data. Simulations run with this calibrated model are performed to study the impact of obstacles and sidewalks representative of urban areas. It is found that obstacles located in the downstream branch can highly perturb the velocities distribution downstream of the junction, whereas obstacles located in the upstream branches have less influence. The presence of sidewalks results in reduced flow section and higher velocities, but additional effects occur within and downstream of the junction. Simulations presented here show the need of considering detailed topography and elements of urban furniture if local velocities have to be represented.
Because stakes are concentrated in urban environment, flood modelling should be carried out there with high accuracy. However, uncertainties remain important because of:-the estimate of the inputs, these inputs being either rainfalls, or flows coming from the upstream basin or from the exchanges with the sewage network;-the complexity of the processes, which includes a frequent change of the flow regime-from subcritical to supercritical and oppositely-, the difficulty in predicting the flow distribution at the street junctions, the oscillations created by waves reflecting against , for instance, obstacles or walls of houses;-the parameters of the flooded area: variable roughness, very irregular topography, moving obstacles in the streets, water entering the built-up areas, etc. An assessment of these uncertainties is presented for a few examples coming from laboratory experiments or from the two-dimensional modelling of flood events in French towns. These latter results can be used in order to estimate the range of uncertainty during field studies.
With the growing numbers of aging wellbores, recompletion programs help to reduce temporarily abandoned well counts, identify and prove future development potential, boost production and maximize return on investment. Typically base well completion programs have been composed of four main project types: recompletions, rework in the existing zone, sidetracks, and deepenings. This paper summarizes the lessons learned and recommendations from an active deepening campaign in the Permian Basin. Deepening projects provide a cheaper and lower risk alternative to drilling new wellbores and can achieve the same objectives of zone testing and infill drilling potential evaluation. Once infill potential is proved up through deepening projects further value and scale can be exploited through infill drilling programs. Two types of deepenings were executed, open hole and cased hole. Casedhole deepenings are more complex and costly, but must be attempted in the cases where openhole deepening is not feasible. Such cases may include deepening across water-bearing or depleted zones, deepening in prolonged pay intervals (>350ft), zones with poor hole stability or incompatible formation fluids. In a stacked pay carbonate rock the stimulation is an important part of the completion process. Therefore deepening projects may have different scopes which may include some isolation work in open or casedhole, single-stage or multi-stage acidizing and fracturing. The three key pillars which must be in place to deliver a successful deepening program are sound wellbore conditions, reliable well history, and proper equipment selection. Given that deepening projects are implemented less frequently than other well intervention activities and new drilling activity, the equipment selection and the understanding of how to operate that equipment become critical success factors in these projects. It was observed that the time and cost associated with wellbore cleanouts before deepening may drastically change the project economics. The risks associated with poor well integrity and the presence of junk or fish in the wellbore need to be quantified in the candidate selection phase. Changing from roller-cone to PDC bits and adjusting drilling parameters increased the deepening ROP by 300%. This paper compares the historical performance of 10 deepening projects. It contains a list of operational risks and follow-up plans needed to ensure cost effective and safe execution.
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