DRAWDOWN

From the above plot, it can be seen that the recovery factor for gas reservoirs depends upon how low an abandonment pressure can be achieved. To produce at a specified delivery pressure, the reservoir pressure has to overcome a series of pressure drops the drawdown pressure (refer to Figure 9.2), and the pressure drops in the tubing, processing facility and export pipeline (refer to Figure 9.12). To improve recovery of gas, compression facilities are often provided on surface to boost the pressure to overcome the pressure drops in the export line and meet the delivery pressure specified. 

The difference between the flowing wellbore pressure (P, ) and the average reservoir pressure reservoir pressure (P) is the pressure drawdown (AP q). 

The relationship between the flowrate (Q) towards the well and the pressure drawdown is approximately linear, and is defined by the productivity index (PI). 

It is common practice to record the bottom hole pressure firstly during a flowing period (pressure drawdown test), and then during a shut-in period (pressure build-up test). During the flowing period, the FBHP is drawn down from the initial pressure, and when the well is subsequently shut in, the bottom hole pressure builds up. 

In the simplest case, for a pressure drawdown survey, the radial inflow equation indicates that the bottom hole flowing pressure is proportional to the logarithm of time. From the straight line plot ot pressure against the log (time), the reservoir permeability can be determined, and subsequently the total skin of the well. For a build-up survey, a similar plot (the so-called Horner plot) may be used to determine the same parameters, whose values act as an independent quality check on those derived from the drawdown survey. 

Drawdown and build-up surveys are typically performed once a production well has been completed, to establish the reservoir property of permeability (k), the well completion efficiency as denoted by its skin factor (S), and the well productivity index (PI). Unless the routine production tests indicate some unexpected change in the well s productivity, only SBHP surveys may be run, say once a year. A full drawdown and build-up survey would be run to establish the cause of unexplained changes in the well s productivity. 

The previous sections have considered the flow of fluid to the wellbore. The productivity index (PI) indicates that as the flowing wellbore pressure (Pwf) reduces, so the drawdown increases and the rate of fluid flow to the well increases. Recall... 

From downhole pressure drawdown and build-up surveys the reservoir permeability, the well productivity index and completion skin can be measured. Any deviation from previous measurements or from the theoretically calculated values should be investigated to determine whether the cause should be treated. 

Drakkar Noir Dramamine DRAM cells DRAM devices Draperies Drawdown Drawing molten glass Draw-texturing Drew-Pfitzner ligands Dried algae meal Driente Driers... 

When drawdown is high, the film may be uniaxially oriented and the properties of the final film isotropic. In the manufacture of strapping tape this effect is accentuated. If the cast or quenched film is to be used to feed an orientation tine, additional attention must be given to the amorphous—crystalline nature of the film ia the draw processes so that maximum strength can be achieved and uniform gauge and optical quality maintained. Slot casting is used for the orientation of these resins, polyesters, polyamides, and a variety of others. 

First,/)-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) are acetylated to produce the low melting acetate esters which are molten at 200°C. In an inert gas, the two monomers are melted together at 200°C. The temperature is raised to 250—280°C and acetic acid is coUected for 0.5 to 3 h. The temperature is raised to 280—340°C and additional acetic acid is removed in vacuum for a period of 10 to 60 min. The opalescent polymer melt produced is extmded through a spinning jet, foUowed by melt drawdown. The use of the paraUel offset monomer, acetylated HNA, results in the formation of a series of random copolyesters of different compositions, many of which faU within the commercially acceptable melting range of... 

Uranium production in 1992 of 36,246 t U was only about 63% of world reactor requirements of 57,182 t U the remainder, 20,950 t U, was met from inventory drawdown. The worldwide production shortfall has developed since 1990 when production exceeded reactor requirements by about 1000 t U (27). 

Supply Projections. Additional supphes are expected to be necessary to meet the projected production shortfall. A significant contribution is likely to come from uranium production centers such as Eastern Europe and Asia, which are not included in the capabihty projections (27). The remaining shortfall between fresh production and reactor requirements is expected to be filled by several alternative sources, including excess inventory drawdown. These shortfalls could also be met by the utili2ation of low cost resources that could become available as a result of technical developments or pohcy changes, production from either low or higher cost resources not identified in production capabihty projections, recycled material such as spent fuel, and low enriched uranium converted from the high enriched uranium (HEU) found in warheads (28). 

Drawdown from the die to nip is typically ca 10%. Sheet extmsion requires that the resin be of high melt viscosity to prevent excessive sag of the melt between the die and the nip. The melt should reach the nip before touching any other part of the middle roU to prevent uncontrolled cooling of the resin. The appearance of the lower surface of the sheet is deterrnined by the middle roU, ie, its poHsh, surface temperature, and freedom from condensed materials. The upper surface is cooled by air and has a more glossy appearance. Neither the top roU nor the bottom roU greatly affect the appearance of the top surface of the sheet. Edges of the sheet are trimmed. 

The melt flows from the extmder iato the die where it flows around the bend and around the core tube. On the far side of the core tube, it forms a weld. Melt sticks to and is pulled by the moving wire. Details of the sizes and shapes of the die parts ia contact with the melt are important ia obtaining a smooth coating at high rates. The die exit usually is the same diameter as that of the coated wire and there is Httle drawdown. Die openings are small and pressures iaside the die are high at ca 35 MPa (5000 psi). Wire takeup systems operate as high as 2000 m /min. 

Extensional Viscosity. AH three types of extensional viscosity can be measured (101,103) uniaxial, biaxial, and pure shear. Only a few commercial instmments are available, however, and most measurements are made with improvised equipment. Extensional viscosity of polymer melts can be estimated from converging flow (entrance pressure) or from a melt strength drawdown test (208). 

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