Short radius well

Short radius wells are usually drilled from a cased or uncased vertical well. Articulated drill collars are used to drill to 90° or beyond. A second stabilized assembly is used to drill the rest of the hole, usually in 4-J or 6-J-in. diameter. 

Figure 4-347. Schematics of different types of wells or drains (a) ultrashort radius (b) short radius (c) medium radius (d) long radius. (From Ref. [127].)...

In this section, we consider the transient adsorption of a solute from a dilute solution in a constant-volume, well-mixed batch system or, equivalently, adsorption of a pure gas. The solutions provided can approximate the response of a stirred vessel containing suspended adsorbent particles, or that of a very short adsorption bed. Uniform, spherical particles of radius are assumed. These particles, initially of uniform adsorbate concentration, are assumed to be exposed to a step change in concentration of the external fluid. 

From profile data to be discussed shortly, it was found that Zone II was approximated only at reaction temperatures of 1305° and higher. The overall rate of reaction curve for this temperature is given in Fig. 11. If it is assumed that the abrupt change in reaction rate after 4-min. reaction time occurs at the onset of equilibrium burning, the measured decrease in external radius of the rod can be assumed to have occurred between 4 and 8 min., and b can be calculated. The value of b is found to agree well with the rate calculated from Fig. 11. 

Consider a molecule above a surface with the distance from the surface being normal to the surface. There are two competitive types of influence occuring (a) repulsion between the cloud of electrons in the atoms that form the surface and those of the molecule and (b) van der Waals nuclear attraction force. The nuclear attraction has a much shorter radius of influence and as a result of the balance of these two forces, there is a well in the potential energy curve at a short distance from the surface, as shown in Figure 2.1. Molecules or atoms that reach this well are trapped or adsorbed by this potential energy well and cannot escape, unless they obtain enough kinetic energy to be desorbed. 

Fig. 31 Overall interaction energy between two DNA-coated colloids, (a) Sketch of the interacting surfaces of two spheres of radius R0 separated by d. The maximum length of hybridized strands is 2L. (b) Total interaction energy as a function of d. It is the sum of the attractive I/DNA from the binding of accessible DNA strands, the repulsive I/rep from electrostatics and/or polymer steric effect, and the van der Waals attraction t/vdw. (c) For weak, short-range I/rep, particles which are unbound at high temperatures are irreversibly trapped in the van der Waals well after DNA hybridization at low temperatures, (d) For strong, medium-range I/rep, DNA binding produces a secondary minimum of reversible aggregation. Reproduced with permission from [138]...

Calculations carried out by Johnson and Morrison [Jj for alumina particles of 0.25 pm radius covered by 22.5 A shells show that the potential energy of interaction is reduced from about —175 kT to about —25 kT. The major effect of the shell is to eliminate the short-range attraction by separating the particles. Differences due to the Hamakcr constant of the shell arc also significant, the difference between the shallowest and deepest well being 20 kT. 

A function of the vacuum chamber for surface spectroscopy is convenient placement of the sample surface at the focal points of the various spectrometers and at appropriate points for ion bombardment, immersion, and electrolysis. A sample manipulator for this purpose typically provides rotation about the axis of the cylindrical vacuum chamber with the sample offset 2.5-6 in. from the axis. By arranging the focal points of the spectrometers (LEED, Auger, XPS, etc.) on a circle of radius equal to the offset, the sample reaches the focal points by means of this single rotation. Short translations ( 0.5 in.) in Cartesian coordinates (X, Y, Z) permit fine adjustment of sample position. A coaxial rotation about an axis parallel to the sample surface allows exact to normal or other angles of incidence or emission, as well as alteration between front and back surfaces of the sample. All motions are bellows-activated. Flexible (braided) electrical connections to the sample allow electrical heating of the sample, and measurement of particle beam currents as well as electrolytic current. 

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