Common Practices

When the pressure is low and mixture conditions are far from critical, activity coefficients are essentially independent of pressure. For such conditions it is common practice to set P = P in Equations (18) and (19). Coupled with the assumption that v = v, substitution gives the familiar equation... 

Because of the existence of numerous isomers, hydrocarbon mixtures having a large number of carbon atoms can not be easily analyzed in detail. It is common practice either to group the constituents around key components that have large concentrations and whose properties are representative, or to use the concept of petroleum fractions. It is obvious that the grouping around a component or in a fraction can only be done if their chemical natures are similar. It should be kept in mind that the accuracy will be diminished when estimating certain properties particularly sensitive to molecular structure such as octane number or crystallization point. 

It is common practice within oil companies to use expectation curves to express ranges of uncertainty. The relationship between probability density functions and expectation curves is a simple one. 

Analytical models using classical reservoir engineering techniques such as material balance, aquifer modelling and displacement calculations can be used in combination with field and laboratory data to estimate recovery factors for specific situations. These methods are most applicable when there is limited data, time and resources, and would be sufficient for most exploration and early appraisal decisions. However, when the development planning stage is reached, it is becoming common practice to build a reservoir simulation model, which allows more sensitivities to be considered in a shorter time frame. The typical sorts of questions addressed by reservoir simulations are listed in Section 8.5. 

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. 

When a production or injection well is drilled, it is common practice to cement in place a casing which extends across the reservoir interval. The alternative is to leave the reservoir uncased, in a so-called bare foot completion, which is rarely done. When the drilling department finishes its work on the well, it is often left in the state of a cased hole, as on the left of Figure 9.14. 

Before entering the detailed discussion of physical and chemical adsorption in the next two chapters, it is worthwhile to consider briefly and in relatively general terms what type of information can be obtained about the chemical and structural state of the solid-adsorbate complex. The term complex is used to avoid the common practice of discussing adsorption as though it occurred on an inert surface. Three types of effects are actually involved (1) the effect of the adsorbent on the molecular structure of the adsorbate, (2) the effect of the adsorbate on the structure of the adsorbent, and (3) the character of the direct bond or local interaction between an adsorption site and the adsorbate. 

Values of are small for weak acids and they range very widely (Table 4.1). It is common practice to quote values as the negative logarithm to the base ten, i.e. — logjo K.. since such numbers are less cumbersome and positive when Aj < 1. The symbol for -logio is by convention "p/ fhus -logjo becomes pK,. Table 4.1 shows some typical pAg values. 

In molecular mechanics and molecular dynamics studies of proteins, assig-ment of standard, non-dynamical ionization states of protein titratable groups is a common practice. This assumption seems to be well justified because proton exchange times between protein and solution usually far exceed the time range of the MD simulations. We investigated to what extent the assumed protonation state of a protein influences its molecular dynamics trajectory, and how often our titration algorithm predicted ionization states identical to those imposed on the groups, when applied to a set of structures derived from a molecular dynamics trajectory [34]. As a model we took the bovine... 

However, it is common practice to sample an isothermal isobaric ensemble NPT, constant pressure and constant temperature), which normally reflects standard laboratory conditions well. Similarly to temperature control, the system is coupled to an external bath with the desired target pressure Pq. By rescaling the dimensions of the periodic box and the atomic coordinates by the factor // at each integration step At according to Eq. (46), the volume of the box and the forces of the solvent molecules acting on the box walls are adjusted. 

It is common practice to omit the second summation on the right hand side of (11.118) on the groiands that it is small compared with the contribution of the conductive flux, which appears on the left hand side. However, this may not be so If the reactions are rapid and the thermal conductivity of the pellet material is low. One should, therefore, at least be aware of the approximation involved in the fona of the enthalpy balance most commonly seen in the literature. 

In most biochemical reactions the pH of the medium is close to 7 At this pH car boxylic acids are nearly completely converted to their conjugate bases Thus it is common practice m biological chemistry to specify the derived carboxylate anion rather than the carboxylic acid itself For example we say that glycolysis leads to lactate by way of pyruvate... 

Nitdles may be prepared by several methods (1). The first nitrile to be prepared was propionitdle, which was obtained in 1834 by distilling barium ethyl sulfate with potassium cyanide. This is a general preparation of nitriles from sulfonate salts and is referred to as the Pelou2e reaction (2). Although not commonly practiced today, dehydration of amides has been widely used to produce nitriles and was the first commercial synthesis of a nitrile. The reaction of alkyl hahdes with sodium cyanide to produce nitriles (eq. 1) also is a general reaction with wide appHcabiUty ... 

Thermodynamic consistency requites 5 1 = q 2y but this requirement can cause difficulties when attempts ate made to correlate data for sorbates of very different molecular size. For such systems it is common practice to ignore this requirement, thereby introducing an additional model parameter. This facihtates data fitting but it must be recognized that the equations ate then being used purely as a convenient empirical form with no theoretical foundation. 

Whatever the physiology of odor perception may be, the sense of smell is keener than that of taste (22). If flavors are classed into odors and tastes as is common practice in science, it can be calculated that there are probably more than 10 possible sensations of odor and only a few, perhaps five, sensations of taste (13,21,35—37). Just as a hereditary or genetic factor may cause taste variations between individuals toward phenylthiourea, a similar factor may be in operation with odor. The odor of the steroid androsterone, found in many foods and human sweat, may eflcit different responses from different individuals. Some are very sensitive to it and find it unpleasant. To others, who are less sensitive to it, it has a musk or sandalwood-like smell. Approximately 50% of the adults tested cannot detect any odor even at extremely high concentrations. It is befleved that this abiUty is genetically determined (38). 

Steam also is blended with air in some gasification units to promote the overall process via the endothermic steam—carbon reaction to form carbon monoxide and hydrogen. This was common practice at the turn of the nineteenth century, when so-called producer gasifiers were employed to manufacture LHV gas from different types of biomass and wastes. The producer gas from biomass and wastes had heating values around 5.9 MJ /mr at... 

---