Rankings

Once a given lead compound is selected, the design project for a safer analog is defined. In all, the whole computer-aided process can be simply described in six major steps  

manipulation and optimization of lead compound(s) and soft drugs  

calculation of the necessary electronic properties and charge distributions 

calculation of log Po and log W using either equations from regression analysis or neural network approaches  

Following synthesis and experimental testing of a few best candidates, further refinements are possible for example, experimental results might suggest different weighting for properties used in ranking. Some illustrative examples are provided in the following chapter. 

---

Clearly, the conflicts that have arisen in this problem have not been too helpful in identifying sequences which are candidates for further evaluation. A little more intelligence could be used in apphcation of the heuristics, and they could be ranked in order of... 

Equation (5.8) tends to predict vapor loads slightly higher than those predicted by the full multicomponent form of the Underwood equation. The important thing, however, is not the absolute value but the relative values of the alternative sequences. Porter and Momoh have demonstrated that the rank order of total vapor load follows the rank order of total cost. 

Rank order Total vapor flow (kmol h )... 

Solution Table 5.4 gives the total vapor flow for difierent sequences in rank order. The sequence with the lowest total vapor flow is shown in Fig. 5.4. 

Had only one of the four heuristics been used throughout, the rank order for the sequence from each heuristic would have been... 

Heuristic Rank order of sequence from Table 5.4... 

In Example 5.3, heuristic 4 seemed to be the most important. Had heuristic 4 been used exclusively for this example, the sequence ranked fifth in Table 5.6 would have been obtained. 

The properties of the various coals in this ranking will vary considerably and many are used only for specific purposes. 

For similar molecular weights, the following are ranked by order of decreasing solubility ... 

The parametric method is an established statistical technique used for combining variables containing uncertainties, and has been advocated for use within the oil and gas industry as an alternative to Monte Carlo simulation. The main advantages of the method are its simplicity and its ability to identify the sensitivity of the result to the input variables. This allows a ranking of the variables in terms of their impact on the uncertainty of the result, and hence indicates where effort should be directed to better understand or manage the key variables in order to intervene to mitigate downside and/or take advantage of upside in the outcome. 

One significant feature of the Parametric Method is that it indicates, through the (1 + K 2) value, the relative contribution of each variable to the uncertainty in the result. Subscript i refers to any individual variable. (1 + K ) will be greater than 1.0 the higher the value, the more the variable contributes to the uncertainty in the result. In the following example, we can rank the variables in terms of their impact on the uncertainty in UR. We could also calculate the relative contribution to uncertainty. 

Figure 6.12 Ranking of impact of variables on uncertainty in reserves...

Keywords reducing uncertainty, cost-effective information, ranking sources of uncertainty, re-processing seismic, interference tests, aquifer behaviour, % uncertainty, decision tree analysis, value of information, fiscal regime, suspended wells, phased development. 

The same procedure may be used to rank the parameters themselves (GRV, N/G, ((>, S, Bg, recovery factor), to indicate which has the greatest influence on the HCIIP or ultimate recovery (UR). 

The ranking process is an important part of deciding an appraisal programme, since the activities should aim to reduce the uncertainty in those parameters which have the most impact on the range of uncertainty in HCIIP or UR. 

Keywords economic model, shareholder s profit, project cashflow, gross revenue, discounted cashflow, opex, capex, technical cost, tax, royalty, oil price, marker crude, capital allowance, discount rate, profitability indicators, net present value, rate of return, screening, ranking, expected monetary value, exploration decision making. 

With unlimited resources, the investor would take on all projects which meet the screening criteria. Project ranking is necessary to optimise the business when the investor s resources are limited and there are two or more projects to choose between. 

At discount rates less than 18%, Proposal 1 is more favourable in terms of NPV, whereas at discount rates above 18%, Proposal 2 is more attractive. NPV is being used here as a ranking tool for the projects. At a typical cost of capital of, say, 10%, Proposal 1... 

The plot immediately shows whioh of the parameters the 10% NPV is most sensitive to the one with the steepest slope. Consequently the variables can be ranked in order of their relative impact. 

When considering exploration economics, the possibility of spending funds with no future returns must be taken into account. A typical world-wide success rate for rank exploration activity is one commercial discovery for every ten wells drilled. Hence a probabilistic estimation of the reserves resulting from exploration activity must take into account the main risks and uncertainties in the volume of hydrocarbons in place, the recoverable hydrocarbons, and importantly the risk of finding no hydrocarbons at all. 

H. Schmidli. Reduced Rank Regression. Physica-Verlag, 1995. 

The multipole moment of rank n is sometimes called the 2"-pole moment. The first non-zero multipole moment of a molecule is origin independent but the higher-order ones depend on the choice of origin. Quadnipole moments are difficult to measure and experimental data are scarce [17, 18 and 19]. The octopole and hexadecapole moments have been measured only for a few highly syimnetric molecules whose lower multipole moments vanish. Ab initio calculations are probably the most reliable way to obtain quadnipole and higher multipole moments [20, 21 and 22]. 

There are higher multipole polarizabilities tiiat describe higher-order multipole moments induced by non-imifonn fields. For example, the quadnipole polarizability is a fourth-rank tensor C that characterizes the lowest-order quadnipole moment induced by an applied field gradient. There are also mixed polarizabilities such as the third-rank dipole-quadnipole polarizability tensor A that describes the lowest-order response of the dipole moment to a field gradient and of the quadnipole moment to a dipolar field. All polarizabilities of order higher tlian dipole depend on the choice of origin. Experimental values are basically restricted to the dipole polarizability and hyperpolarizability [21, 24 and 21]. Ab initio calculations are an imponant source of both dipole and higher polarizabilities [20] some recent examples include [26, 22] ... 

The exponential fiinction of the matrix can be evaluated tln-ough the power series expansion of exp(). c is the coliinm vector whose elements are the concentrations c.. The matrix elements of the rate coefficient matrix K are the first-order rate constants W.. The system is called closed if all reactions and back reactions are included. Then K is of rank N- 1 with positive eigenvalues, of which exactly one is zero. It corresponds to the equilibrium state, witii concentrations r detennined by the principle of microscopic reversibility ... 

Figure Bl.12.11. Angular variation of the second- and fourth-rank Legendre polynomials.

---