The areas

In the K-diagram some equations can be set up for the areas below the concentration functions. In the case of a simple consecutive reaction 

This equation can be veriHed by complete induction, since obviously the integral is given by 

In the case of the more complicated reactions the areas can be calculated accordingly. 

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Reject the areas of integrity, and operate the process as a single system. 

Figure 6.22 The areas of integrity can be targeted separately and then the combination targeted.

Find a way to overcome the constraint while still maintaining the areas. This is often possible by using indirect heat transfer between the two areas. The simplest option is via the existing utility system. For example, rather than have a direct match between two streams, one can perhaps generate steam to be fed into the steam mains and the other use steam from the same mains. The utility system then acts as a buffer between the two areas. Another possibility might be to use a heat transfer medium such as a hot oil which circulates between the two streams being matched. To maintain operational independence, a standby heater and cooler supplied by utilities is needed in the hot oil circuit such that if either area is not operational, utilities could substitute heat recovery for short periods. 

The area target is usually slightly less than the area observed in design. 

Figure 16.215 shows an alternative match for stream 1 which also obeys the CP inequality. The tick-off" heuristic also fixes its duty to be 12 MW. The area for this match is 5087 m , and the target for the remaining problem above the pinch is 3788 m . Tlius the match in Fig. 16.216 causes the overall target to be exceeded by 16 m (0.2 percent). This seems to be a better match and therefore is accepted. 

To establish the shells target, the composite curves are first divided into vertical enthalpy intervals as done for the area target algorithm. It was shown in App. B that it is always possible to design a network for an enthalpy interval with (5, -1) matches, with each match having the same temperature profile as the enthalpy interval. 

The area target, Eq. (7.6), sums the area contributions from each enthalpy interval. This equation can be rearranged to an equivalent expression which sums the area contribution of each stream ... 

Equation (F.l) shows that each stream makes a contribution to total heat transfer area defined only by its duty, position in the composite curves, and its h value. This contribution to area means also a contribution to capital cost. If, for example, a corrosive stream requires special materials of construction, it will have a greater contribution to capital cost than a similar noncorrosive stream. If only one cost law is to be used for a network comprising mixed materials of construction, the area contribution of streams requiring special materials must somehow increase. One way this may be done is by weighting the heat transfer coefficients to reflect the cost of the material the stream requires. 

The simulated distillation method uses gas phase chromatography in conjunction with an apolar column, that is, a column where the elution of components is a function of their boiling points. The column temperature is increased at reproducible rate (programed temperature) and the area of the chromatogram is recorded as a function of elution time. 

After often a lengthy period (several months) of acquisition and processing, the data may be loaded onto a seismic workstation for interpretation. These workstations are UNIX based, dual screen systems (sections on one side, maps on the other, typically) where all the trace data is stored on fast access disk, and where the picked horizons and faults can be digitised from the screen Into a database. Of vital Importance is access to all existing well data in the area for establishing the well - seismic tie. 2D data will be interpreted line by intersecting line, and 3D as a volume. 

If no prior drilling activities have been recently carried out in the area, usually an environmental impact assessment (EIA) will be carried out as a first step. An EIA is usually undertaken to ... 

Fig. 3.24 shows the cost breakdown of a typical development well. As can be seen, drilling operations are the area with the largest scope for cost savings. The actual costs of a well show considerable variations and are dependent on a number of factors, e.g. ... 

The time taken to complete a base line study and EIA should not be underestimated. The baseline study describes and inventorises the natural initial flora, fauna, the aquatic life, land and seabed conditions prior to any activity. In seasonal climates, the baseline study may need to cover the whole year. The duration of an EIA depends upon the size and type of area under study, and the previous work done in the area, but may typically take six months. The EIA is often an essential step in project development and should not be omitted from the planning schedule. 

Correlations on paper panels are made easier if a type log has been creafed of a fypical and complete sequence of the area. If this log is available as a transparency, it can be easily compared against the underlying paper copy. Type logs are also handy if the reservoir development has to be documented in reports or presentations. 

GRV is the gross rock volume of the hydrocarbon-bearing interval and is the product of the area (A) containing hydrocarbons and the interval thickness (H), hence... 

The area can be measured from a map. Figure 6.1 clarifies some of the reservoir definitions used in reserves estimation. 

From a top reservoir map (Fig. 6.2) the area within a selected depth interval is measured. This is done using a planimeter, a hand operated device that measures areas. 

The stylus of the planimeter is guided around the depth to be measured and the respective area contained within this contour can then be read off. The area is now plotted for each depth as shown in Figure 6.2 and entered onto the area - depth graph. Since the structure is basically cut into slices of increasing depth the area measured for each depth will also increase. 

Connecting the measured points will result in a curve describing the area - depth relationship of the top of fhe reservoir. If we know the gross thickness (H) from logs we can establish a second curve representing the area - depth plot for the base of the reservoir. The area between the two lines will equal the volume of rock between the two markers. The area above the OWC is the oil bearing GRV. The other parameters to calculate STOIIP can be taken as averages from our petrophysical evaluation (see Section 5.4.). Note that this method assumes that the reservoir thickness is constant across the whole field. If this is not a reasonable approximation, then the method is not applicable, and an alternative such as the area - thickness method must be used (see below). 

This procedure can be easily carried out for a set of reservoirs or separate reservoir blocks. It is especially practical if stacked reservoirs with common contacts are to be evaluated. In cases where parameters vary across the field we could divide the area into sub blocks of equal values which we measure and calculate separately. 

It is clear that if the area - depth method had been applied to the above example, it would have led to a gross over-estimation of STOMP. It would also have been impossible to target the best developed reservoir area with the next development well. 

If there is insufficient data to describe a continuous probability distribution for a variable (as with the area of a field in an earlier example), we may be able to make a subjective estimate of high, medium and low values. If those are chosen using the p85, p50, pi 5 cumulative probabilities described in Section 6.2.2, then the implication is that the three values are equally likely, and therefore each has a probability of occurrence of 1/3. Note that the low and high values are not the minimum and maximum values. 

If the development is so far from shore that direct line of sight communication is not possible, then satellite communications will be installed, with one platform acting as a satellite link for the area. 

In Section 13.2, it was suggested that opex is estimated at the development planning stage based upon a percentage of cumulafive capex (fixed opex) plus a cosf per barrel of hydrocarbon production (variable opex). This method has been widely applied, with the percentages and cost per barrel values based on previous experience in the area. One obvious flaw in this method is that as oil production declines, so does the estimate of opex, which is nof the common experience as equipment ages it requires more maintenance and breaks down more frequently. 

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