Saying

The pressure at which standard-state fugacities are most conveniently evaluated is suggested by considerations based on the Gibbs-Duhem equation which says that at constant temperature and pressure... 

If the vapor mixture contains only ideal gases, the integrals in Equations (3) and (6) are zero, z is unity for all compositions, and ()i equals 1 for each component i. At low pressures, typically less than 1 bar, it is frequently a good assumption to set ( ) = 1, but even at moderately low pressures, say in the vicinity of 1 to 10 bars, (f) is often significantly different from unity, especially if i is a polar component. 

Figure 3.8a shows the temperature-composition diagram for a minimum-boiling azeotrope that is sensitive to changes in pressure. This azeotrope can be separated using two columns operating at different pressures, as shown in Fig. 3.86. Feed with mole fraction of A Ufa)) of, say, 0.3 is fed to the high-pressure column. The bottom product from this high-pressure column is relatively pure B, whereas the overhead is an azeotrope with jcda = 0-8, jcdb = 0.2. This azeotrope is fed to the low-pressure column, which produces relatively pure A in the bottom and in the overhead an azeotrope with jcda = 0.6, jcdb = 0.4. This azeotrope is added to the feed of the high-pressure column.

Equation (5.3) can be written at minimum reflux and then at finite reflux, say, 1.1 times minimum reflux. The calculation is then repeated for all columns in the sequence. 

In choosing to transfer heat, say XP, from the system above the pinch to the system below the pinch, as shown in Fig. 6.8a, then above the pinch there is a heat deficit of XP. The only way this can... 

Analogous effects are caused by the inappropriate use of utilities. Utilities are appropriate if they are necessary to satisfy the enthalpy imbalance in that part of the process. Above the pinch in Fig. 6.7a, steam is needed to satisfy the enthalpy imbalance. Figure 6.86 illustrates what happens if inappropriate use of utilities is made and some cooling water is used to cool hot streams above the pinch, say, XP. To satisfy the enthalpy imbalance above the pinch, an import of (Q mjj,+XP) is needed from steam. Overall, (Qcmin+AP) of cooling water is used. ... 

This wetness fraction is possibly too high, since high levels of wetness can cause damage to the turbine. To allow a lower wetness fraction of, say, a = 0.15, then the outlet pressure of the turbine must be raised 0.2 bar, corresponding to a condensing temperature of 60°C. However, in so doing, the shaftwork generation decreases to 4.2 MW. 

A simple method to achieve this is based on the fact that for any value of R there is a maximum asymptotic value for P, say, P axi which is given as Ft tends to - c and is given by ... 

Calculate the weighted network area Anetwork from Eq. (7.22). When the weighted h values i4>h) vary appreciably, say, by more than one order of magnitude, an improved estimate of Anetwork can be evaluated by linear programming. ... 

In this accident, the steam was isolated from the reactor containing the unfinished batch and the agitator was switched ofiF. The steam used to heat the reactor was the exhaust from a steam turbine at 190 C but which rose to about 300°C when the plant was shutdown. The reactor walls below the liquid level fell to the same temperature as the liquid, around 160°C. The reactor walls above the liquid level remained hotter because of the high-temperature steam at shutdown (but now isolated). Heat then passed by conduction and radiation from the walls to the top layer of the stagnant liquid, which became hot enough for a runaway reaction to start (see Fig. 9.3). Once started in the upper layer, the reaction then propagated throughout the reactor. If the steam had been cooler, say, 180 C, the runaway could not have occurred. ... 

It is easy to say that operation of a reactor at higher temperature might lead to a safer plant if the inventory can be reduced as a result, but how do we assess such changes quantitatively Lowering the inventory makes the plant safer, but raising the temperature makes it less safe. Which effect is more significant ... 

Fuel switch. Fuel switch from, say, coal to natural gas reduces the CO2 emissions for the same heat release because of the lower carbon content of natural gas. 

To arrive at the electronic configuration of an atom the appropriate number of electrons are placed in the orbitals in order of energy, the orbitals of lower energy being filled first (Aufbau principle ), subject to the proviso that for a set of equivalent orbitals - say the three p orbitals in a set - the electrons are placed one... 

This is the reason for numerous studies that have been conducted with X-ray diffraction, a method not described here. Suffice it to say that X-ray diffraction is useful in providing values of aromaticity, the distances between layers and between aliphatic chains, the thickness of particles, etc. 

Sicily) 7.8%, which are too high to be able to say with certainty that sulfur comes only from organic material alone. 

It is fair to say that advances in seismic surveys over the last decade have changed the way fields are developed and managed. From being a predominantly exploration focused tool, seismic has progressed to become one of the most cost effective methods for optimising field production. In many cases, seismic has allowed operators to extend the life of mature fields by several years. 

Phase behaviour describes the phase or phases in which a mass of fluid exists at given conditions of pressure, volume (the inverse of the density) and temperature (PVT). The simplest way to start to understand this relationship is by considering a single component, say water, and looking at just two of the variables, say pressure and temperature. 

Now using a hydrocarbon component, say ethane, as an example, let us consider the other parameter, volume, using a plot of pressure versus specific volume (i.e. volume per unit mass of the component, the inverse of the density). The process to be described could be performed physically by placing the liquid sample into a closed cell (PVT cell), and then reducing the pressure of the sample by withdrawing the piston of the cell and increasing the volume contained by the sample. 

So far we have considered only a single component. However, reservoir fluids contain a mixture of hundreds of components, which adds to the complexity of the phase behaviour. Now consider the impact of adding one component to the ethane, say n-heptane (C7H.,g). We are now discussing a binary (two component) mixture, and will concentrate on the pressure-temperature phase diagram. 

When the two components are mixed together (say in a mixture of 10% ethane, 90% n-heptane) the bubble point curve and the dew point curve no longer coincide, and a two-phase envelope appears. Within this two-phase region, a mixture of liquid and gas exist, with both components being present in each phase in proportions dictated by the exact temperature and pressure, i.e. the composition of the liquid and gas phases within the two-phase envelope are not constant. The mixture has its own critical point C g. 

Structural maps display the top (and sometimes the base) of the reservoir surface below the datum level. The depth values are always true vertical sub sea. One could say that the contours of structure maps provide a picture of the subsurface topography. They display the shape and extent of a hydrocarbon accumulation and indicate the dip and strike of the structure. The dip is defined as the angle of a plane with the horizontal, and Is perpendicular to the strike, which runs along the plane. 

The estimated probabilities of each of these events occurring are multiplied together to estimate the POS, since they must a//occur simultaneously if a hydrocarbon accumulation is to be formed. If the POS is estimated at say 30%, then the probability of failure must be 70%, and the expectation curve for an exploration prospect may look as shown in figure 6.9. 

Some variables often have dependencies, such as reservoir porosity and permeability (a positive correlation) or the capital cost of a specific equipment item and its lifetime maintenance cost (a negative correlation). We can test the linear dependency of two variables (say x and y) by calculating the covariance between the two variables (o ) and the correlation coefficient (r) ... 

This is the method used by the commercial software packages Crystal Ball and RISK . The method is ideally suited to computers as the description of the method will reveal. Suppose we are trying to combine two independent variables, say gross reservoir thickness and net-to-gross ratio (the ratio of the net sand thickness to the gross thickness of the reservoir section) which need to be multiplied to produce a net sand thickness. We have described the two variables as follows ... 

If no appraisal was performed, and the development was started based, say, on the medium case STOMP of 48 MMstb, then the actual STOMP would not be found until the facilities were built and the early development wells were drilled. If it turned out that the STOMP was only 20 MMstb, then the project would lose 40 million, because the facilities were oversized. If the STOMP is actually 48 MMstb, then the NPV is assumed to be the same as for the medium case after appraisal. If the STOMP was actually 100 MMstb, then the NPV of + 40 million is lower than for the case after appraisal (+ 66 million) since the facilities are too small to handle the extra production potential. 

Once production commences, data such as reservoir pressure, cumulative production, GOR, water cut and fluid contact movement are collected, and may be used to history match the simulation model. This entails adjusting the reservoir model to fit the observed data. The updated model may then be used for a more accurate prediction of future performance. This procedure is cyclic, and a full field reservoir simulation model will be updated whenever a significant amount of new data becomes available (say, every two to five years). 

Polymer flooding alms at reducing the amount of by-passed oil by increasing the viscosity of the displacing fluid, say water, and thereby improving the mobility ratio (M). 

The number of injectors required may be estimated in a similar manner, but it is unlikely that the exploration and appraisal activities will have included injectivity tests, of say water injection into the water column of the reservoir. In this case, an estimate must be made of the injection potential, based on an assessment of reservoir quality in the water column, which may be reduced by the effects of compaction and diagenesis. Development plans based on water injection or natural aquifer drive often suffer from lack of data from the water bearing part of the reservoir, since appraisal activity to establish the reservoir properties in the water column is frequently overlooked. In the absence of any data, a range of assumptions of injectivity should be generated, to yield a range of number of wells required. If this range introduces large uncertainties into the development plan, then appraisal effort to reduce this uncertainty may be justified. 

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. 

For any one case, say the base case, the project cashflow is constructed by calculating on an annual basis the revenue items (the payments received by the project) and then subtracting the expenditure items (the payments made by the project capex, opex and host government take). For each year the balance is the annual cash surplus (or cash deficit). Flence, on an annual basis... 

The project cashflow s constructed by performing the calculation for every year of the project life. Atypical project cashflow is shown in Figure 13.9, along with a cumulative cashflow showing how cumulative revenue is typically split between the capex, opex, the host government (through tax and royalty) and the investor (say the oil company). The cumulative amount of money accruing to the company at the endof the project is the cumulative cash surplus or field life net cash flow. 

The point at which the cumulative cash flow turns positive indicates the payout time (or payback time). This is the length of time required to receive accumulated net revenues equal to the investment. This indicator says nothing about the cash flow after the payback time and does not consider the total profitability of the investment opportunity. 

The example just shown assumed one discount rate and one oil price. Since the oil price is notoriously unpredictable, and the discount rate is subjective, it is useful to calculate the NPV at a range of oil prices and discount rates. One presentation of this data would be in the form of a matrix. The appropriate discount rates would be 0% (undiscounted),.say 10% (the cost of capital), and say 20% (the cost of capital plus an allowance for risk). The range of oil prices is again a subjective judgement. 

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