Re: Post: Reflexiones sobre el modelo ETP y el colapso (AMT)

Posted by Julio on
URL: http://foro-crashoil.109.s1.nabble.com/Post-Reflexiones-sobre-el-modelo-ETP-y-el-colapso-AMT-tp37290p37328.html

Aquí, en el foro de Ron Patterson, hay un tío que no está muy de acuerdo con el modelo ETP. Aviso que es inglés y además introduce ecuaciones termodinámicas, por lo que, al menos para mi, bien podría estar hablando en chino. Pero doctores tiene la iglesia que sabrán apreciar (o no) lo que dice.

"Seppo Korpela says:
02/10/2017 AT 8:33 PM
The report by the Hills Group claims to rely on thermodynamics arguments to predict oil’s price-volume trajectory going forward. If does not stand up to scrutiny.

Thermodynamic analysis of engineering systems is typically based on the first law of thermodynamics together with mass balances.
The second law of thermodynamics introduces the entropy as a thermodynamic property and the related concepts of reversible processes and reversible heat transfer.
Irreversibilities in real processes are taken into account by assigning a value of experimentally determined efficiency to equipment such as pumps, compressors and turbines and
this way the reversible processes are related to the actual ones.

A relatively recent development has been to develop a systematic use of an exergy balance to examine where in a complex energy system irreversibilities
take place. Exergy is defined as the maximum theoretical work that can be obtained from a system and its environment as the system comes to equilibrium
with its environment. By combining the first and second laws of thermodynamics an exergy balance can be written down.

Rudimentary exergy analysis can be found in the 1941 book Thermodynamics by Joseph Keenan. It was called availability analysis at that time. The most systematic development
of the exergy analysis is in the textbook Fundamentals of Engineering Thermodynamics by M. Moran, H. Shapiro, D. Boettner and M. Bailey, 7th ed. John Wiley, 2011.

Although the entropy balance equation can be used (although typically only for steady state systems) to determine the entropy production, to carry it out requires that sufficient number of
thermodynamic properties and interactions are known at the system boundaries. Since such a calculation needs to be carried out after the thermodynamic analysis has been completed,
it is seldom carried out in engineering practice because the knowledge of the same properties allows the efficiency of the machine or system be determined.

The advocates of exergy accounting claim that knowing where the exergy destruction takes place in a system is a good way of allocating development money to improve it.
This kind of analysis has not taken hold in industry either, simply because, manufacturer, say of turbines know that the irreversibilities are quantified by measuring the efficiency
of the turbine, and they direct their efforts toward understanding how the blades of the turbine can be shaped in order to reduce the irreversibilities. Such a task is based on aerodynamic
calculations. Compressors and pump are by the nature of the flow through them machines with lower efficiency and their improvement requires again experts with fluid dynamic knowledge to
improve them. Similarly improving the heat transfer in a heat exchanger is carried out by making improvements in the heat exchanger surfaces and reducing pressure losses.
If these improve the heat transfer, the entropy production is reduced. Here the expertise of a heat transfer specialist rather than a thermodynamicists is needed.

One interesting application of exergy analysis is to calculate the second law efficiency. A high second law efficiency means that the source of energy is well matched with the application.
Thus heating shower water with a thermal solar heater is a good match as unfocused solar energy raises the water temperature high enough to serve as shower water, but not nearly so high as to create superheated steam to power a steam turbine. Thus the most important insight to be obtained is to match the source of energy to the application, and once this insight is internalized, calculation of the second law efficiency adds only marginally to understanding. For this reason it is seldom used in industry. To be sure, optimization of a system’s second law efficiency is still worth while, but using other metrics this can be done with topics based on heat transfer, fluid dynamics, stress analysis and the like.

Where thermodynamic analysis is helpful is in seeing how a thermodynamic efficiency of a system such as a coal or nuclear power plant can be improved by increasing the maximum steam temperature of the plant in which the turbine is but one component. This requires that blades are made of materials that withstand the stresses generated at these temperatures. Such developments have increased the maximum temperature of these power plants to about 1000 F, but further improvements have now stalled over the last half a century. For gas fired power plants combustion temperature is higher and and turbine designers implement both cooling technology for the blades and use high temperature materials, that today are made of single crystals, that withstand the hot combustion gases. Interestingly exergy analysis shows that most of the exergy
destruction takes place in the combustion of the fuel, but there is not much one can do to reduce this destruction. For this reason a naive application of exergy analysis may lead the poor allocation of development funds.

The report by the Hills Group proposes to use the second law of thermodynamics as the starting point. The unsteady entropy balance for a control volume with one exit and no inlet is given as

dS_cv/dt= Q^dot_j/T_j – m^dot_e s_e = \sigma^dot_cv

Next comes the assumption that at all times dS_cv/dt = m^dot s_e$. It is based on the observation that because at the end of oil production when the reservoir has been completely depleted
the flow will stop and nothing much takes place, then both of these terms are zero. After cancelling these terms the entropy production is seen to be related to the heat transfer. But his assumption is clearly unjustified while the oil is being extracted and these two terms do not cancel each other. The neglect of the terms leads to an equation that omits the entropy production that is caused by the irreversibilities of the oil flow through the permeable reservoir rock.

The incorrect canceling leads to the equation
dot Q^dot_j/T_j = sigma^dot_cv or sigma^dot_cv= Q^dot_j/T_j

and this can be cast in these two forms, depending which term is known and which is unknown. The report by Hills Group does not tell the reader which is a known quantity and which is to be calculated. In fact, there is no indication in the report how the heat transfer is calculated? In thinking about the heat transfer, for a control volume that includes the reservoir only, it appears that the heat interaction between the system and the surroundings is mainly caused by the geothermal gradient. That is, heat enters from the lower boundary and leaves across the upper boundary. This is a passive process.
The fact that the oil and water in the reservoir have some average temperature in the geological setting only influences the viscosity of the fluids and thus how well they move through the reservoir,
but from the energetic standpoint the sensible energy is not important. That is, there is no attempt made to extract this energy in a heat exchanger, nor is the high pressure used to extract energy in an expander. Rather the oil and water mixture flows through a set of throttling valves, in which the exergy is destroyed.

If the entropy production were known independently, then this equation could be used to calculate the heat transfer, but the answer would be incorrect because entropy production is caused by both heat transfer and irreversible processes taking place inside
the control volume. For the control volume consisting of the reservoir, entropy production takes place mainly in the pores of the permeable reservoir rock as the flow is forced out.
This takes place by local viscous dissipation and although it can be calculated in principle, in practice such a calculation is nearly impossible to carry out from first principles. The entropy production rate for the system would then be calculated by integration of the local values over the entire reservoir.

Next in the analysis is a calculation of E_Tp. It is defined as the total production energy, or the total work required to extract, process, and distribute a volumetric quantity (a gallon) of crude oil. The report offers the equation

E_Tp = [(m_c C_c + m_o C_o ) (T_R-T_O)]/[m_c]

as a way to calculate it. But this is the energy of the sensible part of the oil-water mixture above the reference temperature T_O. It does not include the chemical energy of the crude oil and the formula cannot be reconciled with the definition of E_Tp.

The following equation also appears in the report

E_Tp = integral_{t_1}^{t_2} T_0 \sigma^dot_cv dt
\]
Thus there are two equations to use for calculating E_Tp and there is no mention what the independent variables are and what is calculated using these equations.
If the value of E_Tp is calculated this way then how is the previous equation used? The only unknowns are the reservoir temperature T_R and the oil-water ratio, if the total flow rate is determined from the depletion rate equation. The reservoir temperature can be measured, so the unknown seems to be the water oil ratio. However, the report makes use of an empirical equation for the oil/water ratio as a function of the percent depletion of the reservoir.
Finally last equation can only be used to calculate the change in exergy, and this would necessitate a new symbol to be introduced for exergy, and this is not the same as energy.

The report next presents calculation of the oil extraction trajectory that is based on Hubbert’s methodology. The calculations are in close agreement what others have found., with cumulative production 2357 Gb that is somewhat larger than what
Campbell and Laherrere’s value 2123 Gb. It is now well known that the in the calculations based on logistic equation there is a slow drift to large values of the ultimate production as more data has been included in the calculations with the passing of the

In the same section is also a discussion of the surface water cut as a function of the percent of oil extracted from a reservoir. The curve is then rotated in order to satisfy two criteria set by the authors. Now a rotation of a curve is
a mathematical transformation and a curve cannot be arbitrarily rotated without destroying the underlying mathematical theory. Furthermore, the report states that E_Tp cannot exceed E_G, the crude oil’s specific exergy. The terminology is again used loosely applied to both energy and exergy.

Returning to the calculation in Section 4.1 of the report for calculating $E_{Tp}$ by the equation

E_Tp = [(m_c C_c + m_o C_o ) (T_R-T_O)]/[m_c]

The statement on top of page 19 suggests that the water cut is an input parameter, in which case the value of E_Tp depends only on the reservoir temperature.
The reservoir temperature in turn is a function of the depth of the well, owing to the geothermal gradient. This would allow this equation to be used to calculate the sensible energy of oil-water mixture. But what purpose does this serve?
The sensible heat of the crude oil is not used in any significant way. The crude oil cools as it enters the ground facilities and it cools further as it is transported in the pipelines. No power is generated from the sensible part of the crude oil’s energy. Only the chemical energy is valuable upon combustion. The rest of the report relates to how prices are linked to the energy delivered. There is no theory to predict how prices adjust to either temporary surplus or deficit.

From what has been discussed above, the thermodynamic analysis is incorrect and therefore any calculations and graphs based on this analysis must also be unreliable. Readers have noted that the so called analysis predicts a peak in oil production during
the 2017-2018 time frame and troubles by 2023. That this coincides with the time others have judged the difficulties to appear, seems to give the report a superficial credibility.
If the authors have a better handle on how much energy is expended in oil production, they can form the EROIE ratio and
it would constitute an independent check on the work of Hall and his coworkers on EROEI. Such an independent analysis would have some value"