A Theoretical and Experimental Study of Combustion Tubes

8/20/2019 A Theoretical and Experimental Study of Combustion Tubes

1/12

PLEASE SCROLL DOWN FOR ARTICLE

This article was downloaded by: [Consortio Colombia] On: 15 April 2011Access details: Access Details: [subscription number 933080201] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Petroleum Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713597288

A Theoretical and Experimental Study of Combustion TubesO. Cazarez-Candia a; J. Cruz-Hernández a; R. Islas-Juáreza; E. Márquez-Ramírez aa Instituto Mexicano del Petróleo, México D.F., Mexico

Online publication date: 23 June 2010

To cite this Article Cazarez-Candia, O. , Cruz-Hernández, J. , Islas-Juárez, R. and Márquez-Ramírez, E.(2010) 'ATheoretical and Experimental Study of Combustion Tubes', Petroleum Science and Technology, 28: 12, 1186 — 1196To link to this Article DOI 10.1080/10916460802611192URL http://dx.doi.org/10.1080/10916460802611192

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly

or indirectly in connection with or arising out of the use of this material.

http://www.informaworld.com/smpp/title~content=t713597288http://dx.doi.org/10.1080/10916460802611192http://www.informaworld.com/terms-and-conditions-of-access.pdfhttp://www.informaworld.com/terms-and-conditions-of-access.pdfhttp://dx.doi.org/10.1080/10916460802611192http://www.informaworld.com/smpp/title~content=t713597288


2/12

Petroleum Science and Technology , 28:1186–1196, 2010Copyright © Taylor & Francis Group, LLCISSN: 1091-6466 print/1532-2459 onlineDOI: 10.1080/10916460802611192

A Theoretical and Experimental Studyof Combustion Tubes

O. CAZAREZ-CANDIA,1 J. CRUZ-HERNÁNDEZ,1R. ISLAS-JUÁREZ,1 AND E. MÁRQUEZ-RAMÍREZ11Instituto Mexicano del Petróleo, México D.F., Mexico

Abstract When the air injection technique is used in a reservoir, the usual way todetermine the fuel that would be burned and the temperature proles, among other parameters, is by experimentation in a combustion tube. In this work, using mediumoil (27 API) from the Gulf of Mexico, combustion tube experiments were carried out. Amathematical model, which takes into account the heat transfer ahead and behind fromthe combustion front, the combustion zone thickness, and the heat generated and lossin the combustion front, was solved numerically and used to predict the experimentaltemperature proles. After validation of the mathematical model, further investigationsof the effect of heat losses (along, at the top, and at the bottom of the combustiontube) on temperature proles were done. The calculated combustion zone temperatureand temperature proles are in good agreement with our experimental data. It was found that not considering an isolated boundary in the mathematical model allowsobtaining better predictions for the temperature proles behind and ahead from thecombustion front. On the other hand, the combustion front temperature increases as

the heat losses decrease and the combustion front temperature attains its maximumvalue when there is no heat loss.

Keywords combustion tube, heat losses, in situ combustion, temperature proles

1. Introduction

In situ combustion is a thermal process for recovering crude oil from reservoirs asa consequence of thermal energy released during the combustion of an amount of the oil in place, which aids in the displacement of the remaining oil. The amount of the fuel available for in situ combustion varies with the crude oil and porous mediacharacteristics, oil saturation, air ux, and time–temperature relationships. For this reasonit is necessary to carry out combustion tube experiments when one is studying the possibleeld application of in situ combustion processes to exploit a reservoir.

Combustion tubes used by various researchers vary in size, length, and mode of operation. Then, it is very important to understand combustion tube experiments andresults, which will be used for to plan a pilot test or a eld application. For example, onemust know the amount of energy that is dissipated by the tube during a test and its effecton the temperature proles along the tube among other parameters, like combustion fronttemperature, combustion front velocity, amount of air required for combustion, etc.

Address correspondence to O. Cazarez-Candia, Instituto Mexicano del Petróleo, Eje centralLázaro Cárdenas No. 152, Col. San Bartolo Atepehuacan, C.P. 07730, México D.F., Mexico. E-mail:[email protected]

1186


3/12

Study of Combustion Tubes 1187

On the other hand, in the literature there are works that are focused on the sim-ulation of in situ combustion in laboratory tubes. For example, Verma et al. (1978)presented a mathematical model to simulate the forward combustion that incorporatesthe principal kinetic, thermodynamic, and hydrodynamic aspects of the process. Solimanet al. (1981) developed and applied a model to simulate a laboratory combustion tube,considering mass and heat balance equations, and ow of different uid phases. Gottfried(1965) proposed a mathematical model in which conduction–convection heat transfer,the chemical reaction between oxygen and oil, and aqueous phase change are included,making the model applicable to a variety of thermal recovery processes. They used themodel for detailed simulation of combustion tube laboratory experiments. Penberthy andRamey (1965) developed an analytical model of movement of a burning front axiallyalong a combustion tube with heat loss through an annular insulation. The model allowsidentication of steady-state temperature distributions both ahead and behind the burningfront with and without heat loss but considering isolated boundary conditions. In thespecialized literature there are more mathematical models that are similar to the model

mentioned above; however, in any model the authors take into account the heat losses atthe beginning and at the end of the tube.

In this work combustion tube experiments for medium oil (27 API) from the Gulf of Mexico were done. With the idea of studying the effect of non-isolated boundaries onthe temperature proles the beginning and the nal of the tube were not isolated.

Also, considering non-isolated boundary conditions, Penberthy and Ramey’s (1965)mathematical model was solved numerically. The mathematical model was used to predictthe temperature prole behind, ahead, and at the combustion front during the combustionprocesses in a combustion tube and to evaluate the amount of heat loss across thebeginning and nal of the tube.

2. Experimental Work

Two experiments (E-1 and E-2) were carried out in a combustion tube (Figure 1) of stainless steel with an external diameter of 0.079375 m, a width of 0.015875 m, anda length of 0.9906 m. The tube contains about 0.94996 m of a uniform mixture of sand, water, and oil; the values for saturation, porosity, and other parameters are shownon Table 1. An insulating band was placed along the tube. However, with the idea of studying the effect of non-isolated boundaries on the temperature proles the top andthe bottom of the tube were not isolated. The oil used has an activation energy of 1.56 107 J/kg-mol and 27 API. The space between the sample and the top of the

tube was lled with clean sand. An electric igniter was placed at the sample beginning.Electric current was gradually introduced into the igniter until the temperature in thecombustion tube at the igniter location reached about 241 ı C and air injection wasinitiated at 3.166 10 5 m3 /s. The production pressure was maintained at 4.13

Table 1

Saturations and porosity used in the experiments

Experiment Oil saturation Water saturation Porosity

E-1 0.325 0.23 0.41E-2 0.383 0.275 0.41


4/12

1188 O. Cazarez-Candia et al.

Figure 1. Combustion tube system.

105

Pa. The temperatures when the ignition occurred inside the combustion tube were427 ı C and 462 ı C for E-1 and E-2, respectively. After ignition, the combustion frontmoved from the igniter to the bottom of the combustion tube. The combustion gasesand the production liquids went out from the bottom of the tube. The experimentwas nished when the sand pack was burned to the bottom ange of the combustiontube.

In Figure 2 the temperature proles from E-1 are shown. Temperature ignition wasabout 241 ı C and the combustion front temperature when the ignition was reached wasabout 427 ı C. However, after 2 hr the combustion front temperature remained almostconstant at a value of 324 ı C with an averaged combustion front velocity of 2.65 10 5 m/s. As can be shown, the rst temperature prole has a combustion front with a

large width ( Š 0.05 m), which is due to the electric igniter being turned off 30 min afterignition occurred. The oil and water production was made every 15 min, and then heatwent out from the combustion tube, so temperature was affected at the bottom of thecombustion tube even when an isolated boundary was put.

The temperature proles from E-2 (Figure 3) have similar behaviors to the prolesfrom E-1. However, the combustion front temperature when ignition was reached was462 ı C. In this case, after 2.55 hr the combustion front temperature remained almostconstant at a value of 355 ı C with an average combustion front velocity of 3.41 10 5 m/s. Contrary to E-1, in E-2 once ignition occurred the electric igniter was turnedoff, and all the combustion fronts had a thin width.

In Figure 4 the accumulated oil recovery from E-1 and E-2 are shown. The totaloil recovery from E-1 was 84%, whereas the total oil recovery from E-2 was 73%.Apparently, this was due to a lower oil and water saturation used in E-1.


5/12


Figure 2. Experimental temperature proles from E-1.

3. Mathematical Models

In this work the simulation of the in situ combustion phenomenon in a combustion tubeconsists of mathematical models for (1) the combustion zone thickness, (2) the heatgenerated and lost in the combustion front, and (3) the heat transfer through porousmedia. In the rst one a stoichiometric equation for combustion is solved to determinethe combustion zone thickness. In the second one a heat balance is done to determine the

Figure 3. Experimental temperature proles from E-2.


6/12


Figure 4. Cumulative oil recovery for E-1 and E-2.

combustion front temperature. In the third one the heat conduction equation is solved inorder to obtain the temperature proles behind and ahead of the combustion front. Theinformation about the models for the combustion zone thickness and the heat generatedand lost in the combustion front can be found in the work of Rodriguez (2004). Themodel for the heat transfer through the porous media is presented below.

3.1. Heat Transfer Model

The heat transfer model solved in this work is similar to the model presented by Penberthyand Ramey (1965) except that in this work the model was solved numerically andNeumann boundary conditions were imposed at the top and bottom of the tube. Themodel includes many of the important characteristics of combustion tube experiments.The equation for the heat transfer through the porous media to determine the temperatureproles behind and ahead of the burning front is given by (Penberthy and Ramey, 1965):

˛ @2T @x2

C ˇ @T @x

.T T a / D@T @t

(1)

The original initial and boundary conditions are

T.x;0/ D 0 (2)

At the combustion front, T.0; t/ D T c (3)

At the top and bottom of the combustion tube, limx !1

@T @x

.x;t/ D 0 (4)


7/12


8/12


where the subscript j can be 0 or L for the top or bottom of the combustion tube, and

a i D I i D 1 ; : : : M (11)

bi D Œ .2C x D / C 1 (12)

ci D .1 C x D / (13)

d i D .c 1/T tD 1 (14)

In Eqs. (10)–(14) the subscript i represents actual node, the superscripts t and t C trepresent previous and current times, and is given by:

Dt

x 2 (15)

where t is time size step and x is spatial size step.Before solving Eq. (10) it is necessary to solve a stoichiometric equation for the

combustion process and then to know the combustion front velocity and the combustionzone thickness. The combustion front velocity allows us to know where the combustionfront is in the tube and the combustion zone thickness lets us know the locationsfrom which the temperature proles behind and ahead of the combustion front will besolved. Rodriguez (2004) worked with heavy oil and suggested values for the combustionzone thickness from 0.0127 to 0.02286 m; however, in this work the experiments weremade with medium oil (27 API) and values of 0.004318 and 0.00762 m were used. Aheat balance on the combustion zone must be done to determine the combustion fronttemperature. The stoichiometric equation, the equations to calculate the velocity and the

combustion zone thickness, and the heat balance are given in the work of Rodriguez(2004).The solution of Eq. (10) also requires knowing the overall heat transfer coefcient

(U ). For this, Penberthy and Ramey (1965) proposed a second heat loss constant, C ,given by

C D˛ ˇ 2

(16)

Then, U and can be calculated from Eqs. (9) and (16), respectively. For the calculationof , C one takes values until the experimental and predicted temperatures of thecombustion front are equal. That is, C takes values from 0 to 1, where 0 means that thecombustion tube has a perfect insulation and 1 means that the combustion tube has noinsulation.

3.1.2. Results and Analysis. The results from the mathematical model were comparedagainst the experimental data presented in Section 2. The mathematical model wasestablished supposing that the combustion front temperature and velocity are constant(Penberthy and Ramey, 1965). Figure 5 shows the comparison between experimentaldata from E-1 and the results from the mathematical model with the boundary conditiongiven by Eq. (4). The combustion front temperature used was 324 ı C, which was obtainedusing C D 0.1163 and a combustion front thickness of 0.0127 m. The suppositions

mentioned cause that both the position and value of the combustion front temperaturematch with only some experimental temperature proles. It is noted that the temperatureproles behind the combustion front obtained with the model are in agreement with the


9/12


Figure 5. Experimental data (thick line) and predictions (thin line) for temperature proles. E-1,insulated boundaries.

experimental data only near the combustion front; however, near the top of the tube

(length D 0 m in Figure 5) the predicted temperatures proles move away from theexperimental ones, and the maximum error was of 68%. The temperature proles aheadof the combustion front, predicted by the model, are far from the experimental temperatureproles principally near the bottom of the tube (length D 0.9 m in Figure 5), and themaximum error was of 81%.

If the boundaries given by Eqs. (5) and (6) are used instead Eq. (4), the predictionsobtained for temperature proles present better tting. This is shown in Figure 6. In thiscase, for the temperature proles behind and ahead of the combustion front maximumerrors of 33 and 20% were found, respectively.

In Figure 7 the predicted temperature proles are compared with the temperatureprole obtained from Experiment 2. In this case the combustion front temperature used

was 355 ı C, which was obtained using C D 0.096 and a combustion front thickness of 0.0127 m. The idea was to maintain a constant value for the front thickness (the samevalue as that for E-1) and give values for C until the combustion front temperature attainsa value similar to the experimental one. In this case the maximum errors between thepredicted and experimental temperature proles were 67% behind and 82% ahead of the combustion front. If the boundaries given by Eqs. (5) and (6) are used instead Eq.(4), the predictions obtained for temperature proles present better tting. This is shownin Figure 8. In this case the maximum errors between the predicted and experimentaltemperature proles were 23% behind and 20% ahead of the combustion front.

The values for the heat ux ( q) used to obtain Figures 6 and 8 are shown in Figure 9,

where it can be seen that after 4 hr, q

takes higher values ahead of than behind thecombustion front. This is because every 15 min uids are yielded from the tube. Theheat loss at the top of the tube for E-1 is larger that for E-2; however, after 3 hr the heat


10/12


Figure 6. Experimental data (thick line) and predictions (thin line) for temperature proles. E-1,Neumann boundary conditions.

Figure 7. Experimental data (thick line) and predictions (thin line) for temperature proles. E-2,insulated boundaries.


11/12


Figure 8. Experimental data (thick line) and predictions (thin line) for temperature proles. E-2,Neumann boundary conditions.

Figure 9. Heat losses at the top and bottom of the combustion tube.


12/12


loss is similar for both experiments, because for E-1 the electrical igniter was turned off 30 min after the ignition occurred.

4. Conclusions

Experiments for in situ combustion for medium (27 API) oil were carried out withoutthermally insulating the top and bottom of the combustion tube.

It is well known that heat losses occur along the combustion tube and we think that heat losses at the top and bottom of the tube are small and unimportant. Sometimesmathematical models are formulated supposing insulated boundaries; however, in thiswork it was shown that better predictions for temperature proles are obtained usingNeumann boundaries. This, even when the bottom of the tube was perfectly insulated,because heat losses occur due in part for the uids that go out from the tube.

A predictive model for in situ combustion processes was used to determine thebehavior of the temperature proles. Through this model it was found mainly that (a) the

boundary conditions play a very important role when in situ combustion is mathematicallymodeled and (b) temperature ahead and behind the combustion front is well predictedwhen Neumann boundary conditions are used in the mathematical model.

References

Gottfried, B. S. (1965). A mathematical model of thermal oil recovery in linear systems. PaperNo. SPE 1117, SPE Production Research Symposium , Tulsa, OK, May 3–4, pp. 196–210.

Penberthy, W. L., and Ramey, H. J. (1965). Design and operation of laboratory combustion tubes.Paper No. SPE 1290, SPE Annual Fall Meeting , Denver, CO, October 3–6, pp. 183–198.

Rodriguez, J. R. (2004). Experimental and analytical study to model temperature proles and

stoichiometry in oxygen-enriched in-situ combustion . Ph.D. Dissertation, College Station:Texas A&M University.

Soliman, M. Y., Brigham, W. E., and Raghavan, R. (1981). Numerical simulation of thermalrecovery processes. Paper No. SPE 9942, SPE California Regional Meeting , Bakerseld, CA,March 25–26, pp. 625–640.

Verma, V. B., Reynolds, A. C., and Thomas, G. W. (1978). A theoretical investigation of forwardcombustion in a one-dimensional system. Paper No. SPE 7526, SPE-AIME 53rd Annual FallTechnical Conference and Exhibition , Houston, TX, October 1–3, pp. 1–12.

A Theoretical and Experimental Study of Combustion Tubes

Documents