- Email: [email protected]
An Analysis of Insulation of Abandoned Oil Wells Reused for Geothermal Power Generation
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 61 (2014) 607 – 610
An analysis of insulation of Abandoned Oil Wells reused for Geothermal Power Generation Wen-Long Cheng1, *, Tong-Tong Li1, Yong-Le Nian1, Kun Xie1, 2 1
Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui, 230027, China
2
Anhui Electric Power Design Institute, Hefei, Anhui, 230601, China
————————————————————————————————————————————————————————————
Abstract: Geothermal power generation from abandoned oil wells is a new way to utilize geothermal energy. An analysis model based on transient formation heat transfer is presented in this paper. Through the double-pipe heat exchanger, R143a is used as working fluid for obtaining geothermal energy from abandoned oil wells. The influence of insulation on heat transfer from the recovery well to the injection well is investigated. The result shows that the outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. The outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K as compared to the outlet temperature with the perfect insulation. At the same thickness of insulation, the difference of the outlet temperature between with the insulation of polystyrene and with the perfect insulation decreases with the inlet velocity of fluid entering the injection well increasing. Keywords: Geothermal power generation, Abandoned oil wells, Transient formation heat transfer, The influence of insulation ————————————————————————————————————————————————————————————
1.
Introduction
Extracted
Geothermal energy is the thermal energy stored in the form of heat beneath the earth’s surface. The geothermal power plants are established in 24 countries and the total installed capacity of geothermal facilities worldwide is more than 10000MW in 2010 [1]. However the wide application of
Injected fluid
fluid
Injected fluid
heat flow from formation
geothermal power is restricted by the expensive cost of drilling [2]. Meanwhile there are 20-30 millions abandoned oil wells around the world [3]. These abandoned oil wells
formation
have a large amount of heat energy and can be changed into geothermal wells by a double-pipe heat exchanger for power generation [4-7]. In this way the cost of drilling can be
insulation
reduced and pollution problems of abandoned oil can be solved. It is a new way to utilize geothermal energy.
sealing bottom
The purpose of this paper is to analyze the influence of
of the well
insulation on heat transfer from the recovery well to the injection well. Fig.1 shows the structure of a double-pipe heat
Fig.1. Structure diagram of a double-pipe heat exchanger
exchanger, which is composed of two concentric pipes. The outer wall of the inner pipe is wrapped with the insulation of polystyrene (thermal conductivity of polystyrene = 0.027W.m-1.K-1) and the bottom of the well is sealed. The borehole is all lined with a steel casing to prevent leakage into the formation. The diameter of the steel pipe is 0.28/0.25m. R143a is injected into the ring-shaped channel named injection well and flows down. As being heated constantly by geothermal energy, R143a becomes high-temperature fluid at the bottom of the well and then are reversed to flow out to the ground through the inside channel named recovery well. The external radius of recovery well (including the thickness of insulation) is 0.06m. R143a leaves the recovery well at a high temperature and high pressure because the loss of heat from the recovery well to the injection well is prevented by the insulation. ———————————————————————————————————————————————————————————— *Corresponding author, Tel.:086-551-63600305, Fax: 086-551-63600305, Email: [email protected]
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi:10.1016/j.egypro.2014.11.1181
608
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
Nomenclature Ainj
flow area of injection well, m2
Tf,inj
temperature of fluid in injection well, K
Arec
flow area of recovery well, m2
Tf,rec
temperature of fluid in recovery well, K
geothermal gradient, K m-1
a
-1
cp,f
specific heat capacity of fluid, J kg K
-1
t
thickness of insulation, m
u
dummy variable for integration
h
well depth, m
uf
fluid flow velocity, m s-1
hr
convective heat transfer coefficient for recovery
uin
inlet velocity of fluid entering injection well, m s-1
well , W m-2 K-1 hw
z
convective heat transfer coefficient for injection -2
well , W m K
-1
variable well depth from surface, m
α
e
thermal diffusivity of formation, m-2 s
λ
e
thermal conductivity of formation, W m-1 K-1
f
thermal conductivity of fluid, W m-1 K-1
pf,inj
pressure of fluid in injection well, Pa
λ
pf,rec
pressure of fluid in recovery well, Pa
λ s
thermal conductivity of insulation, W m-1 K-1
Rinj
external radius of injection well, m
ρ
density of the fluid, kg m-3
Rrec
external radius of recovery well, m
ω
rinj
internal radius of injection well, m
rrec
internal radius of recovery well, m
τ
operating time, d
T0
surface temperature of formation, K
τD
dimensionless time
Tei
formation temperature at the infinite distance from
τf
friction-loss gradient, Pa/m
I
ratio of formation heat capacity and wellbore heat capacity, dimensionless
well axis, K 2. Theory Using Ramey’s definition the radial heat flow from the formation at the heat exchanger/formation interface is expressed as follows [8]: d Q 2SO (T T ) e
dz
ei
(1)
w
f (t )
The novel transient heat conduction function considering the effect of the heat capacity of wellbore is written as [4, 5,9]: 16Z 2
f (t )
S
2
f
1 exp(W Du 2 ) du u 3'(u, Z ) 0
(2)
³
Assuming that the formation temperature at the infinite distance from well axis along the vertical direction changes linearly, that is: (3)
T0 a z
Tei
The total pressure changes of fluid in the recovery well results from momentum changes, friction and gravity. According to the momentum balance principle, the total pressure gradient can be determined as follows [10]:
dprec dz
U f g W f U f u f
du f
Heat transfer from the recovery well to the injection well can be written as: S (T f ,rec T f ,inj ) d Q rec
dz
(4)
dz (5)
R 1 1 1 ln rec 2hw Rrec 2Os rrec 2hr rrec
where hw is convective heat transfer coefficient for injection well, which can be calculated as follows [11]:
hw
0.023O f Re0.8 Pr 0.4 / de
(6)
hr is convective heat transfer coefficient for recovery well, which can be calculated as follows [11]:
hr
0.023O f Re0.8 Pr 0.3 / rrec
Then the energy equation of the fluid in the recovery well can be acquired as the following equation:
(7)
609
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
d Q rec wW wz dz The total pressure changes of fluid in the injection well can be determined as follows [10]: w ( U f Arec c pT f ,rec )
w ( U f Arec u f c pT f ,rec )
(8)
dpinj
du U f g -W f U f u f f dz dz Heat transfer between the working fluid in the injection well and the formation can be written as: d Q 2S rinj hw (Tw T f ,inj )= dz Then the energy equation of the fluid in the injection well can be acquired as the following equation: w ( U f Ainj c pT f ,inj ) w ( U f Ainj u f c pT f ,inj ) d Q d Q rec + wW wz dz dz
(9)
(10)
(11)
3. Results and discussions Table 1. Basic parameters of the double-pipe heat exchanger and the formation Parameter
Value
Well depth h (m)
4000
Inlet pressure of fluid pin (MPa) Thermal conductivity of formationλ
2.0 e
Thermal conductivity of polystyreneλ
( W m-1 K-1)
1.8
( W m-1 K-1)
s
0.027
Surface temperature of formation T0 (K)
288.15
Equivalent absolute roughness Δ (m)
0.00026
Operating time τ (d)
300
The basic parameters of the double-pipe heat exchanger and the formation are presented in Table 1.The properties of R143a are not constant but change with the pressure as well as temperature in the simulation and can be obtained from Ref. [12].The power generation from abandoned oil wells can achieve stable state after 300 days operation [4]. Hence the operating time is 300d in the simulation.
380
360
340
Fluid in injection well Perfect insulation t=0.04m t=0.03m t=0.02m t=0.01m
320
300
0
1000
2000
Well depth (m)
3000
4000
Fluid temperature (K)
Fluid temperature (K)
380
360
340
320
v=0.1m/s v=0.2m/s v=0.3m/s
300
0
1000
2000
3000
4000
Well depth (m)
Fig.2. (a) fluid temperature change with well depth for different thickness of insulation (b) fluid temperature change with well depth for different uin
Fig.2a describes the temperature of fluid in the injection well and the recovery well change with well depth at a=0.04K/m after 300 days operation for different thickness of insulation and uin=0.1m/s. The outlet temperature of fluid
610
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
leaving the recovery well is 373K at the perfect insulation. The outlet temperature of R143a is respectively 347K, 361K, 367K and 370K for the thickness of 0.01m, 0.02m, 0.03m and 0.04m insulation. The outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. The outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K as compared to the temperature of fluid with the perfect insulation and the loss of heat from the recovery well to the injection well is little. Fig.2b shows the temperature of fluid in the injection well and the recovery well change with well depth at a=0.04K/m after 300 days operation for different uin and the insulation of 0.03m polystyrene as well. And the outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K, 4K and 1K as compared to the temperature of fluid with the perfect insulation when uin is respectively 0.1m/s, 0.2m/s and 0.3m/s. Hence the difference of the outlet temperature decreases with uin increasing. 4. Conclusions In this paper, an analysis model based on transient formation heat transfer is set up. For different thicknesses of insulation and inlet velocities of fluid entering injection well, the temperature of R143a in the injection well and the recovery well is simulated. The conclusions are summarized as follows: (1) The outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. With the insulation of 0.03m polystyrene, the loss of heat from the recovery well to the injection well is little. (2) At the insulation of 0.03m polystyrene, the difference of the outlet temperature between with the insulation of polystyrene and with the perfect insulation decreases with the inlet velocity of fluid entering the injection well increasing. Acknowledgments The authors would like to thank the National Natural Science Foundation of China (grant no. 51176182) for the financial support. References [1] Bertani R. Geothermal power generation in the World 2005-2010 update report. Geothermics 2012; 41:1-29. [2] Barbier E. Geothermal energy technology and current status: an overview. Renewable and Sustainable Energy Reviews 2002; 6: 3-65. [3] Kotler S. Abandoned Oil and gas Wells Are Leaking. http://www.zcommunications.org/abandoned-oil-and-gas-wellsare-leaking-by-steven-kotler; 2011. [4] Cheng WL, Li TT, Nian YL, Wang CL. Studies on geothermal power generation using abandoned oil wells. Energy 2013; 59:248-254. [5] Cheng WL, Li TT, Nian YL, Xie K. Evaluation of Working Fluids for Geothermal Power Generation from Abandoned Oil Wells. Applied Energy 2014; 118: 238-245. [6] Kujawa T, Nowak W, Stachel AA. Utilization of existing deep geological wells for acquisitions of geothermal energy. Energy 2006; 31: 650-664. [7] Davis AP, Michaelides EE. Geothermal power production from abandoned oil wells. Energy 2009; 34: 866-872. [8] Ramey HJ. Wellbore heat transmission. Journal of Petroleum Technology 1962; 14: 427-435. [9] Cheng WL, Huang YH, Lu DT, Yin HR.A novel analytical transient heat-conduction time function for heat transfer in steam injection wells considering the wellbore heat capacity. Energy 2011; 36: 4080-4088. [10] Chen YL. Physical Fluid Dynamics. Hefei: China Science and Technology Press; 2008. [11] Incropera FP, DeWitt DP, Bergman TL, Lavine AS. Fundamentals of Heat and Mass Transfer. 6th ed. John Wiley & Sons, Inc; 2007. [12] Outcalt SL, McLinden MO. An equation of state for the thermodynamic properties of R143a (1,1,1-trifluoroethane). National Institute of Standards and Technology. International Journal of Thermophysics 1997.
ScienceDirect Energy Procedia 61 (2014) 607 – 610
An analysis of insulation of Abandoned Oil Wells reused for Geothermal Power Generation Wen-Long Cheng1, *, Tong-Tong Li1, Yong-Le Nian1, Kun Xie1, 2 1
Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui, 230027, China
2
Anhui Electric Power Design Institute, Hefei, Anhui, 230601, China
————————————————————————————————————————————————————————————
Abstract: Geothermal power generation from abandoned oil wells is a new way to utilize geothermal energy. An analysis model based on transient formation heat transfer is presented in this paper. Through the double-pipe heat exchanger, R143a is used as working fluid for obtaining geothermal energy from abandoned oil wells. The influence of insulation on heat transfer from the recovery well to the injection well is investigated. The result shows that the outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. The outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K as compared to the outlet temperature with the perfect insulation. At the same thickness of insulation, the difference of the outlet temperature between with the insulation of polystyrene and with the perfect insulation decreases with the inlet velocity of fluid entering the injection well increasing. Keywords: Geothermal power generation, Abandoned oil wells, Transient formation heat transfer, The influence of insulation ————————————————————————————————————————————————————————————
1.
Introduction
Extracted
Geothermal energy is the thermal energy stored in the form of heat beneath the earth’s surface. The geothermal power plants are established in 24 countries and the total installed capacity of geothermal facilities worldwide is more than 10000MW in 2010 [1]. However the wide application of
Injected fluid
fluid
Injected fluid
heat flow from formation
geothermal power is restricted by the expensive cost of drilling [2]. Meanwhile there are 20-30 millions abandoned oil wells around the world [3]. These abandoned oil wells
formation
have a large amount of heat energy and can be changed into geothermal wells by a double-pipe heat exchanger for power generation [4-7]. In this way the cost of drilling can be
insulation
reduced and pollution problems of abandoned oil can be solved. It is a new way to utilize geothermal energy.
sealing bottom
The purpose of this paper is to analyze the influence of
of the well
insulation on heat transfer from the recovery well to the injection well. Fig.1 shows the structure of a double-pipe heat
Fig.1. Structure diagram of a double-pipe heat exchanger
exchanger, which is composed of two concentric pipes. The outer wall of the inner pipe is wrapped with the insulation of polystyrene (thermal conductivity of polystyrene = 0.027W.m-1.K-1) and the bottom of the well is sealed. The borehole is all lined with a steel casing to prevent leakage into the formation. The diameter of the steel pipe is 0.28/0.25m. R143a is injected into the ring-shaped channel named injection well and flows down. As being heated constantly by geothermal energy, R143a becomes high-temperature fluid at the bottom of the well and then are reversed to flow out to the ground through the inside channel named recovery well. The external radius of recovery well (including the thickness of insulation) is 0.06m. R143a leaves the recovery well at a high temperature and high pressure because the loss of heat from the recovery well to the injection well is prevented by the insulation. ———————————————————————————————————————————————————————————— *Corresponding author, Tel.:086-551-63600305, Fax: 086-551-63600305, Email: [email protected]
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi:10.1016/j.egypro.2014.11.1181
608
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
Nomenclature Ainj
flow area of injection well, m2
Tf,inj
temperature of fluid in injection well, K
Arec
flow area of recovery well, m2
Tf,rec
temperature of fluid in recovery well, K
geothermal gradient, K m-1
a
-1
cp,f
specific heat capacity of fluid, J kg K
-1
t
thickness of insulation, m
u
dummy variable for integration
h
well depth, m
uf
fluid flow velocity, m s-1
hr
convective heat transfer coefficient for recovery
uin
inlet velocity of fluid entering injection well, m s-1
well , W m-2 K-1 hw
z
convective heat transfer coefficient for injection -2
well , W m K
-1
variable well depth from surface, m
α
e
thermal diffusivity of formation, m-2 s
λ
e
thermal conductivity of formation, W m-1 K-1
f
thermal conductivity of fluid, W m-1 K-1
pf,inj
pressure of fluid in injection well, Pa
λ
pf,rec
pressure of fluid in recovery well, Pa
λ s
thermal conductivity of insulation, W m-1 K-1
Rinj
external radius of injection well, m
ρ
density of the fluid, kg m-3
Rrec
external radius of recovery well, m
ω
rinj
internal radius of injection well, m
rrec
internal radius of recovery well, m
τ
operating time, d
T0
surface temperature of formation, K
τD
dimensionless time
Tei
formation temperature at the infinite distance from
τf
friction-loss gradient, Pa/m
I
ratio of formation heat capacity and wellbore heat capacity, dimensionless
well axis, K 2. Theory Using Ramey’s definition the radial heat flow from the formation at the heat exchanger/formation interface is expressed as follows [8]: d Q 2SO (T T ) e
dz
ei
(1)
w
f (t )
The novel transient heat conduction function considering the effect of the heat capacity of wellbore is written as [4, 5,9]: 16Z 2
f (t )
S
2
f
1 exp(W Du 2 ) du u 3'(u, Z ) 0
(2)
³
Assuming that the formation temperature at the infinite distance from well axis along the vertical direction changes linearly, that is: (3)
T0 a z
Tei
The total pressure changes of fluid in the recovery well results from momentum changes, friction and gravity. According to the momentum balance principle, the total pressure gradient can be determined as follows [10]:
dprec dz
U f g W f U f u f
du f
Heat transfer from the recovery well to the injection well can be written as: S (T f ,rec T f ,inj ) d Q rec
dz
(4)
dz (5)
R 1 1 1 ln rec 2hw Rrec 2Os rrec 2hr rrec
where hw is convective heat transfer coefficient for injection well, which can be calculated as follows [11]:
hw
0.023O f Re0.8 Pr 0.4 / de
(6)
hr is convective heat transfer coefficient for recovery well, which can be calculated as follows [11]:
hr
0.023O f Re0.8 Pr 0.3 / rrec
Then the energy equation of the fluid in the recovery well can be acquired as the following equation:
(7)
609
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
d Q rec wW wz dz The total pressure changes of fluid in the injection well can be determined as follows [10]: w ( U f Arec c pT f ,rec )
w ( U f Arec u f c pT f ,rec )
(8)
dpinj
du U f g -W f U f u f f dz dz Heat transfer between the working fluid in the injection well and the formation can be written as: d Q 2S rinj hw (Tw T f ,inj )= dz Then the energy equation of the fluid in the injection well can be acquired as the following equation: w ( U f Ainj c pT f ,inj ) w ( U f Ainj u f c pT f ,inj ) d Q d Q rec + wW wz dz dz
(9)
(10)
(11)
3. Results and discussions Table 1. Basic parameters of the double-pipe heat exchanger and the formation Parameter
Value
Well depth h (m)
4000
Inlet pressure of fluid pin (MPa) Thermal conductivity of formationλ
2.0 e
Thermal conductivity of polystyreneλ
( W m-1 K-1)
1.8
( W m-1 K-1)
s
0.027
Surface temperature of formation T0 (K)
288.15
Equivalent absolute roughness Δ (m)
0.00026
Operating time τ (d)
300
The basic parameters of the double-pipe heat exchanger and the formation are presented in Table 1.The properties of R143a are not constant but change with the pressure as well as temperature in the simulation and can be obtained from Ref. [12].The power generation from abandoned oil wells can achieve stable state after 300 days operation [4]. Hence the operating time is 300d in the simulation.
380
360
340
Fluid in injection well Perfect insulation t=0.04m t=0.03m t=0.02m t=0.01m
320
300
0
1000
2000
Well depth (m)
3000
4000
Fluid temperature (K)
Fluid temperature (K)
380
360
340
320
v=0.1m/s v=0.2m/s v=0.3m/s
300
0
1000
2000
3000
4000
Well depth (m)
Fig.2. (a) fluid temperature change with well depth for different thickness of insulation (b) fluid temperature change with well depth for different uin
Fig.2a describes the temperature of fluid in the injection well and the recovery well change with well depth at a=0.04K/m after 300 days operation for different thickness of insulation and uin=0.1m/s. The outlet temperature of fluid
610
Wen-Long Cheng et al. / Energy Procedia 61 (2014) 607 – 610
leaving the recovery well is 373K at the perfect insulation. The outlet temperature of R143a is respectively 347K, 361K, 367K and 370K for the thickness of 0.01m, 0.02m, 0.03m and 0.04m insulation. The outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. The outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K as compared to the temperature of fluid with the perfect insulation and the loss of heat from the recovery well to the injection well is little. Fig.2b shows the temperature of fluid in the injection well and the recovery well change with well depth at a=0.04K/m after 300 days operation for different uin and the insulation of 0.03m polystyrene as well. And the outlet temperature of fluid with the insulation of 0.03m polystyrene drops by 6K, 4K and 1K as compared to the temperature of fluid with the perfect insulation when uin is respectively 0.1m/s, 0.2m/s and 0.3m/s. Hence the difference of the outlet temperature decreases with uin increasing. 4. Conclusions In this paper, an analysis model based on transient formation heat transfer is set up. For different thicknesses of insulation and inlet velocities of fluid entering injection well, the temperature of R143a in the injection well and the recovery well is simulated. The conclusions are summarized as follows: (1) The outlet temperature of fluid leaving the recovery well gradually increases with thickness of insulation increasing. With the insulation of 0.03m polystyrene, the loss of heat from the recovery well to the injection well is little. (2) At the insulation of 0.03m polystyrene, the difference of the outlet temperature between with the insulation of polystyrene and with the perfect insulation decreases with the inlet velocity of fluid entering the injection well increasing. Acknowledgments The authors would like to thank the National Natural Science Foundation of China (grant no. 51176182) for the financial support. References [1] Bertani R. Geothermal power generation in the World 2005-2010 update report. Geothermics 2012; 41:1-29. [2] Barbier E. Geothermal energy technology and current status: an overview. Renewable and Sustainable Energy Reviews 2002; 6: 3-65. [3] Kotler S. Abandoned Oil and gas Wells Are Leaking. http://www.zcommunications.org/abandoned-oil-and-gas-wellsare-leaking-by-steven-kotler; 2011. [4] Cheng WL, Li TT, Nian YL, Wang CL. Studies on geothermal power generation using abandoned oil wells. Energy 2013; 59:248-254. [5] Cheng WL, Li TT, Nian YL, Xie K. Evaluation of Working Fluids for Geothermal Power Generation from Abandoned Oil Wells. Applied Energy 2014; 118: 238-245. [6] Kujawa T, Nowak W, Stachel AA. Utilization of existing deep geological wells for acquisitions of geothermal energy. Energy 2006; 31: 650-664. [7] Davis AP, Michaelides EE. Geothermal power production from abandoned oil wells. Energy 2009; 34: 866-872. [8] Ramey HJ. Wellbore heat transmission. Journal of Petroleum Technology 1962; 14: 427-435. [9] Cheng WL, Huang YH, Lu DT, Yin HR.A novel analytical transient heat-conduction time function for heat transfer in steam injection wells considering the wellbore heat capacity. Energy 2011; 36: 4080-4088. [10] Chen YL. Physical Fluid Dynamics. Hefei: China Science and Technology Press; 2008. [11] Incropera FP, DeWitt DP, Bergman TL, Lavine AS. Fundamentals of Heat and Mass Transfer. 6th ed. John Wiley & Sons, Inc; 2007. [12] Outcalt SL, McLinden MO. An equation of state for the thermodynamic properties of R143a (1,1,1-trifluoroethane). National Institute of Standards and Technology. International Journal of Thermophysics 1997.