- Email: [email protected]
Gas Production from Methane Hydrate in Cubic Hydrate Simulator Using Depressurization Method by Experimental and Numerical Studies
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 61 (2014) 803 – 807
The 6th International Conference on Applied Energy – ICAE2014
Gas Production from Methane Hydrate in Cubic Hydrate Simulator using Depressurization Method by Experimental and Numerical Studies Gang Li, Xiao-Sen Li*, Yi Wang Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
Abstract Dissociation processes of methane hydrate in porous media using the depressurization method were investigated by a combination of experimental observations and numerical simulations. In situ methane hydrate was synthesized in the Cubic Hydrate Simulator (CHS), a 5.832-L cubic pressure vessel. During the experiment, constant-pressure depressurization method was used during the hydrate dissociation process. A single horizontal well at the center of the CHS was used as the production well. The hydrate is dissociated continuously under both depressurization and heat transfer from the boundaries. An interface separates the hydrate dissociated zone containing only gas and water from the undissociated zone containing the hydrate. The cumulative gas and water produced, the hydrate in the vessel and the temperature spatial distribution are simulated numerically. © 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 Keywords: hydrate dissociation; porous media; depressurization; horizontal well;
1. Introduction Natural gas hydrates (NGH) are solid, non-stoichiometric compounds formed by host water molecules with small guest molecules, such as CH4, C2H6, CO2, H2S, etc. Natural gas hydrate deposits involve mainly CH4, and occur in the permafrost and in deep ocean sediment, where the necessary conditions of low temperature and high pressure exist for hydrate stability. Several methods for gas production from hydrate have been proposed: (1) Depressurization [1], (2) Thermal stimulation [2], (3) Thermodynamic inhibitor effects [3]. In recent years, 3D experimental apparatus have been developed to simulate the hydrate dissociation behaviors. Zhou et al. [4] developed a 72 L large-scale reactor vessel, and investigated the gas production from hydrate. Yang et al. [5] developed a 3D reactor with an inner
* Corresponding author. Tel.: +86 20 87057037; fax: +86 20 87034664. E-mail address: [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.2014.11.969
804
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
diameter of 300mm and an effective height of 100 mm. The maximum operating pressure of the reactor was 16 MPa. Recently, a 3D Cubic Hydrate Simulator (CHS) has been developed for the gas production from the methane hydrate in the sediment by using depressurization [6] and the huff and puff [7] methods. The primary objective of the present study is to investigate the gas production behavior from a methane hydrate reservoir using depressurization method with a single horizontal well by a combination of experimental observations in the CHS and numerical simulations. A horizontal well at the axis of the CHS was used as the production well. The gas and water produced from the methane hydrate reservoir in the CHS under depressurization were monitored. 2. Experiments and Numerical simulations 2.1. Apparatus and Procedure The complete description of the CHS has been introduced in the previous studies [7]. For this study, we used the TOUGH+HYDRATE code [8]. The porosity and the intrinsic permeability of the system is 0.472 and 3.0 Darcies, respectively. The following procedure was used to investigate into the hydrate dissociation characteristics. When the system pressure decreased to approximately 4.64 MPa, the experimental and numerical simulation began (t = 0 min), and the initial temperature before dissociation T0 = 5.81 oC. The initial saturations of hydrate and aqueous are SH0 = 26.27% and SA0 = 13.42% in volume. Subsequently, the hydrate began to dissociate, and the gas and water were produced from the vessel through the production well. When there was little gas release, it was considered as the end of the gas production process (t = 582 min).
Fig. 1. The grid of the numerical simulations. 2.2. Domain Discretization
Fig. 2. P of experiment and Tbon of numerical simulation.
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
Figure 1 shows the grid used in the numerical simulations. The internal length of side of the CHS is 'X = 'Y = 'Z = 0.18 m. Because of symmetry about the well, only half of the cubic domain of the CHS (x t 0) is simulated. The hybrid grid in Figure 1 comprises 8 (layers) u 2,156 = 17,248 non-uniformly sized elements, of which 12,205 are active. A very fine discretization is used in the region defined by the center of the well and for r < 0.045 (Figure 1). Outside this region, discretizations along both the x-axis and the z-axis are uniform with 'x = 'z = 0.003 m.This grid results in 51,744 coupled equations that are solved simultaneously. 3. Results and discussion 3.1. Pressure and Boundary Temperature Figure 2 shows the system pressure P of experimental results and the temperature of boundaries Tbon of numerical simulation results during hydrate dissociation in the CHS. Due to the high porosity and permeability of the sediment, the pressures at the different measuring points in the CHS have little discrepancy. Thus, the pressure at any point can be taken as the system pressure. The pressure P remains constant, with the average value of approximately 4.64 MPa. During the numerical simulation, the temperature of the boundaries Tbon (Figure 2), increases from 7.05 to 7.25 oC with an increment of 0.015 o C each 40 min.
Figure 3. Comparison of VP and MW.
Figure 4. Comparison of the spatial distributions of T.
3.2. Gas and Water Production Figure 3 shows the comparisons of the gas produced VP and the water produced MW over time of experimental and numerical simulation results during hydrate dissociation in the CHS. Both the experimental and numerical simulation results in Figure 3 indicates that (i) the hydrate in the CHS is dissociated continuously until the end of the production process; (ii) the gas and water production rates and the hydrate dissociation rate decrease over time while using the constant-pressure depressurization method. Of those, (i) is caused by the depressurization effect and the continuous heat transfer from the boundaries of the CHS; the main reason for (ii) is the continuous decrease of the hydrate dissociation interface over time. 3.3. Spatial Distribution of T
805
806
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
Figure 4 shows the comparison of the spatial distributions of the temperature T over time of experimental (a1-a4) and numerical simulation (b1-b4) results during hydrate dissociation in the CHS. In Figure 4(b1), the coordinate of T13A is x = 0, z = 0.045 m, while that of T15A is x = 0.09 m, z = 0.045 m. The solid rectangle of T13A, T13C, T15C and T15A in Figure 4(b1) corresponds to that in Figure 4(b2b4). Figure 4 shows (i) the fine agreements of the T spatial distributions and their evolutions over time between numerical and experimental results; (ii) the evolution of the temperature gradient in the CHS over time; (iii) the temperature increase of the hydrate deposit over time, especially in the area near the stainless steel boundaries of the CHS; (iv) the limited temperature increase around the center (r = 0, z = 0) of the CHS and the existence of the low-T area. (ii) and (iii) are caused by the heat transfer from the boundaries with relative high temperature Tbon; (iv) is caused by the effect of the undissociated hydrate in the vicinity of the CHS center, and the energy transferred from the surrounding is used as the latent heat during the equilibrium reaction of hydrate dissociation. 4. Conclusions
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
The following conclusions are drawn from both the experimental and the numerical simulation results: (1) The hydrate is dissociated continuously and there is little hydrate remained at the end. The gas and water production rates and the hydrate dissociation rate decrease over time. (2) The hydrate dissociation is an analog of a moving boundary ablation process. With heat transfer from boundaries, the hydrate dissociation interface moves from the boundaries of the CHS toward the center. Acknowledgements The authors appreciate National Science Fund for Distinguished Young Scholars of China (51225603), and National Natural Science Foundation of China (51376183) for providing financial aids. References [1] Li G, Moridis GJ, Zhang KN, Li XS. Evaluation of Gas Production Potential from Marine Gas Hydrate Deposits in Shenhu Area of South China Sea. Energy Fuels 2010;24:6018-33. [2] Kamath WA, Godbole SR. Evaluation of Hot-Brine Stimulation Technique for Gas Production From Natural Gas Hydrates. Journal of Petroleum Technology 1987;39:1379-88. [3] Li G, Li XS, Tang LG, Zhang Y. Experimental investigation of production behavior of methane hydrate under ethylene glycol injection in unconsolidated sediment. Energy Fuels 2007;21:3388-93. [4] Zhou Y, Castaldi MJ, Yegulalp TM. Experimental Investigation of Methane Gas Production from Methane Hydrate. Industrial Engineering Chemistry Research 2009;48:3142-9. [5] Yang X, Sun C-Y, Yuan Q, Ma P-C, Chen G-J. Experimental Study on Gas Production from Methane Hydrate-Bearing Sand by Hot-Water Cyclic Injection. Energy Fuels 2010;24:5912-20. [6] Li X-S, Zhang Y, Li G, Chen Z-Y, Wu H-J. Experimental Investigation into the Production Behavior of Methane Hydrate in Porous Sediment by Depressurization with a Novel Three-Dimensional Cubic Hydrate Simulator. Energy Fuels 2011;25:4497-505. [7] Li G, Li XS, Wang Y, Zhang Y. Production behavior of methane hydrate in porous media using huff and puff method in a novel three-dimensional simulator. Energy 2011;36:3170-8. [8] Moridis GJ, Kowalsky MB, Pruess K. TOUGH+HYDRATE v1.1 user’s manual: a code for the simulation of system behavior in hydrate-bearing geologic media: Lawrence Berkeley National laboratory, Berkeley, CA; 2009.
Biography Dr Gang Li, an associate professor at the natural gas hydrate research center in Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, is currently working on experimental and numerical simulation of the natural gas hydrate phase equilibrium, kinetics and dissociation technologies.
807
ScienceDirect Energy Procedia 61 (2014) 803 – 807
The 6th International Conference on Applied Energy – ICAE2014
Gas Production from Methane Hydrate in Cubic Hydrate Simulator using Depressurization Method by Experimental and Numerical Studies Gang Li, Xiao-Sen Li*, Yi Wang Key Laboratory of Renewable Energy and Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China
Abstract Dissociation processes of methane hydrate in porous media using the depressurization method were investigated by a combination of experimental observations and numerical simulations. In situ methane hydrate was synthesized in the Cubic Hydrate Simulator (CHS), a 5.832-L cubic pressure vessel. During the experiment, constant-pressure depressurization method was used during the hydrate dissociation process. A single horizontal well at the center of the CHS was used as the production well. The hydrate is dissociated continuously under both depressurization and heat transfer from the boundaries. An interface separates the hydrate dissociated zone containing only gas and water from the undissociated zone containing the hydrate. The cumulative gas and water produced, the hydrate in the vessel and the temperature spatial distribution are simulated numerically. © 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 Keywords: hydrate dissociation; porous media; depressurization; horizontal well;
1. Introduction Natural gas hydrates (NGH) are solid, non-stoichiometric compounds formed by host water molecules with small guest molecules, such as CH4, C2H6, CO2, H2S, etc. Natural gas hydrate deposits involve mainly CH4, and occur in the permafrost and in deep ocean sediment, where the necessary conditions of low temperature and high pressure exist for hydrate stability. Several methods for gas production from hydrate have been proposed: (1) Depressurization [1], (2) Thermal stimulation [2], (3) Thermodynamic inhibitor effects [3]. In recent years, 3D experimental apparatus have been developed to simulate the hydrate dissociation behaviors. Zhou et al. [4] developed a 72 L large-scale reactor vessel, and investigated the gas production from hydrate. Yang et al. [5] developed a 3D reactor with an inner
* Corresponding author. Tel.: +86 20 87057037; fax: +86 20 87034664. E-mail address: [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.2014.11.969
804
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
diameter of 300mm and an effective height of 100 mm. The maximum operating pressure of the reactor was 16 MPa. Recently, a 3D Cubic Hydrate Simulator (CHS) has been developed for the gas production from the methane hydrate in the sediment by using depressurization [6] and the huff and puff [7] methods. The primary objective of the present study is to investigate the gas production behavior from a methane hydrate reservoir using depressurization method with a single horizontal well by a combination of experimental observations in the CHS and numerical simulations. A horizontal well at the axis of the CHS was used as the production well. The gas and water produced from the methane hydrate reservoir in the CHS under depressurization were monitored. 2. Experiments and Numerical simulations 2.1. Apparatus and Procedure The complete description of the CHS has been introduced in the previous studies [7]. For this study, we used the TOUGH+HYDRATE code [8]. The porosity and the intrinsic permeability of the system is 0.472 and 3.0 Darcies, respectively. The following procedure was used to investigate into the hydrate dissociation characteristics. When the system pressure decreased to approximately 4.64 MPa, the experimental and numerical simulation began (t = 0 min), and the initial temperature before dissociation T0 = 5.81 oC. The initial saturations of hydrate and aqueous are SH0 = 26.27% and SA0 = 13.42% in volume. Subsequently, the hydrate began to dissociate, and the gas and water were produced from the vessel through the production well. When there was little gas release, it was considered as the end of the gas production process (t = 582 min).
Fig. 1. The grid of the numerical simulations. 2.2. Domain Discretization
Fig. 2. P of experiment and Tbon of numerical simulation.
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
Figure 1 shows the grid used in the numerical simulations. The internal length of side of the CHS is 'X = 'Y = 'Z = 0.18 m. Because of symmetry about the well, only half of the cubic domain of the CHS (x t 0) is simulated. The hybrid grid in Figure 1 comprises 8 (layers) u 2,156 = 17,248 non-uniformly sized elements, of which 12,205 are active. A very fine discretization is used in the region defined by the center of the well and for r < 0.045 (Figure 1). Outside this region, discretizations along both the x-axis and the z-axis are uniform with 'x = 'z = 0.003 m.This grid results in 51,744 coupled equations that are solved simultaneously. 3. Results and discussion 3.1. Pressure and Boundary Temperature Figure 2 shows the system pressure P of experimental results and the temperature of boundaries Tbon of numerical simulation results during hydrate dissociation in the CHS. Due to the high porosity and permeability of the sediment, the pressures at the different measuring points in the CHS have little discrepancy. Thus, the pressure at any point can be taken as the system pressure. The pressure P remains constant, with the average value of approximately 4.64 MPa. During the numerical simulation, the temperature of the boundaries Tbon (Figure 2), increases from 7.05 to 7.25 oC with an increment of 0.015 o C each 40 min.
Figure 3. Comparison of VP and MW.
Figure 4. Comparison of the spatial distributions of T.
3.2. Gas and Water Production Figure 3 shows the comparisons of the gas produced VP and the water produced MW over time of experimental and numerical simulation results during hydrate dissociation in the CHS. Both the experimental and numerical simulation results in Figure 3 indicates that (i) the hydrate in the CHS is dissociated continuously until the end of the production process; (ii) the gas and water production rates and the hydrate dissociation rate decrease over time while using the constant-pressure depressurization method. Of those, (i) is caused by the depressurization effect and the continuous heat transfer from the boundaries of the CHS; the main reason for (ii) is the continuous decrease of the hydrate dissociation interface over time. 3.3. Spatial Distribution of T
805
806
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
Figure 4 shows the comparison of the spatial distributions of the temperature T over time of experimental (a1-a4) and numerical simulation (b1-b4) results during hydrate dissociation in the CHS. In Figure 4(b1), the coordinate of T13A is x = 0, z = 0.045 m, while that of T15A is x = 0.09 m, z = 0.045 m. The solid rectangle of T13A, T13C, T15C and T15A in Figure 4(b1) corresponds to that in Figure 4(b2b4). Figure 4 shows (i) the fine agreements of the T spatial distributions and their evolutions over time between numerical and experimental results; (ii) the evolution of the temperature gradient in the CHS over time; (iii) the temperature increase of the hydrate deposit over time, especially in the area near the stainless steel boundaries of the CHS; (iv) the limited temperature increase around the center (r = 0, z = 0) of the CHS and the existence of the low-T area. (ii) and (iii) are caused by the heat transfer from the boundaries with relative high temperature Tbon; (iv) is caused by the effect of the undissociated hydrate in the vicinity of the CHS center, and the energy transferred from the surrounding is used as the latent heat during the equilibrium reaction of hydrate dissociation. 4. Conclusions
Gang Li et al. / Energy Procedia 61 (2014) 803 – 807
The following conclusions are drawn from both the experimental and the numerical simulation results: (1) The hydrate is dissociated continuously and there is little hydrate remained at the end. The gas and water production rates and the hydrate dissociation rate decrease over time. (2) The hydrate dissociation is an analog of a moving boundary ablation process. With heat transfer from boundaries, the hydrate dissociation interface moves from the boundaries of the CHS toward the center. Acknowledgements The authors appreciate National Science Fund for Distinguished Young Scholars of China (51225603), and National Natural Science Foundation of China (51376183) for providing financial aids. References [1] Li G, Moridis GJ, Zhang KN, Li XS. Evaluation of Gas Production Potential from Marine Gas Hydrate Deposits in Shenhu Area of South China Sea. Energy Fuels 2010;24:6018-33. [2] Kamath WA, Godbole SR. Evaluation of Hot-Brine Stimulation Technique for Gas Production From Natural Gas Hydrates. Journal of Petroleum Technology 1987;39:1379-88. [3] Li G, Li XS, Tang LG, Zhang Y. Experimental investigation of production behavior of methane hydrate under ethylene glycol injection in unconsolidated sediment. Energy Fuels 2007;21:3388-93. [4] Zhou Y, Castaldi MJ, Yegulalp TM. Experimental Investigation of Methane Gas Production from Methane Hydrate. Industrial Engineering Chemistry Research 2009;48:3142-9. [5] Yang X, Sun C-Y, Yuan Q, Ma P-C, Chen G-J. Experimental Study on Gas Production from Methane Hydrate-Bearing Sand by Hot-Water Cyclic Injection. Energy Fuels 2010;24:5912-20. [6] Li X-S, Zhang Y, Li G, Chen Z-Y, Wu H-J. Experimental Investigation into the Production Behavior of Methane Hydrate in Porous Sediment by Depressurization with a Novel Three-Dimensional Cubic Hydrate Simulator. Energy Fuels 2011;25:4497-505. [7] Li G, Li XS, Wang Y, Zhang Y. Production behavior of methane hydrate in porous media using huff and puff method in a novel three-dimensional simulator. Energy 2011;36:3170-8. [8] Moridis GJ, Kowalsky MB, Pruess K. TOUGH+HYDRATE v1.1 user’s manual: a code for the simulation of system behavior in hydrate-bearing geologic media: Lawrence Berkeley National laboratory, Berkeley, CA; 2009.
Biography Dr Gang Li, an associate professor at the natural gas hydrate research center in Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, is currently working on experimental and numerical simulation of the natural gas hydrate phase equilibrium, kinetics and dissociation technologies.
807