PROSPECT OF CO 2 SEQUESTRATION IN THE ISHIKARI COAL FIELD, JAPAN

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1 PROSPECT OF CO 2 SEQUESTRATION IN THE ISHIKARI COAL FIELD, JAPAN ABSTRACT S. Yamaguchi 1*, K. Ohga 2, M. Fujioka 3, and S. Muto 4 1 Dept. of Earth Science and Technology, Faculty of Engineering and Resource Science, Akita University, 1-1, Tegata Gakuencho, Akita , Japan 2 Graduate School of Engineering, Hokkaido University, Kita 8-jyo, Nishi 5-chome, Kita-ku, Sapporo City, Hokkaido, , Japan 3 Japan Coal Energy Center, Meiji-Seimei Building 9F, Mita, Minato-ku, Tokyo, , Japan 4 Kansai Environmental Engineering Center, 1-3-5, Azuchimachi, Chuo-ku, Osaka, , Japan The Japanese Ministry of Economy, Trade and Industry began, in 2002, a five-year project on CO 2 sequestration in coal seams. This project involves fundamental research into CH 4 -CO 2 -coal interaction, CO 2 monitoring technologies, cost reduction of CO 2 capture from flue gases, and the economics of sequestration. Another component of the project is a micro pilot test. After preliminary screening of potential sites, the Ishikari Coal Field in Hokkaido, Japan, was selected as the micro pilot test site. In 2003, a well (Shuparo IW-1) was drilled in the South Oh-Yubari district within the Ishikari Coal Field. It was the first well drilled in Japan from the surface to a coal seam for CO 2 sequestration. During drilling, coal cores were collected and sent to laboratories for analysis to determine several parameters such as the initial adsorbed volume of gas and the Langmuir constants. After the well was drilled, down-hole investigations that included well-logging, a water-injection falloff test, and a mini-frac test were also carried out. Based on the results, the coal-seam temperature, cleat porosity, absolute permeability, thickness, initial pressure, initial water saturation, fracturing pressure and fracture-closing pressure have all been estimated. In 2004, a second well (Shuparo PW-1) will be drilled. The two wells are together intended to constitute a multi-well micro pilot test site. A CO 2 huff-and-puff test will be carried out at IW-1, and a multi-well CO 2 - injection/ch 4 -production test conducted using both IW-1 and PW-1. This paper introduces the overall coal-seam CO 2 -sequestration project and presents the results of the laboratory analyses, well-logging and water-injection falloff tests conducted to date. The data are used to predict the likely results of the future CO 2 huff-and-puff and multi-well tests. The final section of this paper presents an estimate of the likely volume of CO 2 that can be sequestered in the Ishikari Coal Field. INTRODUCTION Global warming is one of the most important environmental problems facing the world and is widely considered to be caused by an atmospheric greenhouse effect. The contribution of CO 2 to this greenhouse effect is estimated to equate approximately to 50% of the effect of all greenhouse gases together, making the reduction of CO 2 emissions an important goal. One possible contributory solution to CO 2 emission reduction is to collect and store CO 2 in coal seams, the technology for which has been extensively studied in recent years [1] to [6]. In Japan, a CO 2 -sequestration project entitled Technology Development for Carbon Dioxide Sequestration in Coal Seams commenced in FY2002 as one part of the Carbon Dioxide Sequestration and Effective Use Program, promoted by the Japanese Ministry of Economy, Trade and Industry (METI). The purpose of this project is to develop a series of processes that can a) extract the CO 2 discharged from thermal power plants and other large-scale emitters, b) fix it within coal seams in a stable state, and c) in the process, recover methane as a clean energy source. Following an open tender process for the project in May 2002, Kansai Environmental Engineering Center Co. Ltd. (KANSO) was chosen as a consignee of the project. To undertake the project, KANSO put together research groups including representatives from universities, national laboratories, and private companies. * Corresponding author, dsy@lfp03.mine.akita-u.ac.jp

2 This project involves the following five key R&D activities (Table 1). 1. Carry out fundamental research to determine the volume of CO 2 that could potentially be stored in coal seams. This research is being undertaken by a consortium consisting of Hokkaido University, Akita University, Waseda University, Kyoto University, and the Research Institute of Innovative Technology for the Earth to address the following subsidiary objectives: a) understanding the CO 2 /CH 4 exchange mechanism, b) establishing optimum conditions for CO 2 sequestration in coal seams, c) simulating CO 2 behaviour in coal seams, and d) estimating the amount of CO 2 that could be fixed in coal seams. 2. Establish monitoring techniques to confirm that CO 2 is safely sequestered in coal seams, with a particular emphasis on methodologies appropriate to the geological structures present at the test site. This research is being conducted by KANSO, and the NPO Think Tank Kyoto Institute of Natural History. 3. Develop methods to reduce the cost of CO 2 separation and recovery from flue gas. Kansai Electric Power Co., Inc., and Mitsubishi Heavy Industries Ltd. are undertaking this research. 4. Appraise the economic viability of CO 2 sequestration. This research is being performed by Waseda University and KANSO. 5. Conduct a micro pilot test using research groups organized by the Japan Coal Energy Center (JCOAL). TABLE 1: R&D ITEMS OF THE CO 2 -SEQUESTRATION PROJECT IN JAPAN. R&D Item Fundamental Research Work Monitoring Technology Cost Reduction of CO 2 Capturing from Flue Gas Economics Micro Pilot Test Contractor Hokkaido University, Akita University, Kyoto University, RITE KANSO NPO Think Tank Kyoto Institute of Natural History KEPCO, MHI Waseda University, KANSO JCOAL Most of the basic research was undertaken in FY2002 and FY2003. A small-scale field test is being conducted in FY2004 and FY2005. At the end of FY2004, an overall evaluation of whether coal-seam sequestration in the Ishikari Coal Field is feasible will be made based on the results to date. If those results are favourable, the project will be continued in the form of a large-scale field test in FY2006. FIELD TEST In FY2002, JCOAL assessed the suitability for CO 2 sequestration of coal mining areas throughout Japan and selected the field-test site [7]. Despite little previous research within Japan into either coalbed methane or the use of coalbeds as gas reservoirs, some pertinent data obtained during underground mining were available. Based on information including gas volumes emitted from coal mines, gas-desorption rates during gas drainage at underground coal mines, subsurface temperatures, and water-drainage volume, the Yubari district located in the southern part of the Ishikari Coal Field was selected as the micro pilot test site (Figure 1). In FY2003, the Shuparo IW-1 well was drilled to evaluate the geological character of the coal seams and associated formations and to prepare for the subsequent pilot test. It was the first well drilled from the surface to a coal seam for CO 2 sequestration in Japan. Shuparo is another name for the test site s location and IW-1 indicates that the well will be used as an injection well during the pilot test. IW-1 was drilled down to m and encountered three major coal seams, namely the upper (H10), middle (Y68), and lower (Y10) coal seams, at depths of to m, to m, and to m, respectively. The target coal seam for CO 2 sequestration is the lower (Y10) coal seam. Cores of the mudstone caprock and of the coal seams were taken at depths between m and m and analyzed to determine their CH 4 - and CO 2 -adsorption properties. In addition, oriented cores were taken from the bottom part of the hole in order to estimate in situ stress. Six well-logs temperature, resistivity, natural gamma ray, caliper, sonic, and density of the interval between and m were acquired. After cementing the hole, a cement-bond log was also obtained. IW-1 was cased, and then

3 perforated between 890 and 895 m. After this, a water-injection falloff test was performed to estimate the absolute permeability of the coal seam, and the fracture-opening and -closing pressures. In situ pressure and coal-seam temperature were also measured. Following these tests, the well was closed at the end of November as the test site is covered by heavy snow during winter making it difficult to continue the pilot test. Sapporo Yubari Ishikari Coal Field Coal Seams Figure 1: Map of the Ishikari Coal Field. A huff-and-puff test is planned for Shuparo IW-1 in the summer of Another well, Shuparo PW-1, will be drilled during the summer, and multi-well CO 2 injection/ch 4 production tests are planned for the autumn. The multi-well test will be repeated in FY2005, and if the results of these tests are favourable, a large-scale field test will be conducted in FY2006. ISHIKARI MODEL The Ishikari model has been constructed to perform numerical simulations of the planned huff-and-puff and multiwell tests at the pilot site. The main purpose of the simulations is to help design the field tests. Figure 2 shows isopachs for the Y10 coal seam in relation to faults and the IW-1 and PW-1 wellhead locations. The test area is surrounded by faults, which are expected to act as barriers to the injected CO 2. Table 2 lists the reservoir properties of the Y10 coal seam [8]. The gross interval top and bottom depths and the net coal thickness are based on drilling data. The average absolute permeability and fracture water saturation have been estimated from type curvematching analysis of the water-injection falloff test. The temperature and pressure have been measured during the test. The average temperature and fracture water saturation estimates have also been double-checked against well logs. The average in situ coal density was obtained during well-logging, and the average in situ moisture and ash contents were obtained from core measurements. The average in situ gas content was estimated from the measured gas volume and lost gas volume, via the t method. The Langmuir pressure and volumes of CH 4 and CO 2 were obtained by laboratory analysis of the coal cores. Two different methods were used for these measurements: the first method was to measure the mass of gas adsorbed on coal with a gravimetric method using a magnetic suspension balance; the second method was to calculate the adsorbed gas based on the pressure change in a reaction vessel containing coal and a buffer tank. The gas-water relative permeability curve described by Gash [9] was used for the model. The measured original gas composition is presented in Table 3. It should be noted from Table 2 that

4 the in situ gas content is very high, but that the absolute permeability is low. Based on the Langmuir isotherm, the saturated gas content is estimated to be 21.5 m 3 /t for the coal seam, implying that the seam is slightly undersaturated. Faults 6.00 Shuparo IW Shuparo PW Existing Wells Road Isopach Contour Figure 2: Isopach map of the Y10 coal seam of the test area (contour interval: one metre). TABLE 2: RESERVOIR PARAMETERS OF THE Y10 COAL SEAM IN THE ISHIKARI COAL FIELD. Property Value Gross interval top depth, m Gross interval bottom depth, m Net coal thickness, m 5.55 Average temperature, C 30.0 Initial average pressure, kpa Absolute permeability, md 1.0 Relative permeability Gash [9] Natural fracture water saturation, % 1.0 Natural fracture porosity, % 1.0 Cleat spacing, mm 7.5 Average in situ moisture content, % 0.87 Average in situ ash content (moist), % 3.62 Dry, ash-free Langmuir CH 4 storage capacity, m 3 /t 28 CH 4 Langmuir pressure, kpa 1785 CH 4 sorption time, day 5.0 Dry, ash-free Langmuir CO 2 storage capacity, m 3 /t 44 CO 2 Langmuir pressure, kpa 972 CO 2 sorption time, day 2.5 Dry, ash-free Langmuir N 2 storage capacity, m 3 /t 14 Average in situ gas content, m 3 /t 21.5 (Undersaturated) Original gas composition See Table 3

5 Figure 3 shows the computational grid division used in the model. The shaded area denotes active cells surrounded by closed boundaries, which correspond to sealing faults. The smallest mesh size used for cells near wells is 10 m, which was determined following sensitivity studies. TABLE 3: MEASURED GAS COMPOSITION OF THE Y10 COAL SEAM. Sample Name CH 4 Ethane Propane n-butane i-butane N 2 CO 2 Sample <0.01 < Sample <0.01 < Sample <0.01 < Average Figure 3: Grid division of the Ishikari model. HUFF-AND-PUFF TEST A huff-and-puff test, scheduled for the summer of 2004, will be conducted in four steps. In Step 1, coalbed methane gas will be produced from Shuparo IW-1 for four weeks under a constant water-production rate of 30 m 3 /day until the bottom-hole flowing pressure reaches a minimum pressure of 414 kpa. In Step 2, CO 2 will be injected into Shuparo IW-1 at a constant injection rate of 1 t/h until the wellhead pressure reaches a maximum pressure of 15 MPa (corresponding to a total mass of injected CO 2 of 16 t). In Step 3, Shuparo IW-1 will be shut in for a two-week soak period. In Step 4, coalbed methane gas will be produced from Shuparo IW-1 for three weeks under the same conditions as during Step 1. After the production phase, Shuparo IW-1 will be shut in and the volume of CO 2 adsorbed by the coal will be estimated. Figure 4 shows the results of a simulated huff-and-puff test. Water is initially produced at 8.0 m 3 /day reducing gradually to 2.9 m 3 /day. The coalbed methane production rate during Step 1 is almost 500 m 3 /day; CO 2 comprises 1.6% by volume of the produced gas. During Step 2, CO 2 is injected over a 21-hour period. The time required for the1 t/h CO 2 injection is very short and mostly controlled by the 15 MPa wellhead pressure constraint. In Step 4, the initial coalbed methane gas production rate is relatively high; this is because a free gas phase exists associated with CH 4 /CO 2 exchange during Step 3. The coalbed methane gas production rate gradually decreases to almost the same production rate as during Step 1. During this period, CO 2 is produced at a rate of 160 m 3 /day. On the basis of the

6 injected and produced volumes of CO 2, approximately 11.5 t of CO 2 is estimated to have been adsorbed onto the coal. This amount corresponds to almost 72% of the injected CO 2. Gas Production/Injection Rate (m 3 /day) 13,000 12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 CH4 Production Rate CO2 Injection Rate CO2 Production Rate Water Rate Elapsed Time (days) Water Production Rate (m 3 /day) Figure 4: Simulation results of the huff-and-puff test. MULTI-WELL TEST The drilling of Shuparo PW-1 is scheduled to start in summer The distance between IW-1 and PW-1 at the coal seam is intended to be 50 m. This distance was determined on the basis of numerical studies so that the injected CO 2 breaks through in September A multi-well test is scheduled to begin in autumn Coalbed methane gas production from Shuparo PW-1 is planned to begin in October 2004 under the same test regime as used for the huff-and-puff test, and CO 2 injection into Shuparo IW-1 will begin in November. The total amount of CO 2 to be injected is 200 t. Both PW-1 and IW-1 will be shut in at the end of November 2004 for safety reasons, and reopened in Coalbed methane gas production from Shuparo PW-1 will begin in May 2005, and CO 2 injection into Shuparo IW-1 will begin the following month; once again, both phases will be conducted using the same test regime as used in 2004, and the total amount of injected CO 2 will be 400 t. At the end of November 2005, both wells will be shut in again. Figure 5 shows simulation results for the multi-well test. In late 2004, the coalbed methane gas production rate from PW-1 is 500 m 3 /day at the start of production but increases to 1300 m 3 /day once CO 2 is injected into IW-1. This effect may be due to CH 4 /CO 2 exchange in the coalbed. In 2005, the coalbed methane gas production rate from PW-1 is estimated to be 1600 m 3 /day due to the existence of free gas. The coalbed methane gas production rate decreases to 800 m 3 /day. Once CO 2 is injected into IW-1, the coalbed methane gas production rate increases to 2200 m 3 /day, and subsequently decreases to 400 m 3 /day at the end of November 2005, when both PW-1 and IW-1 are shut in. The injected CO 2 breaks through in September, assuming that a 2% increase in CO 2 production gas is indicative of the breakthrough. Considering the injected and produced volumes of CO 2, almost 590 t of CO 2 is estimated to be adsorbed on coal during the test, corresponding to almost 96% of the CO 2 injected. ESTIMATION OF CO 2 SEQUESTRATION The total amount of possible CO 2 sequestration for the 4 km 2 Y10 coal seam in the Ishikari Coal Field can also be estimated using the simulation results. A five spot well pattern is assumed as shown in Figure 6. The distance between the wells is set at 125 m, and all wells are assumed to be vertical. Production and injection start

7 simultaneously under the same schedule used for the huff-and-puff and multi-well pilot tests. The injected CO 2 breaks through after 4.6 years of operation, and based on the initial and final adsorbed amounts of CO 2, almost 1.0 x 10 4 t of injected CO 2 is estimated to be adsorbed within each grid cell. This equates to a total amount of 1.2 x 10 6 t CO 2 that may be sequestrated within the Y10 coal seam throughout the entire Ishikari Coal Field. Gas Production/Injection Rate (m 3 /day) 13,000 12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 CH4 Production Rate CO2 Injection Rate CO2 Production Rate Water Rate Elapsed Time (days) Water Production Rate (m 3 /day) Figure 5: Simulation results of the multi-well test. 2km 2km Production Well Injection Well Figure 6: Production and injection well pattern.

8 CONCLUSIONS The CO 2 -sequestration project entitled Technology Development for Carbon Dioxide Sequestration in Coal Seams started in FY2002 as a part of the Carbon Dioxide Sequestration and Effective Use Program promoted by the Japanese Ministry of Economy, Trade and Industry. The purpose of this project is to develop a series of processes that can extract the CO 2 discharged from thermal power plants and other large-scale emitters of CO 2, and fix it in coal seams in a stable form while recovering methane as a clean energy source. This paper has introduced the coal-seam CO 2 -sequestration project and presented analytical results for the Y10 coal seam in the Ishikari Coal Field based on laboratory experiments, well-logging, and water-injection falloff tests. The expected results of future CO 2 huff-and-puff tests and multi-well test have been simulated based on these analyses in order to aid the field-test design. From the simulations, it is estimated that the initial coalbed methane gas production rate is likely to be almost 500 m 3 /day and that this rate will increase by a factor of two or three once CO 2 is injected due to CH 4 /CO 2 exchange within the coal seam. The adsorbed CO 2 volume is estimated to be 72% of the injected CO 2 for the huff-and-puff field test, and 96% for the multi-well test. Finally, using the simulation results, the amount of CO 2 that can potentially be sequestered in the Y10 coal seam throughout the entire Ishikari Coal Field has been estimated to be approximately 1.2x10 6 t. ACKNOWLEDGEMENTS This research has been carried out as part of the Technology Development for Carbon Dioxide Sequestration in Coal Seams Project supported by the Ministry of Economy, Trade and Industry of the Japan Government. REFERENCES 1. Wong, S., K. MacLeod, W.D. Gunter, M.J. Mavor, and J. Gale CO 2 -enhanced coalbed methane recovery demonstration pilot - A case for Australia. In: Proceedings of the 2001 International Coalbed Methane Symposium, Tuscaloosa, Alabama, USA, May 14-18, 2001, Paper 0148: Maoyuan S. and F. Zhiqiang China s coalbed methane development can benefit from carbon dioxide sequestration. In: Proceedings of the Japan International Workshop on the Present Status and Perspective of CO 2 Sequestration in Coal Seam, Tokyo, Japan, Sept. 5, 2002: Mavor, M.J., W.D. Gunter, J.R. Robinson, D.H.-S. Law, and J. Gale Testing for CO 2 sequestration and enhanced methane production from coal. SPE Paper 75683, presented at the SPE Gas Technology Symposium, Calgary, Alberta, Canada, April 30-May 2, 2002, 14p. 4. Reeves, S Coal-Seq project update: Field studies of ECBM recovery/co 2 sequestration in coalseams. In: Proceedings of the Japan International Workshop on the Present Status and Perspective of CO 2 Sequestration in Coal Seam, Tokyo, Japan, Sept. 5, 2002: Gunter, W.D. and M.J. Mavor Enhanced coalbed methane recovery and CO 2 storage: Micro-pilot testing at Fenn-Big Valley, Alberta, Canada. In: Proceedings of the Japan International Workshop on the Present Status and Perspective of CO 2 Sequestration in Coal Seam, Tokyo, Japan, Sept. 5, 2002: van Bergen, F., H.J.M. Pagnier, L.G.H. van der Meer, F.J.G. van den Belt, P.L.A. Winthaegen, and R.S. Westerhoff The RECOPOL project: Developing a field experiment of CO 2 storage in coal seams in Poland. In: Proceedings of the Japan International Workshop on the Present Status and Perspective of CO 2 Sequestration in Coal Seam, Tokyo, Japan, Sept. 5, 2002: Fujioka, M., H. Hirasawa, and S. Matsuyama CO 2 -ECBM tests in Japan. In: Proceedings of the 2 nd International Workshop on Research Relevant to CO 2 Sequestration in Coal Seam, Tokyo, Japan, Sept. 25, 2003: Yamaguchi, S., K. Ohga, and M. Fujioka Prospect of coalbed methane gas production from the Ishikari Coal Field in Japan. In: Proceedings of the 2004 International Coalbed Methane Symposium, Tuscaloosa, Alabama, USA, May 4-7, 2004, Paper 0148, 12 p. 9. Gash, B.W Measurement of rock properties in coal for coalbed methane production. SPE Paper 22909, presented at the 66 th Annual Technical Conference and Exhibition, Dallas, Texas, USA, October 6-9, 1991: