1 ABSTRACT 0702 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND W.F.C. van Wageningen and J.G. Maas Shell International Exploration & Production Kesslerpark 1, 2288 GS Rijswijk, The Netherlands The RECOPOL project is a joint industry project (JIP) and the RECOPOL site is located in the west central Upper Silesian basin in the South of Poland near the Czech border. The pilot area consists of a small fault-block, which has a triangular shape. The deposits in the block dip 12 degrees to the north and consist of alternating layers of sandstone, clay and coal. The main objective of the RECOPOL project is to demonstrate that CO 2 injection in coal is a feasible option under European conditions and that CO 2 storage in coal layers is a safe and permanent solution. The RECOPOL pilot was simulated with Shell's proprietary simulator MoReS and the results were compared to the existing field data. The reservoir simulations have been conducted to obtain a better understanding of the field behavior in the RECOPOL pilot. Buoyancy proves to be important for the transport of methane in a coal-bed. Because of the high cleat permeability and because vertical cleat permeability is likely of the same order as horizontal cleat permeability, the gas and water segregate in the cleat system due to buoyancy. A small grid in the vertical direction was necessary to model this effect. Because gas accumulates at the top of the coal layer, gas may escape to surface if there is no sealing cap-rock. Therefore, cap-rock integrity is important for both CBM and ECBM. The RECOPOL pilot shows that CO 2 injection enhances the production of methane in two ways: (1) CO 2 enhances de-sorption of methane and (2) The injected CO 2 pushes methane towards the producer (CO 2 drive). In RECOPOL, the CO 2 adsorption was very slow, which likely enhanced the drive effect. An unexpected early breakthrough of CO 2 was also observed in the RECOPOL pilot, which was likely caused by CO 2 overshooting the water in the cleats. Thus, it is likely hat the lower part of the coal seam never came into contact with the CO 2. As a result, there was less CO 2 sequestration and enhanced methane recovery than anticipated. The RECOPOL pilot helped to identify two important mechanisms: slow matrix diffusion and phase segregation in the cleats. These mechanisms are relevant for both CBM and ECBM. INTRODUCTION Today, coalbed methane (CBM) is a mature technology. In 2005, the annual CBM production in the US was 1.7 Tscf and the proved reserves were 20 Tscf (source: EIA-DOE). The CBM process can be enhanced by injecting CO 2 into the coalbed, so called enhanced coalbed methane (ECBM). ECBM has a double goal: the enhanced production of methane and the storage of CO 2 in coal beds. Contrary to CBM, ECBM is far from mature as is pointed out by White  in his review on the status of ECBM technology. Worldwide a few pilots on ECBM have been conducted. In 1996, Burlington Resources started the first largescale (4 injectors, 7 producers) CO 2 -ECBM pilot in the San Juan basin, [2-4]. The pilot was a technical success. The methane recovery was enhanced and at the same time CO 2 was sequestered. However, without additional credits for CO 2 storage the economics are poor. Outside the US only a few other ECBM pilots have been conducted. The Alberta Research Council (ARC) has conducted a single well (huff and puff) ECBM micro-pilot with
2 2 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND flue gas and CO 2 in Alberta, Canada. ARC also has completed a similar pilot in the Shanxi province in China together with the Chinese State company CUCBM, . The Japanese company JCOAL has an active (two-wells) ECBM pilot in Hokkaido Japan. The study presented here will present the modeling and interpretation of the RECOPOL (two-wells) ECBM pilot in Poland, . The RECOPOL project is a joint industry project (JIP) funded by the European Union. The RECOPOL pilot is lead by TNO and takes place in the upper Silesian basin in Poland. The main objective of the RECOPOL project is to demonstrate that CO 2 injection in coal is a feasible option under European conditions and that CO 2 storage in coal layers is a safe and permanent solution. Although CO 2 injection ended June 2005, the pilot is still on going. Currently, the focus is on monitoring and verification. Shell has joined the project in 2002 as an end-user and has participated actively in the planning of the field activities and all project meetings. The successful frac-job in April 2005 was designed and supervised by Shell experts and resulted in the first significant CO 2 injection of the project, which turned the pilot into a success. Today a new consortium has been formed and the RECOPOL pilot continues under a different name: MOVECBM. GEOLOGY AND WELL LOCATIONS The RECOPOL test site is located in the west central Upper Silesian basin in the South of Poland (Fig. 1) near the Czech border and falls under the concession area of a Silesian mine. The pilot area consists of a small fault-block, which has a triangular shape. The deposits in the block dip 12 o to the north and consist of alternating layers of sandstone, clay and coal. A detailed description of the geology can be found in . A small summary of some key features is given below. The Upper Silesian coal basin is bound by the Carpathian fore-deep and is structurally complex compared to commercial CBM basins in the US. Faults cut into the underlying coal seams and have destroyed the lateral continuity of the coal seams. Like most other European basins, the Upper Silesian basin underwent several subsequent burial and uplift phases. Because the coal seams were buried deeper in the past than at present times, permeability is relatively low, in the range of 0.5 to 2 md. On the test site, there are two old wells (MS-1 and MS-4), which were used for a CBM production pilot in the period The distance between MS-1 and MS-4 is about 375m, where MS-4 is located up dip from MS-1. Initially, both MS-1 and MS-4 were considered for the ECBM pilot. However, reservoir simulations conducted by TNO,  indicated that the distance between MS-1 and MS-4 was too large to achieve breakthrough of CO 2 within the project lifetime. Therefore, a new well (MS-3) was drilled between MS-1 and MS-4. During the pilot CO 2 was injected in the new well MS-3 and production took place in MS-4. The MS-1 well was not used during the project. Several coal layers having thicknesses in the range of 1 to 3m are located in the Upper Carboniferous (Fig. 2), which are covered by Miocene shale. It was planned to inject CO 2 in three coal layers (364, 401 and 405), but there were indications that CO 2 only entered into the top layer 364. Six layers ( ) were completed in the old production wells MS-1 and MS-4, whereas the new injection well MS-3 was completed in three layers (364, 401 and 405). The bottom layers 501 and 510 of MS-4 were plugged off with a bridge plug. Table 1 shows an overview of the completions, coal seam thickness and depth of each well. Note that initially the completions of the newly drilled well MS-3 were not fracced, which resulted in poor injectivity. A successful frac-job of MS-3 was completed in April 2005, which resolved the injectivity problems. It can be observed (Tab. 1) that the producer MS-4 was only fracced in three layers (364, 405 and 510). A frac-job is usually necessary to connect the well to the cleat system and proppants are often used to keep the cleats open. Several layers of MS-4 were not fracced so it can be assumed that these layers did not contribute to the production. Furthermore, well tests in MS-3 had indicated that layer 405 has almost no permeability (~1 µd). Layer 357 and 401 were not fracced and the lower layers (501 and 510) were plugged off. This makes it likely that the only significant contribution to CBM production came from layer 364. The low production rates (water and gas) observed in the RECOPOL pilot support this assumption. THEORY: TRANSPORT, EOS AND SORPTION MODEL The basic transport mechanisms of ECBM considered in our modeling are: Bulk transport of the gases through the natural fracture or cleat system (Darcy flow) including buoyancy effects.
3 W.F.C. VAN WAGENINGEN AND J.G. MAAS 3 Cleat to matrix transport by diffusion and vice versa. Exchange of methane and CO 2 inside the coal matrix (adsorption/desorption) The main part of the flow will take place through the vertical (unstressed) cleats. The horizontal cleats are mainly closed due to the overburden pressure. The vertical and horizontal cleat permeability are likely of the same order, because the cleats are connected and extend in the vertical direction. The permeability of a cleat can be estimated by considering the flow through a cleat assuming it is similar to the flow between two parallel plates. Note that in reality the flow through a cleat system deviates from the (ideal) flow through two parallel plates due to obstacles or other imperfections of the cleat system, . The solution of this flow is the well-known Poiseuille profile and can be adequately modeled with the Darcy equation. The permeability of the coal matrix is very small, which limits Darcy flow from matrix to cleat and vice versa. The main transport mechanism between matrix and cleat is therefore diffusion. We model the diffusion with Fick's law: (1) where Φ m is the mass flow-rate, D is the diffusion coefficient, c/ x the concentration gradient and A the cross sectional area through which the mass transfer takes place. In this study the diffusion coefficient sets the transport rates of the different gases between matrix and cleat. In reality, the diffusion process between matrix and cleat is very complex. Furthermore, the water content has a large influence on the diffusion rate, especially at the smallest pore scale. In the literature, more detailed (bidisperse diffusion) models based on the work of Ruckenstein  are currently used, e.g. . We believe that currently there are too many unknowns to justify a more detailed diffusion model. More accurate experimental data is necessary to have a solid basis for the more advanced models. Hence, a simple empirical approach is our preferred option and used in this study. We used the Shell Modified and Improved Redlich-Kwong equation of state (SMIRK-EOS), .The SMIRK- EOS is a two parameter Redlich-Kwong type EOS, in which both parameters, a and b, are a function of temperature T. The SMIRK-EOS is equal to (2) where R is the gas constant and v the specific volume. The sorption process is modeled by means of the (extended) Langmuir equation, which describes the amount of adsorbed gas of each component, G cmp as a function of pressure p and composition: (3) where V L,cmp and p L are the Langmuir volume and pressure, y cmp is the mol fraction of a component in the gas phase, and w a and w we are the ash and moisture content, respectively. In practice, both V L and p L are used to fit experimental sorption data to the Langmuir isotherm. The Langmuir isotherm is modeled in Shell's proprietary reservoir simulator, MoReS , via chemical reaction modeling, where it is assumed that adsorption is in equilibrium with desorption for a given p and T. The chemical equilibrium is effectively equal to Eq. 3. Fort the simulation of the RECOPOL pilot no swelling model was used. Instead, field data and the outcome of reservoir simulations were compared and analyzed for evidence of swelling (e.g. change in the injection pressure during the CO 2 injection). FIELD OPERATIONS A graphic overview of the historic injection and production data is shown in the figures 4 and 5, respectively. The total amount of injected CO 2 was m 3, the cumulative water production was 580 m 3, the total produced CH4 was m 3 and the back-produced CO 2 was m 3. It follows that 93% of the injected CO 2 was stored in the coal seam and 7% was back-produced. The main events of the pilot are summarized below: Begin CBM operation (day 0; 28 May 2004) Begin CO 2 injection (day 70; 6 Aug 2004)
4 4 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND Observed increase in methane production (day 90; 26 Aug 2004) Pump frozen (day ; 8-14 Feb 2005) Fall off test injector (day ; 14 Feb - 1 Mar 2005) Observed decrease in methane production (day 272; 23 Feb 2005) First (unsuccessful) Frac-jobs with brine only (day ; 2-3 Mar 2005) Injection resumed but at very low rate (day 279; 2 Mar 2005) Successful Frac-Job with proppant (day 327; 19 Apr 2005) Dramatic increase in CO 2 injection (day 328; 20 Apr 2005) Big increase in methane production (day 334; 26 Apr 2005) Significant CO 2 breakthrough in producer (day 336; 28 Apr 2005) Pump broken (day 352; 14 May 2005) RESERVOIR MODEL The reservoir is located at a depth of 1000m and dipping 12~degrees north. The reservoir model represents a triangular area of 1.35 km 2 (333 acre) and a single coal seam (364) having a thickness of about 3m is modeled. The GIIP of the model area equals 9.1 Mm 3 (0.32 Bscf). A dual-porosity dual-permeability model has been used for this study. We assume that the matrix is in Langmuir equilibrium and that there is segregated flow in the cleat system and that the relative permeability depends linearly on the saturation (Sat=0, Kr=0; Sat=1, Kr=1). Transport between matrix and cleats is dominated by diffusion. The permeability was determined by laboratory experiments, well tests and history match. All methods indicate an average effective permeability of the reservoir in the range of 1 to 2 md, except for the bottom coal layer (405), which has a much lower permeability of about 1 µd. It is therefore not likely that CO 2 entered into this layer. The cleat porosity is around 0.5% and the cleat spacing is 0.025m. Together with a permeability of 1.3 md, these values gave a best match for the water production and CO 2 injection/breakthrough. The permeability is the effective permeability of both cleats and matrix. The cleat porosity was in the order of 0.5% so the cleat permeability equals 1.3/0.005 =260mD. Due to the large density difference (ρ H2O /ρ CH4 ~ 15), the relatively low radial pressure gradient and the large cleat permeability, it is likely that the desorbed CH 4 and water will segregate in the cleats. As a consequence, CH 4 will accumulate near the top of the coal seam, which brings about the importance of a sealing cap-rock for CBM in order to prevent the flow of methane to surface. The segregation of gas and water was confirmed with simulations with a radial flow model (Fig. 6). To accurately describe the phase segregation, the 3 meter thick coal-seam was modeled with 10 grid blocks in the vertical direction, which were refined (factor 1.5) towards the top of the seam (Tab. 2). The full field model has a [7x5x10] grid with local grid refinement around the wells (Fig. 7). If the grid block of the well would be taken too large, the matrix near the well would depressurize by a too large extent. This would result in more desorption of methane and hence production would be over-predicted. This issue is addressed in MoReS via local grid refinement near the wells (Tab. 2) and (Fig. 7). The radial model was also used to determine the correct level of grid refinement in the X and Y direction. For that, the radial model was compared to the full field model, which has larger grid blocks in the horizontal plane. There was good agreement between the two models indicating that the grid refinement in the X-Y direction was sufficient (Fig. 8). It is known that CO 2 dissolves in water. The solubility proved to be small. At the most 3% of the injected CO 2 dissolves into the brine. To keep the model simple, this effect was neglected in this study. DIFFUSION AND SORPTION PARAMETERS Busch et al  have investigated the diffusion process on coal particles. They have indicated that there are two sorption processes in coal, a fast and a slow process. The results were obtained by fitting the sorption data with two first order reactions representing the fast and slow sorption process. Van Krevelen  describes the diffusion processes in coal at different scales. The fast and slow diffusion process can be linked to the different pore scales of coal. The measurements of  show that for large particles (>0.3mm) about 65% of the CH4 sorption is fast and 35% is slow. Smaller particles (<0.3mm) show a trend of increasing percentage of fast sorption with decreasing particle size. Particles larger than 0.3 mm all show about the same small percentage of fast sorption indicating that large particles could represent the coal matrix. The observation that there are two diffusion processes is in line with
5 W.F.C. VAN WAGENINGEN AND J.G. MAAS 5 the observed behavior in the desorption analysis on cores to determine the gas content. After 100 days only 60% of the gas was de-sorbed. The other 40% remained trapped in the coal matrix. It appears that at least 35% of the gas in the RECOPOL is diffusing at a very slow rate and as a result will not contribute much to the production. This effect is incorporated in the simulator by reducing the Langmuir volumes. In order to obtain a good history match the Langmuir parameters had to reduced by a factor of 6.5, which can indicate that the amount of slow diffusion is larger under field conditions. There are also other explanations possible for the low gas rates observed in the field such as a higher ash and moisture content or reduced thickness of the coal seam due to shale/sandstones. In other words there are different ways to explain the field data. However, the main principle remains the same: there are only a limited amount of sorption sites available or accessible for methane and carbon dioxide. In the reservoir simulations, the diffusion coefficient was set to 10-9 m 2 /s, which represents a fast diffusion process. The effect of the slow diffusion process was not modeled; by adjusting the Langmuir parameters the amount of coal accessible by fast diffusion has been reduced to 15%. The physics behind this is that part of the coal is not accessible, because diffusion into the coal matrix is very slow. The adsorption/desorption process is described by the Langmuir relation (Eq. 3). The coal parameters as obtained in the lab are: p L (CH 4 ) = 2490 kpa, p L (CO 2 ) = 2300 kpa, V L (CH 4 ) = 17 sm 3 /ton and V L (CO 2 ) = 17 sm 3 /ton. The average ash and moisture content are 25% and 5%, respectively. The plot of the gas content as function of pressure is shown in figure 9. The vertical line at 100 bar indicates the field gas content as measured from cores and cuttings. RESULTS AND DISCUSSION The pilot's aim was to prove the feasibility of CO 2 sequestration in coal. It was not aimed at economical production of methane, which indeed was marginal. The main reasons for the low methane production rates are: the adsorption of CO 2 and desorption of CH 4 are slow in Silesia coal the gas content of the coal is low the coal seam is thin and has a relatively high ash content Reservoir simulations have been conducted to get a better understanding of the field behavior in the RECOPOL pilot. We used a simple geological model considering only one coal seam. To accurately simulate the segregation of the phases in the cleats, the model has a relatively dense grid in the vertical direction that was refined toward the top of the coal seam. The grid blocks around the wells were also refined in the x and direction in order to get a more accurate pressure distribution and sorption behavior around the wells. The level of grid refinement was based upon a 2D radial model, which was also used to determine the CBM baseline. The CBM baselines of the full field and 2D radial models are in good agreement with each other (Fig. 8). This shows that the level of gridrefinement is adequate. The CBM baseline was established as follows. First, the water rate of the model was matched by varying the permeability and cleat porosity. Subsequently, the Langmuir parameters were decreased with a constant factor to obtain the CBM baseline. The main differences between the final model and field were: The CBM baseline of the model is somewhat too high The decline of the water-production of the model is somewhat too slow No further adjustments have been made to the model to get a better match. This keeps the model simple. Note that the aim was not to get a perfect match, but to understand main features of the field behavior. The base (CBM) model (Fig. 8) was used to study the effect of CO 2 injection (Fig. 10). The CO 2 injection of the model was set to the field rate (all other parameters were left unchanged) and its response on the production was studied. The response of the methane production to the CO 2 injection was similar to the field (Fig. 10). Shortly after the injection, the methane production started to increase although to a lesser extent than the field rate. The field reached a higher ECBM plateau than the model, but we obtained the correct response. Previous models not considering the phase segregation all failed to predict the early enhancement of methane due to CO 2 injection. This demonstrates that phase segregation most likely takes place in the coal seam and that small grid cells near top of coal layer are necessary to describe this effect. The new model shows that early enhancement of CH 4 can be the result of CO 2 flooding. The injected CO 2 pushes the methane that has accumulated at the top of the coal seam toward the producer. Note that the breakthrough of the CO 2 occurred too early in the model (Fig. 11), which was likely caused by the over-prediction of dispersion of CO 2. In a grid-block, CO 2 and CH 4 mix instantly, while in reality there will be a delay due to diffusion. We summarize the main differences between the field data and simulation below:
6 6 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND The enhancement of methane at the start of the CO 2 injection is under-predicted leading to a lower (simulated) ECBM plateau. The break-down of the pump was not modeled The decline in methane production due to the decrease in injection rate in the period just before the fracjob is too short in the simulation result. This can be related to the breakdown of the pump, which was not modeled. The break-through of CO 2 is too fast and the amount of CO 2 production after the frac-job is underpredicted The main shortcomings of the current model are believed to be: There is too much adsorption of CO 2 to the coal The dispersion of CO 2 is too fast (numerical effect) These issues are currently investigated and addressed in a new model, which will contain a better description of the diffusion processes at different scales (micro-pore and macro-pore diffusion). The influence of the amount adsorption of CO 2 was studied by investigating the sensitivity of the Langmuir parameters of CO 2 (Fig ). The Langmuir parameters of CO 2 were changed and it was found that when the amount of adsorption of CO 2 was decreased, the enhancement of methane production was closer to the field rate. However, the decline of the methane rate before the frac-job was still too slow. The post-frac CO 2 production was closer to the field rate, but it was still lower. The fact that the simulated rates were closer to the historic rates, can be an indication that less adsorption of CO 2 took place in the field test. Although there is no direct evidence of coal swelling in the RECOPOL pilot, it appeared that the cleat permeability reduced after the post-frac CO 2 injection. The pressure decline of the field was much slower than the pressure decline of the simulation (Fig. 14, day day 550). This indicates reduced cleat permeability due to coal swelling. Moreover, after a shut-in period of 4 months the injector was still over-pressured (THP ~50 bar). In the next phase of the pilot (MOVECBM), it is planned to produce back the (former) injector. If there was indeed a strong reduction in permeability, it is expected that this effect can also be observed in the amount of produced water. We also hope to establish the amount of CO 2 that is physically adsorbed to the coal and the amount remaining in the cleats. CONCLUSION Buoyancy, which is often neglected in (E)CBM simulations, proves to be important for the transport of methane in a coal-bed. Because of the high cleat permeability and since vertical permeability is most likely of the same order as horizontal permeability, the gas and water segregate in the cleat system due to buoyancy. The gas accumulates at the top of the coal layer, which brings about that the cap-rock integrity is important for both CBM and ECBM. The RECOPOL pilot showed that CO 2 injection enhances the production of methane. We found that methane is not only enhanced by the sorption mechanism, but also due to CO 2 flooding. The injected CO 2 pushes the methane that has accumulated near the top of the coal layer toward the producer. Due to slow diffusion into the coal matrix, there was less adsorption of CO 2, which likely enhanced the flooding effect. Furthermore, the CO 2 breakthrough occurred much faster than anticipated earlier. Two likely causes for the early breakthrough observed in both pilot and reservoir simulations are that the bulk of the CO 2 overshoots the water (Fig. 15) and that due to slow diffusion there is less CO 2 adsorption to the coal matrix. We expected that more CO 2 will adsorb to the coal and more CH 4 will desorb, if diffusion is faster. This will lead to a later breakthrough of CO 2. Faster diffusion is not expected to have any effect on the overshooting of the CO 2. When the matrix is saturated, CO 2 will still migrate to the top of the coal seam. The only way to prevent the overshooting of CO 2 is by lowering the water level in the coal seam. Because the CO 2 overshoots the water in the cleats, it is likely that in RECOPOL a mayor part of the coal seam never got into contact with the CO 2. As a result, there will be less CO 2 sequestration and enhanced methane recovery. Furthermore, it indicates the importance of injector location and design of an ECBM operation. Ideally, the CO 2 should be injected in the bottom part of the coal seam to maximize exposure of the coal to CO 2. Multilaterals may be used to achieve this. The RECOPOL pilot helped to identify two important mechanisms (diffusion and phase segregation in the cleats) relevant for both CBM and ECBM. This novel insight can help find ways to enhance diffusion into coal matrix (e.g. dewatering prior to injection) and to optimize the location of injectors and producers (e.g. using multilaterals).
7 W.F.C. VAN WAGENINGEN AND J.G. MAAS 7 ACKNOWLEDGEMENTS The authors would like to acknowledge Henk Pagnier and Frank van Bergen from TNO for their efforts in making the RECOPOL project a success. REFERENCES 1. White, C.M,et al., 2005: "Sequestration of Carbon Dioxide in Coal with Enhanced Coal bed Methane Recovery-A Review", Energy & Fuels, V.19, No Stevens, S.H., Spector, D. and Riemer, P., 1998: "Enhanced Coal bed Methane Recovery Using CO 2 Injection: Worldwide Resource and CO 2 Sequestration Potential", SPE Reeves, S.R. et al., 2004: "The Tiffany Unit N2 ECBM Pilot: A Reservoir Modeling Study", Topical Report DOE, DE-FC26-0NT Reeves, S.R. et al., 2002: Selected Field Practices for ECBM Recovery and CO 2 Sequestration in Coals based on Experience Gained at the Allison and Tiffany Units, San Juan Basin,Topical Report DOE, DE-FC26-00NT Wong, S., Law D. and Gunter B.,2005: "Enhanced Coal-Bed Methane Test at South Qinshui Basin, China", Greenhouse Issues, V Pagnier, H., et al., 2006: "Reduction of CO 2 emission by means of CO 2 storage in coal seams in the Silesian Coal Basin of Poland", TNO, RECOPOL Final Report. 7. LeGrain, P.H. 2006: "Etude de l'influence de la rugosite sur l'ecoulement de fluide dans les fissures rocheuses, PhD-Thesis, Faculte Polytechnique de Mons. 8. Ruckenstein, A.S., et al., 1971: "Sorption by solids with bidisperse pore structures",chem. Eng. Sc., V Shi, J.G. and Durucan S. 2003: "A bidisperse pore diffusion model for methane displacement desorption in coal by CO 2 injection", Fuel, V Drexhage, J.J. and Welsenes, A.J., 1990: "Physical properties of pure compounds. Parameters for the SMIRK equation of state", Shell Internal report. 11. Por, G.J., Boerrigter, P., Maas, J.G. and De Vries, A., 1989: "A Fractured Reservoir Simulator Capable of Modeling Block-Block Interaction", SPE Busch, A. et al., 2004: "Methane and carbon dioxide adsorption-diffusion experiments on coal: upscaling and modeling", Int. J. Coal Geol., V Van Krevelen, D.W., 1993: Coal: Amsterdam, Elsevier Science Publishers B.V., ISBN TABLES Table 1: Coal layers and completion types Table 2: Grid block sizes in X,Y and Z direction
8 8 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND FIGURES Figure 1: Location of RECOPOL Pilot (source: TNO) Figure 2: Coal layers and wells (source: TNO)
9 W.F.C. VAN WAGENINGEN AND J.G. MAAS 9 Coal matrix vertical cleat top view butt cleat horizontal cleat inaccessible matrix (slow diffusion) face cleat fast diffusion layer Figure 3: Cleats in Coal matrix Injection Production Injection Figure 4:Historic CO2 injection and production data
10 10 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND CH4 H2O Figure 5: Historic CH4 and water production data S=0.9 Gas Saturation Radial Model S=0.05 Figure 6: Gas saturation (Radial model ) on log scale
11 W.F.C. VAN WAGENINGEN AND J.G. MAAS 11 Top View Side View Grid in between wells (Top View) Figure 7: Grid [7x5x10] with local grid refinement near wells CH4 (field) CH4 (2D sim) H2O (sim) CH4 (3D sim) H2O (field) Figure 8: Comparison of 3D model and 2D radial model, water and CH 4 production (CBM base case)
12 12 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND CO2 CH4 CH4 (field) Figure 9: Adsorption characteristics for RECOPOL coal (DAF). The vertical line at 100 bar indicates the expected gas content of the field. CH4 (field) CH4 (ECBM base case) CH4 (CBM base case) H2O (sim) H2O (field) Figure 10: Effect of CO 2 injection on produced CH 4 (ECBM base case)
13 W.F.C. VAN WAGENINGEN AND J.G. MAAS 13 CO2 (Field) CO2 (sim) Figure 11: Back-produced CO 2 (ECBM base case) CH4 (ECBM VL(CO2) * 0.1) CH4 (field) CH4 (ECBM base case) CH4 (CBM base case) H2O (field) H2O (sim) Figure 12: Water and Methane production (ECBM: V L (CO 2 ) * 0.1)
14 14 RESERVOIR SIMULATION AND INTERPRETATION OF THE RECOPOL ECBM PILOT IN POLAND CO2 (Field) CO2 (ECBM VL(CO2) * 0.1) CO2 (ECBM base case) Figure 13: Back-produced CO 2 (ECBM: V L (CO 2 ) * 0.1) BHP (field) BHP (sim) Figure 14: Injection pressure: comparison of simulated and field BHP
15 W.F.C. VAN WAGENINGEN AND J.G. MAAS 15 Figure 15: ECBM base case; Gas saturation and CO 2 mole fraction in cleats (matrix is not shown) at day 375 (end of the CO 2 injection), Dark Gray = 0 and White = 1