Secondary Porosity and Permeability of Coal vs. Gas Composition and Pressure
- Matthew J. Mavor (Tesseract Corp.) | William D. Gunter (Alberta Research Council)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- April 2006
- Document Type
- Journal Paper
- 114 - 125
- 2006. Society of Petroleum Engineers
- 5.4 Enhanced Recovery, 5.8.6 Naturally Fractured Reservoir, 1.6.9 Coring, Fishing, 5.2.2 Fluid Modeling, Equations of State, 5.5 Reservoir Simulation, 4.1.5 Processing Equipment, 5.6.4 Drillstem/Well Testing, 5.6.3 Pressure Transient Testing, 6.5.1 Air Emissions, 6.5.2 Water use, produced water discharge and disposal, 5.2.1 Phase Behavior and PVT Measurements, 5.8.3 Coal Seam Gas, 5.6.9 Production Forecasting, 5.4.2 Gas Injection Methods, 5.6.1 Open hole/cased hole log analysis, 6.5.7 Climate Change, 4.1.2 Separation and Treating
- 12 in the last 30 days
- 1,593 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 10.00|
|SPE Non-Member Price:||USD 30.00|
We have been investigating the sequestration of atmospheric pollutants by injection into coal seams while at the same time enhancing hydrocarbon productivity by displacement of methane with pollutants. Our effort is one of several field-based research efforts into CO2 storage in coal seams that are currently operating in Canada (Mavor et al. 2004), China (Robinson et al. 2004), Japan (Nago and Komaki 2004), and Poland (Van Bergen et al. 2004). During the course of our field measurements, we have been using single-well injection, soak, and production tests to collect data required to understand and predict enhanced coalbed methane (ECBM) recovery potential and sequestration capacity. We found that changing the composition of the gas sorbed into the coal changes the porosity and permeability of the coal natural-fracture system owing to gas-content changes, which cause matrix swelling or shrinkage due to relative adsorption of different gases.
We collected sufficient information to develop a method for predicting the permeability and porosity of a coalbed as a function of the secondary porosity system (SPS) pressure and the gas content and composition of the primary porosity system (PPS). The method uses data from injection/falloff tests with water and/or a weaker adsorbing gas (WAG) than CH4 and a stronger adsorbing gas (SAG) than CH4. Estimates of effective permeability to gas and water obtained from these tests are used with an iterative computation procedure subject to constraints to solve for equivalent SPS porosity and absolute permeability at atmospheric pressure.
Once calibrated, the model can be used to predict a coalbed's permeability and porosity as a function of injection pressure and injected-fluid composition, which in turn are used to predict injection performance. The model is applicable to production forecasts to account for SPS permeability and porosity changes as reservoir pressure declines with changes in gas composition.
This paper describes the new model and discusses well-test procedures to obtain the data required for model calibration. Also included are coal property estimates resulting from Alberta Medicine River (Manville) coal core and test data and an example model calibration.
Commercial production of gas from coal seams is highly dependent upon natural fractures that control the absolute permeability magnitude and distribution throughout the reservoir. Natural-fracture absolute permeability and porosity vary as a function of location, pressure within the natural-fracture system, and the composition of gas within the coal matrix. Variations in fracture porosity cause variations in fluid saturations that in turn cause variations in the relative and effective permeability to gas and water.
Coal-gas reservoirs are dual-porosity reservoirs consisting of primary and secondary storage and mass transfer systems. The PPS contains the vast majority of the gas-in-place volume stored by sorption, while the SPS provides the conduit for mass transfer to wells (Mavor and Nelson 1997). The SPS generally consists of two or more natural-fracture sets created at different times. The more continuous, greater-permeability natural-fracture set is referred to as face cleats. There is often a more discontinuous, lower-permeability set referred to as butt cleats oriented at roughly right angles to face cleats. There also can be additional fracture sets present (Close 1993).
Coal permeability has been known for some time to be dependent upon net stress and changes in sorbed-gas content. Gray (1987) discussed both of these phenomena. The general belief was that as reservoirs are depleted, the increase in net stress decreases the aperture of natural fractures, which decreases the absolute permeability. However, Gray reported that permeability might increase as pressure and gas content decreased because an absolute permeability increase caused by gas desorption could overcome the decrease caused by net stress increase.
|File Size||1 MB||Number of Pages||12|
Chalaturnyk, R. 1999. Scoping Experiments on the Permeability/Volume Changein Coal Due to CO2 Adsorption Phenomena, Final Report. Edmonton, Alberta,Canada: Alberta Research Council.
Chikatamarla, L., Xiojun, C., and Bustin, M. 2004. Implications ofVolumetric Swelling/Shrinkage of Coal in Sequestration of Acid Gases. InProc., 2004 Intl. Coalbed Methane Symposium, paper 435. Tuscaloosa: U.of Alabama (3-7 May).
Close, J.C. 1993. Natural Fractures in Coal. In Hydrocarbons From Coal,AAPG Studies in Geology #38. Tulsa: AAPG.
Gash, B.W., Volz, R.F., Potter, G., and Corgan, J.M. 1993. The Effects ofCleat Orientation and Confining Pressure on Cleat Porosity, Permeability andRelative Permeability in Coal. In Proc., 1993 Intl. Coalbed MethaneSymposium, paper 9321. Tuscaloosa: U. of Alabama (17-21 May).
Gray, I. 1987. ReservoirEngineering in Coal Seams: Part 1—The Physical Process of Gas Storage andMovement in Coal Seams. SPERE 2 (1):28-34. SPE12514-PA.
Harpalani, S. and Schraufnagel, R.A. 1990. Influence of Matrix Shrinkage andCompressibility on Gas Production From Coalbed Methane Reservoirs. PaperSPE 20729 presented at the SPE Annual Technical Conference and Exhibition, NewOrleans, 23-26 September.
Levine, J.R. 1996. Model Study of the Influence of Matrix Shrinkage onAbsolute Permeability of Coalbed Reservoirs. In Coalbed Methane & CoalGeology, Special Publication No. 109, 197-212. London: GeologicalSociety.
Mavor, M.J., Gunter, W.D., and Robinson, J.R. 2004. Alberta Multiwell Micro-Pilot Testingfor CBM Properties, Enhanced Methane Recovery and CO2 Storage Potential.Paper SPE 90256 presented at the SPE Annual Technical Conference andExhibition, Houston, 26-29 September.
Mavor, M.J. and Nelson, C.R. 1997. Coalbed Reservoir Gas-In-Place Analysis.Chicago: Gas Research Inst. Rpt No. GRI-97/0263 (October 1997).
Mavor, M.J. and Robinson, J.R. 1993. Analysis of Coal Gas ReservoirInterference and Cavity Well Tests. Paper SPE 25860 presented at the SPERocky Mountain Regional/Low Permeability Reservoirs Symposium, Denver, 26-28April.
Mavor, M.J. and Saulsberry, J.L. 1996. Coalbed Methane Well Testing. In AGuide to Coalbed Methane Reservoir Engineering. Chicago: Gas Research Inst.Rpt. GRI-94/0397 (March 1996).
Mavor, M.J. and Vaughn, J.E. 1998. Increasing Coal Absolute Permeabilityin the San Juan Basin Fruitland Formation. SPEREE1(3):201-206. SPE-39105-PA.
Nago, M. and Komaki, H. 2004. Summary and Monitoring of the Japan CO2Sequestration in Coal Seams Project. In Proc., 3rd Intl. Workshop ofProspective Roles of CO2 Sequestration in Coal Seams. Sapporo, Japan: HokkaidoU. (October 2004).
Palmer I. and Mansoori, J. 1996. How Permeability Depends on Stressand Pore Pressure in Coalbeds: A New Model. Paper SPE 36737 presented atthe SPE Annual Technical Conference and Exhibition, Denver, 6-9 October.
Palmer, I. and Mansoori, J. 1998. How Permeability Depends on Stressand Pore Pressure in Coalbeds: A New Model. SPEREE1(6):539-544. SPE-52607-PA.
Puri, R. and Seidle, J. 1991. Measurement of Stress Dependent Permeabilityin Coals and Its Influence on Coalbed Methane Production. In Proc., 1991Coalbed Methane Symposium, 415-424. Tuscaloosa: U. of Alabama (13-16 May 1991).Paper 9142.
Robertson, E.P. and Christiansen, R.L. 2004. Optically-Based StrainMeasurement of Coal Swelling and Shrinkage. In Proc., 2004 Intl. CoalbedMethane Symposium, Tuscaloosa: U. of Alabama (3-7 May). Paper 417.
Robinson, J. et al. 2004. ECBM Micro-Pilot Test in the Anthracitic Coals ofthe Qinshue Basin, China: Field Results and Preliminary Analysis. InProc., 3rd Intl. Workshop of Prospective Roles of CO2 Sequestration inCoal Seams. Sapporo, Japan: Hokkaido U. (October 2004).
Seidle, J.P. and Huitt, L.G. 1995. Experimental Measurement of CoalMatrix Shrinkage Due to Gas Desorption and Implications for Cleat PermeabilityIncreases. Paper SPE 30010 presented at the SPE International Meeting onPetroleum Engineering, Beijing, 14-17 November.
Seidle, J.P., Jeansonne, M.W., and Erickson, D.J. 1992. Application of Matchstick Geometry toStress Dependent Permeability in Coals. Paper SPE 24361 presented at theSPE Rocky Mountain Regional Meeting, Casper, Wyoming, 18-21 May.
Sereshki, F., Aziz, N.I, and Porter, I. 2004. Influence of Gas Type andPressure on Permeability and Volumetric Characteristics of Coal. InProc., 2004 Intl. Coalbed Methane Symposium, paper 415. Tuscaloosa: U.of Alabama (3-7 May).
Shi, J.Q. and Durucan, S. 2003a. Changes in Permeability of Coalbeds DuringPrimary Recovery—Part I: Model Formulation and Analysis. In Proc., 2003Intl. Coalbed Methane Symposium, paper 341. Tuscaloosa: U. of Alabama (5-7May).
Shi, J.Q. and Durucan, S. 2003b. Changes in Permeability of Coalbeds DuringPrimary Recovery—Part II: Model Formulation and Field Application. InProc., 2003 Intl. Coalbed Methane Symposium, paper 341. Tuscaloosa: U.of Alabama (5-7 May).
Shi, J.Q. and Durucan, S. 2005. A Model for Changes in CoalbedPermeability During Primary and Enhanced Methane Recovery.SPEREE 8 (4):291-299. SPE-87230-PA.
Van Bergen, F. et al. 2004. Field Experiment of ECBM-CO2 in the UpperSilesian Basin of Poland. In Proc., 3rd Intl. Workshop of ProspectiveRoles of CO2 Sequestration in Coal Seams. Sapporo, Japan: Hokkaido U. (October2004).
Yang, R.T. 1997. Gas Separation by Adsorption Processes, 49-51.London: Imperial College Press.
Zheng, Z.Z., Khodaverdian, M., and McLennan, J.D. 1991. Static and DynamicTesting of Coal Specimens. Paper 9120 presented at the Soc. of Core Analysts5th Annual Technical Conference, August.
Zheng, Z.Z., McLennan, J.D., Jones, A.H., and Spafford, S. 1992. Pore VolumeCompressibility and Permeability of Coal Under Different Stress Conditions. InProc., Intl. Gas Research Conf., V.1, 77-86. Rockville, Maryland: Gov.Inst. Inc. (16-19 November).
Zutshi, A. and Harpalani, S. 2004. Matrix Swelling With CO2 Injection in aCBM Reservoir and Its Impact on Permeability of Coal. In Proc., 2004Intl. Coalbed Methane Symposium, paper 425. Tuscaloosa: U. of Alabama (3-7May).