C. Rodrigues , C. Laiginhas M. Fernandes and M.J. Lemos de...
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C. Rodrigues1, C. Laiginhas2, M. Fernandes2 and M.J. Lemos de Sousa1
1 University Fernando Pessoa, CEMAS, Porto, Portugal2 Consultant Geologists, Portugal
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NoticeNotice
Part of the research team of the Part of the research team of the ““Organic Organic Petrology and Geochemistry UnitPetrology and Geochemistry Unit””, Faculty of , Faculty of Sciences, University of Porto, has moved to a Sciences, University of Porto, has moved to a new entity entitled new entity entitled ““Research Unit for Research Unit for Environment Systems Modelling and AnalysisEnvironment Systems Modelling and Analysis””at University Fernando Pessoa, Porto, at University Fernando Pessoa, Porto, Portugal. Researchers who moved to Portugal. Researchers who moved to University Fernando Pessoa are those University Fernando Pessoa are those specialized in Coalbed Methane (CBM) and specialized in Coalbed Methane (CBM) and CO2 sequestration in coal seams.CO2 sequestration in coal seams.
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Universidade Fernando Pessoa, Porto, Portugal
Main objectives:
To develop R & D projects related with Modelling and Analysis of Environment Systems (5 + 2 current R & D projects)
To assist Post-graduated teaching and student training
Staff: 22 researchers of which
17 Ph D
2 M Sc
3 with Graduation
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Contacts:Contacts:
Professor Manuel Lemos de SousaProfessor Manuel Lemos de [email protected]@[email protected]@gmail.com
Dr Cristina F. A. RodriguesDr Cristina F. A. [email protected]@[email protected]@gmail.com
Mail address:Mail address: PraPraçça de 9 de Abril 349, 4249a de 9 de Abril 349, 4249--004 Porto, Portugal.004 Porto, Portugal.
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Research Team Practice in CBM studies
Lorraine Basin (France) – Conoco, Dupont
Waterberg Basin (South Africa) – Anglo Coal
Spain
Brazil
Chile
Publications: 19 papers, abstracts and posters
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Research Team main Publications
see:
www.ufp.pt
Bibliotecas
B-DIGITAL UFP
Geosciences and Environment
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Presented to the AAPG International Conference, Barcelona, September 21-24, 2003.
The abstract was published by AAPG in the Conference Abstracts book and in the corresponding CD-ROM.
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Key words
Abstract
1. Introduction• WHY to study the “cleat system”?• WHAT is the main problem?• WHERE is applicable?• WHEN is applicable?• WHO is interested?• HOW much?
2. The Duality cleat-Macroporosity
3. Creating a new Methodology
4. The "Coal-core tectonics" (CCT) method
5. Summarizing and Concluding
6. References
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The Coalbed Methane (CBM) generated by coal is located in coal pores and the drainage of the coalbed gas to the production well is made through the so-called "cleat system", i.e., the natural fracture network of coal. This justifies the classic method of CBM production by providing fracture-stimulation with fluids under pressure to open coal natural fractures.
However, natural fracturing system of any coal is very complex, depending on coalification process and local and regional tectonics. Additionally, the cleat network cannot be inferred using conventional regional micro-tectonics studies.
Cleat system, Coal, Coalbed Methane (CBM), Natural gas, Exploration, Prospection
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Therefore, what really matters is to know, in each case, the spatial orientation of the different classes of fracturing, ordered by connectivity frequencies, to make possible an orientated injection of fluids to open the cleat permitting higher amounts of gas release/drainage. In fact, the cleat family of highest connectivity frequency is the one that define the gas circulation network to the producing well, and consequently the most favorable one to be opened by fluids injected in the correct direction.
The current investigation refers to a new and innovative proposal to develop a method for determining cleat family orientation in the space, ordered by cleat connectivity frequency. This new semi-automatic method is based in the study of "cleat characteristics" by image analysis in orientated core samples of boreholes for CBM prospection/exploration. The information from image analysis is studied by statistical CCT ("coal-core tectonics") methodology and subsequently combined with Geographic Information System, thus referring to location of the real case under study.
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to to studystudy thethe
““cleatcleat systemsystem””??
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isis thethe
mainmain problemproblem??
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isis applicableapplicable??
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is applicable?
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See: Lemos de Sousa, M.J.; Pinheiro, H.J. and Rodrigues, C., 2003. Prerequisites, general criteria and primary studies required in the Coalbed Methane prospecting and exploring: A review. In:AAPG International Conference, Barcelona. (Abstract published in the Conference Abstracts book and in the corresponding CD-ROM; Full presentation in digital library, Universidade Fernando Pessoa, Porto, Portugal at https://bdigital.ufp.pt/dspace)
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isis interestedinterested??
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Reducing gas emissionsQuality control of water produced with CBMCO2 injection/sequestration
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much?
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In fact, drilling more and more holes do not solve per se the problem of gas production from coal seams!
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2. The Duality2. The Duality2. The Duality
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conceptually is thevolume fraction of coal occupied by emptyspaces”, however, this is not strictlymeasurable. Operationally, porosity is thevolume fraction of coal that may be occupiedby a particular fluid. This varies from fluid to fluid.
(Levine, 1993)
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is defined by the microporestructure of the coal matrix; the micropore space
accounting for as much as 85% of coal total porosity.
represents the openings of coal that are too large to be considered part of the molecular structure such as cracks, cleat, fissures, which are not isotropic and tend to be parallel to the cleavage plane of the coal seam.
(Rojey et al 1997)
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Volumetric fluiddisplacement
Vapor sorption studies
Electron scatteringScanning electron
microscopy Heats of wetting
NMR spectroscopy
Neutron scatteringTransmission electron
microscopy
Low angle x-raysattering
Optical microscopy
ESR spin label probe
Method
Major category
Scatteringmethods
Microscopicmethods
Fluid probemethods
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He and Hg density (Levine, 1993)
Sorption isotherms(Rodrigues and Lemos de Sousa, 2002)
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Schematic illustration of coal cleat (Laubach et al 1998): (a) cleat characteristics in plan view; (b) cleat hierarchies in cross- section view
Schematic illustration of coal cleat (Laubach et al 1998): (a) cleat characteristics in plan view; (b) cleat hierarchies in cross- section view
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Cleat frequency;Cleat height;
Cleat directions relative to a reference;
Cleat length;Cleat spacing;Number of cleat connectivity/intersections;Cleat aperture;Number of cleats filled by minerals.
(Laubach et al 1998)
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Manual (take photos, stick them to each other, mark the cleat on a transparency)
Manual (take photos, stick them to each other, mark the cleat on a transparency)
“Coal-core tectonics” (CCT) – Rodrigues 2002(Semi-automated computerized: GIS combined with a set of different softwares, such as “Georient”, “Rockworks”)
“Coal-core tectonics” (CCT) – Rodrigues 2002(Semi-automated computerized: GIS combined with a set of different softwares, such as “Georient”, “Rockworks”)
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cm
0 4
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40
cm
Image obtained from high resolution scanning
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to mention the plane where the data were collectedto mention the plane where the data were collected
to measure the azimuth of the cleat, expressed by cleat dip directionto measure the azimuth of the cleat, expressed by cleat dip direction
to calculate cleat directionto calculate cleat direction
to measure cleat lengthto measure cleat length
to observe if the cleat is opened or closedto observe if the cleat is opened or closed
to see if cleat is fulfilled by minerals to see if cleat is fulfilled by minerals
to consider additional informationto consider additional information
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Cleat frequency;Cleat frequency;Cleat height;
Cleat length;Cleat spacing;Number of cleat connectivity/intersections;Cleat aperture;Number of cleats filled by minerals.
Cleat directions relative to a reference;Cleat directions relative to a reference;
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40
cm
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Cleat elements three-dimensionally represented in core sampleCleat elements three-dimensionally represented in core sample
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Plane W-E (W dip direction)
0
20
40
60
80
100
dip (degree)
Freq
uenc
y (%
)
10 20 30 40 50 60 70 80
Cleat frequency (decrease order)
Cleat lines measured in N-S plane (N dip direction)
Cleat lines measured in W-E plane (E dip direction)
1 88º → 0º 88º → 90º
2 89º → 0º 87º → 90º
3 87º → 0º 85º → 90º
4 85º → 0º 86º →90º
5 86º → 0º 84º → 90º
6 80º → 0º 89º → 90º
7 3º → 0º; 83º → 0º and 84º → 0º 83º → 90º
8 2º → 0º 3º → 90º
9 5º → 0º 82º → 90º
10 82º → 0º 7º → 90º and 5º → 90º
Mean Orientation = 87/037Mean Resultant dir'n = 87-037Mean Resultant length = 1,00
(Variance = 0,00)Calculated. girdle: 8/145Calculated beta axis: 82-325
N
Mean Plane: N 127º, 87ºE
Dip direction interval 120º - 150ºDip direction interval 120º - 150º
Mean Direction = 89-045Mean Resultant dir'n = 89/045Mean Resultant length = 1,00
(Variance = 0,00)Calculated. girdle: 89/045
N
Plane: N 135º, 89ºE
Cleat frequency 1Cleat frequency 1
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Class designation Dip interval
Class 0 0ºClass 1 > 0º and ≤ 30ºClass 2 > 30º and ≤ 60ºClass 3 > 60º and ≤ 90ºClass 4 90
Connectivity frequency
0%10%20%30%40%50%
0-1 0-2 0-3 0-4 1-2 1-3 1-4 2-3 2-4 3-4Classes
Freq
uenc
y (%
)
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Schematic representation of the preferential planesSchematic representation of the preferential planes
N
Horizontal
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In a classical approach:In a classical approach:In a classical approach:
Drainage of CBM to the production well Drainage of CBM to the production well is made through the sois made through the so--called called ““cleat cleat systemsystem””, i.e. the natural network of , i.e. the natural network of fractures present in the coal.fractures present in the coal.
Only in very Only in very ““favourablefavourable”” conditions it conditions it is possible to obtain good (economic) is possible to obtain good (economic) levels of production.levels of production.
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Natural fracturing (cleat) of any coal depends of both
Natural fracturing (cleat) of any Natural fracturing (cleat) of any coal depends of both coal depends of both
genetic conditionsgenetic conditionsgenetic conditionsregional tectonicsregional tectonicsregional tectonics
andandand
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However:However:
The cleat network cannot be inferred using The cleat network cannot be inferred using conventional regional microconventional regional micro--tectonic tectonic studies.studies.
In terms of mechanical properties, coal In terms of mechanical properties, coal have a very particular have a very particular rheologicalrheologicalbehaviour, different of the other local behaviour, different of the other local rocks, particularly at seam roofs and rocks, particularly at seam roofs and floors.floors.
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Therefore:Therefore:To make possible, in each case, an orientated To make possible, in each case, an orientated injection of fluids to open fracturing (cleat) system, injection of fluids to open fracturing (cleat) system, permitting the highest amount of gas release, one permitting the highest amount of gas release, one dramatically need to know the spatial orientation of dramatically need to know the spatial orientation of the different classes of fracturing (cleat), ordered the different classes of fracturing (cleat), ordered by connectivity frequencies. This is also applicable by connectivity frequencies. This is also applicable to CO2 injection/sequestration by coal seams.to CO2 injection/sequestration by coal seams.
The CCT methodology herein presented is a new The CCT methodology herein presented is a new fast and precise approach in response to the above fast and precise approach in response to the above addressed critical issue.addressed critical issue.
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Yet, new developments are needed:Yet, new developments are needed:
A further major goal will be to correlate CCT methodology data (core analysis) with both logdata whilst drilling and geophysical logged data.
A further major goal will be to correlate CCT A further major goal will be to correlate CCT methodology data (core analysis) with both methodology data (core analysis) with both logdatalogdata whilst drilling and geophysical whilst drilling and geophysical logged data.logged data.
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Rodrigues, C.F.A., 2002. The application of isotherm studies to evaluate to Coalbed Methane potential of the Waterberg Basin, South Africa, 289 pp. Universidade do Porto, Faculdade de Ciências, Departamento de Geologia. (Ph D Thesis).
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